Substructure formation and nonuniformity in strain during high temperature creep of copper single crystals

Abstract

The change in substructure during high temperature creep of copper single crystals was examined to make clear the relation between the substructure and the creep rate. The structural observations by means of etch-pit technique were made in the same area of the specimen surface after successive straining by creep. Different types of substructures were formed in different localities at an early stage of transient creep. Small subgrains elongating in the direction of the deformation band were found in some regions (region A). Large subgrains containing cells within them were observed in other regions (region B). With the progress of creep, the substructures in both regions underwent gradual changes to become alike in their appearance with each other. The creep strains in regions A and B were examined at various creep stages. The ratio of creep strain to the average creep strain throughout the specimen,ε/ε _av, was a few times larger in region B than in region A at an early stage of transient creep. With the structural changes mentioned above, the difference between the ratios in the two regions came to disappear, both becoming almost unity at the later stage of creep. These results suggest the close relation between the substructure and the creep rate.