<p>Through thousands of years of evolution, natural biological systems have optimized their structures to thrive in diverse ecological conditions. Extracting and leveraging the inherent design principles of these biological systems can provide inspiration for the development of advanced lightweight structural materials. To effectively facilitate this transition, it is crucial to understand the specific mechanisms by which the microstructure of biological materials influences their mechanical properties. This dissertation focuses on understanding microstructure-property correlations in three biological systems: Venus flower basket, Cholla cactus, and Organ pipe coral.</p> <p>The Venus flower basket exhibits a cylindrical cage-like structure made from a complex network of silica fibers which exhibit a core-shell like layered architectures. A novel multimodal approach involving nanoindentation, ex situ and in situ fiber testing, and post-failure fractography was utilized to precisely understand the impact of the layered structure on the tensile and fracture behavior of fibers. The observation of fibers in real-time revealed, for the first time, that the initiation of failure occurs at the fiber's surface and progressively advances towards the core, traversing multiple layers. The concentric layers encompassing the central core act sacrificially, employing various toughening mechanisms to protect the core. Furthermore, nanoindentation experiments performed in situ in water shed light on the significance of the layered fiber structure in a marine environment. Another interesting system is the Cholla cactus. In arid environments, Cholla cactus produces porous wood with a mesh-like structure. To comprehensively understand the structure, properties, and designs of Cholla cactus wood, various techniques such as x-ray tomography, scanning electron microscopy, nanoindentation, and finite element simulations were employed. The structure and function of different wood components was investigated from both biological and mechanical behavior perspectives. The impact of the unique structure of wood components on the design of engineering materials is discussed. Finally, the dissertation focuses on the Organ pipe coral, which exhibits a hierarchical structure comprising vertical tubes and horizontal platforms at the macrostructure level. At the microstructure level, cells are formed through a unique arrangement of micrometer-sized plates made of calcium carbonate. Nanoindentation was used to assess the impact of this hierarchical structure on micromechanical properties. The results unveiled distinct toughening mechanisms operating at different length scales within the coral.</p> <p>17</p> <p>By gaining a precise understanding of the correlations between microstructure and properties in various biological materials, this research provides valuable insights for the design of advanced architected structural materials. The unique interplay between microstructure, function, and properties is discussed.</p>

Additive manufacturing technologies, particularly electron beam powder bed fusion (PBF-EB/M), are becoming increasingly important for the processing of intermetallic titanium aluminides. This study presents the effects of hot isostatic pressing (HIP) and subsequent two-step heat treatments on the microstructure and mechanical properties of the TNM-B1 alloy (Ti–43.5Al–4Nb–1Mo–0.1B) fabricated via PBF-EB/M. Adequate solution heat treatment temperatures allow the adjustment of fully lamellar (FL) and nearly lamellar (NL-β) microstructures. The specimens are characterized by optical microscopy and scanning electron microscopy (SEM), X-ray computed tomography (CT), X-ray diffraction (XRD), and electron backscatter diffraction (EBSD). The mechanical properties at ambient temperatures are evaluated via tensile testing and subsequent fractography. While lack-of-fusion defects are the main causes of failure in the as-built condition, the mechanical properties in the heat-treated conditions are predominantly controlled by the microstructure. The highest ultimate tensile strength is achieved after HIP due to the elimination of lack-of-fusion defects. The results reveal challenges originating from the PBF-EB/M process, for example, local variations in chemical composition due to aluminum evaporation, which in turn affect the microstructures after heat treatment. For designing suitable heat treatment strategies, particular attention should therefore be paid to the microstructural characteristics associated with additive manufacturing.