Rearrangement of Fatigue Dislocation Structure in a Pure-Aluminium Single Crystal Associated with Change in Deformation Temperature

Fully reversed tension-compression low-cycle fatigue tests were performed at room temperature (RT) and 77 K on single-slip-oriented pure aluminum single crystals having different Schmid factor (SF) values (0, 0.14 and 0.24) for the cross-slip system under constant plastic shear-strain amplitudes. Cyclic deformation curves showed no stress saturation at RT, regardless of the applied strain amplitude. The cyclic deformation behavior at RT was as follows: initial hardening, softening and secondary hardening in the specimens with non-zero SF, whereas the specimens with SF = 0 exhibited monotonic hardening. However, all the specimens formed and developed the cell structure from the early stage of fatigue. On the other hand, no differences were observed in the cyclic deformation of the three specimens at 77 K. Shear stress amplitudes revealed initial hardening followed by saturation at any shear strain amplitudes applied, and a plateau stress region with a value of 42 MPa appeared in the cyclic stress-strain curve obtained at 77 K. Dislocation structures in the tested specimens were almost identical to those observed in single-slip-oriented pure Cu single crystals fatigued at RT.