Internal Stress and Dislocation Structure during Sigmoidal Transient Creep of a Copper–16 at.-% Aluminium Alloy

Abstract

AbstractCreep tests on pure copper and single-phase copper-aluminium alloys (5.8, 11.5, and 16.0 at.-% Al) have been made at 450, 550, and 650° C (723, 823, and 923K) and 19.6, 39.2 and 58.8 MN/m2 (2.0, 4.0, and 6.0 kgf/mm2). Both normal and sigmoidal transient-creep curves were observed, according to the creep-stress and temperature conditions. Dislocation structures in Cu-16 at.-% Al were examinedby transmission electron microscopy, to clarify the origin of the sigmoidal transient creep, in which an inverse transient creep at an early stage was followed by a normal transient creep after the creep rate had passed through a maximum. Average internal stress during creep was also determined by the so-called stress dip test. The main results obtained were as follows: Normal transient creep behaviour changed to sigmoidal with decreasing stress and temperature and with increasing aluminium content of the alloys. In pure copper, however, only normal transient creep was observ...