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All sourcesNASA NTRSDOE OSTI
NASA NTRSDate not supplied

Open-source Numerical Modeling of Solidification Cracking Susceptibility: Application to Refractory Alloy Systems

Introduction. Alloys such as aluminum, nickel-base, and austenitic stainless steels are susceptible to solidification cracking during welding and 3D printing. Compositional optimization is one method used to effectively mitigate solidification cracking of those alloy systems. With the surge in hypersonic and in-space propulsion activities, refractory metals (Nb, Mo, Ta, W, and Re) and their alloy derivatives are increasing in importance due to their extreme high melting point and retention of high-temperature strength; however, their chemistry was most typically optimized to promote ductility during mechanical operations such as drawing and forming. Welding of such alloys has been a challenge due to a number of issues including solidification cracking, atmospheric contamination (O, C, and N), as well as a shift in ductile-to-brittle transition to higher temperature following grain growth induced by welding. Compositional optimization of refractory alloys for solidification cracking resistance in particular is desirable as their usage increases with the advent of advanced manufacturing methods such as 3D printing. This work evaluates the effect of compositional variation in refractory metal systems on the solidification cracking susceptibility with the goals of optimizing existing alloys and joining process techniques, and formulating new alloys with increased solidification cracking resistance. Experimental Procedures. A python code was developed in a Jupyter notebook environment (Michael and Sowards, 2023) to facilitate the calculation of crack susceptibility index proposed by Kou (2015). Composition is entered as a single point, or as a 1-D or 2-D array. The notebook calls pycalphad (Otis and Liu, 2017 and Bocklund et al, 2020) to calculate the evolution of fraction solid as a function of temperature (under either Scheil or equilibrium assumptions) and then evaluates steepness of the fraction solid curve near the terminal stage of solidification to predict solidification cracking resistance. Open source thermodynamic databases available at online repositories are used (van de Walle). The process is setup in an automated fashion to generate plots that show variation in solidification cracking susceptibility according to composition on 1-D line plots or 2-D contour plots. The Jupyter notebook and crack susceptibility algorithm was also integrated with a widely used commercial CALPHAD code for validation and alloy exploration. Results and Discussion. The crack susceptibility model was first validated against a series of refractory alloy compositions evaluated in past work which utilized a specialized Varestraint test built inside a vacuum chamber environment (Lessman and Gold, 1971). The alloys tested in the Varestraint apparatus included T-111 (Ta-8W-2Hf), ASTAR-811C (Ta-8W-1Re-0.7Hf-0.025C), FS-85 (Nb-27Ta-10W-1Zr), T-222 (Ta-9.6W-2.4Hf-0.01C), Ta-10W, B-66 (Nb-5Mo-5V-1Zr), and SCb-291 (Nb-10W-10Ta). The initial test of the model showed a strong correlation with empirical Varestraint data, i.e., a Spearman rank correlation between model predictions and hot cracking measurements was observed to be greater than 0.8. Following the validation, a set of refractory metal binary mixtures was investigated to evaluate sensitivity of Nb, Mo, W, and Ta to C, N, and O content. A series of plots were produced that suggest ppmw ranges of C, N, and O where solidification cracking increases significantly and reaches a maximum. Also comparative ranking of each primary refractory metal to each interstitial was produced. For example C produces greater cracking response in Mo whereas O produces greater cracking response in Ta and Nb. Such compositional values have utility in setting limits on pickup of these interstitial elements during welding and printing rather than using a one-size-fits-all approach. Furthermore, the results have use in determining additive powder recycling requirements, which is especially pertinent for refractory metal powders due to their high cost compared to conventional alloys. Another application created thousands of hypothetical alloys within the nominal specified composition range of two widely used refractory alloys C103 (Nb-10Hf-1Ti) and TZM (Mo-0.5Ti-0.1Zr). The cracking index was calculated for the alloys and results were fed into machine learning regression techniques including Multiple Linear Regression, Ridge Regression, and Lasso Regression to determine relative potency each alloying element had on computed solidification cracking index. A series of linear equations were produced that relate composition of C103 and TZM to solidification cracking index. The crack susceptibility of C103 for example is described by an equation of the form: cracking index ~ O + 0.667*C + 0.635*N + 0.00037*Ta – 0.0008*Hf (in wt.%) From that equation, it is clear that O has strong propensity to induce solidification cracking. Interestingly, Hf is shown to reduce calculated cracking response. Finally, realizing the potential of this method to discover new refractory alloy formulations across the period table that have low solidification cracking sensitivity, the code was applied to new untested alloy systems including W-Zr-C, W-Ta-C, and others. Conclusions. In summary, an open source numerical method has been developed using Python code to calculate Kou’s crack susceptibility index. The method was applied to refractory metals which are inherently difficult to study from a weldability testing standpoint since inert shielding gas is not sufficient and welding is typically done in vacuum, especially in light of findings presented here where oxygen has profound influence on solidification cracking. This work revealed the effect of compositional variations on a series of refractory metals and showed the framework defined here will be useful in 1) the development of new alloys that have improved weldability and 3D printability, 2) placing compositional limits on existing alloys, and 3) ensuring adequate controls of manufacturing processes such as 3D printing where powder reuse is critical. Keywords. pycalphad; Python; refractory metals; solidification cracking. References. B. Bocklund et. al. (2020) http://doi.org/10.5281/zenodo.3630657. S. Kou. (2015) https://doi.org/10.1016/j.actamat.2015.01.034. G.G. Lessmann and R.E. Gold. Welding Journal, issue 1, pp. 1-s – 8-s (1971). F.N. Michael and J.W. Sowards. NASA/TM-20230002218 (2023). R. Otis and Z.-K. Liu. (2017) http://doi.org/10.5334/jors.140. A. Van de Wallle et. al. (2018) https://doi.org/10.1016/j.calphad.2018.04.003.

