<p>Aluminum-Silicon (Al-Si) alloys are often preferred in the die casting industry due to excellent castability, high strength, corrosion resistance and low cost. Commonly, iron (Fe) is alloyed with the alloys to prevent die soldering. However, the addition of Fe in most of Al-Si alloys leads to formation of the intermetallic β-AlFeSi. The β-AlFeSi is harmful to the alloy structural integrity due to its needle-like morphology that creates stress concentration at the microscopic level. The phase presence is unfavorable to the mechanical properties and significantly reduces the elongation of the alloys. This research attempted to find viable way to control the morphology and formation of the β-AlFeSi phase.</p> <p>Thermodynamic simulations were done to investigate the sequence of intermetallic formation and other phases at different alloy compositions. The analysis of solidification paths of different alloys provided the correlation between the phase formation sequence and the fraction of the β-AlFeSi phase. The analysis also identified the feasible region of alloy design for minimizing the β-AlFeSi formation. Based on the thermodynamics simulation analysis, five alloys of different compositions were designed to validate the finding of the simulation. </p> <p>The tensile test results of the alloys indicated that lowering the Fe content increases the elongation of the alloy. The results also showed that elongation was reduced with the increase of Si level due to the formation of eutectic Silicon. The change of both Fe and Mn did not significantly affect the mechanical property of the alloy when the ratio of Fe to Mn was constant. Microscopic analysis showed that lowering the Fe level had effectively altered the morphology of the β-AlFeSi needle like structure. The β-AlFeSi was found to be smaller in terms of size when Fe is lower, subsequently reducing the probability of β-AlFeSi phase to be stress riser and crack initiation. </p> <p>The influence of heat treatment to the mechanical property of the alloys was also studied. The mechanical result on the heat-treated samples indicated that heat treatment is a viable method to improve the elongation property of the alloy. Microscopic observations showed that the β-AlFeSi phase was broken into shorter structures over the solution heat treatment process, resulting in better elongation. </p>

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A hot chamber die casting machine designed for zinc was donated to Purdue University. This machine was slated for retrofit of components necessary for aluminum hot chamber die casting. Existing components designed for zinc, mainly H-13 and cast iron, do not have the necessary service life to economically produce castings due to chemical attack on machine components from molten aluminum. Multiple systems were redesigned, including the pot, plunger, gooseneck, furnace, and cooling lines. All components were upgraded to allow for the higher service temperatures needed for molten aluminum, along with a niobium gooseneck and anviloy nozzle to resist chemical attack of injection components. Once design and retrofitting were complete aluminum alloy A380 was used in conjunction with a niobium gooseneck design to create tensile bars. These tensile bars were subsequently tested and mechanical properties evaluated.

<p> Ferritic- Martensitic (F/M) alloys have been used in reactors as cladding steels, wrapper steels. They have Good creep strength, longer lifetimes, less corrosion Powder Metallurgy Hot Isostatic Pressing (PM- HIP) alloys have been suggested as an alternative to be able to improve reactor safety. Gaining a better understanding on how PM-HIP microstructures change under irradiation could make them more viable for widespread use in reactors   </p>

<p>Room-temperature liquid metal, such as eutectic gallium indium (EGaIn), has attracted significant attention for the fabrication of high-density electronics, functional composites, and two-dimensional nanomaterials due to the high electrical conductivity, high thermal conductivity, low toxicity, and its naturally formed oxide skin. Pulsed laser beams are proved to be promising to process liquid metal due to laser induced high temperature and high pressure. Although extraordinary progresses are made, limitations that remain in advanced manufacturing and material performance are crucial to overcome before liquid metal can be more practically used. The goal of this dissertation is to utilize the unique interaction between laser and liquid metal to design and fabricate nanomaterials with scalable functionalities towards potential device applications. </p> <p>This dissertation is composed of a general review of related background and experimental methods, followed by three chapters of detailed research and one chapter of conclusion. In the first research chapter, liquid metal is used, due to its high electrical conductivity and high fluidity, to create self-packaged, high-resolution liquid metal patterns by the advanced pulsed laser lithography (PLL) technology. The PLL method here, for the first time, can directly generate self-packaged liquid metal nano-patterns with high resolution without being limited by laser beam size. The electrically self-packaged material is an intriguing candidate to serve in demanding applications with high integration densities. In the second research chapter, liquid metal is utilized to boost the thermal conductivity of porous metal-organic frameworks (MOFs) to realize a high energy-harvesting efficiency. In this work, a facile and straightforward manufacturing method, laser shock-induced evaporation, is devised to deposit liquid metal nanoparticle (LMNP) thin layers to the surface of MOFs, resulting in the MOF@LMNP nanocomposites with a boosted thermal conductivity. In the last research chapter, liquid metal is employed to create large-scale metal oxide thin film patterns by an advanced confined laser transfer printing (CLTP) technique. This technology can generate metal oxide thin films patterns with tunable thickness and electrical property in nano-second scale that were previously inaccessible with conventional methods. This room temperature confined laser transfer printing method is promising to provide the possibility to pattern metal oxide thin films into advanced electronic components. As a summary, these studies present different laser manufacturing approaches in addressing liquid metal fabrication challenges from fundamental materials perspective. </p>

