Microstructure and tribological properties of Ti/TiN/DLC coating for piston pin hole

To enhance the wear resistance of piston pin-hole surfaces and prolong piston service life, titanium (Ti)/titanium nitride (TiN)/diamond-like carbon (DLC) composite coatings were prepared on aluminium alloy substrates by multi-arc ion plating. The effects of the dinitrogen (N2):argon (Ar) flow ratio on the microstructure, adhesion strength, mechanical properties, and tribological behaviour of the coatings were investigated. The results show that, with increasing dinitrogen:argon flow ratio, the surface morphology became more uniform, the Micro-Vickers composite hardness of the coating/substrate system gradually increased, and the adhesion strength first decreased and then increased. When the dinitrogen:argon flow ratio was 4:1, the titanium/titanium nitride/DLC coating exhibited the best overall performance, with the lowest surface roughness of 0.18 μm, the lowest ID/IG value of 0.75, the highest adhesion strength of 53 N, and the highest composite hardness of 331 HV. In addition, the coating prepared at a dinitrogen:argon flow ratio of 4:1 showed the lowest coefficient of friction of 0.09, which was lower than those of the coatings prepared at dinitrogen:argon flow ratios of 1:4, 2:3, and 3:2. The dominant wear mechanism of the coatings is abrasive wear.