Relationship between Small-Angle Dislocation Boundaries and Creep

Abstract

Small-angle dislocation boundaries of controlled nature (sharp or diffuse) and density were introduced (by prestraining at room temperature and annealing at 800°C) into high-purity polycrystalline nickel prior to creep at 700°C. By this method, the shape of the creep curve was varied drastically. The initial density of small-angle boundaries ranged from an average of nearly zero per grain, to a large number which was limited by the occurrence of recrystallization. X-ray microscopic examination showed that the dislocation networks developed during creep were nearly identical and were independent of the initial density and nature. The density of small-angle boundaries developed during creep is also independent of the creep strain within the limits of 1% and 7.5%, the strain at which the most ductile specimens fractured. The near identity of the substructure developed during creep was further verified by the substantial equality of the specimens' tensile strengths after creep. The only detectable difference in the substructures was an increase of the average boundary angle with increasing total strain. The type of substructure uniquely developed during high-temperature deformation is discussed in terms of dislocation climb and the interaction of local stress fields from climbing dislocations with those in piled-up arrays.