Mechanical properties and tribological behavior of magnetron sputtered TiAlN/TiAl multilayer coatings

The mechanical properties, microstructure, adhesion and wear resistance of a Ti0.45Al0.55N monolithic coating and Ti0.45Al0.55N/Ti0.45Al0.55 multilayer coatings were comparatively studied. The coatings were deposited on stainless steel substrates by DC magnetron sputtering. The multilayer coatings exhibited a lower hardness and reduced elastic modulus when compared to those of the monolithic coating. However, the multilayers were characterized by higher critical loads under scratch testing that testifies to their improved toughness and adherence. This resulted in the enhancement of the wear resistance of the multilayer coatings under pin-on-disk wear tests. The optimal thickness of Ti0.45Al0.55N and Ti0.45Al0.55 layers in the multilayers was determined to provide more than a three-fold decrease of the wear rate as compared with the monolithic coating. The applicability of different mechanical parameters such as the H/E* ratio, plasticity index and crack propagation resistance parameter for comparative prediction of the wear resistance of the monolithic and multilayer coatings was evaluated. It was shown that the crack propagation resistance parameter is the most promising for this purpose.