Characterization and tribological properties of W-Ti-N/Al-Si multilayer surface coating for iron alloy pistons

Abstract

Piston skirts undergo important wear and abrasion due to poor tribological properties. A surface coating system with appropriate friction and hardness properties is proposed in this work to enhance the base material durability of iron alloy pistons. Aluminum-Silicon (Al-Si) thin film was deposited using vacuum evaporation process from 85 at.% Al and 15 at.% Si powders. The W-Ti-N thin film was deposited on the top of the Al-Si thin film using a PVD sputtering process from a W-Ti (70 at.% W and 30 at.% Ti) target onto a stainless steel substrate. The microstructural, mechanical and tribological properties of the multilayer were studied for potential applications on piston skirts manufactured from iron alloys. W-Ti-N/Al-Si multilayer shows a dense microstructure morphology with W2N (200) is the main phase present. Hardness measurements indicate that Al-Si thin film reached a value of 8.8 ± 0.37 GPa, while that of W-Ti-N/Al-Si multilayer reaches values as high as 17.2 ± 0.25 GPa. Tribological tests conducted on the multilayer system revealed interesting results, namely the very low values of the friction coefficient reaching μ ≈ 0.084±0.018 and that of the wear rate showing a value of k <8.7 ± 0.1·10-13 m3/N·m. Results from the present study are promising and provide an good alternative approach toward the reduction of important energy losses related to friction of the iron alloys piston skirts