Experimental study of a potential weakening effect in spheres with thin hard coatings

A potential weakening effect caused by very thin hard coatings on spherical substrates is investigated experimentally. This weakening effect reduces the resistance of the coated system to onset of plasticity. Half-coated spheres are prepared using an ion beam assisted deposition system. The coated and uncoated portions of these half-coated spheres are loaded by a rigid flat into their elastic–plastic regime of deformation and then unloaded. The resulting maximum interference after loading and residual interference at the completion of unloading are measured and used in an elastic–plastic loading index model to evaluate the plasticity levels of both the uncoated and coated portions on each sphere. The experimental results validate qualitatively the potential weakening effect, which was predicted theoretically in previous publications.