Effect of Deformation Twinning on the Fatigue Properties of Cu-8 at.%Al Single Crystals

Abstract

This study concerns the effect of deformation twinning on the fatigue properties of single phase Cu-8 at.% Al single crystals. The analysis was performed for two different physical states, i.e.: (i) material pre-deformed plastically to the stage just before the activation of deformation twinning, which corresponds to a true strain level of approximately 0.8 and (ii) material pre-deformed to the stage after activation of deformation twinning, which is characterised by a layered T/M microstructure with a large number of Σ3 twin boundaries and a dislocation density comparable to that of material just before the twinning process. In the first case, the material did not fracture even after 100,000 cycles. However, in the second case, the material has fractured after approximately 61,000 cycles. Three different stages of fatigue testing were identified. At first, the very initial stage up to 20 cycles characterized by a significant increase in the recorded strain. Second, the stabilisation stage of very slight changes of strain, and at last, the failure stage, again of significant increase of strain at different cycles leading to the final stage of material failure.