<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>

No description available.

The Reduced Enrichment for Research and Test Reactor (RERTR) now known as the Material Minimization and Management Reactor Control program (MMMRC) seeks to replace the use of highly enriched uranium (HEU) fuels used in research and test nuclear reactors around the world. The low enriched uranium (LEU) fuels must have fissionable uranium densities comparable to the HEU fuels. After extensive investigation by various researchers around the world, the U-Mo alloys were selected as a promising candidate. The Mo alloyed with U allows for the stabilization of the face-centered cubic ?-U phase, which demonstrated favorable irradiation behavior. However, deleterious diffusional interaction between the fuel and the cladding, typically Al-base alloy, remain a challenge to overcome for application of U-Mo alloys as the LEU fuel. Zr has been identified as a potential diffusion barrier between monolithic U-10 wt.% Mo (U10Mo) metallic fuel and AA6061 cladding alloys for the development of a LEU fuel system. However, interdiffusion and reaction between the Zr barrier and U10Mo fuel can produce phases such as Mo2Zr, and promote the destabilization of ?-U phase into ?'-U (U2Mo) and ?-U. In order to better understand this phenomenon, this study examined the phases that are present in the U10Mo alloys with varying Zr concentration, 0, 0.5, 1.0, 2.0, 5.0, 10.0, 20.0 wt.% at room temperature after heat treatment at 900°C for 168 hours and 650°C for 3 hours. These two temperatures are relevant to fuel plate fabrication process of homogenization and hot-rolling, respectively. Scanning electron microscopy and X-ray diffraction were employed to identify and quantitatively document the constituent phases and microstructure to elucidate the nature of phase transformations. For U10Mo alloys containing less than 1.0 wt.% Zr, there was no significant formation of Mo2Zr after 900?C homogenization and subsequent heat treatment at 650?C for 3 hours. The ?-U phase also remained stable correspondingly for these alloys containing less than 1.0 wt.% Zr. For U10Mo alloys containing 2 wt.% or more Zr, a significant amount of Mo2Zr formation was observed after 900?C homogenization and subsequent heat treatment at 650?C for 3 hours. For these alloys, destabilization of ?-U into ?'-U (U2Mo), UZr2 and ?-U was observed. The alloy containing 20 wt.% Zr, however, did not demonstrate ?-U decomposition even though Mo2Zr was observed after heat treatments. The formation of Mo2Zr effectively reduced the stability of the metastable ?-U phase by depleting the ?-stabilizing Mo. The destabilization of ?-U phase into the ?-U phase is not favorable due to anisotropic and poor irradiation behavior of ?-U phase. Therefore the formation of Mo2Zr at the interface between U10Mo fuel and Zr diffusion barrier must be carefully controlled during the fabrication of monolithic LEU fuel system for successful implementation.

Yes / Titanium alloys are known for their excellent corrosion resistance; however, low surface hardness results in poor wear resistance, which limits its potential application. This study employs a novel two-step process to embed a hard Ni coating containing a mixture of nanosized particles (Al2O3 and TiO2) into the surface of the Ti-6Al-4V alloy using an electric arc produced during the inert tungsten gas welding process. The surface of the sample was evaluated using Vickers Microhardness, Scanning electron microscopy, Energy dispersive spectroscopy and pin-on-plate wear testing. Microstructural analysis showed that impregnating the titanium surface with Ni/(Al2O3 and TiO2) nanomaterials resulted in the formation of a hard martensitic structure to a depth of approximately 2 mm below the surface. The changes observed are driven by modification of the surface chemistry and the presence of nickel, causing grain size reduction, solid solution strengthening and dispersion strengthening of the treated layer by the nanoparticles. The hardness of the treated layer increased by more than 180% when 40 nm Al2O3 and 30 nm TiO2 particles were embedded into the surface. Similarly, the wear resistance of the treated surface improved by 100%.

<p> The stress relieving mechanisms in two different batches of thermal-shock resistant calcia-PSZ have been investigated. The nature of the stress relief in the two materials appears to result from the transformation of the pure ZrO₂ component of the microstructure at temperatures below, within, and above the normal transformation temperature range. In the batch #1 material, which contains a larger volume fraction of monoclinic phase, the cubic matrix material behaves in a "brittle" fashion resulting in the production of a high density of microcracks in the body. The density of these cracks is such that the level of energy that can be stored in the body is limited and thermal shock resistance results. The batch #2 material contains considerably less monoclinic material and the evidence suggests that the cubic matrix within it can act in a ductile fashion. This ductility together with the twinning of the monoclinic component of the microstructure possibly relieves the stresses developed in the material on thermal shock. </p> <p> In the batch #2 material, large platelets were observed to develop following thermal cycling from temperatures above those of the normal transformation. It has been demonstrated that stress plays a major role in the development of these features. In view of the possible ductility of the cubic matrix in this material it is suggested that the thermal cycling "works" the material, texturing the pure zirconia component in it, so leading to the development of the observed platelets. </p> / Thesis / Master of Engineering (ME)

No description available.

