Laser weldability of 21Cr-6Ni-9Mn stainless steel: Part I - Impurity effects and solidifcation mode

DOE PAGES

Tate, Stephen B.; Javernick, Daniel Anthony; Lienert, Thomas J.; ...

2016-11-02

For laser welded type 21Cr-6Ni-9Mn (21-6-9) stainless steels, the relationship between solidification cracking susceptibility and chemical composition was examined, and primary solidification mode (PSM) diagrams were developed to predict solidification mode. Sigmajig testing was used with experimental heats of type 21-6-9 to determine the effect of P and S on solidification cracking w hen primary austenite solidification occurred. Phosphorus showed a larger influence on solidification cracking relative to S, and a relationship of (P+0.2S ) was found for total impurity content. PSM diagrams to predict solidification mode were developed by analyzing welds made at three travel speeds for a widemore » range of 21-6-9 alloys and some other similar alloys. The minimum Cr eq/Ni eq required for primary ferrite solidification increased as travel speed increased, with more alloys showing primary austenite solidification at higher travel rates. Furthermore, as travel speed increased from 21 to 85 mm/s, the average solidification rate increased from 6 to 25 mm/s.« less

DEMONSTRATION BULLETIN - SOLIDIFICATION/ STABILIZATION PROCESS, SOLIDTECH, INC.

EPA Science Inventory

The Soliditech solidification/stabilization technology mixes hazardous waste materials in soils or sludges with pozzolanic material (cement, fly ash, or kiln dust), a proprietary additive called Urrichem, other proprietary additives, and water. The process is designed to aid ...

Efficient estimation of diffusion during dendritic solidification

NASA Technical Reports Server (NTRS)

Yeum, K. S.; Poirier, D. R.; Laxmanan, V.

1989-01-01

A very efficient finite difference method has been developed to estimate the solute redistribution during solidification with diffusion in the solid. This method is validated by comparing the computed results with the results of an analytical solution derived by Kobayashi (1988) for the assumptions of a constant diffusion coefficient, a constant equilibrium partition ratio, and a parabolic rate of the advancement of the solid/liquid interface. The flexibility of the method is demonstrated by applying it to the dendritic solidification of a Pb-15 wt pct Sn alloy, for which the equilibrium partition ratio and diffusion coefficient vary substantially during solidification. The fraction eutectic at the end of solidification is also obtained by estimating the fraction solid, in greater resolution, where the concentration of solute in the interdendritic liquid reaches the eutectic composition of the alloy.

EVALUATION OF SOLIDIFICATION/STABILIZATION AS A BEST DEMONSTRATED AVAILABLE TECHNOLOGY FOR CONTAMINATED SOILS

EPA Science Inventory

This project involved the evaluation of solidification/stabilization technology as a BDAT for contaminated soil. Three binding agents were used on four different synthetically contaminated soils. Performance evaluation data included unconfined compressive strength (UCS) and the T...

Hazcon Solidification Process, Douglassville, Pa.: Applications Analysis Report

EPA Science Inventory

This document is an evaluation of the HAZCON solidification technology and its applicability as an on-site treatment method for waste site cleanup. A Demonstration was held at the Douglassville, Pennsylvania Superfund site in the fall of 1987. Operational data and sampling and an...

Single Crystal Casting with Fluidized Carbon Bed Cooling: A Process Innovation for Quality Improvement and Cost Reduction

NASA Astrophysics Data System (ADS)

Hofmeister, M.; Franke, M. M.; Koerner, C.; Singer, R. F.

2017-12-01

Superalloy gas turbine blades are being produced by investment casting and directional solidification. A new process, Fluidized Carbon Bed Cooling (FCBC), has been developed and is now being optimized in a prototype casting unit with 10 kg pouring weight. In early test runs with still rather simple mold cluster geometries, a reduction of the primary dendrite arm spacing of around 40 pct compared to the standard radiation cooling process (HRS) could be demonstrated. The improvement is mainly attributed to higher temperature gradients driving solidification, made possible by a functioning Dynamic Baffle. Compared to earlier development efforts in the literature, contamination of the melt and damage to the equipment are avoided using carbon-based fluidized bed materials and the so-called "counter pressure concept."

Laser weldability of 21Cr-6Ni-9Mn stainless steel: Part II - Weldability diagrams

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tate, Stephen B.; Javernick, Daniel Anthony; Lienert, Thomas J.

In this second part of the study, weldability diagrams developed to relate solidification crack susceptibility and chemical composition for laser welded type 21Cr-6Ni-9Mn (21-6-9) stainless steel are presented. Sigmajig testing on 14 commercial 21-6-9 alloys, 20 experimental 21-6-9 alloys, and 7 other high-N, high-Mn austenitic stainless steels was used to develop weldability diagrams for solidification crack susceptibility for laser welding of type 21-6-9. Three travel speeds were used to show the changes in minimum Cr eq/Ni eq for primary ferrite solidification as solidification rate increase d with travel speed . Primary austenite solidification was observed below 1.55 Cr eq/Ni eqmore » (Espy equivalents) at 21 mm/s travel speed. At 42 mm/s travel speed , a mix of solidification modes were displayed for alloys from 1.55-1.75 Cr eq/Ni eq. Primary ferrite solidification was observed above 1.75 Cr eq/Ni eq at both 42 and 85 mm/s travel speeds. No solidification cracking was observed for alloys with primary ferrite solidification. Lastly, variable cracking behavior was found in alloys with primary austenite solidification, but in general cracking was observed in alloys with greater than 0.02 wt-% combined impurity content according to (P+0.2S).« less

Laser weldability of 21Cr-6Ni-9Mn stainless steel: Part II - Weldability diagrams

DOE PAGES

Tate, Stephen B.; Javernick, Daniel Anthony; Lienert, Thomas J.; ...

2016-11-02

In this second part of the study, weldability diagrams developed to relate solidification crack susceptibility and chemical composition for laser welded type 21Cr-6Ni-9Mn (21-6-9) stainless steel are presented. Sigmajig testing on 14 commercial 21-6-9 alloys, 20 experimental 21-6-9 alloys, and 7 other high-N, high-Mn austenitic stainless steels was used to develop weldability diagrams for solidification crack susceptibility for laser welding of type 21-6-9. Three travel speeds were used to show the changes in minimum Cr eq/Ni eq for primary ferrite solidification as solidification rate increase d with travel speed . Primary austenite solidification was observed below 1.55 Cr eq/Ni eqmore » (Espy equivalents) at 21 mm/s travel speed. At 42 mm/s travel speed , a mix of solidification modes were displayed for alloys from 1.55-1.75 Cr eq/Ni eq. Primary ferrite solidification was observed above 1.75 Cr eq/Ni eq at both 42 and 85 mm/s travel speeds. No solidification cracking was observed for alloys with primary ferrite solidification. Lastly, variable cracking behavior was found in alloys with primary austenite solidification, but in general cracking was observed in alloys with greater than 0.02 wt-% combined impurity content according to (P+0.2S).« less

Experimental Study on the Anisotropic Stress-Strain Behavior of Polycrystalline Ni-Mn-Ga in Directional Solidification

NASA Astrophysics Data System (ADS)

Teng, Yao; Shi, Tao; Zhu, Yuping; Li, Zongbin; Deng, Tao; Bai, Guonan

2016-03-01

A polycrystalline Ni-Mn-Ga ferromagnetic shape memory alloy produced by directional solidification is the subject of this research paper. The compressive stress-strain curves of the material for different cutting angles to the solidification direction are tested. The martensite Young's modulus, macroscopic reorientation strain, and phase transition critical stress are analyzed experimentally. The results show that mechanical behaviors in the loading-unloading cycle of the material present nonlinear and anisotropic characteristics, which are all closely related to the material's orientation to the solidification direction. The martensite Young's modulus, macroscopic reorientation strain, and phase transition critical stress achieve maximum values in the solidification direction. A 50° orientation to the solidification direction is the cut-off direction of the mechanical properties, where the martensite Young's modulus and reorientation start critical stress reach minimum values. The present study is expected to provide sound guidance for practical applications.

Technology Demonstration Summary: International Waste Technologies In Situ Stabilization/Solidification, Hialeah, Florida

EPA Science Inventory

An evaluation was performed of the International Waste Technologies (IWT) HWT-20 additive and the Geo-Con, Inc. deep-soil-mixing equipment for an in situ stabilization/solidification process and its applicability as an on-site treatment method for waste site cleanup. The analysis...

Incorporating interfacial phenomena in solidification models

NASA Technical Reports Server (NTRS)

Beckermann, Christoph; Wang, Chao Yang

1994-01-01

A general methodology is available for the incorporation of microscopic interfacial phenomena in macroscopic solidification models that include diffusion and convection. The method is derived from a formal averaging procedure and a multiphase approach, and relies on the presence of interfacial integrals in the macroscopic transport equations. In a wider engineering context, these techniques are not new, but their application in the analysis and modeling of solidification processes has largely been overlooked. This article describes the techniques and demonstrates their utility in two examples in which microscopic interfacial phenomena are of great importance.

Thermal modeling of phase change solidification in thermal control devices including natural convection effects

NASA Technical Reports Server (NTRS)

Ukanwa, A. O.; Stermole, F. J.; Golden, J. O.

1972-01-01

Natural convection effects in phase change thermal control devices were studied. A mathematical model was developed to evaluate natural convection effects in a phase change test cell undergoing solidification. Although natural convection effects are minimized in flight spacecraft, all phase change devices are ground tested. The mathematical approach to the problem was to first develop a transient two-dimensional conduction heat transfer model for the solidification of a normal paraffin of finite geometry. Next, a transient two-dimensional model was developed for the solidification of the same paraffin by a combined conduction-natural-convection heat transfer model. Throughout the study, n-hexadecane (n-C16H34) was used as the phase-change material in both the theoretical and the experimental work. The models were based on the transient two-dimensional finite difference solutions of the energy, continuity, and momentum equations.

Incorporation of fragmentation into a volume average solidification model

NASA Astrophysics Data System (ADS)

Zheng, Y.; Wu, M.; Kharicha, A.; Ludwig, A.

2018-01-01

In this study, a volume average solidification model was extended to consider fragmentation as a source of equiaxed crystals during mixed columnar-equiaxed solidification. The formulation suggested for fragmentation is based on two hypotheses: the solute-driven remelting is the dominant mechanism; and the transport of solute-enriched melt through an interdendritic flow in the columnar growth direction is favorable for solute-driven remelting and is the necessary condition for fragment transportation. Furthermore, a test case with Sn-10 wt%Pb melt solidifying vertically downward in a 2D domain (50 × 60 mm2) was calculated to demonstrate the model’s features. Solidification started from the top boundary, and a columnar structure developed initially with its tip growing downward. Furthermore, thermo-solutal convection led to fragmentation in the mushy zone near the columnar tip front. The fragments transported out of the columnar region continued to grow and sink, and finally settled down and piled up in the bottom domain. The growing columnar structure from the top and pile-up of equiaxed crystals from the bottom finally led to a mixed columnar-equiaxed structure, in turn leading to a columnar-to-equiaxed transition (CET). A special macrosegregation pattern was also predicted, in which negative segregation occurred in both columnar and equiaxed regions and a relatively strong positive segregation occurred in the middle domain near the CET line. A parameter study was performed to verify the model capability, and the uncertainty of the model assumption and parameter was discussed.

SolTrack: an automatic video processing software for in situ interface tracking.

PubMed

Griesser, S; Pierer, R; Reid, M; Dippenaar, R

2012-10-01

High-Resolution in situ observation of solidification experiments has become a powerful technique to improve the fundamental understanding of solidification processes of metals and alloys. In the present study, high-temperature laser-scanning confocal microscopy (HTLSCM) was utilized to observe and capture in situ solidification and phase transformations of alloys for subsequent post processing and analysis. Until now, this analysis has been very time consuming as frame-by-frame manual evaluation of propagating interfaces was used to determine the interface velocities. SolTrack has been developed using the commercial software package MATLAB and is designed to automatically detect, locate and track propagating interfaces during solidification and phase transformations as well as to calculate interfacial velocities. Different solidification phenomena have been recorded to demonstrate a wider spectrum of applications of this software. A validation, through comparison with manual evaluation, is included where the accuracy is shown to be very high. © 2012 The Authors Journal of Microscopy © 2012 Royal Microscopical Society.

LOW COST SOLIDIFICATION/STABILIZATION TREATMENT FOR SOILS CONTAMINATED WITH DIOXIN, PCP AND CREOSOTE

EPA Science Inventory

The USEPA's NRMRL conducted successful treatability tests of innovative solidification/stabilization (S/S) formulations to treat soils contaminated with dioxins, pentachlorophenol (PCP), and creosote from four wood preserving sites. Formulations developed during these studies wer...

LOW COST SOLIDIFICATION/STABILIZATION TREATMENT FOR SOILS CONTAMINATED WITH DIOXIN, PCP, AND CREOSOTE

EPA Science Inventory

The USEPA's National Risk Management Research Laboratory condcuted successful treatability tests of innovative solidification/stablization (S/S) formulations to treat soils contaminated with dioxins, pentachlorophenol (PCP), and creosote from four wood preserving sites. For one o...

SUPERFUND TREATABILITY CLEARINGHOUSE: BDAT FOR SOLIDIFICATION/STABILIZATION TECHNOLOGY FOR SUPERFUND SOILS (DRAFT FINAL REPORT)

EPA Science Inventory

This report evaluates the performance of solidification as a method for treating solids from Superfund sites. Tests were conducted on four different artificially contaminated soils which are representative of soils found at the sites. Contaminated soils were solidified us...

Research on metal solidification in zero-g state

NASA Technical Reports Server (NTRS)

Papazian, J. M.; Larson, D. J., Jr.

1975-01-01

The containerless solidification of several pure metals and metallic alloys was studied in a low gravity environment. The tests were performed in the MSFC 4.2 s drop tower using a rapid wire melting apparatus designed and built for this purpose. Pure iron and nickel, and alloys of iron-nickel, iron-carbon, nickel-aluminum and tungsten-rhenium were all melted and solidified at a gravity level of approximately 100.000/-4 g. Interpretation of the results has led to an appreciation of the factors controlling the successful execution of this drop test experiment and to a delineation of the limits of applicability of the apparatus. Preliminary metallurgical evaluations are presented of the overall shapes, lattice parameters, surface microstructure,, cross-sectional microstructures, solidification and transformation sequences, evaporative segregation, and localized solute redistribution observed in the low-gravity specimens. The effects of low gravity on metallic solidification are discussed with particular emphasis on observations of spontaneous undercooling and evaporative segregation in uncontained melts.

Analytical description of the ternary melt and solution crystallization with a non-linear phase diagram

NASA Astrophysics Data System (ADS)

Toropova, L. V.; Alexandrov, D. V.

2018-05-01

The directional solidification of a ternary system with an extended phase transition region is theoretically studied. A mathematical model is developed to describe quasi-stationary solidification, and its analytical solution is constructed with allowance for a nonlinear liquids line equation. We demonstrate that the phase diagram nonlinearity leads to substantial changes of analytical solutions.

TECHNOLOGY EVALUATION REPORT: CHEMFIX TECHNOLOGIES, INC. - SOLIDIFICATION/STABILIZATION PROCESS - CLACKAMAS, OREGON - VOLUME I

EPA Science Inventory

The CHEMFIX solidification/stabilization process was evaluated in the U.S. Environment Protection Agency's SITE program. Waste from an uncontrolled hazardous waste site was treated by the CHEMFIX process and subjected to a variety of physical and chemical test methods. Physical t...

TECHNOLOGY EVALUATION REPORT: CHEMFIX TECHNOLOGIES, INC. - SOLIDIFICATION/STABILIZATION PROCESS - CLACKAMAS, OREGON - VOLUME II

EPA Science Inventory

The CHEMFIX solidification/stabilization process was evaluated in the U.S. Environmental Protection Agency's SITE program. Waste from an uncontrolled hazardous waste site was treated by the CHEMFIX process and subjected to a variety of physical and chemical test methods. Physical...

Solidification of a binary alloy: Finite-element, single-domain simulation and new benchmark solutions

NASA Astrophysics Data System (ADS)

Le Bars, Michael; Worster, M. Grae

2006-07-01

A finite-element simulation of binary alloy solidification based on a single-domain formulation is presented and tested. Resolution of phase change is first checked by comparison with the analytical results of Worster [M.G. Worster, Solidification of an alloy from a cooled boundary, J. Fluid Mech. 167 (1986) 481-501] for purely diffusive solidification. Fluid dynamical processes without phase change are then tested by comparison with previous numerical studies of thermal convection in a pure fluid [G. de Vahl Davis, Natural convection of air in a square cavity: a bench mark numerical solution, Int. J. Numer. Meth. Fluids 3 (1983) 249-264; D.A. Mayne, A.S. Usmani, M. Crapper, h-adaptive finite element solution of high Rayleigh number thermally driven cavity problem, Int. J. Numer. Meth. Heat Fluid Flow 10 (2000) 598-615; D.C. Wan, B.S.V. Patnaik, G.W. Wei, A new benchmark quality solution for the buoyancy driven cavity by discrete singular convolution, Numer. Heat Transf. 40 (2001) 199-228], in a porous medium with a constant porosity [G. Lauriat, V. Prasad, Non-darcian effects on natural convection in a vertical porous enclosure, Int. J. Heat Mass Transf. 32 (1989) 2135-2148; P. Nithiarasu, K.N. Seetharamu, T. Sundararajan, Natural convective heat transfer in an enclosure filled with fluid saturated variable porosity medium, Int. J. Heat Mass Transf. 40 (1997) 3955-3967] and in a mixed liquid-porous medium with a spatially variable porosity [P. Nithiarasu, K.N. Seetharamu, T. Sundararajan, Natural convective heat transfer in an enclosure filled with fluid saturated variable porosity medium, Int. J. Heat Mass Transf. 40 (1997) 3955-3967; N. Zabaras, D. Samanta, A stabilized volume-averaging finite element method for flow in porous media and binary alloy solidification processes, Int. J. Numer. Meth. Eng. 60 (2004) 1103-1138]. Finally, new benchmark solutions for simultaneous flow through both fluid and porous domains and for convective solidification processes are presented, based on the similarity solutions in corner-flow geometries recently obtained by Le Bars and Worster [M. Le Bars, M.G. Worster, Interfacial conditions between a pure fluid and a porous medium: implications for binary alloy solidification, J. Fluid Mech. (in press)]. Good agreement is found for all tests, hence validating our physical and numerical methods. More generally, the computations presented here could now be considered as standard and reliable analytical benchmarks for numerical simulations, specifically and independently testing the different processes underlying binary alloy solidification.

Adaptive-Grid Methods for Phase Field Models of Microstructure Development

NASA Technical Reports Server (NTRS)

Dantzig, Jonathan A.; Goldenfeld, Nigel

2001-01-01

Modeling solidification microstructures has become an area of intense study in recent years. The properties of large scale cast products, ranging from automobile engine blocks to aircraft components and other industrial applications, are strongly dependent on the physics that occur at the mesoscopic and microscopic length scales during solidification. The predominant morphology found in solidification microstructures is the dendrite, a tree-like pattern of solid around which solidification proceeds. The microscopic properties of cast products are determined by the length scales of these dendrites, and their associated segregation profiles. For this reason understanding the mechanisms for pattern selection in dendritic growth has attracted a great deal of interest from the experimental and theoretical communities. In particular, a great deal of research has been undertaken to understand such issues as dendrite morphology, shape and growth speed. Experiments on dendrite evolution in pure materials by Glicksman and coworkers on succinonitrile (SCN), and more recently pivalic acid (PVA), as well as other transparent analogs of metals, have provided tests of theories for dendritic growth, and have stimulated considerable theoretical progress. These experiments have clearly demonstrated that in certain parameter ranges the physics of the dendrite tip can be characterized by a steady value for the dendrite tip velocity, radius of curvature and shape. Away from the tip, the time-dependent dendrite exhibits a characteristic sidebranching as it propagates, which is not yet well understood. These experiments are performed by observing individual dendrites growing into an undercooled melt. The experiments are characterized by the dimensionless undercooling. Most experiments are performed at low undercooling.

Functional Nanoclay Suspension for Printing-Then-Solidification of Liquid Materials.

PubMed

Jin, Yifei; Compaan, Ashley; Chai, Wenxuan; Huang, Yong

2017-06-14

Additive manufacturing (AM) enables the freeform fabrication of complex structures from various build materials. The objective of this study is to develop a novel Laponite nanoclay-enabled "printing-then-solidification" additive manufacturing approach to extrude complex three-dimensional (3D) structures made of various liquid build materials. Laponite, a member of the smectite mineral family, is investigated to serve as a yield-stress support bath material for the extrusion printing of liquid build materials. Using the printing-then-solidification approach, the printed structure remains liquid and retains its shape with the help of the Laponite support bath. Then the completed liquid structures are solidified in situ by applying suitable cross-linking mechanisms. Finally, the solidified structures are harvested from the Laponite nanoclay support bath for any further processing as needed. Due to its chemical and physical stability, liquid build materials with different solidification/curing/gelation mechanisms can be fabricated in the Laponite bath using the printing-then-solidification approach. The feasibility of the proposed Laponite-enabled printing-then-solidification approach is demonstrated by fabricating several complicated structures made of various liquid build materials, including alginate with ionic cross-linking, gelatin with thermal cross-linking, and SU-8 with photo-cross-linking. During gelatin structure printing, living cells are included and the postfabrication cell viability is above 90%.

Solidification effects on sill formation: An experimental approach

NASA Astrophysics Data System (ADS)

Chanceaux, L.; Menand, T.

2014-10-01

Sills represent a major mechanism for constructing continental Earth's crust because these intrusions can amalgamate and form magma reservoirs and plutons. As a result, numerous field, laboratory and numerical studies have investigated the conditions that lead to sill emplacement. However, all previous studies have neglected the potential effect magma solidification could have on sill formation. The effects of solidification on the formation of sills are studied and quantified with scaled analogue laboratory experiments. The experiments presented here involved the injection of hot vegetable oil (a magma analogue) which solidified during its propagation as a dyke in a colder and layered solid of gelatine (a host rock analogue). The gelatine solid had two layers of different stiffness, to create a priori favourable conditions to form sills. Several behaviours were observed depending on the injection temperature and the injection rate: no intrusions (extreme solidification effects), dykes stopping at the interface (high solidification effects), sills (moderate solidification effects), and dykes passing through the interface (low solidification effects). All these results can be explained quantitatively as a function of a dimensionless temperature θ, which describes the experimental thermal conditions, and a dimensionless flux ϕ, which describes their dynamical conditions. The experiments reveal that sills can only form within a restricted domain of the (θ , ϕ) parameter space. These experiments demonstrate that contrary to isothermal experiments where cooling could not affect sill formation, the presence of an interface that would be a priori mechanically favourable is not a sufficient condition for sill formation; solidification effects restrict sill formation. The results are consistent with field observations and provide a means to explain why some dykes form sills when others do not under seemingly similar geological conditions.

The study of flow pattern and phase-change problem in die casting process

NASA Technical Reports Server (NTRS)

Wang, T. S.; Wei, H.; Chen, Y. S.; Shang, H. M.

1996-01-01

The flow pattern and solidification phenomena in die casting process have been investigated in the first phase study. The flow pattern in filling process is predicted by using a VOF (volume of fluid) method. A good agreement with experimental observation is obtained for filling the water into a die cavity with different gate geometry and with an obstacle in the cavity. An enthalpy method has been applied to solve the solidification problem. By treating the latent heat implicitly into the enthalpy instead of explicitly into the source term, the CPU time can be reduced at least 20 times. The effect of material properties on solidification fronts is tested. It concludes that the dependence of properties on temperature is significant. The influence of the natural convection over the diffusion has also been studied. The result shows that the liquid metal solidification phenomena is diffusion dominant, and the natural convection can affect the shape of the interface. In the second phase study, the filling and solidification processes will be considered simultaneously.

Microgravity

NASA Image and Video Library

2004-04-15

The M512 Materials Processing Facility (MPF) with the M518 Multipurpose Electric Facility (MEF) tested and demonstrated a facility approach for materials process experimentation in space. It also provided a basic apparatus and a common interface for a group of metallic and nonmetallic materials experiments. The MPF consisted of a vacuum work chamber and associated mechanical and electrical controls. The M518 Multipurpose Electric Furnace (MEF) was an electric furnace system in which solidification, crystal growth, and other experiments involving phase changes were performed.

Phase selection during crystallization of undercooled liquid eutectic lead-tin alloys

NASA Technical Reports Server (NTRS)

Fecht, H. J.

1991-01-01

During rapid solidification substantial amounts of undercooling are in general required for formation of metastable phases. Crystallization at varying levels of undercooling and melting of metastable phases were studied during slow cooling and heating of emulsified PB-Sn alloys. Besides the experimental demonstration of the reversibility of metastable phase equilibra, two different principal solidification paths have been identified and compared with the established metastable phase diagram and predictions from classical nucleation theory. The results suggest that the most probable solidification path is described by the 'step rule' resulting in the formation of metastable phases at low undercooling, whereas the stable eutectic phase mixture crystallizes without metastable phase formation at high undercooling.

Macrosegregation Resulting from Directional Solidification Through an Abrupt Change in Cross-Sections

NASA Technical Reports Server (NTRS)

Lauer, M.; Poirier, D. R.; Ghods, M.; Tewari, S. N.; Grugel, R. N.

2017-01-01

Simulations of the directional solidification of two hypoeutectic alloys (Al-7Si alloy and Al-19Cu) and resulting macrosegregation patterns are presented. The casting geometries include abrupt changes in cross-section from a larger width of 9.5 mm to a narrower 3.2 mm width then through an expansion back to a width of 9.5 mm. The alloys were chosen as model alloys because they have similar solidification shrinkages, but the effect of Cu on changing the density of the liquid alloy is about an order of magnitude greater than that of Si. The simulations compare well with experimental castings that were directionally solidified in a graphite mold in a Bridgman furnace. In addition to the simulations of the directional solidification in graphite molds, some simulations were effected for solidification in an alumina mold. This study showed that the mold must be included in numerical simulations of directional solidification because of its effect on the temperature field and solidification. For the model alloys used for the study, the simulations clearly show the interaction of the convection field with the solidifying alloys to produce a macrosegregation pattern known as "steepling" in sections with a uniform width. Details of the complex convection- and segregation-patterns at both the contraction and expansion of the cross-sectional area are revealed by the computer simulations. The convection and solidification through the expansions suggest a possible mechanism for the formation of stray grains. The computer simulations and the experimental castings have been part of on-going ground-based research with the goal of providing necessary background for eventual experiments aboard the ISS. For casting practitioners, the results of the simulations demonstrate that computer simulations should be applied to reveal interactions between alloy solidification properties, solidification conditions, and mold geometries on macrosegregation. The simulations also presents the possibility of engineering the mold-material to avoid, or mitigate, the effects of thermosolutal convection and macrosegregation by selecting a mold material with suitable thermal properties, especially its thermal conductivity.

Ageless Aluminum-Cerium-Based Alloys in High-Volume Die Casting for Improved Energy Efficiency

DOE PAGES

Stromme, Eric T.; Henderson, Hunter B.; Sims, Zachary C.; ...

2018-04-25

Strong chemical reactions between Al and Ce lead to the formation of intermetallics with exceptional thermal stability. The rapid formation of intermetallics directly from the liquid phase during solidification of Al-Ce alloys leads to an ultrafine microconstituent structure that effectively strengthens as-cast alloys without further microstructural optimization via thermal processing. Die casting is a high-volume manufacturing technology that accounts for greater than 40% of all cast Al products, whereas Ce is highly overproduced as a waste product of other rare earth element (REE) mining. Reducing heat treatments would stimulate significant improvements in manufacturing energy efficiency, exceeding (megatonnes/year) per large-scale heat-treatmentmore » line. In this study, multiple compositions were evaluated with wedge mold castings to test the sensitivity of alloys to the variable solidification rate inherent in high-pressure die casting. Once a suitable composition was determined, it was successfully demonstrated at 800 lbs/h in a 600-ton die caster, after which the as-die cast parts performed similarly to ubiquitous A380 in the same geometry without requiring heat treatment. Furthermore, this work demonstrates the compatibility of Al REE alloys with high-volume die-casting applications with minimal heat treatments.« less

Ageless Aluminum-Cerium-Based Alloys in High-Volume Die Casting for Improved Energy Efficiency

NASA Astrophysics Data System (ADS)

Stromme, Eric T.; Henderson, Hunter B.; Sims, Zachary C.; Kesler, Michael S.; Weiss, David; Ott, Ryan T.; Meng, Fanqiang; Kassoumeh, Sam; Evangelista, James; Begley, Gerald; Rios, Orlando

2018-06-01

Strong chemical reactions between Al and Ce lead to the formation of intermetallics with exceptional thermal stability. The rapid formation of intermetallics directly from the liquid phase during solidification of Al-Ce alloys leads to an ultrafine microconstituent structure that effectively strengthens as-cast alloys without further microstructural optimization via thermal processing. Die casting is a high-volume manufacturing technology that accounts for greater than 40% of all cast Al products, whereas Ce is highly overproduced as a waste product of other rare earth element (REE) mining. Reducing heat treatments would stimulate significant improvements in manufacturing energy efficiency, exceeding (megatonnes/year) per large-scale heat-treatment line. In this study, multiple compositions were evaluated with wedge mold castings to test the sensitivity of alloys to the variable solidification rate inherent in high-pressure die casting. Once a suitable composition was determined, it was successfully demonstrated at 800 lbs/h in a 600-ton die caster, after which the as-die cast parts performed similarly to ubiquitous A380 in the same geometry without requiring heat treatment. This work demonstrates the compatibility of Al REE alloys with high-volume die-casting applications with minimal heat treatments.

Ageless Aluminum-Cerium-Based Alloys in High-Volume Die Casting for Improved Energy Efficiency

NASA Astrophysics Data System (ADS)

Stromme, Eric T.; Henderson, Hunter B.; Sims, Zachary C.; Kesler, Michael S.; Weiss, David; Ott, Ryan T.; Meng, Fanqiang; Kassoumeh, Sam; Evangelista, James; Begley, Gerald; Rios, Orlando

2018-04-01

Strong chemical reactions between Al and Ce lead to the formation of intermetallics with exceptional thermal stability. The rapid formation of intermetallics directly from the liquid phase during solidification of Al-Ce alloys leads to an ultrafine microconstituent structure that effectively strengthens as-cast alloys without further microstructural optimization via thermal processing. Die casting is a high-volume manufacturing technology that accounts for greater than 40% of all cast Al products, whereas Ce is highly overproduced as a waste product of other rare earth element (REE) mining. Reducing heat treatments would stimulate significant improvements in manufacturing energy efficiency, exceeding (megatonnes/year) per large-scale heat-treatment line. In this study, multiple compositions were evaluated with wedge mold castings to test the sensitivity of alloys to the variable solidification rate inherent in high-pressure die casting. Once a suitable composition was determined, it was successfully demonstrated at 800 lbs/h in a 600-ton die caster, after which the as-die cast parts performed similarly to ubiquitous A380 in the same geometry without requiring heat treatment. This work demonstrates the compatibility of Al REE alloys with high-volume die-casting applications with minimal heat treatments.

Ageless Aluminum-Cerium-Based Alloys in High-Volume Die Casting for Improved Energy Efficiency

DOE Office of Scientific and Technical Information (OSTI.GOV)

Stromme, Eric T.; Henderson, Hunter B.; Sims, Zachary C.

Strong chemical reactions between Al and Ce lead to the formation of intermetallics with exceptional thermal stability. The rapid formation of intermetallics directly from the liquid phase during solidification of Al-Ce alloys leads to an ultrafine microconstituent structure that effectively strengthens as-cast alloys without further microstructural optimization via thermal processing. Die casting is a high-volume manufacturing technology that accounts for greater than 40% of all cast Al products, whereas Ce is highly overproduced as a waste product of other rare earth element (REE) mining. Reducing heat treatments would stimulate significant improvements in manufacturing energy efficiency, exceeding (megatonnes/year) per large-scale heat-treatmentmore » line. In this study, multiple compositions were evaluated with wedge mold castings to test the sensitivity of alloys to the variable solidification rate inherent in high-pressure die casting. Once a suitable composition was determined, it was successfully demonstrated at 800 lbs/h in a 600-ton die caster, after which the as-die cast parts performed similarly to ubiquitous A380 in the same geometry without requiring heat treatment. Furthermore, this work demonstrates the compatibility of Al REE alloys with high-volume die-casting applications with minimal heat treatments.« less

Optimal design of solidification processes

NASA Technical Reports Server (NTRS)

Dantzig, Jonathan A.; Tortorelli, Daniel A.

1991-01-01

An optimal design algorithm is presented for the analysis of general solidification processes, and is demonstrated for the growth of GaAs crystals in a Bridgman furnace. The system is optimal in the sense that the prespecified temperature distribution in the solidifying materials is obtained to maximize product quality. The optimization uses traditional numerical programming techniques which require the evaluation of cost and constraint functions and their sensitivities. The finite element method is incorporated to analyze the crystal solidification problem, evaluate the cost and constraint functions, and compute the sensitivities. These techniques are demonstrated in the crystal growth application by determining an optimal furnace wall temperature distribution to obtain the desired temperature profile in the crystal, and hence to maximize the crystal's quality. Several numerical optimization algorithms are studied to determine the proper convergence criteria, effective 1-D search strategies, appropriate forms of the cost and constraint functions, etc. In particular, we incorporate the conjugate gradient and quasi-Newton methods for unconstrained problems. The efficiency and effectiveness of each algorithm is presented in the example problem.

GPU-accelerated phase-field simulation of dendritic solidification in a binary alloy

NASA Astrophysics Data System (ADS)

Yamanaka, Akinori; Aoki, Takayuki; Ogawa, Satoi; Takaki, Tomohiro

2011-03-01

The phase-field simulation for dendritic solidification of a binary alloy has been accelerated by using a graphic processing unit (GPU). To perform the phase-field simulation of the alloy solidification on GPU, a program code was developed with computer unified device architecture (CUDA). In this paper, the implementation technique of the phase-field model on GPU is presented. Also, we evaluated the acceleration performance of the three-dimensional solidification simulation by using a single NVIDIA TESLA C1060 GPU and the developed program code. The results showed that the GPU calculation for 5763 computational grids achieved the performance of 170 GFLOPS by utilizing the shared memory as a software-managed cache. Furthermore, it can be demonstrated that the computation with the GPU is 100 times faster than that with a single CPU core. From the obtained results, we confirmed the feasibility of realizing a real-time full three-dimensional phase-field simulation of microstructure evolution on a personal desktop computer.

Liquid-liquid phase separation and solidification behavior of Al55Bi36Cu9 monotectic alloy with different cooling rates

NASA Astrophysics Data System (ADS)

Bo, Lin; Li, Shanshan; Wang, Lin; Wu, Di; Zuo, Min; Zhao, Degang

2018-03-01

The cooling rate has a significant effect on the solidification behavior and microstructure of monotectic alloy. In this study, different cooling rate was designed through casting in the copper mold with different bore diameters. The effects of different cooling rate on the solidification behavior of Al55Bi36Cu9 (at.%) immiscible alloy have been investigated. The liquid-liquid phase separation of Al55Bi36Cu9 immiscible alloy melt was investigated by resistivity test. The solidification microstructure and phase analysis of Al55Bi36Cu9 immiscible alloy were performed by the SEM and XRD, respectively. The results showed that the liquid-liquid phase separation occurred in the solidification of Al55Bi36Cu9 monotectic melt from 917 °C to 653 °C. The monotectic temperature, liquid phase separation temperature and immiscibility zone of Al55Bi36Cu9 monotectic alloy was lower than those of Al-Bi binary monotectic alloy. The solidification morphology of Al55Bi36Cu9 monotectic alloy was very sensitive to the cooling rate. The Al/Bi core-shell structure formed when Al55Bi36Cu9 melt was cast in the copper mold with a 8 mm bore diameter.

Benefits of rapid solidification processing of modified LaNi{sub 5} alloys by high pressure gas atomization for battery applications

DOE Office of Scientific and Technical Information (OSTI.GOV)

Anderson, I.E.; Pecharsky, V.K.; Ting, J.

1997-12-31

A high pressure gas atomization approach to rapid solidification has been employed to investigate simplified processing of Sn modified LaNi{sub 5} powders that can be used for advanced Ni/metal hydride (Ni/MH) batteries. The current industrial practice involves casting large ingots followed by annealing and grinding and utilizes a complex and costly alloy design. This investigation is an attempt to produce powders for battery cathode fabrication that can be used in an as-atomized condition without annealing or grinding. Both Ar and He atomization gas were tried to investigate rapid solidification effects. Sn alloy additions were tested to promote subambient pressure absorption/desorptionmore » of hydrogen at ambient temperature. The resulting fine, spherical powders were subject to microstructural analysis, hydrogen gas cycling, and annealing experiments to evaluate suitability for Ni/MH battery applications. The results demonstrate that a brief anneal is required to homogenize the as-solidified microstructure of both Ar and He atomized powders and to achieve a suitable hydrogen absorption behavior. The Sn addition also appears to suppress cracking during hydrogen gas phase cycling in particles smaller than about 25 {micro}m. These results suggest that direct powder processing of a LaNi{sub 5{minus}x}Sn{sub x} alloy has potential application in rechargeable Ni/MH batteries.« less

Benefits of rapid solidification processing of modified LaNi{sub 5} alloys by high pressure gas atomization for battery applications

DOE Office of Scientific and Technical Information (OSTI.GOV)

Anderson, I.E.; Pecharsky, V.K.; Ting, J.

1998-07-01

A high pressure gas atomization approach to rapid solidification has been employed to investigate simplified processing of Sn modified LaNi{sub 5} powders that can be used for advanced Ni/metal hydride (Ni/MH) batteries. The current industrial practice involves casting large ingots followed by annealing and grinding and utilizes a complex and costly alloy design. This investigation is an attempt to produce powders for battery cathode fabrication that can be used in an as-atomized condition without annealing or grinding. Both Ar and He atomization gas were tried to investigate rapid solidification effects. Sn alloy additions were tested to promote subambient pressure absorption/desorptionmore » of hydrogen at ambient temperature. The resulting fine, spherical powders were subject to microstructural analysis, hydrogen gas cycling, and annealing experiments to evaluate suitability for Ni/MH battery applications. The results demonstrate that a brief anneal is required to homogenize the as-solidified microstructure of both Ar and He atomized powders and to achieve a suitable hydrogen absorption behavior. The Sn addition also appears to suppress cracking during hydrogen gas phase cycling in particles smaller than about 25{micro}m. These results suggest that direct powder processing of a LaNi{sub 5{minus}x}Sn{sub x} alloy has potential application in rechargeable Ni/MH batteries.« less

Formation of Al15Mn3Si2 Phase During Solidification of a Novel Al-12%Si-4%Cu-1.2%Mn Heat-Resistant Alloy and Its Thermal Stability

NASA Astrophysics Data System (ADS)

Suo, Xiaojing; Liao, Hengcheng; Hu, Yiyun; Dixit, Uday S.; Petrov, Pavel

2018-02-01

The formation of Al15Mn3Si2 phase in Al-12Si-4Cu-1.2Mn (wt.%) alloy during solidification was investigated by adopting CALPHAD method and microstructural observation by optical microscopy, SEM-EDS, TEM-EDS/SAD and XRD analysis; SEM fixed-point observation method was applied to evaluate its thermal stability. As-cast microstructural observation consistently demonstrates the solidification sequence of the studied alloy predicted by phase diagram calculation. Based on the phase diagram calculation, SEM-EDS, TEM-EDS/SAD and XRD analysis, as well as evidences on Al-Si-Mn-Fe compounds from the literature, the primary and eutectic Mn-rich phases with different morphologies in the studied alloy are identified to be Al15Mn3Si2 that has a body-centered cubic (BCC) structure with a lattice constant of a = 1.352 nm. SEM fixed-point observation and XRD analysis indicate that Al15Mn3Si2 phase has more excellent thermal stability at high temperature than that of CuAl2 phase and can serve as the major strengthening phase in heat-resistant aluminum alloy that has to face a high-temperature working environment. Results of tension test show that addition of Mn can improve the strength of Al-Si-Cu alloy, especially at elevated temperature.

Screening and assessment of solidification/stabilization amendments suitable for soils of lead-acid battery contaminated site.

PubMed

Zhang, Zhuo; Guo, Guanlin; Teng, Yanguo; Wang, Jinsheng; Rhee, Jae Seong; Wang, Sen; Li, Fasheng

2015-05-15

Lead exposure via ingestion of soil and dust generally occurs at lead-acid battery manufacturing and recycling sites. Screening solidification/stabilization (S/S) amendments suitable for lead contaminated soil in an abandoned lead-acid battery factory site was conducted based on its chemical forms and environmental risks. Twelve amendments were used to immobilize the Pb in soil and assess the solidification/stabilization efficiency by toxicity leaching tests. The results indicated that three amendments, KH₂PO₄ (KP), KH₂PO₄:oyster shell power=1:1 (by mass ratio; SPP), and KH₂PO₄:sintered magnesia=1:1 (by mass ratio; KPM) had higher remediation efficiencies that led to a 92% reduction in leachable Pb with the addition of 5% amendments, while the acid soluble fraction of Pb (AS-Pb) decreased by 41-46% and the residual fraction (RS-Pb) increased by 16-25%. The S/S costs of the three selected amendments KP, SPP, and KPM could be controlled to $22.3 per ton of soil when the Pb concentration in soil ranged from 2000 to 3000 mg/kg. The results of this study demonstrated that KP, SPP, and KPM can effectively decrease bioavailability of Pb. These findings could provide basis for decision-making of S/S remediation of lead-acid battery contaminated sites. Copyright © 2015 Elsevier B.V. All rights reserved.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ahmed, A.; Chadwick, T.; Makhlouf, M.

This paper deals with the effects of various solidification variables such as cooling rate, temperature gradient, solidification rate, etc. on the microstructure and shrinkage defects in aluminum alloy (A356) castings. The effects are first predicted using commercial solidification modeling softwares and then verified experimentally. For this work, the authors are considering a rectangular bar cast in a sand mold. Simulation is performed using SIMULOR, a finite volume based casting simulation program. Microstructural variables such as dendritic arm spacing (DAS) and defects (percentage porosity) are calculated from the temperature fields, cooling rate, solidification time, etc. predicted by the computer softwares. Themore » same variables are then calculated experimentally in the foundry. The test piece is cast in a resin (Sodium Silicate) bonded sand mold and the DAS and porosity variables are calculated using Scanning Electron Microscopy and Image Analysis. The predictions from the software are compared with the experimental results. The results are presented and critically analyzed to determine the quality of the predicted results. The usefulness of the commercial solidification modeling softwares as a tool for the foundry are also discussed.« less

Technique Incorporating Cooling & Contraction / Expansion Analysis to Illustrate Shrinkage Tendency in Cast Irons

NASA Astrophysics Data System (ADS)

Stan, S.; Chisamera, M.; Riposan, I.; Neacsu, L.; Cojocaru, A. M.; Stan, I.

2017-06-01

With the more widespread adoption of thermal analysis testing, thermal analysis data have become an indicator of cast iron quality. The cooling curve and its first derivative display patterns that can be used to predict the characteristics of a cast iron. An experimental device was developed with a technique to simultaneously evaluate cooling curves and expansion or contraction of cast metals during solidification. Its application is illustrated with results on shrinkage tendency of ductile iron treated with FeSiMgRECa master alloy and inoculated with FeSi based alloys, as affected by mould rigidity (green sand and resin sand moulds). Undercooling at the end of solidification relative to the metastable (carbidic) equilibrium temperature and the expansion within the solidification sequence appear to have a strong influence on the susceptibility to macro - and micro - shrinkage in ductile iron castings. Green sand moulds, as less rigid moulds, encourage the formation of contraction defects, not only because of high initial expansion values, but also because of a higher cooling rate during solidification, and consequently, increased undercooling below the metastable equilibrium temperature up to the end of solidification.

Effect of Secondary Cooling Conditions on Solidification Structure and Central Macrosegregation in Continuously Cast High-Carbon Rectangular Billet

NASA Astrophysics Data System (ADS)

Zeng, Jie; Chen, Weiqing

2015-10-01

Solidification structures of high carbon rectangular billet with a size of 180 mm × 240 mm in different secondary cooling conditions were simulated using cellular automaton-finite element (CAFE) coupling model. The adequacy of the model was compared with the simulated and the actual macrostructures of 82B steel. Effects of the secondary cooling water intensity on solidification structures including the equiaxed grain ratio and the equiaxed grain compactness were discussed. It was shown that the equiaxed grain ratio and the equiaxed grain compactness changed in the opposite direction at different secondary cooling water intensities. Increasing the secondary cooling water intensity from 0.9 or 1.1 to 1.3 L/kg could improve the equiaxed grain compactness and decrease the equiaxed grain ratio. Besides, the industrial test was conducted to investigate the effect of different secondary cooling water intensities on the center carbon macrosegregation of 82B steel. The optimum secondary cooling water intensity was 0.9 L/kg, while the center carbon segregation degree was 1.10. The relationship between solidification structure and center carbon segregation was discussed based on the simulation results and the industrial test.

Strength characteristics of lightly solidified dredged marine clay admixed with bentonite

NASA Astrophysics Data System (ADS)

Ariffin, Syazwana Tajul; Chan, Chee-Ming

2017-11-01

Strength characteristic is a significant parameter in measuring the effect of soil improvement and effective composition of solidification. In this study, the dredged marine sediment (DMS) collected from Kuala Perlis (Malaysia) was examined to determine its strength characteristics under light cement solidification with bentonite. Dredged marine clay generally has the low shear strength and high void ratio, and consists mainly of soil particles of the fine-grained type. As a discarded geo-waste, it can be potentially treated to for reuse as a backfill material instead of being disposed of, hence reducing the negative impact on the environment. Physico-chemical parameters of the dredged sample were first determined, then solidification was carried out to improve the engineering properties by admixing ordinary Portland cement (OPC) as the binder and bentonite as a volume enhancer to the soil. The DMS was treated with the addition of 3 % and 6 % cement and bentonite within the range of 0-30 %. The specimens were cured at room temperature for 3, 7 and 14 days. The strength gain was measured by unconfined compression test and vane shear test. The laboratory test results were analyzed to establish the relationship between strength properties and solidification specifications. In summary, the strength of specimens increased with the increase of the quantity of bentonite and cement to get the effective composition of the specimen.

Development of a High Chromium Ni-Base Filler Metal Resistant to Ductility Dip Cracking and Solidification Cracking

NASA Astrophysics Data System (ADS)

Hope, Adam T.

Many nuclear reactor components previously constructed with Ni-based alloys containing 20 wt% Cr have been found to be susceptible to stress corrosion cracking. The nuclear power industry now uses high chromium (˜30wt%) Ni-based filler metals to mitigate stress corrosion cracking. Current alloys are plagued with weldability issues, either solidification cracking or ductility dip cracking (DDC). Solidification cracking is related to solidification temperature range and the DDC is related to the fraction eutectic present in the microstructure. It was determined that an optimal alloy should have a solidification temperature range less than 150°C and at least 2% volume fraction eutectic. Due to the nature of the Nb rich eutectic that forms, it is difficult to avoid both cracking types simultaneously. Through computational modeling, alternative eutectic forming elements, Hf and Ta, have been identified as replacements for Nb in such alloys. Compositions have been optimized through a combination of computational and experimental techniques combined with a design of experiment methodology. Small buttons were melted using commercially pure materials in a copper hearth to obtain the desired compositions. These buttons were then subjected to a gas tungsten arc spot weld. A type C thermocouple was used to acquire the cooling history during the solidification process. The cooling curves were processed using Single Sensor Differential Thermal Analysis to determine the solidification temperature range, and indicator of solidification cracking susceptibility. Metallography was performed to determine the fraction eutectic present, an indicator of DDC resistance. The optimal level of Hf to resist cracking was found to be 0.25 wt%. The optimal level of Ta was found to be 4 wt%. gamma/MC type eutectics were found to form first in all Nb, Ta, and Hf-bearing compositions. Depending on Fe and Cr content, gamma/Laves eutectic was sometimes found in Nb and Ta-bearing compositions, while Hf-bearing compositions had gamma/Ni7Hf2 as the final eutectic to solidify. This study found that the extra Cr in the current generation alloys promotes the gamma/Laves phase eutectic, which expands the solidification temperature range and promotes solidification cracking. Both Ta-bearing and Hf-bearing eutectics were found to solidify at higher temperatures than Nb-bearing eutectics, leading to narrower solidification temperature ranges. Weldability testing on the optimized Ta-bearing compositions revealed good resistance to both DDC and solidification cracking. Unexpectedly, the optimized Hf-bearing compositions were quite susceptible to solidification cracking. This led to an investigation on the possible wetting effect of eutectics on solidification cracking susceptibly, and a theory on how wetting affects the solidification crack susceptibility and the volume fraction of eutectic needed for crack healing has been proposed. Alloys with eutectics that easily wet the grain boundaries have increased solidification crack susceptibility at low volume fraction eutectics, but as the fraction eutectic is increased, experience crack healing at relatively lower fraction eutectics than alloys with eutectics that don't wet as easily. Hf rich eutectics were found to wet grain boundaries significantly more than Nb rich eutectics. Additions of Mo were also found to increase the wetting of eutectics in Nb-bearing alloys.

TEMHD Effects on Solidification Under Microgravity Conditions

NASA Technical Reports Server (NTRS)

Kao, Andrew; Pericleous, Koulis

2012-01-01

An unexplored potential exists to control microstructure evolution through the use of external DC magnetic fields. Thermoelectric currents form during solidification and interact with this external field to drive microscopic fluid dynamics within the inter-dendritic region. The convective heat and mass transport can lead to profound changes on the dendritic structure. In this paper the effect of high magnetic fields is demonstrated through the use of both 3-dimensional and 2-dimensional numerical models. The results show that the application of a magnetic field causes significant disruption to the dendritic morphology. Investigation into the underlying mechanism gives initial indicators of how external magnetic fields can either lead to unexpected growth behaviour, or alternatively can be used to control the evolution of microstructure in undercooled melts as encountered in levitated droplet solidification.

Minimizing Segregation During the Controlled Directional Solidification of Dendritic Alloys Publication: Metallurgical and Materials Transactions

NASA Technical Reports Server (NTRS)

Grugel, R. N.; Fedoseyev, A. I.; Kim, S.; Curreri, Peter A. (Technical Monitor)

2002-01-01

Gravity-driven thermosolutal convection that arises during controlled directional solidification (DS) of dendritic alloys promotes detrimental macro-segregation (e.g. freckles and steepling) in products such as turbine blades. Considerable time and effort has been spent to experimentally and theoretically investigate this phenomena; although our knowledge has advanced to the point where convection can be modeled and accurately compared to experimental results, little has been done to minimize its onset and deleterious effects. The experimental work demonstrates that segregation can be. minimized and microstructural uniformity promoted when a slow axial rotation is applied to the sample crucible during controlled directional solidification processing. Numerical modeling utilizing continuation and bifurcation methods have been employed to develop accurate physical and mathematical models with the intent of identifying and optimizing processing parameters.

Continuous Solidification of Immiscible Alloys and Microstructure Control

NASA Astrophysics Data System (ADS)

Jiang, Hongxiang; Zhao, Jiuzhou

2018-05-01

Immiscible alloys have aroused considerable interest in last few decades due to their excellent physical and mechanical characteristics as well as potential industrial applications. Up to date, plenty of researches have been carried out to investigate the solidification of immiscible alloys on the ground or in space and great progress has been made. It is demonstrated that the continuous solidification technique have great future in the manufacturing of immiscible alloys, it also indicates that the addition of surface active micro-alloying or inoculants for the nucleation of the minority phase droplets and proper application of external fields, e.g., static magnetic field, electric current, microgravity field, etc. may promote the formation of immiscible alloys with an expected microstructure. The objective of this article is to review the research work in this field.

Metastable and unstable cellular solidification of colloidal suspensions

NASA Astrophysics Data System (ADS)

Deville, Sylvain; Maire, Eric; Bernard-Granger, Guillaume; Lasalle, Audrey; Bogner, Agnès; Gauthier, Catherine; Leloup, Jérôme; Guizard, Christian

2009-12-01

Colloidal particles are often seen as big atoms that can be directly observed in real space. They are therefore becoming increasingly important as model systems to study processes of interest in condensed-matter physics such as melting, freezing and glass transitions. The solidification of colloidal suspensions has long been a puzzling phenomenon with many unexplained features. Here, we demonstrate and rationalize the existence of instability and metastability domains in cellular solidification of colloidal suspensions, by direct in situ high-resolution X-ray radiography and tomography observations. We explain such interface instabilities by a partial Brownian diffusion of the particles leading to constitutional supercooling situations. Processing under unstable conditions leads to localized and global kinetic instabilities of the solid/liquid interface, affecting the crystal morphology and particle redistribution behaviour.

Applications analysis report: Silicate Technology Corporation's solidification/stabilization technology for organic and inorganic contaminants in soils

NASA Astrophysics Data System (ADS)

Bates, E.

1992-12-01

The STC demonstration was conducted under EPA's Superfund Innovative Technology Evaluation (SITE) Program in November, 1990, at the Selma Pressure Treating (SPT) wood preserving site in Selma, California. The SPT site was contaminated with both organics, predominantly pentachlorophenol (PCP), inorganics, mainly arsenic, chromium, and copper. Extensive sampling and analyses were performed on the waste both before and after treatment to compare physical, chemical, and leaching characteristics of raw and treated wastes. STC's contaminated soil treatment process was evaluated based on contaminant mobility measured by numerous leaching tests, structural integrity of the solidified material, measured by physical and engineering tests and morphological examinations; and economic analysis, using cost information supplied by STC and the results of the SITE demonstration, the vendor's design and test data, and other laboratory and field applications of the technology. It discusses the advantages, disadvantages, and limitations, as well as estimated costs of the technology.

Solidification Using the Baffle in Sealed Ampoules

NASA Technical Reports Server (NTRS)

Ostrogorsky, A.; Marin, C.; Churilov, A.; Volz, M. P.; Bonner, W. A.; Spivey, R. A.; Smith, G.

2003-01-01

Solidification Using a Baffle in Sealed Ampoules (SUBSA) is the first investigation conducted in the Microgravity Science Glovebox (MSG) Facility at the International Space Station (ISS) Alpha. In July, August and September of 2002, 8 single crystals of InSb, doped with Te and Zn, were directionally solidified in microgravity. Ground based tests, related numerical modeling and images of the growth process obtained in microgravity are presented.

Modeling the interaction of biological cells with a solidifying interface

NASA Astrophysics Data System (ADS)

Chang, Anthony; Dantzig, Jonathan A.; Darr, Brian T.; Hubel, Allison

2007-10-01

In this article, we develop a modified level set method for modeling the interaction of particles with a solidifying interface. The dynamic computation of the van der Waals and drag forces between the particles and the solidification front leads to a problem of multiple length scales, which we resolve using adaptive grid techniques. We present a variety of example problems to demonstrate the accuracy and utility of the method. We also use the model to interpret experimental results obtained using directional solidification in a cryomicroscope.

The effect of axial crucible rotation on microstructural uniformity during horizontal directional solidification

NASA Technical Reports Server (NTRS)

Grugel, R. N.; Kim, Shinwoo; Woodward, Tracey; Wang, T. G.

1992-01-01

The effects on microstructure of crucible orientation with respect to the earth's gravitational vector, g, during directional solidification of low-volume fraction copper and aluminum, Pb-Cu, and Sn-Al alloys are examined. It is demonstrated that horizontal alignment (i.e. perpendicular to g) in combination with axial rotation of the crucible during growth is sufficient to negate factors which initiate macrosegregation, e.g. density gradients attributed to temperature and/or compositional differences, and promotes a uniform microstructure.

Fundamental Studies of Solidification in Microgravity Using Real-Time X-Ray Microscopy

NASA Technical Reports Server (NTRS)

Curreri, Peter A.; Kaukler, William; Sen, Subhayu; Bhat, Biliyar N.

1999-01-01

This research applies a state of the art X-ray Transmission Microscope, XTM, to image (with resolutions up to 3 micrometers) the solidification of metallic or semiconductor alloys in real-time. We have successfully imaged in real-time: interfacial morphologies, phase growth, coalescence, incorporation of phases into the growing interface, and the solute boundary layer in the liquid at the solid-liquid interface. We have also measured true local growth rates and can evaluate segregation structures in the solid; a form of in-situ metallography. During this study, the growth of secondary phase fibers and lamellae from eutectic and monotectic alloys have been imaged during solidification, in real-time, for the first time in bulk metal alloys. Current high resolution X-ray sources and high contrast X-ray detectors have advanced to allow systematic study of solidification dynamics and the resulting microstructure. We have employed a state-of-the-art sub-micron source with acceleration voltages of 10-100 kV to image solidification of metals. One useful strength of the XTM stems from the manner an image is formed. The radiographic image is a shadow formed by x-ray photons that are not absorbed as they pass through the specimen. Composition gradients within the specimen cause variations in absorption of the flux such that the final image represents a spatial integral of composition (or thickness). The ability to image these features in real-time enables more fundamental and detailed understanding of solidification dynamics than has previously been possible. Hence, application of this technique towards microgravity experiments will allow rigorous testing of critical solidification models.

Alkali activated solidification/stabilisation of air pollution control residues and co-fired pulverised fuel ash.

PubMed

Shirley, Robin; Black, Leon

2011-10-30

This paper examines the potential treatment by solidification/stabilisation (S/S) of air pollution control (APC) residues using only waste materials otherwise bound for disposal, namely a pulverised fuel ash (PFA) from a co-fired power station and a waste caustic solution. The use of waste materials to stabilise hazardous wastes in order to meet waste acceptance criteria (WAC) would offer an economical and efficient method for reducing the environmental impact of the hazardous waste. The potential is examined against leach limits for chlorides, sulphates and total dissolved solids, and compressive strength performance described in the WAC for stable non-reactive (SNR) hazardous waste landfill cells in England and Wales. The work demonstrates some potential for the treatment, including suitable compressive strengths to meet regulatory limits. Monolithic leach results showed good encapsulation compared to previous work using a more traditional cement binder. However, consistent with previous work, SNR WAC for chlorides was not met, suggesting the need for a washing stage. The potential problems of using a non-EN450 PFA for S/S applications were also highlighted, as well as experimental results which demonstrate the effect of ionic interactions on the mobility of phases during regulatory leach testing. Copyright © 2011 Elsevier B.V. All rights reserved.

Mechanism of Macrosegregation Formation in Continuous Casting Slab: A Numerical Simulation Study

NASA Astrophysics Data System (ADS)

Jiang, Dongbin; Wang, Weiling; Luo, Sen; Ji, Cheng; Zhu, Miaoyong

2017-12-01

Solidified shell bulging is supposed to be the main reason for slab center segregation, while the influence of thermal shrinkage rarely has been considered. In this article, a thermal shrinkage model coupled with the multiphase solidification model is developed to investigate the effect of the thermal shrinkage, solidification shrinkage, grain sedimentation, and thermal flow on solute transport in the continuous casting slab. In this model, the initial equiaxed grains contract freely with the temperature decrease, while the coherent equiaxed grains and columnar phase move directionally toward the slab surface. The results demonstrate that the center positive segregation accompanied by negative segregation in the periphery zone is mainly caused by thermal shrinkage. During the solidification process, liquid phase first transports toward the slab surface to compensate for thermal shrinkage, which is similar to the case considering solidification shrinkage, and then it moves opposite to the slab center near the solidification end. It is attributed to the sharp decrease of center temperature and the intensive contract of solid phase, which cause the enriched liquid to be squeezed out. With the effect of grain sedimentation and thermal flow, the negative segregation at the external arc side (zone A1) and the positive segregation near the columnar-to-equiaxed transition at the inner arc side (position B1) come into being. Besides, it is found that the grain sedimentation and thermal flow only influence solute transport before equiaxed grains impinge with each other, while the solidification and thermal shrinkage still affect solute redistribution in the later stage.

Successful Isothermal Dendritic Growth Experiment (IDGE) Proves Current Theories of Dendritic Solidification are Flawed

NASA Technical Reports Server (NTRS)

1996-01-01

The scientific objective of the Isothermal Dendritic Growth Experiment (IDGE) is to test fundamental assumptions about dendritic solidification of molten materials. "Dendrites"-- from the ancient Greek word for tree--are tiny branching structures that form inside molten metal alloys when they solidify during manufacturing. The size, shape, and orientation of the dendrites have a major effect on the strength, ductility (ability to be molded or shaped), and usefulness of an alloy. Nearly all of the cast metal alloys used in everyday products (such as automobiles and airplanes) are composed of thousands to millions of tiny dendrites. Gravity, present on Earth, causes convection currents in molten alloys that disturb dendritic solidification and make its precise study impossible. In space, gravity is negated by the orbiting of the space shuttle. Consequently, IDGE (which was conducted on the space shuttle) gathered the first precise data regarding undisturbed dendritic solidification. IDGE is a microgravity materials science experiment that uses an apparatus which was designed, built, tested, and operated by people from the NASA Lewis Research Center. This experiment was conceived by the principal investigator, Professor Martin E. Glicksman, from Rensselaer Polytechnic Institute in Troy, New York. The experiment was a team effort of Lewis civil servants, contractors from Aerospace Design & Fabrication Inc. (ADF), and personnel at Rensselaer.

Reduction in secondary dendrite arm spacing in cast eutectic Al-Si piston alloys by cerium addition

NASA Astrophysics Data System (ADS)

Ahmad, R.; Asmael, M. B. A.; Shahizan, N. R.; Gandouz, S.

2017-01-01

The effects of Ce on the secondary dendrite arm spacing (SDAS) and mechanical behavior of Al-Si-Cu-Mg alloys were investigated. The reduction of SDAS at different Ce concentrations was evaluated in a directional solidification experiment via computer-aided cooling curve thermal analysis (CA‒CCTA). The results showed that 0.1wt%-1.0wt% Ce addition resulted in a rapid solidification time, Δ t s, and low solidification temperature, Δ T S, whereas 0.1wt% Ce resulted in a fast solidification time, Δ t a-Al, of the α-Al phase. Furthermore, Ce addition refined the SDAS, which was reduced to approximately 36%. The mechanical properties of the alloys with and without Ce were investigated using tensile and hardness tests. The quality index ( Q) and ultimate tensile strength of (UTS) Al-Si-Cu-Mg alloys significantly improved with the addition of 0.1wt% Ce. Moreover, the base alloy hardness was improved with increasing Ce concentration.

Directional Solidification and Mechanical Properties of NiAl-NiAlTa Alloys

NASA Technical Reports Server (NTRS)

Johnson, D. R.; Chen, X. F.; Oliver, B. F.; Noebe, R. D.; Whittenberger, J. D.

1995-01-01

Directional solidification of eutectic alloys is a promising technique for producing in-situ composite materials exhibiting a balance of properties. Consequently, the microstructure, creep strength and fracture toughness of directionally solidified NiAl-NiAlTa alloys were investigated. Directional solidification was performed by containerless processing techniques to minimize alloy contamination. The eutectic composition was found to be NiAl-15.5 at% Ta and well-aligned microstructures were produced at this composition. A near-eutectic alloy of NiAl-14.5Ta was also investigated. Directional solidification of the near-eutectic composition resulted in microstructures consisting of NiAl dendrites surrounded by aligned eutectic regions. The off-eutectic alloy exhibited promising compressive creep strengths compared to other NiAl-based intermetallics, while preliminary testing indicated that the eutectic alloy was competitive with Ni-base single crystal superalloys. The room temperature toughness of these two-phase alloys was similar to that of polycrystalline NiAl even with the presence of the brittle Laves phase NiAlTa.

