High temperature negative wear behaviour of VN/Ag composites induced by expansive oxidation reaction

Ultra-low wear or non-wear of moving parts is highly desirable because wear limits the service life and reliability of components, particularly under high temperatures. In this study, VN/Ag composites were prepared using vacuum hot-pressing sintering, and their microstructure and high-temperature tribological behaviour were studied. The results demonstrated that the tribological properties of VN ceramics remarkably improved because of metallic Ag. In particular, negative wear was detected in the VN/Ag composites at 700 °C. During the high-temperature tribology process, the evolution of Ag, V2O5, Ag3VO4, and AgVO3 caused by Ag and VN on the worn surface played a significant role in lubrication. In addition, the cell volumes of AgVO3 and Ag3VO4, which were produced via the expansive tribochemical reaction, were 75% and 103% larger than the sum of the cell volumes of VN and Ag. The cell volume expansion compensated for the mechanical damage caused by the wear, possessed an excellent role in wear reduction, and thus contributed to the improvement of high-temperature lubricating materials with high reliability and long service lives.