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

Abstract

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/(Cr xAl ySi z)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 Si 3N 4 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.