Effect of γ-phase and grain size on the contact damage response of cemented carbides

The Hertzian contact response and damage evolution induced through spherical indentation was investigated in four cemented carbide grades by means of acoustic emission (AE) monitoring. Cemented carbides studied included two plain WC-Co grades (fine- and medium-grained) and their corresponding counterparts containing secondary mixed cubic carbides (γ-phase). AE analysis enabled in-situ identification of critical loads for distinct damage events, as supported by optical, confocal and scanning electron microscopy. These results allowed the construction of damage maps showing the evolution of the discerned damage mechanisms, as well as the transition from quasi-plastic to brittle behavior. The fine-grained γ-phase grade exhibited surface ring and subsurface cone cracks at lower critical loads than its WC-Co counterpart, with preferential transgranular crack propagation through γ-phase carbides. In contrast, both medium-grained grades showed only quasi-plastic, depression-induced circular cracks, without cone crack formation. The effect of the different grades on the fracture resistance of the material was discussed.