Microstructures and cyclic oxidation behaviour of Pt-free and low-Pt NiAl coatings on the Ni-base superalloy Rene-80

Aluminizing of bare and 3 μm-Pt-electroplated specimens has been utilised to prepare NiAl and low platinum (Ni,Pt)Al coatings. Cyclic oxidation of the coatings was investigated by exposing samples to 1 h cyclic oxidation at 1100 °C. The modified coating exhibited an external layer of NiAl-25 vol.% PtAl2 above a three-zone structure. This structure endured over the whole testing time, while the NiAl coating failed after 77 cycles. The (Ni,Pt)Al coating did not reduce the scale growth rate, but it improved scale adhesion. In addition, Pt limited the outward diffusion of Ti from substrate and hence prohibited formation of undesirable TiO2.

► High activity aluminizing of 3 μm-Pt-plated superalloy results in a 4-zone coating.
► The external layer of Pt-modified coating consists of NiAl-23 vol.% PtAl2.
► 2.5–11 at.% Of Pt improves the cyclic oxidation resistance of the aluminides.
► Pt inhibits formation of undesirable oxide of TiO2 in protective alumina scale.
► Pt does not reduce rate of scale growth but it clearly improves scale adhesion.