| The effects of process parameters on the microstructural and textural evolution during directional recrystallization processing were investigated. Microstructural evolution during primary directional recrystallization of 80% cold-rolled, single crystal, high purity copper, showed that columnar grain structures only occurred at an optimum hot zone velocity range, outside of which equi-axed grain structures were produced. The hot zone velocity for both the onset and termination of the columnar grain structure increased with increasing annealing temperature, features that can be explained by the increase in both nucleation rate ahead of the hot zone and grain boundary mobility with temperature.; 90% cold-rolled polycrystalline nickel specimens were directionally annealed at a variety of temperatures with different temperature gradients. Equi-axed grain structures were produced at 1000°C with a temperature gradient of 50°C/cm at hot zone velocities from 2–100 mm/h. The average grain size decreased with increasing hot zone velocity, which is explained as the decrease of specimen residence time in the hot zone. However, large columnar grains were produced during directional recrystallization at both 1000°C and 800°C with temperature gradients of 1000°C/cm and 800°C/cm, respectively. The orientations of the secondarily recrystallized columnar grains and the small grains in front of the hot zone, which were produced by primary recrystallization, were measured using Electron Backscattering Patterns (EBSP). It was found that most of the columnar grains have {lcub}124{rcub}<211¯> orientations, and that the small grains were cube-oriented. Isothermal annealing of cold-rolled nickel showed that {lcub}124{rcub}<211¯> is the preferred texture for secondary recrystallization. {lcub}124{rcub}<211¯> oriented grains form 40°/<111> high mobility grain boundaries with the cube textured grains. Therefore, the formation of the columnar grains results from oriented grain growth. Island grains often found inside the columnar grains or single crystals were shown to be twin or low angle mis-oriented to the surrounding grains. They were left behind the growth front during directional recrystallization due to their low grain boundary energy and mobility.; A front-tracking, curvature-driven computer model was successfully modified to simulate the directional recrystallization in the presence or absence of particles. Thus it was shown that randomly-distributed particles restrain directional recrystallization, whereas, linearly distributed particles propagate directional recrystallization. |
