Creep analysis and laser-induced cracking in (Ti,Al)N coatings

This paper concerns the thermomechanical response of (Ti,Al)N coatings (on WC 6%Co substrates) subjected to short time thermal laser pulses. The relaxation of compressive stress at transient high temperature leads to tensile stress at ambient temperature and eventually to crack formation. The related inelastic deformation mechanism was identified as obstacle-controlled plasticity. The parameters of this mechanism were determined via stress evolution in (Ti,Al)N films on Si wafers at constant temperature. By means of these parameters, the maximum residual film stress, caused by a single laser pulse can be evaluated. As cracks appeared with maximum film temperature TM in the range of 700 deg C<TM<750 deg C, the film strength c can be estimated to be in the region 1.6 GPa<c<2.1 GPa.