Comparison of the dry and wet oxidation at 900 °C of η-Fe2Al5 and δ-Ni2Al3 coatings

η-Fe2Al5 and δ-Ni2Al3 coatings were correspondingly prepared by aluminizing a carbon steel without and with pre-electrodeposition of a Ni film. Compared to the η-Fe2Al5/steel system, the δ-Ni2Al3/Ni film/steel system is much better oxidation resistant at 900 °C in the airs without and with 40% water vapor, because of prevention of numerous cavities at the alumina scale/coating interface, and because of mitigation of degradation of the coating due to decreased interdiffusion between the aluminide and the Ni film. Moreover, each aluminide coating has different oxidation kinetics in the dry- and wet air. The reasons for the results are discussed.

Research highlights
► The addition of water vapor favored to prevent breakaway oxidation of η-Fe2Al5.
► The addition of water vapor promoted the growth of θ-alumina on δ-Ni2Al3.
► Large interface cavities occurred for the oxidation of η-Fe2Al5.
► Cavities occurred in the bulk not at the interface for the oxidation of Ni2Al3.
► Recession of Ni2Al3 in comparison to Fe2Al5 by interdiffusion was greatly minimized.