Direct observation of twinning–detwinning–retwinning on magnesium single crystal subjected to strain-controlled cyclic tension–compression in [0 0 0 1] direction

Abstract

2011) Direct observation of twinning-detwinning-retwinning on magnesium single crystal subjected to strain-controlled cyclic tension-compression in [0 0 0 1] direction, Philosophical Magazine Letters, 91:12, 757-765, Cyclic deformation of magnesium single crystal under fully reversed tension-compression along the [0 0 0 1] direction at a strain amplitude of 0.5% was investigated in ambient air. In situ light microscopy of f1 0 1 2g twins was conducted on the ð1 0 1 0Þ prismatic plane. Fundamental morphology evolution of twinning-detwinning-retwinning was characterized in situ. The critical resolved shear stress of f1 0 1 2g twinning was found to be $2.4 MPa. With increasing loading cycles, the activity of twinningdetwinning-retwinning exhausted and the residual twins accumulated. During detwinning at each loading cycle, the residual twins were observed to form on the vicinities of twin boundaries which had been fully expanded at the previous tensile peak. Microcracks were found on the boundaries of residual twins and the basal slip bands.

Co-zone {1¯012} Twin Interaction in Magnesium Single Crystal

“…As a consequence, their interaction and reactions develop a characteristic locked 'quilted looking' twinning structure (Figure 1(a)) which affects subsequent twinning and de-twinning, causes twinning-induced hardening, and potentially results in crack initiation. [3][4][5][6][7] Jiang et al [8] and Yang and Zhang [9] reported that different twin variants and twin-twin intersections are associated with the deformation stage with a higher strain hardening rate in AZ31 Mg alloy which is subjected to compression along the extrusion direction. Ma et al [10] and Oppedal et al [11] found that multivariants are activated to accommodate large straining and the subsequent twin-twin interaction contributes to a significant strain hardening.…”

“…The stress-strain response, texture evolution, and microstructure evolution under cyclic loading and non-proportional loading paths have been extensively studied using experiment and modeling. [2][3][4][5][6] Twinning and de-twinning are recognized to play crucial roles in developing the asymmetric stress-strain hysteresis loop, texture evolution, and initiation of fracture. [3,5,7] In properly oriented single crystals, multiple twins can be activated and interact with each other.…”

“…[2][3][4][5][6] Twinning and de-twinning are recognized to play crucial roles in developing the asymmetric stress-strain hysteresis loop, texture evolution, and initiation of fracture. [3,5,7] In properly oriented single crystals, multiple twins can be activated and interact with each other. As a consequence, their interaction and reactions develop a characteristic locked 'quilted looking' twinning structure (Figure 1(a)) which affects subsequent twinning and de-twinning, causes twinning-induced hardening, and potentially results in crack initiation.…”

“…Before mechanical testing, the observation surface of the specimen was chemically polished using a solution of one part of nitric acid, two parts of hydrochloric acid, and seven parts of ethanol. [15] The details of the mechanical testing setup can be found in [5]. The specimen was initially compressed to a strain of −0.75% and slightly unloaded to a strain of −0.725%, where we characterized the specimen surface by scanning electron microscopy and EBSD with a scan resolution of 0.5 μm.…”

The effect of thermo-mechanical processing on the structure, static mechanical properties and fatigue behaviour of pure Mg

“…The values of 2.2-3.0 MPa were measured for such behaviour in a single crystal by Q. Yu et al 25 and also the value of 2.4 MPa was published by the same author for a different monocrystal orientation. 26 Due to such limitations, complex dislocation structures are rather unlikely in magnesium under cyclic loading. 24,27 In the case of pure Mg, cyclic hardening is expected as has already been proved in 28 .…”