Abstract: Thetribological properties of the substrate of M42 tool steel surface-modified with Al₆₆Cr₃₄N and Ti₆₂ Al₃₄Si₄N hard coatings, deposited by cathodic multi arc ion plating, were investigated with X-ray diffraction, scanning electron microscopy, energy dispersive spectroscopy and conventional mechanical probes like SFT-2 M disk-onpin rig against 40 Cr gear steelat room temperature.The results show that the adhesive wear accompanied by oxidative wear explained the failure mechanisms of both hard coatings.In sliding against 40 Cr gear-steel, high strength adhesive joints easily formed on the surface of Ti₆₂Al₃₄Si₄Ncoating possibly because of a strong affinity and a high frictional heat; the friction coefficient and highest initial wear-rate were estimated to be 0.6~0.7 and 7.5×10^-15 m³/N·m, respectively.In contrast, the friction coefficient and lowest initial wear-rate of the Al₆₆Cr₃₄N coating were 0.45~0.6, 2×10^-16 m³/N·m, respectively, due to low affinity.