THE OXIDATION MECHANISM OF PT20NI30AL50

Additions of platinum to aluminium oxide forming alloys are known to i mprove their high temperature corrosion resistance. This is known as t he ''precious metal effect''. In this study the effect of platinum on the oxidation mechanism was investigated by comparing the oxidation me chanism of beta-NiAl and Pt20Ni30Al50. This composition agrees with th e average composition of a platinum modified aluminide coating. The al loys were oxidized at temperatures from 1000 to 1200-degrees-C. The gr owth of the oxide scale on the NiAl alloy proceeds both by aluminium a nd by oxygen diffusion through the scale resulting in growth within th e scale. However, on Pt20Ni30Al50 the growth of the scale is limited t o the oxide/gas interface due to a predominant aluminium transport thr ough the scale. Therefore the growth stresses are reduced. Another dif ference is the extensive void formation at the beta-NiAl/oxide interfa ce. This was not observed on the Pt20Ni30Al50 samples. The phenomena m entioned above are the two likely reasons for the improved oxide scale adherence.