Structural stability of topologically close-packed phases: understanding experimental trends in terms of the electronic structure
T. Hammerschmidt, B. Seiser, M. Čák, R. Drautz, D. G. Pettifor.Eric S. Huron, Roger C. Reed, Mark C. Hardy, Michael J. Mills, Rick E. Montero, Pedro D. Portella, Jack Telesman,
Superalloys 2012, TMS (The Minerals, Metals and Materials Society), 135-142, (2012)
Topologically close-packed (TCP) phases in single crystal Ni-based superalloys have a detrimental effect on the mechanical properties. In order to gain a microscopic understanding of the factors that control TCP phase stability, we carry out atomistic calculations based on the electronic structure. In particular, we use a hierarchy of methods that treat the electronic structure at different levels of coarse-graining, i.e. at different levels of computational cost and accuracy. The applied levels of approximation range from density functional theory (DFT) to tight-binding (TB) to bond-order potentials (BOPs). This hierarchy of electronic structure methods allows us to interpret the findings of a recently derived structure map of experimentally observed TCP stability. The TB and BOP calculations are compared to extensive high-throughput DFT calculations for the TCP phases A15, C14, C15, C36, mu, sigma, and chi of transition-metal elements. These findings are extended to binary systems based on DFT heat-of-formations for TCP phases in the systems V/Nb-Ta, Nb/Mo-Ru, V/Cr/Nb/Mo-Re, V/Cr/Nb/Mo-Co. By pairwise comparisons of selected systems, we illustrate the interplay of the difference in average valence electron concentration N and the composition-dependent relative volume difference dV/V . Such an approach could be useful to predict the change of expected TCP phase stability due to changes of the composition for a given multi-component alloy.
Keyword(s): TCP phases; density functional theory; bond order potential; structure maps