Low-gravity homogenization and solidification of aluminum antimonide. [Apollo-Soyuz test project

NASA Technical Reports Server (NTRS)

Ang, C.-Y.; Lacy, L. L.

1976-01-01

The III-V semiconducting compound AlSb shows promise as a highly efficient solar cell material, but it has not been commercially exploited because of difficulties in compound synthesis. Liquid state homogenization and solidification of AlSb were carried out in the Apollo-Soyuz Test Project Experiment MA-044 in the hope that compositional homogeneity would be improved by negating the large density difference between the two constituents. Post-flight analysis and comparative characterization of the space-processed and ground-processed samples indicate that there are major homogeneity improvements in the low-gravity solidified material.

Solidification and Microstructure of Ni-Containing Al-Si-Cu Alloy

NASA Astrophysics Data System (ADS)

Fang, Li; Ren, Luyang; Geng, Xinyu; Hu, Henry; Nie, Xueyuan; Tjong, Jimi

2018-01-01

2 wt. % nickel (Ni) addition was introduced into a conventional cast aluminum alloy A380. The influence of transition alloying element nickel on the solidification behavior of cast aluminum alloy A380 was investigated via thermal analyses based on temperature measurements recorded on cooling curves. The corresponding first and second derivatives of the cooling curves were derived to reveal the details of phase changes during solidification. The nucleation of the primary α-Al phase and eutectic phases were analyzed. The microstructure analyses by scanning electron microscopy (SEM) with energy dispersive X-ray spectroscopy (EDS) indicate that different types and amount of eutectic phases are present in the tested two alloys. The introduction of Ni forms the complex Ni-containing intermetallic phases with Cu and Al.

Fully-Implicit Orthogonal Reconstructed Discontinuous Galerkin for Fluid Dynamics with Phase Change

DOE PAGES

Nourgaliev, R.; Luo, H.; Weston, B.; ...

2015-11-11

A new reconstructed Discontinuous Galerkin (rDG) method, based on orthogonal basis/test functions, is developed for fluid flows on unstructured meshes. Orthogonality of basis functions is essential for enabling robust and efficient fully-implicit Newton-Krylov based time integration. The method is designed for generic partial differential equations, including transient, hyperbolic, parabolic or elliptic operators, which are attributed to many multiphysics problems. We demonstrate the method’s capabilities for solving compressible fluid-solid systems (in the low Mach number limit), with phase change (melting/solidification), as motivated by applications in Additive Manufacturing (AM). We focus on the method’s accuracy (in both space and time), as wellmore » as robustness and solvability of the system of linear equations involved in the linearization steps of Newton-based methods. The performance of the developed method is investigated for highly-stiff problems with melting/solidification, emphasizing the advantages from tight coupling of mass, momentum and energy conservation equations, as well as orthogonality of basis functions, which leads to better conditioning of the underlying (approximate) Jacobian matrices, and rapid convergence of the Krylov-based linear solver.« less

Gravitational modulation of thermosolutal convection during directional solidification

NASA Astrophysics Data System (ADS)

Murray, B. T.; Coriell, S. R.; McFadden, G. B.; Wheeler, A. A.; Saunders, B. V.

1993-03-01

During directional solidification of a binary alloy at constant velocity, thermosolutal convection may occur due to the temperature and solute gradients associated with the solidification process. For vertical growth in an ideal furnace (lacking horizontal gradients) a quiescent state is possible. The effect of a time-periodic vertical gravitational acceleration (or equivalently vibration) on the onset of thermosolutal convection is calculated based on linear stability using Floquet theory. Numerical calculations for the onset of instability have been carried out for a semiconductor alloy with Schmidt number of 10 and Prandtl number of 0.1 with primary emphasis on large modulation frequencies in a microgravity environment for which the background gravitational acceleration is negligible. The numerical results demonstrate that there is a significant difference in stability depending on whether a heavier or lighter solute is rejected. For large modulation frequencies, the stability behavior can be described by either the method of averaging or an asymptotic resonant mode analysis.

Study on solidification of immisible alloys (M-10)

NASA Technical Reports Server (NTRS)

Kamio, Akihiko

1993-01-01

Alloying of immiscible alloys under microgravity is of interest in metallurgical processes. Several experiments investigating the alloying of immiscible alloys, such as Al-In, Al-Bi, Zn-Bi, and Zn-Pb, were done in space. Homogeneous distribution of small L2 particles in the matrix, such as an emulsion structure, was expected in the space-solidifed alloys. However, the alloys demonstrated an extremely segregated structure. To date insufficient information was obtained to explain these unexpected results. Our experiment was proposed to clarify the solidification manner of immiscible alloys and to obtain fundamental information concerning structural control of the alloys. In space, density differences between the two liquids separated in immiscible regions can be neglected, so that no sedimentation of L(sub 2) phase will take place. When the growth of the alloys is interrupted and this status is frozen by an adequate rapid cooling procedure, it will provide much information concerning decomposing homogeneous liquid and the interaction between the monotectic growth front morphology and the distribution of L(sub 2) phase. It is anticipated that the results will be useful for elucidating the monotectic solidification manner and it will be instructive to explain the segregated structures obtained in the past space experiments.

Progress on Numerical Modeling of the Dispersion of Ceramic Nanoparticles During Ultrasonic Processing and Solidification of Al-Based Nanocomposites

NASA Astrophysics Data System (ADS)

Zhang, Daojie; Nastac, Laurentiu

2016-12-01

In present study, 6061- and A356-based nano-composites are fabricated by using the ultrasonic stirring technology (UST) in a coreless induction furnace. SiC nanoparticles are used as the reinforcement. Nanoparticles are added into the molten metal and then dispersed by ultrasonic cavitation and acoustic streaming assisted by electromagnetic stirring. The applied UST parameters in the current experiments are used to validate a recently developed magneto-hydro-dynamics (MHD) model, which is capable of modeling the cavitation and nanoparticle dispersion during UST processing. The MHD model accounts for turbulent fluid flow, heat transfer and solidification, and electromagnetic field, as well as the complex interaction between the nanoparticles and both the molten and solidified alloys by using ANSYS Maxwell and ANSYS Fluent. Molecular dynamics (MD) simulations are conducted to analyze the complex interactions between the nanoparticle and the liquid/solid interface. The current modeling results demonstrate that a strong flow can disperse the nanoparticles relatively well during molten metal and solidification processes. MD simulation results prove that ultrafine particles (10 nm) will be engulfed by the solidification front instead of being pushed, which is beneficial for nano-dispersion.

Treatment of Petroleum Sludge By Using Solidification/Stabilization (S/S) Method : Effect of Hydration Days to Heavy Metals Leaching and Strength

NASA Astrophysics Data System (ADS)

Murshid, N.; Kamil, N. A. F. M.; Kadir, A. A.

2018-04-01

Petroleum sludge is one of the major solid wastes generated in the petroleum industry. Generally, there are numbers of heavy metals in petroleum sludge and one treatment that is gaining prominence to treat a variety of mixed organic and inorganic waste is solidification/stabilization (S/S) method. The treatment protects human health and the environment by immobilizing contaminants within the treated material and prevents migration of the contaminants. In this study, solidification/stabilization (S/S) method has been used to treat the petroleum sludge. The comparison of hydration days, namely, 7th and 28th days in these cement-based waste materials were studied by using Synthetic Precipitate Leaching Procedure (SPLP). The results were compared to the United States Environmental Protection Agency (USEPA) standards. The results for leaching test concluded that less percentage OPC gave maximum concentration of heavy metals leaching due to deficient in Calcium Oxide (CaO), which is can caused weak solidification in the mixture. Physical and mechanical properties conducted such as compressive strength and density test. From the results, it shows addition up to of 30percentage PS give results which comply with minimum landfill dispose limit. The results shows correlation between strength and density are strong regression coefficient of 82.7%. In conclusion, S/S method can be alternative disposal method for PS in the same time complies with standard for minimum landfill disposal limit. The results for leaching test concluded the less OPC percentage gave maximum concentration of heavy metals leaching.

The effect of solidification rate on the formability of nickel aluminide containing iron and boron

NASA Technical Reports Server (NTRS)

Carro, G.; Flanagan, W. F.

1987-01-01

Following reports that rapid solidification improves the ductility of some nickel aluminides, an investigation has been conducted of the possibility of additional improvement in a nickel aluminide containing both Fe and B. Free fall-solidified and free fall/splat-quenched samples similar to those producible under microgravity conditions in space were prepared, and their microstructure was characterized. Attention is given to the preliminary results of tests quantitatively measuring mechanical properties.

Stabilization/solidification of hot dip galvanizing ash using different binders.

PubMed

Vinter, S; Montanes, M T; Bednarik, V; Hrivnova, P

2016-12-15

This study focuses on solidification of hot dip-galvanizing ash with a high content of zinc and soluble substances. The main purpose of this paper is to immobilize these pollutants into a matrix and allow a safer way for landfill disposal of that waste. Three different binders (Portland cement, fly ash and coal fluidized-bed combustion ash) were used for the waste solidification. Effectiveness of the process was evaluated using leaching test according to EN 12457-4 and by using the variance analysis and the categorical multifactorial test. In the leaching test, four parameters were observed: pH, zinc concentration in leachate, and concentration of chlorides and dissolved substances in leachate. The acquired data was then processed using statistical software to find an optimal solidifying ratio of the addition of binder, water, and waste to the mixture, with the aim to fulfil the requirement for landfill disposal set by the Council Decision 2003/33/EC. The influence on the main observed parameters (relative amount of water and a binder) on the effectiveness of the used method and their influence of measured parameters was also studied. Copyright © 2016 Elsevier B.V. All rights reserved.

Effect of Marangoni Convection Generated by Voids on Segregation During Low-G and 1-G Solidification

NASA Technical Reports Server (NTRS)

Kassemi, M.; Fripp, A.; Rashidnia, N.; deGroh, H.

2001-01-01

Solidification experiments, especially microgravity solidification experiments, are often compromised by the evolution of unwanted voids or bubbles in the melt. Although these voids and/or bubbles are highly undesirable, there is currently no effective means of preventing their formation or of eliminating their adverse effects, particularly during microgravity experiments. Marangoni convection caused by these voids can drastically change the transport processes in the melt. Recent microgravity experiments by Matthiesen (1) Andrews (2) and Fripp (3) are perfect examples of how voids and bubbles can affect the outcome of costly space experiments and significantly increase the level of difficulty in interpreting their results. Formation of bubbles have caused problems in microgravity experiments for a long time. Even in the early Skylab mission an unexpectedly large number of bubbles were detected in the four materials processing experiments reported by Papazian and Wilcox (4). They demonstrated that while during ground-based tests bubbles were seen to detach from the interface easily and float to the top of the melt, in low-gravity tests no detachment from the interface occurred and large voids were grown in the crystal. More recently, the lead-tin-telluride crystal growth experiment of Fripp et al.(3) flown aboard the USMP-3 mission has provided very interesting results. The purpose of the study was to investigate the effect of natural convection on the solidification process by growing the samples at different orientations with respect to the gravitational field. Large pores and voids were found in the three solid crystal samples processed in space. Post-growth characterization of the compositional profiles of the cells indicated considerable levels of mixing even in the sample grown in the hot-on-top stable configuration. The mixing was attributed to thermocapillary convection caused by the voids and bubbles which evolved during growth. Since the thermocapillary convection is orientation-independent, diffusion-controlled growth was not possible in any of the samples, even the top-heated one. These results are consistent with recent studies of thermocapillary convection generated by a bubble on a heated surface undertaken by Kassemi and Rashidnia (5-7) where it is numerically and experimentally shown that the thermocapillary flow generated by a bubble in a model fluid (silicone oil) can drastically modify the temperature field through vigorous mixing of the fluid around it, especially under microgravity conditions.

Finite Element Multi-scale Modeling of Chemical Segregation in Steel Solidification Taking into Account the Transport of Equiaxed Grains

NASA Astrophysics Data System (ADS)

Nguyen, Thi-Thuy-My; Gandin, Charles-André; Combeau, Hervé; Založnik, Miha; Bellet, Michel

2018-02-01

The transport of solid crystals in the liquid pool during solidification of large ingots is known to have a significant effect on their final grain structure and macrosegregation. Numerical modeling of the associated physics is challenging since complex and strong interactions between heat and mass transfer at the microscopic and macroscopic scales must be taken into account. The paper presents a finite element multi-scale solidification model coupling nucleation, growth, and solute diffusion at the microscopic scale, represented by a single unique grain, while also including transport of the liquid and solid phases at the macroscopic scale of the ingots. The numerical resolution is based on a splitting method which sequentially describes the evolution and interaction of quantities into a transport and a growth stage. This splitting method reduces the non-linear complexity of the set of equations and is, for the first time, implemented using the finite element method. This is possible due to the introduction of an artificial diffusion in all conservation equations solved by the finite element method. Simulations with and without grain transport are compared to demonstrate the impact of solid phase transport on the solidification process as well as the formation of macrosegregation in a binary alloy (Sn-5 wt pct Pb). The model is also applied to the solidification of the binary alloy Fe-0.36 wt pct C in a domain representative of a 3.3-ton steel ingot.

Solidification of II-VI Compounds in a Rotating Magnetic Field

NASA Technical Reports Server (NTRS)

Gillies, D. C.; Volz, M. P.; Mazuruk, K.; Motakef, S.; Dudley, M.; Matyi, R.

1999-01-01

This project is aimed at using a rotating magnetic field (RMF) to control fluid flow and transport during directional solidification of elemental and compound melts. Microgravity experiments have demonstrated that small amounts of residual acceleration of less than a micro-g can initiate and prolong fluid flow, particularly when there is a static component of the field perpendicular to the liquid solid interface. Thus a true diffusion boundary layer is not formed, and it becomes difficult to verify theories of solidification or to achieve diffusion controlled solidification. The RMF superimposes a stirring effect on an electrically conducting liquid, and with appropriate field strengths and frequencies, controlled transport of material through a liquid column can be obtained. As diffusion conditions are precluded and complete mixing conditions prevail, the technique is appropriate for traveling solvent zone or float zone growth methods in which the overall composition of the liquid can be maintained throughout the growth experiment. Crystals grown by RMF techniques in microgravity in previous, unrelated missions have shown exceptional properties. The objective of the project is two-fold, namely (1) using numerical modeling to simulate the behavior of a solvent zone with applied thermal boundary conditions and demonstrate the effects of decreasing gravity levels, or an increasing applied RMF, or both, and (2) to grow elements and II-VI compounds from traveling solvent zones both with and without applied RMFs, and to determine objectively how well the modeling predicts solidification parameters. Numerical modeling has demonstrated that, in the growth of CdTe from a tellurium solution, a rotating magnetic field can advantageously modify the shape of the liquid solid interface such that the interface is convex as seen from the liquid. Under such circumstances, the defect structure is reduced as any defects which are formed tend to grow out and not propagate. The flow of liquid, however, is complex due to the competing flow induced by the rotating magnetic field and the buoyancy driven convection. When the acceleration forces are reduced to one thousandth of gravity, the flow pattern is much simplified and well controlled material transport through the solvent zone can be readily achieved. Triple axis diffractometry and x-ray synchrotron topography have demonstrated that there is no significant improvement in crystal quality for HgCdTe grown on earth from a tellurium solution when a rotating magnetic field is applied. However, modeling shows that the flow in microgravity with a rotating magnetic field would produce a superior product.

Microstructure and Solidification Crack Susceptibility of Al 6014 Molten Alloy Subjected to a Spatially Oscillated Laser Beam.

PubMed

Kang, Minjung; Han, Heung Nam; Kim, Cheolhee

2018-04-23

Oscillating laser beam welding for Al 6014 alloy was performed using a single mode fiber laser and two-axis scanner system. Its effect on the microstructural evolution of the fusion zone was investigated. To evaluate the influence of oscillation parameters, self-restraint test specimens were fabricated with different beam patterns, widths, and frequencies. The behavior of hot cracking propagation was analyzed by high-speed camera and electron backscatter diffraction. The behavior of crack propagation was observed to be highly correlated with the microstructural evolution of the fusion zone. For most oscillation conditions, the microstructure resembled that of linear welds. A columnar structure was formed near the fusion line and an equiaxed structure was generated at its center. The wide equiaxed zone of oscillation welding increased solidification crack susceptibility. For an oscillation with an infinite-shaped scanning pattern at 100 Hz and 3.5 m/min welding speed, the bead width, solidification microstructure, and the width of the equiaxed zone at the center of fusion fluctuated. Furthermore, the equiaxed and columnar regions alternated periodically, which could reduce solidification cracking susceptibility.

Microstructure and Solidification Crack Susceptibility of Al 6014 Molten Alloy Subjected to a Spatially Oscillated Laser Beam

PubMed Central

Kang, Minjung; Han, Heung Nam

2018-01-01

Oscillating laser beam welding for Al 6014 alloy was performed using a single mode fiber laser and two-axis scanner system. Its effect on the microstructural evolution of the fusion zone was investigated. To evaluate the influence of oscillation parameters, self-restraint test specimens were fabricated with different beam patterns, widths, and frequencies. The behavior of hot cracking propagation was analyzed by high-speed camera and electron backscatter diffraction. The behavior of crack propagation was observed to be highly correlated with the microstructural evolution of the fusion zone. For most oscillation conditions, the microstructure resembled that of linear welds. A columnar structure was formed near the fusion line and an equiaxed structure was generated at its center. The wide equiaxed zone of oscillation welding increased solidification crack susceptibility. For an oscillation with an infinite-shaped scanning pattern at 100 Hz and 3.5 m/min welding speed, the bead width, solidification microstructure, and the width of the equiaxed zone at the center of fusion fluctuated. Furthermore, the equiaxed and columnar regions alternated periodically, which could reduce solidification cracking susceptibility. PMID:29690630

Cytogenotoxicity of sewage sludge leachate before and after calcium oxide-based solidification in human lymphocytes.

PubMed

Gajski, Goran; Oreščanin, Višnja; Garaj-Vrhovac, Vera

2011-07-01

Present study aimed to establish the chemical composition of sewage sludge leachate before/after calcium oxide-based solidification using energy dispersive X-ray fluorescence (EDXRF). The other aim was to determine leachate effects on human lymphocyte and DNA integrity in vitro using a battery of bioassays (DNA diffusion assay, micronucleus test and comet assay) to determine effects of those complex mixtures of elements on cell and DNA integrity. EDXRF showed that nickel concentration in the leachate of untreated sludge was 18.5 times higher than the upper permissible limit for inert waste landfills. Other elements were kept below the permissible values. After sludge solidification, leachate concentrations of Cr, Mn, Fe, Ni, Cu, Zn, and Pb dropped 1.6, 2.7, 37, 5.9, 3.2, 7.8, and 2.6 times, respectively. Untreated sludge leachate was cytogenotoxic to lymphocytes, and may lead to adverse effects on the exposed human populations, but calcium oxide-based solidification reduced these effects in significant manner. Copyright © 2011 Elsevier Inc. All rights reserved.

Favorite Demonstrations: Exothermic Crystallization from a Supersaturated Solution.

ERIC Educational Resources Information Center

Kauffman, George B.; And Others

1986-01-01

The use of sodium acetate solution to show supersaturation is a favorite among lecture demonstrations. However, careful adjustment of the solute-to-water ratio must be made to attain the most spectacular effect--complete solidification of the solution. Procedures to accomplish this are provided and discussed. (JN)

Dendritic growth and structure of undercooled nickel base alloys

NASA Technical Reports Server (NTRS)

Flemings, M. C.; Shiohara, Y.

1988-01-01

The principal objectives of this overall investigation are to: study means for obtaining high undercooling in levitation melted droplets, and study structures produced upon the solidification of these undercooled specimens. Thermal measurements are made of the undercooling, and of the rapid recalescence, to develop an understanding of the solidification mechanism. Comparison of results is made with the modeling studies. Characterization and metallographic work is done to gain an understanding of the relationship between rapid solidification variables and the structures so produced. In ground based work to date, solidification of undercooled Ni-25 wt percent Sn alloy was observed by high-speed cinematography and the results compared with optical temperature measurements. Also in ground based work, high-speed optical temperature measurements were made of the solidification behavior of levitated metal samples within a transparent glass medium. Two undercooled Ni-Sn alloys were examined. Measurements were carried out on samples at undercoolings up to 330 K. Microstructures of samples produced in ground based work were determined by optical metallography and by SEM, and microsegregation by electron microprobe measurements. A series of flight tests were planned to conduct experiments similar to the ground based experiments. The Space Shuttle Columbia carried an alloy undercooled experiment in the STS 61-C mission in January 1986. A sample of Ni-32.5 wt percent Sn eutectic was melted and solidified under microgravity conditions.

Development of a chromium-free consumable for joining stainless steels

NASA Astrophysics Data System (ADS)

Sowards, Jeffrey William

Government regulations in the United States (OSHA Standards: 1910; 1915; 1917; 1918; 1926) and abroad are decreasing allowable exposure levels of hexavalent chromium to welding related personnel. The latest OSHA ruling in 2006 reduced the permissible exposure limit of airborne hexavalent chromium from 52 to 5 mug m-3. Achieving the new level may not be practical from an engineering controls standpoint during the fabrication of tightly enclosed stainless steel components such as the inside of ship hulls and boiler vessels. One method of addressing this problem is to implement a chromium-free welding consumable that provides equivalent mechanical performance and corrosion characteristics to current stainless steel welding consumables. This project was aimed at developing such a consumable and evaluating its suitability for replacement of current stainless steel consumables such as E308L-16. A new shielded metal arc welding (SMAW) consumable based on the Ni-Cu-Ru system was developed for austenitic stainless steel welding. The focus of this work was evaluating the mechanical properties, weldability, and fume formation characteristics of the various iterations of consumables developed. Welds deposited on Type 304 stainless steel were evaluated with weldability tests including: mechanical testing, hot ductility testing, Strain-to-fracture testing, Transverse Varestraint testing, and button melting. Mechanical properties of weld deposits of each consumable were found to exceed minimum values of Type 304 stainless steel based on tensile testing. Guide bend testing showed that weld deposits met minimum weld ductility requirements for stainless steel consumables, such as E308-16. Hot ductility testing revealed a narrow crack susceptible region (33 to 54°C) indicating a low susceptibility to weld metal liquation cracking. GTA welds exhibited superior ductility when compared to SMA welds. This was attributed to a lack of slag inclusions in the weld deposit, which are effective weld strengtheners. Varestraint testing revealed that weld deposits have a higher solidification cracking susceptibility than stainless steel consumables used to join Type 304. Higher cracking susceptibility was attributed to austenitic solidification of the weld metal resulting in increased weld segregation and stabilization of a TiC eutectic reaction at the end of solidification. No solidification cracks were observed in actual weld deposits. Evaluation of weld microsegregation patterns showed higher dilutions of Type 304 increased segregation of Ti, promoting a TiC eutectic reaction at the end of solidification. Thermodynamic modeling techniques were used to describe the solidification the Ni-Cu weld deposits as a function of dilution with Type 304. Solidification cracking susceptibility was shown to increase with dilution during evaluation with the Cast Pin Tear Test indicating high dilution welds should be avoided to minimize solidification cracking during welding. The Strain-to-fracture test was used to examine DDC cracking susceptibility, and revealed that this alloy has a higher susceptibility to solid-state weld cracking than austenitic stainless alloys such as 304. Threshold strain levels necessary to initiate cracking in the weld deposits were in the range of 2 to 3%. These values are comparable to other Ni-base alloys with a moderate to high susceptibility to DDC. Fume generation rates (FGR) of the new consumable were measured and bulk fume phases were analyzed with X-ray diffraction. FGR values were found to be similar to current SMAW and flux cored arc welding consumables. No chromium bearing compounds were observed during X-ray diffraction measurements, and the bulk fume consisted primarily of halides and metallic-oxides. Fume generated by the new consumable was subjected to colorimetric testing showing hexavalent Cr content (0.02 wt-%) was reduced by two orders of magnitude compared to E308-16 (2.6 wt-%). The source of this hexavalent chromium was from evaporation of the base metal due to the welding heat source. The consumable developed in this study, having a nominal composition of Ni-7.5Cu-1Ru-0.5Al-0.5Ti-0.02C, met virtually all the design criteria that were initially established. Work performed by the Fontana Corrosion Center showed that the weld deposits met corrosion design criteria to prevent localized attack of the weld metal. Work performed in this study showed that mechanical properties were comparable to stainless steel consumables, and weld cracking susceptibility was comparable to Ni-base welding consumables. The consumable was also found to have good operability characteristics. (Abstract shortened by UMI.)

Quantitative determination of zero-gravity effects on electronic materials processing germanium crystal growth with simultaneous interface demarcation. Experiment MA-060

NASA Technical Reports Server (NTRS)

Gatos, H. C.; Witt, A. F.

1977-01-01

Experiment MA-060 was designed to establish the crystal growth and segregation characteristics of a melt in a directional solidification configuration under near zero-g conditions. The interface demarcation technique was incorporated into the experiment since it constitutes a unique tool for recording the morphology of the growth rate throughout solidification, and for establishing an absolute time reference framework for all stages of the solidification process. An extensive study was performed of the germanium crystals grown during the Apollo-Soyuz Test Project mission. It was found that single crystal growth was achieved and that the interface demarcation functioned successfully. There was no indication that convection driven by thermal or surface tension gradients was present in the melt. The gallium segregation, in the absence of gravity, was found to be fundamentally different in its initial and its subsequent stages from that of the ground-based tests. None of the existing theoretical models for growth and segregation can account for the observed segregation behavior in the absence of gravity.

Injectable barriers for waste isolation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Persoff, P.; Finsterle, S.; Moridis, G.J.

In this paper the authors report laboratory work and numerical simulation done in support of development and demonstration of injectable barriers formed from either of two fluids: colloidal silica or polysiloxane. Two principal problems addressed here are control of gel time and control of plume emplacement in the vadose zone. Gel time must be controlled so that the viscosity of the barrier fluid remains low long enough to inject the barrier, but increases soon enough to gel the barrier in place. During injection, the viscosity must be low enough to avoid high injection pressures which could uplift or fracture themore » formation. To test the grout gel time in the soil, the injection pressure was monitored as grouts were injected into sandpacks. When grout is injected into the vadose zone, it slumps under the influence of gravity, and redistributes due to capillary forces as it gels. The authors have developed a new module for the reservoir simulator TOUGH2 to model grout injection into the vadose zone, taking into account the increase of liquid viscosity as a function of gel concentration and time. They have also developed a model to calculate soil properties after complete solidification of the grout. The numerical model has been used to design and analyze laboratory experiments and field pilot tests. The authors present the results of computer simulations of grout injection, redistribution, and solidification.« less

The interaction of bubbles with solidification interfaces. [during coasting phase of sounding rocket flight

NASA Technical Reports Server (NTRS)

Papazian, J. M.; Wilcox, W. R.

1977-01-01

The behavior of bubbles at a dendritic solidification interface was studied during the coasting phase of a sounding rocket flight. Sequential photographs of the gradient freeze experiment showed nucleation, growth and coalescence of bubbles at the moving interface during both the low-gravity and one-gravity tests. In the one-gravity test the bubbles were observed to detach from the interface and float to the top of the melt. However, in the low-gravity tests no bubble detachment from the interface or steady state bubble motion occurred and large voids were grown into the crystal. These observations are discussed in terms of the current theory of thermal migration of bubbles and in terms of their implications on the space processing of metals.

Application of Solidification Theory to Rapid Solidification Processing

DTIC Science & Technology

1984-07-01

solubility; _NiAl -Cr quasibinary alloys ; Rapid solidification ; Solidification theory I’.ASRACT ICfene an roerso aid it 000e..yV SON identify0 by Week...110100a) ~j ~apid solidification allows the production of alloys with new compositions and * uphases and also allows production of improved alloys by...control of microstructure;L and homogeneity. The effect of rapid solidification velocity on the micro- structure of Ag-Cu alloys is comprehensively

Utilization of air pollution control residues for the stabilization/solidification of trace element contaminated soil.

PubMed

Travar, I; Kihl, A; Kumpiene, J

2015-12-01

The aim of this study was to evaluate the stabilization/solidification (S/S) of trace element-contaminated soil using air pollution control residues (APCRs) prior to disposal in landfill sites. Two soil samples (with low and moderate concentrations of organic matter) were stabilized using three APCRs that originated from the incineration of municipal solid waste, bio-fuels and a mixture of coal and crushed olive kernels. Two APCR/soil mixtures were tested: 30% APCR/70% soil and 50% APCR/50% soil. A batch leaching test was used to study immobilization of As and co-occurring metals Cr, Cu, Pb and Zn. Solidification was evaluated by measuring the unconfined compression strength (UCS). Leaching of As was reduced by 39-93% in APCR/soil mixtures and decreased with increased amounts of added APCR. Immobilization of As positively correlated with the amount of Ca in the APCR and negatively with the amount of soil organic matter. According to geochemical modelling, the precipitation of calcium arsenate (Ca3(AsO4)2/4H2O) and incorporation of As in ettringite (Ca6Al2(SO4)3(OH)12 · 26H2O) in soil/APCR mixtures might explain the reduced leaching of As. A negative effect of the treatment was an increased leaching of Cu, Cr and dissolved organic carbon. Solidification of APCR/soil was considerably weakened by soil organic matter.

Characterization of weld metal microstructure in a Ni-30Cr alloy with additions of niobium and molybdenum

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wheeling, Rebecca A., E-mail: wheeling.8@osu.edu; Lippold, John C., E-mail: lippold.1@osu.edu

2016-05-15

Additions of niobium (Nb) and molybdenum (Mo) were made to an Alloy 690 base alloy in order to investigate the formation of a eutectic constituent at the end of solidification and to evaluate the effect of the eutectic liquid on backfilling (or healing) of solidification cracks. Solidification cracking was induced using the cast pin tear test (CPTT) and regions of backfilling were located and characterized via optical and electron microscopy. Computational predictions of fraction eutectic and composition of the eutectic constituent were compared to experimental findings and were found to correlate well in both cases. The extent of crack backfillingmore » increased significantly with increasing Nb content, but the addition of Mo did not seem to influence the amount of eutectic constituent or the degree of backfilling. SEM/EDS analysis confirmed that the eutectic composition is constant and that increasing Nb above 4 wt% has little effect on expanding the solidification temperature range, but has a beneficial effect on mitigating solidification cracking by a crack healing effect. - Highlights: • Increasing fraction eutectic as a function of Nb, as predicted by ThermoCalc™, is consistent with image analysis results. • Nb, unlike Mo, had a significant effect on the fraction eutectic formed. • Both influence the composition of the eutectic. • Thermocalc™ predictions regarding Nb content in eutectic are consistent with EDS results, but are high for the Mo content. • Increased levels of niobium resulted in a higher degree of crack backfilling and leads to a lower cracking susceptibility. • Mo may influence the eutectic liquid along solidification grain boundaries, improving backfill and thus cracking resistance.« less

Ultrasound Flow Mapping for the Investigation of Crystal Growth.

PubMed

Thieme, Norman; Bonisch, Paul; Meier, Dagmar; Nauber, Richard; Buttner, Lars; Dadzis, Kaspars; Patzold, Olf; Sylla, Lamine; Czarske, Jurgen

2017-04-01

A high energy conversion and cost efficiency are keys for the transition to renewable energy sources, e.g., solar cells. The efficiency of multicrystalline solar cells can be improved by enhancing the understanding of its crystallization process, especially the directional solidification. In this paper, a novel measurement system for the characterization of flow phenomena and solidification processes in low-temperature model experiments on the basis of ultrasound (US) Doppler velocimetry is described. It captures turbulent flow phenomena in two planes with a frame rate of 3.5 Hz and tracks the shape of the solid-liquid interface during multihour experiments. Time-resolved flow mapping is performed using four linear US arrays with a total of 168 transducer elements. Long duration measurements are enabled through an online, field-programmable gate array (FPGA)-based signal processing. Nine single US transducers allow for in situ tracking of a solid-liquid interface. Results of flow and solidification experiments in the model experiment are presented and compared with numerical simulation. The potential of the developed US system for measuring turbulent flows and for tracking the solidification front during a directional crystallization process is demonstrated. The results of the model experiments are in good agreement with numerical calculations and can be used for the validation of numerical models, especially the selection of the turbulence model.

Modeling of Dendritic Structure and Microsegregation in Solidification of Al-Rich Quaternary Alloys

NASA Astrophysics Data System (ADS)

Dai, Ting; Zhu, Mingfang; Chen, Shuanglin; Cao, Weisheng

A two-dimensional cellular automaton (CA) model is coupled with a CALPHAD tool for the simulation of dendritic growth and microsegregation in solidification of quaternary alloys. The dynamics of dendritic growth is calculated according to the difference between the local equilibrium liquidus temperature and the actual temperature, incorporating with the Gibbs—Thomson effect and preferential dendritic growth orientations. Based on the local liquid compositions determined by solving the solutal transport equation in the domain, the local equilibrium liquidus temperature and the solid concentrations at the solid/liquid (SL) interface are calculated by the CALPHAD tool. The model was validated through the comparisons of the simulated results with the Scheil predictions for the solid composition profiles as a function of solid fraction in an Al-6wt%Cu-0.6wt%Mg-1wt%Si alloy. It is demonstrated that the model is capable of not only reproducing realistic dendrite morphologies, but also reasonably predicting microsegregation patterns in solidification of Al-rich quaternary alloys.

Laser recrystallization and inscription of compositional microstructures in crystalline SiGe-core fibres

PubMed Central

Coucheron, David A.; Fokine, Michael; Patil, Nilesh; Breiby, Dag Werner; Buset, Ole Tore; Healy, Noel; Peacock, Anna C.; Hawkins, Thomas; Jones, Max; Ballato, John; Gibson, Ursula J.

2016-01-01

Glass fibres with silicon cores have emerged as a versatile platform for all-optical processing, sensing and microscale optoelectronic devices. Using SiGe in the core extends the accessible wavelength range and potential optical functionality because the bandgap and optical properties can be tuned by changing the composition. However, silicon and germanium segregate unevenly during non-equilibrium solidification, presenting new fabrication challenges, and requiring detailed studies of the alloy crystallization dynamics in the fibre geometry. We report the fabrication of SiGe-core optical fibres, and the use of CO2 laser irradiation to heat the glass cladding and recrystallize the core, improving optical transmission. We observe the ramifications of the classic models of solidification at the microscale, and demonstrate suppression of constitutional undercooling at high solidification velocities. Tailoring the recrystallization conditions allows formation of long single crystals with uniform composition, as well as fabrication of compositional microstructures, such as gratings, within the fibre core. PMID:27775066

Laser recrystallization and inscription of compositional microstructures in crystalline SiGe-core fibres

NASA Astrophysics Data System (ADS)

Coucheron, David A.; Fokine, Michael; Patil, Nilesh; Breiby, Dag Werner; Buset, Ole Tore; Healy, Noel; Peacock, Anna C.; Hawkins, Thomas; Jones, Max; Ballato, John; Gibson, Ursula J.

2016-10-01

Glass fibres with silicon cores have emerged as a versatile platform for all-optical processing, sensing and microscale optoelectronic devices. Using SiGe in the core extends the accessible wavelength range and potential optical functionality because the bandgap and optical properties can be tuned by changing the composition. However, silicon and germanium segregate unevenly during non-equilibrium solidification, presenting new fabrication challenges, and requiring detailed studies of the alloy crystallization dynamics in the fibre geometry. We report the fabrication of SiGe-core optical fibres, and the use of CO2 laser irradiation to heat the glass cladding and recrystallize the core, improving optical transmission. We observe the ramifications of the classic models of solidification at the microscale, and demonstrate suppression of constitutional undercooling at high solidification velocities. Tailoring the recrystallization conditions allows formation of long single crystals with uniform composition, as well as fabrication of compositional microstructures, such as gratings, within the fibre core.

Influence of Pressure Field in Melts on the Primary Nucleation in Solidification Processing

NASA Astrophysics Data System (ADS)

Rakita, Milan; Han, Qingyou

2017-10-01

It is well known that external fields applied to melts can cause nucleation at lower supercoolings, fragmentation of growing dendrites, and forced convection around the solidification front. All these effects contribute to a finer microstructure of solidified material. In this article, we analyze how the pressure field created with ultrasonic vibrations influences structure refinement in terms of supercooling. It is shown that only high cavitation pressures of the order of 104 atmospheres are capable of nucleating crystals at minimal supercoolings. We demonstrate the possibility of sononucleation even in superheated liquid. Simulation and experiments with water samples show that very high cavitation pressures occur in a relatively narrow zone where the drive acoustic field has an appropriate combination of pressure amplitude and frequency. In order to accurately predict the microstructure formed by ultrasonically assisted solidification of metals, this article calls for the development of equations of state that would describe the pressure-dependent behavior of molten metals.

Phase-field simulation of weld solidification microstructure in an Al Cu alloy

NASA Astrophysics Data System (ADS)

Farzadi, A.; Do-Quang, M.; Serajzadeh, S.; Kokabi, A. H.; Amberg, G.

2008-09-01

Since the mechanical properties and the integrity of the weld metal depend on the solidification behaviour and the resulting microstructural characteristics, understanding weld pool solidification is of importance to engineers and scientists. Thermal and fluid flow conditions affect the weld pool geometry and solidification parameters. During solidification of the weld pool, a columnar grain structure develops in the weld metal. Prediction of the formation of the microstructure during welding may be an important and supporting factor for technology optimization. Nowadays, increasing computing power allows direct simulations of the dendritic and cell morphology of columnar grains in the molten zone for specific temperature conditions. In this study, the solidification microstructures of the weld pool at different locations along the fusion boundary are simulated during gas tungsten arc welding of Al-3wt%Cu alloy using the phase-field model for the directional solidification of dilute binary alloys. A macroscopic heat transfer and fluid flow model was developed to assess the solidification parameters, notably the temperature gradient and solidification growth rate. The effect of the welding speed is investigated. Computer simulations of the solidification conditions and the formation of a cellular morphology during the directional solidification in gas tungsten arc welding are described. Moreover, the simulation results are compared with existing theoretical models and experimental findings.

The solidification velocity of nickel and titanium alloys

NASA Astrophysics Data System (ADS)

Altgilbers, Alex Sho

2002-09-01

The solidification velocity of several Ni-Ti, Ni-Sn, Ni-Si, Ti-Al and Ti-Ni alloys were measured as a function of undercooling. From these results, a model for alloy solidification was developed that can be used to predict the solidification velocity as a function of undercooling more accurately. During this investigation a phenomenon was observed in the solidification velocity that is a direct result of the addition of the various alloying elements to nickel and titanium. The additions of the alloying elements resulted in an additional solidification velocity plateau at intermediate undercoolings. Past work has shown a solidification velocity plateau at high undercoolings can be attributed to residual oxygen. It is shown that a logistic growth model is a more accurate model for predicting the solidification of alloys. Additionally, a numerical model is developed from simple description of the effect of solute on the solidification velocity, which utilizes a Boltzmann logistic function to predict the plateaus that occur at intermediate undercoolings.

In situ Investigation of Magnetism in Metastable Phases of Levitated Fe83 B17 During Solidification

NASA Astrophysics Data System (ADS)

Quirinale, D. G.; Messina, D.; Rustan, G. E.; Kreyssig, A.; Prozorov, R.; Goldman, A. I.

2017-11-01

In situ measurements of structure, density, and magnetization on samples of Fe83 B17 using an electrostatic levitation furnace allow us to identify and correlate the magnetic and structural transitions in this system during its complex solidification process. In particular, we identify magnetic ordering in the metastable Fe23 B6 /fcc Fe coherently grown structures and primitive tetragonal Fe3 B metastable phase in addition to characterizing the equilibrium Fe2 B phase. Our measurements demonstrate that the incorporation of a tunnel-diode oscillator circuit within an electrostatic levitation furnace enables investigations of the physical properties of high-temperature metastable structures.

GTA weld cracking-alloy 625 to 304L

DOE Office of Scientific and Technical Information (OSTI.GOV)

Patterson, R.A.; Milewski, J.O.

1985-08-01

Autogenous gas tungsten arc welds joining alloy 625 and 304L stainless steel were found to be susceptible to weld solidification cracking. Utilization of pulsed current GTA welding produced a higher sensitivity to solidification cracks than continuous current welding. Spot Varestraint tests show that the sensitivity of this dissimilar metal combination to cracking exists over the entire range of dilutions while the greatest sensitivity is in 304L stainless steel rich compositions. Auger electron spectroscopy indicates that segregation of sulfur and phosphorous to the interdendritic phase promotes the hot cracking.

Measurement of the Density of Base Fluids at Pressures 0.422 to 2.20 Gpa

NASA Technical Reports Server (NTRS)

Hamrock, B. J.; Jacobson, B. O.; Bergstroem, S. I.

1985-01-01

The influence of pressure on the density of six base fluids is experimentally studied for a range of pressures from 0.422 to 2.20 GPa. An important parameter used to describe the results is the change in relative volume with change in pressure dv sub r/dp. For pressures less than the solidification pressure (p ps) a small change in pressure results in a large change in dv sub r/ps. For pressures greater than the solidification pressure (p ps) there is no change in dv sub r/dp with changing pressure. The solidification pressures of the base fluids varies considerably, as do the slopes that the experimental data assumes for p ps. A new formula is developed that describes the effect of pressure on density in terms of four constants. These constants vary for the different base fluids tested.

Influence of Secondary Cooling Mode on Solidification Structure and Macro-segregation Behavior for High-carbon Continuous Casting Bloom

NASA Astrophysics Data System (ADS)

Dou, Kun; Yang, Zhenguo; Liu, Qing; Huang, Yunhua; Dong, Hongbiao

2017-07-01

A cellular automaton-finite element coupling model for high-carbon continuously cast bloom of GCr15 steel is established to simulate the solidification structure and to investigate the influence of different secondary cooling modes on characteristic parameters such as equiaxed crystal ratio, grain size and secondary dendrite arm spacing, in which the effect of phase transformation and electromagnetic stirring is taken into consideration. On this basis, evolution of carbon macro-segregation for GCr15 steel bloom is researched correspondingly via industrial tests. Based on above analysis, the relationship among secondary cooling modes, characteristic parameters for solidification structure as well as carbon macro-segregation is illustrated to obtain optimum secondary cooling strategy and alleviate carbon macro-segregation degree for GCr15 steel bloom in continuous casting process. The evaluating method for element macro-segregation is applicable in various steel types.

Recovery and safer disposal of phosphate coating sludge by solidification/stabilization.

PubMed

Ucaroglu, Selnur; Talinli, Ilhan

2012-08-30

Solidification/stabilization (S/S) of automotive phosphate coating sludge (PS) containing potentially toxic heavy metals was studied. The hazardous characteristics of this waste were assessed according to both Turkish and U.S. Environmental Protection Agency (EPA) regulations for hazardous solid waste. Unconfined compressive strength (UCS) and leaching behavior tests of the solidified/stabilized product were performed. Solidification studies were conducted using Portland cement (PC) as the binder. UCS was found to decrease with increasing waste content. It was found that recovery of the waste for construction applications was possible when the waste content of the mortar was 20% and below, but solidification for safe disposal was achieved only when higher waste concentrations were added. Cu, Cr, Ni, Pb and Zn were found to be significantly immobilized by the solidification/stabilization process. Ni and Zn, which were present at particularly high concentrations (2.281 and 135.318 g/kg respectively) in the PS, had highest the retention levels (94.87% and 98.74%, respectively) in the PC mortars. The organic contaminants and heavy metals present in PS were determined to be immobilized by the S/S process in accordance with the BS 6920 standard. Thus, the potential for hazardous PS waste to adversely impact human health and the environment was effectively eliminated by the S/S procedure. We conclude that S/S-treated PS is safe for disposal in landfills, while recovery of S/S-treated PS constituents remains possible. Copyright © 2012 Elsevier Ltd. All rights reserved.

Solidified structure and leaching properties of metallurgical wastewater treatment sludge after solidification/stabilization process.

PubMed

Radovanović, Dragana Đ; Kamberović, Željko J; Korać, Marija S; Rogan, Jelena R

2016-01-01

The presented study investigates solidification/stabilization process of hazardous heavy metals/arsenic sludge, generated after the treatment of the wastewater from a primary copper smelter. Fly ash and fly ash with addition of hydrated lime and Portland composite cement were studied as potential binders. The effectiveness of the process was evaluated by unconfined compressive strength (UCS) testing, leaching tests (EN 12457-4 and TCLP) and acid neutralization capacity (ANC) test. It was found that introduction of cement into the systems increased the UCS, led to reduced leaching of Cu, Ni and Zn, but had a negative effect on the ANC. Gradual addition of lime resulted in decreased UCS, significant reduction of metals leaching and high ANC, due to the excess of lime that remained unreacted in pozzolanic reaction. Stabilization of more than 99% of heavy metals and 90% of arsenic has been achieved. All the samples had UCS above required value for safe disposal. In addition to standard leaching tests, solidificates were exposed to atmospheric conditions during one year in order to determine the actual leaching level of metals in real environment. It can be concluded that the EN 12457-4 test is more similar to the real environmental conditions, while the TCLP test highly exaggerates the leaching of metals. The paper also presents results of differential acid neutralization (d-AN) analysis compared with mineralogical study done by scanning electron microscopy and X-ray diffraction analysis. The d-AN coupled with Eh-pH (Pourbaix) diagrams were proven to be a new effective method for analysis of amorphous solidified structure.

Visualization of solidification front phenomena

NASA Technical Reports Server (NTRS)

Workman, Gary L.; Smith, Guy A.

1993-01-01

Directional solidification experiments have been utilized throughout the Materials Processing in Space Program to provide an experimental platform which minimizes variables in solidification experiments. Because of the wide-spread use of this experimental technique in space-based research, it has become apparent that a better understanding of all the phenomena occurring during solidification can be better understood if direct visualization of the solidification interface were possible.

Microstructure Evolution in the Presence of Constraints and Implications on the Properties of Mg - Li and Nb - Al Composites

DTIC Science & Technology

1991-05-30

alloys and composites Solidification experiments with Succinonitrile-acetone system Experimerts with Salol I Directional Solidification of Mg-Li alloys ...Directional Solidification of Mg-Li Composites Microstructural Analysis and Modeling Combustion Synthesis Principles ( theory ) Nb-AI alloys made by...Combustion Synthesis Nb-AI - NbB composites made by Combustion Synthesis Directional Solidification of Nb-AI Alloys Directional Solidification of Nb- Al

The influence of gravity level during directional solidification of immiscible alloys

NASA Technical Reports Server (NTRS)

Andrews, J. B.; Schmale, A. L.; Sandlin, A. C.

1992-01-01

During directional solidification of immiscible (hypermonotectic) alloys it is theoretically possible to establish a stable macroscopically-planar solidification front, and thus avoid sedimentation. Unfortunately, convective instabilities often occur which interfere with the directional solidification process. In this paper, stability conditions are discussed and results presented from directional solidification studies carried out aboard NASA's KC-135 zero-g aircraft. Samples were directionally solidified while the effective gravity level was varied from approximately 0.01 g for 25 s to 1.8 g for 45 s. Dramatic variations in microstructure were observed with gravity level during solidification.

Research on medium and high temperature solar heat storage materials

NASA Technical Reports Server (NTRS)

Heine, D.; Jucker, J.; Koch, D.; Krahling, H.; Supper, W.

1979-01-01

Characteristics of solar heat storage materials, preliminary tests in which melting and solidification characteristics are tested, and service life and cycling tests are reported. Various aspects of corrosion are discussed as well as decision about ultimate selection of materials. A program for storage and evaluation of data is included.

Fiber Laser Weldability of Austenitic Nickel Alloys

NASA Astrophysics Data System (ADS)

Watson, Jonathan

Recent developments of fiber lasers allow for easier beam delivery facilitating greater applications for laser welding in industry. Welding with high energy density heat sources allows for faster travel speeds, faster cooling rates, and smaller heat affected zones. However, there is a still a lack of knowledge base on how laser welding process parameters affect the weldability of austenitic nickel alloys. In this work, laser welds were made on several austenitic nickel alloys from different alloy families: HAYNESRTM 214RTM alloy, HAYNESRTM 282RTM alloy, HAYNESRTM 230RTM alloy, HAYNESRTM HR-120RTM alloy, HAYNESRTM HR-160 RTM alloy, HAYNESRTM 188 alloy, HAYNESRTM 718 alloy. Welds were made at 25 mm/s at laser powers ranging from 400 to 600 Watts. Solidification cracking was observed in cross-sections of the fusion zone of HR-160RTM alloy and HR-120RTM alloy. Dendritic solidification was found in all alloys, and partitioning within the dendritic structure compared well with Scheil calculations performed using ThermoCalc software. A eutectic liquid rich in carbide forming elements was found at the interdendritic regions in 188, 230RTM, 282 RTM, and 718 alloys and was quantified by processing backscatter electron images of the fusion zone. This interdendritic liquid was found to back fill solidification cracks that formed in the fusion zone during weldability testing. Transverse Varestraint and Sigma-Jig testing were performed to rank the weldability of alloys. During Transvarestraint testing, the ram drop timing was recorded in relation to the laser output, and a type R thermocouple was also placed in the laser path, and the approximate cooling rate of the fusion zone was recorded and used to calculate the solidification cracking temperature range. Rankings of the weldability compared well between Sigma-Jig and Transvarestraint testing, with the exception of 214 alloy and HR-120 alloy, which ranked much better and worse, respectively in Sigma-Jig tests. A possible explanation for this difference is the higher thermal conductivity and lower yields strength of 214 alloy and high temperatures, allowing it to accommodate more stress in the Sigma-Jig test. The final ranking of alloys from more weldable to less weldable by Sigma-Jig testing is 188, 214, 282, 718, 230, HR-120, and HR-160. The final ranking by maximum crack length in Transvarestraint specimens listed from more weldable to less weldable is: 188, 282, HR-120, 718, 230, 214, and HR-160.

On the Role of Mantle Overturn during Magma Ocean Solidification

NASA Astrophysics Data System (ADS)

Boukaré, C. E.; Parmentier, E.; Parman, S. W.

2017-12-01

Solidification of potential global magma ocean(s) (MO) early in the history of terrestrial planets may play a key role in the evolution of planetary interiors by setting initial conditions for their long-term evolution. Constraining this initial structure of solid mantles is thus crucial but remains poorly understood. MO fractional crystallization has been proposed to generate gravitationally unstable Fe-Mg chemical stratification capable of driving solid-state mantle overturn. Fractional solidification and overturn hypothesis, while only an ideal limiting case, can explain important geochemical features of both the Moon and Mars. Current overturn models consider generally post-MO overturn where the cumulate pile remains immobile until the end of MO solidification. However, if the cumulate pile overturns during MO solidification, the general picture of early planet evolution might differ significantly from the static crystallization models. We show that the timing of mantle overturn can be characterized with a dimensionless number measuring the ratio of the MO solidification time and the purely compositional overturn timescale. Syn-solidification overturn occurs if this dimensionless parameter, Rc, exceeds a critical value. Rc is mostly affected by the competition between the MO solidification time and mantle viscosity. Overturn that occurs during solidification can result in smaller scales of mantle chemical heterogeneity that could persist for long times thus influencing the whole evolution of a planetary body. We will discuss the effects of compaction/percolation on mantle viscosity. If partially molten cumulate do not have time to compact during MO solidification, viscosity of cumulates would be significantly lower as the interstitcial melt fraction would be large. Both solid mantle remelting during syn-solidification overturn and porous convection of melt retained with the cumulates are expected to reduce the degree of fractional crystallization. Syn-solidification overturn of a sluggish mantle can thus be an alternative to solid-state post-MO solidification overturn.

Modelling directional solidification

NASA Technical Reports Server (NTRS)

Wilcox, William R.

1991-01-01

The long range goal of this program is to develop an improved understanding of phenomena of importance to directional solidification and to enable explanation and prediction of differences in behavior between solidification on Earth and in space. Current emphasis is on determining the influence of perturbations on directional solidification.

Improved Crystal Quality By Detached Solidification in Microgravity

NASA Technical Reports Server (NTRS)

Regel, Liya L.; Wilcox, William R.; Wang, Yaz-Hen; Wang, Jian-Bin

2003-01-01

Many microgravity directional solidification experiments yielded ingots with portions that grew without contacting the ampoule wall, leading to greatly improved crystallographic perfection. Our long term goals have been: (1) To develop a complete understanding of all of the phenomena of detached solidification.; (2) To make it possible to achieve detached solidification reproducibly; (3) To increase crystallographic perfection through detached solidification. We have three major achievements to report here: (1) We obtained a new material balance solution for the Moving Meniscus Model of detached solidification. This solution greatly clarifies the physics as well as the roles of the parameters in the system; (2) We achieved detached solidification of InSb growing on earth in BN-coated ampoules; (3) We performed an extensive series of experiments on freezing water that showed how to form multiple gas bubbles or tubes on the ampoule wall. However, these did not propagate around the wall and lead to fully detached solidification unless the ampoule wall was extremely rough and non-wetted.

Relationships Between Solidification Parameters in A319 Aluminum Alloy

NASA Astrophysics Data System (ADS)

Vandersluis, E.; Ravindran, C.

2018-03-01

The design of high-performance materials depends on a comprehensive understanding of the alloy-specific relationships between solidification and properties. However, the inconsistent use of a particular solidification parameter for presenting materials characterization in the literature impedes inter-study comparability and the interpretation of findings. Therefore, there is a need for accurate expressions relating the solidification parameters for each alloy. In this study, A319 aluminum alloy castings were produced in a permanent mold with various preheating temperatures in order to control metal cooling. Analysis of the cooling curve for each casting enabled the identification of its liquidus, Al-Si eutectic, and solidus temperatures and times. These values led to the calculation of the primary solidification rate, total solidification rate, primary solidification time, and local solidification time for each casting, which were related to each other as well as to the average casting SDAS and material hardness. Expressions for each of their correlations have been presented with high coefficients of determination, which will aid in microstructural prediction and casting design.

Modeling of Detached Solidification

NASA Technical Reports Server (NTRS)

Regel, Liya L.; Wilcox, William R.; Popov, Dmitri

1997-01-01

Our long term goal is to develop techniques to achieve detached solidification reliably and reproducibly, in order to produce crystals with fewer defects. To achieve this goal it is necessary to understand thoroughly the physics of detached solidification. It was the primary objective of the current project to make progress toward this complete understanding. 'Me products of this grant are attached. These include 4 papers and a preliminary survey of the observations of detached solidification in space. We have successfully modeled steady state detached solidification, examined the stability of detachment, and determined the influence of buoyancy-driven convection under different conditions. Directional solidification in microgravity has often led to ingots that grew with little or no contact with the ampoule wall. When this occurred, crystallographic perfection was usually greatly improved -- often by several orders of magnitude. Indeed, under the Soviet microgravity program the major objective was to achieve detached solidification with its resulting improvement in perfection and properties. Unfortunately, until recently the true mechanisms underlying detached solidification were unknown. As a consequence, flight experiments yielded erratic results. Within the past three years, we have developed a new theoretical model that explains many of the flight results. This model gives rise to predictions of the conditions required to yield detached solidification.

Welding Behavior of Free Machining Stainless Steel

DOE Office of Scientific and Technical Information (OSTI.GOV)

BROOKS,JOHN A.; ROBINO,CHARLES V.; HEADLEY,THOMAS J.

2000-07-24

The weld solidification and cracking behavior of sulfur bearing free machining austenitic stainless steel was investigated for both gas-tungsten arc (GTA) and pulsed laser beam weld processes. The GTA weld solidification was consistent with those predicted with existing solidification diagrams and the cracking response was controlled primarily by solidification mode. The solidification behavior of the pulsed laser welds was complex, and often contained regions of primary ferrite and primary austenite solidification, although in all cases the welds were found to be completely austenite at room temperature. Electron backscattered diffraction (EBSD) pattern analysis indicated that the nature of the base metalmore » at the time of solidification plays a primary role in initial solidification. The solid state transformation of austenite to ferrite at the fusion zone boundary, and ferrite to austenite on cooling may both be massive in nature. A range of alloy compositions that exhibited good resistance to solidification cracking and was compatible with both welding processes was identified. The compositional range is bounded by laser weldability at lower Cr{sub eq}/Ni{sub eq} ratios and by the GTA weldability at higher ratios. It was found with both processes that the limiting ratios were somewhat dependent upon sulfur content.« less

FIELD QUALITY CONTROL STRATEGIES ASSESSING SOLIDIFICATION/STABILIZATION

EPA Science Inventory

Existing regulatory mobility reduction (leaching) tests are not amenable to real time quality control because of the time required to perform sample extraction and chemical analysis. This is of conccern because the leaching test is the most important parameter used to relate trea...

Three-dimensional control of crystal growth using magnetic fields

NASA Astrophysics Data System (ADS)

Dulikravich, George S.; Ahuja, Vineet; Lee, Seungsoo

1993-07-01

Two coupled systems of partial differential equations governing three-dimensional laminar viscous flow undergoing solidification or melting under the influence of arbitrarily oriented externally applied magnetic fields have been formulated. The model accounts for arbitrary temperature dependence of physical properties including latent heat release, effects of Joule heating, magnetic field forces, and mushy region existence. On the basis of this model a numerical algorithm has been developed and implemented using central differencing on a curvilinear boundary-conforming grid and Runge-Kutta explicit time-stepping. The numerical results clearly demonstrate possibilities for active and practically instantaneous control of melt/solid interface shape, the solidification/melting front propagation speed, and the amount and location of solid accrued.

In situ Investigation of Magnetism in Metastable Phases of Levitated Fe 83 B 17 During Solidification

DOE Office of Scientific and Technical Information (OSTI.GOV)

Quirinale, D. G.; Messina, D.; Rustan, G. E.

In situ measurements of structure, density, and magnetization on samples of Fe 83 B 17 using an electrostatic levitation furnace allow us to identify and correlate the magnetic and structural transitions in this system during its complex solidification process. In particular, we identify magnetic ordering in the metastable Fe 23 B 6 / fcc Fe coherently grown structures and primitive tetragonal Fe 3 B metastable phase in addition to characterizing the equilibrium Fe 2 B phase. Our measurements demonstrate that the incorporation of a tunnel-diode oscillator circuit within an electrostatic levitation furnace enables investigations of the physical properties of high-temperaturemore » metastable structures.« less

Microstructural properties and evolution of nanoclusters in liquid Si during a rapid cooling process

NASA Astrophysics Data System (ADS)

Gao, T.; Hu, X.; Li, Y.; Tian, Z.; Xie, Q.; Chen, Q.; Liang, Y.; Luo, X.; Ren, L.; Luo, J.

2017-11-01

The formation of amorphous structures in Si during the rapid quenching process was studied based on molecular dynamics simulation by using the Stillinger-Weber potential. The evolution characteristics of nanoclusters during the solidification were analyzed by several structural analysis methods. The amorphous Si has been formed with many tetrahedral clusters and few nanoclusters. During the solidification, tetrahedral polyhedrons affect the local structures by their different positions and connection modes. The main kinds of polyhedrons randomly linked with one another to form an amorphous network structures in the system. The structural evolution of crystal nanocluster demonstrates that the nanocluster has difficulty to growth because of the high cooling rate of 1012 K/s.

Modelling Directional Solidification

NASA Technical Reports Server (NTRS)

Wilcox, William R.; Regel, Liya L.; Zhou, Jian; Yuan, Weijun

1992-01-01

The long range goal of this program has been to develop an improved understanding of phenomena of importance to directional solidification, in order to enable explanation and prediction of differences in behavior between solidification on Earth and in space. Current emphasis is on determining the influence of perturbations on directional solidification.

Solidification Sequence of Spray-Formed Steels

NASA Astrophysics Data System (ADS)

Zepon, Guilherme; Ellendt, Nils; Uhlenwinkel, Volker; Bolfarini, Claudemiro

2016-02-01

Solidification in spray-forming is still an open discussion in the atomization and deposition area. This paper proposes a solidification model based on the equilibrium solidification path of alloys. The main assumptions of the model are that the deposition zone temperature must be above the alloy's solidus temperature and that the equilibrium liquid fraction at this temperature is reached, which involves partial remelting and/or redissolution of completely solidified droplets. When the deposition zone is cooled, solidification of the remaining liquid takes place under near equilibrium conditions. Scanning electron microscopy (SEM) and optical microscopy (OM) were used to analyze the microstructures of two different spray-formed steel grades: (1) boron modified supermartensitic stainless steel (SMSS) and (2) D2 tool steel. The microstructures were analyzed to determine the sequence of phase formation during solidification. In both cases, the solidification model proposed was validated.

Onset of solid state mantle convection and mixing during magma ocean solidification

NASA Astrophysics Data System (ADS)

Maurice, Maxime; Tosi, Nicola; Samuel, Henri; Plesa, Ana-Catalina; Hüttig, Christian; Breuer, Doris

2017-04-01

The fractional crystallization of a magma ocean can cause the formation of a compositional layering that can play a fundamental role for the subsequent long-term dynamics of the interior, for the evolution of geochemical reservoirs, and for surface tectonics. In order to assess to what extent primordial compositional heterogeneities generated by magma ocean solidification can be preserved, we investigate the solidification of a whole-mantle Martian magma ocean, and in particular the conditions that allow solid state convection to start mixing the mantle before solidification is completed. To this end, we performed 2-D numerical simulations in a cylindrical geometry. We treat the liquid magma ocean in a parametrized way while we self-consistently solve the conservation equations of thermochemical convection in the growing solid cumulates accounting for pressure-, temperature- and, where it applies, melt-dependent viscosity as well as parametrized yield stress to account for plastic yielding. By testing the effects of different cooling rates and convective vigor, we show that for a lifetime of the liquid magma ocean of 1 Myr or longer, the onset of solid state convection prior to complete mantle crystallization is likely and that a significant part of the compositional heterogeneities generated by fractionation can be erased by efficient mantle mixing.

Effects of grain size on the corrosion resistance of pure magnesium by cooling rate-controlled solidification

NASA Astrophysics Data System (ADS)

Liu, Yichi; Liu, Debao; You, Chen; Chen, Minfang

2015-09-01

The aim of this study was to investigate the effect of grain size on the corrosion resistance of pure magnesium developed for biomedical applications. High-purity magnesium samples with different grain size were prepared by the cooling rate-controlled solidification. Electrochemical and immersion tests were employed to measure the corrosion resistance of pure magnesium with different grain size. The electrochemical polarization curves indicated that the corrosion susceptibility increased as the grain size decrease. However, the electrochemical impedance spectroscopy (EIS) and immersion tests indicated that the corrosion resistance of pure magnesium is improved as the grain size decreases. The improvement in the corrosion resistance is attributed to refine grain can produce more uniform and density film on the surface of sample.

DEMONSTRATION BULLETIN: SOLIDIFICATION/STABILIZATION OF ORGANIC/INORGANIC CONTAMINANTS - SILICATE TECHNOLOGY CORPORATION

EPA Science Inventory

Silicate Technology Corporation's (STC's) technology for treating hazardous waste utilizes silicate compounds to stabilize organic and inorganic constituents in contaminated soils and sludges. STC has developed two groups of reagents: SOILSORB HM for treating wastes with inorgan...

Characterization of the Fe-Co-1.5V soft ferromagnetic alloy processed by Laser Engineered Net Shaping (LENS)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kustas, Andrew B.; Susan, Donald F.; Johnson, Kyle L.

