Fabrication of iron nitride coatings by reactive RF plasma spraying

Abstract

Reactive plasma spraying is a promising process to fabricate thick non-oxide ceramics coatings. In this study, fabrication of iron nitride (Fe 4N) coatings by reactive RF (Radio Frequency) plasma spraying was investigated. Iron particles were injected in Ar/N 2 plasma and were deposited onto carbon steel substrates. In the case of applying conventional iron powder (particle size of 75 μm and under), it was possible to fabricate Fe/Fe 4N composite coatings by reactive RF plasma spraying with using water-cooled substrate holder. However, the microstructure of the coatings was porous and lower concentration of the nitride phase. Moreover, it was difficult to increase the concentration of the nitride phase in the coatings by controlling spraying conditions such as N 2 flow rate and RF power. On the other hand, it was possible to fabricate thick, dense microstructure and higher concentration of the nitride phase with applying fine iron powder as a feedstock powder material. And it was possible to control the concentration of the nitride phase in the coatings by changing N 2 flow rate in the plasma gas. Moreover, the coating which did not include original Fe phase was also fabricated with the spraying condition of higher N 2 flow rate. However, excessive N 2 flow rate and RF power decrease the nitride phase due to increasing both in plasma and substrate temperature above the decomposition temperature of Fe 4N (974 K). Therefore, fabrication of iron nitride coatings by reactive RF plasma spraying was possible with applying fine iron powder and substrate cooling.