A new type-γ′/γ" coprecipitation behavior and its evolution mechanism in wrought Ni-based ATI 718Plus superalloy

In the precipitation-hardened Ni-based superalloy, typified by ATI 718Plus, the nano-scale y' and y '' phase in duplet or triple coprecipitate morphology can provide superior high-temperature strength. Thus, it is of great sense to study the evolution of y'/y '' coprecipitate during long term service at elevated temperature. In this study, the new-type y'/y '' coprecipitates with a sandwich or compact configuration were found firstly in wrought ATI 718Plus superalloy during long term thermal exposure at 705 degrees C. These co-structure of the y'/y '' precipitates evidently inhibit the coarsening of y' phase. The increase of thermal exposure time evidently leads to the increase of the volume fraction of y'/y '' coprecipitate and transformation of sandwich-type y'/y '' coprecipitate to compact-type y'/y '' coprecipitate, which is characterized as y '' phase precipitate at several faces of the y' phase. The main evolution mechanism of y'/y '' coprecipitates is element segregation, especially the composition variations of Al Ti and Nb and their ratio of Al+Ti/Nb. In addition, the interfacial energy between y '' phase and y matrix also plays a key role on the y'/y '' coprecipitates evolution. The calculated results show that the longer thermal exposure time leads to the higher interfacial energy, which is beneficial for nucleation and precipitation of y '' phase on the faces of y' phase. (C) 2022 Published by Elsevier Ltd on behalf of The editorial office of Journal of Materials Science & Technology.