Contact damage and residual strength in hardmetals

In most of the applications where hardmetals are implemented, mechanical contact plays an important role from a design viewpoint, either as direct key parameter (e.g. wear resistance) or as indirect relevant factor (e.g. residual strength associated with contact-induced damage). In this work, the contact response of three cemented carbides WC–Co with different microstructural features is evaluated. The study is performed using spherical indenters (Hertzian contact) and it is focused on: 1) determining the critical loading parameters affiliated to the emergence and evolution of damage; and 2) investigating the relevance of microstructure on the levels of residual strength attained. It is found that strength retention is improved as contact damage mode goes from brittle to quasi-plastic, a transition directly dependent on microstructure. Hence, microstructural design searching for higher damage tolerance (i.e. deformation prevailing over fracture as damage mode) is concluded to be an optimal approach for the development of hardmetals with improved reliability. In practical terms, this is achieved by enhancing toughness through either higher binder content and/or microstructural coarsening, as far as the field application requirements are satisfied.

► Spherical indentation is a suitable technique for inducing controlled extrinsic damage in hardmetals. ► The combined influence of microstructure, hardness and toughness defines strength retention in hardmetals. ► Damage tolerance of cemented carbides is the result of the mutual competition between deformation and fracture phenomena. ► Microstructural design searching for higher damage tolerance is an optimal approach for improving reliability of hardmetals.