Nickel effect on the structure and properties of adaptive wear-resistant arc-PVD Ti–Al–Mo–N coatings

Abstract

Comparative studies of the structural characteristics and functional properties of Ti–Al–Mo–N and Ti–Al–Mo–Ni–N coatings obtained by the arc-PVD method were carried out in order to study the effect of nanostructuring nickel additive. The coatings featured by multilayered architecture with alternating layers of titanium and molybdenum nitrides. Molybdenum and nickel concentrations were about 22 at.% and 7 at.%, respectively, which corresponds to optimal quantities for the best strength and tribological properties. It was shown that nickel introduction reduces the coating modulation period from 60 to 30 nm with a simultaneous increase in hardness from 37 to 45 GPa. At the same time, an increase in the tensile strength of coatings was noted, which was judged by the relative plastic deformation behavior as well as H/E, H 3 /E 2 parameters. Ductile nickel added into the solid nitride coating structure led to a decrease in the level of compressive macrostresses in the material from –2.25 to –0.58 GPa, without, however, any decrease in hardness and fracture toughness that was shown by scratch tests. It is concluded that the factor determining mechanical characteristics of the coating is not the macrostressed state, but the refinement of the coating material grain structure. Nickel positively affected the coating heat resistance successfully protecting the substrate material from oxidation at temperatures up to 700°C, which may be associated with the likelihood of the formation of NiMoO 4 and NiTiO 3 nickel-containing oxides on the surface. However, their formation, fracture, and action as abrasive particles can cause a change in the friction wear mechanism at high temperatures.