Microstructure and oxidation behavior of low pressure plasma sprayed iron aluminides

Microstructure and oxidation behavior of plasma sprayed iron aluminide have been investigated focusing on the spraying conditions of atmosphere and pressure. Iron aluminide powder for spraying was prepared by ball milling of turnings fabricated from an Fe-40at%Al ingot. Microstructure of laminated layers including cavities was observed in all samples and particles with a size of about 100 μm were observed only in the sample sprayed in 50 Torr Ar atmosphere. Chemical analysis revealed an amount of aluminum loss and oxygen pick-up in samples sprayed in air, while X-ray diffraction analysis exhibited only the iron aluminide spectra without the second phase. The intensity of superlattice spectra of aluminide was strong in the samples sprayed in Ar compared with in air. Change of mass gain in oxidation testing was small in the sample sprayed in 50 Torr Ar, which is equivalent to as-cast bulk sample, while large in other samples. SEM observation revealed the evolution of iron oxides in the samples sprayed in air, which was not observed in the sample sprayed in Ar. The mechanism for superior resistance to oxidation in the sample sprayed in 50 Torr Ar is attributed to infusible particles deposition, which inherited the intrinsic oxidation resistant property of iron aluminides.