In situ observation of the effect of the twin boundary orientation on the mechanical properties of single crystalline Ni

The construction of twin boundaries (TBs) in materials is a remarkable way of promoting their strength and ductility. However, the effects of TB orientation on the mechanical properties have not been reported experimentally so far. Using a state-of-the-art in situ tensile stage equipped in a transmission electron microscope, uniaxial tensile tests were performed on three single-crystalline Ni samples with TB parallel and perpendicular to the tensile direction and no TB. The results showed that the uniform tensile elongation strongly depends on TB, 120% for the perpendicular TB sample, 99% for the parallel TB sample, and only 55% for the no TB sample. In addition, dislocation interaction before reaching the perpendicular CTB contribute to cross-slip and dynamic formation of dislocation jogs, thereby improving strain hardening and resulting in a large uniform tensile elongation.