Influence of carbon on the formation of γ/γ′ microstructure and κ-phase in the WC/Co–Ni–Al–W system: ab initio calculations and experimental studies

Abstract Modifications of the binder phase ( γ ) of cemented carbides have the potential to increase the hardness and wear resistance of the whole material. Partially, coherent precipitations with L1 2 structure (γ’) promise these improved properties without sacrificing tensile strength or toughness. γ ’ is a metastable phase in the Al–Co–W ternary system in the form of Co 3 (Al,W) which is stabilized by the substitution of cobalt with nickel. Superalloys of the composition Co–(30Ni)–9Al–7 W with different carbon contents were prepared by inductive melting, and the resulting microstructures were analysed using SEM–EDS, XRD and Vickers hardness. Cemented carbides with γ / γ ’ binder microstructure were prepared via DTA, and the phase equilibria in the composite material were investigated experimentally and in silico. It was shown that nickel stabilizes the γ ’ phase in superalloys as well as in cemented carbides. Carbon leads to the formation of an additional phase with E2 1 structure (κ). DTA measurements of cemented carbides with different aluminium–cobalt–nickel mixtures as binder gave an overview of the compositional influence. Enthalpies of formation for compounds with L1 2 and E2 1 structure were calculated using ab initio methods and compared to experimental results. Graphical Abstract