Unraveling the origin of ductility in multilayered Ti/Nb composites: role of dislocation evolution

Dislocation evolution in multilayered Ti/Nb composites processed by accumulative roll bonding under uniaxial tension was quantitatively evaluated by high-energy X-ray diffraction. The composites with different heterogeneous microstructures show distinct dislocation activities in Ti, which majorly contributes to their different ductility. For the composite in which extensive shear bands have formed before loading, the stable fraction of < c+a > dislocations and the suppressed activation of < c > dislocations contribute to its uniform deformation. We emphasize that tracking the dynamic evolution of dislocations is fundamental for understanding ductility of the multilayers, whereas the increased < c+a > dislocations found by post-mortem analysis do not necessarily dominate.