pycalphad↗
NASA NTRS1988

A study of surface tension driven segregation in monotectic alloy systems

The compatibilities of various monotectic alloy systems with several different crucible materials were evaluated. The study was carried out using small candidate alloy samples of compositions that produced fifty volume percent of each liquid phase at the monotectic temperature. Compatibility was based on the evaluation of the wetting tendency of the two immiscible phases with the crucible material in a one-g solidified sample. Three types of wetting phenomena were observed during the evaluation. Type 1 indicates an alloy-crucible combination where the L2 phase preferentially wets the crucible material. Since L2 is usually the minority phase in desirable alloys, this material combination would be difficult to process and is therefore considered incompatible. Type 2 behavior indicates an alloy-crucible combination where the L1 phase preferentially wets the crucible material. This type of combination is considered compatible since surface tension effects should aid in processing the alloy to a useful form. Type 3 indicates any combination that leads to major reactions between the alloy and crucible material, gas entrapment, or separation of the metal from the crucible wall. Additional compatibility evaluations would have to be carried out on combinations of this category. The five alloy systems studied included aluminum-bismuth, copper-lead, aluminum-indium, aluminum-lead and cadmium-gallium. The systems were combined with crucibles of alumina, boron nitride, mullite, quartz, silicon carbide and zirconia.

Andrews, J. Barry↗
DOE OSTI2017

An informatics guided classification of miscible and immiscible binary alloy systems

The classification of miscible and immiscible systems of binary alloys plays a critical role in the design of multicomponent alloys. By mining data from hundreds of experimental phase diagrams, and thousands of thermodynamic data sets from experiments and high-throughput first-principles (HTFP) calculations, we have obtained a comprehensive classification of alloying behavior for 813 binary alloy systems consisting of transition and lanthanide metals. Among several physics-based descriptors, the slightly modified Pettifor chemical scale provides a unique two-dimensional map that divides the miscible and immiscible systems into distinctly clustered regions. Based on an artificial neural network algorithm and elemental similarity, the miscibility of the unknown systems is further predicted and a complete miscibility map is thus obtained. Impressively, the classification by the miscibility map yields a robust validation on the capability of the well-known Miedema’s theory (95% agreement) and shows good agreement with the HTFP method (90% agreement). Our results demonstrate that a state-of-the-art physics-guided data mining can provide an efficient pathway for knowledge discovery in the next generation of materials design.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Putative quantum criticality in the (Cr{sub 90}Ir{sub 10}){sub 100−y}V{sub y} alloy system