Processing of the low workability Fe-Co-1.5V (Hiperco® equivalent) alloy is demonstrated using the Laser Engineered Net Shaping (LENS) metals additive manufacturing technique. As an innovative and highly localized solidification process, LENS is shown to overcome workability issues that arise during conventional thermomechanical processing, enabling the production of bulk, near net-shape forms of the Fe-Co alloy. Bulk LENS structures appeared to be ductile with no significant macroscopic defects. Atomic ordering was evaluated and significantly reduced in as-built LENS specimens relative to an annealed condition, tailorable through selection of processing parameters. Fine equiaxed grain structures were observed in as-built specimens following solidification,more » which then evolved toward a highly heterogeneous bimodal grain structure after annealing. The microstructure evolution in Fe-Co is discussed in the context of classical solidification theory and selective grain boundary pinning processes. In conclusion, magnetic properties were also assessed and shown to fall within the extremes of conventionally processed Hiperco® alloys.« less

Characterization of the Fe-Co-1.5V soft ferromagnetic alloy processed by Laser Engineered Net Shaping (LENS)

DOE PAGES

Kustas, Andrew B.; Susan, Donald F.; Johnson, Kyle L.; ...

2018-02-21

Processing of the low workability Fe-Co-1.5V (Hiperco® equivalent) alloy is demonstrated using the Laser Engineered Net Shaping (LENS) metals additive manufacturing technique. As an innovative and highly localized solidification process, LENS is shown to overcome workability issues that arise during conventional thermomechanical processing, enabling the production of bulk, near net-shape forms of the Fe-Co alloy. Bulk LENS structures appeared to be ductile with no significant macroscopic defects. Atomic ordering was evaluated and significantly reduced in as-built LENS specimens relative to an annealed condition, tailorable through selection of processing parameters. Fine equiaxed grain structures were observed in as-built specimens following solidification,more » which then evolved toward a highly heterogeneous bimodal grain structure after annealing. The microstructure evolution in Fe-Co is discussed in the context of classical solidification theory and selective grain boundary pinning processes. In conclusion, magnetic properties were also assessed and shown to fall within the extremes of conventionally processed Hiperco® alloys.« less

Real-time monitoring of laser powder bed fusion process using high-speed X-ray imaging and diffraction

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhao, Cang; Fezzaa, Kamel; Cunningham, Ross W.

Here, we employ the high-speed synchrotron hard X-ray imaging and diffraction techniques to monitor the laser powder bed fusion (LPBF) process of Ti-6Al-4V in situ and in real time. We demonstrate that many scientifically and technologically significant phenomena in LPBF, including melt pool dynamics, powder ejection, rapid solidification, and phase transformation, can be probed with unprecedented spatial and temporal resolutions. In particular, the keyhole pore formation is experimentally revealed with high spatial and temporal resolutions. The solidification rate is quantitatively measured, and the slowly decrease in solidification rate during the relatively steady state could be a manifestation of the recalescencemore » phenomenon. The high-speed diffraction enables a reasonable estimation of the cooling rate and phase transformation rate, and the diffusionless transformation from β to α’ phase is evident. The data present here will facilitate the understanding of dynamics and kinetics in metal LPBF process, and the experiment platform established will undoubtedly become a new paradigm for future research and development of metal additive manufacturing.« less

Real-time monitoring of laser powder bed fusion process using high-speed X-ray imaging and diffraction

DOE PAGES

Zhao, Cang; Fezzaa, Kamel; Cunningham, Ross W.; ...

2017-06-15

Here, we employ the high-speed synchrotron hard X-ray imaging and diffraction techniques to monitor the laser powder bed fusion (LPBF) process of Ti-6Al-4V in situ and in real time. We demonstrate that many scientifically and technologically significant phenomena in LPBF, including melt pool dynamics, powder ejection, rapid solidification, and phase transformation, can be probed with unprecedented spatial and temporal resolutions. In particular, the keyhole pore formation is experimentally revealed with high spatial and temporal resolutions. The solidification rate is quantitatively measured, and the slowly decrease in solidification rate during the relatively steady state could be a manifestation of the recalescencemore » phenomenon. The high-speed diffraction enables a reasonable estimation of the cooling rate and phase transformation rate, and the diffusionless transformation from β to α’ phase is evident. The data present here will facilitate the understanding of dynamics and kinetics in metal LPBF process, and the experiment platform established will undoubtedly become a new paradigm for future research and development of metal additive manufacturing.« less

Novel method of realizing metal freezing points by induced solidification

NASA Astrophysics Data System (ADS)

Ma, C. K.

1997-07-01

The freezing point of a pure metal, tf, is the temperature at which the solid and liquid phases are in equilibrium. The purest metal available is actually a dilute alloy. Normally, the liquidus point of a sample, tl, at which the amount of the solid phase in equilibrium with the liquid phase is minute, provides the closest approximation to tf. Thus the experimental realization of tf is a matter of realizing tl. The common method is to cool a molten sample continuously so that it supercools and recalesces. The highest temperature after recalescence is normally the best experimental value of tl. In the realization, supercooling of the sample at the sample container and the thermometer well is desirable for the formation of dual solid-liquid interfaces to thermally isolate the sample and the thermometer. However, the subsequent recalescence of the supercooled sample requires the formation of a certain amount of solid, which is not minute. Obviously, the plateau temperature is not the liquidus point. In this article we describe a method that minimizes supercooling. The condition that provides tl is closely approached so that the latter may be measured. As the temperature of the molten sample approaches the anticipated value of tl, a small solid of the same alloy is introduced into the sample to induce solidification. In general, solidification does not occur as long as the temperature is above or at tl, and occurs as soon as the sample supercools minutely. Thus tl can be obtained, in principle, by observing the temperature at which induced solidification begins. In case the solid is introduced after the sample has supercooled slightly, a slight recalescence results and the subsequent maximum temperature is a close approximation to tl. We demonstrate that the principle of induced solidification is indeed applicable to freezing point measurements by applying it to the design of a copper-freezing-point cell for industrial applications, in which a supercooled sample is reheated and then induced to solidify by the solidification of an auxiliary sample. Further experimental studies are necessary to assess the practical advantages and disadvantages of the induction method.

Casting And Solidification Technology (CAST): Directional solidification phenomena in a metal model at reduced gravity

NASA Technical Reports Server (NTRS)

Mccay, M. H.

1988-01-01

The Casting and Solidification Technology (CAST) experiment will study the phenomena that occur during directional solidification of an alloy, e.g., constitutional supercooling, freckling, and dendrite coarsening. The reduced gravity environment of space will permit the individual phenomena to be examined with minimum complication from buoyancy driven flows.

Simulation Computation of 430 Ferritic Stainless Steel Solidification

NASA Astrophysics Data System (ADS)

Pang, Ruipeng; Li, Changrong; Wang, Fuming; Hu, Lifu

The solidification structure of 430 ferritic stainless steel has been calculated in the solidification process by using 3D-CAFE model under the condition of water cooling. The calculated results consistent with those obtained from experiment. Under watercooling condition, the solidification structure consists of chilled layer, columnar grain zone, transition zone and equiaxed grain zone.

Fully-Implicit Reconstructed Discontinuous Galerkin Method for Stiff Multiphysics Problems

NASA Astrophysics Data System (ADS)

Nourgaliev, Robert

2015-11-01

A new reconstructed Discontinuous Galerkin (rDG) method, based on orthogonal basis/test functions, is developed for fluid flows on unstructured meshes. Orthogonality of basis functions is essential for enabling robust and efficient fully-implicit Newton-Krylov based time integration. The method is designed for generic partial differential equations, including transient, hyperbolic, parabolic or elliptic operators, which are attributed to many multiphysics problems. We demonstrate the method's capabilities for solving compressible fluid-solid systems (in the low Mach number limit), with phase change (melting/solidification), as motivated by applications in Additive Manufacturing. We focus on the method's accuracy (in both space and time), as well as robustness and solvability of the system of linear equations involved in the linearization steps of Newton-based methods. The performance of the developed method is investigated for highly-stiff problems with melting/solidification, emphasizing the advantages from tight coupling of mass, momentum and energy conservation equations, as well as orthogonality of basis functions, which leads to better conditioning of the underlying (approximate) Jacobian matrices, and rapid convergence of the Krylov-based linear solver. This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344, and funded by the LDRD at LLNL under project tracking code 13-SI-002.

Effective solidification/stabilisation of mercury-contaminated wastes using zeolites and chemically bonded phosphate ceramics.

PubMed

Zhang, Shaoqing; Zhang, Xinyan; Xiong, Ya; Wang, Guoping; Zheng, Na

2015-02-01

In this study, two kinds of zeolites materials (natural zeolite and thiol-functionalised zeolite) were added to the chemically bonded phosphate ceramic processes to treat mercury-contaminated wastes. Strong promotion effects of zeolites (natural zeolite and thiol-functionalised zeolite) on the stability of mercury in the wastes were obtained and these technologies showed promising advantages toward the traditional Portland cement process, i.e. using Portland cement as a solidification agent and natural or thiol-functionalised zeolite as a stabilisation agent. Not only is a high stabilisation efficiency (lowered the Toxicity Characteristic Leaching Procedure Hg by above 10%) obtained, but also a lower dosage of solidification (for thiol-functionalised zeolite as stabilisation agent, 0.5 g g(-1) and 0.7 g g(-1) for chemically bonded phosphate ceramic and Portland cement, respectively) and stabilisation agents (for natural zeolite as stabilisation agent, 0.35 g g(-1) and 0.4 g g(-1) for chemically bonded phosphate ceramic and Portland cement, respectively) were used compared with the Portland cement process. Treated by thiol-functionalised zeolite and chemically bonded phosphate ceramic under optimum parameters, the waste containing 1500 mg Hg kg(-1) passed the Toxicity Characteristic Leaching Procedure test. Moreover, stabilisation/solidification technology using natural zeolite and chemically bonded phosphate ceramic also passed the Toxicity Characteristic Leaching Procedure test (the mercury waste containing 625 mg Hg kg(-1)). Moreover, the presence of chloride and phosphate did not have a negative effect on the chemically bonded phosphate ceramic/thiol-functionalised zeolite treatment process; thus, showing potential for future application in treatment of 'difficult-to-manage' mercury-contaminated wastes or landfill disposal with high phosphate and chloride content. © The Author(s) 2015.

Directional solidification of eutectic composites in space environment

NASA Technical Reports Server (NTRS)

Yue, A. S.

1972-01-01

The Ni-Ni3Ta eutectic and a nickel-base alloy containing 30 wt pct Ta were solidified unidirectionally in an electron beam floating zone melting apparatus. It was found that the volume fraction of the Ni3Ta phase in the Ni-Ni3Ta eutectic mixture was increased from 7.6 to 36 volume pct in agreement with the theory as predicted. Tensile properties of the randomly solidified and unidirectionally solidified Ni-Ni3Ta eutectic were determined as function of solidification rate and temperature. It was found that the ultimate tensile strength decreased as both the test temperature and solidification rate increased. An elongation of 40 pct was obtained for a nickelbase alloy containing 30 wt at room temperature. This unusually large elongation was attributed to the superplastic behavior of the alloy. The critical currents versus the external fields at 2.5, 3.0, 3.5 and 4.2 deg for the unidirectionally solidified Pb-Sn eutectic were measured. The values of critical fields at zero critical currents were obtained by extrapolation.

Freezing Range, Melt Quality, and Hot Tearing in Al-Si Alloys

NASA Astrophysics Data System (ADS)

Uludağ, Muhammet; Çetin, Remzi; Dispinar, Derya

2018-02-01

In this study, three different aluminum-silicon alloys (A356, A413, and A380) that have different solidification morphology and solidification ranges were examined with an aim to evaluate the hot tearing susceptibility. T-shape mold and Constrained Rod Casting (CRC) mold were used for the characterization. Reduced Pressure Test (RPT) was used to quantify the casting quality by measuring bifilm index. It was found that bifilm index and solidification range have an important role on the hot tearing formation. As it is known, bifilms can cause porosity and in this case, it was shown that porosity formed by bifilms decreased hot tearing tendency. As the freezing range of alloy increases, bifilms find the time to unravel that reduces hot tearing. However, for eutectic alloy (A413), due to zero freezing range, regardless of bifilm content, hot tearing was never observed. A380.1 alloy had the highest tendency for hot tearing due to having the highest freezing range among the alloys investigated in this work.

Solidification of Dredged Sludge by Hydraulic Ash-Slag Cementitious Materials

NASA Astrophysics Data System (ADS)

Zhu, Shu-Jing; Qin, Ying; Hwang, Jiann-Yang

Solidification treatment is used to treat hazardous wastes for disposal and to remediate the contaminated land. It is an increasingly popular technology for redevelopment of brown fields since treated wastes can often be left on-site, which can improve the site's soil for subsequent construction. In order to find home for the dredged sludge from the Pearl River Estuary Channel in China, the potential uses of treated dredged sludge by solidification treatment as valuable structural fill was investigated. Structure fills were prepared under various formula and curing conditions. Modulus of elasticity was detemined at 7 days, 14 days and 28 days with different types of load application. Atterberg limit, compactibility and CBR values are reported. The relationship between the microstructure and engineering properties of treated sludge are examined. The results clearly show the technical benefits by stabilizing soft soils with Hydraulic ash-slag cementitious materials. XRD and DTA-TG tests were carried out on certain samples to characterize the hydraulic compounds formed.

Treatment of waste printed wire boards in electronic waste for safe disposal.

PubMed

Niu, Xiaojun; Li, Yadong

2007-07-16

The printed wire boards (PWBs) in electronic waste (E-waste) have been found to contain large amounts of toxic substances. Studies have concluded that the waste PWBs are hazardous wastes because they fails the toxicity characteristic leaching procedure (TCLP) test with high level of lead (Pb) leaching out. In this study, two treatment methods - high-pressure compaction and cement solidification - were explored for rendering the PWBs into non-hazardous forms so that they may be safely disposed or used. The high-pressure compaction method could turn the PWBs into high-density compacts with significant volume reduction, but the impact resistance of the compacts was too low to keep them intact in the environment for a long run. In contrast, the cement solidification could turn the PWBs into strong monoliths with high impact resistance and relatively high compressive strength. The leaching of the toxic heavy metal Pb from the solidified samples was evaluated by both a dynamic leaching test and the TCLP test. The dynamic leaching results revealed that Pb could be effectively confined in the solidified products under very harsh environmental conditions. The TCLP test results showed that the leaching level of Pb was far below the regulatory level of 5mg/L, suggesting that the solidified PWBs are no longer hazardous. It was concluded that the cement solidification is an effective way to render the waste PWBs into environmentally benign forms so that they can be disposed of as ordinary solid wastes or beneficially used in the place of concrete in some applications.

Columnar and Equiaxed Solidification of Al-7 wt.% Si Alloys in Reduced Gravity in the Framework of the CETSOL Project

NASA Astrophysics Data System (ADS)

Zimmermann, G.; Sturz, L.; Nguyen-Thi, H.; Mangelinck-Noel, N.; Li, Y. Z.; Gandin, C.-A.; Fleurisson, R.; Guillemot, G.; McFadden, S.; Mooney, R. P.; Voorhees, P.; Roosz, A.; Ronaföldi, A.; Beckermann, C.; Karma, A.; Chen, C.-H.; Warnken, N.; Saad, A.; Grün, G.-U.; Grohn, M.; Poitrault, I.; Pehl, T.; Nagy, I.; Todt, D.; Minster, O.; Sillekens, W.

2017-08-01

During casting, often a dendritic microstructure is formed, resulting in a columnar or an equiaxed grain structure, or leading to a transition from columnar to equiaxed growth (CET). The detailed knowledge of the critical parameters for the CET is important because the microstructure affects materials properties. To provide unique data for testing of fundamental theories of grain and microstructure formation, solidification experiments in microgravity environment were performed within the European Space Agency Microgravity Application Promotion (ESA MAP) project Columnar-to-Equiaxed Transition in SOLidification Processing (CETSOL). Reduced gravity allows for purely diffusive solidification conditions, i.e., suppressing melt flow and sedimentation and floatation effects. On-board the International Space Station, Al-7 wt.% Si alloys with and without grain refiners were solidified in different temperature gradients and with different cooling conditions. Detailed analysis of the microstructure and the grain structure showed purely columnar growth for nonrefined alloys. The CET was detected only for refined alloys, either as a sharp CET in the case of a sudden increase in the solidification velocity or as a progressive CET in the case of a continuous decrease of the temperature gradient. The present experimental data were used for numerical modeling of the CET with three different approaches: (1) a front tracking model using an equiaxed growth model, (2) a three-dimensional (3D) cellular automaton-finite element model, and (3) a 3D dendrite needle network method. Each model allows for predicting the columnar dendrite tip undercooling and the growth rate with respect to time. Furthermore, the positions of CET and the spatial extent of the CET, being sharp or progressive, are in reasonably good quantitative agreement with experimental measurements.

Solidification/Stabilization Resource Guide

EPA Pesticide Factsheets

This Solidification/Stabilization Resource Guide is intended to inform site cleanup managers of recently-published materials such as field reports and guidance documents that address issues relevant to solidification/stabilization technologies.

The Solidification of Multicomponent Alloys

PubMed Central

Boettinger, William J.

2017-01-01

Various topics taken from the author’s research portfolio that involve multicomponent alloy solidification are reviewed. Topics include: ternary eutectic solidification and Scheil-Gulliver paths in ternary systems. A case study of the solidification of commercial 2219 aluminum alloy is described. Also described are modifications of the Scheil-Gulliver analysis to treat dendrite tip kinetics and solid diffusion for multicomponent alloys. PMID:28819348

X-ray imaging and controlled solidification of Al-Cu alloys toward microstructures by design

DOE PAGES

Clarke, Amy J.; Tourret, Damien; Imhoff, Seth D.; ...

2015-01-30

X-ray imaging, which permits the microscopic visualization of metal alloy solidification dynamics, can be coupled with controlled solidification to create microstructures by design. In this study, this x-ray image shows a process-derived composite microstructure being made from a eutectic Al-17.1 at.%Cu alloy by successive solidification and remelting steps.

Parabolic aircraft solidification experiments

NASA Technical Reports Server (NTRS)

Workman, Gary L. (Principal Investigator); Smith, Guy A.; OBrien, Susan

1996-01-01

A number of solidification experiments have been utilized throughout the Materials Processing in Space Program to provide an experimental environment which minimizes variables in solidification experiments. Two techniques of interest are directional solidification and isothermal casting. Because of the wide-spread use of these experimental techniques in space-based research, several MSAD experiments have been manifested for space flight. In addition to the microstructural analysis for interpretation of the experimental results from previous work with parabolic flights, it has become apparent that a better understanding of the phenomena occurring during solidification can be better understood if direct visualization of the solidification interface were possible. Our university has performed in several experimental studies such as this in recent years. The most recent was in visualizing the effect of convective flow phenomena on the KC-135 and prior to that were several successive contracts to perform directional solidification and isothermal casting experiments on the KC-135. Included in this work was the modification and utilization of the Convective Flow Analyzer (CFA), the Aircraft Isothermal Casting Furnace (ICF), and the Three-Zone Directional Solidification Furnace. These studies have contributed heavily to the mission of the Microgravity Science and Applications' Materials Science Program.

Solidification/stabilization of dredged marine sediments for road construction.

PubMed

Wang, Dong Xing; Abriak, Nor Edine; Zentar, Rachid; Xu, WeiYa

2012-01-01

Cement/lime-based solidification is an environmentally sound solution for the management of dredged marine sediments, instead of traditional solutions such as immersion. Based on the mineralogical composition and physical characteristics of Dunkirk sediments, the effects of cement and lime are assessed through Atterberg limits, modified Proctor compaction, unconfined compressive strength and indirect tensile strength tests. The variation of Atterberg limits and the improvement in strength are discussed at different binder contents. The potential of sediments solidified with cement or lime for road construction is evaluated through a proposed methodology from two aspects: I-CBR value and material classification. The test results show the feasibility of solidified dredged sediments for beneficial use as a material in road construction. Cement is superior to lime in terms of strength improvement, and adding 6% cement is an economic and reasonable method to stabilize fine sediments.

Solidification kinetics of a Cu-Zr alloy: ground-based and microgravity experiments

NASA Astrophysics Data System (ADS)

Galenko, P. K.; Hanke, R.; Paul, P.; Koch, S.; Rettenmayr, M.; Gegner, J.; Herlach, D. M.; Dreier, W.; Kharanzhevski, E. V.

2017-04-01

Experimental and theoretical results obtained in the MULTIPHAS-project (ESA-European Space Agency and DLR-German Aerospace Center) are critically discussed regarding solidification kinetics of congruently melting and glass forming Cu50Zr50 alloy samples. The samples are investigated during solidification using a containerless technique in the Electromagnetic Levitation Facility [1]. Applying elaborated methodologies for ground-based and microgravity experimental investigations [2], the kinetics of primary dendritic solidification is quantitatively evaluated. Electromagnetic Levitator in microgravity (parabolic flights and on board of the International Space Station) and Electrostatic Levitator on Ground are employed. The solidification kinetics is determined using a high-speed camera and applying two evaluation methods: “Frame by Frame” (FFM) and “First Frame - Last Frame” (FLM). In the theoretical interpretation of the solidification experiments, special attention is given to the behavior of the cluster structure in Cu50Zr50 samples with the increase of undercooling. Experimental results on solidification kinetics are interpreted using a theoretical model of diffusion controlled dendrite growth.

Study of Solidification Cracking in a Transformation-Induced Plasticity-Aided Steel

NASA Astrophysics Data System (ADS)

Agarwal, G.; Kumar, A.; Gao, H.; Amirthalingam, M.; Moon, S. C.; Dippenaar, R. J.; Richardson, I. M.; Hermans, M. J. M.

2018-04-01

In situ high-temperature laser scanning confocal microscopy is applied to study solidification cracking in a TRIP steel. Solidification cracking was observed in the interdendritic region during the last stage of solidification. Atom probe tomography revealed notable enrichment of phosphorus in the last remaining liquid. Phase field simulations also confirm phosphorus enrichment leading to severe undercooling of more than 160 K in the interdendritic region. In the presence of tensile stress, an opening at the interdendritic region is difficult to fill with the remaining liquid due to low permeability and high viscosity, resulting in solidification cracking.

Microstructural development during solidification of stainless steel alloys

NASA Astrophysics Data System (ADS)

Elmer, J. W.; Allen, S. M.; Eagar, T. W.

1989-10-01

The microstructures that develop during the solidification of stainless steel alloys are related to the solidification conditions and the specific alloy composition. The solidification conditions are determined by the processing method, i.e., casting, welding, or rapid solidification, and by parametric variations within each of these techniques. One variable that has been used to characterize the effects of different processing conditions is the cooling rate. This factor and the chemical composition of the alloy both influence (1) the primary mode of solidification, (2) solute redistribution and second-phase formation during solidification, and (3) the nucleation and growth behavior of the ferrite-to-austenite phase transformation during cooling. Consequently, the residual ferrite content and the microstructural morphology depend on the cooling rate and are governed by the solidification process. This paper investigates the influence of cooling rate on the microstructure of stainless steel alloys and describes the conditions that lead to the many microstructural morphologies that develop during solidification. Experiments were performed on a series of seven high-purity Fe-Ni-Cr alloys that spanned the line of twofold saturation along the 59 wt pct Fe isopleth of the ternary alloy system. High-speed electron-beam surface-glazing was used to melt and resolidify these alloys at scan speeds up to 5 m/s. The resulting cooling rates were shown to vary from 7°C/s to 7.5×106°C/s, and the resolidified melts were analyzed by optical metallographic methods. Five primary modes of solidification and 12 microstructural morphologies were characterized in the resolidified alloys, and these features appear to be a complete “set” of the possible microstructures for 300-series stainless steel alloys. The results of this study were used to create electron-beam scan speed vs composition diagrams, which can be used to predict the primary mode of solidification and the microstructural morphology for different processing conditions. Furthermore, changes in the primary solidification mode were observed in alloys that lie on the chromium-rich side of the line of twofold saturation when they are cooled at high rates. These changes were explained by the presence of metastable austenite, which grows epitaxially and can dominate the solidification microstructure throughout the resolidified zone at high cooling rates.

Preliminary study on immobilization of buffing dust by solidification method in ceramic brick

NASA Astrophysics Data System (ADS)

Yuliansyah, Ahmad Tawfiequrrahman; Prasetya, Agus; Putra, Arif Eka; Satriawan, Humam Budi

2017-11-01

Leather-based industries generate a substantial amount of hazardous solid and liquid wastes in their process. One of the solid wastes is buffing dust, which is fine particulates containing fat, tanning, dyes and chromium. From 1 ton of leather processed, approximately 2-6 kg of buffing dust is generated. Chromium in the buffing dust is carcinogenic, so a proper handling is highly required. Solidification is a method commonly used to immobilize toxic material. Hence, the material is trapped in a matrix made of binding agents to minimize its mobility. However, a very small amount of the materials is sometimes released to the environment during storage. This study investigates leaching process of chromium from immobilized buffing dust in ceramic brick. Buffing dust, which contains chromium, is solidified by mixing it with clay at certain compositions and fired in a muffle furnace to produce a ceramic brick. Performance of the solidification process is evaluated by measuring the leaching of chromium in the leaching test. The results show that the solidification has significantly reduced the potential release of chromium to the environment. Higher of the firing temperature, less chromium is leached from ceramic brick. The chromium concentration of leachate water from 800°C brick is 0.376 ppm, while those from 850 and 900°C brick are 0.212 and 0.179 ppm respectively.

Test and evaluation of Apollo 14 composite casting demonstration specimens 6, 9, and 12, phase 1

NASA Technical Reports Server (NTRS)

Reger, J. L.

1971-01-01

Flight and control specimens 6, 9, and 12 from the Apollo 14 composite casting demonstration were evaluated with respect to the degree of dispersion achieved for mixtures of immiscible materials under one-gravity and low gravity environments. The flight and control capsules 6, 9, and 12 contained paraffin and sodium acetate; paraffin, sodium acetate and argon; and paraffin, sodium acetate and 100 micrometer diameter tungsten microspheres, respectively. The evaluation and documentation utilized photographic and microstructure examinations, density measurements, and droplet size and distribution determinations. In addition, theoretical analyses were performed in order to aid in the understanding of the fluid behavior of the specimens during processing and subsequent solidification. A comparison of evaluated data with the theoretical analyses reveals that although the immiscible materials were uniquely dispersed in a low gravity environment, nonuniform dispersions were obtained primarily due to insufficient initial mixing and an essentially unidirectional thermal gradient during cooldown.

Analysis and calculation of macrosegregation in a casting ingot. MPS solidification model. Volume 3: Operating manual

NASA Technical Reports Server (NTRS)

Maples, A. L.

1980-01-01

The operation of solidification model 1 is described. Model 1 calculates the macrosegregation in a rectangular ingot of a binary alloy as a result of horizontal axisymmetric bidirectional solidification. The calculation is restricted to steady-state solidification; there is no variation in final local average composition in the direction of isotherm movement. The physics of the model are given.

Investigating gas-phase defect formation in late-stage solidification using a novel phase-field crystal alloy model

NASA Astrophysics Data System (ADS)

Wang, Nan; Smith, Nathan; Provatas, Nikolas

2017-09-01

We study late-stage solidification and the associated formation of defects in alloy materials using a novel model based on the phase-field-crystal technique. It is shown that our model successfully captures several important physical phenomena that occur in the late stages of solidification, including solidification shrinkage, liquid cavitation and microsegregation, all in a single framework. By examining the interplay of solidification shrinkage and solute segregation, this model reveals that the formation of gas pore defects at the late stage of solidification can lead to nucleation of second phase solid particles due to solute enrichment in the eutectic liquid driven by gas-phase nucleation and growth. We also predict a modification of the Gulliver-Scheil equation in the presence of gas pockets in confined liquid pools.

Core solidification and dynamo evolution in a mantle-stripped planetesimal

NASA Astrophysics Data System (ADS)

Scheinberg, A.; Elkins-Tanton, L. T.; Schubert, G.; Bercovici, D.

2016-01-01

The physical processes active during the crystallization of a low-pressure, low-gravity planetesimal core are poorly understood but have implications for asteroidal magnetic fields and large-scale asteroidal structure. We consider a core with only a thin silicate shell, which could be analogous to some M-type asteroids including Psyche, and use a parameterized thermal model to predict a solidification timeline and the resulting chemical profile upon complete solidification. We then explore the potential strength and longevity of a dynamo in the planetesimal's early history. We find that cumulate inner core solidification would be capable of sustaining a dynamo during solidification, but less power would be available for a dynamo in an inward dendritic solidification scenario. We also model and suggest limits on crystal settling and compaction of a possible cumulate inner core.

Size-dependent microstructures in rapidly solidified uranium-niobium powder particles

DOE PAGES

McKeown, Joseph T.; Hsiung, Luke L.; Park, Jong M.; ...

2016-06-14

The microstructures of rapidly solidified U-6wt%Nb powder particles synthesized by centrifugal atomization were characterized using scanning electron microscopy and transmission electron microscopy. Observed variations in microstructure are related to particle sizes. All of the powder particles exhibited a two-zone microstructure. The formation of this two-zone microstructure is described by a transition from solidification controlled by internal heat flow and high solidification rate during recalescence (micro-segregation-free or partitionless growth) to solidification controlled by external heat flow with slower solidification rates (dendritic growth with solute redistribution). The extent of partitionless solidification increased with decreasing particle size due to larger undercoolings in smallermore » particles prior to solidification. The metastable phases that formed are related to variations in Nb concentration across the particles. Lastly, the microstructures of the powders were heavily twinned.« less

Directional Solidification and Liquidus Projection of the Sn-Co-Cu System

NASA Astrophysics Data System (ADS)

Chen, Sinn-Wen; Chang, Jui-Shen; Pan, Kevin; Hsu, Chia-Ming; Hsu, Che-Wei

2013-04-01

This study investigates the Sn-Co-Cu ternary system, which is of interest to the electronics industry. Ternary Sn-Co-Cu alloys were prepared, their as-solidified microstructures were examined, and their primary solidification phases were determined. The primary solidification phases observed were Cu, Co, Co3Sn2, CoSn, CoSn2, Cu6Sn5, Co3Sn2, γ, and β phases. Although there are ternary compounds reported in this ternary system, no ternary compound was found as the primary solidification phase. The directional solidification technique was applied when difficulties were encountered using the conventional quenching method to distinguish the primary solidification phases, such as Cu6Sn5, Cu3Sn, and γ phases. Of all the primary solidification phases, the Co3Sn2 and Co phases have the largest compositional regimes in which alloys display them as the primary solidification phases. There are four class II reactions and four class III reactions. The reactions with the highest and lowest reaction temperatures are both class III reactions, and are L + CoSn2 + Cu6Sn5 = CoSn3 at 621.5 K (348.3 °C) and L + Co3Sn2 + CoSn = Cu6Sn5 at 1157.8 K (884.6 °C), respectively.

Application of stabilization/solidification technology on oil refinery sludge contaminated by heavy metals.

PubMed

Karamalidis, Athanasios K; Voudrias, Evangelos A

2004-01-01

The oily sludge produced by petroleum refineries is classified as a solid hazardous waste, according to European regulations. The objective of this work was to investigate whether stabilization/solidification can be used as a management method for the oily sludge. The sludge samples used originated from a petroleum-storing tank and a centrifuge unit of two Greek refineries. The experiments were designed to study the leachability of the heavy metals Pb, Cr, Cd, Ni, and Cu, which are contained in the sludge, using the Toxicity Characteristic Leaching Procedure (TCLP). Despite the fact that the metals were immobilized in a cement-based environment in the presence of organic load, leaching tests have shown a low metal leachability, less than 5%. Acid Neutralizing Capacity (ANC) tests were employed in order to estimate the acid resistance of the stabilized/solidified waste. In addition to ANC, a sequential TCLP test was employed in order to understand how the pH affects the leachability of Ni from the stabilized/solidified specimen.

Thrust chamber material technology program

NASA Technical Reports Server (NTRS)

Andrus, J. S.; Bordeau, R. G.

1989-01-01

This report covers work performed at Pratt & Whitney on development of copper-based materials for long-life, reusable, regeneratively cooled rocket engine thrust chambers. The program approached the goal of enhanced cyclic life through the application of rapid solidification to alloy development, to introduce fine dispersions to strengthen and stabilize the alloys at elevated temperatures. After screening of alloy systems, copper-based alloys containing Cr, Co, Hf, Ag, Ti, and Zr were processed by rapid-solidification atomization in bulk quantities. Those bulk alloys showing the most promise were characterized by tensile testing, thermal conductivity testing, and elevated-temperature, low-cycle fatigue (LFC) testing. Characterization indicated that Cu- 1.1 percent Hf exhibited the greatest potential as an improved-life thrust chamber material, exhibiting LCF life about four times that of NASA-Z. Other alloys (Cu- 0.6 percent Zr, and Cu- 0.6 percent Zr- 1.0 percent Cr) exhibited promise for use in this application, but needed more development work to balance properties.

Rapid Solidification in Bulk Ti-Nb Alloys by Single-Track Laser Melting

NASA Astrophysics Data System (ADS)

Roehling, John D.; Perron, Aurélien; Fattebert, Jean-Luc; Haxhimali, Tomorr; Guss, Gabe; Li, Tian T.; Bober, David; Stokes, Adam W.; Clarke, Amy J.; Turchi, Patrice E. A.; Matthews, Manyalibo J.; McKeown, Joseph T.

2018-05-01

Single-track laser melting experiments were performed on bulk Ti-Nb alloys to explore process parameters and the resultant macroscopic structure and microstructure. The microstructures in Ti-20Nb and Ti-50Nb (at.%) alloys exhibited cellular growth during rapid solidification, with average cell size of approximately 0.5 µm. Solidification velocities during cellular growth were calculated from images of melt tracks. Measurements of the composition in the cellular and intercellular regions revealed nonequilibrium partitioning and its dependence on velocity during rapid solidification. Experimental results were used to benchmark a phase-field model to describe rapid solidification under conditions relevant to additive manufacturing.

Evolutions of lamellar structure during melting and solidification of Fe9577 nanoparticle from molecular dynamics simulations

NASA Astrophysics Data System (ADS)

Wu, Yongquan; Shen, Tong; Lu, Xionggang

2013-03-01

A structural evolution during solidification and melting processes of nanoparticle Fe9577 was investigated from MD simulations. A perfect lamellar structure, consisting alternately of fcc and hcp layers, was obtained from solidification process. A structural heredity of early embryo is proposed to explain the structural preference of solidification. Defects were found inside the solid core and play the same role as surface premelting on melting. hcp was found more stable than fcc in high temperature. The difference between melting and solidification points can be deduced coming fully from the overcoming of thermodynamic energy barrier, instead of kinetic delay of structural relaxation.

The Solidification Velocity of Undercooled Nickel and Titanium Alloys with Dilute Solute

NASA Technical Reports Server (NTRS)

Algoso, Paul R.; Altgilbers, A. S.; Hofmeister, William H.; Bayuzick, Robert J.

2003-01-01

The study of solidification velocity is important for two reasons. First, understanding the manner in which the degree of undercooling of the liquid and solidification velocity affect the microstructure of the solid is fundamental. Second, there is disagreement between theoretical predictions of the relationship between undercooling and solidification velocity and experimental results. Thus, the objective of this research is to accurately and systematically quantify the solidification velocity as a function of undercooling for dilute nickel-and titanium-based alloys. The alloys chosen for study cover a wide range of equilibrium partition coefficients, and the results are compared to current theory.

Space Processing Applications Rocket (SPAR) project, SPAR 9

NASA Technical Reports Server (NTRS)

Poorman, R. (Compiler)

1984-01-01

SPAR 9 (R-17) payload configuration, rocket performance, payload support, science payload instrumentation, and payload recovery are discussed. Directional solidification of magnetic composites, directional solidification of immiscible aluminum-indium alloys, and comparative alloy solidification experiments are reported.

Modelling direction solidification

NASA Technical Reports Server (NTRS)

Wilcox, W. R.

1986-01-01

The overall objective of this program is to develop an improved understanding of some phenomena of importance to directional solidification. The aim of this research is also to help predict differences in behavior between solidification on Earth and solidification in space. In this report, the validity of the Burton-Primslichter equation is explored. The influence of operating variables on grain and twin generation and propagation in single crystals of In sub (x) Ga sub (1-x) Sb is also investigated.

Optimization of Superaustenitic Stainless Steel Filler Metals for Welding Advanced Double Hull Combatant Ships

DTIC Science & Technology

2005-02-16

alloy is also given. The solidification mode of martensitic samples has been omitted and replaced with ’M’. Mo Ni +Cr Cr Ni ... alloys composed predominately of austenite. The four solidification modes present in the remaining 64 alloys , in order of increasing Cr/ Ni content, were...result in Fe- Ni -Cr-Mo alloys from the arc-melt condition. Solidification Solidification Primar- Secondar- Final microstrncture Mode

Application of Solidification Theory to Rapid Solidification Processing

DTIC Science & Technology

1983-08-01

1879 (1982). E 7] W. J. Boettinger, R. J. Schaefer, F. Biancaniello, and D. Shechtman, Met. Trans. A ., to be published. E 8] W. J. Bettinger , S. R...solidification velocity which produce a special "banded" microstructure in Ag-Cu alloys. Related lower bound to theoretical limits on solidification...partitionless rapid solidifi- cation of NiAl-Cr quasibinary eutectic alloy rather than a disordered structure incorporating Ni and Al into Cr randomly

Melt Flow Control in the Directional Solidification of Binary Alloys

NASA Technical Reports Server (NTRS)

Zabaras, Nicholas

2003-01-01

Our main project objectives are to develop computational techniques based on inverse problem theory that can be used to design directional solidification processes that lead to desired temperature gradient and growth conditions at the freezing front at various levels of gravity. It is known that control of these conditions plays a significant role in the selection of the form and scale of the obtained solidification microstructures. Emphasis is given on the control of the effects of various melt flow mechanisms on the local to the solidification front conditions. The thermal boundary conditions (furnace design) as well as the magnitude and direction of an externally applied magnetic field are the main design variables. We will highlight computational design models for sharp front solidification models and briefly discuss work in progress toward the development of design techniques for multi-phase volume-averaging based solidification models.

Nanoparticle-induced unusual melting and solidification behaviours of metals

PubMed Central

Ma, Chao; Chen, Lianyi; Cao, Chezheng; Li, Xiaochun

2017-01-01

Effective control of melting and solidification behaviours of materials is significant for numerous applications. It has been a long-standing challenge to increase the melted zone (MZ) depth while shrinking the heat-affected zone (HAZ) size during local melting and solidification of materials. In this paper, nanoparticle-induced unusual melting and solidification behaviours of metals are reported that effectively solve this long-time dilemma. By introduction of Al2O3 nanoparticles, the MZ depth of Ni is increased by 68%, while the corresponding HAZ size is decreased by 67% in laser melting at a pulse energy of 0.18 mJ. The addition of SiC nanoparticles shows similar results. The discovery of the unusual melting and solidification of materials that contain nanoparticles will not only have impacts on existing melting and solidification manufacturing processes, such as laser welding and additive manufacturing, but also on other applications such as pharmaceutical processing and energy storage. PMID:28098147

Solidification and stabilization of the incinerated wastewater sludge from textile industry

NASA Astrophysics Data System (ADS)

Aziz, Hamidi Abdul; Ghazali, Miskiah Fadzilah; Omran, Abdelnaser; Umar, Muhammad

2017-10-01

This paper describes the investigation of solidification and stabilization (S/S) process for the safe disposal of incinerated wastewater sludge produced from a textile industry in Penang, Malaysia. Physical and chemical properties of the samples were first characterized. Various ratios of ordinary Portland cement (OPC) as a binder were used to immobilize the metals. The leachability of metals in these cement-based waste materials was studied by standard toxicity characteristic leaching procedure (TCLP) and the mechanical strength was tested by a compressive strength test. TCLP results showed the ability of OPC to immobilize various metals such as Zn, Cu, Fe, Al, Ti, and K within the limits set by USEPA and Malaysia Environment Quality Act, 1974. However, the strength of the solidified matrixes was generally lower than the control specimens, ranging from 1-23 Mpa, which was well above the specified limit of 414 kPa for such matrices for their disposal in landfills.

Materials for Advanced Ultrasupercritical Steam Turbines Task 4: Cast Superalloy Development

DOE Office of Scientific and Technical Information (OSTI.GOV)

Thangirala, Mani

The Steam Turbine critical stationary structural components are high integrity Large Shell and Valve Casing heavy section Castings, containing high temperature steam under high pressures. Hence to support the development of advanced materials technology for use in an AUSC steam turbine capable of operating with steam conditions of 760°C (1400°F) and 35 Mpa (5000 psia), Casting alloy selection and evaluation of mechanical, metallurgical properties and castability with robust manufacturing methods are mandated. Alloy down select from Phase 1 based on producability criteria and creep rupture properties tested by NETL-Albany and ORNL directed the consortium to investigate cast properties of Haynesmore » 282 and Haynes 263. The goals of Task 4 in Phase 2 are to understand a broader range of mechanical properties, the impact of manufacturing variables on those properties. Scale up the size of heats to production levels to facilitate the understanding of the impact of heat and component weight, on metallurgical and mechanical behavior. GE Power & Water Materials and Processes Engineering for the Phase 2, Task 4.0 Castings work, systematically designed and executed casting material property evaluation, multiple test programs. Starting from 15 lbs. cylinder castings to world’s first 17,000 lbs. poured weight, heavy section large steam turbine partial valve Haynes 282 super alloy casting. This has demonstrated scalability of the material for steam Turbine applications. Activities under Task 4.0, Investigated and characterized various mechanical properties of Cast Haynes 282 and Cast Nimonic 263. The development stages involved were: 1) Small Cast Evaluation: 4 inch diam. Haynes 282 and Nimonic 263 Cylinders. This provided effects of liquidus super heat range and first baseline mechanical data on cast versions of conventional vacuum re-melted and forged Ni based super alloys. 2) Step block castings of 300 lbs. and 600 lbs. Haynes 282 from 2 foundry heats were evaluated which demonstrated the importance of proper heat treat cycles for Homogenization, and Solutionizing parameters selection and implementation. 3) Step blocks casting of Nimonic 263: Carried out casting solidification simulation analysis, NDT inspection methods evaluation, detailed test matrix for Chemical, Tensile, LCF, stress rupture, CVN impact, hardness and J1C Fracture toughness section sensitivity data and were reported. 4) Centrifugal Casting of Haynes 282, weighing 1400 lbs. with hybrid mold (half Graphite and half Chromite sand) mold assembly was cast using compressor casing production tooling. This test provided Mold cooling rates influence on centrifugally cast microstructure and mechanical properties. Graphite mold section out performs sand mold across all temperatures for 0.2% YS; %Elongation, %RA, UTS at 1400°F. Both Stress-LMP and conditional Fracture toughness plots data were in the scatter band of the wrought alloy. 5) Fundamental Studies on Cooling rates and SDAS test program. Evaluated the influence of 6 mold materials Silica, Chromite, Alumina, Silica with Indirect Chills, Zircon and Graphite on casting solidification cooling rates. Actual Casting cooling rates through Liquidus to Solidus phase transition were measured with 3 different locations based thermocouples placed in each mold. Compared with solidification simulation cooling rates and measurement of SDAS, microstructure features were reported. The test results provided engineered casting potential methods, applicable for heavy section Haynes 282 castings for optimal properties, with foundry process methods and tools. 6) Large casting of Haynes 282 Drawings and Engineering FEM models and supplemental requirements with applicable specifications were provided to suppliers for the steam turbine proto type feature valve casing casting. Molding, melting and casting pouring completed per approved Manufacturing Process Plan during 2014 Q4. The partial valve casing was successfully cast after casting methods were validated with solidification simulation analysis and the casting met NDT inspection and acceptance criteria. Heat treated and sectioned to extract trepan samples at different locations comparing with cast on coupons test data. Material properties requisite for design, such as tensile, creep/rupture, LCF, Fracture Toughness, Charpy V-notch chemical analysis testing were carried out. The test results will be presented in the final report. The typical Haynes 282 large size Steam Turbine production casting from Order to Delivery foundry schedule with the activity break up is shown in Figures 107 and 108. • From Purchase Order placement to Casting pouring ~ 26 weeks. 1. Sales and commercial review 3 2. Engineering Drawings/models review 4 3. Pattern and core box manufacturing 6 4. Casting process engineering review 4 5. FEM and solidification simulation analysis 4 6. Gating & Feeder Attachments, Ceramic tiling 2 7. Molding and coremaking production scheduling 6 8. Melting planning and schedule 3 9. Pouring, cooling and shake out 2 • From Pouring to casting Delivery ~ 29 weeks 10. Shot blast and riser cutting, gates removal 3 11. Homogenizing , solutionizing HT furnace prep 4 12. Grinding, Fettling 2 13. Aging HT Cycle, cooling 2 14. VT and LPT NDT inspections 2 15. Radiographic inspection 4 16. Mechanical testing, Chemical analysis test certs 4 17. Casting weld repair upgrades and Aging PWHT 4 18. NDT after weld repairs and casting upgrades 3 19. Casting Final Inspection and test certifications 3 20. Package and delivery 2 Hence the Total Lead time from P.O to Casting delivery is approximately 55 weeks. The Task 4.2 and Task 4.3 activities and reporting completed.« less

Acoustic levitation technique for containerless processing at high temperatures in space

NASA Technical Reports Server (NTRS)

Rey, Charles A.; Merkley, Dennis R.; Hammarlund, Gregory R.; Danley, Thomas J.

1988-01-01

High temperature processing of a small specimen without a container has been demonstrated in a set of experiments using an acoustic levitation furnace in the microgravity of space. This processing technique includes the positioning, heating, melting, cooling, and solidification of a material supported without physical contact with container or other surface. The specimen is supported in a potential energy well, created by an acoustic field, which is sufficiently strong to position the specimen in the microgravity environment of space. This containerless processing apparatus has been successfully tested on the Space Shuttle during the STS-61A mission. In that experiment, three samples wer successfully levitated and processed at temperatures from 600 to 1500 C. Experiment data and results are presented.

Two-color holography concept (T-CHI)

NASA Technical Reports Server (NTRS)

Vikram, C. S.; Caulfield, H. J.; Workman, G. L.; Trolinger, J. D.; Wood, C. P.; Clark, R. L.; Kathman, A. D.; Ruggiero, R. M.

1990-01-01

The Material Processing in the Space Program of NASA-MSFC was active in developing numerous optical techniques for the characterization of fluids in the vicinity of various materials during crystallization and/or solidification. Two-color holographic interferometry demonstrates that temperature and concentration separation in transparent (T-CHI) model systems is possible. The experiments were performed for particular (succinonitrile) systems. Several solutions are possible in Microgravity Sciences and Applications (MSA) experiments on future Shuttle missions. The theory of the T-CHI concept is evaluated. Although particular cases are used for explanations, the concepts developed will be universal. A breadboard system design is also presented for ultimate fabrication and testing of theoretical findings. New developments in holography involving optical fibers and diode lasers are also incorporated.

Premature melt solidification during mold filling and its influence on the as-cast structure

NASA Astrophysics Data System (ADS)

Wu, M.; Ahmadein, M.; Ludwig, A.

2018-03-01

Premature melt solidification is the solidification of a melt during mold filling. In this study, a numerical model is used to analyze the influence of the pouring process on the premature solidification. The numerical model considers three phases, namely, air, melt, and equiaxed crystals. The crystals are assumed to have originated from the heterogeneous nucleation in the undercooled melt resulting from the first contact of the melt with the cold mold during pouring. The transport of the crystals by the melt flow, in accordance with the socalled "big bang" theory, is considered. The crystals are assumed globular in morphology and capable of growing according to the local constitutional undercooling. These crystals can also be remelted by mixing with the superheated melt. As the modeling results, the evolutionary trends of the number density of the crystals and the volume fraction of the solid crystals in the melt during pouring are presented. The calculated number density of the crystals and the volume fraction of the solid crystals in the melt at the end of pouring are used as the initial conditions for the subsequent solidification simulation of the evolution of the as-cast structure. A five-phase volume-average model for mixed columnar-equiaxed solidification is used for the solidification simulation. An improved agreement between the simulation and experimental results is achieved by considering the effect of premature melt solidification during mold filling. Finally, the influences of pouring parameters, namely, pouring temperature, initial mold temperature, and pouring rate, on the premature melt solidification are discussed.

Solution of free-boundary problems using finite-element/Newton methods and locally refined grids - Application to analysis of solidification microstructure

NASA Technical Reports Server (NTRS)

Tsiveriotis, K.; Brown, R. A.

1993-01-01

A new method is presented for the solution of free-boundary problems using Lagrangian finite element approximations defined on locally refined grids. The formulation allows for direct transition from coarse to fine grids without introducing non-conforming basis functions. The calculation of elemental stiffness matrices and residual vectors are unaffected by changes in the refinement level, which are accounted for in the loading of elemental data to the global stiffness matrix and residual vector. This technique for local mesh refinement is combined with recently developed mapping methods and Newton's method to form an efficient algorithm for the solution of free-boundary problems, as demonstrated here by sample calculations of cellular interfacial microstructure during directional solidification of a binary alloy.

Assessment of the leaching of metallic elements in the technology of solidification in aqueous solution.

PubMed

Rossetti, V Alunno; Di Palma, L; Medici, F

2002-01-01

Results are presented of experiments performed to optimize the solidification/stabilization system for metallic elements in aqueous solution. This system involves mixing cement and a solution of metallic elements in a conventional mixer: the paste thus obtained is transferred drop by drop into a recipient filled with an aqueous solution of NaOH at 20% by weight, in which it solidifies immediately. The separate use of chloride solutions of Li+, Cr3+, Pb2+ and Zn2+ makes it possible to obtain granules displaying various levels of compressive strength. Three different inertization matrices were used in the experiments, the first consisting solely of Portland cement, the second of Portland cement and a superplasticizer additive, and the third of Portland cement partially replaced with silica-fume and superplasticizer. The results of the tests performed showed a very low level of leaching into the alkaline solidification solution for Cr3+, the quantity leached being under 2% as against higher levels for the other metallic elements. For all the considered elements, the best results were obtained by using silica-fume in the inertization matrix.

Measurements of microhardness during transient horizontal directional solidification of Al-Rich Al-Cu alloys: Effect of thermal parameters, primary dendrite arm spacing and Al2Cu intermetallic phase

NASA Astrophysics Data System (ADS)

Barros, André Santos; Magno, Igor Alexsander; Souza, Fabrício Andrade; Mota, Carlos Alberto; Moreira, Antonio Luciano; Silva, Maria Adrina; Rocha, Otávio Lima

2015-05-01

In this work, the effect of the growth rate (VL) and cooling rate (TR), primary dendritic arm spacing (λ1) and Al2Cu intermetallic phase on the microhardness was investigated during transient horizontal directional solidification of Al-3wt%Cu and Al-8wt%Cu alloys. Microstructural characterization of the investigated alloys was performed using traditional techniques of metallography, optical and SEM microscopy and X-Ray diffraction. The microhardness evolution as a function of the thermal and microstructural parameters (VL, TR, and λ1) was evaluated using power and Hall-Petch type experimental laws, which were compared with other laws in the literature. In order to examine the effect of the Al2Cu intermetallic phase, microhardness measurements were performed in interdendritic regions. Finally, a comparative analysis was performed between the experimental data of this work and theoretical models from the literature that have been proposed to predict primary dendrite arm spacing, which have been tested in numerous works considering upward directional solidification.

Computational modelling for the embolization of brain arteriovenous malformations.

PubMed

Orlowski, Piotr; Summers, Paul; Noble, J Alison; Byrne, James; Ventikos, Yiannis

2012-09-01

Treatment of arteriovenous malformations (AVMs) of the brain often requires the injection of a liquid embolic material to reduce blood flow through the malformation. The type of the liquid and the location of injection have to be carefully planned in a pre-operative manner. We introduce a new model of the interaction of liquid embolic materials with blood for the simulation of their propagation and solidification in the AVM. Solidification is mimicked by an increase of the material's viscosity. Propagation is modelled by using the concept of two-fluids modelling and that of scalar transport. The method is tested on digital phantoms and on one anatomically derived patient AVM case. Simulations showed that intuitive behaviour of the two-fluid system can be confirmed and that two types of glue propagation through the malformation can be reproduced. Distinction between the two types of propagation could be used to identify fistulous and plexiform compartments composing the AVM and to characterize the solidification of the embolic material in them. Copyright © 2011 IPEM. Published by Elsevier Ltd. All rights reserved.

Eutectic Experiment Development for Space Processing

NASA Technical Reports Server (NTRS)

Hopkins, R. H.

1972-01-01

A ground base test plan and a specimen evaluation scheme have been developed for the aluminum-copper eutectic solidification experiment to be run in the M518 multipurpose electric furnace during the Skylab mission. Besides thermal and solidification studies a detailed description is given of the quantitative metallographic technique which is appropriate for characterizing eutectic structures. This method should prove a key tool for evaluating specimen microstructure which is the most sensitive indicator of changes produced during solidification. It has been recommended that single grain pre-frozen eutectic specimens be used to simplify microstructural evaluation and to eliminate any porosity in the as-cast eutectic specimens. High purity (99.999%) materials from one supplier should be employed for all experiments. Laboratory studies indicate that porosity occurs in the MRC as-cast eutectic ingots but that this porosity can be eliminated by directional freezing. Chemical analysis shows that the MRC ingots are slightly Al rich and contain about .03% impurity. Because of the impurity content the lower cooldown rate (1.2 C/min) should be used for eutectic freezing if MRC material is used in the M518 furnace.

Directional Solidification of Mercury Cadmium Telluride During the Second United States Microgravity Payload Mission (USMP-2)

NASA Technical Reports Server (NTRS)

Gillies, D. C.; Lehoczky, S. L.; Szofran, F. R.; Watring, D. A.; Alexander, H. A.; Jerman, G. A.

1996-01-01

As a solid solution semiconductor having, a large separation between liquidus and solidus, mercury cadmium telluride (MCT) presents a formidable challenge to crystal growers desiring an alloy of high compositional uniformity. To avoid constitutional supercooling during Bridgman crystal growth it is necessary to solidify slowly in a high temperature gradient region. The necessary translation rate of less than 1 mm/hr results in a situation where fluid flow induced by gravity on earth is a significant factor in material transport. The Advanced Automated Directional Solidification Furnace (AADSF) is equipped to provide the stable thermal environment with a high gradient, and the required slow translation rate needed. Ground based experiments in AADSF show clearly the dominance of flow driven transport. The first flight of AADSF in low gravity on USMP-2 provided an opportunity to test theories of fluid flow in MCT and showed several solidification regimes which are very different from those observed on earth. Residual acceleration vectors in the orbiter during the mission were measured by the Orbital Acceleration Research Experiment (OARE), and correlated well with observed compositional differences in the samples.

Mechanical Properties and Microstructural Characterization of Aged Nickel-based Alloy 625 Weld Metal

NASA Astrophysics Data System (ADS)

Silva, Cleiton Carvalho; de Albuquerque, Victor Hugo C.; Miná, Emerson Mendonça; Moura, Elineudo P.; Tavares, João Manuel R. S.

2018-03-01

The aim of this work was to evaluate the different phases formed during solidification and after thermal aging of the as-welded 625 nickel-based alloy, as well as the influence of microstructural changes on the mechanical properties. The experiments addressed aging temperatures of 650 and 950 °C for 10, 100, and 200 hours. The samples were analyzed by electron microscopy, microanalysis, and X-ray diffraction in order to identify the secondary phases. Mechanical tests such as hardness, microhardness, and Charpy-V impact test were performed. Nondestructive ultrasonic inspection was also conducted to correlate the acquired signals with mechanical and microstructural properties. The results show that the alloy under study experienced microstructural changes when aged at 650 °C. The aging was responsible by the dissolution of the Laves phase formed during the solidification and the appearance of γ″ phase within interdendritic region and fine carbides along the solidification grain boundaries. However, when it was aged at 950 °C, the Laves phase was continuously dissolved and the excess Nb caused the precipitation of the δ-phase (Ni3Nb), which was intensified at 10 hours of aging, with subsequent dissolution for longer periods such as 200 hours. Even when subjected to significant microstructural changes, the mechanical properties, especially toughness, were not sensitive to the dissolution and/or precipitation of the secondary phases.

Convection and Solidification with Applications to Crystal Growth

NASA Technical Reports Server (NTRS)

DeVahl Davis, Graham

1994-01-01

An outline is given of research on the directional solidification of a liquid, and of the effects of natural convection thereon. Three problems which have been studied are described. Finally, current work on solidification in microgravity conditions is discussed.

Investigation of the Relationship between Undercooling and Solidification Velocity

NASA Technical Reports Server (NTRS)

Bayuzick, Robert J.; Hofmeister, William H.

2004-01-01

This work was aimed at reconciling the differences between experimental measurements of the theoretical predictions of the solidification velocity as a function of undercooling. The theory proposed by Boettinger, Coriell and Trivedi (the BCT theory) has been one of the most widely used models for describing the nature of the solidification of undercooled metals and alloys. However, for undercoolings greater than about 5% of the absolute melting temperature, there is considerable discrepancy between theory and experiment. At these large undercoolings, experimental results exhibit a much lessened dependency of solidification velocity on undercooling than is predicted by theory. Furthermore, unpredicted plateaus in the solidification velocity as a function of undercooling are observed.

MPS Solidification Model. Volume 2: Operating guide and software documentation for the unsteady model

NASA Technical Reports Server (NTRS)

Maples, A. L.

1981-01-01

The operation of solidification Model 2 is described and documentation of the software associated with the model is provided. Model 2 calculates the macrosegregation in a rectangular ingot of a binary alloy as a result of unsteady horizontal axisymmetric bidirectional solidification. The solidification program allows interactive modification of calculation parameters as well as selection of graphical and tabular output. In batch mode, parameter values are input in card image form and output consists of printed tables of solidification functions. The operational aspects of Model 2 that differ substantially from Model 1 are described. The global flow diagrams and data structures of Model 2 are included. The primary program documentation is the code itself.

Modeling of Microstructure Evolution During Alloy Solidification

NASA Astrophysics Data System (ADS)

Zhu, Mingfang; Pan, Shiyan; Sun, Dongke

In recent years, considerable advances have been achieved in the numerical modeling of microstructure evolution during solidification. This paper presents the models based on the cellular automaton (CA) technique and lattice Boltzmann method (LBM), which can reproduce a wide variety of solidification microstructure features observed experimentally with an acceptable computational efficiency. The capabilities of the models are addressed by presenting representative examples encompassing a broad variety of issues, such as the evolution of dendritic structure and microsegregation in two and three dimensions, dendritic growth in the presence of convection, divorced eutectic solidification of spheroidal graphite irons, and gas porosity formation. The simulations offer insights into the underlying physics of microstructure formation during alloy solidification.

Effect of solidification rate on microstructure evolution in dual phase microalloyed steel

PubMed Central

Kostryzhev, A. G.; Slater, C. D.; Marenych, O. O.; Davis, C. L.

2016-01-01

In steels the dependence of ambient temperature microstructure and mechanical properties on solidification rate is not well reported. In this work we investigate the microstructure and hardness evolution for a low C low Mn NbTi-microalloyed steel solidified in the cooling rate range of 1–50 Cs−1. The maximum strength was obtained at the intermediate solidification rate of 30 Cs−1. This result has been correlated to the microstructure variation with solidification rate. PMID:27759109

Al and Mg Alloys for Aerospace Applications Using Rapid Solidification and Power Metallurgy Processing.

DTIC Science & Technology

1981-10-07

primary solidification phase in the alloy in this condition was identified by CBED as Mg 2 Si , which formed dendrites within the matrix. Each... solidification below the extended c-liquidus. Evolution of Microstructure in Melt-spun Mg- Si Alloys -, The microstructurcs observed in the alloys can...solidificaion pr(es .. in the cellular (dendritic) regime. Solidification of the 5.0 wt.% Si alloy occurs in the coupled eutectic region, and the 8.0 wt.% Si

Rapid solidification of levitation melted Ni-Sn alloy droplets with high undercooling

NASA Technical Reports Server (NTRS)

Shiohara, Yuh; Flemings, Merton C.; Wu, Yanzhong; Piccone, Thomas J.

1985-01-01

Experimental results obtained by high-speed optical temperature sensing for the rapid solidification of highly undercooled, levitation-melted Ni-Sn alloy droplets are presented. These data suggest a solidification model proceeding according to overlapping steps: (1) dendritic growth within the bulk undercooled melt, (2) continued recalescence as supersaturation of the interdendritic liquid dissipates, (3) fine-scale remelting within the dendrites, (4) ripening of the fine structure, and (5) solidification of remaining liquid at the end of recalescence.

Fundamentals of rapid solidification processing

NASA Technical Reports Server (NTRS)

Flemings, Merton C.; Shiohara, Yuh

1985-01-01

An attempt is made to illustrate the continuous change that occurs in the solidification behavior of undercooled melts, as cooling rates increase from 0.0001 K/sec to about 1000 K/sec. At the higher cooling rates, more significant changes occur as the dendrite tip temperature begins to drop from the equilibrium liquidus. Discontinuous solidification behavior changes will occur if absolute stability is reached, or a metastable phase forms, or solidification proceeds to a glass rather than to a crystalline solid, or if there is significant undercooling prior to nucleation.

Materials Science Laboratory - Columnar-to-Equiaxed Transition in Solidification Processing and Microstructure Formation in Casting of Technical Alloys under Diffusive and Magnetically Controlled Convective Conditions

NASA Technical Reports Server (NTRS)

Gandin, Charles-Andre; Ratke, Lorenz

2008-01-01

The Materials Science Laboratory - Columnar-to-Equiaxed Transition in Solidification Processing and Microstructure Formation in Casting of Technical Alloys under Diffusive and Magnetically Controlled Convective Conditions (MSL-CETSOL and MICAST) are two investigations which supports research into metallurgical solidification, semiconductor crystal growth (Bridgman and zone melting), and measurement of thermo-physical properties of materials. This is a cooperative investigation with the European Space Agency (ESA) and National Aeronautics and Space Administration (NASA) for accommodation and operation aboard the International Space Station (ISS). Research Summary: Materials Science Laboratory - Columnar-to-Equiaxed Transition in Solidification Processing (CETSOL) and Microstructure Formation in Casting of Technical Alloys under Diffusive and Magnetically Controlled Convective Conditions (MICAST) are two complementary investigations which will examine different growth patterns and evolution of microstructures during crystallization of metallic alloys in microgravity. The aim of these experiments is to deepen the quantitative understanding of the physical principles that govern solidification processes in cast alloys by directional solidification.

21 CFR 172.862 - Oleic acid derived from tall oil fatty acids.

Code of Federal Regulations, 2012 CFR

2012-04-01

... titer (solidification point) shall not exceed 13.5 °C and unsaponifiable matter shall not exceed 0.5.... (2) The resin acid content does not exceed 0.01 as determined by ASTM method D1240-82, “Standard Test... the American Society for Testing Materials, 100 Barr Harbor Dr., West Conshohocken, Philadelphia, PA...

