Effect of nickel on the formation of γ/γ’ microstructures in WC/Co-Ni-Al-W

Abstract

Cuboidal and coherent precipitates form in ternary cobalt-aluminium‑tungsten systems and are described to increase high temperature toughness of superalloys for gas turbines. γ’ is a metastable phase in the form of Co3(Al,W) which is stabilized by the substitution of cobalt with nickel. Strengthening of cobalt binder (γ) in cemented carbides by precipitation hardening is of interest as it potentially increases hardness and wear resistance without sacrificing tensile strength or toughness of the composite materials. Infiltration of preliminary produced cobalt-base and cobalt‑nickel-base superalloys into tungsten carbide powder beds yielded a γ/γ’ binder microstructure. It was shown that nickel stabilizes the γ’ phase in superalloys as well as in cemented carbides, but carbon may lead to the formation of an additional κ phase with E21 structure.