Effect of Cr2O3 nanoparticle dispersions on oxidation kinetics and phase transformation of thermally grown alumina on a nickel aluminide coating

Cr2O3-free and-dispersed Ni2Al3 coatings were prepared by correspondingly aluminizing as-electrodeposited Ni films without and with dispersion of Cr2O3 nanoparticles. The Cr2O3-dispersed aluminide coating has a lower oxidation rate than the Cr2O3-free one in air at 900 degrees C. The reason lies in that the Cr2O3 dispersion promoted the theta-to-alpha alumina transformation on the aluminide coating during oxidation, on a basis of investigations of scanning electron microscopy (SEM), transmission electron microscopy (TEM) and photo stimulated luminescence spectroscopy (PSLS). The result also indicates that the faster theta-to-alpha phase transformation can significantly prevent the cavities formation at the alumina/coating interface.