Secondary Waste Cast Stone Waste Form Qualification Testing Plan

DOE Office of Scientific and Technical Information (OSTI.GOV)

Westsik, Joseph H.; Serne, R. Jeffrey

2012-09-26

The Hanford Tank Waste Treatment and Immobilization Plant (WTP) is being constructed to treat the 56 million gallons of radioactive waste stored in 177 underground tanks at the Hanford Site. The WTP includes a pretreatment facility to separate the wastes into high-level waste (HLW) and low-activity waste (LAW) fractions for vitrification and disposal. The LAW will be converted to glass for final disposal at the Integrated Disposal Facility (IDF). Cast Stone – a cementitious waste form, has been selected for solidification of this secondary waste stream after treatment in the ETF. The secondary-waste Cast Stone waste form must be acceptablemore » for disposal in the IDF. This secondary waste Cast Stone waste form qualification testing plan outlines the testing of the waste form and immobilization process to demonstrate that the Cast Stone waste form can comply with the disposal requirements. Specifications for the secondary-waste Cast Stone waste form have not been established. For this testing plan, Cast Stone specifications are derived from specifications for the immobilized LAW glass in the WTP contract, the waste acceptance criteria for the IDF, and the waste acceptance criteria in the IDF Permit issued by the State of Washington. This testing plan outlines the testing needed to demonstrate that the waste form can comply with these waste form specifications and acceptance criteria. The testing program must also demonstrate that the immobilization process can be controlled to consistently provide an acceptable waste form product. This testing plan also outlines the testing needed to provide the technical basis for understanding the long-term performance of the waste form in the disposal environment. These waste form performance data are needed to support performance assessment analyses of the long-term environmental impact of the secondary-waste Cast Stone waste form in the IDF« less

75 FR 15423 - U.S. Nuclear Regulatory Commission Technical Evaluation Report for the Phase 1 Decommissioning...

Federal Register 2010, 2011, 2012, 2013, 2014

2010-03-29

... DOE to carry out a high-level radioactive waste management demonstration project at the Western New... solidification of high-level radioactive waste for disposal in a Federal repository for permanent disposal. The... and other facilities where the solidified high-level radioactive waste was stored, the facilities used...

Brazing Inconel 625 Using the Copper Foil

NASA Astrophysics Data System (ADS)

Chen, Wen-Shiang; Wang, Cheng-Yen; Shiue, Ren-Kae

2013-12-01

Brazing Inconel 625 (IN-625) using the copper foil has been investigated in this research. The brazed joint is composed of nanosized CrNi3 precipitates and Cr/Mo/Nb/Ni quaternary compound in the Cu/Ni-rich matrix. The copper filler 50 μm in thickness is enough for the joint filling. However, the application of Cu foil 100 μm in thickness has little effect on the shear strength of the brazed joint. The specimen brazed at 1433 K (1160 °C) for 1800 seconds demonstrates the best shear strength of 470 MPa, and its fractograph is dominated by ductile dimple fracture with sliding marks. Decreasing the brazing temperature slightly decreases the shear strength of the brazed joint due to the presence of a few isolated solidification shrinkage voids smaller than 15 μm. Increasing the brazing temperature, especially for the specimen brazed at 1473 K (1200 °C), significantly deteriorates the shear strength of the joint below 260 MPa because of coalescence of isothermal solidification shrinkage voids in the joint. The Cu foil demonstrates potential in brazing IN-625 for industrial application.

Technology Performance Review: Selecting And Using Solidification/Stabilization Treatment For Site Remediation

EPA Science Inventory

Solidification/Stabilization (S/S) is a widely used treatment technology to prevent migration and exposure of contaminants from a contaminated media (i.e., soil, sludge and sediment). Solidification refers to a process that binds a contaminated media with a reagent changing its ...

Effect of the temperature-rate parameters of directional solidification on the structure formation in high-temperature materials

NASA Astrophysics Data System (ADS)

Svetlov, I. L.; Neiman, A. V.

2017-03-01

The effect of the temperature gradient and the crystal growth rate on the structure formation in nickel and niobium superalloys is studied under the conditions of the flat, cellular, dendritic, or dendritic-cellular configuration of a solidification front during directional solidification.

Analysis and calculation of macrosegregation in a casting ingot. MPS solidification model. Volume 2: Software documentation

NASA Technical Reports Server (NTRS)

Maples, A. L.

1980-01-01

The software developed for the solidification model is presented. A link between the calculations and the FORTRAN code is provided, primarily in the form of global flow diagrams and data structures. A complete listing of the solidification code is given.

SOLIDIFICATION/STABILIZATION FOR REMEDIATON OF WOOD PRESERVING SITES: TREATMENT FOR DIOXINS, PCP, CREOSOTE, AND METALS

EPA Science Inventory

This article discusses the use of solidification/stabilization (S/S) to treat soils contaminated with organic and inorganic chemicals at wood preserving sites. Solidification is defined for this article as making a material into a free standing solid. Stabilization is defined as ...

Numerical simulation of freckle formation in directional solidification of binary alloys

NASA Technical Reports Server (NTRS)

Felicelli, Sergio D.; Heinrich, Juan C.; Poirier, David R.

1992-01-01

A mathematical model of solidification is presented which simulates the formation of segregation models known as 'freckles' during directional solidification of binary alloys. The growth of the two-phase or dendritic zone is calculated by solving the coupled equations of momentum, energy, and solute transport, as well as maintaining the thermodynamic constraints dictated by the phase diagram of the alloy. Calculations for lead-tin alloys show that the thermosolutal convection in the dendritic zone during solidification can produce heavily localized inhomogeneities in the composition of the final alloy.

Microsegregation during directional solidification

NASA Technical Reports Server (NTRS)

Coriell, S. R.; Mcfadden, G. B.

1984-01-01

During the directional solidification of alloys, solute inhomogeneities transverse to the growth direction arise due to morphological instabilities (leading to cellular or dendritic growth) and/or due to convection in the melt. In the absence of convection, the conditions for the onset of morphological instability are given by the linear stability analysis of Mullins and Sekerka. For ordinary solidification rates, the predictions of linear stability analysis are similar to the constitutional supercooling criterion. However, at very rapid solidification rates, linear stability analysis predicts a vast increase in stabilization in comparison to constitutional supercooling.

Evolution of solidification texture during additive manufacturing.

PubMed

Wei, H L; Mazumder, J; DebRoy, T

2015-11-10

Striking differences in the solidification textures of a nickel based alloy owing to changes in laser scanning pattern during additive manufacturing are examined based on theory and experimental data. Understanding and controlling texture are important because it affects mechanical and chemical properties. Solidification texture depends on the local heat flow directions and competitive grain growth in one of the six <100> preferred growth directions in face centered cubic alloys. Therefore, the heat flow directions are examined for various laser beam scanning patterns based on numerical modeling of heat transfer and fluid flow in three dimensions. Here we show that numerical modeling can not only provide a deeper understanding of the solidification growth patterns during the additive manufacturing, it also serves as a basis for customizing solidification textures which are important for properties and performance of components.

In Situ X-Ray Observations of Dendritic Fragmentation During Directional Solidification of a Sn-Bi Alloy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gibbs, John W.; Tourret, Damien; Gibbs, Paul J.

2015-09-25

Dendrite fragmentation is an important phenomenon in microstructural development during solidification. For instance, it plays a key role in initiating the columnar-to-equiaxed transition (CET). Here, we use x-ray radiography to study dendrite fragmentation rate in a Sn-39.5 wt.% Bi alloy during directional solidification. Experiments were performed in which solidification was parallel and anti-parallel to gravity, leading to significantly different fragmentation rates. We quantify the distribution of fragmentation rate as a function of distance from the solidification front, time in the mushy zone, and volume fraction of solid. While the observed fragmentation rate can be high, there is no evidence ofmore » a CET, illustrating that it requires more than just fragmentation to occur.« less

Scaling Analysis of Alloy Solidification and Fluid Flow in a Rectangular Cavity

NASA Astrophysics Data System (ADS)

Plotkowski, A.; Fezi, K.; Krane, M. J. M.

A scaling analysis was performed to predict trends in alloy solidification in a side-cooled rectangular cavity. The governing equations for energy and momentum were scaled in order to determine the dependence of various aspects of solidification on the process parameters for a uniform initial temperature and an isothermal boundary condition. This work improved on previous analyses by adding considerations for the cooling bulk fluid flow. The analysis predicted the time required to extinguish the superheat, the maximum local solidification time, and the total solidification time. The results were compared to a numerical simulation for a Al-4.5 wt.% Cu alloy with various initial and boundary conditions. Good agreement was found between the simulation results and the trends predicted by the scaling analysis.

The growth of metastable peritectic compounds

NASA Technical Reports Server (NTRS)

Larson, D. J., Jr.

1984-01-01

The influence of gravitationally driven convection on the directional solidification of peritectic alloys was evaluated. The Pb-Bi peritectic was studied as a model solidification system. Analyses of directionally solidified Pb-Bi peritectic samples indicate that appreciable macrosegregation occurs due to thermosolutal convection and/or Soret diffusion. The macrosegregation results in sequantial change of phase and morphology as solidification progresses down the length of the sample. Banding was eliminated when furnace conditions were selected which resulted in a planar solidification interface. The directional solidification that occurs in the vicinity of the Pb-Bi peritectic isothermal was found to be isocompositional and to consist solely of the equilibrium terminal solid solution and peritectic phases on an extremely fine scale. Evidence was found to support the peritectic supercooling mechanism, but not the proposed peritectic superheat mechanism.

In Situ X-Ray Observations of Dendritic Fragmentation During Directional Solidification of a Sn-Bi Alloy

DOE PAGES

Gibbs, John W.; Tourret, Damien; Gibbs, Paul J.; ...

2015-09-25

Dendrite fragmentation is an important phenomenon in microstructural development during solidification. For instance, it plays a key role in initiating the columnar-to-equiaxed transition (CET). In this paper, we use x-ray radiography to study dendrite fragmentation rate in a Sn-39.5 wt.% Bi alloy during directional solidification. Experiments were performed in which solidification was parallel and anti-parallel to gravity, leading to significantly different fragmentation rates. We quantify the distribution of fragmentation rate as a function of distance from the solidification front, time in the mushy zone, and volume fraction of solid. Finally, while the observed fragmentation rate can be high, there ismore » no evidence of a CET, illustrating that it requires more than just fragmentation to occur.« less

Multiscale X-ray and Proton Imaging of Bismuth-Tin Solidification

NASA Astrophysics Data System (ADS)

Gibbs, P. J.; Imhoff, S. D.; Morris, C. L.; Merrill, F. E.; Wilde, C. H.; Nedrow, P.; Mariam, F. G.; Fezzaa, K.; Lee, W.-K.; Clarke, A. J.

2014-08-01

The formation of structural patterns during metallic solidification is complex and multiscale in nature, ranging from the nanometer scale, where solid-liquid interface properties are important, to the macroscale, where casting mold filling and intended heat transfer are crucial. X-ray and proton imaging can directly interrogate structure, solute, and fluid flow development in metals from the microscale to the macroscale. X-rays permit high spatio-temporal resolution imaging of microscopic solidification dynamics in thin metal sections. Similarly, high-energy protons permit imaging of mesoscopic and macroscopic solidification dynamics in large sample volumes. In this article, we highlight multiscale x-ray and proton imaging of bismuth-tin alloy solidification to illustrate dynamic measurement of crystal growth rates and solute segregation profiles that can be that can be acquired using these techniques.

Modeling of Rapid Solidification with Undercooling Effect During Droplet Flattening on a Substrate in Coating Formation

NASA Astrophysics Data System (ADS)

Shukla, Rajesh Kumar; Patel, Virendra; Kumar, Arvind

2018-02-01

The coating deposit on the substrate in thermal spray coating process develops by solidification of individual molten particle which impacts, flattens and solidifies on the surface of the substrate. Droplet flattening and solidification typically involves rapid cooling. In this paper, a model for non-equilibrium rapid solidification of a molten droplet spreading onto a substrate is presented. Transient flow during droplet impact and its subsequent spreading is considered using the volume of fluid surface tracking method which was fully coupled with the rapid solidification model. The rapid solidification model includes undercooling, nucleation, interface tracking, non-equilibrium solidification kinetics and combined heat transfer and fluid flow as required to treat a non-stagnant splat formed from droplet flattening. The model is validated with the literature results on stagnant splats. Subsequently, using the model the characteristics of the rapidly solidifying interface for non-stagnant splat, such as interface velocity and interface temperature, are described and the effect of undercooling and interfacial heat transfer coefficient are highlighted. In contrast to the stagnant splat, the non-stagnant splat considered in this study displays interesting features in the rapidly solidifying interface. These are attributed to droplet thinning and droplet recoiling that occur during the droplet spreading process.

Utilization of coal fly ash in solidification of liquid radioactive waste from research reactor.

PubMed

Osmanlioglu, Ahmet Erdal

2014-05-01

In this study, the potential utilization of fly ash was investigated as an additive in solidification process of radioactive waste sludge from research reactor. Coal formations include various percentages of natural radioactive elements; therefore, coal fly ash includes various levels of radioactivity. For this reason, fly ashes have to be evaluated for potential environmental implications in case of further usage in any construction material. But for use in solidification of radioactive sludge, the radiological effects of fly ash are in the range of radioactive waste management limits. The results show that fly ash has a strong fixing capacity for radioactive isotopes. Specimens with addition of 5-15% fly ash to concrete was observed to be sufficient to achieve the target compressive strength of 20 MPa required for near-surface disposal. An optimum mixture comprising 15% fly ash, 35% cement, and 50% radioactive waste sludge could provide the solidification required for long-term storage and disposal. The codisposal of radioactive fly ash with radioactive sludge by solidification decreases the usage of cement in solidification process. By this method, radioactive fly ash can become a valuable additive instead of industrial waste. This study supports the utilization of fly ash in industry and the solidification of radioactive waste in the nuclear industry.

Solidification characteristics and segregation behavior of a P-containing Ni-Fe-Cr-based alloy

NASA Astrophysics Data System (ADS)

Wang, Changshuai; Su, Haijun; Guo, YongAn; Guo, Jianting; Zhou, Lanzhang

2017-09-01

Solidification characteristics and segregation behavior of a P-containing Ni-Fe-Cr-based alloy, considered as boiler and turbine materials in 700 °C advanced ultra-supercritical coal-fired power plants, have been investigated by differential thermal analysis and directional solidification quenching technique. Results reveal that P decreases the solidus temperature, but only has negligible influence on liquidus temperature. After P was added, the solidification sequence has no apparent change, but the width of the mushy zone increases and dendritic structures become coarser. Moreover, P increases the amount and changes the morphology of MC carbide. Energy-dispersive spectroscopy analysis reveals that P has obvious influence on the segregation behavior of the constitute elements with equilibrium partition coefficients (ki) far away from unity, whereas has negligible effect on the constituent elements with ki close to unity and has more influence on the final stage of solidification than at early stage. The distribution profiles reveal that P atoms pile up ahead of the solid/liquid (S/L) interface and strongly segregate to the interdendritic liquid region. The influence of P on solidification characteristics and segregation behavior of Ni-Fe-Cr-based alloy could be attributed to the accumulation of P ahead of the S/L interface during solidification.

Timing of mantle overturn during magma ocean solidification

NASA Astrophysics Data System (ADS)

Boukaré, C.-E.; Parmentier, E. M.; Parman, S. W.

2018-06-01

Solidification of magma oceans (MOs) formed early in the evolution of planetary bodies sets the initial condition for their evolution on much longer time scales. Ideal fractional crystallization would generate an unstable chemical stratification that subsequently overturns to form a stably stratified mantle. The simplest model of overturn assumes that cumulates remain immobile until the end of MO solidification. However, overturning of cumulates and thermal convection during solidification may act to reduce this stratification and introduce chemical heterogeneity on scales smaller than the MO thickness. We explore overturning of cumulates before the end of MO crystallization and the possible consequences for mantle structure and composition. In this model, increasingly dense iron-rich layers, crystallized from the overlying residual liquid MO, are deposited on a thickening cumulate layer. Overturn during solidification occurs if the dimensionless parameter, Rc, measuring the ratio of the MO time of crystallization τMO to the timescale associated with compositional overturn τov = μ / ΔρgH exceeds a threshold value. If overturn did not occur until after solidification, this implies that the viscosity of the solidified mantle must have been sufficiently high (possibly requiring efficient melt extraction from the cumulate) for a given rate of solidification. For the lunar MO, possible implications for the generation of the Mg-suites and mare basalt are suggested.

Traveling Magnetic Field Applications for Materials Processing in Space

NASA Technical Reports Server (NTRS)

Grugel, R. N.; Mazuruk, K.; Curreri, Peter A. (Technical Monitor)

2001-01-01

Including the capability to induce a controlled fluid flow in the melt can significantly enrich research on solidification phenomena in a microgravity environment. The traveling magnetic field (TMF) is a promising technique to achieve this goal and is the aim of our ground-based project. In this presentation we will discuss new theoretical as well as experimental results recently obtained by our group. In particular, we experimentally demonstrated efficient mixing of metal alloys in long tubes subjected to TMF during processing. Application of this technique can provide an elegant solution to ensure melt homogenization prior to solidification in a microgravity environment where natural convection is generally absent. Results of our experimental work of applying the TMF technique to alloy melts will be presented. Possible applications of TMF on board the International Space Station will also be discussed.

The effects of solidification on sill propagation dynamics and morphology

NASA Astrophysics Data System (ADS)

Chanceaux, L.; Menand, T.

2016-05-01

Sills are an integral part of the formation and development of larger plutons and magma reservoirs. Thus sills are essential for both the transport and the storage of magma in the Earth's crust. However, although cooling and solidification are central to magmatism, their effects on sills have been so far poorly studied. Here, the effects of solidification on sill propagation dynamics and morphology are studied by means of analogue laboratory experiments. Hot fluid vegetable oil (magma analogue), that solidifies during its propagation, is injected as a sill in a colder layered gelatine solid (elastic host rock analogue). The injection flux and temperature are maintained constant during an experiment and systematically varied between each experiment, in order to vary and quantify the amount of solidification between each experiments. The oil is injected directly at the interface between the two gelatine layers. When solidification effects are small (high injection temperatures and fluxes), the propagation is continuous and the sill has a regular and smooth surface. Inversely, when solidification effects are important (low injection temperatures and fluxes), sill propagation is discontinuous and occurs by steps of surface-area creation interspersed with periods of momentary arrest. The morphology of these sills displays folds, ropy structures on their surface, and lobes with imprints of the leading fronts that correspond to each step of area creation. These experiments show that for a given, constant injected volume, as solidification effects increase, the area of the sills decreases, their thickness increases, and the number of propagation steps increases. These results have various geological and geophysical implications. The morphology of sills, such as lobate structures (interpretation of 3D seismic studies in sedimentary basin) and ropy flow structures (field observations) can be related to solidification during emplacement. Moreover, a non-continuous morphology as observed in the field does not necessarily involve multiple injections, but could instead reflect a continuous, yet complex morphology induced by solidification effects during emplacement. Also, a discontinuous sill propagation induced by solidification effects should be associated with bursts of seismic activity. Finally, our study shows that once a sill has initiated, the dimensionless flux influences the sill thermal state, and in turn its propagation, and final extent and thickness. In restricting the lateral extent of sills, magma cooling and solidification are likely to impact directly the size of plutons constructed by amalgamated sills.

Equipment evaluation for low density polyethylene encapsulated nitrate salt waste at the Rocky Flats Plant

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yamada, W.I.; Faucette, A.M.; Jantzen, R.C.

1993-08-30

Mixed wastes at the Rocky Flats Plant (RFP) are subject to regulation by the Resource Conservation and Recovery Act (RCRA). Polymer solidification is being developed as a final treatment technology for several of these mixed wastes, including nitrate salts. Encapsulation nitrate salts with low density polyethylene (LDPE) has been the preliminary focus of the RFP polymer solidification effort. Literature reviews, industry surveys, and lab-scale and pilot-scale tests have been conducted to evaluate several options for encapsulating nitrate salts with LDPE. Most of the effort has focused on identifying compatible drying and extrusion technologies. Other processing options, specifically meltration and non-heatedmore » compounding machines, were also investigated. The best approach appears to be pretreatment of the nitrate salt waste brine in either a vertical or horizontal thin film evaporator followed by compounding of the dried waste with LDPE in an intermeshing, co-rotating, twin-screw extruder. Additional pilot-scale tests planned for the fall of 1993 should further support this recommendation. Preliminary evaluation work indicates that meltration is not possible at atmospheric pressure with the LDPE (Chevron PE-1409) provided by RFP. However, meltration should be possible at atmospheric pressure using another LDPE formulation with altered physical and rheological properties: Lower molecular weight and lower viscosity (Epoline C-15). Contract modifications are now in process to allow a follow-on pilot scale demonstration. Questions regarding changed safety and physical properties of the resultant LDPE waste form due to use of the Epoline C-15 will be addressed. No additional work with non-heated mixer compounder machines is planned at this time.« less

Processing eutectics in space

NASA Technical Reports Server (NTRS)

Douglas, F. C.; Galasso, F. S.

1974-01-01

Studies which have been done in an earth-based laboratory environment have generally not yielded specimens with the degree of perfection required of the eutectic microstructure to provide test data to evaluate their nonstructural applications. It has been recognized that the low-g environment of an orbiting space laboratory provides a unique environment to re-examine the process of solidification with the goal of producing better microstructures. The objective of this program is to evaluate the feasibility of using the space environment for producing eutectics with microstructures which can be of value on earth. In carrying out this objective, evaluative investigations were carried out on the technology of solidification in a 1-g environment to provide sound baseline data for planning space laboratory experiments.

Spatial considerations during cryopreservation of a large volume sample.

PubMed

Kilbride, Peter; Lamb, Stephen; Milne, Stuart; Gibbons, Stephanie; Erro, Eloy; Bundy, James; Selden, Clare; Fuller, Barry; Morris, John

2016-08-01

There have been relatively few studies on the implications of the physical conditions experienced by cells during large volume (litres) cryopreservation - most studies have focused on the problem of cryopreservation of smaller volumes, typically up to 2 ml. This study explores the effects of ice growth by progressive solidification, generally seen during larger scale cryopreservation, on encapsulated liver hepatocyte spheroids, and it develops a method to reliably sample different regions across the frozen cores of samples experiencing progressive solidification. These issues are examined in the context of a Bioartificial Liver Device which requires cryopreservation of a 2 L volume in a strict cylindrical geometry for optimal clinical delivery. Progressive solidification cannot be avoided in this arrangement. In such a system optimal cryoprotectant concentrations and cooling rates are known. However, applying these parameters to a large volume is challenging due to the thermal mass and subsequent thermal lag. The specific impact of this to the cryopreservation outcome is required. Under conditions of progressive solidification, the spatial location of Encapsulated Liver Spheroids had a strong impact on post-thaw recovery. Cells in areas first and last to solidify demonstrated significantly impaired post-thaw function, whereas areas solidifying through the majority of the process exhibited higher post-thaw outcome. It was also found that samples where the ice thawed more rapidly had greater post-thaw viability 24 h post-thaw (75.7 ± 3.9% and 62.0 ± 7.2% respectively). These findings have implications for the cryopreservation of large volumes with a rigid shape and for the cryopreservation of a Bioartificial Liver Device. Copyright © 2016 The Authors. Published by Elsevier Inc. All rights reserved.

Production, pathways and budgets of melts in mid-ocean ridges: An enthalpy based thermo-mechanical model

NASA Astrophysics Data System (ADS)

Mandal, Nibir; Sarkar, Shamik; Baruah, Amiya; Dutta, Urmi

2018-04-01

Using an enthalpy based thermo-mechanical model we provide a theoretical evaluation of melt production beneath mid-ocean ridges (MORs), and demonstrate how the melts subsequently develop their pathways to sustain the major ridge processes. Our model employs a Darcy idealization of the two-phase (solid-melt) system, accounting enthalpy (ΔH) as a function of temperature dependent liquid fraction (ϕ). Random thermal perturbations imposed in this model set in local convection that drive melts to flow through porosity controlled pathways with a typical mushroom-like 3D structure. We present across- and along-MOR axis model profiles to show the mode of occurrence of melt-rich zones within mushy regions, connected to deeper sources by single or multiple feeders. The upwelling of melts experiences two synchronous processes: 1) solidification-accretion, and 2) eruption, retaining a large melt fraction in the framework of mantle dynamics. Using a bifurcation analysis we determine the threshold condition for melt eruption, and estimate the potential volumes of eruptible melts (∼3.7 × 106 m3/yr) and sub-crustal solidified masses (∼1-8.8 × 106 m3/yr) on an axis length of 500 km. The solidification process far dominates over the eruption process in the initial phase, but declines rapidly on a time scale (t) of 1 Myr. Consequently, the eruption rate takes over the solidification rate, but attains nearly a steady value as t > 1.5 Myr. We finally present a melt budget, where a maximum of ∼5% of the total upwelling melt volume is available for eruption, whereas ∼19% for deeper level solidification; the rest continue to participate in the sub-crustal processes.

Ultrafast synchrotron X-ray imaging studies of microstructure fragmentation in solidification under ultrasound

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wang, Bing; Tan, Dongyue; Lee, Tung Lik

Ultrasound processing of metal alloys is an environmental friendly and promising green technology for liquid metal degassing and microstructural refinement. However many fundamental issues in this field are still not fully understood, because of the difficulties in direct observation of the dynamic behaviours caused by ultrasound inside liquid metal and semisolid metals during the solidification processes. In this paper, we report a systematic study using the ultrafast synchrotron X-ray imaging (up to 271,554 frame per second) technique available at the Advanced Photon Source, USA and Diamond Light Source, UK to investigate the dynamic interactions between the ultrasonic bubbles/acoustic flow andmore » the solidifying phases in a Bi-8%Zn alloy. The experimental results were complimented by numerical modelling. The chaotic bubble implosion and dynamic bubble oscillations were revealed in-situ for the first time in liquid metal and semisolid metal. The fragmentation of the solidifying Zn phases and breaking up of the liquid-solid interface by ultrasonic bubbles and enhanced acoustic flow were clearly demonstrated and agreed very well with the theoretical calculations. The research provides unambiguous experimental evidence and robust theoretical interpretation in elucidating the dominant mechanisms of microstructure fragmentation and refinement in solidification under ultrasound.« less

Detachment of secondary dendrite arm in a directionally solidified Sn-Ni peritectic alloy under deceleration growth condition

PubMed Central

Peng, Peng; Li, Xinzhong; Li, Jiangong; Su, Yanqing; Guo, Jingjie; Fu, Hengzhi

2016-01-01

In order to better understand the detachment mechanism of secondary dendrite arm during peritectic solidification, the detachment of secondary dendrite arm from the primary dendrite arms in directionally solidified Sn-36at.%Ni peritectic alloys is investigated at different deceleration rates. Extensive detachment of secondary dendrite arms from primary stem is observed below peritectic reaction temperature TP. And an analytical model is established to characterize the detachment process in terms of the secondary dendrite arm spacing λ2, the root radius of detached arms and the specific surface area (SV) of dendrites. It is found that the detachment mechanism is caused by not only curvature difference between the tips and roots of secondary branches, but also that between the thicker secondary branches and the thinner ones. Besides, this detachment process is significantly accelerated by the temperature gradient zone melting (TGZM) effect during peritectic solidification. It is demonstrated that the reaction constant (f) which is used to characterize the kinetics of peritectic reaction is crucial for the determination of the detachment process. The value of f not only changes with growth rate but also with solidification time at a given deceleration rate. In conclusion, these findings help the better understanding of the detachment mechanism. PMID:27270334

Ultrafast synchrotron X-ray imaging studies of microstructure fragmentation in solidification under ultrasound

DOE PAGES

Wang, Bing; Tan, Dongyue; Lee, Tung Lik; ...

2017-11-03

Ultrasound processing of metal alloys is an environmental friendly and promising green technology for liquid metal degassing and microstructural refinement. However many fundamental issues in this field are still not fully understood, because of the difficulties in direct observation of the dynamic behaviours caused by ultrasound inside liquid metal and semisolid metals during the solidification processes. In this paper, we report a systematic study using the ultrafast synchrotron X-ray imaging (up to 271,554 frame per second) technique available at the Advanced Photon Source, USA and Diamond Light Source, UK to investigate the dynamic interactions between the ultrasonic bubbles/acoustic flow andmore » the solidifying phases in a Bi-8%Zn alloy. The experimental results were complimented by numerical modelling. The chaotic bubble implosion and dynamic bubble oscillations were revealed in-situ for the first time in liquid metal and semisolid metal. The fragmentation of the solidifying Zn phases and breaking up of the liquid-solid interface by ultrasonic bubbles and enhanced acoustic flow were clearly demonstrated and agreed very well with the theoretical calculations. The research provides unambiguous experimental evidence and robust theoretical interpretation in elucidating the dominant mechanisms of microstructure fragmentation and refinement in solidification under ultrasound.« less

SOLIDIFICATION/STABILIZATION OF SLUDGE AND ASH FROM WASTEWATER TREATMENT PLANTS

EPA Science Inventory

Tests were performed to determine the physical properties and chemical leaching characteristics of the residuals and the stabilized/solidified products from two publicly-owned wastewater treatment works (POTW). The two POTW waste products included in this study were an anaerobic ...

ONSITE ENGINEERING REPORT FOR SOLIDIFICATION/ STABILIZATION TREATMENT TESTING OF CONTAMINATED SOILS

EPA Science Inventory

The EPA's Office of Solid Waste and Emergency Response (OSWER) is currently developing land disposal restrictions (LDRs) for contaminated soil and debris (CS&D). The Office of Research and Development, through its Risk Reduction Engineering Laboratory (RREL), is providing support...

Investigation of the growth of directionally solidified eutectics with potential as electron emitters

NASA Technical Reports Server (NTRS)

Chapman, A. T.; Cochran, J. K.

1976-01-01

The construction of a solar furnace was completed and it was tested after a preliminary alignment of the heliostat mirrors. After final alignment, the solar furnace is used for directional solidification experiments designed to simulate space conditions.

On the hot cracking susceptibility of a semisolid aluminium 6061 weld: Application of a coupled solidification- thermomechanical model

NASA Astrophysics Data System (ADS)

Zareie Rajani, H. R.; Phillion, A. B.

2015-06-01

A coupled solidification-thermomechanical model is presented that investigates the hot tearing susceptibility of an aluminium 6061 semisolid weld. Two key phenomena are considered: excessive deformation of the semisolid weld, initiating a hot tear, and the ability of the semisolid weld to heal the hot tear by circulation of the molten metal. The model consists of two major modules: weld solidification and thermomechanical analysis. 1) By means of a multi-scale model of solidification, the microstructural evolution of the semisolid weld is simulated in 3D. The semisolid structure, which varies as a function of welding parameters, is composed of solidifying grains and a network of micro liquid channels. The weld solidification module is utilized to obtain the solidification shrinkage. The size of the micro liquid channels is used as an indicator to assess the healing ability of the semisolid weld. 2) Using the finite element method, the mechanical interaction between the weld pool and the base metal is simulated to capture the transient force field deforming the semisolid weld. Thermomechanical stresses and shrinkage stresses are both considered in the analysis; the solidification contractions are extracted from the weld solidification module and applied to the deformation simulation as boundary conditions. Such an analysis enables characterization of the potential for excessive deformation of the weld. The outputs of the model are used to study the effect of welding parameters including welding current and speed, and also welding constraint on the hot cracking susceptibility of an aluminium alloy 6061 semisolid weld.

Interaction of Multiple Particles with a Solidification Front: From Compacted Particle Layer to Particle Trapping.

PubMed

Saint-Michel, Brice; Georgelin, Marc; Deville, Sylvain; Pocheau, Alain

2017-06-13

The interaction of solidification fronts with objects such as particles, droplets, cells, or bubbles is a phenomenon with many natural and technological occurrences. For an object facing the front, it may yield various fates, from trapping to rejection, with large implications regarding the solidification pattern. However, whereas most situations involve multiple particles interacting with each other and the front, attention has focused almost exclusively on the interaction of a single, isolated object with the front. Here we address experimentally the interaction of multiple particles with a solidification front by performing solidification experiments of a monodisperse particle suspension in a Hele-Shaw cell with precise control of growth conditions and real-time visualization. We evidence the growth of a particle layer ahead of the front at a close-packing volume fraction, and we document its steady-state value at various solidification velocities. We then extend single-particle models to the situation of multiple particles by taking into account the additional force induced on an entering particle by viscous friction in the compacted particle layer. By a force balance model this provides an indirect measure of the repelling mean thermomolecular pressure over a particle entering the front. The presence of multiple particles is found to increase it following a reduction of the thickness of the thin liquid film that separates particles and front. We anticipate the findings reported here to provide a relevant basis to understand many complex solidification situations in geophysics, engineering, biology, or food engineering, where multiple objects interact with the front and control the resulting solidification patterns.

Proposal of a sequential treatment methodology for the safe reuse of oil sludge-contaminated soil.

PubMed

Mater, L; Sperb, R M; Madureira, L A S; Rosin, A P; Correa, A X R; Radetski, C M

2006-08-25

In this study sequential steps were used to treat and immobilize oil constituents of an oil sludge-contaminated soil. Initially, the contaminated soil was oxidized by a Fenton type reaction (13 wt% for H(2)O(2); 10mM for Fe(2+)). The oxidative treatment period of 80 h was carried out under three different pH conditions: 20 h at pH 6.5, 20 h at pH 4.5, and 40 h at pH 3.0. The oxidized contaminated sample (3 kg) was stabilized and solidified for 2h with clay (1 kg) and lime (2 kg). Finally, this mixture was solidified by sand (2 kg) and Portland cement (4 kg). In order to evaluate the efficiency of different processes to treat and immobilize oil contaminants of the oil sludge-contaminated soil, leachability and solubility tests were performed and extracts were analyzed according to the current Brazilian waste regulations. Results showed that the Fenton oxidative process was partially efficient in degrading the oil contaminants in the soil, since residual concentrations were found for the PAH and BTEX compounds. Leachability tests showed that clay-lime stabilization/solidification followed by Portland cement stabilization/solidification was efficient in immobilizing the recalcitrant and hazardous constituents of the contaminated soil. These two steps stabilization/solidification processes are necessary to enhance environmental protection (minimal leachability) and to render final product economically profitable. The treated waste is safe enough to be used on environmental applications, like roadbeds blocks.

Powder-Metallurgy Process And Product

NASA Technical Reports Server (NTRS)

Paris, Henry G.

1988-01-01

Rapid-solidification processing yields alloys with improved properties. Study undertaken to extend favorable property combinations of I/M 2XXX alloys through recently developed technique of rapid-solidification processing using powder metallurgy(P/M). Rapid-solidification processing involves impingement of molten metal stream onto rapidly-spinning chill block or through gas medium using gas atomization technique.

Flight Planning for the International Space Station-Levitation Observation of Dendrite Evolution in Steel Ternary Alloy Rapid Solidification

NASA Technical Reports Server (NTRS)

Flemings, M. C.; Matson, D. M.; Loser, W.; Hyers, R. W.; Rogers, J. R.; Curreri, Peter A. (Technical Monitor)

2002-01-01

The paper is an overview of the status and science for the LODESTARS (Levitation Observation of Dendrite Evolution in Steel Ternary Alloy Rapid Solidification) research project. The program is aimed at understanding how melt convection influences phase selection and the evolution of rapid solidification microstructures.

Secondary Waste Simulant Development for Cast Stone Formulation Testing

DOE Office of Scientific and Technical Information (OSTI.GOV)

Russell, Renee L.; Westsik, Joseph H.; Rinehart, Donald E.

Washington River Protection Solutions, LLC (WRPS) funded Pacific Northwest National Laboratory (PNNL) to conduct a waste form testing program to implement aspects of the Secondary Liquid Waste Treatment Cast Stone Technology Development Plan (Ashley 2012) and the Hanford Site Secondary Waste Roadmap (PNNL 2009) related to the development and qualification of Cast Stone as a potential waste form for the solidification of aqueous wastes from the Hanford Site after the aqueous wastes are treated at the Effluent Treatment Facility (ETF). The current baseline is that the resultant Cast Stone (or grout) solid waste forms would be disposed at the Integratedmore » Disposal Facility (IDF). Data and results of this testing program will be used in the upcoming performance assessment of the IDF and in the design and operation of a solidification treatment unit planned to be added to the ETF. The purpose of the work described in this report is to 1) develop simulants for the waste streams that are currently being fed and future WTP secondary waste streams also to be fed into the ETF and 2) prepare simulants to use for preparation of grout or Cast Stone solid waste forms for testing.« less

Solidification of arsenic and heavy metal containing tailings using cement and blast furnace slag.

PubMed

Kim, Jung-Wook; Jung, Myung Chae

2011-01-01

The objective of this study is to examine the solidification of toxic elements in tailings by the use of cement and blast furnace slag. Tailings samples were taken at an Au-Ag mine in Korea. To examine the best mixing ratio of tailings and the mixture of ordinary Portland cement (OPC) and blast furnace slag (SG) of 5:5, 6:6, 7:3, and 8:2, the 7:3 ratio of tailings and OPC+SG was adapted. In addition, the mixing ratios of water and OPC + SG were applied to 10, 20, and 30 wt%. After 7, 14, and 28 days' curing, the UCS test was undertaken. A relatively high strength of solidified material (137.2 kg cm⁻² in average of 3 samples) at 28 days' curing was found in 20 wt% of water content (WC). This study also examined the leachability of arsenic and heavy metals (Cd, Cu, Pb, and Zn) under the Korean Standard Leaching Test, and it showed that the reductions in leachabilities of As and heavy metals of solidified samples were ranged from 76 to 99%. Thus, all the solidified samples were within the guidelines for special and hazardous waste materials by the Waste Management Act in Korea. In addition, the result of freeze-thaw cycle test of the materials indicated that the durability of the materials was sufficient. In conclusion, solidification using a 7:3 mixing ratio of tailings and a 1:1 mixture of OPC + SG with 20% of WC is one of the best methods for the remediation of arsenic and heavy metals in tailings and other contaminated materials.

Evolution of solidification texture during additive manufacturing

PubMed Central

Wei, H. L.; Mazumder, J.; DebRoy, T.

2015-01-01

Striking differences in the solidification textures of a nickel based alloy owing to changes in laser scanning pattern during additive manufacturing are examined based on theory and experimental data. Understanding and controlling texture are important because it affects mechanical and chemical properties. Solidification texture depends on the local heat flow directions and competitive grain growth in one of the six <100> preferred growth directions in face centered cubic alloys. Therefore, the heat flow directions are examined for various laser beam scanning patterns based on numerical modeling of heat transfer and fluid flow in three dimensions. Here we show that numerical modeling can not only provide a deeper understanding of the solidification growth patterns during the additive manufacturing, it also serves as a basis for customizing solidification textures which are important for properties and performance of components. PMID:26553246

Evolution of solidification texture during additive manufacturing

DOE PAGES

Wei, H. L.; Mazumder, J.; DebRoy, T.

2015-11-10

Striking differences in the solidification textures of a nickel based alloy owing to changes in laser scanning pattern during additive manufacturing are examined based on theory and experimental data. Understanding and controlling texture are important because it affects mechanical and chemical properties. Solidification texture depends on the local heat flow directions and competitive grain growth in one of the six <100> preferred growth directions in face centered cubic alloys. Furthermore, the heat flow directions are examined for various laser beam scanning patterns based on numerical modeling of heat transfer and fluid flow in three dimensions. Here we show that numericalmore » modeling can not only provide a deeper understanding of the solidification growth patterns during the additive manufacturing, it also serves as a basis for customizing solidification textures which are important for properties and performance of components.« less

Influences on Distribution of Solute Atoms in Cu-8Fe Alloy Solidification Process Under Rotating Magnetic Field

NASA Astrophysics Data System (ADS)

Zou, Jin; Zhai, Qi-Jie; Liu, Fang-Yu; Liu, Ke-Ming; Lu, De-Ping

2018-05-01

A rotating magnetic field (RMF) was applied in the solidification process of Cu-8Fe alloy. Focus on the mechanism of RMF on the solid solution Fe(Cu) atoms in Cu-8Fe alloy, the influences of RMF on solidification structure, solute distribution, and material properties were discussed. Results show that the solidification behavior of Cu-Fe alloy have influenced through the change of temperature and solute fields in the presence of an applied RMF. The Fe dendrites were refined and transformed to rosettes or spherical grains under forced convection. The solute distribution in Cu-rich phase and Fe-rich phase were changed because of the variation of the supercooling degree and the solidification rate. Further, the variation in solute distribution was impacted the strengthening mechanism and conductive mechanism of the material.

Evolution of Secondary Phases Formed upon Solidification of a Ni-Based Alloy

NASA Astrophysics Data System (ADS)

Zuo, Qiang; Liu, Feng; Wang, Lei; Chen, Changfeng

2013-07-01

The solidification of UNS N08028 alloy subjected to different cooling rates was studied, where primary austenite dendrites occur predominantly and different amounts of sigma phase form in the interdendritic regions. The solidification path and elemental segregation upon solidification were simulated using the CALPHAD method, where THERMO-CALC software packages and two classical segregation models were employed to predict the real process. It is thus revealed that the interdendritic sigma phase is formed via eutectic reaction at the last stage of solidification. On this basis, an analytical model was developed to predict the evolution of nonequilibrium eutectic phase, while the isolated morphology of sigma phase can be described using divorced eutectic theory. Size, fraction, and morphology of the sigma phase were quantitatively studied by a series of experiments; the results are in good agreement with the model prediction.

Design of model experiments for melt flow and solidification in a square container under time-dependent magnetic fields

NASA Astrophysics Data System (ADS)

Meier, D.; Lukin, G.; Thieme, N.; Bönisch, P.; Dadzis, K.; Büttner, L.; Pätzold, O.; Czarske, J.; Stelter, M.

2017-03-01

This paper describes novel equipment for model experiments designed for detailed studies on electromagnetically driven flows as well as solidification and melting processes with low-melting metals in a square-based container. Such model experiments are relevant for a validation of numerical flow simulation, in particular in the field of directional solidification of multi-crystalline photovoltaic silicon ingots. The equipment includes two square-shaped electromagnetic coils and a melt container with a base of 220×220 mm2 and thermostat-controlled heat exchangers at top and bottom. A system for dual-plane, spatial- and time-resolved flow measurements as well as for in-situ tracking of the solid-liquid interface is developed on the basis of the ultrasound Doppler velocimetry. The parameters of the model experiment are chosen to meet the scaling laws for a transfer of experimental results to real silicon growth processes. The eutectic GaInSn alloy and elemental gallium with melting points of 10.5 °C and 29.8 °C, respectively, are used as model substances. Results of experiments for testing the equipment are presented and discussed.

Dimensionless numbers in additive manufacturing

NASA Astrophysics Data System (ADS)

Mukherjee, T.; Manvatkar, V.; De, A.; DebRoy, T.

2017-02-01

The effects of many process variables and alloy properties on the structure and properties of additively manufactured parts are examined using four dimensionless numbers. The structure and properties of components made from 316 Stainless steel, Ti-6Al-4V, and Inconel 718 powders for various dimensionless heat inputs, Peclet numbers, Marangoni numbers, and Fourier numbers are studied. Temperature fields, cooling rates, solidification parameters, lack of fusion defects, and thermal strains are examined using a well-tested three-dimensional transient heat transfer and fluid flow model. The results show that lack of fusion defects in the fabricated parts can be minimized by strengthening interlayer bonding using high values of dimensionless heat input. The formation of harmful intermetallics such as laves phases in Inconel 718 can be suppressed using low heat input that results in a small molten pool, a steep temperature gradient, and a fast cooling rate. Improved interlayer bonding can be achieved at high Marangoni numbers, which results in vigorous circulation of liquid metal, larger pool dimensions, and greater depth of penetration. A high Fourier number ensures rapid cooling, low thermal distortion, and a high ratio of temperature gradient to the solidification growth rate with a greater tendency of plane front solidification.

Solidification/stabilization of fly ash from city refuse incinerator facility and heavy metal sludge with cement additives.

PubMed

Cerbo, Atlas Adonis V; Ballesteros, Florencio; Chen, Teng Chien; Lu, Ming-Chun

2017-01-01

Solidification and stabilization are well-known technologies used for treating hazardous waste. These technologies that use cementitious binder have been applied for decades as a final treatment procedure prior to the hazardous waste disposal. In the present work, hazardous waste like fly ash containing high concentrations of heavy metals such Zn (4715.56 mg/kg), Pb (1300.56 mg/kg), and Cu (534.72 mg/kg) and amounts of Ag, Cd, Co, Cr, Mn, and Ni was sampled from a city refuse incinerator facility. This fly ash was utilized in the solidification/stabilization of heavy metal sludge since fly ash has cement-like characteristics. Cement additives such as sodium sulfate, sodium carbonate, and ethylenediaminetetraacetic acid (EDTA) was incorporated to the solidified matrix in order to determine its effect on the solidification/stabilization performance. The solidified matrix was cured for 7, 14, 21, and 28 days prior for its physical and chemical characterizations. The results show that the solidified matrix containing 40% fly ash and 60% cement with heavy metal sludge was the formulation that has the highest fly ash content with a satisfactory strength. The solidified matrix was also able to immobilize the heavy metals both found in the fly ash and sludge based on the toxicity characteristic leaching procedure (TCLP) test. It also shows that the incorporation of sodium carbonate into the solidified matrix not only further improved the compressive strength from 0.36 MPa (without Na 2 CO 3 ) to 0.54 MPa (with Na 2 CO 3 ) but also increased its leaching resistance.

Microgravity

NASA Image and Video Library

1991-09-01

The Advanced Automated Directional Solidification Furnace (AADSF) flew during the USMP-2 mission. During USMP-2, the AADSF was used to study the growth of mercury cadmium telluride crystals in microgravity by directional solidification, a process commonly used on earth to process metals and grow crystals. The furnace is tubular and has three independently controlled temperature zones. The sample travels from the hot zone of the furnace (1600 degrees F) where the material solidifies as it cools. The solidification region, known as the solid/liquid interface, moves from one end of the sample to the other at a controlled rate, thus the term directional solidification.

Modelling directional solidification

NASA Technical Reports Server (NTRS)

Wilcox, William R.; Regel, Liya L.

1994-01-01

This grant, NAG8-831, was a continuation of a previous grant, NAG8-541. The long range goal of this program has been to develop an improved understanding of phenomena of importance to directional solidification, in order to enable explanation and prediction of differences in behavior between solidification on Earth and in space. Emphasis in the recently completed grant was on determining the influence of perturbations on directional solidification of InSb and InSb-GaSb alloys. In particular, the objective was to determine the influence of spin-up/spin-down (ACRT), electric current pulses and vibrations on compositional homogeneity and grain size.

Concentrated solar power on demand demonstration: Construction and operation of a 25 kW prototype

NASA Astrophysics Data System (ADS)

Gil, Antoni; Codd, Daniel S.; Zhou, Lei; Trumper, David; Calvet, Nicolas; Slocum, Alexander H.

2016-05-01

Currently, the majority of concentrated solar power (CSP) plants built worldwide integrate thermal energy storage (TES) systems which enable dispatchable output and higher global plant efficiencies. TES systems are typically based on two tank molten salt technology which involves inherent drawbacks such as parasitic pumping losses and electric tracing of pipes, risk of solidification and high capital costs. The concept presented in this paper is based on a single tank where the concentrated sunlight is directly focused on the molten salt. Hot and cold volumes of salt (at 565 °C and 280 °C, respectively) are axially separated by an insulated divider plate which helps maintain the thermal gradient. The concept, based on existing technologies, seeks to avoid the listed drawbacks as well as reducing the final cost of the TES system. In order to demonstrate its feasibility, Masdar Institute (MI) and Massachusetts Institute of Technology are developing a 25 kW prototype to be tested in the Masdar Solar Platform beam down facility.

The Effect of Microgravity Direction on the Growth of PbSnTe

NASA Technical Reports Server (NTRS)

Fripp, A. L.; Debnam, W. J.; Rosch, W. R.; Narayanan, R.

1998-01-01

The Space Shuttle Columbia was launched as STS-75 at 2018 GMT (Greenwich Mean Time) on February 22, 1996. One of the two major experiment packages was the Third United States Microgravity Payload (USMP-3), and one of the principal instruments on the USMP was the Advanced Automated Directional Solidification Furnace (AADSF). The AADSF is a multizone directional solidification furnace, and at the time of the USMP-3 flight was capable of processing only one sample per Shuttle mission which, for that flight, was a lead tin telluride (PbSnTe) crystal growth experiment. In the one year since the flight experiment the sample has been retrieved from the spacecraft and analysis has begun. After presenting introductory material on why PbSnTe was chosen as a test material, why microgravity processing was expected to produce desired results, and what we expected to find in conducting these tests, this report discusses the results to date which are far from complete.

Closed solutions to a differential-difference equation and an associated plate solidification problem.

PubMed

Layeni, Olawanle P; Akinola, Adegbola P; Johnson, Jesse V

2016-01-01

Two distinct and novel formalisms for deriving exact closed solutions of a class of variable-coefficient differential-difference equations arising from a plate solidification problem are introduced. Thereupon, exact closed traveling wave and similarity solutions to the plate solidification problem are obtained for some special cases of time-varying plate surface temperature.

Nature of solidification of nanoconfined organic liquid layers.

PubMed

Lang, X Y; Zhu, Y F; Jiang, Q

2007-01-30

A simple model is established for solidification of a nanoconfined liquid under nonequilibrium conditions. In terms of this model, the nature of solidification is the conjunct finite size and interface effects, which is directly related to the cooling rate or the relaxation time of the undercooled liquid. The model predictions are consistent with available experimental results.

The Effect of Bi Contamination on the Solidification Behavior of Sn-Pb Solders

NASA Astrophysics Data System (ADS)

Moon, Kil-Won; Kattner, Ursula R.; Handwerker, Carol A.

2007-06-01

This paper presents experimental results and theoretical calculations that evaluate the effects of Bi contamination on the solidification behavior of Sn-Pb alloys. The pasty (mushy) range, the type of solidification path, and the microstructure of the solidified alloys are described. The experimental results are obtained from thermal analysis and metallography, and the solidification calculations are performed using the lever rule and Scheil assumptions. The experimental results show that the solidification behavior of the contaminated solder at cooling rates of 5°C/min and 23°C/min is closer to the predictions of the lever rule calculations than those of the Scheil calculations. Although the freezing range of Bi-contaminated Sn-Pb solders is increased, formation of a ternary eutectic reaction at 95°C is not observed for contamination levels below the Bi mass fraction of 6%.

Kinetic Phase Diagrams of Ternary Al-Cu-Li System during Rapid Solidification: A Phase-Field Study

PubMed Central

Yang, Xiong; Zhang, Lijun; Sobolev, Sergey; Du, Yong

2018-01-01

Kinetic phase diagrams in technical alloys at different solidification velocities during rapid solidification are of great importance for guiding the novel alloy preparation, but are usually absent due to extreme difficulty in performing experimental measurements. In this paper, a phase-field model with finite interface dissipation was employed to construct kinetic phase diagrams in the ternary Al-Cu-Li system for the first time. The time-elimination relaxation scheme was utilized. The solute trapping phenomenon during rapid solidification could be nicely described by the phase-field simulation, and the results obtained from the experiment measurement and/or the theoretical model were also well reproduced. Based on the predicted kinetic phase diagrams, it was found that with the increase of interface moving velocity and/or temperature, the gap between the liquidus and solidus gradually reduces, which illustrates the effect of solute trapping and tendency of diffusionless solidification. PMID:29419753

Five-dimensional imaging of freezing emulsions with solute effects.

PubMed

Dedovets, Dmytro; Monteux, Cécile; Deville, Sylvain

2018-04-20

The interaction of objects with a moving solidification front is a common feature of many industrial and natural processes such as metal processing, the growth of single crystals, the cryopreservation of cells, or the formation of sea ice. Interaction of solidification fronts with objects leads to different outcomes, from total rejection of the objects to their complete engulfment. We imaged the freezing of emulsions in five dimensions (space, time, and solute concentration) with confocal microscopy. We showed that the solute induces long-range interactions that determine the solidification microstructure. The local increase of solute concentration enhances premelting, which controls the engulfment of droplets by the front and the evolution of grain boundaries. Freezing emulsions may be a good analog of many solidification systems where objects interact with a solidification interface. Copyright © 2018 The Authors, some rights reserved; exclusive licensee American Association for the Advancement of Science. No claim to original U.S. Government Works.

Traveling Magnetic Field Applications for Materials Processing in Space

NASA Technical Reports Server (NTRS)

Motakef, S.; Grugel, R. N.; Mazuruk, K.; Whitaker, Ann F. (Technical Monitor)

2001-01-01

Including the capability to induce a controlled fluid flow in the melt can significantly enrich research on solidification phenomena in a microgravity environment. The traveling magnetic field (TMF) is a promising technique to achieve this goal and is the aim of our ground-based project. In this presentation we will discuss new theoretical as well as experimental results recently obtained by our group. In particular, we experimentally demonstrated efficient mixing of metal alloys in long tubes subjected to TMF during processing. Application of this technique can be an elegant solution to ensure melt homogenization prior to solidification in a microgravity environment where natural convection is generally absent. Results of our theoretical work on TMF induced flows, such as convection control in Bridgman as well as in the Traveling Heater method, will be presented. Possible applications of TMF on board the ISS will also be discussed.

Trends in Solidification Grain Size and Morphology for Additive Manufacturing of Ti-6Al-4V

NASA Astrophysics Data System (ADS)

Gockel, Joy; Sheridan, Luke; Narra, Sneha P.; Klingbeil, Nathan W.; Beuth, Jack

2017-12-01

Metal additive manufacturing (AM) is used for both prototyping and production of final parts. Therefore, there is a need to predict and control the microstructural size and morphology. Process mapping is an approach that represents AM process outcomes in terms of input variables. In this work, analytical, numerical, and experimental approaches are combined to provide a holistic view of trends in the solidification grain structure of Ti-6Al-4V across a wide range of AM process input variables. The thermal gradient is shown to vary significantly through the depth of the melt pool, which precludes development of fully equiaxed microstructure throughout the depth of the deposit within any practical range of AM process variables. A strategy for grain size control is demonstrated based on the relationship between melt pool size and grain size across multiple deposit geometries, and additional factors affecting grain size are discussed.

Hot cracking during welding and casting

NASA Astrophysics Data System (ADS)

Cao, Guoping

Aluminum welds are susceptible to liquation cracking in the partially melted zone (PMZ). Using the multicomponent Scheil model, curves of temperature vs. fraction solid (T-fS) during solidification were calculated for the PMZ and weld metals (WMs). These curves were used to predict the crack susceptibility by checking if the harmful condition of WM fS > PMZ fS exists during PMZ solidification and reduce the susceptibility by minimizing this condition. This approach was tested against full-penetration welds of alloys 7075 and 2024 and it can be used to guide the selection or development of filler metals. Liquation cracking in the PMZ in welds of Al-Si cast alloys was also investigated. The crack susceptibility was evaluated by circular-patch test, and full-penetration welds made with filler metals 1100, 4043, 4047 and 5356. Liquation cracking was significant with filler metals 1100 and 5356 but slight with filler metals 4043 and 4047. In all welds, liquation cracks were completely backfilled, instead of open as in full-penetration welds of wrought alloys 2219 and 6061. The T-fS curves showed that alloy A357 has a much higher fraction liquid for backfilling before PMZ solidification was essentially over. Hot tearing in Mg-xAl-yCa alloys was studied by constrained rod casting (CRC) in a steel mold. The hot tearing susceptibility decreased significantly with increasing Ca content (y) but did not change much with the Al content (x). An instrumented CRC with a steel mold was developed to detect the onset of hot tearing. The secondary phases, eutectic content, solidification path, and freezing range were examined. Hot tearing in Mg-Al-Sr alloys was also studied by CRC in a steel mold. With Mg-(4,6,8)Al-1.5Sr alloys, the hot tearing susceptibility decreased significantly with increasing Al content. With Mg-(4,6,8)Al-3Sr alloys, the trend was similar but not as significant. At the same Al content, the hot tearing susceptibility decreased significantly with increasing Sr content. Instrumented CRC with a steel mold was also used to test hot tearing of Mg-Al-Sr alloys. Cracking occurred at a higher temperature in alloys most susceptible to cracking than in alloys least susceptible.

Numerical modeling of HgCdTe solidification: Effects of phase diagram, double-diffusion convection and microgravity level

NASA Technical Reports Server (NTRS)

Bune, Andris V.; Gillies, Donald C.; Lehozky, Sandor L.

1997-01-01

A numerical model of HgCdTe solidification was implemented using finite the element code FIDAP. Model verification was done using both experimental data and numerical test problems. The model was used to evaluate possible effects of double-diffusion convection in molten material, and microgravity level on concentration distribution in the solidified HgCdTe. Particular attention was paid to incorporation of HgCdTe phase diagram. It was found, that below a critical microgravity amplitude, the maximum convective velocity in the melt appears virtually independent on the microgravity vector orientation. Good agreement between predicted interface shape and an interface obtained experimentally by quenching was achieved. The results of numerical modeling are presented in the form of video film.

Microgravity

NASA Image and Video Library

1992-03-12

The Advanced Automated Directional Solidification Furnace (AADSF) with the Experimental Apparatus Container (EAC) removed flew during the USMP-2 mission. During USMP-2, the AADSF was used to study the growth of mercury cadmium telluride crystals in microgravity by directional solidification, a process commonly used on earth to process metals and grow crystals. The furnace is tubular and has three independently controlled temperature zones . The sample travels from the hot zone of the furnace (1600 degrees F) where the material solidifies as it cools. The solidification region, known as the solid/liquid interface, moves from one end of the sample to the other at a controlled rate, thus the term directional solidification.

Direct chill casting of aluminium alloys under electromagnetic interaction by permanent magnet assembly

NASA Astrophysics Data System (ADS)

Bojarevičs, Andris; Kaldre, Imants; Milgrāvis, Mikus; Beinerts, Toms

2018-05-01

Direct chill casting is one of the methods used in industry to obtain good microstructure and properties of aluminium alloys. Nevertheless, for some alloys grain structure is not optimal. In this study, we offer the use of electromagnetic interaction to modify melt convection near the solidification interface. Solidification under various electromagnetic interactions has been widely studied, but usually at low solidification velocity and high thermal gradient. This type of interaction may succeed fragmentation of dendrite arms and transport of solidification nuclei thus leading to improved material structure and properties. Realization of experimental small-scale crystallizer and electromagnetic system has been described in this article.

Enthalpies of a binary alloy during solidification

NASA Technical Reports Server (NTRS)

Poirier, D. R.; Nandapurkar, P.

1988-01-01

The purpose of the paper is to present a method of calculating the enthalpy of a dendritic alloy during solidification. The enthalpies of the dendritic solid and interdendritic liquid of alloys of the Pb-Sn system are evaluated, but the method could be applied to other binaries, as well. The enthalpies are consistent with a recent evaluation of the thermodynamics of Pb-Sn alloys and with the redistribution of solute in the same during dendritic solidification. Because of the heat of mixing in Pb-Sn alloys, the interdendritic liquid of hypoeutectic alloys (Pb-rich) of less than 50 wt pct Sn has enthalpies that increase as temperature decreases during solidification.

A Remote Absorption Process for Disposal of Evaporate and Reverse Osmosis Concentrates

DOE Office of Scientific and Technical Information (OSTI.GOV)

Brunsell, D.A.

2008-07-01

Many commercial nuclear plants and DOE facilities generate secondary waste streams consisting of evaporator bottoms and reverse osmosis (RO) concentrate. Since liquids are not permitted in disposal facilities, these waste streams must be converted to dry solids, either by evaporation to dried solids or by solidification to liquid-free solids. Evaporation of the liquid wastes reduces their volume, but requires costly energy and capital equipment. In some cases, concentration of the contaminants during drying can cause the waste to exceed Class A waste for nuclear utilities or exceed DOE transuranic limits. This means that disposal costs will be increased, or that,more » when the Barnwell, SC disposal site closes to waste outside of the Atlantic Compact in July 2008, the waste will be precluded from disposal for the foreseeable future). Solidification with cement agents requires less energy and equipment than drying, but results in a volume increase of 50-100%. The doubling or tripling of waste weight, along with the increased volume, sharply increases shipping and disposal costs. Confronted with these unattractive alternatives, Diversified Technologies Services (DTS), in conjunction with selected nuclear utilities and D and D operations at Rocky Flats, undertook an exploratory effort to convert this liquid wastewater to a solid without using cement. This would avoid the bulking effect of cement, and permit the waste to be disposed of the Energy Solutions facility in Utah as well as some DOE facilities. To address the need for an attractive alternative to drying and cement solidification, a test program was developed using a polymer absorbent media to convert the concentrate streams to a liquid-free waste form that meets the waste acceptance criteria of the pertinent burial sites. Two approaches for mixing the polymer with the liquid were tested: mechanical mixing and in-situ incorporation. As part of this test program, a process control program (PCP) was developed that is 100% scalable from a concentrate test sample as small as 50 grams to full-scale processing of 100 cubic foot containers or larger. In summary: The absorption process offers utilities a viable and less costly alternative to on-site drying or solidification of concentrates. The absorption process can be completed by site personnel or by a vendor as a turnkey service. The process is suitable for multiple types of waste, including RO and evaporator concentrates, sludges, and other difficult to process waters and wet solids. (author)« less

MPS solidification model. Analysis and calculation of macrosegregation in a casting ingot

NASA Technical Reports Server (NTRS)

Poirier, D. R.; Maples, A. L.

1985-01-01

Work performed on several existing solidification models for which computer codes and documentation were developed is presented. The models describe the solidification of alloys in which there is a time varying zone of coexisting solid and liquid phases; i.e., the S/L zone. The primary purpose of the models is to calculate macrosegregation in a casting or ingot which results from flow of interdendritic liquid in this S/L zone during solidification. The flow, driven by solidification contractions and by gravity acting on density gradients in the interdendritic liquid, is modeled as flow through a porous medium. In Model 1, the steady state model, the heat flow characteristics are those of steady state solidification; i.e., the S/L zone is of constant width and it moves at a constant velocity relative to the mold. In Model 2, the unsteady state model, the width and rate of movement of the S/L zone are allowed to vary with time as it moves through the ingot. Each of these models exists in two versions. Models 1 and 2 are applicable to binary alloys; models 1M and 2M are applicable to multicomponent alloys.

Effects of N/C Ratio on Solidification Behaviors of Novel Nb-Bearing Austenitic Heat-Resistant Cast Steels for Exhaust Components of Gasoline Engines

NASA Astrophysics Data System (ADS)

Zhang, Yinhui; Li, Mei; Godlewski, Larry A.; Zindel, Jacob W.; Feng, Qiang

2017-03-01

In order to comply with more stringent environmental and fuel consumption regulations, novel Nb-bearing austenitic heat-resistant cast steels that withstand exhaust temperatures as high as 1,323 K (1,050 °C) is urgently demanded from automotive industries. In the current research, the solidification behavior of these alloys with variations of N/C ratio is investigated. Directional solidification methods were carried out to examine the microstructural development in mushy zones. Computational thermodynamic calculations under partial equilibrium conditions were performed to predict the solidification sequence of different phases. Microstructural characterization of the mushy zones indicates that N/C ratio significantly influenced the stability of γ-austenite and the precipitation temperature of NbC/Nb(C,N), thereby altering the solidification path, as well as the morphology and distribution of NbC/Nb(C,N) and γ-ferrite. The solidification sequence of different phases predicted by thermodynamic software agreed well with the experimental results, except the specific precipitation temperatures. The generated data and fundamental understanding will be helpful for the application of computational thermodynamic methods to predict the as-cast microstructure of Nb-bearing austenitic heat-resistant steels.

Analysis and calculation of macrosegregation in a casting ingot. MPS solidification model. Volume 1: Formulation and analysis

NASA Technical Reports Server (NTRS)

Maples, A. L.; Poirier, D. R.

