Relation between increasing dislocation density and anomalous creep of a Cu-30 mass%Zn alloy during high temperature creep deformation

A fine grain size Cu-30 mass%Zn specimen revealed an anomalous type of cree p curves in which the strain rate at the 3rd creep stage increased with inc reasing strain, attained a peak value at the end of the 3rd creep stage and then decreased during our newly discovered 4th creep stage, which we call quaternary creep. These constant stress creep tests were conducted in an in termediate temperature range. The specimens with a grain size of 12 mu m we re creep tested at 723 K under various stresses. TEM observations were cond ucted for the specimens crept under a stress of 19.6 MPa at various creep s tages. The dislocation density increased rapidly at the Ist and the 4th sta ges. Hardening rates are discussed in terms of increased dislocation densit y associated with the creep deformation. The occurrence of the 4th stage re sults from work-hardening.