Influence of Temperature on Plastic Deformation Behavior and Mechanism of Bismuth Single Crystals

Tensile tests were performed on bismuth single crystals in the [0001] (c-axis), [2\(\bar{1}\bar{1} \)0] (a 1-axis), [10\(\bar{1} \)0] and [1\( \bar{1} \)00] directions of bismuth single crystals to investigate the influence of temperature on plastic deformation behavior. The plastic deformation at 298 K was caused by slip on the secondary slip system in the [0001] direction, or by twinning and slip deformation in twins subsequent to the twining deformation in the [2\(\bar{1}\bar{1} \)0] direction. Those mechanisms resulted in ductile characteristics in tension. Only deformation twinning, however, was observed along the [10\(\bar{1}\)0] and [1\(\bar{1} \)00] directions, which lead to brittle fracture. At elevated temperature (423 K), deformation twinning was not found to occur along any of the examined directions. Crystallographic slip was the predominant deformation mechanism along the [2\(\bar{1}\bar{1} \)0], [10\(\bar{1} \)0] and [1\(\bar{1} \)00] directions at 423 K. This is attributed to the activation of the {1\(\bar{1} \)02} or {1\(\bar{1} \)02} slip system which are inactive at 298 K. Along the [0001] direction at 423 K, the {0\(\bar{1} \)11} was active and its critical resolved shear stress (τ crss) does not coincide with that corresponding to the {1\(\bar{1} \)02} and {1\(\bar{1} \)02} systems. Therefore, it can be concluded that difference in τ crss between slip systems causes anisotropy in mechanical behavior at 423 K.