Influence of film structure on the microstructure and properties of TiAlN coatings on Al-Si alloys

Due to the disadvantages of poor friction and low wear resistance, the application of Al-Si alloys with unique properties in pistons is limited. In this work, TiAlN ceramic coatings were prepared by filtered cathode vacuum arc technique to improve the surface properties of Al-Si alloys. To overcome the high residual stress of hard coatings growth on soft substrate surfaces due to interfacial mismatch and defect accumulation, gradient and multilayer film structures were adopted to improve adhesion strength. The effects of film structure on the microstructure, mechanical and tribological properties of coatings were systematically investigated. The results showed that the coatings with different film structures showed a multiphase microstructure with the dominated phase of TiAlN and a small amount of AlTi and TiN phases. Monolayer and multilayer coatings exhibited TiAlN (111) orientation, while the gradient coating showed (220) orientation due to the growth of columnar to equiaxed crystals. Compared with the monolayer coating, TiAlN coatings with gradient and multilayer structures had significantly reduced compressive stress and improved adhesion and scratch propagation resistance. Among them, the multilayer coating showed the lowest friction coefficient (~0.44) and wear rate (~5.14 × 10−5 mm3/Nm), which were attributed to the high hardness (~31.01 GPa), toughness (H/E = 0.135, H3/E2 = 0.563 GPa), critical load LC3 (~26.58 N). Interfacial effects in the multilayer structure could enhance synergy of the coating, thereby preventing crack initiation and propagation and adhesion failure.