Study on Grain Boundary Characteristic Distribution of Nickel Base 625 Alloy Controlled by Deformation Heat-Treatment Process

Through a series of thermal–mechanical processing (TMP) routes with various ratios of cold rolling (CR) and subsequent high-temperature annealing, Inconel625 alloy samples with different strain states were prepared to investigate the evolution of grain boundary characteristic distribution (GBCD) in the process of grain boundary engineering (GBE). The effects of the TMP parameters on the microstructure of GBE were studied by electron backscattering (EBSD), and the effects of different TMP parameters on the microstructure and hardness of GBE were analyzed. The results show that different restraints have different mechanisms of grain boundary network formation, and that strain is the main mechanism of boundary migration. When the deformation is 5%, the proportion of low ΣCSL grain boundary is relatively large at each annealing temperature, and the proportion of low ΣCSL grain boundary reaches the maximum at 1075°C. With the increase of temperature and deformation, the dominant mechanism of grain boundary fracture gradually changes from the new twin mechanism to the ∑3 regeneration mechanism. The large initial grain size can delay the nucleation of strain-free grains during TMP treatment. Finally, the grain boundary evolution of the sample in each stage of GBE production and the change of hardness of the sample after GBE are described.