Correlation of transverse rupture strength of WC–Co with hardness

The transverse rupture strength (TRS) of WC–Co composites is often loosely viewed as an equivalent of “toughness” which increases as hardness decreases in the industry. The results of this study, conducted using a controlled group of WC–Co samples with consistent TRS values, suggest a different correlation between the TRS and hardness of WC–Co composites. It was shown that TRS is closely related to the hardness and facture toughness. Within a hardness range of 800 <Hv < 1500 kg/mm2, TRS appears to first increase and then decrease as the hardness increases. It reaches a peak value at Hv ≈ 1300 kg/mm2. While in the past TRS of WC–Co has been used as a indicator of porosities of WC–Co materials, the result of this study is understood on the basis that these samples are porosity-free because most products of WC–Co today contains very little (if any) porosity owing to modern advances in processing technologies. When the effect of porosity is negligible, TRS is determined by intrinsic mechanical properties which are dependent of microstructure and compositions. The relationship between TRS and hardness and the fracture toughness is explained by a qualitative model based on the work hardening and flow stress of the cobalt binder phase.