First-Principles Study of a Tungsten-Free γ-γ′ Co-Al-Mo-Nb Class Cobalt-Based Superalloy and the Alloying Effect of Ti Addition

The tungsten-free gamma-gamma' Co-Al-Mo-Nb class cobalt-based superalloy and the alloying effect of Ti were studied by analyzing the phase stability, electronic structure and elastic properties, using first-principles study. It is found that the addition of Nb and Ti decreases the formation enthalpy of the system and stabilizes Co-3 (Al, Mo) phase. For Co-Al-Mo- Nb alloys, Nb prefers to occupy Mo-4 site, while for Co-Al-Mo-Nb-Ti alloys, Nb and Ti prefer Mo-3 site. Moreover, the addition of Nb and Ti in Co-3(Al, Mo) declines the resistance to monoclinic shear in (100) plane and the hardness but improves the ductility which even exceeds that of Ni3Al. As this new alloy solves the problems of high density and low ductility of Co-3(Al, W), it makes Co-based superalloy possess a better prospect.