The structure and hardness of magnetron sputtered Ti–Al–N thin films with low N contents (< 42 at.%)

Thin films of Ti–Al–N were deposited by d.c. magnetron sputtering on M2 (AISI) steel substrates. Two targets configurations were used: pure targets of Ti and Al placed at 90° and two facing targets of titanium encrusted with aluminium rods (composite targets). The nitrogen flow was varied from 0 to 12 sccm. The N/(N + Ti + Al) and Al/(Al + Ti) atomic ratios in the films ranged from 0% to 41.9% and 24% to 28.6%, respectively. The deposition rate was almost two times higher for the films deposited from composite targets. Both the deposition rate and the aluminium content started to decrease at 6 sccm for the films deposited from pure targets and only at 12 sccm for the films deposited from composite targets. For both target configurations, polycrystalline α-Ti was deposited at low N contents and, as more nitrogen was added, a progressive loss of crystallinity was observed until amorphous films are deposited. Ti(Al)N was deposited from pure targets at the highest nitrogen content. The hardness of the films deposited from composite targets smoothly increases from 12.5 to 27 GPa with increasing nitrogen. Within the α-Ti nitrogen deposition range, the hardness of the films deposited from pure targets slowly increases from 15 to 17.5 GPa while much higher hardness values were measured for the amorphous and the Ti(Al)N film (36 and 34.5 GPa, respectively).