Nucleation of Dynamic Recrystallization at the Grain Boundaries of Copper Bicrystals

Abstract

Orientation-controlled copper bicrystals containing symmetrical 70o [0 0 1] tilt boundaries were deformed in tension at 923 K and at three initial strain rates from 4.2 x 10-5s-1 to 4.2 x 10-3s-1. The load was applied parallel to the grain boundary so as to eliminate grain boundary sliding. The nucleation of dynamic recrystallization (DRX) was investigated using optical microscopy and orientation imaging microscopy methods. After grain-boundary migration (GBM) and bulging, nuclei appeared behind the most deeply bulged grain boundary regions. The critical strain for nucleation was less than one-half of the peak strain and largely independent of the strain rate. At a fixed strain, nucleation is more frequent and the grain size finer as the strain rate is increased. All the nuclei were twin-related (Σ3) to the matrices. Furthermore, most of the twinning plane traces were parallel to the inactive slip traces of the bicrystals. This indicates that twin variant selection is essentially unaffected by dislocation motion. The observed mechanism of nucleation of DRX is discussed in relation to the occurrence of GBM and twinning.

Analysis of Dynamic Recrystallization of Ice from EBSD Orientation Mapping

“…In some cases, bulging is accompanied by the presence of nearby subgrain boundaries (see Wusatowska-Sarnek et al, 2002, for instance). Twinning can also play a significant role in DRX nucleation, as has been observed in magnesium (Al-Samman and Gottstein, 2008) and copper (Miura et al, 2007).…”

An integrated full-field model of concurrent plastic deformation and microstructure evolution: Application to 3D simulation of dynamic recrystallization in polycrystalline copper

“…Together with considering the experimentally revealed grain boundary (GB) bulging mechanism (Ponge and Gottstein, 1998;Wusatowska-Sarnek et al, 2002;Miura et al, 2007) , we make the following core assumptions: (a) DRX grains nucleate when some material at a GB undergoes certain atomistic transformations driven by thermal fluctuation and local stress to form a stable nucleus; (b) the time scale of this transformation and the formation of a stable nucleus is at atomic level and hence instantaneous as compared to the applied deformation, and (c) the length scale of this transformation is small relative to the FFT-CP computational grid. These consideration are similar to those made by Niezgoda et al (2014) in modeling of the stochastic twin nucleation, and is illustrated in Fig.…”

“…However, the mechanical behavior was still considered in a macroscopic level in the sense that an average dislocation density was assumed for each grain which evolved according to the Kocks-Mecking model (Mecking and Kocks, 1981). DRX, on the other hand, occurs at a sub-grain level where grain boundary (GB) bulging (Ponge and Gottstein, 1998;Wusatowska-Sarnek et al, 2002;Miura et al, 2007) or other possible mechanisms (Rollett et al, 2004) might operate to initiate the nucleation of new grains. This length scale separation implies that a "homogenized" coupling scheme (Takaki et al, 2014) may limit its application in exploring the underlying physics.…”