Effect of Si content on microstructure, mechanical properties, and cutting performance of TiSiN/AlTiN dual-layer coating

Ti1-xSixN/AlTiN dual-layer coatings with different Si content were prepared by cathode arc evaporation to study the effect of Si-doping on the coatings. The composition, morphology, and microstructure of the coatings were characterized using SEM, XRD, and XPS. The hardness, elastic modulus, and adhesion strength were measured by nano-indentation and micro-scratch. Results show that coatings all consist of TiN grains and Si3N4 amorphous phases. Ti1-xSixN/AlTiN dual-layer coating has the highest hardness of 43.07 GPa at a Si content of 0.19 and the lowest elastic modulus of 314.46 GPa at a Si content of 0.25. High-speed milling of Ti-6Al-4V alloy was performed to evaluate the cutting performance of the coated tools. The value and amplitude of the cutting force were collected to analyze the wear condition of tools. When cutting speed at 120 m/min, the coating with a Si content of 0.19 shows the best cutting performance, having the lowest cutting force and flank wear. The higher silicon content increases the bonding of titanium alloy, influencing the stability during cutting. The lower silicon content reduces the wear resistance of the coating and shorten tool life. Suitable Si content of the coating has been proved effective in improving the cutting performance on Ti-6Al-4V alloy.