Effects of silicon content on the structure and mechanical properties of (AlCrTaTiZr)–Six–N coatings by reactive RF magnetron sputtering

Abstract

Multi-component (AlCrTaTiZr)–Six–N films were deposited on silicon wafers by reactive RF magnetron co-sputtering. The effect of silicon content on the structure, morphology and mechanical properties of the nitride films was investigated. Nitride films with lower silicon content remained as a simple NaCl-type face-centred cubic (FCC) structure. As the silicon content reached 7.9 at%, thermodynamically driven phase separation occurred, leading to a nanocomposite structure consisting of an FCC solid-solution nitride and an amorphous SiNx phase. These nitride films exhibited a high hardness of 34 GPa and remained at a constant level up to 7.9 at% Si. The reduced hardness at a silicon content of 10.2 at% was attributed to the appreciable amounts of softer amorphous segregation. The silicon incorporation significantly improved the oxidation resistance of (AlCrTaTiZr)N films. The film containing 7.9 at% Si annealed at 1000 °C for 2 h in air only had a 330 nm-thick oxide layer. The optimum Si content is 7.9 at% since it gives the best combination of hardness and oxidation resistance.