Mechanical properties of hard W-C physically vapor deposited coatings in monolayer and multilayer configuration

Tungsten-carbon based multilayer coatings obtained by reactive magnetron sputtering were shown to be very effective against sand erosion but their use needs optimization in order to avoid deformation of thin turbine blades due to the high internal stress level of such a coating while maintaining erosion resistance properties. By studying the intrinsic characteristics of each elemental layer (carbon content, stress level and hardness) vs. process parameters (working pressure, bias voltage, reactive gas flow), it was found that the stress level can be decreased without dramatic consequences on the hardness. The carbon content was found to be the leading parameter and a convenient stress level was obtained which allows multilayer deposition onto thin turbine blades. An analytical model able to predict the internal stress in a multilayer arrangement from the stress of each elemental layer was used to optimize the coating. As a result, very good conformity of the coating on the sharp edge of the blade was obtained.