Oxidation behaviour of electron beam physical vapour deposition β-NiAlHf coatings at 1100 °C in dry and humid atmospheres

NiAl intermetallic compounds attract increasing attention for high-temperature applications due to their combination of excellent properties, especially as metallic protective coatings on superalloys or as bond coats in thermal barrier coatings (TBCs). Oxidation behaviour of the beta-NiAlHf coatings prepared by electron beam physical vapour deposition (EB-PVD) was investigated at 1100 degrees C for short time and 100 h in 20 % O-2 + Ar and 15 % H2O + Ar, respectively. The results of mass changes reveal that the addition of minor reactive element Hf significantly improves the cyclic oxidation resistance of the beta-NiAl coatings in both dry and humid atmospheres. During the initial oxidation stage, water vapour retards the phase transformation from theta-Al2O3 to alpha-Al2O3. Moreover, compared with the case in dry atmosphere, water vapour significantly reduces the surface roughness of the oxide scales formed on EB-PVD b-NiAlHf coatings after 100 h cyclic oxidation, which corresponds with the difference of surface morphologies of the oxide scales.