Atomistic observation of in situ fractured surfaces at a V-doped WC Co interface

An in situ mechanical test was performed on a V-doped WCCo specimen in a transmission electron microscope (TEM) to understand the crack propagation dynamics. The fracture occurs along a WCCo interface. Aberration-corrected high-angle annular dark-field (HAADF) imaging and energy-dispersive X-ray spectroscopy (EDS) mapping are combined to investigate the as-fractured surface. The interfacial cleavage plane is atomically flat, taking place between the V-containing trilayers and the abutting cobalt grain. No noticeable structural or compositional change is detected for the trilayer superstructure coherent with the underneath WC grain. Density functional theory (DFT) calculations reveal that the interlayer bonding within the coherent interfacial trilayer superstructure is strong while that between the superstructure and cobalt is substantially weaker due to incoherency. This study provides insights into the interfacial fracture behavior in hard metals and suggests the importance of interfacial coherency to fracture resistance.