Abrasive wear resistance of Ti1 − xAlxN hard coatings deposited by a vacuum arc system with lateral rotating cathodes

In this work, a series of Ti1 − xAlxN (0 ≤ x ≤ 0.7) coatings were deposited on high speed steel (HSS) substrates by a vacuum arc reactive evaporation process from two lateral rotating elemental titanium and aluminium cathodes in a pure nitrogen atmosphere. The composition, crystalline structure and hardness of the as-deposited coatings were analyzed by energy dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), and nanoindentation experiments. The abrasion wear resistance of the TiAlN coatings was measured by a micro-abrasion tester with the presence of SiC water-based slurry with a concentration of 0.35 g/cm3. It was found that with increasing the Al/Ti atomic ratio the hardness of the as-deposited TiAlN coatings initially increased up to a maximum value of about 40 GPa at around Al/Ti = 1.22, and then the coating hardness decreased rapidly with increasing aluminium content further. The abrasion wear resistance of the TiAlN coatings is evidently better, with one order of magnitude lower in the wear rate, than the bare HSS substrate. With increasing Al/Ti atomic ratio, the variation trend of the abrasion wear rate of the TiAlN coatings is generally opposite to that of coating hardness. This means the abrasion wear resistance of the TiAlN PVD hard coatings is predominately determined by the hardness of the coating materials. It was also noted that, besides the coating hardness, the composition of the TiAlN coatings also plays an important role in determining their abrasive wear resistance. The coatings in the higher Al content range (Al/Ti ≥ 1.60) exhibited an evident better abrasive wear resistance than those in the lower aluminium content range (Al/Ti ≤ 0.32) when their hardness is similar. This fact could be related to the finer microstructure of the coatings incorporated with higher aluminium content.