Quantum criticality (QC) in spin-density-wave antiferromagnetic Cr and Cr alloy systems is a topic of current interest. In the present study, V was used as a tuning parameter to drive the Néel transition temperature (T{sub N}) of the (Cr{sub 90}Ir{sub 10}){sub 100−y}V{sub y} alloy series with 0 ≤ y ≤ 14.3 to zero and search for effects of QC in the process. The magnetic properties and possible QC behaviour (QCB) in this alloy system were investigated through electrical resistivity (ρ), specific heat (C{sub p}), and susceptibility (χ) measurements as a function of temperature (T), indicating that T{sub N} is suppressed to zero at a critical concentration y{sub c} ≈ 9. The Sommerfeld coefficient (γ) is considered a key indicator of QCB and a peak is observed in γ(y) at y{sub c} on decreasing y through this concentration, followed by a sharp decreasing trend. This behaviour is reminiscent of that observed for γ of the prototypical Cr{sub 100−x}V{sub x} QC system and allows for the classification of y{sub c} in the (Cr{sub 90}Ir{sub 10}){sub 100−y}V{sub y} alloy system as a possible QC point.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
NASA NTRS1984

The influence of containerless undercooling and rapid solid-state quenching on the superconductive and magnetic properties of some clustering alloy systems

The properties of clustering alloy systems and the manner in which they are influenced by rapid quenching from a containerless undercooled melt are discussed. It was postulated that rapid quenching under such conditions would result in highly disordered metastable alloys, and furthermore, that alloys in such conditions would possess physical properties characteristically different from those of alloys in the annealed equilibrium state. The scope of the program is essentially to gauge the influence of containerless undercooling on the submicrostructure of clustering-type alloys, using certain physical properties as diagnostic tools. Microstructures and macrostructures were to be examined using optical- and scanning-electron microscopy.

Collings, E. W.↗
DOE OSTI2020

Quasicrystalline phase and crystalline approximant in Ni–Mn–In Heusler alloy system

Intermetallic compounds and micro-structures in Ni–Mn–In alloy system were investigated with transmission electron microscopy, selected-area and nano-beam electron diffraction, and energy-dispersive x-ray spectroscopy. Together with two types of Heusler phases, a decagonal quasicrystalline phase and a structurally related crystallite were found in the Ni–Mn–In system. As is well-known, most of the decagonal quasicrystals are aluminum-based intermetallic phases. It is interesting to investigate the aluminum-free decagonal quasicrystalline phase as a new member of the quasicrystal family. Structural characterization was carried out on the decagonal quasicrystalline phase and the crystalline approximant in the Ni–Mn–In alloy system.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Transport properties of the Ce x Y 1-x Pt alloy system: Unusual concenration dependence of the Curie temperature

Here, in order to study Kondo ferromagnetism of CePt, we have investigated the transport properties, resistivity and thermopower, of the Ce x Y 1-x Pt alloy system from 2 K to 320 K. The extracted magnetic contribution to the total resistivity cannot be scaled to the concentration and is much higher than in the Ce x La 1-x Pt alloy system. The maximum of the magnetic contribution of the resistivity moves to lower temperatures with decreasing the Ce content while the temperature of the minimum of the thermopower does not change with concentration. These two facts seem to be in contradiction. Usually one assumes that these extrema represent the Kondo temperature. To the contrary, we show that the Kondo temperature increases with decreasing Ce content. The most intriguing observation in this alloy system is the linear relationship between the Curie temperature and the concentration of the Ce ions and, moreover, that it is the same as in Ce x La 1-x Pt. Lastly, this fact is in contradiction with the conventional picture of small moment Kondo magnetism.

36 MATERIALS SCIENCE↗
NASA NTRS1980

Single-, two-, and three-phase binary-alloy systems

Series of three computer programs solves one-dimensional transient diffusion problems in single-and multiphase binary-alloy systems. Accurate understanding of diffusion process in binary-alloy system is important for development of metal matrix composites, some protective coatings, and thin-film technology.

