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Results for “Concentrated alloys”

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.

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At least 55 records · Page 3
All sourcesNASA NTRSDOE OSTI
DOE OSTI2025

Rationalization of the tensile creep behavior of the Nb45Ta25Ti15Hf15 bcc refractory complex concentrated alloy using Rao-Suzuki screw dislocation glide model

Published experimental tensile creep data for refractory body-centered cubic alloy Nb45Ta25Ti15Hf15 (NTTH) at temperatures ranging from 850–950 °C and applied tensile stresses 50–300 MPa are analyzed using the Rao-Suzuki screw dislocation glide model of solid solution strengthening. It is shown that the experimental creep data as well as transmission electron microscopy observations of post- creep deformation dislocation microstructure are in agreement with the model results. This suggests that the creep deformation of NTTH at 850–950 °C is controlled by screw dislocation glide.

Rao, Satish I↗
DOE OSTI2023

Reconsidering short-range order in complex concentrated alloys

Abstract The seemingly contradictory state of research on short-range order in many-component alloys is addressed through a critical review of the characterization of face-centered-cubic 3 d systems. Despite the paucity of direct observations, the ordering of many widely studied alloys is argued to be primarily interesting for its potential ubiquity. To clarify this situation, future research directions are proposed with reference to historical results, including a review of the fundamental principles of ordering and clustering. Graphical abstract

36 MATERIALS SCIENCE↗
DOE OSTI2022

Modeling of non-equilibrium partitioning in direct metal deposited copper–iron concentrated alloys

The direct metal deposition (DMD) additive manufacturing process produces high cooling rates within a small melt pool and can lead to high amounts of solute trapping. These high cooling rates limit diffusion and lead to the formation of non-equilibrium phases. In this work, we utilize a numerical model to calculate the degree of solute trapping, defined as non-equilibrium partitioning. A theoretical case with overall composition fixed to 50Cu-50Fe at.%. was performed to observe the influence of increasing solidification rates. We then simulate DMD of equimolar Cu-Fe powder printed on mild steel substrate and the calculated non-equilibrium phase compositions were consistent with experimental observations reported earlier on this alloy composition. For a single deposited track, cooling rates are high enough to yield significant solute trapping. Here, the degree of solute trapping is highest near the free surface and has a gradient that correlates with the cooling rate gradient.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Topological alloy engineering and locally linearized gap dependence on concentration

Alloy engineering is a well-established approach to tune various materials’ properties, but its application to topological alloys remains rudimentary. Of special interest is the band gap, the most defining property of topological materials; however, the concentration dependence of energy gaps in topological alloys remains unknown. Here we systematically investigate the band gap evolution of a topological alloy as a function of alloy concentration, using KZnSb 1-x Bi x as a prototype, based on first-principles calculations. In contrast to the well-established smooth bowing curve for a trivial gap in semiconductor alloys, we found that the topological gap evolves generally with a complex fragmented pattern due to topological phase transitions, and most strikingly a linear dependence on concentration locally in each distinct phase. Such gap linearization is fundamentally rooted in the linear dependence on alloy concentration of spin-orbit coupling (SOC) that predominantly determines a topological gap. Furthermore, we demonstrate topological alloy engineering as a general approach to tune the topological order by modulating the band edge composition and degeneracy through the alloying-induced interplay of SOC and atomic orbital on-site energy, while the linear gap dependence on alloy concentration remains independent of the degree of topological order.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Ductility mechanisms in complex concentrated refractory alloys from atomistic fracture simulations

The striking variation in damage tolerance among refractory complex concentrated alloys is examined through the analysis of atomistic fracture simulations, contrasting behavior in elemental Nb with that in brittle NbMoTaW and ductile Nb45Ta25Ti15Hf15. We employ machine-learning interatomic potentials (MLIPs), including a new MLIP developed for NbTaTiHf, in atomistic simulations of crack tip extension mechanisms based on analyses of atomistic fracture resistance curves. While the initial behavior of sharp cracks shows good correspondence with the Rice theory, fracture resistance curves reveal marked changes in fracture modes for the complex alloys as crack extension proceeds. In NbMoTaW, compositional complexity appears to promote dislocation nucleation relative to pure Nb, despite theoretical predictions that the alloy should be relatively more brittle. In Nb45Ta25Ti15Hf15, alloying alters the fracture mode compared to elemental Nb, promoting crack tip blunting and enhancing resistance to crack propagation.

Computational methods↗
DOE OSTI2021

Analytic Binary Alloy Volume–Concentration Relations and the Deviation from Zen’s Law

Alloys expand or contract as concentrations change, and the resulting relationship between atomic volume and alloy content is an important property of the solid. While a well-known approximation posits that the atomic volume varies linearly with concentration (Zen’s law), the actual variation is more complicated. Here we use the apparent size of the solute (solvent) atom and the elasticity to derive explicit analytical expressions for the atomic volume of binary solid alloys. Two approximations, continuum and terminal, are proposed. Deviations from Zen’s law are studied for 22 binary alloy systems.

36 MATERIALS SCIENCE↗
DOE OSTI2026

Probing multi-dimensional composition spaces in search of strong metallic alloys

Refractory complex concentrated alloys (RCCA) offer exceptionally high-temperature strength compared to pure metals and dilute alloys, but predictive theory for RCCA design is lacking. We present large-scale molecular Dynamics (MD) simulations of crystal plasticity to explore alloy compositions for maximum mechanical strength, focusing on Fe-Ta-W and Nb-Ta-Mo-W alloy families modeled with Embedded Atom Model (EAM) and Spectral Neighbor Analysis Potentials (SNAP). To efficiently guide the search for strong alloy compositions, we employ iterative optimization using Gaussian process regression. Many simulated RCCA compositions exhibit pronounced cocktail strengthening, with strengths surpassing their strongest constituent metal, tungsten. Contrary to expectations, the highest strength is found on binary edges of the RCCA composition space. Detailed analyses of atomistic simulations reveal that, similar to pure BCC metals, plastic response in RCCA is primarily governed by screw dislocations. However, at large strains, dislocation multiplication and interactions (Taylor hardening) become the dominant mechanisms contributing to RCCA strength.

Materials science↗