Nanocrystalline WC-Co composite with ultrahigh hardness and toughness

Abstract

The hard WC-Co composites usually have weak toughness. The present work solved this issue by a new strategy of fabricating nanocrystalline composites, which consists of concurrent crystallization, carbonization, and sintering densification of the amorphous compound powder. The resultant nanocrystalline WC-Co composite has distinctly larger proportion of interfacial coherency at the grain- and phase-boundaries compared with that in the conventional counterparts. The formation mechanisms of the coherent WC grain boundaries, Co twinning boundaries, and step-like semi-coherent WC/Co phase boundaries were demonstrated on the atomic scale. Moreover, the contributions of the characteristic interfaces to the resistance against intergranular fracture, which dominates the failure of nanocrystalline composites in the deformation, were illustrated based on the analyses of atomic configuration and crystallographic relationship at interfaces. The reasons were disclosed for the advanced comprehensive properties with simultaneously ultrahigh hardness and fracture toughness of the prepared nanocrystalline composite. The present technology and mechanisms for properties enhancement will be applicable to a large variety of composite materials.