Corrosion mechanisms of ceramic coatings in diesel engines

Abstract

The high costs of fuel oils have necessitated the use of less expensive but lower quality fuels for diesel engines. However, the combustion gases of these fuels are more corrosive, and this has created demands for improved corrosion and wear protection of heat-loaded parts. One way to obtain improved protection is to apply ceramic coating systems. Thes consist of at least two layers: a ceramic heat-insulating top layer and a metallic oxidation-resistant bond layer. Different diesel engine parts have been tested both in the laboratory and on ships in service. The experiences obtained are discussed and related to data in the literature. The principal analytical efforts were focused on degradation mechanisms causing spallation of ceramic coatings. The main reasons for spallation are thermal expansion mismatches between the coating and the substrate, affecting corrosion of the coating, phase transformation in the ceramic coating, salt penetration, wear etc.