Phase formation and characterization of hard coatings in the TiAlN system prepared by the cathodic arc ion plating method

Abstract

Hard Ti x N and (Ti 1− x Al x )N films were prepared using the cathodic arc ion plating method. When the ratio of the partial pressure of N 2 to the evaporation rate of titanium was reduced, the resulting phase in the TiN system changed from cubic TiN to tetragonal Ti 2N, and then to h.c.p. α-Ti. When the AIN content in the TiNAlN solid solution was increased, the films, from TiN up to (Ti 0.3Al 0.7)N, exhibited a cubic structure. As the AlN content increased, the lattice parameter monotonically decreased from 4.26 Å for TiN, to 4.16 Å for (Ti 0.3Al 0.7)N. With a further increase in AlN content, (Ti 0.15Al 0.85)N films were found to have a wurtzite structure. It was concluded that the crystal structure of the ternary TiAlN system along with the wide-ranging solubility of AlN in TiN is typical for the isostructural group of cubic titanium-based nitrides. The (Ti,Al)N coatings were stable in air at a temperature of 800°C, whereas the TiN films began to oxidize at a temperature of 550°C. It was found that protective layers of amorphous aluminum oxides formed on top of the (Ti,Al)N films during elevated temperature oxidation tests which protected the film from further oxidation. The crystallized TiO 2 that was formed on the TiN film did not give the same protection. The nicrohardness and wear resistance of the (Ti,Al)N films were also investigated.