Tenney, D. R.↗
NASA NTRS1978

Effect of concentration dependence of the diffusion coefficient on homogenization kinetics in multiphase binary alloy systems

Diffusion calculations were performed to establish the conditions under which concentration dependence of the diffusion coefficient was important in single, two, and three phase binary alloy systems. Finite-difference solutions were obtained for each type of system using diffusion coefficient variations typical of those observed in real alloy systems. Solutions were also obtained using average diffusion coefficients determined by taking a logarithmic average of each diffusion coefficient variation considered. The constant diffusion coefficient solutions were used as reference in assessing diffusion coefficient variation effects. Calculations were performed for planar, cylindrical, and spherical geometries in order to compare the effect of diffusion coefficient variations with the effect of interface geometries. In most of the cases considered, the diffusion coefficient of the major-alloy phase was the key parameter that controlled the kinetics of interdiffusion.

Tenney, D. R.↗
DOE OSTI2015

Through-thickness recrystallization characteristics of a laminated AA3xxx–AA6xxx aluminum alloy system

The through-thickness annealing behavior of a laminated AA3xxx–AA6xxx alloy system at 300 °C has been studied by scanning electron microscopy, electron backscatter diffraction analysis, electron probe micro-analysis, differential scanning calorimetry, and hardness measurement. Results show that the recrystallization process starts at the interface region between the AA3xxx (clad) and AA6xxx (core) layers. Subsequently, the recrystallization process front progresses into the core layer, while the clad layer is the last region to recrystallize. It is also found that precipitation precedes recrystallization in the entire laminate at the investigated temperature. The preferential onset of recrystallization at the interface region is attributed to the net driving pressure being the highest in this region. The factors that lead to such enhanced net driving pressure are (a) deformation incompatibility between the two alloy layers, (b) lower solute content of the interface, which also leads to lower volume fraction of precipitates, and (c) an accelerated rate of precipitate coarsening due to the presence of a higher density of dislocations. The gradual progress of recrystallization from the interface towards the core layer is dictated by precipitate coarsening and the dependence of its rate on the density of deformation-induced dislocations. The lower driving pressure due to lower work hardening capacity, high solute drag pressure due to Mn, and additional Zener drag from precipitates that form due to solute redistribution during annealing explain the late initiation of recrystallization in the clad layer. - Highlights: • The through-thickness recrystallization of a laminated system is investigated. • The early onset of recrystallization at the interface is discussed. • The effects of precipitation and coarsening on recrystallization are analyzed.

36 MATERIALS SCIENCE↗
NASA NTRS1993

Solidification of eutectic system alloys in space (M-19)

It is well known that in the liquid state eutectic alloys are theoretically homogeneous under 1 g conditions. However, the homogeneous solidified structure of this alloy is not obtained because thermal convection and non-equilibrium solidification occur. The present investigators have clarified the solidification mechanisms of the eutectic system alloys under 1 g conditions by using the in situ observation method; in particular, the primary crystals of the eutectic system alloys never nucleated in the liquid, but instead did so on the mold wall, and the crystals separated from the mold wall by fluid motion caused by thermal convection. They also found that the equiaxed eutectic grains (eutectic cells) are formed on the primary crystals. In this case, the leading phase of the eutectic must agree with the phase of the primary crystals. In space, no thermal convection occurs so that primary crystals should not move from the mold wall and should not appear inside the solidified structure. Therefore no equiaxed eutectic grains will be formed under microgravity conditions. Past space experiments concerning eutectic alloys were classified into two types of experiments: one with respect to the solidification mechanisms of the eutectic alloys and the other to the unidirectional solidification of this alloy. The former type of experiment has the problem that the solidified structures between microgravity and 1 g conditions show little difference. This is why the flight samples were prepared by the ordinary cast techniques on Earth. Therefore it is impossible to ascertain whether or not the nucleation and growth of primary crystals in the melt occur and if primary crystals influence the formation of the equiaxed eutectic grains. In this experiment, hypo- and hyper-eutectic aluminum copper alloys which are near eutectic point are used. The chemical compositions of the samples are Al-32.4mass%Cu (Hypo-eutectic) and Al-33.5mass%Cu (hyper-eutectic). Long rods for the samples are cast by the Ohno Continuous Casting Process and they show the unidirectionally solidified structure. Each flight and ground sample was made of these same rods. The dimensions of all samples are 4.5 mm in diameter and 23.5 mm in length. Each sample is put in a graphite capsule and then vacuum sealed in a double silica ampoule. Then the ampoule is put in the tantalum cartridge and sealed by electron beam welding. For onbard experiments, a Continuous Heating Furnance (CHF) will be used for melting and solidifying samples under microgravity conditions. Six flight samples will be used. Four samples are hypo-eutectic and two are hyper-eutectic alloys. The surface of the two hypo-eutectic alloy samples are covered with aluminum oxide film to prevent Marangoni convection expected under microgravity conditions. Each sample will be heated to 700 C and held at that temperature for 5 min. After that the samples will be allowed to cool to 500 C in the furnace and they will be taken out of the furnace for He gas cooling. The heating and cooling diagrams for the flight experiments are shown. After collecting the flight samples, the solidified structures of the samples will be examined and the mechanisms of eutectic solidification under microgravity conditions will be determined. It is likely that successful flight experiment results will lead to production of high quality eutectic alloys and eutectic composite materials in space.