Currently, there are two major driving forces for considering alternative materials to lead- based products, specifically interconnections, in electronics applications, including the impending legislation or regulations which may tax, restrict, or eliminate the use of lead and the trend toward advanced interconnection technology, which may challenge the limits of present soldering technology. The reliability of solder joints is a concern because fracture failures in solder joints accounts for 70% of failures in electronic components. Lead-free solders are being investigated as replacements for lead solders currently used in electronics. Thermo-mechanical properties describe the stresses accumulated due to thermal fatigue as a result of CTE mismatch within the system. By understanding the failure mechanisms related to lead-free solders, the application of lead- free solders could be more strategically designed for specific applications. The objective of this thesis is to observe microstructural change in large-area solder joints caused by thermal cycling and relate these changes to reliability issues in large-area lead and lead-free solder constructed semiconductor power devices. This study focused on the microstructural changes within the solder alloy of a large-area solder joint under thermal cycling conditions. Two major primary observations were made from this research, they are: 1) due to a combination of testing conditions and material properties, the lead-free solders, Sn/3.5Ag and Sn/Ag/0.7Cu, sustained the most severe damage as compared to Sn/37Pb, and 2) due to elevated stresses at the solder/substrate interface in a simulated power semiconductor device sample damage was found to be most severe. / Master of Science

Yes / Construction and demolition waste (CDW) has been recently identified as a potential aluminosilicate source for geopolymers. However, the available research has mainly focused on developing CDW-based geopolymer pastes and mortars, while studies on geopolymer concretes sourced from CDW have been very limited. Thus, the current study aimed at experimentally identifying different CDW materials suitable for producing geopolymer concretes. Additionally, the study analysed the mechanical, microstructural, and environmental properties of CDW- based geopolymer concrete produced. In this regard, the effect of relevant parameters on the compressive strength development of CDW-based geopolymer concretes was comprehensively investigated, including those related to precursor types/fineness, alkali activator solution, aggregate type/size and curing regimes. Microstructural analyses were also conducted on the selected samples (100% brick waste, 100% tile waste, 100% concrete waste and 75% brick waste + 25% GGBS). Finally, the environmental impact of geopolymer concrete was assessed and compared with similar traditional concrete. Results showed that employing CDWs alone is not suitable to achieve sufficient strengths under all curing regimes. However, the inclusion of 25% GGBS significantly improved the strength performance of CDW-based geopolymer concrete, in comparison to other supplementary cementitious materials (SCMs) such as Class-C fly ash and calcium hydroxide. The particle size of CDWs and concentration of alkaline activators highly affect the performance of CDW-based geopolymer concretes. Utilization of CDWs with particles finer than 75 μm and high concentrations of NaOH (12 M) is recommended to achieve good performance. The results also indicate that almost similar energy is needed for producing CDW-based geopolymer and OPC-based traditional concrete, whereas a huge reduction in CO2 emission (∼40%) was estimated in the case of geopolymers. The outcomes of the current study are expected to contribute to the advancement of geopolymer concrete derived from CDW in addition to providing valuable insights into this type of concrete for practitioners and academics.

In this study, we have investigated the relationship between the process-microstructure to predict and modify the material's properties. Understanding these relationships allows the identification and correction of processing deficiencies when the desired properties are not achieved, depending on the microstructure. Hence, the co-relation between process-microstructure-properties helped reduce the number of experiments, materials & tool costs and saved much time. In the case of high entropy alloys, friction stir welding (FSW) causes improved strength due to the formation of fine grain structure and phase transformation from f.c.c to h.c.p. The phase transformation is temperature sensitive and is studied with the help of differential scanning calorimetry (DSC) to calculate the enthalpy experimentally to obtain ΔGγ→ε. The second process discussed is heat treatment causing precipitation evolution. Fundamental investigations aided in understanding the influence of strengthening precipitates on mechanical properties due to the aging kinetics – solid solution and variable artificial aging temperature and time. Finally, in the third case, the effect of FSW parameters causes the thermal profile to be generated, which significantly influences the final microstructure and weld properties. Therefore, a computational model using COMSOL Multiphysics and TC-Prisma is developed to generate the thermal profile for different weld parameters to understand its effect on the microstructure, which would eventually affect and predict the final properties of the weld. The model's validation is done via DSC, TEM, and mechanical testing.

In the present study both fusion based - laser powder bed fusion (LPBF), and solid state - additive friction stir deposition (AFSD) additive manufacturing processes were employed for the manufacturing of a metastable high entropy alloy (HEA), Fe40Mn20Co20Cr15Si5 (CS-HEA). A processing window was developed for the LPBF and AFSD processings of CS-HEA. In case of LPBF, formation of solidification related defects such as lack of fusion pores (for energy density ≤ 31.24 J/mm3) and keyhole pores (for energy density ≥ 75 J/mm3) were observed. Variation in processing conditions affected the microstructural evolution of the metastable CS-HEA; correlation between processing conditions and microstructure of the alloy is developed in the current study. The tendency to transform and twin near stress concentration sites provided excellent tensile and fatigue properties of the material despite the presence of defects in the material. Moreover, solid state nature of AFSD process avoids formation of solidification related defects. Defect free builds of CS-HEA using AFSD resulted in higher work hardening in the material. In summary, the multi-processing techniques used for CS-HEA in the present study showcase the capability of the AM process in tailoring the microstructure, i.e., grain size and phase fractions, both of which are extremely critical for the mechanical property enhancement of the alloy.