Influence of the film thickness on texture, residual stresses and cracking behavior of PVD tungsten coatings deposited on a ductile substrate

Tungsten coatings are deposited on a steel substrate by magnetron sputtering. For coatings deposited under identical processing conditions, a (111) texture develops, with the increase of the coating thickness mid the decrease of the residual stress. No gradient stress has been observed in the diffracted volume and the residual stress state is isotropic and plane. Tensile and four-point bending tests are performed in a SEM chamber in order to study the cracking kinetics. Taking account of die residual stresses, an intrinsic cracking stress can be determined. Cracking kinetics are found to depend on the coating thickness and the substrate yield stress. No debonding was observed at the interface despite the large plastic deformation of the substrate at the crack tips. This corresponding strain localization has a strong influence on the crack density and the cracking kinetics.