Tribological behaviour of multi-layered PVD nitride coatings

Multi-layers resulting from the combination of layers of different PVD nitrides (TiN, Ti2N, Ti(C,N), (Ti,Al)N) were deposited by arc evaporation on AISI M2 tool steel and their tribological behaviour has been investigated. The effect of a MoS2 layer deposited on top of the PVD nitride multi-layers was also studied. Dry sliding and abrasive wear behaviour have been studied by a slider-on-cylinder tribometer and a micro-scale abrasion tester, respectively. The main sliding wear mechanism was abrasion from hard particles formed at the contact interface as a consequence of extensive oxidation of the counter-material (hard chromium). The prevalence of abrasion damage in the sliding tests explains the good correlation between the results given by sliding tests at low applied loads and the micro-abrasion tests, and shows that hardness plays a key role in influencing the behaviour of the multi-layers. Milling tests, carried out in order to evaluate the cutting performance of coated tools, showed that end mills coated with the TiN-based multi-layers live longer than the others. The difference of performance was much less marked at the highest cutting speed.