Microstructural characterization of cold-sprayed nanostructured FeAl intermetallic compound coating and its ball-milled feedstock powders

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-heat treatment. 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-heat treatment. The microstructural evolution of the Fe-40Al powder during mechanical alloying and the effect of the post-heat treatment on the microstructure of the coldsprayed Fe(Al) coating were characterized by optical microscopy, scanning electron microscopy, transmission electron microscopy (TEM), 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 heat-treatment temperature significantly influences the in-situ evolution of the intermetallic compound. The heat treatment at a temperature of 500 °C results in the complete transformation of Fe(Al) solid solution to FeAl intermetallic compound.