Influence of CrB2 additive on the morphology, structure, microhardness and fracture resistance of diamond composites based on WC‒Co matrix

Abstract

In the paper, structure and properties of novel diamond composite with enhanced properties were presented and discussed. The samples were prepared using the method of cold pressing followed by the originally developed two-stage vacuum hot pressing under electric current activation. It was demonstrated that addition of different amounts of chromium diboride to the WC–6 wt.%Co composite had significant effect on its microstructure, phase composition and, hence, mechanical characteristics. It was found that percentage 4 wt.% of CrB2 provided the most advantageous characteristics. In the second stage of researches, this composition was used as a matrix for the diamond reinforcement. The obtained results of analysis suggested that enhancement of the composite could be attributed to the dispersed strengthening mechanism and structure modification. In particular, important role played reduction of the average grain size of the carbide phase from 5.6 to 3.4 μm, disappearance of pores at the Co binding phase, formation of inhibitor phase clusters at the interphase boundaries, and the specific pattern of phases present in the composite. Chromium diboride contributed also to the formation of dense and strong interface between diamond grits and refractory matrix. Advantageous distribution of residual stresses around the diamond grits appeared in the sintered samples with CrB2, providing additional fixation of the diamond reinforcement in the matrix. It was also demonstrated that further increase of CrB2 content above 4 wt.% in the WC–6 wt.%Co composite material lead to a deterioration in its mechanical properties, which could be attributed to further, disadvantageous changes in the structure, especially in grain size and phase composition.