The stress in ion-plated HfN and TiN coatings

Abstract The X-ray diffraction sin 2 ψ method was used to determine the state of stress in HfN and TiN coatings made by ion plating onto various substrates. Some subsidiary measurements on chemically vapour-deposited coatings are also included. In many cases the results show deviations from the simple linear behaviour: examples of both curvature (stress gradients perpendicular to the surface) and ψ splitting (shear stress effects) are found. Both the chemically vapour-deposited samples show the latter effect together with compressive and tensile stresses in the HfN and TiN coatings respectively in the plane of the coating. The ion-plated coatings are all under compressive stress. On stainless steel the stress level is high owing to a change in the stress distribution in the steel during the ion plating process. The stress in the coatings on cemented carbide and high speed steel, which should be unaffected by the coating process, falls as the coating thickness increases; this appears to be related to a microstructural change in the coating.