Interdependency of Hard Phase and Binder Phase Composition in Ti(C,N)-based Cermets

The binder phase of Ti(C,N)-based cermets is usually made of a Co/Ni alloy it develops due to the use of Co and Ni powders in the starting formulation and upon sintering it dissolves part of the hard-phase powders. The hard phase is usually made of several components, depending on the amount and nature of powders admixed to the starting formulation, i.e. together with Ti(C,N), powders such as WC, (Ti,W)C, Mo2C, TaC, NbC, Cr3C2, etc. are added. These hard-phase powders react with each other via the binder phase to build an fcc phase which is microscopically inhomogeneous by forming grains with a core-rim structure. The influence of the overall non-metal/metal ratio of the hard-phase powders on the dissolution state of the binder phase was studied by means of sintering model alloys. The alloys were investigated by light-optical metallography, electron-probe microanalysis (EPMA) and scanning electron microscopy (SEM) as well as by specific saturation magnetisation measurements (Ms). The higher the gross non-metal deficiency of the hard phase the higher is the concentration of dissolved metals in the binder phase. In some alloys the total of dissolved elements in the binder reached almost 12 mol%. Ms is linear with the amount of dissolved elements irrespective of the Co/Ni ratio.