<p>  </p> <p>Materials performance under extreme conditions is pivotal to the design of advanced nuclear reactor materials. Nanocrystalline metals possess improved radiation resistance and superior mechanical properties. However, it remains a major challenge to stabilize the fine grains in nanocrystalline materials at elevated temperatures. The response of abundant interfaces and triple junctions to thermal annealing, plastic straining and radiation damage profoundly influence the overall performance of nanocrystalline metals. The objective of this thesis is to illustrate a new alloy design strategy via engineering the interfaces and triple junctions of triphase nanocomposites to enhance the thermal stability, mechanical strength and radiation tolerance of nanocrystalline metallic materials simultaneously. </p> <p>In triphase nanocomposites where each phase is nearly immiscible to the others, the triple junctions and phase boundaries form a 3D interlocking network that could significantly increase the thermal and radiation stability. In this thesis, two distinct triphase architectures were explored: nanolaminate and nanocrystalline Cu-Ag-Fe composites fabricated by magnetron sputtering. The effectiveness of Cu-Ag-Fe triphase triple junctions in mitigating thermal grooving was evaluated by considering grooving kinetics. Additionally, micropillar compression tests on Cu-Ag-Fe nanolaminate composites demonstrated substantial enhancement of strength and strain hardening capability comparing to Cu/Fe multilayers. The nanocrystalline Cu-Ag-Fe composites exhibited a distinct texture evolution and greatly enhanced resistance to grain coarsening. In situ sequential dual beam (He + Kr) irradiation studies show nanocrystalline Cu-Ag-Fe composites have a remarkable bubble swelling resistance, suggesting the strong He storage and defect annihilation capability of the triphase nanocomposites. The results obtained from this thesis provide innovative perspectives on the design of high strength nanostructured metals with enhanced thermal stability and radiation tolerance.</p>

<p>Thesis Abstract: Laser powder bed fusion (LPBF), a specialization within additive manufacturing, is a high precision metal powder processing technique that has gained immense attentions in the past decade. The layer-by-layer densification technique provides a unique set of abilities that permits the large-scale production of geometrically complicated structures with highly tunable microstructures. Alloy 718 (718) is one of the most studied materials within the LPBF field due to its extraordinary printability. Although it has a significant industrial and academic focus, there are consequential questions that still need to be addressed because of the immense LPBF design space.</p><p>Our works demonstrate the multiple pathways that an alloy system like 718 can be optimized for specific applications by altering the processing parameters or by the addition of oxide particles to create a fine dispersion for high temperature capabilities. Room temperature tensile testing revealed that the processing parameters directly controlled the mechanical properties, allowing tailoring of the tensile strength and elongation to the needs of specific applications. Similar experiments were conducted to exhibit the flexibility of LPBF by incorporating a wider, economic, bimodal powder size distribution that maintained similar mechanical properties. Additions of oxide particles enabled the findings of the reactive nature within this welding process, which ultimately led to a refined oxide dispersion strengthened (ODS) 718 matrix with superior mechanical properties up to 900$^\circ$C. This novel metal matrix ceramic was lastly showcased by producing a complex microlattice structure. Detailed in-situ tensile tests in combination with electron backscatter diffraction (EBSD) and finite element modeling revealed that crystallographic reorientation around bending nodes enhanced the global ductility of the material.</p>

<p> Low-temperature, lead-free solders mitigate heating-induced warpage caused by the  differences in coefficient of thermal expansion between printed circuit boards (PCBs), substrates,  and dies during package assembly. Eutectic and near-eutectic Sn-Bi solders are promising low  temperature candidates because they show high reliability at low strain rates during thermal  cycling. However, Sn-Bi low temperature solder (LTS) has poor performance at high strain rates  during drop-shock testing. Alloying additions such as Ag, Cu, and Sb have been shown to increase  the ductility and strength of eutectic Sn-Bi and therefore improve the overall reliability during both  thermal cycling and drop-shock. Small Sb additions to Sn-Bi LTS are of particular interest because  these additions significantly increase ductility while maintaining the tensile strength. This increase  in ductility was previously attributed to small SnSb intermetallic particles that form within the Sn  phase on the interface of Sn and Bi in 1.0wt% Sb containing samples. Despite the fact the no SnSb  intermetallic compound (IMC) particles have been found in 0.5Sb-42Sn-Bi samples in any  previous studies or in our own studies, it was thought that the SnSb IMC particles were responsible  for the improved reliability and ductility of Sn-Bi.  This work encloses our efforts to understand how small Sb additions to eutectic Sn-Bi  impact the solder microstructure and the resulting mechanical properties of the solder alloy. We  began by studying possible solidification pathways through phase diagram analysis in Thermo?Calc to understand how the microstructure is predicted to develop and compared these models to  the literature data. Next, we analyzed the microstructures of our custom Sb-containing alloys  through a combination of scanning electron microscopy (SEM), energy dispersive spectroscopy  (EDS), and electron probe microanalyzer-wavelength dispersive spectroscopy (EPMA-WDS) and  determined that no SnSb IMC particles were found in the 0.5Sb-42Sn-Bi alloy and at 0.5 wt% the  Sb remained in solid solution with Sn. Nanoindentation was then used to evaluate the strain rate  sensitivity of Sn-Bi LTS with Sb additions and we found that, while the alloy hardness remains  sensitive to different strain rates, the Sb in solid solution with Sn altered the deformation behavior  of the alloy and decreased the amount of planar slip during indentation. To study the stability of  the microstructure and the alloy behavior in use, shear testing was performed before and after  isothermal aging. Our results suggest that Sb in solid solution with the Sn-rich phase contributes  significantly to the changes in the eutectic microstructure and the mechanical properties. </p>