1980-01-01

The physical and numerical formulation of a model for the horizontal solidification of a binary alloy is described. It can be applied in an ingot. The major purpose of the model is to calculate macrosegregation in a casting ingot which results from flow of interdendritic liquid during solidification. The flow, driven by solidification contractions and by gravity acting on density gradients in the interdendritic liquid, was modeled as flow through a porous medium. The symbols used are defined. The physical formulation of the problem leading to a set of equations which can be used to obtain: (1) the pressure field; (2) the velocity field: (3) mass flow and (4) solute flow in the solid plus liquid zone during solidification is presented. With these established, the model calculates macrosegregation after solidification is complete. The numerical techniques used to obtain solution on a computational grid are presented. Results, evaluation of the results, and recommendations for future development of the model are given. The macrosegregation and flow field predictions for tin-lead, aluminum-copper, and tin-bismuth alloys are included as well as comparisons of some of the predictions with published predictions or with empirical data.

High temperature composites. Status and future directions

NASA Technical Reports Server (NTRS)

Signorelli, R. A.

1982-01-01

A summary of research investigations of manufacturing methods, fabrication methods, and testing of high temperature composites for use in gas turbine engines is presented. Ceramic/ceramic, ceramic/metal, and metal/metal composites are considered. Directional solidification of superalloys and eutectic alloys, fiber reinforced metal and ceramic composites, ceramic fibers and whiskers, refractory coatings, metal fiber/metal composites, matrix metal selection, and the preparation of test specimens are discussed.

Characterization and calibration of a viscoelastic simplified potential energy clock model for inorganic glasses

DOE PAGES

Chambers, Robert S.; Tandon, Rajan; Stavig, Mark E.

2015-07-07

In this study, to analyze the stresses and strains generated during the solidification of glass-forming materials, stress and volume relaxation must be predicted accurately. Although the modeling attributes required to depict physical aging in organic glassy thermosets strongly resemble the structural relaxation in inorganic glasses, the historical modeling approaches have been distinctly different. To determine whether a common constitutive framework can be applied to both classes of materials, the nonlinear viscoelastic simplified potential energy clock (SPEC) model, developed originally for glassy thermosets, was calibrated for the Schott 8061 inorganic glass and used to analyze a number of tests. A practicalmore » methodology for material characterization and model calibration is discussed, and the structural relaxation mechanism is interpreted in the context of SPEC model constitutive equations. SPEC predictions compared to inorganic glass data collected from thermal strain measurements and creep tests demonstrate the ability to achieve engineering accuracy and make the SPEC model feasible for engineering applications involving a much broader class of glassy materials.« less

75 FR 20582 - Record of Decision: Final Environmental Impact Statement for Decommissioning and/or Long-Term...

Federal Register 2010, 2011, 2012, 2013, 2014

2010-04-20

... storage tanks and facilities used in the solidification of high-level radioactive waste, and any material... Act (Pub. L. 96-368, 42 U.S.C. 2021a). The WVDP Act requires DOE to demonstrate that the liquid high... take the following actions: 1. Solidify high-level radioactive waste by vitrification or such other...

Application of Solidification Theory to Rapid Solidification Processing

DTIC Science & Technology

1982-09-01

period were achieved in the following areas : Extended Solid Solubilities -- for Produetion of Alloys with New Compositions and Phases o At high growth... Areas where significant improvements In alloy properties can be produced by rapid solidification will be emphasized. Technical Problem and General...focussed on the science underlying areas where Improved materials can be obtained in order to provide such prediction and control. This work is both

Solidification of basaltic magma during flow in a dike.

USGS Publications Warehouse

Delaney, P.T.; Pollard, D.D.

1982-01-01

A model for time-dependent unsteady heat transfer from magma flowing in a dyke is developed. The ratio of solidification T to magma T is the most important parameter. Observations of volcanic fissure eruptions and study of dykes near Ship Rock, New Mexico, show that the low T at dyke margins and the rapidly advancing solidification front predicted by the model are qualitatively correct.-M.S.

Direct observation of spatially isothermal equiaxed solidification of an Al-Cu alloy in microgravity on board the MASER 13 sounding rocket

NASA Astrophysics Data System (ADS)

Murphy, A. G.; Mathiesen, R. H.; Houltz, Y.; Li, J.; Lockowandt, C.; Henriksson, K.; Melville, N.; Browne, D. J.

2016-11-01

For the first time, isothermal equiaxed solidification of a metallic alloy has been observed in situ in space, providing unique benchmark experimental data. The experiment was completed on board the MASER 13 sounding rocket, launched in December 2015, using a newly developed isothermal solidification furnace. A grain-refined Al-20 wt%Cu sample was fully melted and solidified during 360 s of microgravity and the solidification sequence was recorded using time-resolved X-radiography. Equiaxed nucleation, dendritic growth, solutal impingement, and eutectic transformation were thus observed in a gravity-free environment. Equiaxed nucleation was promoted through application of a controlled cooling rate of -0.05 K/s producing a 1D grain density of 6.5 mm-1, uniformly distributed throughout the field of view (FOV). Primary growth slowed to a visually imperceptible level at an estimated undercooling of 7 K, after which the cooling rate was increased to -1.0 K/s for the remainder of solidification and eutectic transformation, ensuring the sample was fully solidified inside the microgravity time window. The eutectic transformation commenced at the centre of the FOV proceeding radially outwards covering the entire FOV in 3 s Microgravity-based solidification is compared to an identical pre-flight ground-based experiment using the same sample and experiment timeline. The ground experiment was designed to minimise gravity effects, by choice of a horizontal orientation for the sample, so that any differences would be subtle. The first equiaxed nucleation occurred at an apparent undercooling of 0.6 K less than the equivalent event during microgravity. During primary equiaxed solidification, as expected, no buoyant grain motion was observed during microgravity, compared to modest grain rotation and reorientation observed during terrestrial-based solidification. However, when the cooling rate was increased from -0.05 K/s to -1.0 K/s during the latter stages of solidification, in both 1g and micro-g environments, some grain movement was apparent due to liquid feeding and mechanical impingement of neighbouring grains.

Use of Microgravity to Control the Microstructure of Eutectics

NASA Technical Reports Server (NTRS)

Wilcox, William R.; Regel, Liya L.; Smith, Reginald W.

1998-01-01

This grant began in June of 1996. Its long term goal is to be able to control the microstructure of directionally solidified eutectic alloys, through an improved understanding of the influence of convection. The primary objective of the present projects is to test hypotheses for the reported influence of microgravity on the microstructure of three fibrous eutectics (MnBi-Bi, InSb-NiSb, Al3Ni-Al). A secondary objective is to determine the influence of convection on the microstructure of other eutectic alloys. Two doctoral students and a masters student supported as a teaching assistant were recruited for this research. Techniques were developed for directional solidification of MnBi-Bi eutectics with periodic application of current pulses to produce an oscillatory freezing rate. Image analysis techniques were developed to obtain the variation in MnBi fiber spacing, which was found to be normally distributed. The mean and standard deviation of fiber spacing were obtained for several freezing conditions. Eighteen ampoules were prepared for use in the gradient freeze furnace QUELD developed at Queen's University for use in microgravity. Nine of these ampoules will be solidified soon at Queen's in a ground-based model. We hope to solidify the other nine in the QUELD that is mounted on the Canadian Microgravity Isolation Mount on MIR. Techniques are being developed for directional solidification of the Al-Si eutectic at different freezing rates, with and without application of accelerated crucible rotation to induce convection. For the first time, theoretical methods are being developed to analyze eutectic solidification with an oscillatory freezing rate. In a classical sharp-interface model, we found that an oscillatory freezing rate increases the deviation of the average interfacial composition from the eutectic, and increases the undercooling of the two phases by different amounts. This would be expected to change the volume fraction solidifying and the fiber spacing. Because of difficulties in tracking the freezing interfaces of the two solid phases, a phase-field model is also being developed. A paper demonstrating application of phase field methods to periodic structures has been submitted for publication.

Microgravity

NASA Image and Video Library

1998-12-01

Test engineers, TK Pedergrass and Dave McIntosh, are growing multiple dendrites in an undercooled melt of ultra pure succinonitrile (SCN). Images and temperature measurements will give Dr. Christoph Beckerman, the EDSE Principal Investigator, information on the microstructural evolution of and thermal interactions between several equiaxed crystals growing dendritically. This benchmark data will be used to test and develop equiaxed dendritic solidification models. The monitors show both the 4 stinger and 2 stinger chambers that are placed in the isothermal bath for testing.

Steady-state and dynamic models for particle engulfment during solidification

NASA Astrophysics Data System (ADS)

Tao, Yutao; Yeckel, Andrew; Derby, Jeffrey J.

2016-06-01

Steady-state and dynamic models are developed to study the physical mechanisms that determine the pushing or engulfment of a solid particle at a moving solid-liquid interface. The mathematical model formulation rigorously accounts for energy and momentum conservation, while faithfully representing the interfacial phenomena affecting solidification phase change and particle motion. A numerical solution approach is developed using the Galerkin finite element method and elliptic mesh generation in an arbitrary Lagrangian-Eulerian implementation, thus allowing for a rigorous representation of forces and dynamics previously inaccessible by approaches using analytical approximations. We demonstrate that this model accurately computes the solidification interface shape while simultaneously resolving thin fluid layers around the particle that arise from premelting during particle engulfment. We reinterpret the significance of premelting via the definition an unambiguous critical velocity for engulfment from steady-state analysis and bifurcation theory. We also explore the complicated transient behaviors that underlie the steady states of this system and posit the significance of dynamical behavior on engulfment events for many systems. We critically examine the onset of engulfment by comparing our computational predictions to those obtained using the analytical model of Rempel and Worster [29]. We assert that, while the accurate calculation of van der Waals repulsive forces remains an open issue, the computational model developed here provides a clear benefit over prior models for computing particle drag forces and other phenomena needed for the faithful simulation of particle engulfment.

Formation mechanism of axial macrosegregation of primary phases induced by a static magnetic field during directional solidification

PubMed Central

Li, Xi; Fautrelle, Yves; Ren, Zhongming; Moreau, Rene

2017-01-01

Understanding the macrosegregation formed by applying magnetic fields is of high commercial importance. This work investigates how static magnetic fields control the solute and primary phase distributions in four directionally solidified alloys (i.e., Al-Cu, Al-Si, Al-Ni and Zn-Cu alloys). Experimental results demonstrate that significant axial macrosegregation of the solute and primary phases (i.e., Al2Cu, Si, Al3Ni and Zn5Cu phases) occurs at the initial solidification stage of the samples. This finding is accompanied by two interface transitions in the mushy zone: quasi planar → sloping → quasi planar. The amplitude of the macrosegregation of the primary phases under the magnetic field is related to the magnetic field intensity, temperature gradient and growth speed. The corresponding numerical simulations present a unidirectional thermoelectric (TE) magnetic convection pattern in the mushy zone as a consequence of the interaction between the magnetic field and TE current. Furthermore, a model is proposed to explain the peculiar macrosegregation phenomenon by considering the effect of the forced TE magnetic convection on the solute distribution. The present study not only offers a new approach to control the solute distribution by applying a static magnetic field but also facilitates the understanding of crystal growth in the solute that is controlled by the static magnetic field during directional solidification. PMID:28367991

Modeling diffusion-governed solidification of ternary alloys - Part 2: Macroscopic transport phenomena and macrosegregation.

PubMed

Wu, M; Li, J; Ludwig, A; Kharicha, A

2014-09-01

Part 1 of this two-part investigation presented a multiphase solidification model incorporating the finite diffusion kinetics and ternary phase diagram with the macroscopic transport phenomena (Wu et al., 2013). In Part 2, the importance of proper treatment of the finite diffusion kinetics in the calculation of macrosegregation is addressed. Calculations for a two-dimensional (2D) square casting (50 × 50 mm 2 ) of Fe-0.45 wt.%C-1.06 wt.%Mn considering thermo-solutal convection and crystal sedimentation are performed. The modeling result indicates that the infinite liquid mixing kinetics as assumed by classical models (e.g., the Gulliver-Scheil or lever rule), which cannot properly consider the solute enrichment of the interdendritic or inter-granular melt at the early stage of solidification, might lead to an erroneous estimation of the macrosegregation. To confirm this statement, further theoretical and experimental evaluations are desired. The pattern and intensity of the flow and crystal sedimentation are dependent on the crystal morphologies (columnar or equiaxed); hence, the potential error of the calculated macrosegregation caused by the assumed growth kinetics depends on the crystal morphology. Finally, an illustrative simulation of an engineering 2.45-ton steel ingot is performed, and the results are compared with experimental results. This example demonstrates the model applicability for engineering castings regarding both the calculation efficiency and functionality.

Increased corrosion resistance of the AZ80 magnesium alloy by rapid solidification.

PubMed

Aghion, E; Jan, L; Meshi, L; Goldman, J

2015-11-01

Magnesium (Mg) and Mg-alloys are being considered as implantable biometals. Despite their excellent biocompatibility and good mechanical properties, their rapid corrosion is a major impediment precluding their widespread acceptance as implantable biomaterials. Here, we investigate the potential for rapid solidification to increase the corrosion resistance of Mg alloys. To this end, the effect of rapid solidification on the environmental and stress corrosion behavior of the AZ80 Mg alloy vs. its conventionally cast counterpart was evaluated in simulated physiological electrolytes. The microstructural characteristics were examined by optical microscopy, SEM, TEM, and X-ray diffraction analysis. The corrosion behavior was evaluated by immersion, salt spraying, and potentiodynamic polarization. Stress corrosion resistance was assessed by Slow Strain Rate Testing. The results indicate that the corrosion resistance of rapidly solidified ribbons is significantly improved relative to the conventional cast alloy due to the increased Al content dissolved in the α-Mg matrix and the correspondingly reduced presence of the β-phase (Mg17 Al12 ). Unfortunately, extrusion consolidated solidified ribbons exhibited a substantial reduction in the environmental performance and stress corrosion resistance. This was mainly attributed to the detrimental effect of the extrusion process, which enriched the iron impurities and increased the internal stresses by imposing a higher dislocation density. In terms of immersion tests, the average corrosion rate of the rapidly solidified ribbons was <0.4 mm/year compared with ∼2 mm/year for the conventionally cast alloy and 26 mm/year for the rapidly solidified extruded ribbons. © 2014 Wiley Periodicals, Inc.

Improved Crystal Quality by Detached Solidification in Microgravity

NASA Technical Reports Server (NTRS)

Regel, Liya L.; Wilcox, William R.

1999-01-01

Directional solidification in microgravity has often led to ingots that grew with little or no contact with the ampoule wall. When this occurred, crystallographic perfection was usually greatly improved -- often by several orders of magnitude. Unfortunately, until recently the true mechanisms underlying detached solidification were unknown. As a consequence, flight experiments yielded erratic results. Within the past four years, we have developed a new theoretical model that explains many of the flight results. This model gives rise to predictions of the conditions required to yield detached solidification, both in microgravity and on earth. A discussion of models of detachment, the meniscus models and results of theoretical modeling, and future plans are presented.

Modelling directional solidification

NASA Technical Reports Server (NTRS)

Wilcox, William R.

1987-01-01

An improved understanding of the phenomena of importance to directional solidification is attempted to enable explanation and prediction of differences in behavior between solidification on Earth and in space. Emphasis is now on experimentally determining the influence of convection and freezing rate fluctuations on compositional homogeneity and crystalline perfection. A correlation is sought between heater temperature profiles, buoyancy-driven convection, and doping inhomogeneities using naphthalene doped with anthracene. The influence of spin-up/spin-down is determined on compositional homogeneity and microstructure of indium gallium antimonide. The effect is determined of imposed melting - freezing cycles on indium gallium antimonide. The mechanism behind the increase of grain size caused by using spin-up/spin-down in directional solidification of mercury cadimum telluride is sought.

Cooling and solidification of liquid-metal drops in a gaseous atmosphere

NASA Technical Reports Server (NTRS)

Mccoy, J. K.; Markworth, A. J.; Collings, E. W.; Brodkey, R. S.

1992-01-01

The free fall of a liquid-metal drop, heat transfer from the drop to its environment, and solidification of the drop are described for both gaseous and vacuum atmospheres. A simple model, in which the drop is assumed to fall rectilinearly, with behavior like that of a rigid particle, is developed to describe cooling behavior. Recalescence of supercooled drops is assumed to occur instantaneously when a specified temperature is passed. The effects of solidification and experimental parameters on drop cooling are calculated and discussed. Major results include temperature as a function of time, and of drag, time to complete solidification, and drag as a function of the fraction of the drop solidified.

Inverse Thermal Analysis of Alloy 690 Laser and Hybrid Laser-GMA Welds Using Solidification-Boundary Constraints

NASA Astrophysics Data System (ADS)

Lambrakos, S. G.

2017-08-01

An inverse thermal analysis of Alloy 690 laser and hybrid laser-GMA welds is presented that uses numerical-analytical basis functions and boundary constraints based on measured solidification cross sections. In particular, the inverse analysis procedure uses three-dimensional constraint conditions such that two-dimensional projections of calculated solidification boundaries are constrained to map within experimentally measured solidification cross sections. Temperature histories calculated by this analysis are input data for computational procedures that predict solid-state phase transformations and mechanical response. These temperature histories can be used for inverse thermal analysis of welds corresponding to other welding processes whose process conditions are within similar regimes.

Anomalous eutectic formation in the solidification of undercooled Co-Sn alloys

NASA Astrophysics Data System (ADS)

Liu, L.; Wei, X. X.; Huang, Q. S.; Li, J. F.; Cheng, X. H.; Zhou, Y. H.

2012-11-01

Three Co-Sn alloys with compositions around the eutectic point were undercooled to different degrees below the equilibrium liquidus temperature and the solidification behaviors were investigated by monitoring the temperature recalescence and examing the solidification structure. It is revealed that the primary phase during rapid solidification changes complexly with the increasing undercooling in the off-eutectic alloys, while coupled eutectic growth takes place at all undercoolings in the eutectic alloy. Two types of anomalous eutectics form in the alloys: one evolving from coupled eutectics and the other from single phase dendrites or seaweeds. The crystallographic orientation of eutectic phases in the anomalous eutectic is dependent on which type their precursors belong to.

Partially melted zone in aluminum welds

NASA Astrophysics Data System (ADS)

Huang, Chen-Che

The partially melted zone (PMZ) is a region immediately outside the weld metal where grain boundary (GB) liquation can occur and cause intergranular cracking. Aluminum alloys are known to be susceptible to liquation and liquation cracking. The PMZ of alloy 2219 (essentially Al-6.3Cu) was studied. Liquation is initiated eutectically. Solidification of the GB liquid was directional---upward and toward the weld as a result of the temperature gradients across the PMZ. The liquated material solidifies with severe segregation into a low-strength, low-ductility structure consisting of a solute-depleted ductile phase and a solute-rich brittle eutectic. In tensile testing the maximum load and displacement before failure were both far below those of the base metal. The GB eutectic fractured while the adjacent Cu-depleted a deformed readily under tension. The solidification mode of the grain boundary liquid was mostly planar. However, cellular solidification was also observed near the bottom of partial-penetration welds, where temperature gradients were lowest. The liquation mechanisms in wrought multicomponent aluminum alloys during welding were also studied. Three mechanisms were identified. They cover most, if not all, wrought aluminum alloys. Liquation cracking in the PMZ was investigated in full-penetration aluminum welds. Liquation cracking occurs because the solidifying PMZ is pulled by a solidifying and thus contracting weld metal that is stronger than the PMZ. Liquation cracking can occur if there is significant liquation in the PMZ, if there is no solidification cracking in the adjacent weld metal, and if the PMZ becomes lower in solid fraction (and hence strength) during its terminal solidification than the solidifying weld metal. Liquation cracking in the PMZ was also investigated in partial-penetration aluminum welds. The papillary (nipple) type penetration common in welding with spray transfer of the filler wire actually oscillates along the weld and promotes cracking regardless of the filler metal used. The fast-solidifying weld metal immediately behind the penetration tip contracts and pulls the PMZ near the tip and, regardless of the weld-metal composition, cracking can occur if PMZ liquation is significant.

Reduction of Leaching Impacts by Applying Biomass Bottom Ash and Recycled Mixed Aggregates in Structural Layers of Roads

PubMed Central

Cabrera, Manuel; Galvin, Adela P.; Agrela, Francisco; Beltran, Manuel G.; Ayuso, Jesus

2016-01-01

This research is focused on analyzing the environmental pollution potential of biomass bottom ashes as individual materials, as mixtures manufactured with biomass bottom ashes and granular construction aggregates, and these mixtures treated with cement. For the environmental assessment of all of the samples and materials mentioned, the following leaching procedures have been performed: the compliance batch test of UNE-EN 12457-3:2003 for aggregates and bottom ashes; the column test according to NEN 7343:1994 for the mixtures prepared in the laboratory; and the tank test by EA NEN 7375:2004 for analyzing the behavior of mixtures after their solidification/stabilization with 5% cement. After the discussion of the data, the reduction of the pollution load of the most hazardous biomass bottom ashes after their combination with different aggregates can be confirmed, which implies their possible application in civil infrastructures, such as filler embankments and road construction layers, without negatively impacting the environment. In addition, the positive effect of the stabilization/solidification of the cement-treated mixtures with a reduction of the heavy metals that were released at the highest levels, namely As, Hg Cr, Ni, Cu, Se and Mo, was proven. PMID:28773352

Progress in modeling solidification in molten salt coolants

NASA Astrophysics Data System (ADS)

Tano, Mauricio; Rubiolo, Pablo; Doche, Olivier

2017-10-01

Molten salts have been proposed as heat carrier media in the nuclear and concentrating solar power plants. Due to their high melting temperature, solidification of the salts is expected to occur during routine and accidental scenarios. Furthermore, passive safety systems based on the solidification of these salts are being studied. The following article presents new developments in the modeling of eutectic molten salts by means of a multiphase, multicomponent, phase-field model. Besides, an application of this methodology for the eutectic solidification process of the ternary system LiF-KF-NaF is presented. The model predictions are compared with a newly developed semi-analytical solution for directional eutectic solidification at stable growth rate. A good qualitative agreement is obtained between the two approaches. The results obtained with the phase-field model are then used for calculating the homogenized properties of the solid phase distribution. These properties can then be included in a mixture macroscale model, more suitable for industrial applications.

X-Ray Radiographic Observation of Directional Solidification Under Microgravity: XRMON-GF Experiments on MASER12 Sounding Rocket Mission

NASA Technical Reports Server (NTRS)

Reinhart, G.; NguyenThi, H.; Bogno, A.; Billia, B.; Houltz, Y.; Loth, K.; Voss, D.; Verga, A.; dePascale, F.; Mathiesen, R. H.;

Effect of process parameters on hardness, temperature profile and solidification of different layers processed by direct metal laser sintering (DMLS)

NASA Astrophysics Data System (ADS)

Ahmed, Sazzad Hossain; Mian, Ahsan; Srinivasan, Raghavan

2016-07-01

In DMLS process objects are fabricated layer by layer from powdered material by melting induced by a controlled laser beam. Metallic powder melts and solidifies to form a single layer. Solidification map during layer formation is an important route to characterize micro-structure and grain morphology of sintered layer. Generally, solidification leads to columnar, equiaxed or mixture of these two types grain morphology depending on solidification rate and thermal gradient. Eutectic or dendritic structure can be formed in fully equiaxed zone. This dendritic growth has a large effect on material properties. Smaller dendrites generally increase ductility of the layer. Thus, materials can be designed by creating desired grain morphology in certain regions using DMLS process. To accomplish this, hardness, temperature distribution, thermal gradient and solidification cooling rate in processed layers will be studied under change of process variables by using finite element analysis, with specific application to Ti-6Al-4V.

Time-Resolved In Situ Measurements During Rapid Alloy Solidification: Experimental Insight for Additive Manufacturing

NASA Astrophysics Data System (ADS)

McKeown, Joseph T.; Zweiacker, Kai; Liu, Can; Coughlin, Daniel R.; Clarke, Amy J.; Baldwin, J. Kevin; Gibbs, John W.; Roehling, John D.; Imhoff, Seth D.; Gibbs, Paul J.; Tourret, Damien; Wiezorek, Jörg M. K.; Campbell, Geoffrey H.

2016-03-01

Additive manufacturing (AM) of metals and alloys is becoming a pervasive technology in both research and industrial environments, though significant challenges remain before widespread implementation of AM can be realized. In situ investigations of rapid alloy solidification with high spatial and temporal resolutions can provide unique experimental insight into microstructure evolution and kinetics that are relevant for AM processing. Hypoeutectic thin-film Al-Cu and Al-Si alloys were investigated using dynamic transmission electron microscopy to monitor pulsed-laser-induced rapid solidification across microsecond timescales. Solid-liquid interface velocities measured from time-resolved images revealed accelerating solidification fronts in both alloys. The observed microstructure evolution, solidification product, and presence of a morphological instability at the solid-liquid interface in the Al-4 at.%Cu alloy are related to the measured interface velocities and small differences in composition that affect the thermophysical properties of the alloys. These time-resolved in situ measurements can inform and validate predictive modeling efforts for AM.

Time-Resolved In Situ Measurements During Rapid Alloy Solidification: Experimental Insight for Additive Manufacturing

DOE PAGES

McKeown, Joseph T.; Zweiacker, Kai; Liu, Can; ...

2016-01-27

In research and industrial environments, additive manufacturing (AM) of metals and alloys is becoming a pervasive technology, though significant challenges remain before widespread implementation of AM can be realized. In situ investigations of rapid alloy solidification with high spatial and temporal resolutions can provide unique experimental insight into microstructure evolution and kinetics that are relevant for AM processing. Hypoeutectic thin-film Al–Cu and Al–Si alloys were investigated using dynamic transmission electron microscopy to monitor pulsed-laser-induced rapid solidification across microsecond timescales. Solid–liquid interface velocities measured from time-resolved images revealed accelerating solidification fronts in both alloys. We observed microstructure evolution, solidification product, andmore » presence of a morphological instability at the solid–liquid interface in the Al–4 at.%Cu alloy are related to the measured interface velocities and small differences in composition that affect the thermophysical properties of the alloys. These time-resolved in situ measurements can inform and validate predictive modeling efforts for AM.« less

Macrosegregation and Grain Formation Caused by Convection Associated with Directional Solidification Through Cross-Section Increase

NASA Technical Reports Server (NTRS)

Ghods, Masoud; Lauer, Mark; Tewari, Surendra; Poirier, David; Grugel, Richard

2016-01-01

Cylindrical Al-7 wt% Silicon, Al-19 wt% Copper and Lead-6 wt% Antimony alloy samples were directionally solidified (DS) with liquid above, solid below, and gravity pointing down, in graphite crucibles having an abrupt cross-sectional increase. These alloys have similar solidification shrinkage but are expected to have different degrees of thermosolutal convection during solidification. Microstructures in the DS samples in the vicinity of the section change have been studied in order to examine the effect of convection associated with the combined influence of thermosolutal effects and solidification shrinkage. Extensive radial and axial macrosegregation associated with cross-section change is observed. It also appears that steepling and local primary alpha-phase remelting resulting from convection are responsible for stray grain formation at the reentrant corners. Preliminary results from a numerical model, which includes solidification shrinkage and thermosolutal convection in the mushy zone, indicate that these regions are prone to solutal remelting of dendrites.

Solid-liquid and liquid-solid transitions in metal nanoparticles.

PubMed

Hou, M

2017-02-22

The melting and solidification temperatures of nanosystems may differ by several hundred Kelvin. To understand the origin of this difference, transitions in small metallic nanoparticles on the atomic scale were analyzed using molecular dynamics (MD). Palladium was used as a case study, which was then extended to a range of other elemental metals. It was argued that in realistic environments, such as gases at low pressure (of the order of 1 mbar), heat transfers allow the microcanonical thermal equilibrium evolution of the nanoparticles between successive collisions with gas atoms. This is shown to have no significant influence on the mechanism of melting, whereas in an isolated nanoparticle, solidification triggers a huge and rapid increase in temperature. A simple relationship between the melting and solidification temperatures was found, indicating that the magnitude of the latent heat of melting governs undercooling. Whereas melting occurs via heterogeneous nucleation, solidification displays characteristics of spinodal decomposition. Consistently, the melting temperature scales with the surface-to-volume ratio, whereas the solidification temperature displays no significant dependence on the particle size.

Preliminary in situ and real-time study of directional solidification of metallic alloys by x-ray imaging techniques

NASA Astrophysics Data System (ADS)

Nguyen Thi, H.; Jamgotchian, H.; Gastaldi, J.; Härtwig, J.; Schenk, T.; Klein, H.; Billia, B.; Baruchel, J.; Dabo, Y.

2003-05-01

During directional solidification of a binary alloy, the solid-liquid interface exhibits a variety of patterns that are due to the Mullins-Sekerka instability and governed by the growth conditions. It is well known that properties of the grown material are largely controlled by the microstructures left in the solid during processing. Thus, a precise mastering of the solidification is essential to tailor products in a reproducible fashion to a specified quality. One major difficulty for this study is the real-time and in situ observation of the interface, especially for metallic alloys. A possibility is to use an intense and coherent third generation x-ray beam. By combining different x-ray imaging techniques (absorption/phase contrast radiography and diffraction topography), we have studied the directional melting and solidification of aluminium-based alloys. The preliminary results show the great potential of these techniques for the study of the coupling between stress effects and microstructure formation in solidification processing.

Segregation effects during solidification in weightless melts

NASA Technical Reports Server (NTRS)

Li, C.; Gershinsky, M.

1974-01-01

The generalized problem of determining the temperature and solute concentration profiles during directional solidification of binary alloys with surface evaporation was mathematically formulated. Realistic initial and boundary conditions were defined, and a computer program was developed and checked out. The programs computes the positions of two moving boundaries, evaporation and solidification, and their velocities. Temperature and solute concentration profiles in the semiinfinite material body at selected instances of time are also computed.

Matching time and spatial scales of rapid solidification: dynamic TEM experiments coupled to CALPHAD-informed phase-field simulations

NASA Astrophysics Data System (ADS)

Perron, Aurelien; Roehling, John D.; Turchi, Patrice E. A.; Fattebert, Jean-Luc; McKeown, Joseph T.

2018-01-01

A combination of dynamic transmission electron microscopy (DTEM) experiments and CALPHAD-informed phase-field simulations was used to study rapid solidification in Cu-Ni thin-film alloys. Experiments—conducted in the DTEM—consisted of in situ laser melting and determination of the solidification kinetics by monitoring the solid-liquid interface and the overall microstructure evolution (time-resolved measurements) during the solidification process. Modelling of the Cu-Ni alloy microstructure evolution was based on a phase-field model that included realistic Gibbs energies and diffusion coefficients from the CALPHAD framework (thermodynamic and mobility databases). DTEM and post mortem experiments highlighted the formation of microsegregation-free columnar grains with interface velocities varying from ˜0.1 to ˜0.6 m s-1. After an ‘incubation’ time, the velocity of the planar solid-liquid interface accelerated until solidification was complete. In addition, a decrease of the temperature gradient induced a decrease in the interface velocity. The modelling strategy permitted the simulation (in 1D and 2D) of the solidification process from the initially diffusion-controlled to the nearly partitionless regimes. Finally, results of DTEM experiments and phase-field simulations (grain morphology, solute distribution, and solid-liquid interface velocity) were consistent at similar time (μs) and spatial scales (μm).

Matching time and spatial scales of rapid solidification: Dynamic TEM experiments coupled to CALPHAD-informed phase-field simulations

DOE Office of Scientific and Technical Information (OSTI.GOV)

Perron, Aurelien; Roehling, John D.; Turchi, Patrice E. A.

A combination of dynamic transmission electron microscopy (DTEM) experiments and CALPHAD-informed phase-field simulations was used to study rapid solidification in Cu–Ni thin-film alloys. Experiments—conducted in the DTEM—consisted of in situ laser melting and determination of the solidification kinetics by monitoring the solid–liquid interface and the overall microstructure evolution (time-resolved measurements) during the solidification process. Modelling of the Cu–Ni alloy microstructure evolution was based on a phase-field model that included realistic Gibbs energies and diffusion coefficients from the CALPHAD framework (thermodynamic and mobility databases). DTEM and post mortem experiments highlighted the formation of microsegregation-free columnar grains with interface velocities varying frommore » ~0.1 to ~0.6 m s –1. After an 'incubation' time, the velocity of the planar solid–liquid interface accelerated until solidification was complete. In addition, a decrease of the temperature gradient induced a decrease in the interface velocity. The modelling strategy permitted the simulation (in 1D and 2D) of the solidification process from the initially diffusion-controlled to the nearly partitionless regimes. Lastly, results of DTEM experiments and phase-field simulations (grain morphology, solute distribution, and solid–liquid interface velocity) were consistent at similar time (μs) and spatial scales (μm).« less

Matching time and spatial scales of rapid solidification: Dynamic TEM experiments coupled to CALPHAD-informed phase-field simulations

DOE PAGES

Perron, Aurelien; Roehling, John D.; Turchi, Patrice E. A.; ...

2017-12-05

A combination of dynamic transmission electron microscopy (DTEM) experiments and CALPHAD-informed phase-field simulations was used to study rapid solidification in Cu–Ni thin-film alloys. Experiments—conducted in the DTEM—consisted of in situ laser melting and determination of the solidification kinetics by monitoring the solid–liquid interface and the overall microstructure evolution (time-resolved measurements) during the solidification process. Modelling of the Cu–Ni alloy microstructure evolution was based on a phase-field model that included realistic Gibbs energies and diffusion coefficients from the CALPHAD framework (thermodynamic and mobility databases). DTEM and post mortem experiments highlighted the formation of microsegregation-free columnar grains with interface velocities varying frommore » ~0.1 to ~0.6 m s –1. After an 'incubation' time, the velocity of the planar solid–liquid interface accelerated until solidification was complete. In addition, a decrease of the temperature gradient induced a decrease in the interface velocity. The modelling strategy permitted the simulation (in 1D and 2D) of the solidification process from the initially diffusion-controlled to the nearly partitionless regimes. Lastly, results of DTEM experiments and phase-field simulations (grain morphology, solute distribution, and solid–liquid interface velocity) were consistent at similar time (μs) and spatial scales (μm).« less

Effect of Chemical Composition on Susceptibility to Weld Solidification Cracking in Austenitic Weld Metal

NASA Astrophysics Data System (ADS)

Kadoi, Kota; Shinozaki, Kenji

2017-12-01

The influence of the chemical composition, especially the niobium content, chromium equivalent Creq, and nickel equivalent Nieq, on the weld solidification cracking susceptibility in the austenite single-phase region in the Schaeffler diagram was investigated. Specimens were fabricated using the hot-wire laser welding process with widely different compositions of Creq, Nieq, and niobium in the region. The distributions of the susceptibility, such as the crack length and brittle temperature range (BTR), in the Schaeffler diagram revealed a region with high susceptibility to solidification cracking. Addition of niobium enhanced the susceptibility and changed the distribution of the susceptibility in the diagram. The BTR distribution was in good agreement with the distribution of the temperature range of solidification (Δ T) calculated by solidification simulation based on Scheil model. Δ T increased with increasing content of alloying elements such as niobium. The distribution of Δ T was dependent on the type of alloying element owing to the change of the partitioning behavior. Thus, the solidification cracking susceptibility in the austenite single-phase region depends on whether the alloy contains elements. The distribution of the susceptibility in the region is controlled by the change in Δ T and the segregation behavior of niobium with the chemical composition.

Containerless solidification of BiFeO3 oxide under microgravity

NASA Astrophysics Data System (ADS)

Yu, Jianding; Arai, Yasutomo; Koshikawa, Naokiyo; Ishikawa, Takehito; Yoda, Shinichi

1999-07-01

Containerless solidification of BiFeO3 oxide has been carried out under microgravity with Electrostatic Levitation Furnace (ELF) aboard on the sounding rocket (TR-IA). It is a first containerless experiment using ELF under microgravity for studying the solidification of oxide insulator material. Spherical BiFeO3 sample with diameter of 5mm was heated by two lasers in oxygen and nitrogen mixing atmosphere, and the sample position by electrostatic force under pinpoint model and free drift model. In order to compare the solidification behavior in microgravity with on ground, solidification experiments of BiFeO3 in crucible and drop tube were carried out. In crucible experiment, it was very difficult to get single BiFeO3 phase, because segregation of Fe2O3 occured very fast and easily. In drop tube experiment, fine homogeneous BiFeO3 microstructure was obtained in a droplet about 300 μm. It implies that containerless processing can promote the phase selection in solidification. In microgravity experiment, because the heating temperature was lower than that of estimated, the sample was heated into Fe2O3+liquid phase region. Fe2O3 single crystal grew on the surface of the spherical sample, whose sample was clearly different from that observed in ground experiments.

Integrated System of Thermal/Dimensional Analysis for Quality Control of Metallic Melt and Ductile Iron Casting Solidification

NASA Astrophysics Data System (ADS)

Stan, Stelian; Chisamera, Mihai; Riposan, Iulian; Neacsu, Loredana; Cojocaru, Ana Maria; Stan, Iuliana

2018-03-01

The main objective of the present work is to introduce a specific experimental instrument and technique for simultaneously evaluating cooling curves and expansion or contraction of cast metals during solidification. Contraction/expansion analysis illustrates the solidification parameters progression, according to the molten cast iron characteristics, which are dependent on the melting procedure and applied metallurgical treatments, mold media rigidity and thermal behavior [heat transfer parameters]. The first part of the paper summarizes the performance of this two-mold device. Its function is illustrated by representative shrinkage tendency results in ductile cast iron as affected by mold rigidity (green sand and furan resin sand molds) and inoculant type (FeSi-based alloys), published in part previously. The second part of the paper illustrates an application of this equipment adapted for commercial foundry use. It conducts thermal analysis and volume change measurements in a single ceramic cup so that mold media as well as solidification conditions are constants, with cast iron quality as the variable. Experiments compared gray and ductile cast iron solidification patterns. Gray iron castings are characterized by higher undercooling at the beginning and at the end of solidification and lower graphitic expansion. Typically, ductile cast iron exhibits higher graphitic, initial expansion, conducive for shrinkage formation in soft molds.

Influence of Lanthanum on Solidification, Microstructure, and Mechanical Properties of Eutectic Al-Si Piston Alloy

NASA Astrophysics Data System (ADS)

Ahmad, R.; Asmael, M. B. A.

2016-07-01

The effects of Lanthanum (La) concentration on the solidification parameters of the α-Al, Al-Si, and Al-Cu phases and on the microstructure, tensile, and hardness properties of eutectic Al-Si-Cu-Mg alloy were systematically investigated. The solidification parameters were examined using computer-aided cooling curve thermal analysis (CA-CCTA). The cooling curve and microstructure analysis showed that La altered the Si structure. The nucleation and growth temperatures of eutectic Si decreased when 0.3 wt.% La was added, and a high depression temperature was obtained with 1.0 wt.% La. High amounts of La considerably modified the Si structure and decreased the area and aspect ratio by 69.9 and 51%, respectively. The thermal analysis result recorded a faster freezing time with the La addition and a 36% alteration in the secondary dendrite arm spacing. Two secondary or ternary La-rich intermetallic phases were formed with needle- and plate-like structures. Furthermore, the mechanical properties were investigated by hardness and tensile tests with different La concentrations. The addition of small amounts of La (0.1 wt.%) significantly improved the ultimate tensile strength and quality index of the Al-Si-Cu-Mg alloy. In addition, the hardness value of Al-11Si-Cu increased by 7-8% with the increasing amount of La added.

Experimental investigation of solidification in metal foam enhanced phase change material

NASA Astrophysics Data System (ADS)

Beyne, W.; Bağci, O.; Huisseune, H.; Canière, H.; Danneels, J.; Daenens, D.; De Paepe, M.

2017-10-01

A major challenge for the use of phase change materials (PCMs) in thermal energy storage (TES) is overcoming the low thermal conductivity of PCM’s. The low conductivity gives rise to limited power during charging and discharging TES. Impregnating metal foam with PCM, however, has been found to enhance the heat transfer. On the other hand, the effect of foam parameters such as porosity, pore size and material type has remained unclear. In this paper, the effect of these foam parameters on the solidification time is investigated. Different samples of PCM-impregnated metal foam were experimentally tested and compared to one without metal foam. The samples varied with respect to choice of material, porosity and pore size. They were placed in a rectangular cavity and cooled from one side using a coolant flowing through a cold plate. The other sides of the rectangular cavity were Polymethyl Methacrylate (PM) walls exposed to ambient. The temperature on the exterior walls of the cavity was monitored as well as the coolant flow rate and its temperature. The metal foam inserts reduced the solidification times by at least 25 %. However, the difference between the best performing and worst performing metal foam is about 28 %. This shows a large potential for future research.

Thermal analysis of HGFQ using FIDAP(trademark): Solidification front motion

NASA Technical Reports Server (NTRS)

Woodbury, Keith A.

1996-01-01

The High Gradient Furnace with Quench (HGFQ) is being designed by NASA/MSFC for flight on the International Space Station. The furnace is being designed specifically for solidification experiments in metal and metallic alloy systems. The HGFQ Product development Team (PDT) has been active since January 1994 and their effort is now in early Phase B. Thermal models have been developed both by NASA and Sverdrup (support contractor) to assist in the HGFQ design effort. Both these models use SINDA as a solution engine, but the NASA model was developed using PATRAN and includes more detail than the Sverdrup model. These models have been used to guide design decisions and have been validated through experimentation on a prototypical 'Breadboard' furnace at MSFC. One facet of the furnace operation of interest to the designers is the sensitivity of the solidification interface location to changes in the furnace setpoint. Specifically of interest is the motion (position and velocity) of the solidification front due to a small perturbation in the furnace temperature. FIDAP(TM) is a commercially available finite element program for analysis of heat transfer and fluid flow processes. Its strength is in solution of the Navier-Stokes equations for incompressible flow, but among its capabilities is the analysis of transient processes involving radiation and solidification. The models presently available from NASA and Sverdrup are steady-state models and are incapable of computing the motion of the solidification front. The objective of this investigation is to use FIDAP(TM) to compute the motion of the solidification interface due to a perturbation in the furnace setpoint.

A laboratory model for solidification of Earth's core

NASA Astrophysics Data System (ADS)

Bergman, Michael I.; Macleod-Silberstein, Marget; Haskel, Michael; Chandler, Benjamin; Akpan, Nsikan

2005-11-01

To better understand the influence of rotating convection in the outer core on the solidification of the inner core we have constructed a laboratory model for solidification of Earth's core. The model consists of a 15 cm radius hemispherical acrylic tank concentric with a 5 cm radius hemispherical aluminum heat exchanger that serves as the incipient inner core onto which we freeze ice from salt water. Long exposure photographs of neutrally buoyant particles in illuminated planes suggest reduction of flow parallel to the rotation axis. Thermistors in the tank near the heat exchanger show that in experiments with rotation the temperature near the pole is lower than near the equator, unlike for control experiments without rotation or with a polymer that increases the fluid viscosity. The photographs and thermistors suggest that our observation that ice grows faster near the pole than near the equator for experiments with rotation is a result of colder water not readily convecting away from the pole. Because of the reversal of the thermal gradient, we expect faster equatorial solidification in the Earth's core. Such anisotropy in solidification has been suggested as a cause of inner core elastic (and attenuation) anisotropy, though the plausibility of this suggestion will depend on the core Nusselt number and the slope of the liquidus, and the effects of post-solidification deformation. Previous experiments on hexagonal close-packed alloys such as sea ice and zinc-tin have shown that fluid flow in the melt can result in a solidification texture transverse to the solidification direction, with the texture depending on the nature of the flow. A comparison of the visualized flow and the texture of columnar ice crystals in thin sections from these experiments confirms flow-induced transverse textures. This suggests that the convective pattern at the base of the outer core is recorded in the texture of the inner core, and that outer core convection might contribute to the complexity in the seismically inferred pattern of anisotropy in the Earth's inner core.

PREFACE: Third International Conference on Advances in Solidification Processes (ICASP - 3)

NASA Astrophysics Data System (ADS)

Zimmermann, Gerhard; Ratke, Lorenz

2012-01-01

The 3rd International Conference on Advances in Solidification Processes was held in the Rolduc Abbey in the Netherlands a few kilometres away from Aachen. Around 200 scientists from 24 countries come in for the four day meeting. They found a stimulating but also relaxing environment and atmosphere, with beautiful weather and the medieval abbey inviting for walks, discussions, sitting outside and drinking a beer or wine. The contributions given at the conference reflected recent advances in various topics of solidification processes, ranging from fundamental aspects to applied casting technologies. In 20 oral sessions and a large poster session innovative results of segregation phenomena, microstructure evolution, nucleation and growth, phase formation, polyphase solidification, rapid solidification and welding, casting technology, thermophysics of molten alloys, solidification with forced melt flow and growth of single crystals and superalloys together with innovative diagnostic techniques were presented. Thereby, findings from experiments as well as from numerical modeling on different lengths scales were jointly discussed and contribute to new insight in solidification behaviour. The papers presented in this open access proceedings cover about half the oral and poster presentations given. They were carefully reviewed as in classical peer reviewed journals by two independent referees and most of them were revised and thus improved according to the reviewers comments. We think that this collection of papers presented at ICASP-3 gives an impression of the excellent contributions made. The papers embrace both the basic and applied aspects of solidification. We especially wish to express our appreciation for the team around Georg Schmitz and Margret Nienhaus organising this event and giving us their valued advice and support at every stage in preparing the conference. We also thank Lokasenna Lektorat for taking the task of checking all language-associated issues and fixing the papers according to the templates given by IOP Conference Series. We also wish to express our gratitude to the IOP Conference Series publishers, who were always helpful and patient with us. Conference photograph

XRMON-GF: A novel facility for solidification of metallic alloys with in situ and time-resolved X-ray radiographic characterization in microgravity conditions

NASA Astrophysics Data System (ADS)

Nguyen-Thi, H.; Reinhart, G.; Salloum Abou Jaoude, G.; Mathiesen, R. H.; Zimmermann, G.; Houltz, Y.; Voss, D.; Verga, A.; Browne, D. J.; Murphy, A. G.

2013-07-01

As most of the phenomena involved during the growth of metallic alloys from the melt are dynamic, in situ and time-resolved X-ray imaging should be retained as the method of choice for investigating the solidification front evolution. On Earth, the gravity force is the major source of various disturbing effects (natural convection, buoyancy/sedimentation, and hydrostatic pressure) which can significantly modify or mask certain physical mechanisms. Therefore solidification under microgravity is an efficient way to eliminate such perturbations to provide unique benchmark data for the validation of models and numerical simulations. Up to now, in situ observation during microgravity solidification experiments were limited to the investigations on transparent organic alloys, using optical methods. On the other hand, in situ observation on metallic alloys generally required synchrotron facilities. This paper reports on a novel facility we have designed and developed to investigate directional solidification on metallic alloys in microgravity conditions with in situ X-ray radiography observation. The facility consists of a Bridgman furnace and an X-ray radiography device specifically devoted to the study of Al-based alloys. An unprecedented experiment was recently performed on board a sounding rocket, with a 6 min period of microgravity. Radiographs were successfully recorded during the entire experiment including the melting and solidification phases of the sample, with a Field-of-View of about 5 mm×5 mm, a spatial resolution of about 4 µm and a frequency of 2 frames per second. Some preliminary results are presented on the solidification of the Al-20 wt% Cu sample, which validate the apparatus and confirm the potential of in situ X-ray characterization for the investigation of dynamical phenomena in materials processing, and particularly for the studying of metallic alloys solidification.

Directional solidification of silicon in carbon crucibles by an oscillating crucible technique

NASA Technical Reports Server (NTRS)

Daud, T.; Dumas, K. A.; Schwuttke, G. H.; Smetana, P.; Kim, K. M.

1982-01-01

The quality of silicon cast by present techniques is limited by the presence of dislocations and grain boundaries in unseeded growth and by cellular structures with dislocation networks in the case of the seeded growth. To address these concerns, a new method of directional solidification called the oscillating crucible technique (OCT) is developed. During growth, a carbon crucible is oscillated to provide for effective stirring of the melt. This growth technique (seeded growth only), along with material characterization and solar-cell fabrication and testing, is described. Solar-cell efficiencies of up to 13 percent at 100 mW/sq cm area obtained in the single crystalline areas. Minority-carrier diffusion lengths exceeding 100 microns are measured even in the polycrystalline areas of the wafers. Limitations of the present setup and possible future improvements are discussed.

Effects of Traveling Magnetic Field on Dynamics of Solidification

NASA Technical Reports Server (NTRS)

2003-01-01

The Lorentz body force induced in electrically conducting fluids can be utilized for a number of materials processing technologies. An application of strong static magnetic fields can be beneficial for damping convection present during solidification. On the other hand, alternating magnetic fields can be used to reduce as well as to enhance convection. However, only special types of time dependent magnetic fields can induce a non-zero time averaged Lorentz force needed for convection control. One example is the rotating magnetic field. This field configuration induces a swirling flow in circular containers. Another example of a magnetic field configuration is the traveling magnetic field (TMF). It utilizes axisymmetric magnetostatic waves. This type of field induces an axial recirculating flow that can be advantageous for controlling axial mass transport, such as during solidification in long cylindrical tubes. Incidentally, this is the common geometry for crystal growth research. The Lorentz force induced by TMF can potentially counter-balance the buoyancy force, diminishing natural convection, or even setting up the flow in reverse direction. Crystal growth process in presence of TMF can be then significantly modified. Such properties as the growth rate, interface shape and macro segregation can be affected and optimized. Melt homogenization is the other potential application of TMF. It is a necessary step prior to solidification. TMF can be attractive for this purpose, as it induces a basic flow along the axis of the ampoule. TMF can be a practical alloy mixing method especially suited for solidification research in space. In the theoretical part of this work, calculations of the induced Lorentz force in the whole frequency range have been completed. The basic flow characteristics for the finite cylinder geometry are completed and first results on stability analysis for higher Reynolds numbers are obtained. A theoretical model for TMF mixing is also developed. In the experimental part, measurements of flow induced by TMF in a column of mercury (Hg) are presented. Also, an alloy mixing of Bi-Sn of the eutectic composition is demonstrated. A traveling magnetic field of 4mT at 3kHz applied for 120 minutes is found to be sufficient to homogenize an alloy enclosed in a 1cm diameter and 12 cm long tube.

Exploiting the Temperature/Concentration Dependence of Magnetic Susceptibility to Control Convection in Fundamental Studies of Solidification Phenomena

NASA Technical Reports Server (NTRS)

Evans, J. W.; Xu, Dong; Jones, W. Kinzy, Jr.; Szofran, Frank R.

1999-01-01

The objective of this new research project is to demonstrate by experiment, supplemented by mathematical modeling and physical property measurement, that the effects of buoyancy driven convection can be largely eliminated in ground-based experiments, and further reduced in flight, by applying a new technique. That technique exploits the dependence of magnetic susceptibility on composition or temperature. It is emphasized at the outset that the phenomenon to be exploited is fundamentally and practically different from the magnetic damping of convection in conducting liquids that has been the subject of much prior research. The concept suggesting this research is that all materials, even non-conductors, when placed in a magnetic field gradient, experience a force. Of particular interest here are paramagnetic and diamagnetic materials, classes which embrace the "model alloys", such as succinonitrile-acetone, that have been used by others investigating the fundamentals of solidification. Such alloys will exhibit a dependence of susceptibility on composition. The consequence is that, with a properly oriented field (gradient) a force will arise that can be made to be equal to, but opposite, the buoyancy force arising from concentration (or temperature) gradients. In this way convection can be stilled. The role of convection in determining the microstructure, and thereby properties, of materials is well known. Elimination of that convection has both scientific and technological consequences. Our knowledge of diffusive phenomena in solidification, phenomena normally hidden by the dominance of convection, is enhanced if we can study solidification of quiescent liquids. Furthermore, the microstructure, microchemistry and properties of materials (thereby practical value) are affected by the convection occurring during their solidification. Hitherto the method of choice for elimination of convection has been experimentation in microgravity. However, even in low Earth orbit, residual convection has effects. That residual convection arises from acceleration (drag on the spacecraft), displacement from the center of mass or transients in the gravitational field (g-jitter). There is therefore a need for both further reducing buoyancy driven flow in flight and allowing the simulation of microgravity during ground based experiments. Previous investigations, the research project description, theory behind the study and experimental methods as well as plots of magnetic fields and forces are presented.

Solidification Based Grain Refinement in Steels

DTIC Science & Technology

2011-09-27

project (Tasks 7-9). An industrial trial on an investment casting was done using rare earth silicide additions in a furnace prior to pouring (Task 7...an investment casting was done using rare earth silicide additions in a furnace prior to pounng (la.sk 7). Some of the test parts had a finer...poured at the end of a six casting batch. One test tree with no RE addition was poured. Before the second test tree was poured, sufficient RE silicide was

Probes and monitors for the study of solidification of molten semiconductors

NASA Technical Reports Server (NTRS)

Sadoway, D. R.

1986-01-01

The purpose is to examine solidification in the LiCl-KCl system to determine if phenomena such as solute rejection can be obseved by laser schlieren imaging. Molten salts have attributes that make them attractive as physical models in solidification studies. With optical techniques of investigation such as schlieren imaging, it is possible to study fluid flow phenomena in molten salts and to watch the trajectory of the solid-liquid interface.

Materials for the Study of Interesting Phenomena of Solidification on Earth and in Orbit (MEPHISTO)

NASA Technical Reports Server (NTRS)

1987-01-01

The MEPHISTO experiment is a cooperative American and French investigation of the fundamentals of crystal growth. MEPHISTO is a French-designed and built materials processing furnace. MEPHISTO experiments study solidation (also called freezing) during the growth cycle of liquid materials used for semiconductor crystals. Solidification is the process where materials change from liquid (melt) to solid. An example of the solidification process is water changing into ice.

Rapid solidification of metallic particulates

NASA Technical Reports Server (NTRS)

Grant, N. J.

1982-01-01

In order to maximize the heat transfer coefficient the most important variable in rapid solidification is the powder particle size. The finer the particle size, the higher the solidification rate. Efforts to decrease the particle size diameter offer the greatest payoff in attained quench rate. The velocity of the liquid droplet in the atmosphere is the second most important variable. Unfortunately the choices of gas atmospheres are sharply limited both because of conductivity and cost. Nitrogen and argon stand out as the preferred gases, nitrogen where reactions are unimportant and argon where reaction with nitrogen may be important. In gas atomization, helium offers up to an order of magnitude increase in solidification rate over argon and nitrogen. By contrast, atomization in vacuum drops the quench rate several orders of magnitude.

Distribution Behavior of B and P during Al-Si Melt Directional Solidification with Open-Ended Crucible

NASA Astrophysics Data System (ADS)

Bai, Xiaolong; Ban, Boyuan; Li, Jingwei; Peng, Zhijian; Chen, Jian

2018-03-01

Distribution behavior of B and P during directional solidification of Al-20Si, Al-30Si and Al-40Si alloys has been investigated. Macrostructure of the Al-Si alloy ingots and concentration profile of elements B and P reveal that the elements segregate to eutectic Al-Si melt during growth of primary Si flakes, and P gradually segregates to the top of the ingots during directional solidification. An apparent segregation coefficient, ka, is introduced to describe the segregation behavior of B and P between the primary Si and the Al-Si melt and compared with thermodynamic theoretical equilibrium coefficients. The apparent segregation coefficients of B and P decrease with increase of solidification temperature.

Minimizing Segregation during the Controlled Directional Solidification of Dendric Alloys

NASA Technical Reports Server (NTRS)

Grugel, Richard N.; Fedoseyev, Alex; Kim, Shin-Woo

2003-01-01

Gravity-driven convection induced in the liquid by density gradients of temperature or composition disrupts uniform dendritic growth during controlled directional solidification and promotes severe macrosegregation. The solute-rich region about the dendrite tip appears to play a pivotal role in channel initiation. Allen and Hunt referred to this region as an "initial transient" or dynamic region constituting steep concentration gradients. Experimental investigation also point to the role the tip region plays in developing microstructure. Hellawell and co-workers showed that flow-through dendritic channels could be effectively disrupted, and segregation minimized, during the gradient freezing of bulk castings by rotating the melt through a slight angle with respect to Earth's gravity vector. Adapting this principle to controlled directional solidification, it has been shown" that segregation in dendritic alloys can be minimized, and properties improved, by processing the sample near horizontal in conjunction with a slow axial rotation of the crucible. It is postulated that the observed microstructural uniformity arises by maintaining the developing solute field about the dendrite tip. Solute rejected during vertical directional solidification will rise or sink parallel to the primary dendrite arms during axial rotation setting the stage for accumulation, instabilities, and segregation. In contrast, during horizontal growth, the rejected solute will sink or rise perpendicular to the primary dendrite. Now, in the presence of a slight axial rotation, solute that was initially sinking (or rising) will find itself above (or below) its parent dendrite, i.e., still about the tip region. The following is intended to experimentally demonstrate the viability of this concept in coordination with a model that gives predictive insight regarding solute distribution about growing dendrites. Alloys based on the lead-tin eutectic system were used in this study. The system is well characterized, the constituent metals are available in a very pure form, and the thermophysical properties are well known. During solidification of hypoeutectic alloys, e.g., 55 wt pct Pb, the primary dendrites reject the less dense tin, and for the hypereutectic alloys, e.g., 75 wt pct Sn, the primary dendrites reject denser lead. Alloys were prepared by melting appropriate amounts of lead and tin in a glass crucible after which the homogeneous liquid was sucked directly into 5-mm i.d. glass tubes. The sample tube, containing approximately 30 cm of alloy, was then mechanically driven into the directional solidification furnace assembly and positioned such that approx. 20 cm of the sample was remelted. Subsequently, directional solidification was initiated by withdrawing the sample through a water-cooled jacket at a constant growth velocity of 2 ,microns/s. After 5 to 6 cm of growth, the sample was quickly removed from the furnace and quenched in a water bath to preserve the solid-liquid interface. Samples were directionally solidified vertically upward, nearly horizontally, and some in conjunction with an applied axial rotation of the crucible. Temperature gradients at the solid-liquid interface were measured with an in-siru K-type thermocouple. Solidified samples were cut perpendicular and parallel to the growth direction and conventionally prepared for microscopic examination.

Immiscible phase incorporation during directional solidification of hypermonotectics

NASA Technical Reports Server (NTRS)

Andrews, J. Barry; Merrick, Roger A.

1993-01-01

Solidification processes in immiscible samples were investigated by directly observing the events taking place at the solid-liquid interface during directional solidification. Visualization of these events was made possible through the use of a transparent metal analog system and a temperature gradient stage assembly fitted to an optical microscope. The immiscible transparent analog system utilized was the succinonitrile-glycerol system. This system has been shown to exhibit the same morphological transitions as observed in metallic alloys of monotectic composition. Both monotectic and hypermonotectic composition samples were directionally solidified in order to gain an improved understanding of the manner in which the excess hypermonotectic liquid is incorporated into the solidifying structure. The processing conditions utilized prevented sedimentation of the excess hypermonotectic liquid by directionally solidifying the samples in very thin (13 microns), horizontally oriented cells. High thermal gradient to growth rate ratios (G/R) were used in an effort to prevent constitutional supercooling and the subsequent formation of L(sub 2) droplets in advance of the solidification front during the growth of fibrous composite structures. Results demonstrated that hypermonotectic composites could be produced in samples up to two weight percent off of the monotectic composition by using a G/R ratio greater than or equal to 4.6 x 10(exp 4) C(s)/mm(sup 2) to avoid constitutional supercooling. For hypermonotectic samples processed with G/R ratios below 4.6 x 10(exp 4) C(s)/mm(sup 2), constitutional supercooling occurred and resulted in slight interfacial instability. For these samples, two methods of incorporation of the hypermonotectic liquid were observed and are reported. The correlation between the phase spacing, lambda, and the growth rate, R, was examined and was found to obey a relationship generally associated with a diffusion controlled coupled growth process. For samples with compositions ranging from the monotectic composition up to 2 percent off of the monotectic composition, data indicated that the square of the phase spacing (lambda) varied linearly with the inverse of the growth rate (R).

The use of a directional solidification technique to investigate the interrelationship of thermal parameters, microstructure and microhardness of Bi–Ag solder alloys

DOE Office of Scientific and Technical Information (OSTI.GOV)

Spinelli, José Eduardo, E-mail: spinelli@ufscar.br; Silva, Bismarck Luiz; Cheung, Noé

2014-10-15

Bi–Ag alloys have been stressed as possible alternatives to replace Pb-based solder alloys. Although acceptable melting temperatures and suitable mechanical properties may characterize such alloys, as referenced in literature, there is a lack of comprehension regarding their microstructures (morphologies and sizes of the phases) considering a composition range from 1.5 to 4.0 wt.%Ag. In order to better comprehend such aspects and their correlations with solidification thermal parameters (growth rate, v and cooling rate, T-dot), directional solidification experiments were carried out under transient heat flow conditions. The effects of Ag content on both cooling rate and growth rate during solidification aremore » examined. Microstructure parameters such as eutectic/dendritic spacing, interphase spacing and diameter of the Ag-rich phase were determined by optical microscopy and scanning electron microscopy. The competition between eutectic cells and dendrites in the range from 1.5 to 4.0 wt.%Ag is explained by the coupled zone concept. Microhardness was determined for different microstructures and alloy Ag contents with a view to permitting correlations with microstructure parameters to be established. Hardness is shown to be directly affected by both solute macrosegregation and morphologies of the phases forming the Bi–Ag alloys, with higher hardness being associated with the cellular morphology of the Bi-2.5 and 4.0 wt.%Ag alloys. - Highlights: • Asymmetric zone of coupled growth for Bi–Ag is demonstrated. • Faceted Bi-rich dendrites have been characterized for Bi–1.5 wt.%Ag alloy. • Eutectic cells were shown for the Bi-2.5 and 4.0 wt.%Ag solder alloys. • Interphase spacing relations with G × v are able to represent the experimental scatters. • Hall-Petch type equations are proposed relating microstructural spacings to hardness.« less

EVALUATION OF CONTAMINANT LEACHABILITY FACTORS BY COMPARISON OF TREATABILITY STUDY DATA FOR MULTIPLE SOLIDIFIED/STABILIZED MATERIALS

EPA Science Inventory

Solidification/stabilization (S/S) technology is widely used in the treatment of hazardous waste and contaminated soil in the US. In a project sponsored by the US Navy and the USEPA, treatability test data were compiled into a data base listing contaminant concentration and matri...

X-Ray Transmission Microscope Development

NASA Technical Reports Server (NTRS)

Kaukler, William F.

1997-01-01

We have succeeded in meeting the goals set out in the proposal. A cadre of detector technologies is available to suit the requirements of the experiment. Resolutions of both real-time and absolute limits to resolution exceed the initial aspirations. Obtaining sufficient contrast is still a significant limitation but can be overcome by Judicious selection of the specimen composition. This can only take time and trial and error for a successful result. The 4th generation furnace provides the capability of real-time in-situ observations of composite alloy development. A low detection sensitivity however, has still made it difficult to observe dendritic growth, although it has been 'seen' in raw video; it was not a recordable signal. We have examined flight ampoules with XTM to observe particle and thermocouple placement, crucible flaws and cracks in collaboration with the Particle Pushing and Engulfment flight experiment (Dr. Stefanescu, UA, P.I.). The value of an in flight XTM to guard against experiment failure and safety assurance is obvious. Although not attributable to equipment limitations, a quest to observe particle pushing was not successful. We tried at length to prepare specimens that would demonstrate particle pushing. Instead, we were successful in imaging the interface deformation due to the thermal field distortion of a ceramic particle or void and to compare to calculated shapes. In theory, we should have been able to make major inroads to this field if the particles could be pushed and the velocities adjusted to make critical measurements. On the other hand, critical issues of sample preparation for the PEP flight experiment were established, particularly the clustering of particles and trapped voids. In this regard, the XTM did prove very useful so that flight specimens would work as expected and to perform post flight analysis. Although not a clear result, particle pushing of precipitates was observed in an Al-Si-Mn alloy. It may be that to be pushed, the particles need to be small and have clean surfaces like one might obtain from in-situ precipitation. The ability to image features in real time skill enable more fundamental and detailed understanding of solidification dynamics in microgravity than had previously been possible, thus, allowing the full benefits of microgravity experiments be applied towards rigorous testing of critical solidification models. The XTM is also a valuable tool for post solidification metallography. The 3-dimensional distribution of solute and solidification features within the specimen volume can be viewed without sectioning or other treatment when the solute has sufficiently higher atomic mass than the solvent. Thus the XTM could provide the first practical method for on orbit microstructural (metallographic) analysis by the astronauts or by telescience.

