Micromechanical theories of wear processes

This thesis examines wear processes related to tribological coatings in the context of micromechanics and experimental investigation. The concept of fracture based wear is addressed by the stress analysis of fractures that form in embedded and surface layers. This analysis is applied to further determine coating fracture toughness utilizing the nanoscratch technique to measure the effect of fracture shielding on fracture generation in a TiB2/TiC multilayered coating subjected to a sliding contact. Fracture toughness values are obtained and found in good relation to bulk properties of the TiB 2 and TiC coating materials. Nanoindentation is an essential tool to measuring the near surface properties of coatings for wear applications. A relationship between the indenter bluntness shape and the apparent contact area are developed using a self-similarity approach for contact and analysis of depth-area data is used to determine the bluntness of the tip. Oxidational wear is a type of chemical wear that occurs when heat is involved in the contact region. The concepts of friction and oxidational wear are addressed based on an adsorption-desorption modeling effort. The model predicts the friction of hydrogenated DLC films utilizing the concept of adsorbate coverage and removal and compares well to recent tribochemical experiments. The application of TiB2/TiC coatings to dry machining is investigated. Wear processes of the coating are identified to be due to abrasion and fracture and the extent of the coating wear is qualitatively analyzed.