Fatigue behavior and microstructure of 0001 and 1̄014 magnesium single crystals under compression–compression cyclic loading

Compression–compression cyclic tests were performed on the 0001 and 1̄014 single crystal samples for 50 loading cycles at room temperature. The compression stress varied in the range of 19 MPa–97 MPa. The tested samples were then studied using various microstructure characterization tools including X-ray diffraction (XRD), scanning electron microscopy (SEM), and high resolution transmission electron microscopy (HRTEM). The two samples with different orientations had quite different mechanical behavior and microstructural features. For 0001 single crystal, the strain range and ratcheting strain were constant and very small. On the contrary, the sample heavily strained and deformed for 1̄014 single crystal, and the ratcheting strain was about ten times of that for 0001 single crystal. There was no cyclic hardening/softening for 0001 single crystal, while 1̄014 single crystal experienced cyclic strain hardening. Microstructural observations indicated that twinning was the main deformation mechanism for 0001 single crystal and basal slip, pyramidal slip, secondary pyramidal slip, and tension and compression twinning operated for 1̄014 single crystal. The basal slip resulted in the initial plastic deformation region for 1̄014 single crystal. The Schmid factor analyses demonstrated that the deformation mechanisms were consistent with those obtained from the microstructural observations.