The Influence of Ti/Al Molar Ratio on the Hardness and Wear Resistance of CrTiAlN Hard Films

In this study, with the Cr content fixed at approximately 63 at.%, the N content in the range of 44–46 at.%, and the deposition parameters held constant, a series of CrTiAlN hard coatings were deposited by magnetron sputtering via systematically varying the Ti/Al molar ratio, while the Ti/Al molar ratio was systematically varied, the influence of the Ti/Al ratio on phase structure, mechanical properties, and tribological behavior was investigated. With decreasing Ti/Al ratio, the phase structure evolved from a single Fcc-(Cr,Ti,Al)N solid solution to Fcc-(Cr,Ti,Al)N saturated solid solution and finally to a dual-phase structure of Fcc and w-AlN, while the microstructure transformed from dense columnar grains to globular clusters. Hardness, adhesion, and friction coefficient all exhibited a non-monotonic variation feature. When the Ti/Al molar ratio was approximately 1.12, the coating achieved optimized performance, exhibiting a hardness of ~2100 HV, an adhesion strength exceeding 33 N, and a steady-state friction coefficient of ~0.15 with a smooth friction curve. This performance originates from the synergy of saturated solid solution strengthening and dense film structure. Excessively high Ti/Al ratios (>2.08) led to insufficient strengthening, whereas excessively low Ti/Al ratios (<0.64) caused w-AlN precipitation and collapse of the Fcc crystal structure, resulting in a sharp hardness drop and a surge in friction coefficient to 0.45. A comprehensive analysis of the mechanical properties identified the optimal Ti/Al molar ratio range to be 0.6−1.2, within which the films exhibit hardness ≥1800 HV, adhesion ≥30 N, and stable wear resistance.