Plasma-enhanced CVD of (Ti,Al)N films from chloridic precursors in a DC glow discharge

Metastable Ti1-xAlxN films have been deposited from gaseous mixtures of TiC l4-AlCl3-N-2-H-2-Ar in a pulsed DC glow discharge at 510 degreesC. When the discharge voltage was kept constant, the Al content x of the films increas ed linearly with the AlCl3/TiCl4 ratio in the feed gas. Increasing the disc harge voltage also increased the Al content. Up to compositions of Ti0.09Al 0.91N the layers remained single-phase cubic with a strong {100} texture. F ilms with a higher Al content consisted of two phases and their cubic phase showed a weak {111} texture. The lattice parameter of the homogeneous cubi c films decreased with increasing Al content in accordance with Vegard's la w. Films with a low Al content exhibited a columnar morphology, while the f ilms with high Al contents had a fine-grained structure. Increasing the dis charge voltage also caused the grain size to decrease. The microhardness of the single-phase coatings increased with increasing Al content up to 3947 HV 0.05 for x = 0.83, while the two-phase layers showed hardness values of approximately 5000 HV 0.05. The metastable films began to decompose at temp eratures between 750 and 800 degreesC, depending on the Al content. The dec omposition of the films with an Al/Ti ratio below 1 caused the lattice para meter of the cubic phase to increase and the microhardness to decrease. Fil ms with high Al contents did not show any increase in the lattice parameter after annealing and their microhardness strongly increased. Investigation of the oxide layer formed on a Ti0.21Al0.79N film after annealing in air at 800 degreesC showed that an amorphous alumina layer with a thickness of ap proximately 100 nm was formed on the surface, preventing further oxidation. The films with high Al content exhibited advantageous tribological propert ies with friction coefficients of 0.5. Thus, they seem to be especially wel l suited for an application on cutting and metal working tools. (C) 2000 El sevier Science B.V. All rights reserved.