Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “Solidification microstructure”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 217 records · Page 12
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

Selective laser sintering and spark plasma sintering of (Zr,Nb,Ta,Ti,W)C compositionally complex carbide ceramics

Abstract Two advanced manufacturing processes, spark plasma sintering (SPS) and selective laser sintering (SLS), have been developed for synthesis of (Zr,Nb,Ta,Ti,W)C compositionally complex carbide (CCC) via reactive sintering of a powder mixture of constitute monocarbides. X‐ray diffraction analysis confirmed that the single‐phase CCC can be formed by both SPS and SLS. While a homogenous microstructure with uniform metal element distributions was developed during SPS, three‐layer microstructures with a thin TiC‐rich layer and two TaC‐rich layers along with a TiO 2 ‐rich surface layer containing W nanoparticles were formed during SLS. In addition, cellular structures with W, Zr, and Ti element segregation and dislocations on cell boundaries were observed in the SLS‐CCC sample, indicating the effect of nonequilibrium conditions on microstructure formation during laser melting followed by rapid cooling and solidification process. Compared to the SPS‐CCC sample, the SLS‐CCC showed enhanced hardness and reduced thermal conductivity, which may be related to their unique cellular structures.

36 MATERIALS SCIENCE↗
NASA NTRS1986

On the determination of the origin of linear anomaly in the macrostructure of VPPA welded 2219-T87 aluminum alloy: Preliminary report

The cause and significance of the weld radiograph enigma, which is a linear anomaly in the features of the X-ray film is examined. By observing features on available radiographs and in studying published reports of similar features, it was possible to conclude that there are many manifestations of the enigma, and that they are all specific features of fine structure in radiographs due to natural processes connected with welding and to specific X-ray absorption and diffraction phenomena. These processes include the thermal distribution and liquid metal flow in welding, the development of microstructure, morphology, second phase particles and porosity due to the solidification process, and to the pattern of residual stresses after the weld metal has cooled to the ambient temperature. Microdensitometer traces were made across weld radiographs of standard enigmatic types. Similar patterns were produced by computer simulation. These show that the enigma is a relatively low contrast feature compared to real weld defects, such as undercuts or centerline cracks. The enigma can be distinguished from weld defects by these microdensitometer traces. The enigma effect on weld properties is not known but is expected to be minor.

Jemian, W. A.↗
NASA NTRS1986

On the determination of the origin of linear anomaly in the macrostructure of VPPA welded 2219-T87 aluminum alloy

The objective was to determine the cause and significance of the weld radiograph enigma, which is a linear anomaly in the features of the X-ray film. By observing features on available radiographs and in studying published reports of similar features it was possible to conclude that there are many manifestations of the enigma, and that they are all specific features of fine structure in radiographs due to natural processes connected with welding and to specific X-ray absorption and diffraction phenomena. These processes include the thermal distribution and liquid metal flow in welding, the development of microstructure, morpohology, second phase particles and porosity due to the solidification process and to the pattern of residual stresses after the weld metal has cooled to the ambient temperature. Microdensitometer traces were made across weld radiographs of standard and enigmatic types. Similar patterns were produced by computer simulation. These show that the enigma is a relatively low contrast feature compared to real weld defects, such as undercuts or centerline cracks. The enigma can be distinguished from weld defects by these microdensitometer traces. The enigma effect on weld properties is not known but is expected to be minor.

Jemian, W. A.↗
NASA NTRS1990

Experiments for electromagnetic levitation in microgravity

Containerless processing is a promising research tool for investigating the properties of undercooled melts and their solidification. For conducting samples RF-electromagnetic levitation offers the possibility to obtain large undercoolings by avoiding heterogeneous nucleation at container walls. On earth, however, strong magnetic fields are needed to compensate the gravitational force which imposes a lower limit on the available temperatures and on the accessible undercooling range. Under microgravity conditions the magnetic positioning fields can be minimized and hence, undercooling becomes feasible under ultra-high vacuum conditions and lower temperatures become accessible. In contrast to other undercooling and solidification techniques, electromagnetic levitation allows for diagnostic measurements during the early steps of nucleation and phase selection. Experiments cover a wide field of research topics: nucleation, directional solidification at high velocities, generation of metastable phases, evolution of microstructures, properties of undercooled liquids. Examples from these classes including experiments selected for the IML-2 mission are discussed with emphasis on technical requirements. An overview is given on the German TEMPUS (electromagnetic levitation facility) program.

Willnecker, R.↗
NASA NTRS1993

Approximate formula for recalescence in binary eutectic alloys

Supercooling of a liquid prior to the nucleation of a solid and the subsequent rapid growth are necessary conditions for producing novel microstructures including metastable phases which are not formed by conventional solidification processes. Since containerless techniques, such as levitation and free fall of a sample, are capable of achieving a significant supercooling level of liquids, they are under consideration as possible techniques for material processing on earth and in space.

