Effect of grain boundaries on anneal hardening in Cu-Al alloy

Abstract

Low-temperature anneal hardening of a cold-worked Cu-Al solid solution alloy was investigated in single, bi- and polycrystals of Cu-13.5 at.-%Al alloy. In grains of a bicrystal specimen, where piled-up dislocations have a predominant edge component, large increases in Vickers hardness were observed in the vicinity of the grain boundary as a result of low temperature annealing after tensile deformation. However, in grains where piled-up dislocations have a predominant screw component, the Vickers hardness was decreased by the low temperature annealing. In the single crystal specimen, an increase in the Vickers hardness was not observed after low temperature annealing. These results indicate that the grain boundary plays an important role in low-temperature anneal hardening. Due to the formation of a large number of vacancies and a large amount of lattice distortion caused by piled-up dislocations against the grain boundary, the segregation of solute atoms is strongly activated. The Suzuki locking atmosphere is easily formed in the vicinity of the grain boundary and consequently, this region is preferentially hardened by low temperature annealing.