Microstructural and Mechanical Characterization of Additively Manufactured Binary Metallic Alloys

Citation

Tran, Thomas Tuan (2025) Microstructural and Mechanical Characterization of Additively Manufactured Binary Metallic Alloys. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/ej4t-7e95. https://resolver.caltech.edu/CaltechTHESIS:05292025-003646523

Abstract

Hydrogel infusion-based additive manufacturing (HIAM) is a chemically versatile solid-state processing pathway that allows 3D structuring of ceramics and metals with micro-scale precision. Using controlled thermal treatments of 3D-printed metal ion-infused gels, this process generates intricate microstructures which are heavily influenced by the kinetics of gas-solid reactions and their subsequent phase evolution. This work seeks to refine our understanding of the process-structure-property relationships in HIAM-produced alloys and provide general insights for AM-enabled alloy development and microstructure design using metal oxide reduction.

Through HIAM, we demonstrate the arbitrary alloying of Cu_xNi_1-x binary alloys, where systematic characterization of microstructures down to the atomic scale revealed that reduction, or the lack thereof, drove the formation of chemically homogeneous alloy grains with numerous annealing twins and entrapped unreduced oxide nano-inclusions, resulting in a hierarchical two-phase composite. These features appear to elevate the average nanoindentation hardnesses by up to four times that of bulk annealed Cu_xNi_1-x and lead to a composition dependence on the scaling of the “smaller is stronger” size effect in uniaxial micropillar compressions. This compositional dependence of hardness and deformation mechanisms arises from changes in reduction kinetics which influence the density of inclusions and voids developed by HIAM processing. As a result, HIAM demonstrates the capability to fabricate heterogeneous alloy systems as a result of their oxide reduction pathways, which are revealed by thermogravimetry experiments and kinetic analysis.

Thesis Files