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 increased with increasing strain at the beginning of the 3rd creep, attained a peak value at the end of the 3rd creep and decreased again during newly discovered 4th creep stage. The shape of the creep curve depends on stress, temperature and grain size; in particular, during the tertiary creep, the fine-grained specimens showed a sudden peak without rupturing and a sudden decrease of the strain rate in the quaternary creep. Specimens with a grain diameter of 12 μm were creep-tested under various stresses at 723 K. The dislocation density increased rapidly at the 1st and 4th stages. The 4th creep stage can be explained as the result of the sudden increasing work-hardening.