Cemented carbides with gamma/gamma binder microstructure

Abstract

Modifications of the binder phase (γ) of cemented carbides potentially increases the hardness and wear resistance of the whole material. (Partially) coherent precipitations with L12 structure (γ’) promise these improved properties without sacrificing tensile strength or toughness. γ’ is a metastable phase in the aluminum-cobalt-tungsten ternary system in the form of Co3(Al,W) which is stabilized by the substitution of cobalt with nickel. A preparation method for cemented carbides with γ/γ’ binder microstructure was developed in this work and the phase equilibria in the composite material were investigated. Infiltration of preliminary produced cobalt-base and cobalt-nickel-base superalloys into tungsten carbide powder yielded the anticipated microstructure. 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 E21 structure (κ). DTA measurements of cemented carbides with different aluminum-cobalt-nickel mixtures as binder gave an overview of the compositional influence. The aluminum-carbon-cobalt-nickel-tungsten quintenary system was thermodynamically modelled and the relevant literature data was collected. Enthalpies of formation for compounds with L12 and E21 structure were calculated using ab initio methods and discussed afterward.