Fracture behavior of cemented carbides with CoNiFe medium entropy alloy binder

Abstract

In this study, we prepared WC-CoNiFe and WC-Co with different grain sizes by sintering-hot isostatic pressing (SHIP) and evaluated their fracture behavior. The results showed that WC-CoNiFe has a higher fracture toughness (between 13.16 and 17.82 MPam1/2) than WC-Co (between12.08 and 16.21MPam1/2). Moreover, fracture toughness and fatigue crack growth (FCG) were closely related to the corresponding microstructural characteristics. The fracture toughness increased via ductile ligament bridging and crack deflection as the mean free path of the binder phase (λCo) increased, or the contiguity of the carbide phase (CWC) decreased. The fatigue fracture mode showed a transition from a cleavage-like brittle fracture to a ductile dimple-like fracture. The fatigue sensitivity of cemented carbides was positively related to the fracture toughness. As the fracture toughness increased, cemented carbides exhibited a transition from ceramic-like material to metal-like material. Considering two important controlling parameters of FCG behavior, the effect of maximum stress intensity factor (Kmax) on FCG was dominant compared to the stress intensity factor range (∆K). However, the difference in the relative influence of these two parameters diminished as the fracture toughness increased. Moreover, with the rise in Kmax value, we defined three stages of the FCG process: crack initiation, stable crack growth, and unstable crack growth. The results suggest that CoNiFe medium entropy alloy is a promising material for application as a binder phase of cemented carbides with high toughness.