Tribological behaviour of multi-layered PVD nitride coatings

Multi-layers resulting from the combination of layers of different PVD nitr ides (TiN, Ti2N, Ti(C,N), (Ti,AI)N) were deposited by are evaporation on AI SI M2 tool steel and their tribological behaviour has been investigated. Th e effect of a MoS2 layer deposited on top of the PVD nitride multi-layers w as also studied. Dry sliding and abrasive wear behaviour have been studied by a slider-on-cylinder tribometer and a micro-scale abrasion tester, respe ctively. The main sliding wear mechanism was abrasion from hard particles f ormed at the contact interface as a consequence of extensive oxidation of t he counter-material (hard chromium). The prevalence of abrasion damage in t he 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-l ayers. 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 ma rked at the highest cutting speed. (C) 2001 Elsevier Science B.V. All right s reserved.