Microstructure and tensile behavior of nanostructured gradient TWIP steel

Gradient structured metals have shown unique mechanical properties, such as high strength and good ductility. In this study, a gradient TWIP steel was fabricated by surface mechanical grinding treatment. The subsequent gradient structures consist of an outermost nanolaminate layer, a layer of deformation twins mixed with shear bands, and a deformation twinned layer. Tensile studies reveal that the introduction of gradient structures increases the yield strength significantly. Deformation induced hardening reaches maxima at the interface regions between the layers, presumably due to the distinct transition of high angle grain boundaries and twin boundaries near the interfaces and the accumulation of geometrically necessary dislocations under tension. These in-depth studies provide insight into the design of high-strength, strain hardenable metallic materials with gradient structures.