Static and cyclic creep tests on α-solid solution Cu-Zn alloys (5, 10, 30% Zn) have been made at 665K to study the effect of stacking fault energy (SFE) on cyclic creep.
The test temperature, 665K, is about 0.5 Tm of 95Cu-5Zn and 90Cu-10Zn alloys, and about 0.56Tm of 70Cu-30Zn alloy, where Tm is melting temperature of each alloy. The stress is normalized with Young's modulus at test temperature.
The results of the tests are as follows:
(1) Stress exponents of both static and cyclic creep rate decreased with increasing zinc content.
(2) At the same zinc content, stress exponent of cyclic creep rate was observed to be larger than that of static creep rate.
(3) The steady state creep rates of both static and cyclic creep were functions of SFE, and SFE dependence of cyclic creep rate was found to be larger than that of static creep rate. This fact was explained in terms of the theory that excess vacancies created by cyclic stress help the climb of edge dislocations, which is easy in the materials with high SFE.
To confirm the excess vacancy model, static and cyclic creep tests were conducted at higher temperature, 895K, about 0.7 Tm of the alloys. There was no difference between the SFE dependences of static and cyclic creep rates. This was interpreted as less contribution of mechanically generated vacancies to thermal vacancies, compared with lower temperature.
