Fracture and fatigue behavior of cement carbides:3D focused ion beam tomography of crack-microstructure interactions

Abstract

The fracture and fatigue phenomena in WC-cobalt cemented carbides (hard-metals) have been subjects extensively investigated in the last 30 years. From these studies, it is well established that the metallic binder phase plays a key role as the toughening and fatigue-susceptible agent in these materials, as its effective ductility is critical for defining crack-growth resistance and cyclic-induced degradation. However, experimental proof of the role of toughening and fatigue micromechanisms has usually been presented on the basis of post-failure fractographic examination. In this work, the fracture and fatigue behavior of WC-cobalt is investigated and a 3D characterization of crack microstructure interaction during stable crack growth in hardmetals is carried out in order to gain a better understanding of the failure processes in cemented carbides under monotonic and cyclic loads. In doing so, focused ion beam/field emission scanning electron microscopy (FIB/FESE114), 3D tomography, and imaging reconstruction are combined with systematic mechanical and indentation protocols for assessing crack-extension behavior of cemented carbides. Experimental findings clearly highlight existing differences regarding failure mechanisms operative under monotonic and cyclic loads, and provide new and interesting insights for understanding them.