MECHANICAL-PROPERTIES, STRUCTURE AND OXIDATION BEHAVIOR OF TI1-XALXN-HARD COATINGS DEPOSITED BY PULSED DC PLASMA-ASSISTED CHEMICAL-VAPOR-DEPOSITION (PACVD)

Wear resistant Ti1-xAlxN hard coatings with different compositions (0 less than or equal to x less than or equal to 1) were deposited using d.c. plasma-assisted chemical vapour deposition on high-speed steel. T iCl4 and AlCl3 were used as metal precursors. The influence of the AlC l3 partial pressure on the properties of the coatings was examined. Th e aluminum content in the coating increases linearly with the AlCl3 pa rtial pressure. The micro-hardness of the Ti1-xAlxN coatings is about 2000 HV 0.01 for low aluminum contents (x<0.5), but decreases to a val ue of 1300 HV 0.01 for higher aluminum contents. The adhesion, measure d with the scratch test, decreases with increasing aluminum content. X RD measurements reveal the fee structure up to an aluminum content of x=0.8. For x>0.8 a weak (201) peak of the hexagonal Wurtzite structure is visible. But the Wurtzite structure is confirmed only for x=1. The oxidation experiments were carried out in air at 873 K. XPS depth pro files show a better oxidation resistance of Ti1-xAlxN as compared to T iN. The oxidation resistance increases with increasing aluminum conten t. The aluminum content near the surface oi Ti1-xAlxN coatings increas es during the oxidation. Aluminum atoms were found to diffuse up to th e surface. (C) 1998 Elsevier Science S.A. All rights reserved.