Structure and mechanical properties of Ti-Al films deposited by magnetron sputtering

Thin films of Ti-Al were deposited by d.c. magnetron sputtering on M2 (AISI) steel substrates. A composition scan of the Ti-Al system was carried out using pure Ti and Al targets placed at 90°. X-ray diffraction showed that for the high Al content films (71.5-86.1 at.% of Al) only the face centred cubic (f.c.c.) Al phase was deposited with a (111) preferential orientation. Within this range of compositions, both the width of the (111) planes diffraction peaks and the hardness of the films increased (from 8.9-13 GPa) with increasing Ti content. The Ti-Al films deposited with aluminium contents in the range from 32.5 to 57.1 Al at.% showed low hardness (8.8-10.3 GPa) and only a broad diffraction peak centred at 2θ ≈ 45.4° was detected. For the high titanium content films (3.7-19.9 at.% of Al) the hexagonal close packed (h.c.p.) Ti phase peaks were detected by X-ray diffraction, superimposed on a broad diffraction peak centred at 2θ ≈ 44.8°. These films showed the highest hardness values (up to 23 GPa). The composition range from 19.9 to 32.5 at.% of Al was selected for further work since it includes the films that presented the best combination between hardness and friction coefficient.