Ic. Hsu et Sk. Wu, OXIDATION IMPROVEMENT OF TI-48AL-2CR-2NB INTERMETALLICS BY AIR PLASMA-SPRAYED ZRO2-NI-4.5WT.PERCENT-AL COATINGS, Surface & coatings technology, 90(1-2), 1997, pp. 6-13
The air plasma spraying (APS) technique was employed to modify the oxi
dation 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 i
n oxidation resistance of APS-coated Ti-48Al-2Cr-2Nb alloy although th
e oxidation kinetics did not obey the parabolic law. The oxidation rat
e 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 th
e formation of an Al2O3 layer in the inner layer of the bond-coat whic
h can prevented outward diffusion of titanium. A Ti-AI-Ni inter-diffus
ional layer was observed in between the bond-coat and the matrix. A me
chanism of oxidation protection by APS coatings is therefore proposed
in this study.