Oxidation improvement of Ti-48Al-2Cr-2Nb intermetallics by air plasma sprayed ZrO2-Ni-4.5wt.%Al coatings

The air plasma spraying (APS) technique was employed to modify the oxidation resistance of Ti-48Al-2Cr-2Nb intermetallics. The Ni-4.5wt.%Al bond-coat provided a good bonding strength between matrix and thermal barrier top-coat. Static and thermal cyclic tests showed improvement in oxidation resistance of APS-coated Ti-48Al-2Cr-2Nb alloy although the oxidation kinetics did not obey the parabolic law. The oxidation rate was reduced by the formation of NiO scale on the outer layer of the bond-coat which slowed down the oxygen permeation. Tt was healed by the formation of an Al2O3 layer in the inner layer of the bond-coat which can prevented outward diffusion of titanium. A Ti-AI-Ni inter-diffusional layer was observed in between the bond-coat and the matrix. A mechanism of oxidation protection by APS coatings is therefore proposed in this study.