Precipitation characteristics of γ' precipitates of the GH4742 nickel-based superalloy at a slow cooling rate

The double cone samples of the predeformed GH4742 superalloy were treated by subsolid solution heat treatment (Sub-SHT) at 1080 degrees C/8 h and then cooled at a cooling rate of 22 degrees C/min. The evolution of gamma' precipitates by coupling hot deformation and heat treatment was studied by in situ electron backscatter diffraction + scanning electron microscopy. This research explains the morphological variations between the recrystallized and deformed grains of the gamma' precipitates, as well as the relationship between the characteristics of the grain boundaries (GBs) and gamma' precipitates at the GBs. The results show that when the predeformed samples were subjected to an 8 h Sub-SHT and then cooled at 22 degrees C/min, the gamma' precipitates exhibit a tri-modal size distribution, and the primary gamma' precipitates are dendritic. The morphology of gamma' precipitates within deformed grains is related to the accumulation of dislocations and other defects. The maximum size of columnar gamma' precipitates is obtained at the high-angle grain boundary, where the misorientation ranges from 30 degrees to 40 degrees. The length of columnar gamma' precipitates results from the comprehensive effect of the GB energy determined by the GB misorientation and the GB mobility determined by the stored energy difference. Owing to the low energy and low mobility of the sigma 3 twin boundary, the gamma' precipitates at the sigma 3 twin boundaries remain stable, and the morphology and size are no different from those within the grains. These findings may be helpful for the design and optimization of Ni-base superalloys. (c) 2023 Elsevier B.V. All rights reserved.

Automated summary

In this study, the effect of coupling hot deformation and heat treatment on the morphology of gamma' precipitates in GH4742 superalloy was investigated. The results show that after subsolid solution heat treatment and rapid cooling, tri-modal size distribution of gamma' precipitates was observed, with dendritic primary gamma' precipitates. The morphology of gamma' precipitates within deformed grains is influenced by the accumulation of dislocations and other defects. The maximum size of columnar gamma' precipitates is obtained at high-angle grain boundaries. The stable morphology and size of gamma' precipitates at sigma 3 twin boundaries were also observed. These findings provide important insights for the design and optimization of Ni-base superalloys.