ALLOY STRUCTURE FORMATION↗
NASA NTRS1999

In Situ Monitoring of Crystal Growth Using MEPHISTO, Mission STS 87-Program USMP-4: Experimental Analysis

This report summarizes the results of the In situ Monitoring of Crystal Growth Using MEPHISTO (Material por l'Etude des Phenomenes Interessant de la Solidification sur Terre et en Orbite) experiment on USMP-4. The report includes microstructural and compositional data obtained during the first year of the post flight analysis, as well as numerical simulation of the flight experiment. Additional analyses are being continued and will be reported in the near future. The experiments utilized MEPHISTO hardware to study the solidification and melting behavior of bismuth alloyed with 1 at% tin. The experiments involved repeated melting and solidification of three samples, each approximately 90 cm long and 6mm in diameter. Half of each sample also included a 2 mm. diameter growth capillary, to assist in the formation of single grain inside. One sample provided the Seebeck voltage generated during melting and freezing processes. Another one provided temperature data and Peltier pulsed demarcation of the interface shape for post flight analysis. The third sample provided resistance and velocity measurements, as well as additional thermal data. The third sample was also quenched at the end of the mission to preserve the interface composition for post flight determination. A total of more than 45cm of directionally solidified alloy were directionally solidified at the end of the flight for post mission structural and compositional characterization. Metallurgical analysis of the samples has shown that the interfacial kinetics play a key role in controlling the morphological stability of faceted alloys. Substantial differences were observed in the Seebeck signal between the ground-based experiments and the space-based experiments. The temperature gradient in the liquid for the ground-based experiments was also significantly lower than the temperature gradient in the liquid for the space-based experiments. Both of these observations indicate significant influence of liquid convection for the ground-based experiments.

Abbaschian, Reza↗
NASA NTRS1986

Making High-Porosity Alloy Spheroids

Noncontact process yields low-density, porous microstructure. Small spheroids of porous alloys with large surface area per unit volume produced by containerless processing method. Without container walls to serve as nucleation sites, alloy cools to well below normal freezing point without solidifying. Solidification then proceeds rapidly; interdendritic liquid pulled out by growing crystals, resulting in porous microstructure. The more rapid the cooling rate, the faster crystals grow and more porous solid becomes. Drop-tube method useful in creating porous microstructures from other materials including oxides, carbides, and organic materials. Other means of containerless processing - acoustic or air-jet levitation, low-gravity float melting, melt spinning, or jet spraying, adapted to process.

Ethridge, E. C.↗
NASA NTRS1974

Eutectic solidification

The possibilities of using the low-gravity space environment for the processing of directionally solidified materials in order to remove the limitations imposed by the L-g earth environment have led to a careful evaluation of the directional solidification process and the results commonly obtained. Defects in the regularity of the microstructure have been identified as one of the most important areas where present processing technology needs to be improved. One-g environment material processing must also be carefully characterized before it can be determined if zero-g processing will produce significant benefits in eutectic and off-eutectic solidification. It is suggested that a combination of experimental and analytical thermal studies will be required to optimize the solidification process in order to minimize the structural defects which occur due to present processing techniques.

Douglas, F. C.↗
NASA NTRS2019

Intern Designed Modules for Conducting Potential Microgravity Solidification Experiments Aboard the International Space Station

MMaJIC (Microgravity Materials Joining Investigation Chamber) is a modular experiment chamber for performing materials science investigations. MMaJIC was initially designed to provide a controlled and sealed test environment to accommodate a wide variety of soldering and brazing experiments. However, its modular cartridge design is well suited to easily conduct any number and variety of science experiments. SoLIDD (Solid Liquid Interface Directional Device) is an apparatus for conducting directional solidification experiments with low melting temperature alloys. It has capability for varying the sample’s temperature gradient and growth velocity thus ensuring microstructural development under controlled conditions. ICED-T (Interface Control Experiment with Directional Translation) is an apparatus that conducts directional solidification experiments of transparent materials such that direct observation/recording of the advancing solid/liquid interface can be made. Currently, it is a functional breadboard that consists of the components mounted to a surface that allows the sample to be placed in an upright position. Orientation of the experiment (solid on the bottom, liquid on top) is important during testing ground samples to maintain stability. Ultimately, the goal of MMaJIC, SoLIDD and ICED-T is to conduct successful ground tests and then be re-configured for eventual use by aboard the ISS.

