Effect of Different Atomization Gases on the Properties of Cylinder Bore Coatings

Oxidation during coating deposition by means of thermal spraying is a widely investigated and discussed topic. Most of the studies dealing with this subject report negative influences of oxidation on the coating properties, especially with respect to corrosion behavior. On the other hand, positive effects are reported as well, especially with regard to tribological behavior. Within this study, the oxidation phenomena in Plasma Transferred Wire Arc (PTWA) spraying process is investigated in detail. This technology is primarily used to apply coatings on the inner surface of cylinder bores in combustion engines. It is shown that the oxidation can be suppressed effectively by utilizing an alternative atomization gas like nitrogen instead of compressed air without the need of any additional torch modification. Besides the oxidation behavior, further effects depending on the used atomization gas are observed, which influence the properties of the coatings. Significantly higher hardness values are measured for the coatings deposited with nitrogen. This is traced back to different impact and cooling conditions as well as chemical interactions of the in-flight particles with the ambient atmosphere.