Numerical and experimental analysis for solidification and residual stress in the GMAW process for AISI 304 stainless steel

DOE Office of Scientific and Technical Information (OSTI.GOV)

Choi, J.; Mazumder, J.

1996-12-31

Networking three fields of welding--thermal, microstructure, and stress--was attempted and produced a reliable model using a numerical method with the finite element analysis technique. Model prediction was compared with experimental data in order to validate the model. The effects of welding process parameters on these welding fields were analyzed and reported. The effort to correlate the residual stress and solidification was initiated, with some valuable results. The solidification process was simulated using the formulation based on the Hunt-Trivedi model. Based on the temperature history, solidification speed and primary dendrite arm spacing were predicted at given nodes of interest. Results showmore » that the variation during solidification is usually within an order of magnitude. The temperature gradient was generally in the range of 10{sup 4}--10{sup 5} K/m for the given welding conditions (welding power = 6 kW and welding speed = 3.3867 to 7.62 mm/sec), while solidification speed appeared to slow down from an order of 10{sup {minus}1} to 10{sup {minus}2} m/sec during solidification. SEM images revealed that the primary dendrite arm spacing (PDAS) fell in the range of 10{sup 1}--10{sup 2} {micro}m. For grain growth at the heat affected zone (HAZ), Ashby`s model was employed. The prediction was in agreement with experimental results. For the residual stress calculation, the same mesh generation used in the heat transfer analysis was applied to make the simulation consistent. The analysis consisted of a transient heat analysis followed by a thermal stress analysis. An experimentally measured strain history was compared with the simulated result. The relationship between microstructure and the stress/strain field of welding was also obtained. 64 refs., 18 figs., 9 tabs.« less

Effect of Marangoni Convection Generated by Voids on Segregation During Low-G and 1-G Solidification

NASA Technical Reports Server (NTRS)

Kassemi, M.; Fripp, A.; Rashidnia, N.; deGroh, H.

1999-01-01

Solidification experiments, especially microgravity solidification experiments are often hampered by the evolution of unwanted voids or bubbles in the melt. Although these voids and/or bubbles are highly undesirable, there are currently no effective means of preventing their formation or eliminating their adverse effects, particularly, during low-g experiments. Marangoni Convection caused by these voids can drastically change the transport processes in the melt and, therefore, introduce enormous difficulties in interpreting the results of the space investigations. Recent microgravity experiments by Matthiesen, Andrews, and Fripp are all good examples of how the presence of voids and bubbles affect the outcome of costly space experiments and significantly increase the level of difficulty in interpreting their results. In this work we examine mixing caused by Marangoni convection generated by voids and bubbles in the melt during both 1-g and low-g solidification experiments. The objective of the research is to perform a detailed and comprehensive combined numerical-experimental study of Marangoni convection caused by voids during the solidification process and to show how it can affect segregation and growth conditions by modifying the flow, temperature, and species concentration fields in the melt. While Marangoni convection generated by bubbles and voids in the melt can lead to rapid mixing that would negate the benefits of microgravity processing, it could be exploited in some terrestrial processing to ensure effective communication between a melt/solid interface and a gas phase stoichiometry control zone. Thus we hope that this study will not only aid us in interpreting the results of microgravity solidification experiments hampered by voids and bubbles but to guide us in devising possible means of minimizing the adverse effects of Marangoni convection in future space experiments or of exploiting its beneficial mixing features in ground-based solidification.

Microstructural investigation of D2 tool steel during rapid solidification

NASA Astrophysics Data System (ADS)

Delshad Khatibi, Pooya

Solidification is considered as a key processing step in developing the microstructure of most metallic materials. It is, therefore, important that the solidification process can be designed and controlled in such a way so as to obtain the desirable properties in the final product. Rapid solidification refers to the system's high undercooling and high cooling rate, which can yield a microstructure with unique chemical composition and mechanical properties. An area of interest in rapid solidification application is high-chromium, high-carbon tool steels which experience considerable segregation of alloying elements during their solidification in a casting process. In this dissertation, the effect of rapid solidification (undercooling and cooling rate) of D2 tool steel on the microstructure and carbide precipitation during annealing was explored. A methodology is described to estimate the eutectic and primary phase undercooling of solidifying droplets. The estimate of primary phase undercooling was confirmed using an online measurement device that measured the radiation energy of the droplets. The results showed that with increasing primary phase and eutectic undercooling and higher cooling rate, the amount of supersaturation of alloying element in metastable retained austenite phase also increases. In the case of powders, the optimum hardness after heat treatment is achieved at different temperatures for constant periods of time. Higher supersaturation of austenite results in obtaining secondary hardness at higher annealing temperature. D2 steel ingots generated using spray deposition have high eutectic undercooling and, as a result, high supersaturation of alloying elements. This can yield near net shape D2 tool steel components with good mechanical properties (specifically hardness). The data developed in this work would assist in better understanding and development of near net shape D2 steel spray deposit products with good mechanical properties.

Solute redistribution in dendritic solidification with diffusion in the solid

NASA Technical Reports Server (NTRS)

Ganesan, S.; Poirier, D. R.

1989-01-01

An investigation of solute redistribution during dendritic solidification with diffusion in the solid has been performed using numerical techniques. The extent of diffusion is characterized by the instantaneous and average diffusion parameters. These parameters are functions of the diffusion Fourier number, the partition ratio and the fraction solid. Numerical results are presented as an approximate model, which is used to predict the average diffusion parameter and calculate the composition of the interdendritic liquid during solidification.

Solidification drug nanosuspensions into nanocrystals by freeze-drying: a case study with ursodeoxycholic acid.

PubMed

Ma, Yue-Qin; Zhang, Zeng-Zhu; Li, Gang; Zhang, Jing; Xiao, Han-Yang; Li, Xian-Fei

2016-03-01

To elucidate the effect of solidification processes on the redispersibility of drug nanocrystals (NC) during freeze-drying, ursodeoxycholic acid (UDCA) nanosuspensions were transformed into UDCA-NC via different solidification process included freezing and lyophilization. The effect of different concentrations of stabilizers and cryoprotectants on redispersibility of UDCA-NC was investigated, respectively. The results showed that the redispersibility of UDCA-NC was RDI-20 °C < RDI-80 °C < RDI-196 °C during freezing, which indicated the redispersibility of UDCA-NC at the conventional temperature was better more than those at moderate and rigorous condition. Compared to the drying strengthen, the employed amount and type of stabilizers more dramatically affected the redispersibility of UDCA-NC during lyophilization. The hydroxypropylmethylcellulose and PVPK30 were effective to protect UDCA-NC from damage during lyophilization, which could homogeneously adsorb into the surface of NC to prevent from agglomerates. The sucrose and glucose achieved excellent performance that protected UDCA-NC from crystal growth during lyophilization, respectively. It was concluded that UDCA-NC was subjected to agglomeration during solidification transformation, and the degree of agglomeration suffered varied with the type and the amounts of stabilizers used, as well as different solidification conditions. The PVPK30-sucrose system was more effective to protect UDCA-NC from the damage during solidification process.

Gravitational Acceleration Effects on Macrosegregation: Experiment and Computational Modeling

NASA Technical Reports Server (NTRS)

Leon-Torres, J.; Curreri, P. A.; Stefanescu, D. M.; Sen, S.

1999-01-01

Experiments were performed under terrestrial gravity (1g) and during parabolic flights (10-2 g) to study the solidification and macrosegregation patterns of Al-Cu alloys. Alloys having 2% and 5% Cu were solidified against a chill at two different cooling rates. Microscopic and Electron Microprobe characterization was used to produce microstructural and macrosegregation maps. In all cases positive segregation occurred next to the chill because shrinkage flow, as expected. This positive segregation was higher in the low-g samples, apparently because of the higher heat transfer coefficient. A 2-D computational model was used to explain the experimental results. The continuum formulation was employed to describe the macroscopic transports of mass, energy, and momentum, associated with the solidification phenomena, for a two-phase system. The model considers that liquid flow is driven by thermal and solutal buoyancy, and by solidification shrinkage. The solidification event was divided into two stages. In the first one, the liquid containing freely moving equiaxed grains was described through the relative viscosity concept. In the second stage, when a fixed dendritic network was formed after dendritic coherency, the mushy zone was treated as a porous medium. The macrosegregation maps and the cooling curves obtained during experiments were used for validation of the solidification and segregation model. The model can explain the solidification and macrosegregation patterns and the differences between low- and high-gravity results.

Localized melt-scan strategy for site specific control of grain size and primary dendrite arm spacing in electron beam additive manufacturing

DOE Office of Scientific and Technical Information (OSTI.GOV)

Raghavan, Narendran; Simunovic, Srdjan; Dehoff, Ryan

In addition to design geometry, surface roughness, and solid-state phase transformation, solidification microstructure plays a crucial role in controlling the performance of additively manufactured components. Crystallographic texture, primary dendrite arm spacing (PDAS), and grain size are directly correlated to local solidification conditions. We have developed a new melt-scan strategy for inducing site specific, on-demand control of solidification microstructure. We were able to induce variations in grain size (30 μm–150 μm) and PDAS (4 μm - 10 μm) in Inconel 718 parts produced by the electron beam additive manufacturing system (Arcam®). A conventional raster melt-scan resulted in a grain size ofmore » about 600 μm. The observed variations in grain size with different melt-scan strategies are rationalized using a numerical thermal and solidification model which accounts for the transient curvature of the melt pool and associated thermal gradients and liquid-solid interface velocities. The refinement in grain size at high cooling rates (>104 K/s) is also attributed to the potential heterogeneous nucleation of grains ahead of the epitaxially growing solidification front. The variation in PDAS is rationalized using a coupled numerical-theoretical model as a function of local solidification conditions (thermal gradient and liquid-solid interface velocity) of the melt pool.« less

Continuum simulation of heat transfer and solidification behavior of AlSi10Mg in Direct Metal Laser Sintering Process

NASA Astrophysics Data System (ADS)

Ojha, Akash; Samantaray, Mihir; Nath Thatoi, Dhirendra; Sahoo, Seshadev

2018-03-01

Direct Metal Laser Sintering (DMLS) process is a laser based additive manufacturing process, which built complex structures from powder materials. Using high intensity laser beam, the process melts and fuse the powder particles makes dense structures. In this process, the laser beam in terms of heat flux strikes the powder bed and instantaneously melts and joins the powder particles. The partial solidification and temperature distribution on the powder bed endows a high cooling rate and rapid solidification which affects the microstructure of the build part. During the interaction of the laser beam with the powder bed, multiple modes of heat transfer takes place in this process, that make the process very complex. In the present research, a comprehensive heat transfer and solidification model of AlSi10Mg in direct metal laser sintering process has been developed on ANSYS 17.1.0 platform. The model helps to understand the flow phenomena, temperature distribution and densification mechanism on the powder bed. The numerical model takes into account the flow, heat transfer and solidification phenomena. Simulations were carried out for sintering of AlSi10Mg powders in the powder bed having dimension 3 mm × 1 mm × 0.08 mm. The solidification phenomena are incorporated by using enthalpy-porosity approach. The simulation results give the fundamental understanding of the densification of powder particles in DMLS process.

SOLIDIFICATION/STABILIZATION CASE STUDIES AT USEPA SUPERFUND SITES

EPA Science Inventory

Oral presentation dicumenting several completed Superfund remediations using solidification/stabilization, both in situ and ex-situ, to treat soils containing metals and organics.
65 slide presentation.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jo, J.C.; Shin, W.K.; Choi, C.Y.

Transient heat transfer problems with phase changes (Stefan problems) occur in many engineering situations, including potential core melting and solidification during pressurized-water-reactor severe accidents, ablation of thermal shields, melting and solidification of alloys, and many others. This article addresses the numerical analysis of nonlinear transient heat transfer with melting or solidification. An effective and simple procedure is presented for the simulation of the motion of the boundary and the transient temperature field during the phase change process. To accomplish this purpose, an iterative implicit solution algorithm has been developed by employing the dual-reciprocity boundary-element method. The dual-reciprocity boundary-element approach providedmore » in this article is much simpler than the usual boundary-element method in applying a reciprocity principle and an available technique for dealing with the domain integral of the boundary element formulation simultaneously. In this article, attention is focused on two-dimensional melting (ablation)/solidification problems for simplicity. The accuracy and effectiveness of the present analysis method have been illustrated through comparisons of the calculation results of some examples of one-phase ablation/solidification problems with their known semianalytical or numerical solutions where available.« less

Overview of the Tusas Code for Simulation of Dendritic Solidification

DOE Office of Scientific and Technical Information (OSTI.GOV)

Trainer, Amelia J.; Newman, Christopher Kyle; Francois, Marianne M.

2016-01-07

The aim of this project is to conduct a parametric investigation into the modeling of two dimensional dendrite solidification, using the phase field model. Specifically, we use the Tusas code, which is for coupled heat and phase-field simulation of dendritic solidification. Dendritic solidification, which may occur in the presence of an unstable solidification interface, results in treelike microstructures that often grow perpendicular to the rest of the growth front. The interface may become unstable if the enthalpy of the solid material is less than that of the liquid material, or if the solute is less soluble in solid than itmore » is in liquid, potentially causing a partition [1]. A key motivation behind this research is that a broadened understanding of phase-field formulation and microstructural developments can be utilized for macroscopic simulations of phase change. This may be directly implemented as a part of the Telluride project at Los Alamos National Laboratory (LANL), through which a computational additive manufacturing simulation tool is being developed, ultimately to become part of the Advanced Simulation and Computing Program within the U.S. Department of Energy [2].« less

Influence of additional heat exchanger block on directional solidification system for growing multi-crystalline silicon ingot - A simulation investigation

NASA Astrophysics Data System (ADS)

Nagarajan, S. G.; Srinivasan, M.; Aravinth, K.; Ramasamy, P.

2018-04-01

Transient simulation has been carried out for analyzing the heat transfer properties of Directional Solidification (DS) furnace. The simulation results revealed that the additional heat exchanger block under the bottom insulation on the DS furnace has enhanced the control of solidification of the silicon melt. Controlled Heat extraction rate during the solidification of silicon melt is requisite for growing good quality ingots which has been achieved by the additional heat exchanger block. As an additional heat exchanger block, the water circulating plate has been placed under the bottom insulation. The heat flux analysis of DS system and the temperature distribution studies of grown ingot confirm that the established additional heat exchanger block on the DS system gives additional benefit to the mc-Si ingot.

Onset of Curved Dendrite Growth in an Al-Cu Welding Pool: A Phase Field Study

NASA Astrophysics Data System (ADS)

Wang, Lei; Wei, Yanhong

2018-02-01

A phase field model is developed to predict curved dendrite growth in the gas tungsten arc (GTA) welding pool of an Al-Cu alloy. The equations of temperature gradient, pulling velocity and dendrite growth orientation are proposed to consider the transient solidification process during welding. Solidification microstructures and solute diffusion along the fusion boundary in the welding pool are predicted by using the phase field model coupled with transient solidification conditions. Predicted primary dendrites are curved and point toward the welding direction. Welding experiments are carried out to observe solidification microstructures of the weld. Comparisons of simulation results with experimental measurements are conducted. Predicted dendritic morphology, dendrite growth orientation, primary dendrite arm spacing and initial cell spacing give a good agreement with experimental measurements.

The growth of metastable peritectic compounds

NASA Technical Reports Server (NTRS)

Larson, D. J., Jr.; Pirich, R. G.

1981-01-01

The influence of gravitationally driven thermosolutal convection on the directional solidification of peritectic alloys is considered as well as the relationships between the solidification processing conditions, and the microstructure, chemistry, and magnetic properties of such alloys. Analysis of directionally solidified Pb-Bi peritectic samples indicates that appreciable macrosegregation occurs due to thermosolutal convection and/or Soret diffusion. A peritectic solidification model which accounts for partial mixing in the liquid ahead of the planar solidification interface and describes macrosegregation has been developed. Two-phase dendritic and banded microstructures were grown in the Pb-Bi peritectic system, refined two-phase microstructures have were observed, and candidate formation mechanisms proposed. Material handling, containment, casting, microstructural and magnetic characterization techniques were developed for the Sm-Co system. Alloys produced with these procedures are homogeneous.

Comparative study of solute trapping and Gibbs free energy changes at the phase interface during alloy solidification under local nonequilibrium conditions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sobolev, S. L., E-mail: sobolev@icp.ac.ru

An analytical model has been developed to describe the influence of solute trapping during rapid alloy solidification on the components of the Gibbs free energy change at the phase interface with emphasis on the solute drag energy. For relatively low interface velocity V < V{sub D}, where V{sub D} is the characteristic diffusion velocity, all the components, namely mixing part, local nonequilibrium part, and solute drag, significantly depend on solute diffusion and partitioning. When V ≥ V{sub D}, the local nonequilibrium effects lead to a sharp transition to diffusionless solidification. The transition is accompanied by complete solute trapping and vanishingmore » solute drag energy, i.e. partitionless and “dragless” solidification.« less

Solidification/Stabilization Use at Superfund Sites

EPA Pesticide Factsheets

To provide interested stakeholders such as project managers, technology service providers, consulting engineers, site owners, and the general public with the most recent information about solidification/stabilization applications at Superfund sites...

Particle Engulfment and Pushing by Solidifying Interfaces. Pt. 2; Micro-Gravity Experiments and Theoretical Analysis

NASA Technical Reports Server (NTRS)

Stefanescu, Doru M.; Juretzko, Frank R.; Dhindaw, Brij K.; Catalina, Adrian; Sen, Subhayu; Curreri, Peter A.

1998-01-01

Results of the directional solidification experiments on Particle Engulfment and Pushing by Solidifying Interfaces (PEP) conducted on the space shuttle Columbia during the Life and Microgravity Science Mission are reported. Two pure aluminum (99.999%) 9 mm cylindrical rods, loaded with about 2 vol.% 500 micrometers diameter zirconia particles were melted and resolidified in the microgravity (microg) environment of the shuttle. One sample was processed at step-wise increased solidification velocity, while the other at step-wise decreased velocity. It was found that a pushing-to-engulfment transition (PET) occurred in the velocity range of 0.5 to 1 micrometers. This is smaller than the ground PET velocity of 1.9 to 2.4 micrometers. This demonstrates that natural convection increases the critical velocity. A previously proposed analytical model for PEP was further developed. A major effort to identify and produce data for the surface energy of various interfaces required for calculation was undertaken. The predicted critical velocity for PET was of 0.775 micrometers/s.

Reproducible Crystal Growth Experiments in Microgravity Science Glovebox at the International Space Station (SUBSA Investigation)

NASA Technical Reports Server (NTRS)

Ostrogorsky, A.; Marin, C.; Volz, M. P.; Bonner, W. A.

2005-01-01

Solidification Using a Baffle in Sealed Ampoules (SUBSA) is the first investigation conducted in the Microgravity Science Glovebox (MSG) Facility at the International Space Station (ISS) Alpha. 8 single crystals of InSb, doped with Te and Zn, were directionally solidified in microgravity. The experiments were conducted in a furnace with a transparent gradient section, and a video camera, sending images to the earth. The real time images (i) helped seeding, (ii) allowed a direct measurement of the solidification rate. The post-flight characterization of the crystals includes: computed x-ray tomography, Secondary Ion Mass Spectroscopy (SIMS), Hall measurements, Atomic Absorption (AA), and 4 point probe analysis. For the first time in microgravity, several crystals having nearly identical initial transients were grown. Reproducible initial transients were obtained with Te-doped InSb. Furthermore, the diffusion controlled end-transient was demonstrated experimentally (SUBSA 02). From the initial transients, the diffusivity of Te and Zn in InSb was determined.

Project Explorer: Get Away Special #007. [alloy solidification, seed germination, crystal growth, and radio transmission of payload data

NASA Technical Reports Server (NTRS)

Henderson, A. J., Jr.

1984-01-01

Tentatively scheduled to fly on STS-17 (41G), this get away special aims to demonstrate amateur radio transmissions to global ground stations in the English language. Experiments No. 1, 2, and 3 use the micro-gravity of space flight to study the solidification of lead-antimony and aluminum-copper alloys, the germination of radish seeds, and the growth of potassium-tetracyanoplatinate hydrate crystals in an aqueous solution. Flight results are to be compared with Earth-based data. Experiment No. 4 (the Marshall Amateur Radio Club Experiment - MARCE) features radio transmissions and also provides timing for the start of all other experiments. A microprocessor obtains real-time data from all experiments as well as temperature and pressure measurements within the GAS canister. These data are to be transmitted on previously announced amateur radio frequencies after they are converted into the English language by a digitalker for general reception. The support structure for the G #007 experiments consists of two primary plates and four bumper assemblies.

Eutectic superalloys strengthened by sigma, Ni3CB lamellae and gamma prime, Ni3Al precipitates

NASA Technical Reports Server (NTRS)

Lemkey, F. D.

1973-01-01

By means of a screening and solidification optimization study of certain alloys located on the gamma-sigma liquidus surface within the Ni-Cb-Cr-Al system, alloys with high temperature properties superior to those of all known superalloys were defined. One alloy, Ni - 19.7w/o Cb - 6.0w/o Cr - 2.5w/o Al, directionally solidified at 3 cm/hr met or exceeded each program goal. A second alloy, Ni-21.75 w/o Cb-2.55 w/o Al, although deficient in its inherent oxidation resistance, met the other program goals and combined a remarkable insensitivity of composite microstructure to solidification parameters with excellent low temperature toughness. This investigation demonstrated that useful properties for gas turbine airfoil application have been achieved by reinforcing a strong and tough gamma solid solution matrix containing precipitated gamma prime by a lamellar intermetallic compound Ni3 Cb having greater strength at elevated temperature.

Direct Cast U-6Nb – 2017 Progress on Cylindrical Castings

DOE Office of Scientific and Technical Information (OSTI.GOV)

Aikin, Jr., Robert M.

2017-10-04

This report describes work to further develop a sound technical basis and best practices for mold design and process parameters for the Direct Casting of U-6wt%Nb components. One major challenge to the production of U-6Nb components is the propensity for niobium segregation during casting and solidification. This is especially true for cylindrical castings where the vertical side walls allow flotation of Nb resulting in severe inverse macrosegregation. In this work, a small (120 mm diameter by 180 mm tall) and large cylinder (250 mm diameter by 310 mm tall) are examined with a focus on reducing, or eliminating, niobium segregation.more » It is demonstrated that counter gravity casting (top-to-bottom solidification) can be used to minimize segregation in the small cylinder. Attempts to counter gravity cast the large cylinder were unsuccessful, in large part due to size limitations of the current furnace. A path forward for casting of the large cylinders is discussed.« less

Real-Time Investigation of Solidification of Metal Matrix Composites

NASA Technical Reports Server (NTRS)

Kaukler, William; Sen, Subhayu

1999-01-01

Casting of metal matrix composites can develop imperfections either as non- uniform distributions of the reinforcement phases or as outright defects such as porosity. The solidification process itself initiates these problems. To identify or rectify the problems, one must be able to detect and to study how they form. Until, recently this was only possible by experiments that employed transparent metal model organic materials with glass beads to simulate the reinforcing phases. Recent results obtained from a Space Shuttle experiment (using transparent materials) will be used to illustrate the fundamental physics that dictates the final distribution of agglomerates in a casting. We have further extended this real time investigation to aluminum alloys using X-ray microscopy. A variety of interface-particle interactions will be discussed and how they alter the final properties of the composite. A demonstration of how a solid-liquid interface is distorted by nearby voids or particles, particle pushing or engulfment by the interface, formations of wormholes, Aggregation of particles, and particle-induced segregation of alloying elements will be presented.

Numerical modeling of keyhole dynamics in laser welding

NASA Astrophysics Data System (ADS)

Zhang, Wen-Hai; Zhou, Jun; Tsai, Hai-Lung

2003-03-01

Mathematical models and the associated numerical techniques have been developed to study the following cases: (1) the formation and collapse of a keyhole, (2) the formation of porosity and its control strategies, (3) laser welding with filler metals, and (4) the escape of zinc vapor in laser welding of galvanized steel. The simulation results show that the formation of porosity in the weld is caused by two competing mechanisms: one is the solidification rate of the molten metal and the other is the speed that molten metal backfills the keyhole after laser energy is terminated. The models have demonstrated that porosity can be reduced or eliminated by adding filler metals, controlling laser tailing power, or applying an electromagnetic force during keyhole collapse process. It is found that a uniform composition of weld pool is difficult to achieve by filler metals due to very rapid solidification of the weld pool in laser welding, as compared to that in gas metal arc welding.

Microstructural Characterization of a Directionally-Solidified Ni-33 (at. %)Al-31Cr-3Mo Eutectic Alloy as a Function of Withdrawal Rate

NASA Technical Reports Server (NTRS)

Raj, S. V.; Locci, I. E.; Whittenberger, J. D.; Salem, J. A.

2000-01-01

The Ni-33 (at. %)Al-3lCr-3Mo eutectic alloy was directionally-solidified (DS) at different rates, V(sub I), varying between 2.5 to 508 mm/ h. Detailed qualitative and quantitative metallographic and chemical analyses were conducted on the directionally-solidified rods. The microstructures consisted of eutectic colonies with parallel lamellar NiAl/(Cr,Mo) plates for solidification rates at and below 12.7 mm/ h. Cellular eutectic microstructures were observed at higher solidification rates, where the plates exhibited a radial pattern. The microstructures were demonstrated to be fairly uniform throughout a 100 mm length of the DS zone by quantitative metallography. The average cell size, bar-d, decreased with increasing growth rate to a value of 125 microns at 508 mm/ h according to the relation bar-d (microns) approx. = 465 V(sup -0.22, sub I), where V(sub I) is in mm/ h. Both the average NiAl plate thickness, bar-Delta(sub NiAl), and the interlamellar spacing, bar-lambda, were observed to be constant for V(sub I) less than or = 50.8 mm/ h but decreased with increasing growth rate above this value as 0.93 bar-Delta(sub NiAl)(microns) = 61.2 V(sup -0.93, sub I) and bar-lambda (microns) = 47.7 V(sup -0.64, sub I), respectively. The present results are detailed on a microstructural map. Keywords Optical microscopy, microstructure, compounds intermetallic, directional solidification

Dispersive solid-phase extraction followed by vortex-assisted dispersive liquid-liquid microextraction based on the solidification of a floating organic droplet for the determination of benzoylurea insecticides in soil and sewage sludge.

PubMed

Peng, Guilong; He, Qiang; Mmereki, Daniel; Lu, Ying; Zhong, Zhihui; Liu, Hanyang; Pan, Weiliang; Zhou, Guangming; Chen, Junhua

2016-04-01

A novel dispersive solid-phase extraction combined with vortex-assisted dispersive liquid-liquid microextraction based on solidification of floating organic droplet was developed for the determination of eight benzoylurea insecticides in soil and sewage sludge samples before high-performance liquid chromatography with ultraviolet detection. The analytes were first extracted from the soil and sludge samples into acetone under optimized pretreatment conditions. Clean-up of the extract was conducted by dispersive solid-phase extraction using activated carbon as the sorbent. The vortex-assisted dispersive liquid-liquid microextraction based on solidification of floating organic droplet procedure was performed by using 1-undecanol with lower density than water as the extraction solvent, and the acetone contained in the solution also acted as dispersive solvent. Under the optimum conditions, the linearity of the method was in the range 2-500 ng/g with correlation coefficients (r) of 0.9993-0.9999. The limits of detection were in the range of 0.08-0.56 ng/g. The relative standard deviations varied from 2.16 to 6.26% (n = 5). The enrichment factors ranged from 104 to 118. The extraction recoveries ranged from 81.05 to 97.82% for all of the analytes. The good performance has demonstrated that the proposed methodology has a strong potential for application in the multiresidue analysis of complex matrices. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Some Pecularities of Solidification of the Almandine Impact Melt

NASA Astrophysics Data System (ADS)

Feldman, V. I.; Kozlov, E. A.; Zhugin, Yu. N.

1996-03-01

SOME PECULIARITIES OF SOLIDIFICATION OF THE ALMANDINE IMPACT MELT. Feldman V.I. Moscow State University, Geological Faculty, Department of Petrology, 119899, Moscow, Russia. Kozlov E.A., Zhugin Yu.N. Russian Federal nuclear Center - Research Institute of Technical Physics, P.O.Box 245, 456770, Snezhinsk, Russia. The aim of these investigations is a description of the experiments and the first results of a loading of the garnet sand by spherical converging shock waves. These experiments show that impact liquid have by solidification three stage of liquid immiscibility.

The use of molten salts as physical models for the study of solidification in metals and semiconductors

NASA Technical Reports Server (NTRS)

Koziol, Jurek K.; Sadoway, Donald R.

1987-01-01

It is presently noted that molten salts possess attributes rendering them attractive as physical models of cast metals in solidification studies. Molten alkali halides have an approximately correct Prandtl number for this modeling of metallic melts, and are transparent to visible light. Attention is given to solidification in the LiCl-KCl system, in order to determine whether such phenomena as solute rejection can be observed and characterized through the application of laser schlieren imaging.

An approximate formula for recalescence in binary eutectic alloys

NASA Technical Reports Server (NTRS)

Ohsaka, K.; Trinh, E. H.

1993-01-01

In alloys, solidification takes place along various paths which may be ascertained via phase diagrams; while there would be no single formula applicable to all alloys, an approximate formula for a specific solidification path would be useful in estimating the fraction of the solid formed during recalescence. A formulation is here presented of recalescence in binary eutectic alloys. This formula is applied to Ag-Cu alloys which are of interest in containerless solidification, due to their formation of supersaturated solutions.

B Removal by Zr Addition in Electromagnetic Solidification Refinement of Si with Si-Al Melt

NASA Astrophysics Data System (ADS)

Lei, Yun; Ma, Wenhui; Sun, Luen; Dai, Yongnian; Morita, Kazuki

2016-02-01

This study investigated a new process of enhancing B removal by adding small amounts of Zr in the electromagnetic solidification refinement of Si with Si-Al melt. B in Si was removed by as much as 97.2 pct by adding less than 1057 ppma Zr, and the added Zr was removed by as much as 99.7 pct. In addition, Zr is more effective in enhancing B removal than Ti in the same electromagnetic solidification refining process.

Absence of solute drag in solidification

NASA Astrophysics Data System (ADS)

Kittl, J. A.; Aziz, M. J.; Brunco, D. P.; Thompson, M. O.

1994-05-01

The interface response functions for alloy solidification were measured in the nondegenerate regime of partial solute trapping. We used a new technique to measure temperatures and velocities simultaneously during rapid solidification of Si-As alloys induced by pulsed laser melting. In addition, partition coefficients were determined using Rutherford backscattering. The results are in good agreement with predictions of the Continuous Growth Model without solute drag of M. J. Aziz and T. Kaplan [Acta Metall. 36, 1335 (1988)] and are inconsistent with all solute drag models.

Design of a High Thermal Gradient Bridgman Furnace

NASA Technical Reports Server (NTRS)

LeCroy, J. E.; Popok, D. P.

1994-01-01

The Advanced Automated Directional Solidification Furnace (AADSF) is a Bridgman-Stockbarger microgravity processing facility, designed and manifested to first fly aboard the second United States Microgravity Payload (USMP-2) Space Shuttle mission. The AADSF was principally designed to produce high axial thermal gradients, and is particularly suitable for metals solidification experiments, including non-dilute alloys. To accommodate a wider range of experimental conditions, the AADSF is equipped with a reconfigurable gradient zone. The overall design of the AADSF and the relationship between gradient zone design and furnace performance are described. Parametric thermal analysis was performed and used to select gradient zone design features that fulfill the high thermal gradient requirements of the USMP-2 experiment. The thermal model and analytical procedure, and parametric results leading to the first flight gradient zone configuration, are presented. Performance for the USMP-2 flight experiment is also predicted, and analysis results are compared to test data.

Overview of waste stabilization with cement.

PubMed

Batchelor, B

2006-01-01

Cement can treat a variety of wastes by improving physical characteristics (solidification) and reducing the toxicity and mobility of contaminants (stabilization). Potentially adverse waste-binder interactions are an important consideration because they can limit solidification. Stabilization occurs when a contaminant is converted from the dissolved (mobile) phase to a solid (immobile) phase by reactions, such as precipitation, sorption, or substitution. These reactions are often strongly affected by pH, so the presence of components of the waste that control pH are critical to stabilization reactions. Evaluating environmental impacts can be accomplished in a tiered strategy in which simplest approach would be to measure the maximum amount of contaminant that could be released. Alternatively, the sequence of release can be determined, either by microcosm tests that attempt to simulate conditions in the disposal zone or by mechanistic models that attempt to predict behavior using fundamental characteristics of the treated waste.

Alloy and structural optimization of a directionally solidified lamellar eutectic alloy

NASA Technical Reports Server (NTRS)

Sheffler, K. D.

1976-01-01

Mechanical property characterization tests of a directionally solidified Ni-20 percent Cb-2.5 percent Al-6 percent Cr cellular eutectic turbine blade alloy demonstrated excellent long time creep stability and indicated intermediate temperature transverse tensile ductility and shear strength to be somewhat low for turbine blade applications. Alloy and structural optimization significantly improves these off-axis properties with no loss of longitudinal creep strength or stability. The optimized alloy-structure combination is a carbon modified Ni-20.1 percent Cb-2.5 percent Al-6.0 percent Cr-0.06 percent C composition processed under conditions producing plane front solidification and a fully-lamellar microstructure. With current processing technology, this alloy exhibits a creep-rupture advantage of 39 C over the best available nickel base superalloy, directionally solidified MAR M200+ Hf. While improved by about 20 percent, shear strength of the optimized alloy remains well below typical superalloy values.

Physico-chemical characterisation, cytotoxic activity, and biocompatibility studies of tamoxifen-loaded solid lipid nanoparticles prepared via a temperature-modulated solidification method.

PubMed

Lakkadwala, Sushant; Nguyen, Sanko; Lawrence, Joseph; Nauli, Surya M; Nesamony, Jerry

2014-01-01

Solid lipid nanoparticles (SLNs) can efficiently and efficaciously incorporate anti-cancer agents. To prepare and characterise tamoxifen (TAM)-loaded SLNs. Glyceryl monostearate, Tween-80, and trehalose were used in SLNs. SLNs were tested via dynamic light scattering (DLS), transmission electron microscopy (TEM), differential scanning calorimetry (DSC), X-ray diffraction (XRD), and Fourier transform infrared spectroscopy (FTIR). Characterisation studies revealed SLNs of about 540 nm with a negative surface charge and confirmed the entrapment of TAM in the SLNs. The entrapment efficiency was estimated to be 60%. The in vitro drug release profile demonstrated a gradual increase followed by a release plateau for several days. A drug concentration-dependent increase in cytotoxic activity was observed when the SLNs were evaluated in cell cultures. Biocompatible and stable lyophilised SLNs were successfully prepared and found to possess properties that may be utilised in an anti-cancer drug delivery system.

Two-dimensional freezing criteria for crystallizing colloidal monolayers

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wang Ziren; Han Yilong; Alsayed, Ahmed M.

Video microscopy was employed to explore crystallization of colloidal monolayers composed of diameter-tunable microgel spheres. Two-dimensional (2D) colloidal liquids were frozen homogenously into polycrystalline solids, and four 2D criteria for freezing were experimentally tested in thermal systems for the first time: the Hansen-Verlet freezing rule, the Loewen-Palberg-Simon dynamical freezing criterion, and two other rules based, respectively, on the split shoulder of the radial distribution function and on the distribution of the shape factor of Voronoi polygons. Importantly, these freezing criteria, usually applied in the context of single crystals, were demonstrated to apply to the formation of polycrystalline solids. At themore » freezing point, we also observed a peak in the fluctuations of the orientational order parameter and a percolation transition associated with caged particles. Speculation about these percolated clusters of caged particles casts light on solidification mechanisms and dynamic heterogeneity in freezing.« less

Fundamentals of Alloy Solidification Applied to Industrial Processes

NASA Technical Reports Server (NTRS)

1984-01-01

Solidification processes and phenomena, segregation, porosity, gravity effects, fluid flow, undercooling, as well as processing of materials in the microgravity environment of space, now available on space shuttle flights were discussed.

A Citizen's Guide to Solidification and Stabilization

EPA Pesticide Factsheets

This guide describes how solidification and stabilization refer to a group of cleanup methods that prevent or slow the release of harmful chemicals from wastes, such as contaminated soil, sediment, and sludge.

Large Eddy Simulation of Transient Flow, Solidification, and Particle Transport Processes in Continuous-Casting Mold

NASA Astrophysics Data System (ADS)

Liu, Zhongqiu; Li, Linmin; Li, Baokuan; Jiang, Maofa

2014-07-01

The current study developed a coupled computational model to simulate the transient fluid flow, solidification, and particle transport processes in a slab continuous-casting mold. Transient flow of molten steel in the mold is calculated using the large eddy simulation. An enthalpy-porosity approach is used for the analysis of solidification processes. The transport of bubble and non-metallic inclusion inside the liquid pool is calculated using the Lagrangian approach based on the transient flow field. A criterion of particle entrapment in the solidified shell is developed using the user-defined functions of FLUENT software (ANSYS, Inc., Canonsburg, PA). The predicted results of this model are compared with the measurements of the ultrasonic testing of the rolled steel plates and the water model experiments. The transient asymmetrical flow pattern inside the liquid pool exhibits quite satisfactory agreement with the corresponding measurements. The predicted complex instantaneous velocity field is composed of various small recirculation zones and multiple vortices. The transport of particles inside the liquid pool and the entrapment of particles in the solidified shell are not symmetric. The Magnus force can reduce the entrapment ratio of particles in the solidified shell, especially for smaller particles, but the effect is not obvious. The Marangoni force can play an important role in controlling the motion of particles, which increases the entrapment ratio of particles in the solidified shell obviously.

A study on polypropylene encapsulation and solidification of textile sludge.

PubMed

Kumari, V Krishna; Kanmani, S

2011-10-01

The textile sludge is an inevitable solid waste from the textile wastewater process and is categorised under toxic substances by statutory authorities. In this study, an attempt has been made to encapsulate and solidify heavy metals and dyes present in textile sludge using polypropylene and Portland cement. Sludge samples (2 Nos.) were characterized for pH (8.5, 9.5), moisture content (1.5%, 1.96%) and chlorides (245mg/L, 425.4mg/L). Sludge samples were encapsulated into polypropylene with calcium carbonate (additive) and solidified with cement at four different proportions (20, 30, 40, 50%) of sludge. Encapsulated and solidified cubes were made and then tested for compressive strength. Maximum compressive strength of cubes (size, 7.06cm) containing sludge (50%) for encapsulation (16.72 N/mm2) and solidification (18.84 N/mm2) was more than that of standard M15 mortar cubes. The leachability of copper, nickel and chromium has been effectively reduced from 0.58 mg/L, 0.53 mg/L and 0.07 mg/L to 0.28mg/L, 0.26mg/L and BDL respectively in encapsulated products and to 0.24mg/L, BDL and BDL respectively in solidified products. This study has shown that the solidification process is slightly more effective than encapsulation process. Both the products were recommended for use in the construction of non-load bearing walls.

Small hazardous waste generators in developing countries: use of stabilization/solidification process as an economic tool for metal wastewater treatment and appropriate sludge disposal.

PubMed

Silva, Marcos A R; Mater, Luciana; Souza-Sierra, Maria M; Corrêa, Albertina X R; Sperb, Rafael; Radetski, Claudemir M

2007-08-25

The aim of this study was to propose a profitable destination for an industrial sludge that can cover the wastewater treatment costs of small waste generators. Optimized stabilization/solidification technology was used to treat hazardous waste from an electroplating industry that is currently released untreated to the environment. The stabilized/solidified (S/S) waste product was used as a raw material to build concrete blocks, to be sold as pavement blocks or used in roadbeds and/or parking lots. The quality of the blocks containing a mixture of cement, lime, clay and waste was evaluated by means of leaching and solubility tests according to the current Brazilian waste regulations. Results showed very low metal leachability and solubility of the block constituents, indicating a low environmental impact. Concerning economic benefits from the S/S process and reuse of the resultant product, the cost of untreated heavy metal-containing sludge disposal to landfill is usually on the order of US$ 150-200 per tonne of waste, while 1tonne of concrete roadbed blocks (with 25% of S/S waste constitution) has a value of around US$ 100. The results of this work showed that the cement, clay and lime-based process of stabilization/solidification of hazardous waste sludge is sufficiently effective and economically viable to stimulate the treatment of wastewater from small industrial waste generators.

The management of arsenic wastes: problems and prospects.

PubMed

Leist, M; Casey, R J; Caridi, D

2000-08-28

Arsenic has found widespread use in agriculture and industry to control a variety of insect and fungicidal pests. Most of these uses have been discontinued, but residues from such activities, together with the ongoing generation of arsenic wastes from the smelting of various ores, have left a legacy of a large number of arsenic-contaminated sites. The treatment and/or removal of arsenic is hindered by the fact that arsenic has a variety of valence states. Arsenic is most effectively removed or stabilized when it is present in the pentavalent arsenate form. For the removal of arsenic from wastewater, coagulation, normally using iron, is the preferred option. The solidification/stabilization of arsenic is not such a clear-cut process. Factors such as the waste's interaction with the additives (e.g. iron or lime), as well as any effect on the cement matrix, all impact on the efficacy of the fixation. Currently, differentiation between available solidification/stabilization processes is speculative, partly due to the large number of differing leaching tests that have been utilized. Differences in the leaching fluid, liquid-to-solid ratio, and agitation time and method all impact significantly on the arsenic leachate concentrations. This paper reviews options available for dealing with arsenic wastes, both solid and aqueous through an investigation of the methods available for the removal of arsenic from wastewater as well as possible solidification/stabilization options for a variety of waste streams.

Improved Foundry Castings Utilizing CAD/CAM (Computer Aided Design/ Computer Aided Manufacture). Volume 1. Overview

DTIC Science & Technology

1988-06-30

casting. 68 Figure 1-9: Line printer representation of roll solidification. 69 Figure I1-1: Test casting model. 76 Figure 11-2: Division of test casting...writing new casting analysis and design routines. The new routines would take advantage of advanced criteria for predicting casting soundness and cast...properties and technical advances in computer hardware and software. 11 2. CONCLUSIONS UPCAST, a comprehensive software package, has been developed for

Segregation and convection in dendritic alloys

NASA Technical Reports Server (NTRS)

Poirier, D. R.

1990-01-01

Microsegregation in dentritic alloys is discussed, including solidification with and without thermal gradient, the convection of interdendritic liquid. The conservation of momentum, energy, and solute is considered. Directional solidification and thermosolutal convection are discussed.

Positive segregation as a function of buoyancy force during steel ingot solidification.

PubMed

Radovic, Zarko; Jaukovic, Nada; Lalovic, Milisav; Tadic, Nebojsa

2008-12-01

We analyze theoretically and experimentally solute redistribution in the dendritic solidification process and positive segregation during solidification of steel ingots. Positive segregation is mainly caused by liquid flow in the mushy zone. Changes in the liquid steel velocity are caused by the temperature gradient and by the increase in the solid fraction during solidification. The effects of buoyancy and of the change in the solid fraction on segregation intensity are analyzed. The relationships between the density change, liquid fraction and the steel composition are considered. Such elements as W, Ni, Mo and Cr decrease the effect of the density variations, i.e. they show smaller tendency to segregate. Based on the modeling and experimental results, coefficients are provided controlling the effects of chemical composition, secondary dendrite arm spacing and the solid fraction.

Improvements to quality of needle coke by controlled carbonized conditions

NASA Astrophysics Data System (ADS)

Liu, Dong; Lou, Bin; Yu, Ran; Chen, Qingtai; Li, Zhiheng; Zhang, Yadong

2018-06-01

In this study, the selected aromatic-rich fraction derived from hydrocracking tail oil was carbonized and further improvement in the quality of resultant coke was achieved by promoting temperature at the solidification stage. In comparison with conventional process carried out isothermally and isobarically, the coupling analysis between formation and subsequent uni-axial orientation of mesophase textures during the controlled process was systematically discussed on the basis of the mutual relevance among mesophase texture evolution, gas evolution rate and solidification rate of intermediates. The results show that on the premise that formation of bulk mesophase, appropriate rate of gas evolution at a right time of solidification contributes to fine produces fine fibrous mesophase aligned uni-axially and less pores. Moreover, the intermediates with solidification index of 2˜6 are suitable for deformation induced by gas evolution.

Solidification Dynamics of Spherical Drops in a Free Fall Environment

NASA Technical Reports Server (NTRS)

Grugel, Richard N.; Brush, Lucien N.

2006-01-01

Silver drops (99.9%, 4, 5, 7, and 9 mm diameter) were levitated, melted, and released to fall through Marshall Space Flight Center's 105 meter drop tube in helium - 6% hydrogen and pure argon atmospheres. By varying a drop s initial superheat the extent of solidification prior to impact ranged from complete to none during the approx. 4.6s of free fall time. Comparison of the experimental observations is made with numerical solutions to a model of the heat transfer and solidification kinetics associated with cooling of the drop during free fall, particularly with regard to the fraction of liquid transformed. Analysis reveals the relative importance ,of the initial parameters affecting the cooling and solidification rates within the drop. A discussion of the conditions under which the actual observations deviate from the assumptions used in the model is presented.

Solidification Dynamics of Metal Drops in a Free Fall Environment

NASA Technical Reports Server (NTRS)

Grugel, R. N.; Brush, L. N.; Curreri, Peter A. (Technical Monitor)

2001-01-01

Comparison of experimental observations were made with numerical solutions to a model of the heat transfer and solidification kinetics associated with the cooling of a molten drop during free fall, particularly with regard to the fraction of liquid transformed. Experimentally, silver drops (99.9%, 4-9 mm diameter) were levitated, melted, and released to fall through Marshall Space Flight Center's 105m drop tube in helium - 6% hydrogen and argon atmospheres. By systematically varying the drops initial superheat the extent of solidification prior to impact ranged from complete to none during the approximately 4.6s of free fall time. Analysis reveals the relative importance of the initial parameters affecting the cooling and solidification rates within the drop. A discussion of the conditions under which the actual observations deviate from the assumptions used in the model is presented.

Microstructure Formations in the Two-Phase Region of the Binary Peritectic Organic System TRIS-NPG

NASA Technical Reports Server (NTRS)

Mogeritsch, Johann; Ludwig, Andreas

2012-01-01

In order to prepare for an onboard experiment on the International Space Station (ISS), systematic directional solidification experiments with transparent hypoperitectic alloys were carried out at different solidification rates around the critical velocity for morphological stability of both solid phases. The investigations were done in the peritectic region of the binary transparent organic TRIS-NPG system where the formation of layered structures is expected to occur. The transparent appearance of the liquid and solid phase enables real time observations of the dynamic of pattern formation during solidification. The investigations show that frequently occurring nucleation events govern the peritectic solidification morphology which occurs at the limit of morphological stability. As a consequence, banded structures lead to coupled growth even if the lateral growth is much faster compared to the growth in pulling direction.

Effect of boundary heat flux on columnar formation in binary alloys: A phase-field study

NASA Astrophysics Data System (ADS)

Du, Lifei; Zhang, Peng; Yang, Shaomei; Chen, Jie; Du, Huiling

2018-02-01

A non-isothermal phase-field model was employed to simulate the columnar formation during rapid solidification in binary Ni-Cu alloy. Heat flux at different boundaries was applied to investigate the temperature gradient effect on the morphology, concentration and temperature distributions during directional solidifications. With the heat flux input/extraction from boundaries, coupling with latent heat release and initial temperature gradient, temperature distributions are significantly changed, leading to solute diffusion changes during the phase-transition. Thus, irregular columnar structures are formed during the directional solidification, and the concentration distribution in solid columnar arms could also be changed due to the different growing speeds and temperature distributions at the solid-liquid interfaces. Therefore, applying specific heat conditions at the solidifying boundaries could be an efficient way to control the microstructure during solidifications.

Development of cement solidification process for sodium borate waste generated from PWR plants

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hirofumi Okabe; Tatsuaki Sato; Yuichi Shoji

2013-07-01

A cement solidification process for treating sodium borate waste produced in pressurized water reactor (PWR) plants was studied. To obtain high volume reduction and high mechanical strength of the waste, simulated concentrated borate liquid waste with a sodium / boron (Na/B) mole ratio of 0.27 was dehydrated and powdered by using a wiped film evaporator. To investigate the effect of the Na/B mole ratio on the solidification process, a sodium tetraborate decahydrate reagent with a Na/B mole ratio of 0.5 was also used. Ordinary portland cement (OPC) and some additives were used for the solidification. Solidified cement prepared from powderedmore » waste with a Na/B mole ratio 0.24 and having a high silica sand content (silica sand/cement>2) showed to improved uniaxial compressive strength. (authors)« less

Improved stress corrosion cracking resistance of a novel biodegradable EW62 magnesium alloy by rapid solidification, in simulated electrolytes.

PubMed

Hakimi, O; Aghion, E; Goldman, J

2015-06-01

The high corrosion rate of magnesium (Mg) and Mg-alloys precludes their widespread acceptance as implantable biomaterials. Here, we investigated the potential for rapid solidification (RS) to increase the stress corrosion cracking (SCC) resistance of a novel Mg alloy, Mg-6%Nd-2%Y-0.5%Zr (EW62), in comparison to its conventionally cast (CC) counterpart. RS ribbons were extrusion consolidated in order to generate bioimplant-relevant geometries for testing and practical use. Microstructural characteristics were examined by SEM. Corrosion rates were calculated based upon hydrogen evolution during immersion testing. The surface layer of the tested alloys was analyzed by X-ray photoelectron spectroscopy (XPS). Stress corrosion resistance was assessed by slow strain rate testing and fractography. The results indicate that the corrosion resistance of the RS alloy is significantly improved relative to the CC alloy due to a supersaturated Nd enrichment that increases the Nd2O3 content in the external oxide layer, as well as a more homogeneous structure and reduced grain size. These improvements contributed to the reduced formation of hydrogen gas and hydrogen embrittlement, which reduced the SCC sensitivity relative to the CC alloy. Therefore, EW62 in the form of a rapidly solidified extruded structure may serve as a biodegradable implant for biomedical applications. Copyright © 2015 Elsevier B.V. All rights reserved.

Solidification Microstructure, Segregation, and Shrinkage of Fe-Mn-C Twinning-Induced Plasticity Steel by Simulation and Experiment

NASA Astrophysics Data System (ADS)

Lan, Peng; Tang, Haiyan; Zhang, Jiaquan

2016-06-01

A 3D cellular automaton finite element model with full coupling of heat, flow, and solute transfer incorporating solidification grain nucleation and growth was developed for a multicomponent system. The predicted solidification process, shrinkage porosity, macrosegregation, grain orientation, and microstructure evolution of Fe-22Mn-0.7C twinning-induced plasticity (TWIP) steel match well with the experimental observation and measurement. Based on a new solute microsegregation model using the finite difference method, the thermophysical parameters including solid fraction, thermal conductivity, density, and enthalpy were predicted and compared with the results from thermodynamics and experiment. The effects of flow and solute transfer in the liquid phase on the solidification microstructure of Fe-22Mn-0.7C TWIP steel were compared numerically. Thermal convection decreases the temperature gradient in the liquid steel, leading to the enlargement of the equiaxed zone. Solute enrichment in front of the solid/liquid interface weakens the thermal convection, resulting in a little postponement of columnar-to-equiaxed transition (CET). The CET behavior of Fe-Mn-C TWIP steel during solidification was fully described and mathematically quantized by grain morphology statistics for the first time. A new methodology to figure out the CET location by linear regression of grain mean size with least-squares arithmetic was established, by which a composition design strategy for Fe-Mn-C TWIP steel according to solidification microstructure, matrix compactness, and homogeneity was developed.

Sill and Laccolith growth by Inflation and Propagation--just not necessarily at the same time

NASA Astrophysics Data System (ADS)

Currier, R. M.; Marsh, B. D.

2013-12-01

Sill and laccolith growth is achieved by two key mechanisms, inflation (vertical growth) and propagation (radial growth). Of the myriad of models proposed for magmatic intrusion, all are variations on the same theme--some combination of inflation and propagation. Because of the inherent observational limitations in studying actual high-level crustal magma emplacement, there remains a poor consensus on any preferred model. To gain insight we have performed a series of simple experiments using layered gelatin as a viscoelastic crustal analog, and molten wax as magma analog. Wax is injected from the base of the gelatin mold, begins ascent as a dike, and is captured by the overlying, more rigid, layer of gelatin. The use of a solidifying magma analog separates these experiments from other gelatin-based studies. When water is used, a common choice for magma analog, the intrusion propagates in an extremely smooth manner. However, at the tip of any magma filled crack, where thickness is at a minimum, propagation and solidification are in fierce competition. The introduction of solidification reveals that emplacement actually occurs as a series of ensuing pulses--at times propagating and inflating concurrently, and at other times growth is achieved solely through propagation, or solely inflation. Unlike models without solidification, here no single combination of propagation and inflation accounts for growth, but rather, the different styles of emplacement reflect the relative competitiveness of propagation and solidification at that time and location. When propagation is fast relative to solidification, growth is smooth, and propagation and inflation occur simultaneously. When solidification dominates, propagation ceases, and growth by inflation becomes the chief emplacement mechanism. Nevertheless, regardless of the strong effect of solidification, building backpressure and the associated crack stresses can disrupt the chill zone at the sill edge, and bring on rapid propagation of magma in conjunction with overall sill deflation. Because the competitiveness of solidification increases with decreasing propagation velocity, and because propagation velocity of a growing magma body must necessarily decrease with time, these mechanisms are a fundamental feature of any magma body that grows for any extended period. Generally, larger flux rates correlate to larger radii and thinner sills. For classical laccolith formation, flux rate must be slow enough for solidification to curtail propagation at an early stage, effectively limiting radial growth and promoting further growth solely via inflation. The effects of this overall process occurs on multiple scales, and the history of the chilled margins can be clearly seen with a series of essentially ';chatter rinds' marking the staccato process of emplacement.

Research of metal solidification in zero-g state. [test apparatus and instrumentation

NASA Technical Reports Server (NTRS)

Aubin, W. M.; Larson, D., Jr.; Geschwind, G. I.

1973-01-01

An experiment test apparatus that allows metal melting and resolidification in the three seconds available during free fall in a drop tower was built and tested in the tower. Droplets (approximately 0.05 cm) of pure nickel and 1090 steel were prepared in this fashion. The apparatus, including instrumentation, is described. As part of the instrumentation, a method for measuring temperature-time histories of the free floating metal droplets was developed. Finally, a metallurgical analysis of the specimens prepared in the apparatus is presented.

The influence of buoyant forces and volume fraction of particles on the particle pushing/entrapment transition during directional solidification of Al/SiC and Al/graphite composites

NASA Technical Reports Server (NTRS)

Stefanescu, Doru M.; Moitra, Avijit; Kacar, A. Sedat; Dhindaw, Brij K.

1990-01-01

Directional solidification experiments in a Bridgman-type furnace were used to study particle behavior at the liquid/solid interface in aluminum metal matrix composites. Graphite or silicon-carbide particles were first dispersed in aluminum-base alloys via a mechanically stirred vortex. Then, 100-mm-diameter and 120-mm-long samples were cast in steel dies and used for directional solidification. The processing variables controlled were the direction and velocity of solidification and the temperature gradient at the interface. The material variables monitored were the interface energy, the liquid/particle density difference, the particle/liquid thermal conductivity ratio, and the volume fraction of particles. These properties were changed by selecting combinations of particles (graphite or silicon carbide) and alloys (Al-Cu, Al-Mg, Al-Ni). A model which consideres process thermodynamics, process kinetics (including the role of buoyant forces), and thermophysical properties was developed. Based on solidification direction and velocity, and on materials properties, four types of behavior were predicted. Sessile drop experiments were also used to determine some of the interface energies required in calculation with the proposed model. Experimental results compared favorably with model predictions.

Metal Solidification Imaging Process by Magnetic Induction Tomography.

PubMed

Ma, Lu; Spagnul, Stefano; Soleimani, Manuchehr

2017-11-06

There are growing number of important applications that require a contactless method for monitoring an object surrounded inside a metallic enclosure. Imaging metal solidification is a great example for which there is no real time monitoring technique at present. This paper introduces a technique - magnetic induction tomography - for the real time in-situ imaging of the metal solidification process. Rigorous experimental verifications are presented. Firstly, a single inductive coil is placed on the top of a melting wood alloy to examine the changes of its inductance during solidification process. Secondly, an array of magnetic induction coils are designed to investigate the feasibility of a tomographic approach, i.e., when one coil is driven by an alternating current as a transmitter and a vector of phase changes are measured from the remaining of the coils as receivers. Phase changes are observed when the wood alloy state changes from liquid to solid. Thirdly, a series of static cold phantoms are created to represent various liquid/solid interfaces to verify the system performance. Finally, a powerful temporal reconstruction method is applied to realise real time in-situ visualisation of the solidification and the measurement of solidified shell thickness, a first report of its kind.

The influence of buoyant forces and volume fraction of particles on the particle pushing/entrapment transition during directional solidification of Al/SiC and Al/graphite composites

NASA Astrophysics Data System (ADS)

Stefanescu, Doru M.; Moitra, Avijit; Kacar, A. Sedat; Dhindaw, Brij K.

1990-01-01

Directional solidification experiments in a Bridgman-type furnace were used to study particle behavior at the liquid/solid interface in aluminum metal matrix composites. Graphite or siliconcarbide particles were first dispersed in aluminum-base alloys via a mechanically stirred vortex. Then, 100-mm-diameter and 120-mm-long samples were cast in steel dies and used for directional solidification. The processing variables controlled were the direction and velocity of solidification and the temperature gradient at the interface. The material variables monitored were the interface energy, the liquid/particle density difference, the particle/liquid thermal conductivity ratio, and the volume fraction of particles. These properties were changed by selecting combinations of particles (graphite or silicon carbide) and alloys (Al-Cu, Al-Mg, Al-Ni). A model which considers process thermodynamics, process kinetics (including the role of buoyant forces), and thermophysical properties was developed. Based on solidification direction and velocity, and on materials properties, four types of behavior were predicted. Sessile drop experiments were also used to determine some of the interface energies required in calculation with the proposed model. Experimental results compared favorably with model predictions.

Examination of Multiphase (Zr,Ti)(V,Cr,Mn,Ni)2 Ni-MH Electrode Alloys: Part I. Dendritic Solidification Structure

NASA Astrophysics Data System (ADS)

Boettinger, W. J.; Newbury, D. E.; Wang, K.; Bendersky, L. A.; Chiu, C.; Kattner, U. R.; Young, K.; Chao, B.

2010-08-01

The solidification microstructures of three nine-element Zr-Ni-based AB2 type C14/C15 Laves hydrogen storage alloys are determined. The selected compositions represent a class of alloys being examined for usage as an MH electrode in nickel metal-hydride batteries that often have their best properties in the cast state. Solidification is accomplished by dendritic growth of hexagonal C14 Laves phase, peritectic solidification of cubic C15 Laves phase, and formation of cubic B2 phase in the interdendritic regions. The B2 phase decomposes in the solid state into a complex multivariate platelike structure containing Zr-Ni-rich intermetallics. The observed sequence C14/C15 upon solidification agrees with predictions using effective compositions and thermodynamic assessments of the ternary systems, Ni-Cr-Zr and Cr-Ti-Zr. Experimentally, the closeness of the compositions of the C14 and C15 phases required the use of compositional mapping with an energy dispersive detector capable of processing a very high X-ray flux to locate regions in the microstructure for quantitative composition measurement and transmission electron microscope examination.

Metastable phase formation in undercooled Fe-Co melts under terrestrial and parabolic flight conditions

NASA Astrophysics Data System (ADS)

Hermann, R.; Löser, W.; Lindenkreuz, H. G.; Yang-Bitterlich, W.; Mickel, Ch.; Diefenbach, A.; Schneider, S.; Dreier, W.

2007-12-01

Soft magnetic Fe-Co alloys display primary fcc phase solidification for>19,5 at% Co in conventional near-equilibrium solidification processes. Undercooled Fe-Co melt drops within the composition range of 30 to 50 at% Co have been investigated with the electromagnetic levitation technique. The solidification kinetics was measured in situ using a high-resolution Siphotodiode. Melt drops were undercooled up to 263 K below the liquidus temperature and subsequently quenched onto a chill substrate in order to characterize the solidification sequence and microstructure. The transition from stable fcc phase to metastable bcc primary phase solidification has been observed after reaching a critical undercooling level. The critical undercooling increases with rising Co content. The growth velocity drops obviously after transition to metastable bcc phase formation. Parabolic flight experiments were performed in order to study the phase selection under reduced gravity conditions. Under microgravity conditions, a much smaller critical undercooling and an increased life time of the metastable bcc phase were obtained. This result was validated with TEM investigations. The appearance of Fe-O particles gives an indirect hint for an intermediate fcc phase formation from the metastable bcc phase at elevated temperature.

Effects of Traveling Magnetic Field on Dynamics of Solidification

NASA Technical Reports Server (NTRS)

Mazuruk, Konstantin; Grugel, Richard; Motakef, Shariar

2001-01-01

TMF is based on imposing a controlled phase-shift in a train of electromagnets, forming a stack. Thus, the induced magnetic field can be considered to be travelling along the axis of the stack. The coupling of this traveling wave with an electrically conducting fluid results in a basic flow in a form of a single axisymmetric roll. The magnitude and direction of this flow can be remotely controlled. Furthermore, it is possible to localize the effect of this force field though activating only a number of the magnets. This force field generated in the fluid can, in principle, be used to control and modify convection in the molten material. For example, it can be used to enhance convective mixing in the melt, and thereby modify the interface shape, and macrosegregation. Alternatively, it can be used to counteract thermal and/or solutal buoyancy forces. High frequency TMF can be used in containerless processing techniques, such as float zoning, to affect the very edge of the fluid so that Marangoni flow can be counter balanced. The proposed program consists of basic fundamentals and applications. Our goal in conducting the following experiments and analyses is to establish the validity of TMF as a new tool for solidification processes. Due to its low power consumption and simplicity of design, this tool may find wide spread use in a variety of space experiments. The proposed ground based experiments are intended to establish the advantages and limitations of employing this technique. In the fundamentals component of the proposed program, we will use theoretical tools and experiments with mercury to establish the fundamental aspects of TMF-induced convection through a detailed comparison of theoretical predictions and experimental measurements of flow field. In this work, we will conduct a detailed parametric study involving the effects of magnetic field strength, frequency, wave vector, and the fluid geometry. The applications component of this work will be focused on investigating the effect of TMF on the following solidification and pre-directional solidification processes: (1) Bridgman growth of Ga:Ge with the goal of counteracting the buoyancy-driven convection; (2) Mixing of Pb-Ga and Pb-Sn alloys with the aim of initiating and maintaining a uniform melt prior to solidification processing; and (3) Float Zone growth with the aim of identifying, through simulations and model experiments, conditions needed to counteract Marangoni flow in a microgravity environment. The proposed research has strong relevance to microgravity research and the objectives of the NRA. TMF can provide a unique and accurate mechanism for generation and control of desirable flow patterns for microgravity research. These attributes have significant relevance to 1) Alloy mixing prior to solidification in a microgravity environment. TMF can provide this mixing with a low level of power consumption; (2) TMF can offset the deleterious effects of Marangoni convection in microgravity containerless processing. Thus, TMF can be instrumental in further understanding this phenomena; (3) Generation of controlled flows will allow the investigation of the effect of these flows on growth morphology and growth kinetics; and (4) On Earth, TMF has the potential to significantly counter-balance thermosolutal convection, thereby creating conditions similar to those obtained in microgravity. Once demonstrated, this new tool for use in solidification has the strong potential to find applications in a host of microgravity material research projects.

