Nanoindentation study of ultrafine WC–10Co cemented carbide

Nanocomposite WC–10Co powder produced by spray pyrolysis-continuous reduction and carbonization technology was used to prepare ultrafine WC–10Co cemented carbide by vacuum sintering plus hot isostatic pressing (HIP) technology. In order to study the nanomechanical property such as nanohardness, nanoindentation tests have been carried out in the present study. As reference data, Vickers hardness has also been measured. The nanohardness Hn of polished specimen was from 28.3 GPa to 78.3 GPa. The nanohardness of the polished specimen increased with decreasing maximum indentation load, which has been referred to as indentation size effect (ISE). A deformed and detached surface layer was found on top of the specimen after surface polishing. The work hardening surface layer due to polishing the sample strongly affected not only the nanohardness, but also the Vickers hardness, and the nanohardness is more than that of pure WC or WC–10Co cemented carbide. Because the cobalt phase was partly evaporated at the surface due to the heat-treated process, and the Vickers hardness of specimen was from 13.1 GPa to 13.8 GPa, the surface state of heat-treated specimen is not representative of the bulk of the material and cannot be used to test the indentation size effect. Etching the surface layer to remove deformed and detached surface layer is the best way to test indentation size effect, by this method, the nanohardness Hn of specimen was from 13.2 GPa to 15.8 GPa. By removing deformed and detached surface layer of specimen, indentation size was found to be constant. This shows that there is no indentation size effect.