Microstructural Characterization of Cold-Sprayed Nanostructured FeAl Intermetallic Compound Coating and its Ball-Milled Feedstock Powder

Abstract

It is difficult to deposit dense intermetallic compound coatings by cold spraying directly using the compound feedstock powders due to their intrinsic low temperature brittleness. A method to prepare intermetallic compound coatings in-situ employing cold spraying was developed using a metastable alloy powder assisted with post-annealing. In this study, a nanostructured Fe/Al alloy powder was prepared by ball-milling process. The cold sprayed Fe/Al alloy coating was evolved in-situ to intermetallic compound coating through a post-annealing treatment. The microstructural evolution of the Fe-40Al powder during mechanical alloying and the effect of the post-annealing on the microstructure of the cold sprayed Fe(Al) coatings were characterized by optical microscopy, scanning electron microscopy and X-ray diffraction analysis. The results showed that the milled Fe-40Al powder exhibits lamellar microstructure. The microstructure of the as-sprayed Fe(Al) coating depends significantly on that of the as-milled powder. The annealing temperature significantly influences the in-situ evolution of the intermetallic compound. The annealing treatment at a temperature of 500oC results in the complete transformation of Fe(Al) solid solution to FeAl intermetallic compound.