Investigation on Mechanism of Microstructure Evolution during Multi-Process Hot Forming of GH4169 Superalloy Forging

• Published in: Materials Vol. 17; no. 7; p. 1697
• Main Authors: Chen, Ming-Song, Cai, Hong-Wei, Lin, Yong-Cheng, Wang, Guan-Qiang, Li, Hong-Bin, Liu, An, Li, Ze-Hao, Peng, Shan
• Format: Journal Article
• Language: English
• Published: Switzerland MDPI AG 07.04.2024
• Subjects: Aging; Alloys; Annealing; Deformation; Dynamic recrystallization; Evolution; Forging; Forgings; Grain boundaries; Grain size; Heat treatment; High temperature; Hot forming; Hot working; Microstructure; Misalignment; Nickel alloys; Nickel base alloys; Nucleation; Predeformation; Scanning electron microscopy; Strain distribution; Superalloys; Temperature; United States > US; GH4169 superalloy; δ phase; dynamic recrystallization nucleation; multi-process hot forming
• ISSN: 1996-1944; 1996-1944
• DOI: 10.3390/ma17071697

Typically, in the manufacturing of GH4169 superalloy forgings, the multi-process hot forming that consists of pre-deformation, heat treatment and final deformation is required. This study focuses on the microstructural evolution throughout hot working processes. Considering that δ phase can promote nucleation and limit the growth of grains, a process route was designed, including pre-deformation, aging treatment (AT) to precipitate sufficient δ phases, high temperature holding (HTH) to uniformly heat the forging, and final deformation. The results show that the uneven strain distribution after pre-deformation has a significant impact on the subsequent refinement of the grain microstructure due to the complex coupling relationship between the evolution of the δ phase and recrystallization behavior. After the final deformation, the fine-grain microstructure with short rod-like δ phases as boundaries is easy to form in the region with a large strain of the pre-forging. However, necklace-like mixed grain microstructure is formed in the region with a small strain of the pre-forging. In addition, when the microstructure before final deformation consists of mixed grains, dynamic recrystallization (DRX) nucleation behavior preferentially depends on kernel average misorientation (KAM) values. A large KAM can promote the formation of DRX nuclei. When the KAM values are close, a smaller average grain size of mixed-grain microstructure is more conductive to promote the DRX nucleation. Finally, the interaction mechanisms between δ phase and DRX nucleation are revealed.