Deposition of (Ti,Al)N films on A2 tool steel by reactive r.f. magnetron sputtering

Abstract

(Ti,Al)N thin films were deposited on A2 steel by reactive r.f. magnetron sputtering in a mixture of Ar and N2. A carefully designed target configuration with various surface ratios of Al to Ti resulted in a well-controlled composition of deposited (Ti,Al)N after sputtering. As the surface area of Al on the target was increased, the deposition thickness of the (Ti,Al)N film increased and the colour of the as-deposited film changed from red-yellow for TiN to red-blue for (Ti,Al)N. The structure of (Ti,Al)N films identified as a cubic B1 structure prevailed for AlN contents ranging from 27 to 58 mol%. With the addition of Al in the TiN cell, the lattice parameter of the (Ti,Al)N film decreased linearly as the AlN mole percentage was increased. The pull-off test and the scratch test were used to analyse the adhesion strength of deposited films. The surface hardness of (Ti,Al)N films deposited on A2 steel was higher than that of pure TiN film. With a coating of Ti0.5Al0.5N film the surface hardness of A2 steel was increased more than fourfold. However, when the AlN content exceeded 50 mol%, the surface hardness of the (Ti,Al)N coating decreased. © 1995 Elsevier Science S.A. All rights reserved.