Structural stability of topologically close-packed phases: Understanding experimental trends in terms of the electronic structure

摘要

Topologically close-packed (TCP) phases in single crystalNi-based superalloys have a detrimental effect on themechanical properties. In order to gain a microscopicunderstanding of the factors that control TCP phase stability,we carry out atomistic calculations based on theelectronic structure. In particular, we use a hierarchy ofmethods that treat the electronic structure at differentlevels of coarse-graining, i.e. at different levels of computationalcost and accuracy.The applied levels of approximation range from densityfunctional theory (DFT) to tight-binding (TB) tobond-order potentials (BOPs). This hierarchy of electronicstructure methods allows us to interpret the ndingsof a recently derived structure map of experimentallyobserved TCP stability. The TB and BOP calculationsare compared to extensive high-throughput DFT calculationsfor the TCP phases A15, C14, C15, C36,μ , σ, andχ of transition-metal elements.These findings are extended to binary systems based onDFT heat-of-formations for TCP phases in the systemsV/Nb-Ta, Nb/Mo-Ru, V/Cr/Nb/Mo-Re, V/Cr/Nb/Mo-Co. By pairwise comparisons of selected systems, we illustratethe interplay of the difference in average valenceelectronconcentration (N-) and the composition-dependentrelative volume difference (△V/V) . Such an approach couldbe useful to predict the change of expected TCP phasestability due to changes of the composition for a givenmulti-component alloy.