Tribological behavior of medium entropy boride (Ta,Zr,Ti)B2 densified at a relatively low temperature of 1600 °C

Medium and High entropy borides with high hardness and corrosion resistance are promising wear resistant materials. High temperature (>2000 degrees C) is always necessary for the densification of medium and high entropy borides. Using a mixture of 10 vol% metallic cobalt and 20 vol% SiC as additives, medium entropy (Ti,Zr,Ta)B-2 ceramics were prepared at a relatively low temperature of 1600 degrees C by SPS. The reduced sintering temperature is attributed to the synergistic effect of Co and SiC that wet the grain boundary and promote the interdiffusion. The prepared (Ti,Zr,Ta)B-2 obtains the microhardness of 22.54 +/- 0.92 GPa, comparable with other medium entropy boride ceramics prepared at 2000 degrees C. The tribo-tests results of (Ti,Zr,Ta)B-2 sliding against steel suggests that the tribological performance are load dependent. As the load increases, the friction coefficient first rises and then falls at a load of 10 N, which is associated with the chemical differences of the tribofilm. The tribofilm is primarily composed of O and Fe, along with Zr, Ti and Ta oxides. The iron oxide in the tribofilm will deteriorate the tribological performance. Abrasive wear is the main wear mechanism at lower load of 1 N, while adhesive wear is the predominant wear mechanism at 10 N.