The tungsten-free γ-γ' 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 Co3(Al, Mo) phase. For Co-Al-Mo-Nb alloys, Nb prefers to occupy Mo4 site, while for Co-Al-Mo-Nb-Ti alloys, Nb and Ti prefer Mo3 site. Moreover, the addition of Nb and Ti in Co3(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 Co3(Al, W), it makes Co-based superalloy possess a better prospect.
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