Joint enhancement on strength and toughness provides a cutting-edge research frontier for metals and alloys. Conventional strengthening methods typically lead to suppressed ductility and fracture toughness. Large-scale atomic simulation of the fracture process was performed here, featuring nanocrystals embedded with nano-scaled twin boundaries. Four toughening mechanisms by nano-scaled twin boundaries were identified: (i) crack blunting through dislocation accommodation along the nano-scaled twin boundaries; (ii) crack deflection in a manner of intragranular propagation; (iii) daughter crack formation along the nano-scaled twin boundaries that further enhances the toughness and (iv) curved twin-boundary planes owing to an excessive pileup of geometrically necessary dislocations. These toughening mechanisms jointly dictate the mechanical behavior of nano-structured materials, and provide insights into the application of nano-scaled twin boundaries with an aim to simultaneously obtain enhanced strength and toughness. New approaches to introduce these coherent internal defects into the nanostructure of crystalline materials were also proposed.

Toughening by Nano-Scaled Twin Boundaries in Nanocrystals. H.Zhou, S.Qu, W.Yang: Modelling and Simulation in Materials Science and Engineering, 2010, 18[6], 065002