Microstructural origin and control mechanism of the mixed grain structure in Ni-based superalloys

Mixed grain structure, as an incomplete recrystallization, should be homogenized and refined by subsequent processing to improve the mechanical properties of the aeroengine components. The microstructural origin and control mechanism is quite necessary for the microstructure homogenizing and grain refining through thermo-mechanical processing. In present research, microstructural origin and control mechanism of the mixed grain structure have been conducted deeply. With the consideration of temperature drop in practical industrial forging, the optimum processing parameters can be determined as 1110-1140 degrees C/1.0 s(-1) to obtain homogeneous equiaxed grains. The microstructure evolution corresponding to the identified optimal parameters, viz., deformation temperature and strain rate, were systematically investigated. Higher dynamic recrystallization (DRX) fraction and coarser DRX grains can be observed at super-solvus temperature deformation (1140 degrees C). In addition, sub-solvus deformation (1110 degrees C) shows random orientated distribution while near < 001 > compression texture can be detected in super-solvus deformation. Particular attention was paid to the DRX mechanisms during hot deformation. Discontinuous dynamic recrystallization (DDRX) and continuous dynamic recrystallization (CDRX) occur simultaneously, and the synergistic effect of them contributes to microstructure control. Moreover, DDRX characterized by grain boundary bulging dominants the microstructure control. Progressive subgrain rotation labeled as CDRX can be regarded as an important assistant mechanism. The findings would provide theoretical support for microstructure control of Ni-based superalloys with mixed grain structure, which is of vital importance for components to obtain excellent performance. (C) 2021 Elsevier B.V. All rights reserved.

Automated summary

This study deeply explores the microstructural origin and control mechanism of mixed grain structure and determines the optimum processing parameters through thermo-mechanical processing. The evolution of microstructure corresponding to the identified optimal parameters is systematically investigated. The study reveals that discontinuous dynamic recrystallization and continuous dynamic recrystallization mechanisms occur simultaneously, and the grain boundary bulging discontinuous dynamic recrystallization dominates the microstructure control.