The cyclic stress—strain response of single crystals of Cu-16 at.%Al alloy I: Cyclic hardening and strain localization

Abstract

The cyclic stress-strain response of Cu-16at.%Al alloy has been explored using single crystals and conventional multistep and constant-amplitude tests. The alloy is shown to have a regular cyclic stress-strain curve with a plateau; the plateau stress is the same as that of copper but the strain range is more limited. Cyclic hardening requires large cumulative strains to reach saturation, proceeds irregularly and is associated with a remarkably constant friction stress. Thus the limited hardening which occurs is caused by changes in the back stress. Contrary to previous reports, strain localization is found by interferometric techniques to occur in association with the plateau and the formation of persistent slip bands (PSBs). The magnitude of the localized strain is higher than that of copper, and the volume fraction of PSBs is smaller. Limited results in measuring fatigue life show little difference from that of copper, the damaging effects of the higher localized strain being compensated by greater slip reversibility. The effect of strain cycling at 77 K has also been studied.