ENGINEERING BULLETIN: SOLIDIFICATION/STABILIZATION OF ORGANICS AND INORGANICS

EPA Science Inventory

Solidification refers to techniques that encapsulate hazardous waste into a solid material of high structural integrity. Encapsulation involves either fine waste particles (microencapsulation) or a large block or container of wastes (macroencapsulation). Stabilization refe...

Microstructure of ceramics fabricated by unidirectional solidification

NASA Technical Reports Server (NTRS)

Kokubo, T.

1984-01-01

The unidirectional solidification methods are zone melting, crystal pulling, Bridgemen, and slow cooling. In order to obtain excellent properties (such as transparency), pores, voids and cracks must be avoided, and elimination of such defects is described.

Copper-silicon-magnesium alloys for latent heat storage

DOE PAGES

Gibbs, P. J.; Withey, E. A.; Coker, E. N.; ...

2016-06-21

The systematic development of microstructure, solidification characteristics, and heat of solidification with composition in copper-silicon-magnesium alloys for thermal energy storage is presented. Differential scanning calorimetry was used to relate the thermal characteristics to microstructural development in the investigated alloys and clarifies the location of one of the terminal three-phase eutectics. Repeated thermal cycling highlights the thermal storage stability of the transformation through multiple melting events. In conclusion, two near-terminal eutectic alloys display high enthalpies of solidification, relatively narrow melting ranges, and stable transformation hysteresis behaviors suited to thermal energy storage.

Three-dimensional phase-field simulations of directional solidification

NASA Astrophysics Data System (ADS)

Plapp, Mathis

2007-05-01

The phase-field method has become the method of choice for simulating microstructural pattern formation during solidification. One of its main advantages is that time-dependent three-dimensional simulations become feasible, which makes it possible to address long-standing questions of pattern stability and pattern selection. Here, a brief introduction to the phase-field model and its implementation is given, and its capabilities are illustrated by examples taken from the directional solidification of binary alloys. In particular, the morphological stability of hexagonal cellular arrays and of eutectic lamellar patterns is investigated.

Microgravity Processing of Oxide Superconductors

NASA Technical Reports Server (NTRS)

Hofmeister, William H.; Bayuzick, Robert J.; Vlasse, Marcus; McCallum, William; Peters, Palmer (Technical Monitor)

2000-01-01

The primary goal is to understand the microstructures which develop under the nonequilibrium solidification conditions achieved by melt processing in copper oxide superconductor systems. More specifically, to define the liquidus at the Y- 1:2:3 composition, the Nd-1:2:3 composition, and several intermediate partial substitution points between pure Y-1:2:3 and Nd-1:2:3. A secondary goal has been to understand resultant solidification morphologies and pathways under a variety of experimental conditions and to use this knowledge to better characterize solidification phenomena in these systems.

Fluid mechanics and mass transfer in melt crystal growth: Analysis of the floating zone and vertical Bridgman processes

NASA Technical Reports Server (NTRS)

Brown, R. A.

1986-01-01

This research program focuses on analysis of the transport mechanisms in solidification processes, especially one of interest to the Microgravity Sciences and Applications Program of NASA. Research during the last year has focused on analysis of the dynamics of the floating zone process for growth of small-scale crystals, on studies of the effect of applied magnetic fields on convection and solute segregation in directional solidification, and on the dynamics of microscopic cell formation in two-dimensional solidification of binary alloys. Significant findings are given.

Novel Directional Solidification Processing of Hypermonotectic Alloys

NASA Technical Reports Server (NTRS)

Grugel, Richard N.

1999-01-01

Gravity driven separation precludes uniform microstructural development during controlled directional solidification (DS) processing of hypermonotectic alloys. It is well established that liquid/liquid suspensions, in which the respective components are immiscible and have significant density differences, can be established and maintained by utilizing ultrasound. A historical introduction to this work is presented with the intent of establishing the basis for applying the phenomena to promote microstructural uniformity during controlled directional solidification processing of immiscible mixtures. Experimental work based on transparent organics, as well as salt systems, will be presented in view of the processing parameters.

Acoustic emission from a solidifying aluminum-lithium alloy

NASA Technical Reports Server (NTRS)

Henkel, D. P.; Wood, J. D.

1992-01-01

Physical phenomena associated with the solidification of an AA2090 Al-Li alloy have been characterized by AE methods. Repeatable patterns of AE activity as a function of solidification time are recorded and explained for ultrahigh-purity (UHP) aluminum and an Al-4.7 wt pct Cu binary alloy, in addition to the AA2090 Al-Li alloy, by the complementary utilization of thermal, AE, and metallographic methods. One result shows that the solidification of UHP aluminum produces one discrete period of high AE activity as the last 10 percent of solid forms.

An amino acidic adjuvant to augment cryoinjury of MCF-7 breast cancer cells.

PubMed

Wang, Chuo-Li; Teo, Ka Yaw; Han, Bumsoo

2008-08-01

One of the major challenges in cryosurgery is to minimize incomplete cryodestruction near the edge of the iceball. In the present study, the feasibility and effectiveness of an amino acidic adjuvant, glycine was investigated to enhance the cryodestruction of MCF-7 human breast cancer cell at mild freezing/thawing conditions via eutectic solidification. The effects of glycine addition on the phase change characteristics of NaCl-water binary mixture were investigated with a differential scanning calorimeter and cryo-macro/microscope. The results confirmed that a NaCl-glycine-water mixture has two distinct eutectic phase change events - binary eutectic solidification of water-glycine, and ternary eutectic solidification of NaCl-glycine-water. In addition, its effects on the cryoinjury of MCF-7 cells were investigated by assessing the post-thaw cellular viability after a single freezing/thawing cycle with various eutectic solidification conditions due to different glycine concentrations, end temperatures and hold times. The viability of MCF-7 cells in isotonic saline supplemented with 10% or 20% glycine without freezing/thawing remained higher than 90% (n=9), indicating no apparent toxicity was induced by the addition of glycine. With 10% glycine supplement, the viability of the cells frozen to -8.5 degrees C decreased from 85.9+/-1.8% to 38.5+/-1.0% on the occurrence of binary eutectic solidification of glycine-water (n=3 for each group). With 20% glycine supplement, the viability of the cells frozen to -8.5 degrees C showed similar trends to those with 10% supplement. However, as the end temperature was lowered to -15 degrees C, the viability drastically decreased from 62.5+/-2.0% to 3.6+/-0.7% (n=3 for each group). The influences of eutectic kinetics such as nucleation temperature, hold time and method were less significant. These results imply that the binary eutectic solidification of water-glycine can augment the cryoinjury of MCF-7 cells, and the extent of the eutectic solidification is significant.

In Situ Study of Microstructure Evolution in Solidification of Hypereutectic Al-Si Alloys with Application of Thermal Analysis and Neutron Diffraction

NASA Astrophysics Data System (ADS)

Sediako, Dimitry G.; Kasprzak, Wojciech

2015-09-01

Understanding of the kinetics of solid-phase evolution in solidification of hypereutectic aluminum alloys is a key to control their as-cast microstructure and resultant mechanical properties, and in turn, to enhance the service characteristics of actual components. This study was performed to evaluate the solidification kinetics for three P-modified hypereutectic Al-19 pct Si alloys: namely, Al-Si binary alloy and with the subsequent addition of 2.8 pct Cu and 2.8 pct Cu + 0.7 pct Mg. Metallurgical evaluation included thermodynamic calculations of the solidification process using the FactSage™ 6.2 software package, as well as experimental thermal analysis, and in situ neutron diffraction. The study revealed kinetics of solid α-Al, solid Si, Al2Cu, and Mg2Si evolution, as well as the individual effects of Cu and Mg alloying additions on the solidification path of the Al-Si system. Various techniques applied in this study resulted in some discrepancies in the results. For example, the FactSage computations, in general, resulted in 281 K to 286 K (8 °C to 13 °C) higher Al-Si eutectic temperatures than the ones recorded in the thermal analysis, which are also ~278 K (~5 °C) higher than those observed in the in situ neutron diffraction. None of the techniques can provide a definite value for the solidus temperature, as this is affected by the chosen calculation path [283 K to 303 K (10 °C to 30 °C) higher for equilibrium solidification vs non-equilibrium] for the FactSage analysis; and further complicated by evolution of secondary Al-Cu and Mg-Si phases that commenced at the end of solidification. An explanation of the discrepancies observed and complications associated with every technique applied is offered in the paper.

Undercooling, Rapid Solidification, and Relations to Processing in Low Earth Orbit (A Review of the Works of Bingbo Wei)

NASA Technical Reports Server (NTRS)

deGroh, Henry C., III

1999-01-01

This is a survey of the published works of Prof. Bingbo Wei of the Department of Applied Physics at Northwestern Polytechnical University, Xian P.R. China. Transformations among solid - liquid - and vapor are fundamental to the foundations of life and culture on Earth. The development and understanding of materials has lead the evolution and advancement of the human race since antiquity. Materials and fluids research is continuing today, with us standing on the shoulders of those that have gone before us. Technological and scientific breakthroughs continue due to studies of greater and greater complexity, that include for example, research done at high pressures, in high magnetic fields, at temperatures near absolute zero, and in the low gravity environment of low Earth orbit. Of particular technological importance is the liquid to solid transformation of metals and alloys. Solidification processing is generally the most important factor in the final properties of objects made of metal; and undercooling is the fundamental driving force for all solidification. The interest and resources dedicated to the study of solidification and undercooling are great and World wide. For many years B. Wei and his coworkers have been studying undercooling and rapid solidification and have amassed a significant body of published research in this important field, contributing to the leading edge of the state-of-the-art. It is the goal of this memorandum to provide a review of the research of B. Wei et al.; publications in Chinese are included in the reference list but are not discussed. The bulk of Wei's work has been in the area of undercooling and rapid solidification [1-11, 13-16, 24-36] with papers dating back to 1989, the same year he earned his Ph.D. Below, discussions of Wei's undercooling and rapid solidification research have been grouped together mostly on the basis of alloy type, such as eutectic, intermetallic, or monotectic.

APPLICATIONS ANALYSIS REPORT: CHEMFIX TECHNOLOGIES, INC. - SOLIDIFICATION/STABILIZATION PROCESS

EPA Science Inventory

In support of the U.S. Environmental Protection Agency's (EPA) Superfund Innovative Technology Evaluation (SITE) Program, this report evaluates the Chemfix Technologies, Inc. (Chemfix), solidification/stabilization technology for on-site treatment of hazardous waste. The Chemfix ...

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ahmed, Sazzad Hossain; Mian, Ahsan, E-mail: ahsan.mian@wright.edu; Srinivasan, Raghavan

In DMLS process objects are fabricated layer by layer from powdered material by melting induced by a controlled laser beam. Metallic powder melts and solidifies to form a single layer. Solidification map during layer formation is an important route to characterize micro-structure and grain morphology of sintered layer. Generally, solidification leads to columnar, equiaxed or mixture of these two types grain morphology depending on solidification rate and thermal gradient. Eutectic or dendritic structure can be formed in fully equiaxed zone. This dendritic growth has a large effect on material properties. Smaller dendrites generally increase ductility of the layer. Thus, materialsmore » can be designed by creating desired grain morphology in certain regions using DMLS process. To accomplish this, hardness, temperature distribution, thermal gradient and solidification cooling rate in processed layers will be studied under change of process variables by using finite element analysis, with specific application to Ti-6Al-4V.« less

Segregation effects during solidification in weightless melts. [effects of evaporation and solidification on crystalization

NASA Technical Reports Server (NTRS)

Li, C.

1975-01-01

Computer programs are developed and used in the study of the combined effects of evaporation and solidification in space processing. The temperature and solute concentration profiles during directional solidification of binary alloys with surface evaporation were mathematically formulated. Computer results are included along with an econotechnical model of crystal growth. This model allows: prediction of crystal size, quality, and cost; systematic selection of the best growth equipment or alloy system; optimization of growth or material parameters; and a maximization of zero-gravity effects. Segregation in GaAs crystals was examined along with vibration effects on GaAs crystal growth. It was found that a unique segregation pattern and strong convention currents exist in GaAs crystal growth. Some beneficial effects from vibration during GaAs growth were discovered. The implications of the results in space processing are indicated.

Pattern selection in solidification

NASA Technical Reports Server (NTRS)

Langer, J. S.

1984-01-01

Directional solidification of alloys produces a wide variety of cellular or lamellar structures which, depending upon growth conditions, may be reproducibly regular or may behave chaotically. It is not well understood how these patterns are selected and controlled or even whether there ever exist sharp selection mechanisms. A related phenomenon is the spatial propagation of a pattern into a system which has been caused to become unstable against pattern-forming deformations. This phenomenon has some features in common with the propagation of sidebranching modes in dendritic solidification. In a class of one-dimensional models, the nonlinear system can be shown to select the propagating mode in which the leading edge of the pattern is just marginally stable. This stability principle, when applicable, predicts both the speed of propagation and the geometrical characteristics of the pattern which forms behind the moving front. A boundary-layer model for fully two or three dimensional solidification problems appears to exhibit similar mathematical behavior.

Thermo-Electric-Magnetic Hydrodynamics in Solidification: In Situ Observations and Theory

NASA Astrophysics Data System (ADS)

Fautrelle, Y.; Wang, J.; Salloum-Abou-Jaoude, G.; Abou-Khalil, L.; Reinhart, G.; Li, X.; Ren, Z. M.; Nguyen-Thi, H.

2018-02-01

Solidification of liquid metals contains all the ingredients for the development of the thermo-electric (TE) effect, namely liquid-solid interface and temperature gradients. The combination of TE currents with a superimposed magnetic field gives rise to thermo-electromagnetic (TEM) volume forces acting on both liquid and solid. This results in the generation of fluid flows, which considerably modifies the morphology of the solidification front as well as that of the mushy zone. TEM forces also act on the solid and cause both fragmentation of dendrite branches and a movement of equiaxed grains in suspension. These phenomena have already been unveiled by post-mortem analysis of samples, but they can be analyzed in more detail by using x-ray in situ and real-time observations. Here, we present conclusive evidence of all the aforementioned effects thanks to in situ observations of Al-Cu alloy solidification under static magnetic field.

Numerical Simulation of Polysilicon Solid-liquid Interface Transmogrification in Heat Transfer Process

NASA Astrophysics Data System (ADS)

Yang, Xi; Ma, Wenhui; Lv, Guoqiang; Zhang, Mingyu

2018-01-01

The shape of solid-liquid interface during the directional solidification process, which is difficult to be observed and measured in actual processes, controls the grain orientation and grain size of polysilicon ingot. We carried out numerical calculations of the directional solidification progress of polycrystalline silicon and invested the means to deal with the latent heat of solidification in numerical simulation. The distributions of the temperature field of the melt for the crystallization progress as well as the transformation of the solid-liquid interface were obtained. The simulation results are consistent with the experimental outcomes. The results show that the curvature of solid-liquid interface is small and stability, larger grain sized columnar crystal can be grown in the laboratory-scale furnace at a solidification rate of 10 μm•s-1. It shall provide important theoretical basis for metallurgical process and polysilicon production technology.

A Chebyshev Collocation Method for Moving Boundaries, Heat Transfer, and Convection During Directional Solidification

NASA Technical Reports Server (NTRS)

Zhang, Yiqiang; Alexander, J. I. D.; Ouazzani, J.

1994-01-01

Free and moving boundary problems require the simultaneous solution of unknown field variables and the boundaries of the domains on which these variables are defined. There are many technologically important processes that lead to moving boundary problems associated with fluid surfaces and solid-fluid boundaries. These include crystal growth, metal alloy and glass solidification, melting and name propagation. The directional solidification of semi-conductor crystals by the Bridgman-Stockbarger method is a typical example of such a complex process. A numerical model of this growth method must solve the appropriate heat, mass and momentum transfer equations and determine the location of the melt-solid interface. In this work, a Chebyshev pseudospectra collocation method is adapted to the problem of directional solidification. Implementation involves a solution algorithm that combines domain decomposition, finite-difference preconditioned conjugate minimum residual method and a Picard type iterative scheme.

Dendritic growth of undercooled nickel-tin. I, II

NASA Technical Reports Server (NTRS)

Wu, Y.; Piccone, T. J.; Shiohara, Y.; Flemings, M. C.

1987-01-01

A comparison is made between high speed cinematography and optical temperature measurements of the solidification of an undercooled Ni-25 wt pct Sn alloy. The first part of this study notes that solidification during the recalescence period at all undercoolings studied occurred in the form of a dendritelike front moving across the sample surface, and that the growth velocities observed agree with calculation results for the dendrite growth model of Lipton et al. (1986); it is concluded that the coarse structure observed comprises an array of much finer, solute-controlled dendrites. In the second part, attention is given to the solidification of levitated metal samples within a transparent glass medium for the cases of two undercooled Ni-Sn alloys, one of which is eutectic and another hypoeutectic. The data obtained suggest a solidification model involving dendrites of very fine structure growing into the melt at temperatures near the bulk undercooling temperature.

Effects of Space Environment on Flow and Concentration During Directional Solidification

NASA Technical Reports Server (NTRS)

Benjapiyaporn, C.; Timchenko, V.; Leonardi, E.; deVahlDavis, G.; deGroh, H. C., III

2000-01-01

A study of directional solidification of a weak binary alloy (specifically, Bi - 1 at% Sn) based on the fixed grid single domain approach is being undertaken. The enthalpy method is used to solve for the temperature field over the computational domain including both the solid and liquid phases; latent heat evolution is treated with the aid of an effective specific heat coefficient. A source term accounting for the release of solute into the liquid during solidification has been incorporated into the solute transport equation. The vorticity-stream function formulation is used to describe thermosolutal convection in the liquid region. In this paper we numerically investigate the effects of g-jitter on directional solidification. A background gravity of 1 micro-g has been assumed, and new results for the effects of periodic disturbances over a range of amplitudes and frequencies on solute field and segregation have been presented.

A comparison of acoustic levitation with microgravity processing for containerless solidification of ternary Al-Cu-Sn alloy

NASA Astrophysics Data System (ADS)

Yan, N.; Hong, Z. Y.; Geng, D. L.; Wei, B.

2015-07-01

The containerless rapid solidification of liquid ternary Al-5 %Cu-65 %Sn immiscible alloy was accomplished at both ultrasonic levitation and free fall conditions. A maximum undercooling of 185 K (0.22 T L) was obtained for the ultrasonically levitated alloy melt at a cooling rate of about 122 K s-1. Meanwhile, the cooling rate of alloy droplets in drop tube varied from 102 to 104 K s-1. The macrosegregation was effectively suppressed through the complex melt flow under ultrasonic levitation condition. In contrast, macrosegregation became conspicuous and core-shell structures with different layers were formed during free fall. The microstructure formation mechanisms during rapid solidification at containerless states were investigated in comparison with the conventional static solidification process. It was found that the liquid phase separation and structural growth kinetics may be modulated by controlling both alloy undercooling and cooling rate.

ISS-Experiments of Columnar-to-Equiaxed Transition in Solidification Processing

NASA Technical Reports Server (NTRS)

Sturz, Laszlo; Zimmermann, Gerhard; Gandin, Charles, Andre; Billia, Bernard; Magelinck, Nathalie; Nguyen-Thi, Henry; Browne, David John; Mirihanage, Wajira U.; Voss, Daniela; Beckermann, Christoph;

Solidification Dynamics of Silver Drops in a Free Fall Environment

NASA Technical Reports Server (NTRS)

Grugel, Richard N.; Brush, Lucien N.

1999-01-01

Silver drops (99.9%, 4, 5, 7, and 9 mm diameter) were levitated, melted, and released to fall through Marshall Space Flight Center's 105m drop tube in helium - 6% hydrogen and pure argon atmospheres. By systematically varying the initial superheat condition of the drop the extent of solidification prior to impact ranged from complete to none during the approximately 4.6s of free fall time. Comparison of the experimental observations is made with numerical solutions to a model of the heat transfer and solidification kinetics associated with cooling of the drop during free fall, particularly with regard to the fraction of liquid transformed. Analysis reveals the relative importance of the initial parameters affecting the cooling and solidification rates within the drop. A discussion of the conditions under which the actual observations deviate from the assumptions used in the model is presented.

Atomic concentration effect on thermal properties during solidification of Pt-Rh alloy: A molecular dynamics simulation

NASA Astrophysics Data System (ADS)

Yildiz, A. K.; Celik, F. A.

2017-04-01

The solidification process of Platinum-Rhodium alloy from liquid phase to solid state is investigated at the nano-scale by using Molecular Dynamics Simulation (MDS) for different atomic concentration ratios of Pt. The critical nucleus radius, the bond order parameter, interfacial free energies and total energy based on nucleation theory of the alloy are examined with respect to the temperature changes. The heat of fusion from high temperatures to low temperatures during solidification of the alloy system is determined from molecular dynamics simulation. The structural development is determined from the radial distribution function. It is observed from the results that the melting point of the alloy system decreases with increasing concentration of Pt and that variation of Pt ratio in the alloy shows a remarkable effect on solidification to understand the cooling process of thermal effects.

Linear Stability of Binary Alloy Solidification for Unsteady Growth Rates

NASA Technical Reports Server (NTRS)

Mazuruk, K.; Volz, M. P.

2010-01-01

An extension of the Mullins and Sekerka (MS) linear stability analysis to the unsteady growth rate case is considered for dilute binary alloys. In particular, the stability of the planar interface during the initial solidification transient is studied in detail numerically. The rapid solidification case, when the system is traversing through the unstable region defined by the MS criterion, has also been treated. It has been observed that the onset of instability is quite accurately defined by the "quasi-stationary MS criterion", when the growth rate and other process parameters are taken as constants at a particular time of the growth process. A singular behavior of the governing equations for the perturbed quantities at the constitutional supercooling demarcation line has been observed. However, when the solidification process, during its transient, crosses this demarcation line, a planar interface is stable according to the linear analysis performed.

Cauchy integral method for two-dimensional solidification interface shapes

NASA Astrophysics Data System (ADS)

Siegel, R.; Sosoka, D. J.

1982-07-01

A method is developed to determine the shape of steady state solidification interfaces formed when liquid above its freezing point circulates over a cold surface. The solidification interface, which is at uniform temperature, will form in a shape such that the non-uniform energy convected to it is locally balanced by conduction into the solid. The interface shape is of interest relative to the crystal structure formed during solidification; regulating the crystal structure has application in casting naturally strengthened metallic composites. The results also pertain to phase-change energy storage devices, where the solidified configuration and overall heat transfer are needed. The analysis uses a conformal mapping technique to relate the desired interface coordinates to the components of the temperature gradient at the interface. These components are unknown because the interface shape is unknown. A Cauchy integral formulation provides a second relation involving the components, and a simultaneous solution yields the interface shape.

Microstructure and property of directionally solidified Ni-Si hypereutectic alloy

NASA Astrophysics Data System (ADS)

Cui, Chunjuan; Tian, Lulu; Zhang, Jun; Yu, Shengnan; Liu, Lin; Fu, Hengzhi

2016-03-01

This paper investigates the influence of the solidification rate on the microstructure, solid/liquid interface, and micro-hardness of the directionally solidified Ni-Si hypereutectic alloy. Microstructure of the Ni-Si hypereutectic alloy is refined with the increase of the solidification rate. The Ni-Si hypereutectic composite is mainly composed of α-Ni matrix, Ni-Ni3Si eutectic phase, and metastable Ni31Si12 phase. The solid/liquid interface always keeps planar interface no matter how high the solidification rate is increased. This is proved by the calculation in terms of M-S interface stability criterion. Moreover, the Ni-Si hypereutectic composites present higher micro-hardness as compared with that of the pure Ni3Si compound. This is caused by the formation of the metastable Ni31Si12 phase and NiSi phase during the directional solidification process.

Why solidification has an S-shaped history

PubMed Central

Bejan, A.; Lorente, S.; Yilbas, B. S.; Sahin, A. Z.

2013-01-01

Here we show theoretically that the history of solid growth during “rapid” solidification must be S-shaped, in accord with the constructal law of design in nature. In the beginning the rate of solidification increases and after reaching a maximum it decreases monotonically as the volume of solid tends toward a plateau. The S-history is a consequence of four configurations for the flow of heat from the solidification front to the subcooled surroundings, in this chronological order: solid spheres centered at nucleation sites, needles that invade longitudinally, radial growth by conduction, and finally radial lateral conduction to interstices that are warming up. The solid volume (Bs) vs time (t) is an S-curve because it is a power law of type Bs ~ tn where the exponent n first increases and then decreases in time (n = 3/2, 2, 1, …). The initial portion of the S curve is not an exponential.

On the origin of subgrain boundaries during conventional solidification of austenitic stainless steels

NASA Astrophysics Data System (ADS)

Rahimi, R.; Biermann, H.; Volkova, O.; Mola, J.

2018-06-01

The origin of subgrain formation during conventional casting and solidification of stainless steels was studied using two austenitic stainless steels with 0 and 4 mass-% Al. Whereas the Al-free alloy showed no subgrain formation, the Al-added alloy developed a high density of subgrains separated by low-angle grain boundaries. The occurrence of subgrains in the Al-added alloy was justified by its ferritic mode of solidification as predicted by thermodynamic calculations and confirmed by dynamic scanning calorimetry measurements. The subgrains might be a consequence of the plastic deformation of soft primary ferrite dendrites by the fluid flow and their subsequent inheritance by the austenite. Alternatively, they might have been induced during the austenite formation from delta ferrite, most likely via a peritectic reaction. The absence of subgrains in the Al-free alloy was justified by its austenitic mode of solidification.

Perspectives on integrated modeling of transport processes in semiconductor crystal growth

NASA Technical Reports Server (NTRS)

Brown, Robert A.

1992-01-01

The wide range of length and time scales involved in industrial scale solidification processes is demonstrated here by considering the Czochralski process for the growth of large diameter silicon crystals that become the substrate material for modern microelectronic devices. The scales range in time from microseconds to thousands of seconds and in space from microns to meters. The physics and chemistry needed to model processes on these different length scales are reviewed.

Mechanical properties of turbine blade alloys in hydrogen at elevated temperatures

NASA Technical Reports Server (NTRS)

Deluca, D. P.

1981-01-01

The mechanical properties of single crystal turbine blade alloys in a gaseous hydrogen environment were determined. These alloys are proposed for use in space propulsion systems in pure or partial high pressure hydrogen environments at elevated temperatures. Mechanical property tests included: tensile, creep, low fatigue (LCF), and crack growth. Specimens were in both transverse and longitudinal directions relative to the casting solidification direction. Testing was conducted on solid specimens exposed to externally pressurized environments of gaseous hydrogen and hydrogen-enriched steam.

Oxygen ion conductivity of La0.8Sr0.2Ga0.83Mg0.17-xCoxO3-δ synthesized by laser rapid solidification

NASA Astrophysics Data System (ADS)

Zhang, Jie; Yuan, Chao; Wang, Jun-Qiao; Liang, Er-Jun; Chao, Ming-Ju

2013-08-01

Materials La0.8Sr0.2Ga0.83Mg0.17-xCoxO3-δ with x = 0, 0.05, 0.085, 0.10, and 0.15 are synthesized by laser rapid solidification. It is shown that the samples prepared by laser rapid solidification give rise to unique spear-like or leaf-like microstructures which are orderly arranged and densely packed. Their electrical properties each show a general dependence of the Co content and the total conductivities of La0.8Sr0.2Ga0.83Mg0.085Co0.085O3-δ prepared by laser rapid solidification are measured to be 0.067, 0.124, and 0.202 S·cm-1 at 600, 700, and 800 °C, respectively, which are much higher than by conventional solid state reactions. Moreover, the electrical conductivities each as a function of the oxygen partial pressure are also measured. It is shown that the samples with the Co content values <= 8.5 mol% each exhibit basically ionic conduction while those for Co content values >= 10 mol % each show ionic mixed electronic conduction under oxygen partial pressures from 10-16 atm (1 atm = 1.01325 × 105 Pa) to 0.98 atm. The improved ionic conductivity of La0.8Sr0.2Ga0.83Mg0.085Co0.085O3-δ prepared by laser rapid solidification compared with by solid state reactions is attributed to the unique microstructure of the sample generated during laser rapid solidification.

Cellular monotectic model solidification

NASA Technical Reports Server (NTRS)

Kaukler, William F.

1987-01-01

Succinonitrile (sn) was purified to a superior level using a fractional recrystallization method. The melting point of the best twice recrystallized sn was not raised by following with double distillation. This was tested using differential scanning calorimetry. The peak shape on melting also proved that double distillation after double recrystallization did not improve the quality. Stability and phase diagrams for succinonitrile and glycerol are presented.

Modeling transport phenomena and uncertainty quantification in solidification processes

NASA Astrophysics Data System (ADS)

Fezi, Kyle S.

Direct chill (DC) casting is the primary processing route for wrought aluminum alloys. This semicontinuous process consists of primary cooling as the metal is pulled through a water cooled mold followed by secondary cooling with a water jet spray and free falling water. To gain insight into this complex solidification process, a fully transient model of DC casting was developed to predict the transport phenomena of aluminum alloys for various conditions. This model is capable of solving mixture mass, momentum, energy, and species conservation equations during multicomponent solidification. Various DC casting process parameters were examined for their effect on transport phenomena predictions in an alloy of commercial interest (aluminum alloy 7050). The practice of placing a wiper to divert cooling water from the ingot surface was studied and the results showed that placement closer to the mold causes remelting at the surface and increases susceptibility to bleed outs. Numerical models of metal alloy solidification, like the one previously mentioned, are used to gain insight into physical phenomena that cannot be observed experimentally. However, uncertainty in model inputs cause uncertainty in results and those insights. The analysis of model assumptions and probable input variability on the level of uncertainty in model predictions has not been calculated in solidification modeling as yet. As a step towards understanding the effect of uncertain inputs on solidification modeling, uncertainty quantification (UQ) and sensitivity analysis were first performed on a transient solidification model of a simple binary alloy (Al-4.5wt.%Cu) in a rectangular cavity with both columnar and equiaxed solid growth models. This analysis was followed by quantifying the uncertainty in predictions from the recently developed transient DC casting model. The PRISM Uncertainty Quantification (PUQ) framework quantified the uncertainty and sensitivity in macrosegregation, solidification time, and sump profile predictions. Uncertain model inputs of interest included the secondary dendrite arm spacing, equiaxed particle size, equiaxed packing fraction, heat transfer coefficient, and material properties. The most influential input parameters for predicting the macrosegregation level were the dendrite arm spacing, which also strongly depended on the choice of mushy zone permeability model, and the equiaxed packing fraction. Additionally, the degree of uncertainty required to produce accurate predictions depended on the output of interest from the model.

Undercooling-Induced macrosegregation in directional solidification

NASA Astrophysics Data System (ADS)

de Groh, Henry C.

1994-11-01

The accepted primary mechanism for causing macrosegregation in directional solidification (DS) is thermal and solutal convection in the liquid. This article demonstrates the effects of under-cooling and nucleation on macrosegregation and shows that undercooling, in some cases, can be the cause of end-to-end macrosegregation. Alloy ingots of Pb-Sn were directionally solidified upward and downward, with and without undercooling. A thermal gradient of about 5.1 K/cm and a cooling rate of 7.7 K/h were used. Crucibles of borosilicate glass, stainless steel with Cu bottoms, and fused silica were used. High undercoolings were achieved in the glass crucibles, and very low undercoolings were achieved in the steel/Cu crucible. During under-cooling, large, coarse Pb dendrites were found to be present. Large amounts of macrosegregation developed in the undercooled eutectic and hypoeutectic alloys. This segre-gation was found to be due to the nucleation and growth of primary Pb-rich dendrites, continued coarsening of Pb dendrites during undercooling of the interdendritic liquid, Sn enrichment of the liquid, and dendritic fragmentation and settling during and after recalescence. Eutectic ingots that solidified with no undercooling had no macrosegregation, because both Pb and Sn phases were effectively nucleated at the start of solidification, thus initiating the growth of solid of eutectic composition. It is thus shown that undercooling and single-phase nucleation can cause significant macrosegregation by increasing the amount of solute rejected into the liquid and by the movement of unattached dendrites and dendrite fragments, and that macrosegregation in excess of what would be expected due to diffusion transport is not necessarily caused by convection in the liquid.

STABILIZATION/SOLIDIFICATION OF CERCLA AND RCRA WASTES

EPA Science Inventory

This Handbook provides U.S. EPA regional staff responsible for reviewing CERCLA remedial action plans and RCRA permit applications with a tool for interpreting information on stabilization/solidification treatment. As a practical day-to-day reference guide, it will also provide t...

SOLIDIFICATION/STABILIZATION: IS IT ALWAYS APPROPRIATE?

EPA Science Inventory

The findings of recent research and evaluation efforts are assessed to determine whether solidification/stabilization (S/S) has been properly and appropriately applied for different types of hazardous wastes. Results from these studies are mixed and, as a result, the need for pro...

SURVEY OF SOLIDIFICATION/STABILIZATION TECHNOLOGY FOR HAZARDOUS INDUSTRIAL WASTES

EPA Science Inventory

Stabilization/solidification or fixation is a process for treating industrial solid wastes (primarily sludges) that contain hazardous constituents to prevent dissolution and loss of toxic materials into the environment. Most of these treatment processes are designed to produce a ...

KSC-97PC1462

NASA Image and Video Library

1997-09-15

United States Microgravity Payload-4 (USMP-4) experiments are prepared to be flown on Space Shuttle mission STS-87 in the Space Station Processing Facility at Kennedy Space Center (KSC). A technician is working on the Advanced Automated Directional Solidification Furnace (AADSF), which will be used by researchers to study the solidification of semiconductor materials in microgravity. Scientists will be able to better understand how microgravity influences the solidification process of these materials and develop better methods for controlling that process during future Space flights and Earth-based production. All STS-87 experiments are scheduled for launch on Nov. 19 from KSC

An Overview of the MSFC Electrostatic Levitation Facility

NASA Technical Reports Server (NTRS)

Rogers, J. R.; Robinson, M. B.; Hyers, R. W.; Savage, L.; Rathz, T.

2000-01-01

Electrostatic levitation (ESL) provides a means to study molten materials in a contamination-free environment, including no contact with a container. Many phenomena important to materials science can be studied in the ESL. Solidification of metals, alloys and undercooled materials represent an important topic for research in the ESL. Recent studies of metals and alloys during solidification in the ESL are reported. Measurements include time, temperature and transformation of metallic glass-forming alloys, solidification velocities, and microstructure. This multimedia report includes a video clip showing processing in the ESL, with descriptions of the different segments in the text.

Coupled Heat Transfer and Fluid Dynamics Modeling of InSb Solidification

NASA Astrophysics Data System (ADS)

Barvinschi, Paul; Barvinschi, Floricica

2011-10-01

A method for the directional solidification of melted InSb in a silica ampoule is presented and solved with COMSOL Multiphysics. The configuration and initial boundary settings of the model resemble those used in a de-wetting vertical Bridgman configuration [1]. A slightly modified version of the method presented by Voller and Prakash [2] is used to account for solidification of the liquid phase, including convection and conduction heat transfer with mushy region phase change. Axial-symmetric numerical simulations of temperature and velocity fields, under normal gravity, are carried out using different thermal conditions.

Interferometric measurements of a dendritic growth front solutal diffusion layer

NASA Technical Reports Server (NTRS)

Hopkins, John A.; Mccay, T. D.; Mccay, Mary H.

1991-01-01

An experimental study was undertaken to measure solutal distributions in the diffusion layer produced during the vertical directional solidification (VDS) of an ammonium chloride - water (NH4Cl-H2O) solution. Interferometry was used to obtain concentration measurements in the 1-2 millimeter region defining the diffusion layer. These measurements were fitted to an exponential form to extract the characteristic diffusion parameter for various times after the start of solidification. The diffusion parameters are within the limits predicted by steady state theory and suggest that the effective solutal diffusivity is increasing as solidification progresses.

Solidification processing of intermetallic Nb-Al alloys

NASA Technical Reports Server (NTRS)

Smith, Preston P.; Oliver, Ben F.; Noebe, Ronald D.

1992-01-01

Several Nb-Al alloys, including single-phase NbAl3 and the eutectic of Nb2Al and NbAl3, were prepared either by nonconsumable arc melting in Ar or by zone processing in He following initial induction melting and rod casting, and the effect of the solidification route on the microstructure and room-temperature mechanical properties of these alloys was investigated. Automated control procedures and melt conditions for directional solidification of NbAl3 and the Nb2Al/Nb3Al eutectic were developed; high purity and stoichiometry were obtained. The effects of ternary additions of Ti and Ni are described.

Simulating the Dynamics of Particles Interacting with Solidification Fronts (Preprint - Briefing Charts)

DTIC Science & Technology

2007-07-01

A π =Π )( lslpsp γγγγ +−=Δ A = Hamaker constant ~ Δγ Δγ > 0 repulsive Δγ < 0 attractive VSparticle solid liquid d Previous work on thermal effects of...Solidification velocity = 500 microns/sec, Rp = 1 micron, Hamaker = -8E-19 J, kp/kl = 1.0 (planar), no premelting Vs Vt Vp Velocity vs. t and d vs. t plots...premelting Solidification velocity = 500 microns/sec, Rp = 1 micron, Hamaker = -8E-19 J, kp/kl = 1.0 (planar), premelting kp/kl ≥ 1.0 ALWAYS ENGULFS

Displacement-dispersive liquid-liquid microextraction based on solidification of floating organic drop of trace amounts of palladium in water and road dust samples prior to graphite furnace atomic absorption spectrometry determination.

PubMed

Ghanbarian, Maryam; Afzali, Daryoush; Mostafavi, Ali; Fathirad, Fariba

2013-01-01

A new displacement-dispersive liquid-liquid microextraction method based on the solidification of floating organic drop was developed for separation and preconcentration of Pd(ll) in road dust and aqueous samples. This method involves two steps of dispersive liquid-liquid microextraction based on solidification. In Step 1, Cu ions react with diethyldithiocarbamate (DDTC) to form Cu-DDTC complex, which is extracted by dispersive liquid-liquid microextraction based on a solidification procedure using 1-undecanol (extraction solvent) and ethanol (dispersive solvent). In Step 2, the extracted complex is first dispersed using ethanol in a sample solution containing Pd ions, then a dispersive liquid-liquid microextraction based on a solidification procedure is performed creating an organic drop. In this step, Pd(ll) replaces Cu(ll) from the pre-extracted Cu-DDTC complex and goes into the extraction solvent phase. Finally, the Pd(ll)-containing drop is introduced into a graphite furnace using a microsyringe, and Pd(ll) is determined using atomic absorption spectrometry. Several factors that influence the extraction efficiency of Pd and its subsequent determination, such as extraction and dispersive solvent type and volume, pH of sample solution, centrifugation time, and concentration of DDTC, are optimized.

Experimental and Theoretical Investigations of the Solidification of Eutectic Al-Si Alloy

NASA Technical Reports Server (NTRS)

Sen, S.; Catalina, A. V.; Rose, M. Franklin (Technical Monitor)

2001-01-01

The eutectic alloys have a wide spectrum of applications due to their good castability and physical and mechanical properties. The interphase spacing resulting during solidification is an important microstructural feature that significantly influences the mechanical behavior of the material. Thus, knowledge of the evolution of the interphase spacing during solidification is necessary in order to properly design the solidification process and optimize the material properties. While the growth of regular eutectics is rather well understood, the irregular eutectics such as Al-Si or Fe-graphite exhibit undercoolings and lamellar spacings much larger than those theoretically predicted. Despite of a considerable amount of experimental and theoretical work a clear understanding of the true mechanism underlying the spacing selection in irregular eutectics is yet to be achieved. A new experimental study of the solidification of the eutectic Al-Si alloy will be reported in this paper. The measured interface undercoolings and lamellar spacing will be compared to those found in the literature in order to get more general information regarding the growth mechanism of irregular eutectics. A modification of the present theory of the eutectic growth is also proposed. The results of the modified mathematical model, accounting for a non-isothermal solid/liquid interface, will be compared to the experimental measurements.

The Solidification Behavior of AA2618 Aluminum Alloy and the Influence of Cooling Rate

PubMed Central

Liu, Yulin; Liu, Ming; Luo, Lei; Wang, Jijie; Liu, Chunzhong

2014-01-01

In AA2618 aluminum alloy, the iron- and nickel-rich intermetallics formed during solidification are of great effect on the mechanical properties of the alloy at both room temperature and elevated temperatures. However, the solidification behavior of the alloy and the formation mechanism of the intermetallics during solidification of the alloy are not clear. This research fills the gap and contributes to understanding the intermetallic of the alloy. The results showed that cooling rate was of great influence on the formation of the intermetallics. Under the condition of slow cooling, the as-cast microstructures of the alloy were complex with many coarse eutectic compounds including Al9FeNi, Al7(CuNi)5, Si, Al2Cu and Al2CuMg. The phase Al9FeNi was the dominant intermetallic compound, which precipitated at the earlier stage of the solidification by eutectic reaction L → α-Al + Al9FeNi. Increasing the cooling rate would suppress the formation of the coarse eutectic intermetallics. Under the condition of near-rapid cooling, the as-cast microstructures of the alloy consisted of metastable intermetallics Al9FeNi and Al2Cu; the equilibrium eutectic compounds were suppressed. This research concluded that intermetallics could be refined to a great extent by near-rapid cooling. PMID:28788281

Formation mechanism of atomic cluster structures in Al-Mg alloy during rapid solidification processes

NASA Astrophysics Data System (ADS)

Liu, Feng-xiang; Liu, Rang-su; Hou, Zhao-yang; Liu, Hai-Rong; Tian, Ze-an; Zhou, Li-li

2009-02-01

The rapid solidification processes of Al 50Mg 50 liquid alloy consisting of 50,000 atoms have been simulated by using molecular dynamics method based on the effective pair potential derived from the pseudopotential theory. The formation mechanisms of atomic clusters during the rapid solidification processes have been investigated adopting a new cluster description method—cluster-type index method (CTIM). The simulated partial structure factors are in good agreement with the experimental results. And Al-Mg amorphous structure characterized with Al-centered icosahedral topological short-range order (SRO) is found to form during the rapid solidification processes. The icosahedral cluster plays a key role in the microstructure transition. Besides, it is also found that the size distribution of various clusters in the system presents a magic number sequence of 13, 19, 23, 25, 29, 31, 33, 37, …. The magic clusters are more stable and mainly correspond to the incompact arrangements of linked icosahedra in the form of rings, chains or dendrites. And each magic number point stands correspondingly for one certain combining form of icosahedra. This magic number sequence is different from that generated in the solidification structure of liquid Al and those obtained by methods of gaseous deposition and ionic spray, etc.

Preparation of silicon target material by adding Al-B master alloy in directional solidification

NASA Astrophysics Data System (ADS)

Li, Pengting; Wang, Kai; Ren, Shiqiang; Jiang, Dachuan; Tan, Yi

2017-03-01

The silicon target material was prepared by adding Al-6B master alloy in directional solidification. The microstructure was characterized and the resistivity was studied in this work. The results showed that the purity of the silicon target material was more than 99.999% (5N). The resistivity was ranges from 0.002 to 0.030 Ω·cm along the ingot height. It was revealed that the particles of AlB2 in Al-6B master alloy would react spontaneously and generate clusters of [B] and [Al] in molten silicon at 1723 K. After directional solidification, the content of B and Al were increasing gradually with the increase of solidified fraction. The measured values of B were in good agreement with the curve of the Scheil equation below 80% of the ingot height. The mean concentration of B was about 17.20 ppmw and the mean concentration of Al was about 8.07 ppmw after directional solidification. The measured values of Al were fitting well with the curve of values which the effective segregation coefficient was 0.00378. It was observed that B co-doped Al in directional solidification polysilicon could regulate resistivity mutually. This work provides the theoretical basis and technical support for industrial production of the silicon target material.

Containerless solidification of oxide material using an electrostatic levitation furnace in microgravity

NASA Astrophysics Data System (ADS)

Yu, Jianding; Koshikawa, Naokiyo; Arai, Yasutomo; Yoda, Shinichi; Saitou, Hirofumi

2001-11-01

Containerless solidification of BiFeO 3 has been carried out in microgravity with an electrostatic levitation furnace (ELF) on board a sounding rocket (TR-IA). This was the first time the ELF was used in microgravity to study the solidification behavior of oxide insulator material. A spherical BiFeO 3 specimen with a diameter of 5 mm was laser heated and solidified in an oxygen and nitrogen mixture atmosphere. The microstructure resulting from solidification in the ELF was compared with that obtained from solidification in a 10 m drop tube and in crucibles. In the crucible experiments, the segregation of the primary Fe 2O 3 phase could not be suppressed, even if the cooling speed increased to 5000 K/s. However it did suppress in a 0.3 mm diameter droplet solidified in the drop tube experiment. This suggests that containerless processing effectively promoted the undercooling of the BiFeO 3 phase. In the microgravity experiment, although a homogeneous BiFeO 3 phase was not observed in the 5 mm spherical specimen, an anomalous fine cellular microstructure appeared due to high undercooling. In addition, the phase transitions of BiFeO 3 were measured by DTA from room temperature to 1523 K and its liquidus temperature was estimated to be 1423 K.

Elimination of Hot Tears in Steel Castings by Means of Solidification Pattern Optimization

NASA Astrophysics Data System (ADS)

Kotas, Petr; Tutum, Cem Celal; Thorborg, Jesper; Hattel, Jesper Henri

2012-06-01

A methodology of how to exploit the Niyama criterion for the elimination of various defects such as centerline porosity, macrosegregation, and hot tearing in steel castings is presented. The tendency of forming centerline porosity is governed by the temperature distribution close to the end of the solidification interval, specifically by thermal gradients and cooling rates. The physics behind macrosegregation and hot tears indicate that these two defects also are dependent heavily on thermal gradients and pressure drop in the mushy zone. The objective of this work is to show that by optimizing the solidification pattern, i.e., establishing directional and progressive solidification with the help of the Niyama criterion, macrosegregation and hot tearing issues can be both minimized or eliminated entirely. An original casting layout was simulated using a transient three-dimensional (3-D) thermal fluid model incorporated in a commercial simulation software package to determine potential flaws and inadequacies. Based on the initial casting process assessment, multiobjective optimization of the solidification pattern of the considered steel part followed. That is, the multiobjective optimization problem of choosing the proper riser and chill designs has been investigated using genetic algorithms while simultaneously considering their impact on centerline porosity, the macrosegregation pattern, and primarily on hot tear formation.

Microstructural analysis of laser weld fusion zone in Haynes 282 superalloy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Osoba, L.O.; Ding, R.G.; Ojo, O.A., E-mail: ojo@cc.umanitoba.ca

Analytical electron microscopy and spectroscopy analyses of the fusion zone (FZ) microstructure in autogenous laser beam welded Haynes 282 (HY 282) superalloy were performed. The micro-segregation patterns observed in the FZ indicate that Co, Cr and Al exhibited a nearly uniform distribution between the dendrite core and interdendritic regions while Ti and Mo were rejected into the interdendritic liquid during the weld solidification. Transmission electron diffraction analysis and energy dispersive X-ray microanalysis revealed the second phase particles formed along the FZ interdendritic region to be Ti-Mo rich MC-type carbide particles. Weld FZ solidification cracking, which is sometimes associated with themore » formation of {gamma}-{gamma}' eutectic in {gamma}' precipitation strengthened nickel-base superalloys, was not observed in the HY 282 superalloy. Modified primary solidification path due to carbon addition in the newly developed superalloy is used to explain preclusion of weld FZ solidification cracking in the material. - Highlights: Black-Right-Pointing-Pointer A newly developed superalloy was welded by CO{sub 2} laser beam joining technique. Black-Right-Pointing-Pointer Electron microscopy characterization of the weld microstructure was performed. Black-Right-Pointing-Pointer Identified interdendritic microconstituents consist of MC-type carbides. Black-Right-Pointing-Pointer Modification of primary solidification path is used to explain cracking resistance.« less

An alternative method for the treatment of waste produced at a dye and a metal-plating industry using natural and/or waste materials.

PubMed

Fatta, Despo; Papadopoulos, Achilleas; Stefanakis, Nikos; Loizidou, Maria; Savvides, Chrysanthos

2004-08-01

The aim of this study was to develop cost-effective, appropriate solidification technologies for treating hazardous industrial wastes that are currently disposed of in ways that may threaten the quality of local groundwater. One major objective was to use materials other than cement, and preferably materials that are themselves wastes, as the solidification additives, namely using wastes to treat wastes or locally available natural material. This research examines the cement-based and lime-based stabilization/solidification (S/S) techniques applied for waste generated at a metal-plating industry and a dye industry. For the lime-based S/S process the following binder mixtures were used: cement kiln dust/ lime, bentonite/lime and gypsum/lime. For the cement-based S/S process three binder mixtures were used: cement kiln dust/cement, bentonite/cement and gypsum/cement. The leachability of the wastes was evaluated using the toxicity characteristic leaching procedure. The applicability and optimum weight ratio of the binder mixtures were estimated using the unconfined compressive strength test. The optimum ratio mixtures were mixed with waste samples in different ratios and cured for 28 days in order to find the S/S products with the highest strength and lowest leachability at the same time. The results of this work showed that the cement-and lime-based S/S process, using cement kiln dust and bentonite as additives can be effectively used in order to treat industrial waste.

The Case for a Heat-Pipe Phase of Planet Evolution on the Moon

NASA Technical Reports Server (NTRS)

Simon, J. I.; Moore, W. B.; Webb, A. A. G.

2015-01-01

The prevalence of anorthosite in the lunar highlands is generally attributed to the flotation of less dense plagioclase in the late stages of the solidification of the lunar magma ocean. It is not clear, however, that these models are capable of producing the extremely high plagioclase contents (near 100%) observed in both Apollo samples and remote sensing data, since a mostly solid lithosphere forms (at 60-70% solidification) before plagioclase feldspar reaches saturation (at approximately 80% solidification). Formation as a floating cumulate is made even more problematic by the near uniformity of the alkali composition of the plagioclase, even as the mafic phases record significant variations in Mg/(Mg+Fe) ratios. These problems can be resolved for the Moon if the plagioclase-rich crust is produced and refined through a widespread episode of heat-pipe magmatism rather than a process dominated by density-driven plagioclase flotation. Heat-pipes are an important feature of terrestrial planets at high heat flow, as illustrated by Io's present activity. Evidence for their operation early in Earth's history suggests that all terrestrial bodies should experience an early episode of heat-pipe cooling. As the Moon likely represents the most wellpreserved example of early planetary thermal evolution in our solar system, studies of the lunar surface and of lunar materials provide useful data to test the idea of a universal model of the way terrestrial bodies transition from a magma ocean state into subsequent single-plate, rigid-lid convection or plate tectonic phases.

Compression Freezing Kinetics of Water to Ice VII

DOE PAGES

Gleason, A. E.; Bolme, C. A.; Galtier, E.; ...

2017-07-11

Time-resolved x-ray diffraction (XRD) of compressed liquid water shows transformation to ice VII in 6 nsec, revealing crystallization rather than amorphous solidification during compression freezing. Application of classical nucleation theory indicates heterogeneous nucleation and one-dimensional (e.g., needlelike) growth. In conclusion, these first XRD data demonstrate rapid growth kinetics of ice VII with implications for fundamental physics of diffusion-mediated crystallization and thermodynamic modeling of collision or impact events on ice-rich planetary bodies.

Compression Freezing Kinetics of Water to Ice VII

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gleason, A. E.; Bolme, C. A.; Galtier, E.

Time-resolved x-ray diffraction (XRD) of compressed liquid water shows transformation to ice VII in 6 nsec, revealing crystallization rather than amorphous solidification during compression freezing. Application of classical nucleation theory indicates heterogeneous nucleation and one-dimensional (e.g., needlelike) growth. In conclusion, these first XRD data demonstrate rapid growth kinetics of ice VII with implications for fundamental physics of diffusion-mediated crystallization and thermodynamic modeling of collision or impact events on ice-rich planetary bodies.

The boundary integral theory for slow and rapid curved solid/liquid interfaces propagating into binary systems

NASA Astrophysics Data System (ADS)

Galenko, Peter K.; Alexandrov, Dmitri V.; Titova, Ekaterina A.

2018-01-01

The boundary integral method for propagating solid/liquid interfaces is detailed with allowance for the thermo-solutal Stefan-type models. Two types of mass transfer mechanisms corresponding to the local equilibrium (parabolic-type equation) and local non-equilibrium (hyperbolic-type equation) solidification conditions are considered. A unified integro-differential equation for the curved interface is derived. This equation contains the steady-state conditions of solidification as a special case. The boundary integral analysis demonstrates how to derive the quasi-stationary Ivantsov and Horvay-Cahn solutions that, respectively, define the paraboloidal and elliptical crystal shapes. In the limit of highest Péclet numbers, these quasi-stationary solutions describe the shape of the area around the dendritic tip in the form of a smooth sphere in the isotropic case and a deformed sphere along the directions of anisotropy strength in the anisotropic case. A thermo-solutal selection criterion of the quasi-stationary growth mode of dendrites which includes arbitrary Péclet numbers is obtained. To demonstrate the selection of patterns, computational modelling of the quasi-stationary growth of crystals in a binary mixture is carried out. The modelling makes it possible to obtain selected structures in the form of dendritic, fractal or planar crystals. This article is part of the theme issue `From atomistic interfaces to dendritic patterns'.

Flight Planning for the International Space Station - Levitation Observation of Dendrite Evolution in Steel Ternary Alloy Rapid Solidification (LODESTARS)

NASA Technical Reports Server (NTRS)

Flemings, Merton C.; Matson, Douglas M.; Hyers, Robert W.; Rogers, Jan R.

2003-01-01

During rapid solidification, a molten sample is cooled below its equilibrium solidification temperature to form a metastable liquid. Once nucleation is initiated, growth of the solid phase proceeds and can be seen as a sudden rise in temperature. The heat of fusion is rejected ahead of the growing dendrites into the undercooled liquid in a process known as recalescence. Fe-Cr-Ni alloys may form several equilibrium phases and the hypoeutectic alloys, with compositions near the commercially important 316 stainless steel alloy, are observed to solidify by way of a two-step process known as double recalescence. During double recalescence, the first temperature rise is associated with formation of the metastable ferritic solid phase with subsequent conversion to the stable austenitic phase during the second temperature rise. Selection of which phase grows into the undercooled melt during primary solidification may be accomplished by choice of the appropriate nucleation trigger material or by control of the processing parameters during rapid solidification. Due to the highly reactive nature of the molten sample material and in order to avoid contamination of the undercooled melt, a containerless electromagnetic levitation (EML) processing technique is used. In ground-based EML, the same forces that support the weight of the sample against gravity also drive convection in the liquid sample. However, in microgravity, the force required to position the sample is greatly reduced, so convection may be controlled over a wide range of internal flows. Space Shuttle experiments have shown that the double recalescence behavior of Fe-Cr-Ni alloys changes between ground and space EML experiments. This program is aimed at understanding how melt convection influences phase selection and the evolution of rapid solidification microstructures.

On the Coupling Mechanism of Equiaxed Crystal Generation with the Liquid Flow Driven by Natural Convection During Solidification

NASA Astrophysics Data System (ADS)

Stefan-Kharicha, Mihaela; Kharicha, Abdellah; Wu, Menghuai; Ludwig, Andreas

2018-02-01

The influence of the melt flow on the solidification structure is bilateral. The flow plays an important role in the solidification pattern, via the heat transfer, grain distribution, and segregations. On the other hand, the crystal structure, columnar or equiaxed, impacts the flow, via the thermosolutal convection, the drag force applied by the crystals on the melt flow, etc. As the aim of this research was to further explore the solidification-flow interaction, experiments were conducted in a cast cell (95 * 95 * 30 mm3), in which an ammonium chloride-water solution (between 27 and 31 wt pct NH4Cl) was observed as it solidified. The kinetic energy (KE) of the flow and the average flow velocity were calculated throughout the process. Measurements of the volume extension of the mush in the cell and the velocity of the solid front were also taken during the solidification experiment. During the mainly columnar experiments (8 cm liquid height) the flow KE continuously decreased over time. However, during the later series of experiments at higher liquid height (9.5 cm), the flow KE evolution presented a strong peak shortly after the start of solidification. This increase in the total flow KE correlated with the presence of falling equiaxed crystals. Generally, a clear correlation between the strength of the flow and the occurrence of equiaxed crystals was evident. The analysis of the results strongly suggests a fragmentation origin of equiaxed crystals appearing in the melt. The transition from purely columnar growth to a strongly equiaxed rain (CET) was found to be triggered by (a) the magnitude of the coupling between the flow intensity driven by the equiaxed crystals, and (b) the release and transport of the fragments by the same flow recirculating within the mushy zone.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wu, Zeen; Hu, Rui; Zhang, Tiebang, E-mail: tiebang

The microstructure and solidification behavior of high Nb containing TiAl alloys with the composition of Ti-46Al-8Nb-xC (x = 0.1, 0.7, 1.4, 2.5 at.%) prepared by arc-melting method have been investigated in this work. The results give evidence that the addition of carbon changes the solidification behavior from solidification via the β phase to the peritectic solidification. And carbon in solid solution enriches in the α{sub 2} phase and increases the microhardness. As the carbon content increases to 1.4 at.%, plate-shape morphology carbides Ti{sub 2}AlC (H phase) precipitate from the TiAl matrix which leads to the refinement microstructure. By aging atmore » 1173 K for 24 h after quenching treatment, fine needle-like and granular shape Ti{sub 3}AlC (P phase) carbides are observed in the matrix of Ti-46Al-8Nb-2.5C alloy, which distribute along the lamellar structure or around the plate-shape Ti{sub 2}AlC. Transmission electron microscope observation shows that the Ti{sub 3}AlC carbides precipitate at dislocations. The phase transformation in-situ observations indicate that the Ti{sub 2}AlC carbides partly precipitate during the solid state phase transformation process. - Highlights: •Carbon changes the solidification behavior from β phase to peritectic solidification. •Dislocations in solution treated γ phase act as nucleation sites of Ti{sub 3}AlC precipitations. •Ti{sub 3}AlC precipitates as fine needle-like or granular shape in the solution treated matrix. •Ti{sub 2}AlC carbides precipitate during the solid state phase transformation process.« less

Mushy zone modeling

NASA Astrophysics Data System (ADS)

Glicksman, Martin E.; Smith, Richard N.; Marsh, Steven P.; Kuklinski, Robert

A key element of mushy zone modeling is the description of the microscopic evolution of the lengthscales within the mushy zone and the influence of macroscopic transport processes. This paper describes some recent progress in developing a mean-field statistical theory of phase coarsening in adiabatic mushy zones. The main theoretical predictions are temporal scaling laws that indicate that average lengthscale increases as time 1/3, a self-similar distribution of mushy zone lengthscales based on spherical solid particle shapes, and kinetic rate constants which provide the dependences of the coarsening process on material parameters and the volume fraction of the solid phase. High precision thermal decay experiments are described which verify aspects of the theory in pure material mushy zones held under adiabatic conditions. The microscopic coarsening theory is then integrated within a macroscopic heat transfer model of one-dimensional alloy solidification, using the Double Integral Method. The method demonstrates an ability to predict the influence of macroscopic heat transfer on the evolution of primary and secondary dendrite arm spacings in Al-Cu alloys. Finally, some suggestions are made for future experimental and theoretical studies required in developing comprehensive solidification processing models.

Suppression/Reversal of Natural Convection by Exploiting the Temperature/Composition Dependence of Magnetic Susceptibility

NASA Technical Reports Server (NTRS)

Seybert, C. D.; Evans, J. W.; Leslie, F.; Jones, W. K., Jr.

2000-01-01

Natural convection, driven by temperature-or concentration gradients or both, is an inherent phenomenon during solidification of materials on Earth. This convection has practical consequences (e.g effecting macrosegregation) but also renders difficult the scientific examination of diffusive/conductive phenomena during solidification. It is possible to halt, or even reverse, natural convection by exploiting the variation (with temperature, for example) of the susceptibility of a material. If the material is placed in a vertical magnetic field gradient, a buoyancy force of magnetic origin arises and, at a critical field gradient, can balance the normal buoyancy forces to halt convection. At higher field gradients the convection can be reversed. The effect has been demonstrated in experiments at Marshall Space Flight Center where flow was measured by PIV in MnCl2 solution in a superconducting magnet. In auxiliary experiments the field in the magnet and the properties of the solution were measured. Computations of the natural convection, its halting and reversal, using the commercial software FLUENT were in good agreement with the measurements.

Preliminary flight results from the second U.S. Microgravity Payload (USMP-2)

NASA Technical Reports Server (NTRS)

Curreri, Peter; Reiss, Donald

1994-01-01

The second U.S. Microgravity Payload (USMP-2) was flown on the Space Shuttle in March 1994. It carried four major microgravity experiments plus a sophisticated accelerometer system to record the microgravity environment during USMP-2 operations. The USMP program is designed to accommodate experiments requiring extensive resources short of a full Spacelab mission, and the experiments are remotely operated and monitored. Results are reviewed from the four experiments: the Advanced Automated Directional Solidification Facility (AADSF), the Isothermal Dendrite Growth Experiment (IDGE), the Materiel por Etude des Phenomenes Interessant la Soldification sur Terre et en Orbite (MEPHISTO), and the Critical Fluid Light Scattering Experiment (Zeno). AASDF grew what is expected to be the largest steady-state sample ever of HgCdTe during 240 hours of operation. IDGE provided 60 growth cycles over a wide range of supercooling conditions studying the dendritic solidification of succinonitrile. MEPHISTO achieved 55 melt-solidify cycles and grew over 1 m of Bi/Sn alloy. Zeno located the critical point temperature for liquid Xe to 0.00001 K. IDGE and Zeno also provided the most extensive demonstrations to date of telescience.

Large low-field magnetocaloric effect in directionally solidified Ni55Mn18+xGa27-x (x = 0, 1, 2) alloys

NASA Astrophysics Data System (ADS)

Li, Zhenzhuang; Li, Zongbin; Yang, Bo; Yang, Yiqiao; Zhang, Yudong; Esling, Claude; Zhao, Xiang; Zuo, Liang

2018-01-01

The magnetostructural transformation and magnetocaloric effect of directionally solidified polycrystalline Ni55Mn18+xGa27-x (x = 0, 1, 2) alloys were studied. It is shown the directionally solidified alloys form coarse columnar-shaped grains with strong 〈0 0 1〉A (the subscript A refers to austenite) preferred orientation along the solidification direction. Through Mn substitution for Ga, a coupled magnetostructural transformation was realized in Ni55Mn19Ga26 and Ni55Mn20Ga25 alloys. Large adiabatic temperature variation (ΔTad) of 1.47 K and 1.57 K under the low field change of 1.5 T were achieved in these two alloys, respectively. Such ΔTad values are obviously higher than that obtained from a single martensitic transformation and magnetic transition. The present results demonstrate that proper composition tuning to achieve magnetostructural transformation as well as increasing the grain size and preferential orientation degree through directional solidification could be an economical processing route to optimize magnetocaloric properties in polycrystalline Ni-Mn-Ga based alloys.

