Effect of bias voltage on microstructure, mechanical and wear properties of Al-Si-N coatings deposited by cathodic arc evaporation

Al-Si-N coatings were deposited on tungsten carbide (WC-Co) and silicon wafer substrates using Cr and AlSi (12 at.% Si) alloy targets using a dual cathode source with short straight-duct filter in the cathode arc evaporation system. Al-Si-N coatings were synthesized under a constant flow of nitrogen, using various substrate bias voltages at a fixed AlSi cathode power. To enhance adhesive strength, the Cr/(CrxAlySiz)N graduated layer between the top coating and the substrate was deposited as a buffer interlayer. The effects of bias voltage on the microstructure, mechanical and wear properties of the Al-Si-N films were investigated. Experimental results reveal that the Al-Si-N coatings exhibited a nanocomposite structure of nano-crystalline h-AlN, amorphous Si3N4 and a small amount of free Si and oxides. It was also observed that the deposition rate of as-deposited films gradually decreased from about 25.1 to 18.8 nm/min when the substrate bias was changed from - 30 to - 150 V. The XRD results revealed that h-AlN preferred orientation changed from (002) to (100) as the bias voltage increased. The maximum hardness of approximately 35 GPa was obtained at the bias voltage of -90 V. Moreover, the grain size was inversely proportional to the hardness of the film. Wear test results reveal that the Al-Si-N film had a lower coefficient of friction, between 0.5 and 0.7, than that 0.7 of the AlN film.