Understanding the mechanical properties of hardmetals through mechanical spectroscopy

Composites made of transition metal carbides, with a ferrous metal binder, commonly defined as hardmetals, are used for cutting tool applications. We investigate the mechanical behavior of the two main families of hardmetals: the cemented carbides, constituted of WC–Co, and the cermets made of a combination of TiC–TiN–(Co,Ni). The comparative analysis of internal friction spectra of both hardmetal families as well as the analysis of spectra of the ceramic phases alone (after binder etching) allows associating different relaxation peaks with specific phases or grain boundaries. The mechanical properties of hardmetals are controlled by the binder. Three temperature domains can be defined. Increasing the temperature binder microplasticity occurs first, then binder segregation at the ceramic grain boundaries prepares the way for infiltration and extensive deformation by grain boundary sliding.