Rumpling of CVD (Ni,Pt)Al diffusion coatings under intermediate temperature cycling

The development of surface undulations during cyclic oxidation of diffusion (Ni,Pt)Al coatings on second generation nickel-base superalloys, the phenomenon of “rumpling,” represents one of the major forms of coating degradation during service at high temperatures. Previous studies of the phenomenon have invariably involved cycling between a high temperature, typically 1150 °C, and room temperature, or close to it (~ 50–100 °C). In this work, we show that most of the rumpling occurs on thermal cycling in a narrow temperature range between 1150 °C and a lower temperature of about 1000 °C. Furthermore, there is little difference in the rumpling amplitude when the lower temperature is reduced below 1000 °C, even down to room temperature, suggesting that the mechanisms responsible for rumpling operate principally at temperatures above 1000 °C. These results have important implications for the viability of various mechanisms proposed for rumpling as well as for life prediction models.