Analysis of in-situ oxides formation in the structure of FeAl intermetallic coatings under specific D-gun spraying conditions

The paper concerns a detailed analysis of basic phenomena characteristic for in-situ oxides formation in the structure of FeAl intermetallic coating under controlled D-gun spraying (DGS) conditions. As a result of experimental analysis, the thermodynamic state of the gas detonation flow was determined under real DGS conditions as well as the physico-chemical properties of the feedstock powder material and the as-sprayed Fe-Al multi-phase intermetallic coating with the participation of Al₂O₃ oxide ceramics. The interdependencies of identified basic phenomena concerning heat transfer between FeAl particles and the environment of the gaseous detonation stream as well as the effects of thermal phase transformations of the FeAl phase under controlled DGS conditions were analyzed. The obtained results show that in gas detonation supersonic flux, the FeAl intermetallic powder particles forming a coating are subjected to very strong plastic deformation. As a result, the particles transform into surface-oxidized grains in a polycrystalline coating structure, while the powder particles maintain a solid state. The deposition of the coating is accompanied by the formation of thin oxide films (mainly Al₂O₃). The formation of these oxide films raises the hardness of the coating structure, which is beneficial in terms of the Fe-Al intermetallic coating performance.