Cyclic deformation behaviour of Cu-16at.%Al single crystals part II: Cyclic hardening and slip band behavior

Abstract

In an attempt to understand cyclic hardening and slip band behavior of planar slip alloys, studies have been carried out in strain control on Cu-16at.%Al single crystals oriented for easy glide. The gauge section was observed to become completely filled with slip bands by the repetition of strain bursts irrespective of strain amplitude. Slip in the old bands which carried the whole strain just before a strain burst seem to become inactive after a few successive strain bursts. Since the localized strain shifts around the gauge length because of the short active life of the slip bands, the overall deformation becomes rather homogeneous. This Lüders-band-like behavior persists for a large fraction of the fatigue life, even after crack formation. A regular hill and valley surface morphology develops on the CuAl crystals with cycling. This morphology is related to strain burst behavior, the wavelength of the morphology increasing with strain amplitude because the strain bursts are larger in the early stages of life. The development of sharp extrusions commonly observed in copper is not observed in Cu-16at.%Al single crystals. Sharp extrusions are not expected to develop in this alloy because of its low stacking fault energy and its Lüders-band-like slip behavior.