McElderry, Justin↗
NASA NTRS1979

Gravitational influences on the liquid-state homogenization and solidification of aluminum antimonide

Typical commercial or laboratory-prepared samples of polycrystalline AlSb contain microstructural inhomogeneities of Al- or Sb-rich phases in addition to the primary AlSb grains. The paper reports on gravitational influences, such as density-driven convection or sedimentation, that cause microscopic phase separation and nonequilibrium conditions to exist in earth-based melts of AlSb. A triple-cavity electric furnace is used to homogenize the multiphase AlSb samples in space and on earth. A comparative characterization of identically processed low- and one-gravity samples of commercial AlSb reveals major improvements in the homogeneity of the low-gravity homogenized material.

Ang, C.-Y.↗
NASA NTRS1999

Third and Final Shuttle Mission of the Isothermal Dendritic Growth Experiment Conducted: Highest Supercooling Ever Recorded Achieved

Dendrites describe the treelike crystal morphology commonly assumed in metals and alloys that freeze from supercooled or supersaturated melts. There remains a high level of engineering interest in dendritic solidification because the size, shape, and orientation of the dendrites determine the final microstructure of a material. It is the microstructure that then determines the physical properties of cast or welded products. Although it is well known that dendritic growth is controlled by the transport of latent heat from the moving solid-liquid interface, an accurate and predictive model has not yet been developed. The effects of gravity-induced convection on the transfer of heat from the interface have prevented adequate testing, under terrestrial conditions, of solidification models. The Isothermal Dendritic Growth Experiment (IDGE) constituted a series of three microgravity experiments flown aboard the Space Shuttle Columbia. The apparatus was used to grow and record dendrite solidification in the absence of gravity-induced convective heat transfer, thereby producing a wealth of benchmark-quality data for testing solidification models and theories.

Glicksman, Martin E.↗
NASA NTRS1977

The processing of materials in outer space

Zero-gravity environment may lead to fabrication of new and improved materials. According to comprehensive study of application of this promising technology to superconducting and electrical contact materials, outer space processing could improve microstructure and homogeneity of many single and multicomponent systems formed from solidification of fluid phases. New structures that are impossible to form terrestrially may also be accessible in space environment.

Gelles, S. H.↗
NASA NTRS1990

Intermetallic matrix composites; Proceedings of the MRS Symposium, San Francisco, CA, Apr. 18-20, 1990

The present volume on intermetallic matrix composites discusses the modeling, processing, microstructure/property relationships, and compatibility of intermetallic matrix composites. Attention is given to models for the strength of ductile matrix composites, innovative processing techniques for intermetallic matrix composites, ductile phase toughening of brittle intermetallics, and reactive synthesis of NbAl3 matrix composites. Topics addressed include solidification processing of NbCr2 alloys, Ta and Nb reinforced MoSi2, the microstructure and mechanical behavior of Ni3Al-matrix composites, and ductile-phase toughening of Cr3Si with chromium. Also discussed are dislocation morphologies in TiB2/NiAl, the development of highly impact resistant NiAl matrix composites, the effect of notches on the fatigue life of the SCS-6Ti3Al composite, and the chemical stability of fiber-metal matrix composites.

Anton, D. L.↗
NASA NTRS1997

Evaluation of Optimum HgZnTe Crystal Growth Parameters and USML-2 Flight Support

Work associated with contract provided support for the approved flight experiment 'Crystal Growth of Selected 2-6 Semiconducting Alloys by Directional Solidification.' General activities included ground-based melt studies, compositional and microstructure characterization of the grown crystals, and participation in the continuing assessment of the program. Specifically, work was performed to determine the optimum furnace translation rate at which a HgZnTe sample could be removed from the crystal growth furnace to avoid shrinkage cavities. Additionally, nine HgZnTe ampoules were prepared and delivered to Marshall Space Flight Center for Ground Control Experiment Laboratory Testing.

Scripa, Rosalia N.↗
NASA NTRS2003

Data and Modeling of Dendrites Subject to A Step Change in Pressure (TDSE)

There is considerable interest in dendritic solidification because of the influence dendrites have in the determination of microstructure, and thereby in the physical properties of cast metals and alloys. Current theories and models of dendritic growth generally couple diffusion effects in the melt with the physics of the interface. Data and subsequent analysis prior of the tip growth speed and radii of thermal succinonitrile dendrites in the near-convection free, on-orbit, free-fall environment demonstrate that these theories yield predictions that are reasonably in agreement with the results of experiment. However, data and analysis for assessing the interfacial physics component of theory are not sufficiently detailed or definitive. To study fundamental aspects of dendritic interface stability, we are measuring and modeling the kinetics and morphology of dendrites as they evolve from one well-defined steady state at a pre-set supercooling, through a transient stage, to a different well-defined steady state. More specifically, we subject succinonitrile dendrites, growing under steady-state conditions, to a rapid change in pressure. This leads to a rapid change in thermal driving force from the corresponding change in both the equilibrium melting temperature due to the Clapeyron effect, and a change in the far-field temperature due to adiabatic temperature changes in the bulk liquid and solid. Subsequently, we observe transformations from a well-characterized initial state into a new steady-state. Initial data reveal that the dendrite tip velocity changes almost as fast as the pressure charges, while the tip radius changes occur more slowly, taking from 10 60 seconds depending on the size of the step change and the final supercooling. Computer modeling of this process shows both agreements and disagreements with the experimental data. In making these observations and measurements, we are gaining new understandings of interfacial dynamics and state-selection physics.

