Abstract
The catalyzing effect on nucleation of recrystallization from existing grains resulting from previous lower temperature deformation is analyzed, analogous to the size effect of foreign nucleus in heterogeneous nucleation. Analytical formulation of the effective nucleation site for recrystallization leads to a negative temperature dependence of recrystallized grain size of metals. Non-isochronal annealing—where annealing time is set just enough for the completion of recrystallization at different temperatures—is conducted on pure copper after severe plastic deformation. More homogeneous and smaller grains are obtained at higher annealing temperature. The good fit between analytical and experimental results unveils the intrinsic feature of this negative temperature dependence of recrystallized grain size.
Highlights
The history of metalworking—including the procedures of deformation and heating—can be traced back to the early days of the Neolithic Age, when the first metalsmiths began working with native copper [1]
Consider the catalyzing effectiveness on nucleation of recrystallization from an existing grain with a diameter of d in the as-deformed microstructure with high angle grain boundaries (HAGB), where the catalyzed embryo has a critical radius of r*, which can be calculated from the classical nucleation theory [17]: r∗ =
Formulationanalogous of effectivetonucleation sites leads to a negative temperature dependence of Analytical formulation of effective sites to a negative temperature of recrystallized grain size, where anucleation critical grain sizeleads dc pre-existing in the as-deformeddependence matrix is recrystallized size, where a critical size dc temperature pre-existing thewith as-deformed matrix is formulatedgrain to be negatively dependent on grain the annealing
Summary
The history of metalworking—including the procedures of deformation and heating—can be traced back to the early days of the Neolithic Age, when the first metalsmiths began working with native copper [1]. On the other side, Eastwood et al reported that recrystallized grain size is insensitive to annealing temperature and disclosed that different annealing temperatures yield a similar grain size after recrystallization for brass [12]. In addition to these contradictory experimental results, a basic gap in our knowledge for many years has been the lack of a quantitative model to account for the grain size after recrystallization [13]. The existing high angle grain boundaries (HAGB) in pre-deformed materials play an important role in promoting nucleation for recrystallization, through mechanisms such as strain-induced boundary migration (SIBM) [14]. Analogous to the catalyzed nucleation by “foreign particles” during phase transformation, the catalyzing effect on nucleation of recrystallization from HAGB can be analyzed by following the work on foreign nuclei in heterogeneous nucleation [17,18]
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