Fatigue mechanics of WC–Co cemented carbides

Abstract

The fracture and fatigue behavior of a fine-grained WC–10 wt% Co hardmetal is investigated. Mechanical characterization included flexural strength and fracture toughness as well as fatigue limit and fatigue crack growth (FCG) behavior under monotonic and cyclic loads, respectively. Considering that fatigue lifetime of cemented carbides is given by subcritical crack growth of preexisting defects, a linear elastic fracture mechanics (LEFM) approach is attempted to assess fatigue life–FCG relationships for these materials. Following the experimental finding of an extremely high dependence of FCG rates on the applied stress intensity for the hardmetal studied, the LEFM analysis is concentrated, from a practical design viewpoint, on addressing the fatigue limit–FCG threshold correlation under infinite fatigue life conditions. Thus, fatigue limit associated with natural flaws is estimated from FCG threshold experimentally determined for large cracks under the assumptions that (1) similitude on the FCG behavior of small and large cracks applies for cemented carbides, and (2) critical flaws are the same, in terms of nature, geometry and size, under monotonic and cyclic loading. The reliability of this fatigue mechanics approach is sustained through the excellent agreement observed between estimated and experimentally determined values for the fatigue limit under the different load ratios investigated.