Ohno, Atsumi↗
DOE OSTI2022

Fundamental Effects of Al and Ta on Microstructure and Phase Transformations in the Al–Cr–Mo–Ta–Ti Refractory Complex Concentrated Alloy System

The effect of aluminum and tantalum concentrations on a refractory metal complex concentrated alloy is reported, particularly with respect to their effect on microstructure and phase composition of the alloy in cast and annealed form. Alloys with an equiatomic composition, (AlCrMoTaTi), an aluminum-lean composition (Al 0.75 CrMoTaTi), and a tantalum-lean composition (AlCrMoTa 0.75 Ti) are produced via arc melting. The alloys exhibit multiphase structures, confirmed by X-ray diffraction, microstructural characterization, and thermal analysis. The minor off-equiatomic adjustments of aluminum and tantalum in this alloy system did not drastically alter the prevalence of the Cr–Ta-based Laves phase. Correlations between thermodynamic predictions and observed phase transformations via thermal analysis are improved upon refinement of calculations removing impractical intermediate phases. As a result, experimental findings provide information for the refinement of thermodynamic modeling and deliver additional insight into the optimization of alloy compositions within this five-component system.

36 MATERIALS SCIENCE↗
NASA NTRS1978

Geometric relationships for homogenization in single-phase binary alloy systems

A semiempirical relationship is presented which describes the extent of interaction between constituents in single-phase binary alloy systems having planar, cylindrical, or spherical interfaces. This relationship makes possible a quick estimate of the extent of interaction without lengthy numerical calculations. It includes two parameters which are functions of mean concentration and interface geometry. Experimental data for the copper-nickel system are included to demonstrate the usefulness of this relationship.

Unnam, J.↗
NASA NTRS1979

An empirical relationship for homogenization in single-phase binary alloy systems

A semiempirical formula is developed for describing the extent of interaction between constituents in single-phase binary alloy systems with planar, cylindrical, or spherical interfaces. The formula contains two parameters that are functions of mean concentration and interface geometry of the couple. The empirical solution is simple, easy to use, and does not involve sequential calculations, thereby allowing quick estimation of the extent of interactions without lengthy calculations. Results obtained with this formula are in good agreement with those from a finite-difference analysis.

Unnam, J.↗
DOE OSTI2018

A self-contained algorithm for determination of solid-liquid equilibria in an alloy system

In this paper, we describe a self-contained procedure to evaluate the free energy of liquid and solid phases of an alloy system. The free energy of a single-element solid phase is calculated with thermodynamic integration using the Einstein crystal as the reference system. Then, free energy difference between the solid and liquid phases is calculated by Gibbs-Duhem integration. The central part of our method is the construction of a reversible alchemical path connecting a pure liquid and a liquid alloy to calculate the mixing enthalpy and entropy. We have applied the method to calculate the free energy of solid and liquid phases in the Al-Sm system. Finally, the driving force for fcc-Al nucleation in Al-Sm liquid and the melting curve for fcc-Al and Al 3 Sm are also calculated.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Effects of carbon content and size on Ti-C reaction behavior and resultant properties of Cu-Ti-C alloy system

