Nucleation Mechanism of Discontinuous Dynamic Recrystallization with Restrained Grain Boundary Sliding
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Nucleation Mechanism of Discontinuous Dynamic Recrystallization with Restrained Grain Boundary Sliding Bingchao Xie1 · Baoyun Zhang1 · Hao Yu1 · Yongquan Ning1 Received: 2 May 2020 / Accepted: 3 August 2020 © The Korean Institute of Metals and Materials 2020
Abstract The discontinuous dynamic recrystallization (DDRX) nucleation process was investigated during the TMP of a nickel-based superalloy with a coarse columnar-grain structure. Special attention was focused on the formation mechanism of the ‘newborn boundary’ which separates the free-strain volume from deformed grain. The special grain morphology and large grain size restrained the grain boundary sliding of the studied alloy, and hence made it difficult to form a subboundary through strain induction or twining to separate the free-strain volumes from the deformed grains. This is very different with the classical DDRX theory, where the grain boundary sliding has less restraint and hence leads to grain boundary shearing and the following strain induced boundary or twin boundary. However, the experiment results showed that DDRX took place and developed well during the studied deformation process with restrained grain boundary sliding. It was found that the ‘newborn boundary’, which separates the free-strain volume from deformed grain to close this area, was formed through dislocation piling-up and rearrangement instead of strain induction or twinning caused grain boundary shearing. Hence, a potential nucleation theory was then proposed and discussed, which is expected to enrich the discontinuous dynamic recrystallization theory. Keywords Nickel-based superalloys · Columnar grains · Nucleation mechanism · Dislocation rearrangement
1 Introduction Dynamic recrystallization (DRX) is one of the most important mechanisms to control the microstructure evolution during thermo-mechanical processing (TMP) for metallic materials. It is well know that the DRX process can be classified into three types based on phenomenological method, viz., discontinuous dynamic recrystallization (DDRX), continuous dynamic recrystallization (CDRX) and geometric dynamic recrystallization (GDRX) [1]. DDRX characterized by grain boundary bulging often dominates the microstructure evolution process during the TMP of the alloys exhibiting low stacking fault energy (SFE) [2, 3]. Several theories have been proposed to understand and explain the underlying nucleation mechanism of DDRX, including the nucleation through strain induced grain boundary motion (SIBM) [4], grain boundary sliding [5, 6], etc. [7, 8]. It has * Bingchao Xie [email protected] 1
School of Materials Science and Engineering, Northwestern Polytechnical University, Xi’an 710072, People’s Republic of China
been well accepted that the bulging of initial grain boundaries triggered by stored energy difference initiates DDRX nucleation. However, the formation mechanism of the ‘newborn boundaries’, which separate the bugling volume from the deformed grain to form a closed area, behind the bulging grain boundary is still ambigu
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