Microstructure and performance of a cermet material heat-treated in nitrogen

Abstract A Ti(C,N)–TiN–WC–Co cermet material was subjected to a heat-treatment in nitrogen which substantially improved the plastic deformation resistance during cutting. The microstructure was characterised using analytical electron microscopy. It was found that a surface zone rich in titanium and nitrogen was induced by the heat-treatment. The high nitrogen activity in the surface region was the driving force for outward transport of titanium and inward transport of tungsten in the cobalt binder. An irregularly shaped nitrogen-rich titanium carbonitride reprecipitated from the binder phase during the heat-treatment, often as surrounding layers on already existing carbonitride grains. The morphological change of the hard phase might explain the dramatically improved plastic deformation resistance by obstructing grain boundary sliding. The experimental findings were in accordance with thermodynamic calculations performed using the Thermo-Calc software.