Highlights: • TiC-strengthened Cu alloys were synthesized by an in situ powder metallurgy route. • Effect of C/Ti ratio on electrical and mechanical properties was studied. • Ti-C reaction behavior during powder metallurgy process was discussed. • Microstructure evolution during present process was analyzed. - Abstract: TiC-strengthened Cu alloys with various nominal compositions were prepared by a high-energy ball-milling process, followed by consolidation using spark plasma sintering (SPS), and a subsequent heat treatment. The results indicated that the lower atomic ratio of C/Ti, the more residual Ti in copper matrix, resulting in a lower electrical conductivity but higher microhardness of alloy. The optimal atomic ratio was found to be close to1.0. The reaction behavior of Ti-C in the Cu-Ti-C system during this process was investigated. Microstructural results suggested that TiC formation is through a diffusion-controlled mechanism. A thin TiC layer was formed at the surface of C particles, and the growth of TiC layer was controlled by interdiffusion of C and Ti atoms across the TiC layer. An incomplete chemical reaction between Ti and C, characterized by a core-shell structure, was observed when the initial C particles were large, and the TiC particle size was found to strongly depending on the C particle size.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Thermodynamic Assessment of the Ternary Alloy System Li-Sn-Zn

The goal of this project is to predict thermodynamics and structure-properties relationships of a series of Li-based alloys for the development of advanced tritium breeding materials that exhibit the beneficial properties of pure lithium while mitigating its chemical reactivity issues for fusion applications. This project makes use of phenomenological thermodynamics based on the CALPHAD (CALculation of PHAse Diagrams), and the use of the Thermo-Calc software (see Appendix A), and experimental calorimetric data and structural characterization for the purpose of validating the data. The initial selection of Sn and Zn as solutes is considered in this first report. Originally Li-Sn alloys have shown promise in meeting tritium breeding ratio (TBR) and energy multiplication requirements. However with the addition of Zn, we expect an improvement in the nuclear, thermal, and chemical requirements of the working fluid. Other substitutes will be considered once neutronic calculations are carried out. Hence the objective of this first task is to carry out a thermodynamic assessment of the Li-Sn-Zn alloy system, as part of the development of a self-consistent and validated thermodynamic database that will include other solute elements for optimizing the properties of blanket materials in fusion-based reactors. This obviously involves the thermodynamic assessment of the three binary subsystems, namely Li-Sn, Li-Zn, and Sn-Zn.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Temperature-dependent transformation from whisker- to nanoparticle-strengthened composite interface in the Al{sub 2}O{sub 3}/Ag-based alloy system and mechanical properties of the joints

Al{sub 4}B{sub 2}O{sub 9}-whisker-coated Al{sub 2}O{sub 3} ceramics were bonded by AgCu–4.5 wt.%Ti alloy in vacuum. The microstructure of the whisker-coated Al{sub 2}O{sub 3} joints was investigated by scanning electron microscopy, transmission electron microscopy and X-ray diffraction. A continuous (Cu,Al){sub 3}Ti{sub 3}O layer formed against the alloy at lower bonding temperatures, and a complex transition zone bordering the whiskers was observed, which consisted of Ag nanoparticles, titanium oxides, TiB{sub 2}, (Cu,Al){sub 3}Ti{sub 3}O nanoparticles and possible Ag{sub 3}Al. As the bonding temperature increased, the Al{sub 2}O{sub 3}/AgCuTi interface was found to transform from whisker- to nanoparticle-strengthened composite region. Bend test results revealed that both the whiskers grown on Al{sub 2}O{sub 3} and the dispersive nanoscale products in the alloy played positive roles in improving the joint properties. The maximum bend strength of the whisker-coated Al{sub 2}O{sub 3} joints was 313 MPa at the bonding temperature of 820 °C. - Highlights: • Al{sub 4}B{sub 2}O{sub 9}-whisker-coated Al{sub 2}O{sub 3} ceramics were bonded by AgCu–4.5 wt.%Ti alloy in vacuum. • Microstructures of whisker-coated Al{sub 2}O{sub 3} joints were investigated in detail. • Both whiskers and the dispersive nanoscale products can improve the joint properties. • The maximum bend strength of the whisker-coated Al{sub 2}O{sub 3} joints was 313 MPa.

36 MATERIALS SCIENCE↗