Multiscale Microstructural and Mechanical Characterization of Cu-Ni Binary Alloys Reduced During Hydrogel...

Hydrogel infusion-based additive manufacturing (HIAM) is a chemically versatile solid-state processing pathway that allows 3D structuring of ceramics and alloys with micro-scale precision. Using thermal treatments of 3D-printed metal ion-infused gels, this process generates intricate microstructures throughout their complex phase evolution. Through investigation of the HIAM-produced Cu_xNi_1-x alloy system, substantial grain growth after reduction is shown to drive the formation of numerous annealing twins and entrap unreduced oxide nano-inclusions, resulting in hierarchical composite microstructures. These features appear to elevate the average nanoindentation hardnesses by up to four times that of bulk annealed Cu_xNi_1-x. Uniaxial compression of micropillars milled from individual grains reveals composition dependence on the scaling of the "smaller is stronger" size effect. This compositional dependence of deformation mechanisms arises from changes in reduction kinetics which influence the density of inclusions and voids developed by the HIAM process. This work highlights the rich microstructural landscape accessible to HIAM-produced alloys and provides a useful pathway for the characterization and tuning of superior mechanical performance in additively manufactured alloys.