A preliminary model to predict the special grain boundary fraction in commercial-purity nickel

Special grain boundaries have been shown in numerous studies to be more resistant to creep, fracture behaviour, intergranular degradation, corrosion, and minor element segregation, leading to mechanical property improvements. To manipulate the fraction of special boundaries, thermo-mechanical processing can be used whereby a series of prescribed deformation and annealing heat treatments are used. However, the ranges and combinations of manufacturing process parameters can greatly affect the type and distribution of grain boundaries and therefore their selection is crucial to the resulting material properties. This study looks at an initial experimental attempt to correlate the effects of the manufacturing processing cycle parameters with the fraction of special boundaries produced in commercial-purity nickel. Process parameters such as percent reduction in thickness by cold rolling, annealing temperature, and number of cycles were studied, with annealing time kept constant. The analysis showed complex interactions between the independent variables from processing and the special fraction of grain boundaries as observed by Orientation Imaging Microscopy.