Plastic deformation mechanisms in bimodal structured metals
An emerging class of heterogeneous nanostructured materials, including bimodal, gradient, hierarchical structures, has attracted increasing attention due to the extraordinary mechanical behaviors such as ultrahigh strength and better tensile ductility, when compared with their homogeneous counterparts. This suggests that the structural heterogeneity intentionally engineered into the materials is essential to promote hardening mechanisms and improve the uniform tensile strain. In this thesis, we focus on plastic deformation and its associated mechanisms in bimodal nanostructured metals. By varying the size of small grain in bimodal structure, we find the intragranular plastic deformation is enhanced because of activation and storage of extra dislocations. This dislocation-mediated forest hardening increases the material strength, alleviating the strength softening in the reverse Hall-Petch regime. These findings may be beneficial to designing heterogeneous structured metals with improved ductility-strength synergy.