Abstract

Microstructural evolution of (Ti,Mo)(C,N)–Ni cermets consolidated by hot isostatic pressing (HIP) has been analysed. HIP processing allows full densification of these materials at lower temperatures than those normally employed in vacuum sintering cycles (VS). Solution and reprecipitation phenomena are limited and a nanometric fraction of (Ti,Mo)(C,N) grains is retained in the microstructure leading to a significant increase in hardness with respect to vacuum sintered materials (from 11 to 14 GPa). HIP-ed cermets show more tendency to uncombined carbon precipitation than those obtained by VS. In studied systems, carbon precipitation can be related either to an excess of carbon in the initial mixture of powders or to destabilization of carbonitride phase during HIP. Control of the C/N ratio has been carried out by the adequate selection of powder mixtures and the design of the thermal treatments. It has been proved that free carbon in these cermets can be avoided including presintering cycles under hydrogen before encapsulation.

Research highlights

► Fully dense TiMoCN–Ni cermets have been obtained by HIP in absence of a liquid phase. ► HIP-ed materials show a higher tendency to free carbon precipitation. ► An effective C control is achieved by using different presintering treatments. ► Materials obtained in solid state show nanometric carbonitride grains. ► TiMoCN–Ni cermets obtained by HIP are harder than the standard grades.