LATENT HARDENING BEHAVIOR OF CYCLICALLY DEFORMED CU-16 AT-PERCENT-AL SINGLE-CRYSTALS

The latent hardening behavior of cyclically deformed Cu-16 at. % Al alloy was investigated by measuring the flow stress and the hardening rate on secondary systems in monotonic compression. Latent hardening experiments for cyclic deformation in Cu-16 at. % Al are complicated by an ageing reaction that has time to develop during test interruptions needed to machine specimens, and produces bursts and yield points on reloading (except at the higher stresses). This problem was overcome to some degree, and the Latent Hardening Ratios (LHRs) for coplanar systems were found to be close to unity; also, the LHRs for intersecting systems were greater than 1, in accord with earlier results on wavy slip metals. The LHRs for these intersecting systems, however, were smaller than those for copper because of the large contribution of the friction stress due to alloying. The unit LHR in the coplanar systems can be explained if the multipoles inherited from cycling disintegrate upon reloading and the contribution of secondary dislocation walls to the hardening becomes significant. Generally, the mesh-length theory of hardening is found to explain the LHRs quite well. The LHR for the A3 system was found to be smaller than those of other intersecting systems in this alloy, consistent with an earlier result on pure copper. The lower value of the activation volume along with the observation of frequent double cross slip traces on the surface strongly suggest that cross slip is responsible for the lower LHR for the A3 latent system.