Research On Recrystallization And Grain Growth During Annealing Of Nickel Cold-rolled To High Strain

Nickel and its alloys are ideally suited as substrate materials for second generation superconductors due to the fact that cold rolling to high strain followed by high temperature annealing results in formation of a very sharp cube texture in these materials. Research into the recrystalllization of highly cold rolled nickel and into the formation of the cube texture, therefore, is important for both theoretic understanding and practical application.In the present work the deformed microstructures and microstructural evolution during annealing of pure nickel highly deformed by both conventional rolling and accumulated rolling bonding have been systematically investigated using range of experimental techniques including electron backscattered diffraction (EBSD), micro-hardness measurement and electron channeling contrast . Furthermore a Monte Carlo Potts model was developed and used to systematically simulate the cube texture evolution during grain growth.The main conclusions achieved are as follows: (1) Analysis of the origin in samples annealed at a low temperature for a short time indicates that cube-oriented grains are mainly developed from cube-oriented deformation bands, but a few also develop from twinning of near cube-twin oriented grains. The formation of a sharp cube texture requires that the fraction of cube nuclei (number per unit volume) is higher than 1/6~1/4 of the total nuclei. (2) Results of"in-situ"experiments on the recrystallization process indicate that on average cube-oriented grains grow faster than other grains through the whole recrystallization process, mainly due to the fact that cube-oriented grains have a higher chance than other grains to encounter high-angle boundaries with misorientation rotation axes near the <111> corner. (3) Monte Carlo Potts model simulations of grain growth show that a higher of cube volume fraction (Fcube) and a higher ratio (β) of average grains size for cube-oriented grains compared to non-cube oriented grains in the fully recrystallized microstructure results in a faster the increase of the cube volume fraction. The diagram of Fcube-β-X has been established to show the connection between the structure parameters and to predict the cube volume fraction after grain growth. (4) A sequential annealing investigation of the relationship between each recrystallizing grain and the deformed matrix consumed by each grain during annealing indicates that the misorientation distributions for migrating and non-migrating recrystallizing boundaries are similar. Analysis of the data shows that the jerky movement is typical for recrystallizing boundaries and suggests that simple v=MF formulation does not hold for local recrystallizing boundary segments. (5) A detailed analysis of theΣ3 boundaries formed during recrystallization shows that theΣ3 boundaries can be separated into two groups: twin type and non-twin type. These can be differentiated using the total deviation parameter of each near-Σ3 boundary to the ideal 60°<111> relationship. The mobility for non-twin type ofΣ3 boundaries is substantially higher than that for twin typeΣ3 boundaries.