A Plastic Deformation Mechanism by Necklace Dislocations Near Crack-like Defects in Nanotwinned Metals

Nanotwinned metals are a class of hierarchically structured materials that appear to transcend the limits of conventional material systems by exhibiting an exceptional combination of superior strength, ductility and resistance to fracture, fatigue, and wear. Recently, we reported a type of necklace dislocations in nanotwinned metals which become operative when the twin boundary (TB) spacing falls below a few nanometers. Here, we show that the presence of a cracklike defect as the dominant dislocation source could allow the same mechanism to operate at much larger twin spacings. This finding calls for further theoretical and experimental investigations of a new type of TB related dislocation mechanism which may play particularly important roles in crack-tip deformation in nanotwinned metals.