Incessant tribo-layer formation supresses high temperature wear damage in SiC reinforced equi-volume ZrB2-HfB2 composite

Abstract

The lift-off and re-entry expose space vehicles to kinetically sharp particles, necessitating the study of surface damage resistance of potential materials for this application. For this purpose, room temperature (RT) and high temperature (1000 °C) wear resistance of 20 vol% SiC reinforced ZrB2-HfB2 based composites is investigated. It is observed that usually microhardness follows the same trend as that of densification, which is reflected in room temperature wear performance. As a result, ZrB2-SiC (the most dense composite with % densification of ~98 and possessing the highest microhardness of ~14 GPa) yields lowest cof (0.412). At high temperature, SiC reinforced equi-volume ZrB2-HfB2 composite exhibits minimum wear. The lubricating effect of tribo-chemical product formed in SiC reinforced equi-volume ZrB2-HfB2 composite is manifested through lowering of cof (from 0.484 during RT wear test to 0.381 in wear test performed at 1000 °C) and thus wear rate (wear rate of 0.31 × 10−4 mm3N−1 m−1 compared to other composites (0.41–1.96 × 10−4 mm3N−1 m−1)). The counter body, composed of alumina, in each case showed resistance to any surface damage though elemental analysis confirmed material transfer between the two bodies.