Investigation of surface fatigue of thermally sprayed micro- and nanocrystalline cylinder wall coatings by means of cavitation testing

Abstract

Abstract The future demands of diesel engines require new options for low-friction and wear-resistant materials in order to increase efficiency and achieve environmentally sound solutions. Efforts are made to improve the performance and reduce the weight of engine blocks by coating the aluminium cylinder bores using thermal-spray processes. Thus, along with other means, today nanocrystalline coatings are considered when looking for the desired combination of structural, productional, and topographical properties. Besides sufficient tribological properties it is important that the composite (base material and coating) allows for prolonged endurance under cyclic mechanical and thermal stresses. Prior to engine tests these coatings are characterised in the laboratory by means of bench tests for adhesive tensile strength, tribological properties and fatigue of the composite. Cavitation tests should reveal the tribological stability of these coatings and their ability to resist high-frequency cyclic impact stresses. The objective in this investigation is to describe the cavitation behaviour and the influence of voids such as pores or oxides.