Effect of Coating Geometry on Contact Stresses in Two-Dimensional Discontinuous Coatings

Recent experimental investigations have shown that discontinuous coatings, characterized by island-like coating deposits on dissimilar substrates, can exhibit improved tribological performance over equivalent continuously-coated substrates. In this analysis, the effect of coating geometry on the normal contact pressure profile was examined for several two-dimensional discontinuous coatings using a numerical elastic stress model. Normal pressure singularities were found for discontinuous coatings having both sharp and rounded edges. However, when crowned discontinuous regions were examined, the normal pressure singularities were reduced or eliminated. Interfacial tensile stress, due to an imposed tangential friction force, was also investigated. The magnitude of this tensile stress (and stress singularities due to edge configuration) was most affected by the friction coefficient and by the discontinuous coating geometry in the middle of the contact region, where the normal contact pressure was the highest. The discontinuous coating has the potential to provide reservoirs of sacrificial solid lubricants, which wear away with the coating itself, providing a friction-reduction mechanism over the life of the coating reducing the interfacial tensile stress which can lead to premature coating failure. [S0742-4787(00)01504-6]