Improvement of high entropy alloy nitride coatings (AlCrNbSiTiMo)N on mechanical and high temperature tribological properties by tuning substrate bias

Abstract

High entropy alloy nitride coatings (HEAN), showing superior mechanical strength, high oxidation resistance, and thermal stability, have often been used in protective hard coatings field. However, the high temperature tribological field of novel HEA nitride films has not yet been well studied. The correlations among tribological properties, compressive residual stress, mechanical properties, and self-lubricating oxide are still limited.In this research, the novel (AlCrNbSiTiMo)N coatings were fabricated on both Inconel-718 and Si (100) substrate by radio frequency (RF) magnetron sputtering via tuning both substrate bias at 300 °C deposition temperature. The (AlCrNbSiTiMo)N coatings with a specific substrate bias exhibit an outstanding hardness of 34.5±0.8 GPa.In the wear test at 700 °C, the films deposited at −100 V revealed the lowest wear rate around 1.2 × 10−6 mm3N−1 m−1. With Molybdenum doping, the MoO3 Magnéli phase was observed on the surface at elevated temperature wearing process, and the friction coefficient at high temperature decreased significantly due to a lubricating surface. The coating exhibited the average friction coefficient value of 0.48 in the wear test of 700 °C. The high temperature tribological performance was addressed and related to the mechanical properties, the plastic deformation resistance H3/E2, and the excess residual stress of the films.This study provides a new design for hard coatings applied to severe wearing conditions. By tuning substrate bias, the (AlCrNbSiTiMo)N coatings exhibit outstanding mechanical and tribological characteristics, which will be a promising candidate for high temperature tribological protective film.