On the flow stress of [100]- and [111]-oriented Cu-Mn single crystals: A transmission electron microscopy study

Abstract

Abstract Cu-Mn single crystals oriented for multiple slip with [111] and [100] axis have been deformed in tension at room temperature. The Mn content was 0.8 at.% for the [111] and 3at.% for the [100] crystals. The observed decrease in the workhardening rate with increasing reduced shear stress τ—τ0 coincides with the linear decrease in pure Cu for τ—τ0 15–20 MPa (τ0 is the critical resolved shear stress). The total dislocation density measured for τ—τ0 between 5 and 58 MPa increases proportional to (τ—τ0)2 with a slope which increases with increasing Mn content. The higher dislocation density in the alloys is stored in a cell structure of higher volume fraction of the walls compared with pure Cu. For τ—τ0 exceeding 15—20 MPa, the dislocation density within the walls depends only on τ—τ0 and not on orientation and Mn content. Furthermore, it alone determines, in the pure and alloyed crystals, the flow stress, which is additively composed of contributions from solid-solution and strain hardening. In the symmetrically oriented crystals the flow stress is successfully interpreted by a forest model. The results do not support existing composite models.