Study on properties of zirconia reinforced refractory matrix composites

The research was performed in the context of examinations of refractory matrix composite feasibility for such applications as plow blades or mining drill bits. In the experiments, the WC matrix was used with Co binder, and zirconia played the role of the particulate filler. ZrO2 is known and appreciated for its wear resistance, high fracture toughness, and high hardness. It forms the tetragonal metastable phase t-ZrO2 and the termodynamically stable monoclinic phase m-ZrO2. The WC–Co–ZrO2 composite samples were made of the powders using an innovative, energy-saving, field activated vacuum hot-pressing unit. The alternating current passing through the graphite mold and the sample was the sole heat source, providing high heating rates up to 300 °C/min and a relatively short sintering time of several minutes. As a result, nanoscale features were preserved in the composite structure ensuring high hardness and wear resistance. In particular, during microindentation, the work of elastic deformation was We = 0.162 μJ, while the work of plastic deformation was Wp = 0.484 μJ, which showed that the elastic part of indentation work was ηIT = 26.58%. This can be explained by transformation toughening phenomena, which take place when tetragonal zirconia t-ZrO2 transforms to the monoclinic phase m-ZrO2, which is accompanied by the changes of the specific volume. This, in turn, generates compressive mechanical stresses suppressing crack propagation, improving elasticity of the composite. At the next stage of the investigations, it is planned to perform tribological tests.