Tribological and Microstructural Properties of Carbon Steel Coatings Fabricated by Wire Arc Spray

Thermal spray is a widely used process employed for the reduction of engine weight by replacing heavy cast iron liners inserted in cylinder bores. In particular, twin wire arc spray (TWAS) is one of the most popular thermal spray processes due to its reasonable cost and high deposition rate. In this study, ferrous coatings were fabricated by using TWAS with two variables: gas type and initial carbon content in wire. The investigation was focused on the relationship between variables and their effects on the oxidation, microstructure, and tribological properties. Especially, for evaluation of the tribological properties, a reciprocating sliding wear test was designed by considering realistic engine conditions. Individual splats forming the coating layer undergo oxidation which results in oxide formation, loss of alloying elements, and heat generation during spraying. From the results of experiments, it was figured out that the oxidation state is controlled by gas type, and its effects on microstructure and coating properties vary depending on the initial carbon content of the wire. Finally, it was confirmed that the wear resistance of the ferrous coating containing FeO and more carbon was better than the other for its improved frictional property and high hardness.