Influence of bias voltage variation on the microstructure and comprehensive properties of CrAlSiN coatings

To investigate the effect of bias voltage variation on the microstructure, mechanical, tribological, and cutting properties of CrAlSiN coatings, six coatings were deposited under constant or linearly increasing bias voltages. Results show that all CrAlSiN coatings possess a singular fcc-(Cr,Al)N phase. Chemical compositions of the coatings change little with the bias voltage, while the grain size and surface roughness decrease gradually, leading to higher hardness and residual stress but lower adhesion strength. Compared with the coatings deposited at -160 and -200 V, the hardness of the bias-graded coatings decreases slightly, but their adhesion strength and fracture toughness are enhanced by 3-20% and 11-49% respectively, due to reduced residual stress. This improvement is attributed to the unique grain size gradient along the growth direction in the bias-graded coatings, which effectively reduces stress concentration and inhibits crack propagation. The bias-graded coatings exhibit a 44% longer cutting life compared to those deposited under constant bias voltages, with the cutting life increasing as the ultimate bias voltage rises. This enhanced performance is linked to their superior adhesion strength and toughness.