Cyclic deformation behavior of Cu16at.%Al single crystals Part III: Friction stress and back stress behavior

Abstract

To investigate the cyclic hardening behavior of planar slip alloys, the friction stress and the back stress acting on the dislocations were evaluated from analyses of fatigue hysteresis loops. In the initial stage of deformation the friction stress (12 MPa) is larger than the back stress (7 MPa). With accumulation of cycles the back stress increases and eventually leads the friction stress. The friction stress in the early stage of deformation, which is high relative to that of pure metals, is related to the elastic interaction of dislocations and segregated solute atoms. The cyclic hardening of this alloy is mostly caused by the increase of the back stress, which seems to be caused by the accumulation of multipoles and dislocation pile-ups frequently observed in this alloy. The equality of the back stress and the friction stress observed previously for copper breaks down for the behavior of multipoles in this alloy, because the dislocation structure is modified from that of copper to form kinked multipoles or cross-gridded multipoles, types which cannot occur in copper because of the ease of cross-slip in pure metal. The motion of these multipoles is discussed in relation to the observed friction stress and back stress behavior.