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.