In situ diagnostics of the crystal-growth process through neutron imaging: application to scintillators

DOE PAGES

Tremsin, Anton S.; Makowska, Małgorzata G.; Perrodin, Didier; ...

2016-04-12

Neutrons are known to be unique probes in situations where other types of radiation fail to penetrate samples and their surrounding structures. In this paper it is demonstrated how thermal and cold neutron radiography can provide time-resolved imaging of materials while they are being processed (e.g.while growing single crystals). The processing equipment, in this case furnaces, and the scintillator materials are opaque to conventional X-ray interrogation techniques. The distribution of the europium activator within a BaBrCl:Eu scintillator (0.1 and 0.5% nominal doping concentrations per mole) is studiedin situduring the melting and solidification processes with a temporal resolution of 5–7 s.more » The strong tendency of the Eu dopant to segregate during the solidification process is observed in repeated cycles, with Eu forming clusters on multiple length scales (only for clusters larger than ~50 µm, as limited by the resolution of the present experiments). It is also demonstrated that the dopant concentration can be quantified even for very low concentration levels (~0.1%) in 10 mm thick samples. The interface between the solid and liquid phases can also be imaged, provided there is a sufficient change in concentration of one of the elements with a sufficient neutron attenuation cross section. Tomographic imaging of the BaBrCl:0.1%Eu sample reveals a strong correlation between crystal fractures and Eu-deficient clusters. The results of these experiments demonstrate the unique capabilities of neutron imaging forin situdiagnostics and the optimization of crystal-growth procedures.« less

Shallow cells in directional solidification

NASA Technical Reports Server (NTRS)

Merchant, G. J.; Davis, S. H.

1989-01-01

The existing theory on two-dimensional transitions (appropriate to thin parallel-plate geometries) is presented in such a way that it is possible to identify easily conditions for the onset of shallow cells. Conditions are given under which succinonitrile-acetone mixtures should undergo supercritical bifurcation in experimentally accessible ranges. These results suggest a means for the quantitative test of the Mullins and Sekerka (1964) model and its weakly nonlinear extensions.

Microgravity

NASA Image and Video Library

1999-04-01

The Equiaxed Dendritic Solidification Experiment (EDSE) is a material sciences investigation under the Formation of Microstructures/pattern formation discipline. The objective is to study the microstructural evolution of and thermal interactions between several quiaxed crystals growing dendritically in a supercooled melt of a pure and transparent substance under diffusion controlled conditions. George Myers, controls engineer, monitors the thermal environment of a ground test for the EDSE located in the Microgravity Development Laboratory (MDL).

Microgravity

NASA Image and Video Library

1999-04-01

The Equiaxed Dendritic Solidification Experiment (EDSE) is a material sciences investigation under the Formation of Microstructures/pattern formation discipline. The objective is to study the microstructural evolution of and thermal interactions between several equiaxed crystals growing dendritically in a supercooled melt of a pure and transparent substance under diffusion controlled conditions. EDSE/TDSE project engineer, Zena Hester, monitors a test run of the EDSE located in the Microgravity Development Laboratory (MDL).

SILICATE TECHNOLOGY CORPORATION'S SOLIDIFICATION/ STABILIZATION TECHNOLOGY FOR ORGANIC AND INORGANIC CONTAMINANTS IN SOILS - APPLICATIONS ANALYSIS REPORT

EPA Science Inventory

This Applications Analysis Report evaluates the solidification/stabilization treatment process of Silicate Technology Corporation (STC) for the on-site treatment of hazardous waste. The STC immobilization technology utilizes a proprietary product (FMS Silicate) to chemically stab...

TECHNOLOGY EVALUATION REPORT: SILICATE TECHNOLOGY CORPORATION - SOLIDIFICATION/STABILIZATION OF PCP AND INORGANIC CONTAMINANTS IN SOILS - SELMA, CA

EPA Science Inventory

This Technolgy Evaluation Report evaluates the solidification/stabilization process of Silicate Technology Corporation (STC) for the on-site treatment of contaminated soil The STC immobilization technology uses a proprietary product (FMS Silicate) to chemically stabilize and ...

AN EVALUATION OF FACTORS AFFECTING THE SOLIDIFICATION/STABILIZATION OF HEAVY METAL SLUDGE

EPA Science Inventory

Solidification/stabilization (SIS) of hazardous waste involves mixing the waste with a binder material to enhance the physical properties of the waste and to immobilize contaminants that may be detrimental to the environment. Many hazardous wastes contain materials that are know...

Flight Planning for the International Space Station-Levitation Observation of Dendrite Evolution in Steel Ternary Alloy Rapid Solidification

NASA Technical Reports Server (NTRS)

Flemings, M. C.; Matson, D. M.; Loser, W.; Hyers, R. W.; Rogers, J. R.; Curreri, Peter A. (Technical Monitor)

2002-01-01

The paper is an overview of the status and science for the LODESTARS research project. The program is aimed at understanding how melt convection influences phase selection and the evolution of rapid solidification microstructures

The role of rapid solidification processing in the fabrication of fiber reinforced metal matrix composites

NASA Technical Reports Server (NTRS)

Locci, Ivan E.; Noebe, Ronald D.

1989-01-01

Advanced composite processing techniques for fiber reinforced metal matrix composites require the flexibility to meet several widespread objectives. The development of uniquely desired matrix microstructures and uniformly arrayed fiber spacing with sufficient bonding between fiber and matrix to transmit load between them without degradation to the fiber or matrix are the minimum requirements necessary of any fabrication process. For most applications these criteria can be met by fabricating composite monotapes which are then consolidated into composite panels or more complicated components such as fiber reinforced turbine blades. Regardless of the end component, composite monotapes are the building blocks from which near net shape composite structures can be formed. The most common methods for forming composite monotapes are the powder cloth, foil/fiber, plasma spray, and arc spray processes. These practices, however, employ rapid solidification techniques in processing of the composite matrix phase. Consequently, rapid solidification processes play a vital and yet generally overlooked role in composite fabrication. The future potential of rapid solidification processing is discussed.

Transient Effects in Planar Solidification of Dilute Binary Alloys

NASA Technical Reports Server (NTRS)

Mazuruk, Konstantin; Volz, Martin P.

2008-01-01

The initial transient during planar solidification of dilute binary alloys is studied in the framework of the boundary integral method that leads to the non-linear Volterra integral governing equation. An analytical solution of this equation is obtained for the case of a constant growth rate which constitutes the well-known Tiller's formula for the solute transient. The more physically relevant, constant ramping down temperature case has been studied both numerically and analytically. In particular, an asymptotic analytical solution is obtained for the initial transient behavior. A numerical technique to solve the non-linear Volterra equation is developed and the solution is obtained for a family of the governing parameters. For the rapid solidification condition, growth rate spikes have been observed even for the infinite kinetics model. When recirculating fluid flow is included into the analysis, the spike feature is dramatically diminished. Finally, we have investigated planar solidification with a fluctuating temperature field as a possible mechanism for frequently observed solute trapping bands.

Solidification kinetics of a near eutectic Al-Si alloy, unmodified and modified with Sr

NASA Astrophysics Data System (ADS)

Aparicio, R.; Barrera, G.; Trapaga, G.; Ramirez-Argaez, M.; Gonzalez-Rivera, C.

2013-07-01

The purpose of this work was to explore the differences in solidification kinetics between unmodified and Sr modified eutectic Al-Si alloy as revealed by Fourier Thermal Analysis (FTA) and grain-growth kinetics characterization. Thermal analysis were performed in cylindrical stainless steel cups coated with a thin layer of boron nitride, using two type-K thermocouples connected to a data acquisition system. Grain growth kinetics characterization was carried out using solid fraction evolution and grain density data. FTA results for the non modified and modified alloys suggest that there are changes in the solidification rate during eutectic nucleation followed, during growth, by similar solidification rate evolutions, suggesting that this parameter is governed principally by the heat extraction conditions. On the other hand the change of the grain growth parameters estimated for the experimental probes suggest that the presence of Sr may modify the relationship between grain growth rate and undercooling in eutectic Al-Si.

Mathematical Model of Solidification During Electroslag Casting of Pilger Roll

NASA Astrophysics Data System (ADS)

Liu, Fubin; Li, Huabing; Jiang, Zhouhua; Dong, Yanwu; Chen, Xu; Geng, Xin; Zang, Ximin

A mathematical model for describing the interaction of multiple physical fields in slag bath and solidification process in ingot during pilger roll casting with variable cross-section which is produced by the electroslag casting (ESC) process was developed. The commercial software ANSYS was applied to calculate the electromagnetic field, magnetic driven fluid flow, buoyancy-driven flow and heat transfer. The transportation phenomenon in slag bath and solidification characteristic of ingots are analyzed for variable cross-section with variable input power under the conditions of 9Cr3NiMo steel and 70%CaF2 - 30%Al2O3 slag system. The calculated results show that characteristic of current density distribution, velocity patterns and temperature profiles in the slag bath and metal pool profiles in ingot have distinct difference at variable cross-sections due to difference of input power and cooling condition. The pool shape and the local solidification time (LST) during Pilger roll ESC process are analyzed.

The volume change during solidification

NASA Technical Reports Server (NTRS)

Rittich, M.

1985-01-01

The liquid-solid phase transformation of solidifying metallic melts is accompanied by a volume change Delta-Vm. This volume change produces a gravity-independent microscopic flow near the solidification front. In a ground-based laboratory, solidification processes are also affected by convection due to temperature and concentration gradients. A quantitative evaluation of the effects of these flows on the formation of structure requires reproducible values of Delta-Vm. Alloys with Delta-Vm = 0 would be best suited for such an evaluation, while alloys with a constant value for Delta-Vm are still usable. Another requirement is related to a solidus-liquidus interval which is as small as possible. One-phase alloys, which would be particularly well suited, could not be found. For these reasons, alloys which solidify in two phases, as for example eutectics, have been considered, taking into account the Al-Ge system. Attention is given to the volume change at the melting point, the measurement of this change, the volume change at solidification, and applications to terrestrial technology.

Melting and solidification characteristics of a mixture of two types of latent heat storage material in a vessel

NASA Astrophysics Data System (ADS)

Yu, JikSu; Horibe, Akihiko; Haruki, Naoto; Machida, Akito; Kato, Masashi

2016-11-01

In this study, we investigated the fundamental melting and solidification characteristics of mannitol, erythritol, and their mixture (70 % by mass mannitol: 30 % by mass erythritol) as potential phase-change materials (PCMs) for latent heat thermal energy storage systems, specifically those pertaining to industrial waste heat, having temperatures in the range of 100-250 °C. The melting point of erythritol and mannitol, the melting peak temperature of their mixture, and latent heat were measured using differential scanning calorimetry. The thermal performance of the mannitol mixture was determined during melting and solidification processes, using a heat storage vessel with a pipe heat exchanger. Our results indicated phase-change (fusion) temperatures of 160 °C for mannitol and 113 and 150 °C for the mannitol mixture. Nondimensional correlation equations of the average heat transfer during the solidification process, as well as the temperature and velocity efficiencies of flowing silicon oil in the pipe and the phase-change material (PCM), were derived using several nondimensional parameters.

Thermosolutal convection and macrosegregation in dendritic alloys

NASA Technical Reports Server (NTRS)

Poirier, David R.; Heinrich, J. C.

1993-01-01

A mathematical model of solidification, that simulates the formation of channel segregates or freckles, is presented. The model simulates the entire solidification process, starting with the initial melt to the solidified cast, and the resulting segregation is predicted. Emphasis is given to the initial transient, when the dendritic zone begins to develop and the conditions for the possible nucleation of channels are established. The mechanisms that lead to the creation and eventual growth or termination of channels are explained in detail and illustrated by several numerical examples. A finite element model is used for the simulations. It uses a single system of equations to deal with the all-liquid region, the dendritic region, and the all-solid region. The dendritic region is treated as an anisotropic porous medium. The algorithm uses the bilinear isoparametric element, with a penalty function approximation and a Petrov-Galerkin formulation. The major task was to develop the solidification model. In addition, other tasks that were performed in conjunction with the modeling of dendritic solidification are briefly described.

Resistivity Distribution of Multicrystalline Silicon Ingot Grown by Directional Solidification

NASA Astrophysics Data System (ADS)

Sun, S. H.; Tan, Y.; Dong, W.; Zhang, H. X.; Zhang, J. S.

2012-06-01

The effects of impurities on the resistivity distribution and polarity of multicrystalline silicon ingot prepared by directional solidification were investigated in this article. The shape of the equivalence line of the resistivity in the vertical and cross sections was determined by the solid-liquid interface. Along the solidification height of silicon ingot, the conductive type changed from p-type in the lower part of the silicon ingot to n-type in the upper part of the silicon ingot. The resistivity in the vertical section of the silicon ingot initially increased along the height of the solidified part, and reached its maximum at the polarity transition position, then decreased rapidly along the height of solidified part and approached zero on the top of the ingot because of the accumulation of impurities. The variation of resistivity in the vertical section of the ingot has been proven to be deeply relevant to the distribution of Al, B, and P in the growth direction of solidification.

SPAR X Technical Report for Experiment 76-22 Directional Solidification of Magnetic Composites

NASA Technical Reports Server (NTRS)

Bethin, J.

1984-01-01

The effects of gravity on Bridgman-Stockbarger directional solidification of off-eutectic Bi/MnBi were studied in reduced gravity aboard the SPAR X flight and compared to normal-gravity investigations and previous eutectic Bi/MnBi SPAR flight experiments. The directional solidification of off-eutectic Bi/MnBi results in either a dendritic structure connected with local cooperative growth or a coupled low volume fraction faceted/non faceted aligned rod eutectic whose Mn macrosegregation, MnBi rod size, interrod spacing, and thermal and magnetic properties are sensitive functions of the solidification processing conditions. Two hypoeutectic and two hypereutectic samples were solidified during 605 sec of furnace travel, with an initial 265 sec low-gravity interval. Comparison Earth-gravity samples were solidified in the same furance assembly under identical processing conditions. Macrosegregation in the low-g samples was consistent with a metastable increase in Mn solubility in the Bi matrix, in partial agreement with previous Bi/MnBi SPAR findings of MnBi volume reduction.

Modeling and Validation of a Three-Stage Solidification Model for Sprays

NASA Astrophysics Data System (ADS)

Tanner, Franz X.; Feigl, Kathleen; Windhab, Erich J.

2010-09-01

A three-stage freezing model and its validation are presented. In the first stage, the cooling of the droplet down to the freezing temperature is described as a convective heat transfer process in turbulent flow. In the second stage, when the droplet has reached the freezing temperature, the solidification process is initiated via nucleation and crystal growth. The latent heat release is related to the amount of heat convected away from the droplet and the rate of solidification is expressed with a freezing progress variable. After completion of the solidification process, in stage three, the cooling of the solidified droplet (particle) is described again by a convective heat transfer process until the particle approaches the temperature of the gaseous environment. The model has been validated by experimental data of a single cocoa butter droplet suspended in air. The subsequent spray validations have been performed with data obtained from a cocoa butter melt in an experimental spray tower using the open-source computational fluid dynamics code KIVA-3.

Direct Observation of Pore Formation and Bubble Mobility during Controlled Melting and Resolidification in Microgravity

NASA Technical Reports Server (NTRS)

Grugel, Richard N.; Anilkumar, A. V.; Lee, C. P.

2004-01-01

Detailed studies on the controlled melting and subsequent re-solidification of succinonitrile were conducted in the microgravity environment aboard the International Space Station (ISS) using the PFMI apparatus (Pore Formation and Mobility Investigation) located in the ISS glovebox facility (GBX). Samples were initially prepared on ground by filling glass tubes, 1 cm ID and approximately 30 cm in length, with pure succinonitrile (SCN) under 450 millibar of nitrogen. During Space processing, experimental parameters like temperature gradient and translation speed, for melting and solidification, were remotely monitored and controlled from the ground Telescience Center (TSC) at the Marshall Space Flight Center. Real time visualization during controlled melting revealed bubbles of different sizes initiating at the solid/liquid interface, and traveling up the temperature gradient ahead of them. Subsequent controlled re-solidification of the SCN revealed the details of porosity formation and evolution. A preliminary analysis of the melt back and re- solidification and its implications to future microgravity materials processing is presented and discussed.

A study of reduced chromium content in a nickel-base superalloy via element substitution and rapid solidification processing. Ph.D. ThesisFinal Report

NASA Technical Reports Server (NTRS)

Powers, William O.

1987-01-01

A study of reduced chromium content in a nickel base superalloy via element substitution and rapid solidification processing was performed. The two elements used as partial substitutes for chromium were Si and Zr. The microstructure of conventionally solidified materials was characterized using microscopy techniques. These alloys were rapidly solidified using the chill block melt spinning technique and the rapidly solidified microstructures were characterized using electron microscopy. The spinning technique and the rapidly solidified microstructures was assessed following heat treatments at 1033 and 1272 K. Rapidly solidified material of three alloys was reduced to particulate form and consolidated using hot isostatic pressing (HIP). The consolidated materials were also characterized using microscopy techniques. In order to evaluate the relative strengths of the consolidated alloys, compression tests were performed at room temperature and 1033 K on samples of as-HIPed and HIPed plus solution treated material. Yield strength, porosity, and oxidation resistance characteristics are given and compared.

Mechanical properties of aluminium fused SiO2 particulate composites cast using metallic and non-metallic chills

NASA Astrophysics Data System (ADS)

Harshith, H. S.; Hemanth, Joel

2018-04-01

This research work aims at developing and mechanical characterization of aluminium (LM13) based metal matrix composite reinforced with varying percentage of fused SiO2 (3%,6%,9%,12%). The mechanical properties are completely dependent on the microstructural parameters of the system. Also the microstructure further depends on the cooling rates during solidification process. Various Chills like Silicon carbide, Mild steel, Copper were used during the casting process to increase the rate of solidification, which enhances the mechanical properties of the composite. The chill casted specimens were subjected to tensile and hardness tests followed by microstructure studies. A casting produced using mild steel chill exhibited higher young's modulus and was found to be maximum at 9% reinforcement. Finer microstructure and better UTS were seen for specimen's casted using copper chills, whereas silicon carbide and mild steel chills gave rise to very coarse structure with reduced UTS values compared to copper chills.

EBSD investigation of the effect of the solidification rate on the nucleation behavior of eutectic components in a hypoeutectic Al-Si-Cu alloy

NASA Astrophysics Data System (ADS)

Mohsen Sadrossadat, S.; Johansson, Sten; Peng, Ru Lin

2012-06-01

This article represents a study of the influence of the solidification rate on the crystallographic orientation of eutectic components with respect to the primary α-Al in the tested hypoeutectic alloy. Electron backscattering diffraction (EBSD) patterns were produced from the Al-Si cast specimens that were solidified with different cooling rates and prepared via ion etch polishing as a complementary method after mechanical polishing. The results indicated a strong orientation relationship between the primary α-Al and eutectic Al phase at all cooling rates. It was also found that the silicon eutectic flakes were heterogeneously nucleated in the interdendritic eutectic liquid. The increase of the cooling rate from 2 to 80 mm/min was found to be effective in lowering the intensity of the relationship between the primary α-Al and eutectic Al phases, and changing the misorientation angle clustering between the primary α-Al and eutectic Si phases in the interval from 41-60° to lower angle intervals.

The effect of surface tension, superheat and surface films on the rate of heat transfer from an iron droplet to a water cooled copper mold

NASA Astrophysics Data System (ADS)

Phinichka, Natthapong

In strip casting the cast surface forms during the initial stage of solidification and the phenomenon that occurs during the first 50 milliseconds of contact time between the liquid steel and the mold define the cast surface and its quality. However the exact mechanism of the initial solidification and the process variables that affect initial solidification phenomena during that time are not well understood. The primary goal of this work is to develop a fundamental understanding of factors controlling strip casting. The purpose of the experimental study is to better understand the role of processing parameters on initial solidification phenomena, heat transfer rate and the formation of the cast steel surface. An investigation was made to evaluate the heat transfer rate of different kinds of steels. The experimental apparatus was designed for millisecond resolution of heat transfer behavior. A novel approach of simultaneous in-situ observation and measurement of rapid heat transfer was developed and enabled a coupling between the interfacial heat transfer rate and droplet solidification rate. The solidification rate was estimated from the varying position of the solidification front as captured by a CCD camera. The effects of experimental parameters such as melt superheat, sulfur content and oxide accumulation at the interface on measured heat flux were studied. It was found that the heat flux increased slightly when the percent of sulfur and increased significantly when superheat increased. The oxide accumulation at the interface was found to be manganese and silicon based oxide. When the liquid steel droplets were ejected onto the copper substrate repeatedly, without cleaning the substrate surface between the ejections, a large increase in the interfacial heat flux was observed. The results of the film study indicated that a liquid oxide film existed at the interface. The surface roughness measurement of the solidified specimen decreased with repeated experimentation and better contact between the droplet and the mold was found to be the cause of the improved heat transfer rate.

Space Processing Applications Rocket project, SPAR 1

NASA Technical Reports Server (NTRS)

Reeves, F. (Compiler); Chassay, R. (Compiler)

1976-01-01

The experiment objectives, design/operational concepts, and final results of each of nine scientific experiments conducted during the first Space Processing Applications Rocket (SPAR) flight are summarized. The nine individual SPAR experiments, covering a wide and varied range of scientific materials processing objectives, were entitled: solidification of Pb-Sb eutectic, feasibility of producing closed-cell metal foams, characterization of rocket vibration environment by measurement of mixing of two liquids, uniform dispersions of crystallization processing, direct observation of solidification as a function of gravity levels, casting thoria dispersion-strengthened interfaces, contained polycrystalline solidification, and preparation of a special alloy for manufacturing of magnetic hard superconductor under zero-g environment.

Low-gravity processing of superconducting compounds

NASA Technical Reports Server (NTRS)

Otto, G. H.

1976-01-01

Low gravity conditions can be sustained on earth for several seconds in an evacuated drop tube. Because radiation cooling is most effective at high temperatures, the refractive metals and alloys are prime candidates for free fall solidification. The results of initial experiments on droplet formation, droplet release, critical size and evaporation losses are given. The time required for free fall solidification of different size droplets is calculated. The materials studied were copper, niobium and vanadium, and a niobium-tin alloys. Improvements in purity, composition, homogeneity and stoichiometry are expected during free fall solidification of niobium based alloys which should become evident in an increase in the superconducting transition temperature.

A molecular dynamics study of cooling rate during solidification of metal nanoparticles

NASA Astrophysics Data System (ADS)

Shibuta, Yasushi; Suzuki, Toshio

2011-01-01

The effect of the cooling rate on the solidification behavior of metal nanoparticles is investigated by molecular dynamics simulation. The structure of molybdenum nanoparticles varies with the cooling rate. That is, single-crystalline, polycrystalline then glassy nanoparticles are obtained as the cooling rate is increased from 2.0 × 10 10 to 1.0 × 10 13 K/s. The solidification point decreases with increasing cooling rate then drops rapidly at a cooling rate on the order of 10 12 K/s. These results are summarized in a continuous cooling transformation (CCT) diagram, in which regions corresponding the liquid, single-crystalline, polycrystalline and glassy structures appear.

Numerical model for dendritic solidification of binary alloys

NASA Technical Reports Server (NTRS)

Felicelli, S. D.; Heinrich, J. C.; Poirier, D. R.

1993-01-01

A finite element model capable of simulating solidification of binary alloys and the formation of freckles is presented. It uses a single system of equations to deal with the all-liquid region, the dendritic region, and the all-solid region. The dendritic region is treated as an anisotropic porous medium. The algorithm uses the bilinear isoparametric element, with a penalty function approximation and a Petrov-Galerkin formulation. Numerical simulations are shown in which an NH4Cl-H2O mixture and a Pb-Sn alloy melt are cooled. The solidification process is followed in time. Instabilities in the process can be clearly observed and the final compositions obtained.

Modelling directional solidification

NASA Technical Reports Server (NTRS)

Wilcox, William R.

1990-01-01

The long range goal is to develop an improved understanding of phenomena of importance to directional solidification, to enable explanation and prediction of differences in behavior between solidification on Earth and in space. Emphasis during the period of this grant was on experimentally determining the influence of convection and freezing rate fluctuations on compositional homogeneity and crystalline perfection in the vertical Bridgman-Stockbarger technique. Heater temperature profiles, buoyancy-driven convection, and doping inhomogeneties were correlated using naphthalene doped with azulene. In addition the influence of spin-up/spin-down on compositional homogeneity and microstructure of indium gallium antimonide and the effect of imposed melting-freezing cycles on indium gallium antimonide are discussed.

Thermal analysis and microstructural characterization of Mg-Al-Zn system alloys

NASA Astrophysics Data System (ADS)

Król, M.; Tański, T.; Sitek, W.

2015-11-01

The influence of Zn amount and solidification rate on the characteristic temperature of the evaluation of magnesium dendrites during solidification at different cooling rates (0.6-2.5°C) were examined by thermal derivative analysis (TDA). The dendrite coherency point (DCP) is presented with a novel approach based on second derivative cooling curve. Solidification behavior was examined via one thermocouple thermal analysis method. Microstructural assessments were described by optical light microscopy, scanning electron microscopy and energy dispersive X-ray spectroscopy. These studies showed that utilization of d2T/dt2 vs. the time curve methodology provides for analysis of the dendrite coherency point

The solidification of Al–Pd–Mn studied by high-energy X-ray diffraction from electrostatically levitated samples

DOE Office of Scientific and Technical Information (OSTI.GOV)

Quirinale, Dante G.

Here, we report on the results of a high-energy x-ray diffraction study of Al–Pd–Mn to investigate the solidification products obtained during free-cooling using an electrostatic levitation furnace. The primary solidification product from the melt is i-Al–Pd–Mn which coexists with a significant remaining liquid component. As the sample cools further, we find that the solidification pathway is consistent with the liquidus projection and pseudo-binary cut through the ternary phase diagram reported previously. At ambient temperature we have identified the major phase to be the ξ'-phase orthorhombic approximant, along with minor phases identified as Al and, most likely, the R-phase orthorhombic approximant.more » We have also observed a distinct prepeak in the liquid at high temperature, signifying the presence of extended atomic order. Interestingly, this prepeak was not observed in previous neutron diffraction measurements on the Al–Pd–Mn system. No undercooling was observed preceding the solidification of the i-Al–Pd–Mn phase from the melt which may signal the close similarity of the short-range order in the solid and liquid. However, this can not be clearly determined because of the potential for heterogenous nucleation associated with the presence of an Al2O3 impurity at the surface of the sample.« less

Melting-solidification transition of Zn nanoparticles embedded in SiO2: Observation by synchrotron x-ray and ultraviolet-visible-near-infrared light

NASA Astrophysics Data System (ADS)

Amekura, H.; Tanaka, M.; Katsuya, Y.; Yoshikawa, H.; Ohnuma, M.; Matsushita, Y.; Kobayashi, K.; Kishimoto, N.

2010-11-01

Melting-solidification transition of Zn nanoparticles (NPs) with the mean diameter of 11.5 nm, embedded in silica glass, was investigated by glancing incident x-ray diffraction (GIXRD) at high temperatures using synchrotron radiation (SR). With increasing temperature, 101Zn diffraction peak gradually decreases up to ˜360 °C and then steeply decreases. This is due to the melting of Zn NPs, which completes around 420 °C. With decreasing temperature, the solidification of the NPs begins around ˜310 °C. The temperature hysteresis with a width of ˜110 °C was observed. With temperature, the diffraction angle shows a shift without hysteresis, which is ascribed to thermal expansion of Zn NP lattice. Thermal expansion coefficient of Zn NPs was determined as 24.4×10-6 K-1 along the ⟨101⟩ direction. Optical absorption spectroscopy shows a broad ultraviolet (UV) peak which was observed at even higher temperatures than the melting temperature but shifts to the low-energy side with the melting. The energy shift in the UV peak also shows the temperature hysteresis which resembles with the melting-solidification hysteresis recorded by SR-GIXRD. The melting-solidification transition is also detectable by the optical absorption spectroscopy in the UV-visible-near-infrared region.

Detection and reconstruction of solidification cracks - Laser ultrasonic measurements during the continuous casting process of aluminum

NASA Astrophysics Data System (ADS)

Mitter, Thomas; Grün, Hubert; Roither, Jürgen; Betz, Andreas; Bozorgi, Salar; Reitinger, Bernhard; Burgholzer, Peter

2014-05-01

In the continuous casting process the avoidance and rapid detection of occurring solidification cracks in the slab is a crucial issue, in particular for the maintenance of a high quality level in further production processes. Due to the elevated temperatures of the slab surface a remote sensing non-destructive tool for quality inspection is required, which is also applicable for the harsh industrial environment. In this work the application of laser ultrasound (LUS) technique during the continuous casting process in industrial environment is shown. The proof of principle of the detection of the centered solidification cracks is shown by pulse-echo measurements with laser ultrasonic equipment for inline quality inspection. Preliminary examinations in the lab of different casted samples have shown the distinguishability of slabs with and without any solidification cracks. Furthermore the damping of the bulk wave has been used for the prediction of the dimension of the crack. With an adapted "synthetic aperture focusing technique" (SAFT) algorithm the image reconstruction of multiple measurements at different positions around the circumference has provided enough information for the estimation of the localization and extension of the centered solidification cracks. Subsequent first measurements using this laser ultrasonic setup during the continuous casting of aluminum were carried out and showed the proof of principle in an industrial environment with elevated temperatures, dust, cooling water and vibrations.

Pressurized metallurgy for high performance special steels and alloys

NASA Astrophysics Data System (ADS)

Jiang, Z. H.; Zhu, H. C.; Li, H. B.; Li, Y.; Liu, F. B.

2016-07-01

The pressure is one of the basic parameters which greatly influences the metallurgical reaction process and solidification of steels and alloys. In this paper the history and present situation of research and application of pressurized metallurgy, especially pressurized metallurgy for special steels and alloys have been briefly reviewed. In the following part the physical chemistry of pressurized metallurgy is summarized. It is shown that pressurizing may change the conditions of chemical reaction in thermodynamics and kinetics due to the pressure effect on gas volume, solubility of gas and volatile element in metal melt, activity or activity coefficient of components, and change the physical and chemical properties of metal melt, heat transfer coefficient between mould and ingot, thus greatly influencing phase transformation during the solidification process and the solidification structure, such as increasing the solidification nucleation rate, reducing the critical nucleation radius, accelerating the solidification speed and significant macro/micro-structure refinement, and eliminating shrinkage, porosity and segregation and other casting defects. In the third part the research works of pressured metallurgy performed by the Northeastern University including establishment of pressurized induction melting (PIM) and pressurized electroslag remelting (PESR) equipments and development of high nitrogen steels under pressure are described in detail. Finally, it is considered in the paper that application of pressurized metallurgy in manufacture of high performance special steels and alloys is a relatively new research area, and its application prospects will be very broad and bright.

Experimental study of void formation during aluminum solidification in reduced gravity. Ph.D. Thesis - Toledo Univ.

NASA Technical Reports Server (NTRS)

Chiaramonte, Francis Paul, III

1993-01-01

Void formation due to volumetric shrinkage and liquid/vapor reorientation during aluminum solidification was observed in real time by using a radiographic viewing system in normal and reduced gravity. An end-chill directional solidification furnace with water quench was designed and constructed to solidify aluminum samples during the approximately 16 sec of reduced gravity (+/-0.02g) achieved by flying an aircraft through a parabolic trajectory. In the first series of tests the aluminum was contained in a vacuum sealed, pyrolytic boron nitride crucible. An ullage space was present during each test. Void formation was recorded for two cases: a nonwetting system, and a wetting system where wetting occurred between the aluminum and the crucible lid. The void formation in the nonwetting case was similar in normal and reduced gravity, with a single vapor cavity forming at the top of the crucible. In the wetting case during reduced gravity surface tension caused two voids to form in the top corners of the crucible, but during normal gravity only one large void formed across the top. In the second series of tests the aluminum was contained in a pyrolytic boron nitride crucible that was placed in a stainless steel container and sealed in an environment of argon plus 4 percent hydrogen. An ullage space was present during each test. Void formation was recorded for two cases: a nonwetting system, and a wetting system where wetting occurred between the aluminum and one side wall and the lid. The void for nation in the nonwetting case was similar in normal and reduced gravity, with a single vapor cavity forming at the top of the crucible, although the meniscus became more convex in reduced gravity. In the wetting case the aluminum did not climb up the corners in 1g, and one large symmetric void resulted at the top when the aluminum had solidified. In the wetting case during reduced gravity the molten aluminum was drawn up the wetted wall and partially across the lid by a capillary underpressure; however, on the nonwetting wall the aluminum moved down. One void resulted along the nonwetting side of the container continuing to the top on the same side.

Space processing applications rocket project SPAR 4, engineering report

NASA Technical Reports Server (NTRS)

Reeves, F. (Compiler)

1980-01-01

The materials processing experiments in space, conducted on the SPAR 4 Black Brant VC rocket, are described and discussed. The SPAR 4 payload configuration, the rocket performance, and the flight sequence are reported. The results, analyses, and anomalies of the four experiments are discussed. The experiments conducted were the uniform dispersions of crystallization processing, the contained polycrstalline solidification in low gravity, the containerless processing of ferromagnetic materials, and the containerless processing technology. The instrumentation operations, payload power relay anomaly, relay postflight operational test, and relay postflight shock test are reported.

OVERVIEW OF THE HISTORY, PRESENT STATUS, AND FUTURE DIRECTION OF SOLIDIFICATION/STABILIZATION TECHNOLOGIES FOR HAZARDOUS WASTE TREATMENT

EPA Science Inventory

Solidification/stabilization (S/S) technology processes are currently being utilized in the United States to treat inorganic and organic hazardous waste and radioactive waste. These wastes are generated from operating industry or have resulted from the uncontrolled management of ...

Recent Ground Hold and Rapid Depressurization Testing of Multilayer Systems

NASA Technical Reports Server (NTRS)

Johnson, Wesley L.

2014-01-01

In the development of flight insulation systems for large cryogenic orbital storage (spray on foam and multilayer insulation), testing need include all environments that are experienced during flight. While large efforts have been expended on studying, bounding, and modeling the orbital performance of the insulation systems, little effort has been expended on the ground hold and ascent phases of a mission. Historical cryogenic in-space systems that have flown have been able to ignore these phases of flight due to the insulation system being within a vacuum jacket. In the development phase of the Nuclear Mars Vehicle and the Shuttle Nuclear Vehicle, several insulation systems were evaluated for the full mission cycle. Since that time there had been minimal work on these phases of flight until the Constellation program began investigating cryogenic service modules and long duration upper stages. With the inception of the Cryogenic Propellant Storage and Transfer Technology Demonstration Mission, a specific need was seen for the data and as such, several tests were added to the Cryogenic Boil-off Reduction System liquid hydrogen test matrix to provide more data on a insulation system. Testing was attempted with both gaseous nitrogen (GN2) and gaseous helium (GHe) backfills. The initial tests with nitrogen backfill were not successfully completed due to nitrogen liquefaction and solidification preventing the rapid pumpdown of the vacuum chamber. Subsequent helium backfill tests were successful and showed minimal degradation. The results are compared to the historical data.

The Relative Influence of H2O and CO2 on the Primitive Surface Conditions and Evolution of Rocky Planets

NASA Astrophysics Data System (ADS)

Salvador, A.; Massol, H.; Davaille, A.; Marcq, E.; Sarda, P.; Chassefiere, E.

2016-12-01

Recent literature reveals how different the telluric planets' water content can be, depending on the formation processes and origins of water. Furthermore, for Earth mass planets, estimates of their atmospheric water content range between 0.3 to 1000 water oceans. We simulate the secular convective cooling and solidification of a 1D magma ocean (hereafter "MO") in interaction with the outgassed atmosphere. We vary the initial CO2 and H2O contents (respectively from 0.1×10-2 to 14×10-2wt% and from 0.05 to 2.2 times the Earth Ocean current mass (MEO)), the solar distance - from 0.63 to 1.30 AU -, the radiative heat transfer in the atmosphere (grey or non-grey, with or without clouds) and investigate the relative influence of these parameters on an Earth like planet's surface conditions at the MO phase term, and especially its ability to form a water ocean. We define the end of the MO as the time when the heat flux from the vigorous convecting mantle becomes negligible compared to the incident solar flux, linked to the dramatic increase of viscosity as the MO solidification reaches the surface, which considerably reduces the convection intensity and the heat transfer. This particular time coincides with the possible apparition of a water ocean and with the development of a thermal boundary layer at the surface, thick enough to limit the interactions between the two reservoirs. As a first step, we assume a bottom-up solidification of the MO. The planetary surface pressure-temperature conditions, resulting from the solidification, are conditioned by the sun-planet distance and the initial CO2 and H2O contents. There is a critical sun-planet distance Rc below which water will never condense, whatever the initial volatile content. For distances larger than Rc, water condensation strongly depends on the relative proportion of CO2 and H2O. The higher the H2O content, the easier it is to reach the equilibrium water vapor pressure and therefore to condense water, for the tested range of CO2 contents. Otherwise, for [H2O]t0<1.8 MEO , too much CO2 precludes the formation of a water ocean by greenhouse effect. In order to study exoplanets surface conditions, and the wide diversity of these gas rich extrasolar worlds, we propose a simple scaling law to explain the relative influence of the tested parameters on the water condensation.

Formation of Hot Tear Under Controlled Solidification Conditions

NASA Astrophysics Data System (ADS)

Subroto, Tungky; Miroux, Alexis; Bouffier, Lionel; Josserond, Charles; Salvo, Luc; Suéry, Michel; Eskin, Dmitry G.; Katgerman, Laurens

2014-06-01

Aluminum alloy 7050 is known for its superior mechanical properties, and thus finds its application in aerospace industry. Vertical direct-chill (DC) casting process is typically employed for producing such an alloy. Despite its advantages, AA7050 is considered as a "hard-to-cast" alloy because of its propensity to cold cracking. This type of cracks occurs catastrophically and is difficult to predict. Previous research suggested that such a crack could be initiated by undeveloped hot tears (microscopic hot tear) formed during the DC casting process if they reach a certain critical size. However, validation of such a hypothesis has not been done yet. Therefore, a method to produce a hot tear with a controlled size is needed as part of the verification studies. In the current study, we demonstrate a method that has a potential to control the size of the created hot tear in a small-scale solidification process. We found that by changing two variables, cooling rate and displacement compensation rate, the size of the hot tear during solidification can be modified in a controlled way. An X-ray microtomography characterization technique is utilized to quantify the created hot tear. We suggest that feeding and strain rate during DC casting are more important compared with the exerted force on the sample for the formation of a hot tear. In addition, we show that there are four different domains of hot-tear development in the explored experimental window—compression, microscopic hot tear, macroscopic hot tear, and failure. The samples produced in the current study will be used for subsequent experiments that simulate cold-cracking conditions to confirm the earlier proposed model.

Space Processing Applications Rocket (SPAR) project SPAR 7

NASA Technical Reports Server (NTRS)

Poorman, R. M.

1983-01-01

The postflight reports of each of the Principal Investigators of three selected science payloads are presented in addition to the engineering report as documented by the Marshall Space Flight Center (MSFC). Pertinent portions of ground-based research leading to the ultimate selection of the flight sample composition are described including design, fabrication and testing. Containerless processing technology, containerless processing bubble dynamics, and comparative alloy solidification are the experiments discussed.

Effect of boron on intergranular hot cracking in Ni-Cr-Fe superalloys containing niobium

NASA Technical Reports Server (NTRS)

Thompson, R. G.

1990-01-01

Solidification mechanisms had a dominant influence on microfissuring behavior of the test group. Carbon modified the Laves formation significantly and showed that one approach to alloy design would be balancing carbide formers against Laves formers. Boron's strong effect on microfissuring can be traced to its potency as a Laves former. Boron's segregation to grain boundaries plays at best a secondary role in microfissuring.

Stacked Fresnel Zone Plates for High Energy X-rays

NASA Astrophysics Data System (ADS)

Snigireva, Irina; Snigirev, Anatoly; Vaughan, Gavin; Di Michiel, Marco; Kohn, Viktor; Yunkin, Vyacheslav; Grigoriev, Maxim

2007-01-01

A stacking technique was developed in order to increase focusing efficiency of Fresnel zone plates (FZP) at high energies. Two identical Si chips each of which containing 9 FZPs were used for stacking. Alignment of the chips was achieved by on-line observation of the moiré pattern. The formation of moiré patterns was studied theoretically and experimentally at different experimental conditions. To provide the desired stability Si-chips were bonded together with slow solidification speed epoxy glue. A technique of angular alignment in order to compensate a linear displacement in the process of gluing was proposed. Two sets of stacked FZPs were experimentally tested to focus 15 and 50 keV x rays. The gain in the efficiency by factor 2.5 was demonstrated at 15 keV. The focal spot of 1.8 μm vertically and 14 μm horizontally with 35% efficiency was measured at 50 keV. Forecast for the stacking of nanofocusing FZPs was discussed.

Hard X-ray focusing by stacked Fresnel zone plates

NASA Astrophysics Data System (ADS)

Snigireva, Irina; Snigirev, Anatoly; Kohn, Viktor; Yunkin, Vyacheslav; Grigoriev, Maxim; Kuznetsov, Serguei; Vaughan, Gavin; Di Michiel, Marco

2007-09-01

Stacking technique was developed in order to increase focusing efficiency of Fresnel zone plates at high energies. Two identical Si chips each of which containing Fresnel zone plates were used for stacking. Alignment of the chips was achieved by on-line observation of the moiré pattern from the two zone plates. The formation of moiré patterns was studied theoretically and experimentally at different experimental conditions. To provide the desired stability Si-chips with zone plates were bonded together with slow solidification speed epoxy glue. Technique of angular alignment in order to compensate a linear displacement in the process of gluing was proposed. Two sets of stacked FZPs were produced and experimentally tested to focus 15 and 50 keV X-rays. Gain in the efficiency by factor 2.5 was demonstrated at 15 keV. Focal spot of 1.8 μm vertically and 14 μm horizontally with 35% efficiency was measured at 50 keV. Forecast for the stacking of nanofocusing Fresnel zone plates was discussed.

Ultrasonic Acoustic Velocities During Partial Melting of a Mantle Peridotite KLB-1

NASA Astrophysics Data System (ADS)

Weidner, Donald J.; Li, Li; Whitaker, Matthew L.; Triplett, Richard

2018-02-01

Knowledge of the elastic properties of partially molten rocks is crucial for understanding low-velocity regions in the interior of the Earth. Models of fluid and solid mixtures have demonstrated that significant decreases in seismic velocity are possible with small amounts of melt, but there is very little available data for testing these models, particularly with both P and S waves for mantle compositions. We report ultrasonic measurements of P and S velocities on a partially molten KLB-1 sample at mantle conditions using a multi-anvil device at a synchrotron facility. The P, S, and bulk sound velocities decrease as melting occurs. We find that the quantity, ∂lnVS/∂lnVB (where VB is the bulk sound velocity) is lower than mechanical models estimate. Instead, our data, as well as previous data in the literature, are consistent with a dynamic melting model in which melting and solidification interact with the stress field of the acoustic wave.

Evaluating the Properties of Dissimilar Metal Welding Between Inconel 625 and 316L Stainless Steel by Applying Different Welding Methods and Consumables

NASA Astrophysics Data System (ADS)

Kourdani, Ahmad; Derakhshandeh-Haghighi, Reza

2018-04-01

The current work was carried out to characterize welding of Inconel 625 superalloy and 316L stainless steel. In the present study, shielded metal arc welding (SMAW) and gas tungsten arc welding (GTAW) with two types of filler metals (ERNiCrMo-3 and ERSS316L) and an electrode (ENiCrMo-3) were utilized. This paper describes the selection of the proper welding method and welding consumables in dissimilar metal joining. During solidification of ERNiCrMo-3 filler metal, Nb and Mo leave dendritic cores and are rejected to inter-dendritic regions. However, ERSS316L filler metal has small amounts of elements with a high tendency for segregation. So, occurrence of constitutional super-cooling for changing the solidification mode from cellular to dendritic or equiaxed is less probable. Using GTAW with lower heat input results in higher cooling rate and finer microstructure and less Nb segregation. The interface between weld metal and base metal and also unmixed zones was evaluated by scanning electron microscopy and energy dispersive X-ray (EDX) analysis. Microhardness measurements, tensile test, and Charpy impact test were performed to see the effect of these parameters on mechanical properties of the joints.

Ukrainian Program for Material Science in Microgravity

NASA Astrophysics Data System (ADS)

Fedorov, Oleg

Ukrainian Program for Material Sciences in Microgravity O.P. Fedorov, Space Research Insti-tute of NASU -NSAU, Kyiv, The aim of the report is to present previous and current approach of Ukrainian research society to the prospect of material sciences in microgravity. This approach is based on analysis of Ukrainian program of research in microgravity, preparation of Russian -Ukrainian experiments on Russian segment of ISS and development of new Ukrainian strategy of space activity for the years 2010-2030. Two parts of issues are discussed: (i) the evolution of our views on the priorities in microgravity research (ii) current experiments under preparation and important ground-based results. item1 The concept of "space industrialization" and relevant efforts in Soviet and post -Soviet Ukrainian research institutions are reviewed. The main topics are: melt supercooling, crystal growing, testing of materials, electric welding and study of near-Earth environment. The anticipated and current results are compared. item 2. The main experiments in the framework of Ukrainian-Russian Research Program for Russian Segment of ISS are reviewed. Flight installations under development and ground-based results of the experiments on directional solidification, heat pipes, tribological testing, biocorrosion study is presented. Ground-based experiments and theoretical study of directional solidification of transparent alloys are reviewed as well as preparation of MORPHOS installation for study of succinonitrile -acetone in microgravity.

Theoretical modeling of cellular and dendritic solidification microstructures

NASA Astrophysics Data System (ADS)

Song, Younggil

In this dissertation, we use three-dimensional (3D) phase-field (PF) modeling to investigate (i) 3D solid-liquid interface dynamics observed in microgravity experiments, and (ii) array patterns in a thin-sample geometry. In addition, using the two-dimensional (2D) dendritic-needle-network (DNN) model, we explore (iii) secondary sidebranching dynamics. Recently, solidification experiments are carried out in the DSI (Directional Solidification Insert) of the DECLIC (Device for the study of Critical LIquids and Crystallization) facility aboard the International Space Station (ISS). Thus, the directional solidification experiments are achieved under limited convective currents, and the experimental observations reveal unique dynamics of 3D microstructure in a purely diffusive growth regime. In this directional solidification setup, a temperature field between heat sources could evolve due to two main factors: (i) heat transfer within an adiabatic zone and (ii) latent heat rejection at the interface. These two thermal effects are phenomenologically characterized using a time-dependent thermal shift. In addition, we could quantitatively account for these thermal factors using a numerical calculation of the evolution of temperature field. We introduce these phenomenological and quantitative thermal representations into the PF model. The performed simulations using different thermal descriptions are compared to the experimental measurements from the initial planar interface dynamics to the final spacing selection. The DECLIC-DSI experimental observations exhibit complex grain boundary (GB) dynamics between large grains with a small misorientation. In the observations, several large grains with a small misorientation with respect to the temperature gradient are formed during solidification. Specifically, at a convergent GB, a localized group of misoriented cells penetrates into a nearby grain, which yields the morphological instability of grain boundaries. Remarkably, while the invasion process starts with a group of cells, the leader cell can detach itself from the group and grow continuously as a misoriented solitary cell in the other grain with a different misorientation. We use PF simulations to investigate the GB morphology and dynamics of a solitary cell. Solidification experiments on earth are typically performed in a thin-sample geometry to avoid fluid convection. Thus, we consider various influences on cellular and dendritic array patterns in thin samples. First, we explore the influence of crystal orientation. When a grain in a thin-sample geometry is misoriented with respect to the temperature gradient, primary cells and dendrites drift laterally in both experiments and simulations. At the same time, grain boundaries are systematically formed at the edges of the misoriented grain. The misoriented primary branches move away from the divergent grain boundary. At this boundary, cells/dendrites are generated continuously, and their spacings are larger than the dynamically selected spacings. Primary branches run into the other convergent GB, which leads to their elimination. Thus, at a stationary state, a spacing distribution is uniform with the spacing selected at the divergent GB until it decreases near the convergent GB. We perform simulations to illustrate the global evolutions of a primary spacing. In addition, we suggest a simple geometrical model and a nonlinear advection equation for the dynamics of the primary spacing evolution, which can predict the slow evolution of a primary spacing in a quasi-2D array. Experimental observations point out that the primary spacing selection could be affected by the sample thickness; however, the detailed description for the link between the primary spacing selection and a sample thickness is still missing. Here, we use PF simulations to investigate the primary cellular and dendritic spacing selection mechanisms under the influence of a sample thickness. A thin-sample geometry can limit thermal and solutal convective currents effectively. However, as the sample thickness increases, the convective currents can influence the solid- liquid interface dynamics. Then, the microstructure selection mechanisms can be different from the classical theories that are valid in a diffusive regime. We propose a simple approach for the PF model to demonstrate the microstructure selection when liquid convection is present. These simulations are compared to experimental results. Columnar microstructures with cells and dendrites typically form polycrystalline materials during directional solidification. Then, convergent and divergent grain boundaries form systematically between grains, which are misoriented with respect to the temperature gradient. Moreover, the GB is dynamically selected during the competition between two nearby misoriented grains. In order to investigate the GB orientation selection, we carry out 3D PF simulations in a thin-sample geometry. These simulations reveal the influence of the 3D GB bi-crystallography on grain competition. The results highlight the importance of considering the orientation of the orthogonal planes containing secondary branches in addition to the growth direction of primary branches. Finally, we propose three growth steps to demonstrate the secondary sidebranching growth dynamics under isothermal dendritic growth condition. (Abstract shortened by ProQuest.).

DOE Office of Scientific and Technical Information (OSTI.GOV)

Choi, Jeong

The research program reported here is focused on critical issues that represent conspicuous gaps in current understanding of rapid solidification, limiting our ability to predict and control microstructural evolution (i.e. morphological dynamics and microsegregation) at high undercooling, where conditions depart significantly from local equilibrium. More specifically, through careful application of phase-field modeling, using appropriate thin-interface and anti-trapping corrections and addressing important details such as transient effects and a velocity-dependent (i.e. adaptive) numerics, the current analysis provides a reasonable simulation-based picture of non-equilibrium solute partitioning and the corresponding oscillatory dynamics associated with single-phase rapid solidification and show that this method ismore » a suitable means for a self-consistent simulation of transient behavior and operating point selection under rapid growth conditions. Moving beyond the limitations of conventional theoretical/analytical treatments of non-equilibrium solute partitioning, these results serve to substantiate recent experimental findings and analytical treatments for single-phase rapid solidification. The departure from the equilibrium solid concentration at the solid-liquid interface was often observed during rapid solidification, and the energetic associated non-equilibrium solute partitioning has been treated in detail, providing possible ranges of interface concentrations for a given growth condition. Use of these treatments for analytical description of specific single-phase dendritic and cellular operating point selection, however, requires a model for solute partitioning under a given set of growth conditions. Therefore, analytical solute trapping models which describe the chemical partitioning as a function of steady state interface velocities have been developed and widely utilized in most of the theoretical investigations of rapid solidification. However, these solute trapping models are not rigorously verified due to the difficulty in experimentally measuring under rapid growth conditions. Moreover, since these solute trapping models include kinetic parameters which are difficult to directly measure from experiments, application of the solute trapping models or the associated analytic rapid solidification model is limited. These theoretical models for steady state rapid solidification which incorporate the solute trapping models do not describe the interdependency of solute diffusion, interface kinetics, and alloy thermodynamics. The phase-field approach allows calculating, spontaneously, the non-equilibrium growth effects of alloys and the associated time-dependent growth dynamics, without making the assumptions that solute partitioning is an explicit function of velocity, as is the current convention. In the research described here, by utilizing the phase-field model in the thin-interface limit, incorporating the anti-trapping current term, more quantitatively valid interface kinetics and solute diffusion across the interface are calculated. In order to sufficiently resolve the physical length scales (i.e. interface thickness and diffusion boundary length), grid spacings are continually adjusted in calculations. The full trajectories of transient planar growth dynamics under rapid directional solidification conditions with different pulling velocities are described. As a validation of a model, the predicted steady state conditions are consistent with the analytic approach for rapid growth. It was confirmed that rapid interface dynamics exhibits the abrupt acceleration of the planar front when the effect of the non-equilibrium solute partitioning at the interface becomes signi ficant. This is consistent with the previous linear stability analysis for the non-equilibrium interface dynamics. With an appropriate growth condition, the continuous oscillation dynamics was able to be simulated using continually adjusting grid spacings. This oscillatory dynamics including instantaneous jump of interface velocities are consistent with a previous phenomenological model by and a numerical investigation, which may cause the formation of banded structures. Additionally, the selection of the steady state growth dynamics in the highly undercooled melt is demonstrated. The transition of the growth morphology, interface velocity selection, and solute trapping phenomenon with increasing melt supersaturations was described by the phase-field simulation. The tip selection for the dendritic growth was consistent with Ivantsov's function, and the non-equilibrium chemical partitioning behavior shows good qualitative agreement with the Aziz's solute trapping model even though the model parameter(V D) remains as an arbitrary constant. This work is able to show the possibility of comprehensive description of rapid alloy growth over the entire time-dependent non-equilibrium phenomenon.« less

Real-Time X-Ray Microscopy of Al-Cu Eutectic Solidification

NASA Technical Reports Server (NTRS)

Kaukler, William F.; Curreri, Peter A.; Sen, Subhayu

1998-01-01

Recent improvements in the resolution of the X-ray Transmission Microscope (XTM) for Solidification Studies provide microstructure feature detectability down to 5 micrometers during solidification. This presentation will show the recent results from observations made in real-time of the solid-liquid interfacial morphologies of the Al-CuAI2 eutectic alloy. Lamellar dimensions and spacings, transitions of morphology caused by growth rate changes, and eutectic grain structures are open to measurements. A unique vantage point viewing the face of the interface isotherm is possible for the first time with the XTM due to its infinite depth of field. A video of the solid-liquid interfaces seen in-situ and in real-time will be shown.

Bubble Induced Disruption of a Planar Solid-Liquid Interface During Controlled Directional Solidification in a Microgravity Environment

NASA Technical Reports Server (NTRS)

Grugel, Richard N.; Brush, Lucien N.; Anilkumar, Amrutur V.

2013-01-01

Pore Formation and Mobility Investigation (PFMI) experiments were conducted in the microgravity environment aboard the International Space Station with the intent of better understanding the role entrained porosity/bubbles play during controlled directional solidification. The planar interface in a slowing growing succinonitrile - 0.24 wt% water alloy was being observed when a nitrogen bubble traversed the mushy zone and remained at the solid-liquid interface. Breakdown of the interface to shallow cells subsequently occurred, and was later evaluated using down-linked data from a nearby thermocouple. These results and other detrimental effects due to the presence of bubbles during solidification processing in a microgravity environment are presented and discussed.

Convective stability in the Rayleigh-Benard and directional solidification problems - High-frequency gravity modulation

NASA Technical Reports Server (NTRS)

Wheeler, A. A.; Mcfadden, G. B.; Murray, B. T.; Coriell, S. R.

1991-01-01

The effect of vertical, sinusoidal, time-dependent gravitational acceleration on the onset of solutal convection during directional solidification is analyzed in the limit of large modulation frequency. When the unmodulated state is unstable, the modulation amplitude required to stabilize the system is determined by the method of averaging. When the unmodulated state is stable, resonant modes of instability occur at large modulation amplitude. These are analyzed using matched asymptotic expansions to elucidate the boundary-layer structure for both the Rayleigh-Benard and directional solidification configurations. Based on these analyses, a thorough examination of the dependence of the stability criteria on the unmodulated Rayleigh number, Schmidt number, and distribution coefficient, is carried out.

Electromagnetic containerless undercooling facility and experiments for the Shuttle

NASA Technical Reports Server (NTRS)

Frost, R. T.; Flemings, M. C.; Szekely, J.; El-Kaddah, N.; Shiohara, Y.

1984-01-01

An electromagnetic furnace is being prepared for flights aboard the Space Shuttle. This apparatus is capable of melting metals and alloys up to 1400 C melting point by induction heating with subsequent solidification of the freely levitated melt without contact with any container. The solidification can be carried out with greatly reduced fields resulting in minimal heating and stirring of the free melt. Sequential specimens can be processed during flight. Several experiments are planned for a series of flights, beginning in 1985 with an undercooling experiment of NiSn alloys. These will be interspersed with detailed studies of fluid flow caused by low and high field levels in order to quantify the corresponding effect upon the solidification process.

Technicians monitor USMP-4 experiments being prepared for flight on STS-87 in the SSPF

NASA Technical Reports Server (NTRS)

1997-01-01

Technicians are monitoring experiments on the United States Microgravity Payload-4 (USMP-4) in preparation for its scheduled launch aboard STS-87 on Nov. 19 from Kennedy Space Center (KSC). USMP-4 experiments are prepared in the Space Station Processing Facility at KSC. The large white vertical cylinder in the center of the photo is the Advanced Automated Directional Solidification Furnace (AADSF), which is a sophisticated materials science facility used for studying a common method of processing semiconductor crystals called directional solidification. The white horizontal tube to the right is the Isothermal Dendritic Growth Experiment (IDGE), which will be used to study the dendritic solidification of molten materials in the microgravity environment.

Activities of the Center for the Space Processing of Engineering Materials

NASA Technical Reports Server (NTRS)

1986-01-01

Topics addressed include: containerless processing and purification; directional and rapid solidification; high temperature alloys; oxidation resistant niobium alloys; metallic bonding; effects of solidification mode on structure-property relationships; and dispersion strengthened metal alloys. Each of the projects is reported by company association and follow according to alphabetical order of the company names.

Experimental Study of Sudden Solidification of Supercooled Water

ERIC Educational Resources Information Center

Bochnícek, Zdenek

2014-01-01

The two independent methods of measurement of the mass of ice created at sudden solidification of supercooled water are described. One is based on the calorimetric measurement of heat that is necessary for melting the ice and the second interprets the volume change that accompanies the water freezing. Experimental results are compared with the…

CASE STUDY: IN-SITU SOLIDIFICATION/STABILIZATION OF HAZARDOUS ACID WASTE OIL SLUDGE AND LESSONS LEARNED

EPA Science Inventory

The South 8th Street site contained a 2.5 acre oily sludge pit with very low pH waste produced by oil recycling activities. This sludge was treated using in-situ solidification/stabilization technology applied by deep soil mixing augers. The problems encountered, solutions develo...

Impact of Metal Droplets: A Numerical Approach to Solidification

NASA Astrophysics Data System (ADS)

Koldeweij, Robin; Mandamparambil, Rajesh; Lohse, Detlef

2016-11-01

Layer-wise deposition of material to produce complex products is a subject of increasing technological relevance. Subsequent deposition of droplets is one of the possible 3d printing technologies to accomplish this. The shape of the solidified droplet is crucial for product quality. We employ the volume-of-fluid method (in the form of the open-source code Gerris) to study liquid metal (in particular tin) droplet impact. Heat transfer has been implemented based on the enthalpy approach for the liquid-solid phase. Solidification is modeled by adding a sink term to the momentum equations, reducing Navier-Stokes to Darcy's law for high solid fraction. Good agreement is found when validating the results against experimental data. We then map out a phase diagram in which we distinguish between solidification behavior based on Weber and Stefan number. In an intermediate impact regime impact, solidification due to a retracting phase occurs. In this regime the maximum spreading diameter almost exclusively depends on Weber number. Droplet shape oscillations lead to a broad variation of the morphology of the solidified droplet and determine the final droplet height. TNO.

Ice Layer Spreading along a Solid Substrate during Solidification of Supercooled Water: Experiments and Modeling.

PubMed

Schremb, Markus; Campbell, James M; Christenson, Hugo K; Tropea, Cameron

2017-05-16

The thermal influence of a solid wall on the solidification of a sessile supercooled water drop is experimentally investigated. The velocity of the initial ice layer propagating along the solid substrate prior to dendritic solidification is determined from videos captured using a high-speed video system. Experiments are performed for varying substrate materials and liquid supercooling. In contrast to recent studies at moderate supercooling, in the case of metallic substrates only a weak influence of the substrate's thermal properties on the ice layer velocity is observed. Using the analytical solution of the two-phase Stefan problem, a semiempirical model for the ice layer velocity is developed. The experimental data are well described for all supercooling levels in the entire diffusion limited solidification regime. For higher supercooling, the model overestimates the freezing velocity due to kinetic effects during molecular attachment at the solid-liquid interface, which are not accounted for in the model. The experimental findings of the present work offer a new perspective on the design of anti-icing systems.

TEM investigations on twin boundary structures of feathery crystals in aluminum alloys during Bridgman solidification

NASA Astrophysics Data System (ADS)

Yang, Luyan; Li, Shuangming; Fan, Kai; Li, Yang; Zhong, Hong; Fu, Hengzhi

2018-06-01

Feathery crystals are an ensemble of twinned dendrites, and are characterized by a unique twin boundary (TB) structure in the solidification pattern of aluminum alloys. In this work, the high-density twinned dendrites of Al-4.5 wt% Cu alloys, produced during the Bridgman solidification, have been studied using electron backscattered diffraction (EBSD) and high-resolution transmission electron microscopy (HRTEM). The experimental results showed that, after systematically decreasing the growth rate from 3000 μm/s to 1 μm/s, the TBs remained stable, while the solute field around the TBs changed significantly. According to the HRTEM results, successive stacking faults were occurred near the TBs at 1 μm/s, while slight distortion was observed around the TBs at 3000 μm/s. The composition analysis revealed an obvious solute enrichment near the TBs. Furthermore, the solute gradient profile within the TBs became smoother with the decrease in the growth speed. This is due to the more sufficient solid-state back diffusion occurring perpendicular to the twin plane after the solidification.

Influence of Al content on non-equilibrium solidification behavior of Ni-Al-Ta model single crystal alloys

NASA Astrophysics Data System (ADS)

Ai, Cheng; Zhou, Jian; Zhang, Heng; Zhao, Xinbao; Pei, Yanling; Li, Shusuo; Gong, Shengkai

2016-01-01

The non-equilibrium solidification behaviors of five Ni-Al-Ta ternary model single crystal alloys with different Al contents were investigated by experimental analysis and theoretical calculation (by JMatPro) in this study. These model alloys respectively represented the γ' phase with various volume fractions (100%, 75%, 50%, 25% and 0%) at 900 °C. It was found that with decreasing Al content, liquidus temperature of experimental alloys first decreased and then increased. Meanwhile, the solidification range showed a continued downward trend. In addition, with decreasing Al content, the primary phases of non-equilibrium solidified model alloys gradually transformed from γ' phase to γ phase, and the area fraction of which first decreased and then increased. Moreover, the interdendritic/intercellular precipitation of model alloys changed from β phase (for 100% γ') to (γ+γ')Eutectic (for 75% γ'), (γ+γ')Eutectic+γ' (for 50% γ' and 25% γ') and none interdendritic precipitation (for 0% γ'), and the last stage non-equilibrium solidification sequence of model alloys was determined by the nominal Al content and different microsegregation behaviors of Al element.