| The microstructural and texture evolution during directional recrystallization were investigated in both commercial purity and high-purity nickel. The effects of the deformation temperature and degree of deformation on the recrystallization behaviors were studied in high-purity nickel. A study of microstructral evolution during directional recrystallization of 90% cold-rolled, commercial-purity nickel with a variety of initial microstructures, textures and purity levels, showed that neither columnar grains nor single crystals could be produced. It was found that the primary recrystallization of these commercial-purity nickel specimens failed to produce a primary recrystallization texture with a strong single orientation component. It is proved that, in single phase nickel, a strong primarily recrystallized cube texture is a key factor for the columnar and/or single grain growth during directional recrystallization. It suppresses the normal grain growth after primary recrystallization, and, thus, enables the oriented grain growth of the secondarily recrystallized grains with orientations other than cube.;99.995% high-purity nickel was rolled to 90% thickness reduction at −196ºC, 25ºC and 200ºC. Decreasing the rolling temperature was found to increase the stored energy of rolling and decrease the primary recrystallization temperature. However, changing the rolling temperature did not contribute to the strengthening of the primarily recrystallized cube texture. 99.995% high-purity nickel was also cold-rolled to 90%, 95% and 98% thickness reduction at 25ºC. It was found that increasing the rolling reduction increases the stored energy of cold-rolling, decreases the primary recrystallization temperature, strengthens the cube texture developed after primary recrystallization and increases its thermal stability at elevated temperatures. It was also found that increasing the rolling reduction contributes to the occurrence and completion of secondary recrystallization at high temperatures. 95% thickness reduction was found to be the minimum degree of deformation for growing columnar grained structures or single crystals in this high-purity nickel.;95% cold-rolled 99.995% high-purity nickel specimens were directionally annealed at 1000ºC with a large temperature gradient of 1000ºC/cm. Single crystals were mainly produced at either lower or higher hot zone velocities, while at intermediate velocities, multi-grained structures tended to be formed. Three preferred orientation relationships between the secondary grains and the primary, cube grains were observed at different hot-zone speeds: 18°/27°, , 27°, and 41°, . The results indicate that the {124}<211> texture, which has been found by the previous study [9, 14] to be the preferred texture for secondary recrystallization in nickel, is not the absolute most mobile orientation. The density and/or sizes of the island grains often found inside the columnar grains or single crystals were shown to increase with the increasing hot-zone velocity. |
