Effect of TiAlSiN gradient structure design on mechanical properties and microstructure of coatings

In order to enhance the interface adhesion strength and toughness of TiAlSiN single coating, a TiAlSiN composite coating with a gradient change of Ti and Al content was prepared on the cemented carbide surface using arc ion plating technology. By comparing the single TiAlN and TiAlSiN coatings, the comprehensive properties of the gradient TiAlSiN coatings were evaluated in terms of microstructure, mechanical properties, adhesion, and oxidation resistance. Microstructure analysis shows that the surface layer of the gradient TiAlSiN coating has lower surface roughness and smaller grain size. Its microstructure gradually transitions from columnar grains to equiaxed grains and a nanocrystalline structure along the growth direction of the coating. Additionally, TEM results indicate that composition gradient control can form coherent or semi-coherent interfaces between the transition layers. The mechanical properties and scratch test results demonstrate that the hardness and residual stress of the gradient coating are 36.94 GPa and - 4.34 GPa, respectively, while the interfacial adhesion of the gradient coating exceeds 120 N. These comprehensive properties are significantly superior to those of the single TiAlN and TiAlSiN coatings. The scratch depth and plastic deformation degree of the coating are closely related to the coating structure, as well as H/E* and H3/E*2 values. The scratch failure of the coating primarily involves chevron cracks and brittle tensile cracks, with chevron cracks gradually expanding and evolving into wedgeshaped spalling. The oxidation products and gradient transition interface of the gradient TiAlSiN coating effectively enhance its high-temperature oxidation resistance.