3D FIB/FESEM tomography of grinding-induced damage in WC-Co cemented carbides

WC-Co cemented carbides (hardmetals) represent the backbone materials for the tooling industry. In order to achieve particular tool geometries, diamond wheel grinding is a well-established method for machining hardmetals. Grinding-induced damage has been proven to strongly affect the performance and reliability of the machined tools. Assessment of grinding-mechanisms and induced surface integrity changes has usually been limited to monolithic ceramics, and it is particularly done on the basis of post-failure fractographic examination. In this work, characterization of grinding-induced damage of a WC-Co grade has been conducted by means of focused ion beam (FIB) tomography. The study includes a 3D description of the damage scenario, based on a reconstruction from successive parallel slices. Our results show that grinding induces a 200-400 nm thick surface layer containing fragmented WC grains and smeared Co phase morphology. A highly anisotropic subsurface microcrack network is generated. The discerned microcracks follow different microstructural paths: running through the binder, close to WC/Co interfaces or transgranular within the carbide phase. Very interesting, completely or near- lateral cracks (parallel to the ground surface) are found to be the predominant damage feature, whereas only few completely or near- orthogonal (perpendicular to the ground surface) cracks are discerned. Results are discussed in terms of material removal mechanisms during grinding of cemented carbides and surface integrity effects on the mechanical performance of hardmetal tools under service conditions.