Abstract
Plasma sprayed coatings of 50Ni–50Cr as undercoat coupled with an Al topcoat were investigated with the aim of filling the pores in the Ni–Cr coating with the Al topcoat at high temperatures. For comparison purposes, a thick 50Ni–50Cr coating (∼450 μm) with sealant according to BS 5493 was also applied. The results showed that both the two layer coating of Ni−Cr+Al and the thick coating with the sealant had excellent resistance against steam oxidation at 650°C for up to 3000 h of testing. It is interesting to note that the two layer coating showed a similar performance, despite the lower coating thickness compared to the thick coating. Both Ni and Cr diffused into the Al coating structure. Diffusion of Al into the Ni–Cr system (coating) was slower than that into the Fe–Cr system (substrate).
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