Study on formation and characterization of iron aluminide coatings on 9Cr–1Mo steel substrate

This paper describes the formation and characterization of iron aluminide coatings on 9Cr–1Mo steel substrate. In this regard, first, 9Cr–1Mo steel specimens were immersed into molten bath containing pure aluminum and then laser melted at different laser pulse energies. The microstructure and phase identification of the melted layers were examined by optical microscopy, scanning electron microscopy and X-ray diffraction analysis. The elemental distribution in the coatings was characterized by electron probe microanalysis. The results showed that hot dip aluminized layer was divided into an outer pure aluminum topcoat and an inner intermetallic layer mainly composed of Fe2Al5 with tongue/finger-like morphology. Laser melting of aluminized steel specimens led to the complete transformation of the brittle Fe2Al5 phase to the more ductile FeAl phase. Applying pulse energy of 7 J, the intermetallic FeAl layer formed was found to be sound and free of cracks. However, laser treatment at higher pulse energies resulted in compositional changes of the melted layers.