Hard amorphous Ti-Al-N coatings deposited by sputtering

Ti-Al-N coatings were deposited by direct current reactive magnetron sputtering using two titanium and two aluminum targets. Two series of films with Al/(Al + Ti) atomic ratios of approximate to 23.5 and approximate to 34.5% were studied. The amount of nitrogen in the films was varied from 0 to 44at.%. The incorporation of N atoms led to a change of the alpha-Ti lattice preferential orientation from < 100 > to < 001 >, a decrease in the degree of crystallinity, and subsequently to the collapse of the crystalline structure. Annealing at 975K promotes the formation of the Ti3Al compound. The hardness increases smoothly with the nitrogen content. The high hardness values (31 and 41 GPa) measured for the films with the highest N contents may be explained by the deposition of a nanocomposite phase. For the Ti-Al-N film deposited with Al(Al + Ti) atomic ratio of 34.5% the alpha-Ti structure was completely transformed to TiO2 upon oxidation. The high oxidation resistance of the film deposited with 44at.% N at 1075K is characteristic of Ti-Al-N films. (C) 2008 Elsevier B.V. All rights reserved.