Fang Xiaoying

Preferred orientation of grain boundary plane in recrystallized high purity aluminum

Compared with the research of preferred orientation of crystals (crystallographic texture) which started nearly a century ago, preferred orientation of grain boundary plane in polycrystalline materials is a lately proposed research direction with the development of five parameter analysis which is based on electron backscatter diffraction and stereological method. Systematic investigations into the preferred orientation of grain boundary plane and in-depth understanding on their evolution natures will be important to the manipulation of the microstructures of desired properties. In current paper, high purity aluminum (99.99 wt%) samples were cold rolled with 85% thickness reduction followed by a recrystallization annealing at 330℃ for 15-60 minutes and then the grain boundary plane orientations were studied. The results indicate there indeed exist preferred orientations of grain boundary planes in the recrystallized microstructure and the preferred orientation evolves sequentially from {2 2 3} to {1 1 1} and {1 0 0} planes during grain growth. Further discussion points out the recrystallization of high purity aluminum after cold rolling could be a so-called continuous recrystallization which involves sub-grain coalescence and sub-grain growing, and low angle grain boundary (mis- orientation angles ranging from 2° to 15°) constitutes the main part of the entire grain boundaries in the recrystallized microstructure. During grain growth, the crystallographic texture evolves from {1 1 0} (Brass) to {0 1 1} (Goss) and {0 2 3} co- existed, and low angle grain boundary planes usually orient on the exact position of low energy tilt boundaries due to the effects of crystallographic texture and crystallographic plane energy. This is the reason for the regular evolution of the preferred orientation of grain boundary planes as observed.

In-situ observations on the annealing behavior of triple junctions in a high purity nickel after slight cold rolling

Off-line in-situ electron back scatter diffraction (EBSD) was used to characterize the annealing behavior of triple junctions in a high purity (99.99 wt.%) nickel which had been cold rolled slightly (the thickness reduction was 5%). The results showed that recrystallization nuclei were developed at some triple junctions during the early stage of annealing at 800℃. All such nuclei exhibit /60° orientation relationships with the parent grains, and the bounded Σ3 boundaries are found to be incoherent ones. During further annealing, these nuclei are consumed by other growing grains, indicating that their presence is just a release of the strain concentration at the triple junctions and has no substantial effects on the evolution of grain boundary character distribution during annealing. The growing grains are usually those original grains and they are coarsened rapidly via a mechanism of so-called strain induced boundary migration by which high fraction Σ3 boundaries and large-sized Σ3 n ( n =1, 2, 3…) boundary clusters are introduced.