Influence of fluoride phase on the tribological behaviour of Si3N4–SiC composites under extreme operating conditions

Abstract

For extreme operating conditions such as high temperature and load, Si3N4–SiC composite is often used as wear resistant material. However, it suffers from a moderately high friction coefficient and wear rate at such working conditions; therefore, it is still an ongoing area of research for further development. This work strives to develop a state-of-the-art wear-resistant Si3N4 composite with SiC nanowire as reinforcement phase and MgF2 as an internal lubricating additive, particularly suitable for harsh operating conditions at both high temperatures and high loads. A significant improvement in tribological characteristics is observed when MgF2 is added into the composite matrix tested at 500 °C as compared to its parent Si3N4–SiC composite. When the load is increased from 6 to 14 N, the composite shows better wear resistance by forming a lubricious tribolayer at the contacting surface. Delamination is found to be the dominating wear mode for composites containing fluoride phase as identified by the morphological characterization of the worn surfaces. A comprehensive analysis of the evolution of different wear modes with respect to the variation in extreme operating conditions is articulated here.