Creep in polycrystalline aluminium

The present paper reports a study of creep in large grained polycrystalline aluminium. Two techniques were employed to understand this process in more detail. The first was stereoimaging to measure the local strain in the specimen. This measurement was made by photographing the specimen at various times during the creep test, which was carried out in a scanning electron microscope, and using these images to calculate the strain. The second technique was analysis of electron backscattering diffraction patterns, as generated in a scanning electron microscope. This technique allowed examination of changes in crystallography that accompanied the creep process. The results of the experiments showed that strain built up in different grains at different rates. There was never a discontinuity in strain across the grain boundary, and strain relaxation was observed in different grains at different times during the test. Recrystallisation was also observed to occur. In some cases, an existing grain migrated into another grain, presumably through strain induced grain boundary migration. In other cases, there appeared to be nucleation of a new grain with a different orientation.