ChemInform Abstract: CALCULATION OF PHASE DIAGRAMS OF VANADIUM‐CHROMIUM, VANADIUM‐NIOBIUM, AND CHROMIUM‐NIOBIUM SYSTEMS IN AN APPROXIMATION OF REGULAR SOLUTIONS

Molokanov, V. V.; Chernov, D. B.; Budberg, P.B.

doi:10.1002/chin.197746019

Cited by 2 publications

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“…in the case of Cr-Mo [18] and Nb-V [19], though it is predicted [20,21]. Cr-Nb and Nb-V are predicted [22] to form Laves phases of types cF24 (Strukturbericht C15) and hP12 (Strukturbericht C14).…”

Section: Introductionmentioning

confidence: 99%

“…1 offers a clue to why experiments on Cr-Mo and Nb-V fail to observe the predicted miscibility gaps, while separation is seen in Cr-Nb. The mixing enthalpies are relatively low in Cr-Mo and Nb-V, compared with Cr-Nb, so their estimated critical temperatures for phase separation are low (1,213K and 653K, respectively [20,21]). Meanwhile, the melting temperatures of Cr-Mo and Nb-V are relatively high (2,093K and 2,133K, respectively, compared with 1,893K for Cr-Nb).…”

Section: Introductionmentioning

confidence: 99%

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First-principles prediction of high-entropy-alloy stability

et al. 2017

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High entropy alloys (HEAs) are multicomponent compounds whose high configurational entropy allows them to solidify into a single phase, with a simple crystal lattice structure. Some HEAs exhibit desirable properties, such as high specific strength, ductility, and corrosion resistance, while challenging the scientist to make confident predictions in the face of multiple competing phases. We demonstrate phase stability in the multicomponent alloy system of Cr-Mo-Nb-V, for which some of its binary subsystems are subject to phase separation and complex intermetallic-phase formation. Our first-principles calculation of free energy predicts that the configurational entropy stabilizes a single body-centered cubic (BCC) phase from T = 1700 K up to melting, while precipitation of a complex intermetallic is favored at lower temperatures. We form the compound experimentally and confirm that it develops as a single BCC phase from the melt, but that it transforms reversibly at lower temperatures. INTRODUCTIONExploring new materials with outstanding properties is an eternal pursuit of scientists and engineers. High entropy alloys (HEAs) constitute a newly-emerging class of materials that offer enhanced mechanical and corrosion properties for practical applications, while presenting challenges to the scientist making predictions in the face of compositional complexity.1-13 Alloys of two or three species often phase-separate, and when they form a compound, it is often a complex ordered structure with multiple Wyckoff positions. Thus, HEAs are remarkable for forming single phases that are, moreover, simple lattice structures in which all atomic positions are equivalent. Trial-and-error experimental approaches to test the phase stability of HEAs are costly and time-consuming, while previously-reported phase-formation rules are empirical and susceptible to the alloy, systems 14,15 motivating a first-principles theoretical approach to accelerate the design of HEAs through the prediction of phase stability and microstructure.Here we illustrate these ideas by demonstrating phase stability in the quaternary Cr-Mo-Nb-V alloy system. Some of its binary and ternary subsystems are subject to phase separation and complex intermetallic phase formation. Utilizing fully firstprinciples calculations of the free energies of the full quaternary and its competing binary and ternary phases, we predict that the configurational entropy stabilizes a single body-centered cubic (BCC) solid solution at high temperatures, but that it will precipitate a complex intermetallic Laves phase at lower temperatures. Experimentally, we verify the formation of the single-phase BCC solid solution from the melt, confirm the precipitation of the Laves phase at low temperatures, and observe that it reverts to a single BCC phase upon annealing at high temperatures, thus illustrating the entropic stabilization principle of HEAs.

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