The effect of grain refinement on the oxidation and phase transformation of alumina scale on Ni2Al3 coating

An ultrafine-grained (UFG) and coarse-grained (CG) Ni2Al3 coating were prepared by aluminizing pure nickel substrate with and without nanocrystalline Ni film using an aluminization pack cementation process at 620 °C for 5 h. The oxidation kinetics and cyclic oxidation result show that the UFG-Ni2Al3 coating significantly enhances the oxidation-resistant with respect to the CG-Ni2Al3 coating in air at 900 °C. The SEM/EDS results confirmed that the microstructure of two δ-Ni2Al3 coatings is free of pores, cracks, and voids. The UFG-Ni2Al3 coating promotes the phase transformation with respect to the CG-Ni2Al3 coating after oxidation for various times were investigated by using photo-stimulated luminescence spectroscopy (PSLS) analysis. The experimental result also confirmed that the UFG-Ni2Al3 coating, on which an adherent alumina scale grew, can significantly control the formation of cavities at the scale/coating interface. •Successfully fabricated the coarse-grained (CG) and ultrafine-grained (UFG) Ni2Al3 coatings.•The grain refinement caused faster promotion of thermally grown alumina from θ-to-α phase.•The grain refinement can be noticeably increased the oxidation resistance of Ni2Al3 coatings.•Ultrafine-grained Ni2Al3 coating helped to form an adherent alumina scale.