A new TEM method for the characterization of the tertiaryγ′ nano-precipitates in a PM disk superalloy: influence of ageing

Abstract\n An original method to characterize the ?'-phase tertiary precipitates in a Ni-based superalloy manufactured by powder metallurgy is described. This investigation is made using post-mortem Transmission Electron Microscopy. It is based on the analysis of sheared areas within crept specimens, which allows the precipitates seen by the dislocations in their glide plane to be evidenced. The characteristics of these nano-precipitates, i.e. their size, their volume fraction and the channel width between them, are determined for two different heat treatments (HT). The results show a wide distribution of the microstructural parameters for a same HT, but only slight differences between the microstructures produced by the two different HT. This microstructural information allows understanding the wide variety of the deformation micromechanisms observed during creep at high temperature.