Segregation at defective twin boundaries enables high strength and ductility in a nano-twinned Ni alloy

The nano-twin boundary (NTB) is not perfectly flat, but inherently decorated with certain amounts of steps comprising partial dislocations. With the decreasing of twin spacing, material softening may be induced by the premature gliding of partial dislocations along NTBs. In the present work, the nano-twinned Ni alloy with Cr enrichment at the steps on the NTBs was fabricated via rolling and subsequent annealing treatments. It was found that Cr enrichment could stabilize NTBs for enhancing the strength and uniform elongation simultaneously. The enhanced strength could be ascribed to a similar to 86 MPa increment on the critical resolved shear stress of dislocations gliding along NTBs, which was determined by a combination of miniature tensile testing and electron backscattered diffraction analyses. Furthermore, with plastic straining, Cr enrichment could act as obstacles for dislocation motion, thereby facilitating dislocations accumulation at the NTs, which is indispensable for improving the material tensile ductility.