Mechanisms of structure formation and thermo-physical properties of gas detonation sprayed Fe-Al type coatings

Some particular grains in the multiphase Fe-Al type coating deposited by gas detonation spraying onto the steel substrate are subjected to the detailed analysis. As a result of the recognized the structure properties of the grains, their chemical composition and phase structure, the morphological and crystallographic micro-texture and heritage of FeAl superstructure from the FeAl feedstock particles, the mechanisms of forming the Fe-Al coating structure were determined in the dynamically changing conditions of gas detonation, during the flow of two-phase gas-metallic stream. The structure of Fe-Al coating has shown that in spite of retaining solid state in the volume of strongly softened FeAl particles, their surface layer becomes, for a short time, partially molten, which promotes an intensive in-situ formation of oxide films which constitute an inevitable component of coating structure. As a result of the film formation a selective depletion of Al which diffuses into the oxide phase, was observed resulting in a local formation of the superstructure also involving Fe3Al which causes fragmentation of ultra-fine grains of FeAl and the formation of a two-phase structure containing ordered phases of FeAl (B2), and Fe3Al (D03). Acknowledgments This study was supported by National Science Centre, Poland, Research Project No. 2015/19/B/ST8/02000