Phase composition and formation mechanisms of a high-velocity electric arc-sprayed FeNiCrAl coating

Highlights: • FeNiCrAl coating has improved the brittleness of FeAl intermetallic compound at room temperature. • The formation mechanism of each phase in the coating was thoroughly studied in this paper. • The coating was consists of nanocrystalline and microcrystalline composite microstructure. • The mechanism of grain growth and coalescence in coatings was studied in this paper. • A large number of Fe₂Al₅ and FeAl phases were contained in the coating. FeNiCrAl coatings are wear-resistant and are applied as surface protectants for mechanical parts. The phase composition of a coating strongly impacts its performance; therefore, the internal phase composition and formation mechanisms of FeNiCrAl coatings need to be studied in detail. In this study, a FeNiCrAl coating was prepared using high-velocity arc spraying, and an X-ray diffraction (XRD) analysis of the coating revealed the coexistence of α- and γ-Fe phases, Fe-Al and Ni-Al intermetallic compounds, a Cr_0.19Fe_0.1Ni_0.11Al_0.17 solid solution phase, FeO, Fe₂B and (Fe, Cr)₃C. The FeNiCrAl coating microstructure and phase formation mechanisms were analysed by transmission electron microscopy. The coating consisted of many nanograins and micrograins with diameters of <50 nm and 0.1-0.2 μm, respectively. The presence of large grains indicated that restructuring and recrystallization processes occurred during the coating preparation procedure. The main coating phases included the γ-(Fe, Ni) phase, Al₂O₃ and Cr₂O₃ oxides and NiAl, Ni₃Al, FeAl and Fe₂Al₅ intermetallic compounds. The rapid non-equilibrium solidification processes that occurred during the arc spraying process resulted in the coexistence of multiphase compounds. In addition, high-density dislocation tangles were observed in the coating. The presence of multiphase compounds and high-density dislocation tangles improved the cohesive strength and hardness of the coating.