Tae-Wook Na

Misorientation characteristics of penetrating morphologies at the growth front of abnormally growing grains in aluminum alloy

The initial stage of abnormal grain growth of the aluminum alloy 5052 has been investigated using electron back-scattered diffraction to analyze the characteristic of misorientations of the penetrating morphology at the growth front. Among the 84 penetrating morphologies examined, none of the penetrated grain boundaries has low angles or coincidence site lattice (CSL) relations, whereas 66 penetrating grain boundaries have low angles or CSL relations. These results strongly suggest that the penetrating morphologies should result from triple-junction wetting.

New understanding of the role of coincidence site lattice boundaries in abnormal grain growth of aluminium alloy

The sequential microstructure evolution of abnormal grain growth (AGG) in the aluminium alloy (AA5052) was investigated to analyse the migration behaviour of coincidence site lattice (CSL) boundaries, which are known to play an important role in inducing AGG. The sequential evolution showed that CSL boundaries tend to disappear more slowly than general boundaries at the growth front of abnormally growing grains. Especially, the migration rate of Σ9 boundaries was noticeably low, which is contrary to the previous suggestions.

Parallel three-dimensional Monte Carlo simulations for effects of precipitates and sub-boundaries on abnormal grain growth of Goss grains in Fe–3%Si steel

Using parallel three-dimensional Monte Carlo simulations, we investigated the effects of precipitates and sub-boundaries on abnormal grain growth (AGG) of Goss grains based on real orientation data of primary recrystallized Fe–3%Si steel. The simulations showed that AGG occurred in the presence of precipitates which inhibited the grain growth of matrix grains, whereas it did not in the absence of precipitates. The role of precipitates in enhancing AGG is to maintain a relatively high fraction of high energy boundaries between matrix grains, which increases the probability of sub-boundary-enhanced solid-state wetting of an abnormally growing grain. The microstructure evolved by the simulation could reproduce many realistic features of abnormally growing grains, such as the formation of island and peninsular grains and merging of abnormally growing grains which appeared to be separated initially on the cross-section.

Effect of Asymmetric Hot Rolling on the Texture Evolution of Fe–3%Si Steel

In Fe–3%Si steel, the hot rolling process affects not only the hot rolling texture but also the primary recrystallization texture. Here, the effect of asymmetric hot rolling was studied by comparing the difference in the texture evolved between asymmetric and symmetric hot rolling. The effect of asymmetric hot rolling on the texture of primary recrystallized Fe–3%Si steel was also studied. The symmetric hot rolling of Fe–3%Si steel produces a rotated cube texture at the center but Goss and copper textures near the surface. Asymmetric hot rolling tends to produce Goss and copper textures even at the center like the texture near the surface. After primary recrystallization, the dominant texture at the center changes from {001} <210> to {111} <112> and the new texture has a higher fraction of the grains which make the low energy boundary with Goss grains than that of symmetric hot rolling.