Mechanisms of topography formation of magnetron-sputtered chromium-based coatings on epoxy polymer composites

The tribological protection of stiff technical polymers like epoxy resins, being main component in fiber strengthened composites (CFC), gains increasing interest to enable their use in mechanical engineering applications. Besides hardening of the surfaces to achieve similar properties like low carbon steels, smooth surfaces are essential in sliding contact. However, the conditions of film growth during magnetron sputtering including thermal stresses result in high intrinsic film stresses, which trigger the formation of distinct surface topography. Especially chromium nitride (CrNx) single layer coatings show a fragmentation of the coating by cracking during film growth. Preferential growth of crystallites in subsequent deposition closes these cracks, provides complete covering of the surface, and bulged topographical features. Goal of this work is describing the mechanisms of formation of these topographical features as well as emphasizing influences of higher film toughness by Cr-CrNx multilayer coatings on the density and height of the bulges.