Fabrication of cemented carbides with bidirectional gradient structure via graphene deposition to simultaneously enhance surface hardness and toughness

The adoption of a continuous gradient in Co content stands as the foremost strategy for attaining heightened surface hardness and improved core toughness in cemented carbides. Nevertheless, the reduction in surface toughness stemming from a decreased Co content often precipitates premature surface failure of components. In this paper, WC-11Co powders was utilized as the precursor materials for fabricating a bidirectional gradient cemented carbide using the combined approach of low-temperature presintering and ultrasonic treatment techniques. The resultant cemented carbide exhibited a distinct gradient distribution, characterized by a forward gradient of graphene content, a reverse gradient of Co content, a forward gradient of WC grain size, and a forward gradient of residual compressive stress. The hardening and toughening mechanisms of the fabricated bidirectional gradient cemented carbides were comprehensively characterized and quantitatively discussed. The results provide compelling evidence that the gradient distribution of Co content plays a crucial role in attaining an impressive surface hardness of 1820 kgf/mm2. By utilizing the crack bridging mechanism of graphene, which efficiently exploits its strain transfer capabilities across a semi-coherent interface, in conjunction with the toughening effects of crack deflection and residual compressive stress, an exceptional surface fracture toughness of 17.62 MPa m1/2 is achieved. Additionally, the gradient layer exhibited a higher critical load for cracking. The present findings presents a novel strategy for the fabrication of high-performance ceramic-based composites.