Etch-Pit Observations of Dislocation Arrangements under Reverse Stress in Copper 9at. % Aluminum Alloy Single Crystals

Abstract

With a view of solving the cause and essence of the Bauschinger effect, dislocation behaviour under reverse stress has been investigated in Cu-9at% Al alloy single crystals, using an etch-pitting technique. From the direct measurements of the beginnings of backward movements of dislocations, the frictional resistance force to moving dislocations due to solid solution hardening is estimated to be approximately 0.8kg/㎟, which is ≃4/5 of easy glide stress. It is found that pile-up dislocations against a barrier move well under the reverse stress range from 0.6 to 0.7 to the pre-stress level, but then hardly move more than the reverse stress ratio of 0.8. Evidence of almost complete annihilation of double ended pile-ups which are generated by the same source is presented. Another striking evidence of radical annihilation of dislocations within uniformly aligned dislocation groups of the same sign is also discovered. Mechanisms acceptable for explaining such results are proposed respectively, i.e., the mutual annihilation of dislocations of opposite signs, and the double cross-slip mechanism. It is suggested that the characteristics of rearrangements of dislocations against stress reversal are probably connected with the latter mechanism, which would be responsible for cyclic strain hardening.