Deposition of TiN, TiC and Ti1-xAlxN coatings by pulsed d.c. plasma enhanced chemical vapour deposition methods

Unipolar and bipolar pulsed d.c. plasma enhanced chemical vapour deposition techniques have been used under various process conditions to deposit hard crystalline (Ti,AI)N, TiC and TiN coatings on steel and WC/Co hard metal s ubstrates at temperatures between 500 and 700 degreesC. As process gases mi xtures of titanium tetrachloride (TiCl4), aluminium trichloride (AlCl3) and nitrogen or methane/hydrogen/argon were applied. The golden, violet grey o r dark grey coloured TiN, (TiAl)N, TiC coatings deposited by varying the su bstrate temperature, plasma power density, excitation mode, and titanium to aluminium ratio in the gas phase were investigated with respect to their c omposition and structure. At substrate temperatures up to 700 degreesC and gas mixture ratios of Ti/Al = 0.3-0.5 using the unipolar pulsed d.c. method cubic (Ti,ADN coatings with different aluminium and titanium content could be deposited. At constant gas phase ratios and plasma parameters an increa sed substrate temperature resulted in an increased titanium content. For th e bipolar d.c. excitation mode higher aluminium trichloride concentration h ad to be used in order to obtain the same composition as for the unipolar c ase. Besides the cubic (Ti,AI)N phase, hexagonal AIN was found in samples p repared at 700 degreesC and 4 mbar by XRD measurements. The crystallite siz e of the (Ti,AI)N coatings deposited by unipolar and bipolar activation wer e estimated to be approximately 10 nm. The hardness HV[0.02] was found to b e in the range of 25-30 GPa for Ti1-xAlxN, up to 32 GPa for TiN, and up to 40 GPa for TiC. Coating thickness and element composition were determined b y glow discharge optical emission spectroscopy depth profile analysis. (C) 2001 Elsevier Science B.V. All rights reserved.