Koss, Matthew B.↗
NASA NTRS2001

Directional Solidification of Eutectic Ceramics

Two major problems associated with structural ceramics are lack of damage tolerance and insufficient strength and creep resistance at very high temperatures of interest for aerospace application. This work demonstrated that the directionally solidified eutectics can have unique poly-phase microstructures and mechanical properties superior to either constituent alone. The constraining effect of unique eutectic microstructures result in higher resistance to slow crack growth and creep. Prospect of achieving superior properties through controlled solidification are presented and this technology can also be beneficial to produce new class of materials.

Sayir, Ali↗
NASA NTRS1995

Investigation of Advanced Processed Single-Crystal Turbine Blade Alloys

This investigation studied the influence of thermal processing and microstructure on the mechanical properties of the single-crystal, nickel-based superalloys PWA 1482 and PWA 1484. The objective of the program was to develop an improved single-crystal turbine blade alloy that is specifically tailored for use in hydrogen fueled rocket engine turbopumps. High-gradient casting, hot isostatic pressing (HIP), and alternate heat treatment (HT) processing parameters were developed to produce pore-free, eutectic-free microstructures with different (gamma)' precipitate morphologies. Test materials were cast in high thermal gradient solidification (greater than 30 C/cm (137 F/in.)) casting furnaces for reduced dendrite arm spacing, improved chemical homogeneity, and reduced interdendritic pore size. The HIP processing was conducted in 40 cm (15.7 in.) diameter production furnaces using a set of parameters selected from a trial matrix study. Metallography was conducted on test samples taken from each respective trial run to characterize the as-HIP microstructure. Post-HIP alternate HT processes were developed for each of the two alloys. The goal of the alternate HT processing was to fully solution the eutectic gamma/(gamma)' phase islands and to develop a series of modified (gamma)' morphologies for subsequent characterization testing. This was accomplished by slow cooling through the (gamma)' solvus at controlled rates to precipitate volume fractions of large (gamma)'. Post-solution alternate HT parameters were established for each alloy providing additional volume fractions of finer precipitates. Screening tests included tensile, high-cycle fatigue (HCF), smooth and notched low-cycle fatigue (LCF), creep, and fatigue crack growth evaluations performed in air and high pressure (34.5 MPa (5 ksi)) hydrogen at room and elevated temperature. Under the most severe embrittling conditions (HCF and smooth and notched LCF in 34.5 MPa (5 ksi) hydrogen at 20 C (68 F), screening test results showed increases in fatigue life typically on the order of 1OX, when compared to the current Space Shuttle Main Engine (SSME) Alternate Turbopump (AT) blade alloy (PWA 1480).

Peters, B. J.↗
NASA NTRS1999

Use of Microgravity to Control the Microstructure of Eutectics

The long term goal of this project is to be able to control the microstructure of directionally solidified eutectic alloys, through an improved understanding of the influence of convection. Prior experimental results on the influence of microgravity on the microstructure of fibrous eutectics have been contradictory. Theoretical work at Clarkson University showed that buoyancy-driven convection in the vertical Bridgman configuration is not vigorous enough to alter the concentration field in the melt sufficiently to cause a measurable change in microstructure when the eutectic grows at minimum supercooling. Currently, there are four other hypotheses that might explain the observed changes in microstructure of fibrous eutectics caused by convection: (1) Disturbance of the concentration boundary layer arising from an off-eutectic melt composition and growth at the extremum; (2) Disturbance of the concentration boundary layer of a habit-modifying impurity; (3) Disturbance of the concentration boundary layer arising from an off-eutectic interfacial composition due to non-extremum growth; and (4) A fluctuating freezing rate combined with differences in the kinetics of fiber termination and fiber formation. We favor the last of these hypotheses. Thus, the primary objective of the present grant is to determine experimentally and theoretically the influence of a periodically varying freezing rate on eutectic solidification. A secondary objective is to determine the influence of convection on the microstructure of at least one other eutectic alloy that might be suitable for flight experiments.

Wilcox, William R.↗