Abstract
A fine grain size Cu-30 mass%Zn specimen revealed an anomalous type of creep curves in which the strain rate at the 3rd creep stage increased with increasing 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 intermediate temperature range. The specimens with a grain size of 12 μm were creep tested at 723 K under various stresses. TEM observations were conducted for the specimens crept under a stress of 19.6 MPa at various creep stages. The dislocation density increased rapidly at the 1st and the 4th stages. Hardening rates are discussed in terms of increased dislocation density associated with the creep deformation. The occurrence of the 4th stage results from work-hardening.
