ON THE TRANSITION IN CREEP-BEHAVIOR DURING PRIMARY CREEP OF CU-ZN ALLOYS

The transient creep of Cu–10 wt% Zn and Cu–30 wt% Zn solid solution alloys is investigated in the temperature range of 200 to 325°C and in the stress range of 150 to 400 MPa. The behaviour of the transient creep reveals that these alloys behave as class II “normal” at low stresses and as class I “inverse” at high stresses. The stress exponent m't, associated with the transient creep, is found to be 2.7 ± 0.3 at low stresses and greater than 4 at high stresses. The transition takes place at a stress σc which depends on both, temperature and the concentration of Zn‐solute atoms in the matrix. At low stress region the apparent activation energy Qt of the transient creep is found to be (0.3 ± 0.01) eV for the Cu–10 wt% Zn alloy and (0.6 ± 0.03) eV for the Cu–30 wt% Zn alloy. In the high stress region, Qt amounts to (0.9 ± 0.01) eV for both the alloys. These values of Qt are used to find the expected values of the apparent activation energy associated with the steady state creep. Also the investigation of the effect of pre‐coldwork on the transient creep shows that the processes controlling the creep mechanism in the different transient stages are independent of the dislocation density in the matrix and only depend on the concentation of Zn‐solute atoms in the Cu‐matrix. Copyright © 1990 WILEY‐VCH Verlag GmbH & Co. KGaA