Combining synergetic effects of gradient nanotwins and nanoprecipitates in heterogeneous bronze alloy

Both strengthening effects of gradient nanostructure (especially the gradient nanotwins) and nanoprecipitates have been well-recognized to simultaneously improve the mechanical properties of metallic materials, e.g., the high strength–ductility synergy. In this study, a surface mechanical attrition treatment technique has been applied to fabricate a gradient nanostructured bronze alloy (Cu-12Sn-1.5Ni-0.6Fe) with pre-nanoprecipitates. Atomic-scale investigations were performed to capture the microstructural evolution governing the gradient refinement process along the depth direction of the treated alloy. On one hand, the body-centered cubic (bcc) Fe-rich pre-nanoprecipitates are found to be well-retained in the fabricated gradient nanostructured specimen. On the other hand, it is interesting to reveal that the semi-coherent interfacial zones between the bcc Fe-based nanoprecipitates and face-centered cubic (fcc) Cu matrix with the specific distribution of misfit dislocations could facilitate the nucleation and growth of gradient nanotwins along the depth direction. Specifically, the twinning partials could be associated with the dissociations of the misfit dislocations in the semi-coherent interfacial region, which is evidenced by the concomitant fcc-Cu/bcc-Fe/nanotwin triplex. As a result, the synergetic strengthening effects of gradient nanotwins and nanoprecipitates are combined to enhance the strength–ductility synergy and work hardening capacity. Moreover, in situ transmission electron microscope observations were conducted to understand the synergetic strengthening mechanisms of the gradient nanotwins and nanoprecipitates during the dynamic cracking process in the fabricated gradient nanostructured bronze alloy. The strategy of combining the nanoprecipitates and gradient nanostructure synergetic effects in our work might offer a novel pathway for designing high-performance metallic materials.