Revelation of anomalous creep of the Cu-30 mass % Zn alloy related with dislocation hardening under high-temperature creep deformation

High-temperature constant-stress creep tests of a single-phase Cu-30 mass% Zn alloy revealed an anomalous type of creep curve. The strain rate increas ed with increasing strain at the beginning of the 3rd creep, attained a pea k value at the end of the 3rd creep and decreased again during newly discov ered 4th creep stage. The shape of the creep curve depends on stress, tempe rature and grain size; in particular, during the tertiary creep, the fine-g rained specimens showed a sudden peak without rupturing and a sudden decrea se of the strain rate in the quaternary creep. Specimens with a grain diame ter of 12 mum were creep-tested under various stresses at 723 K. The disloc ation density increased rapidly at the Ist and 4th stages. The 4th creep st age can be explained as the result of the sudden increasing work-hardening.