Abstract
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.
Highlights
Exploring new materials with outstanding properties is an eternal pursuit of scientists and engineers
We verify the formation of the single-phase body-centered cubic (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, illustrating the entropic stabilization principle of High entropy alloys (HEAs)
We note that mixing enthalpies for the BCC solid solution are positive for Cr–Mo, Cr–Nb, and Nb–V, indicating low-temperature phase separation, while the remaining cases, Cr–V, Mo–Nb, and Mo–V, have negative enthalpies,[16,17] indicating stability down to low temperatures
Summary
Exploring new materials with outstanding properties is an eternal pursuit of scientists and engineers. 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 We illustrate these ideas by demonstrating phase stability in the quaternary Cr–Mo–Nb–V alloy system. 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. 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, illustrating the entropic stabilization principle of HEAs
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