ASU Electronic Theses and Dissertations
This collection includes most of the ASU Theses and Dissertations from 2011 to present. ASU Theses and Dissertations are available in downloadable PDF format; however, a small percentage of items are under embargo. Information about the dissertations/theses includes degree information, committee members, an abstract, supporting data or media.
In addition to the electronic theses found in the ASU Digital Repository, ASU Theses and Dissertations can be found in the ASU Library Catalog.
Dissertations and Theses granted by Arizona State University are archived and made available through a joint effort of the ASU Graduate College and the ASU Libraries. For more information or questions about this collection contact or visit the Digital Repository ETD Library Guide or contact the ASU Graduate College at gradformat@asu.edu.
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- All Subjects: chemical engineering
- Creators: Azeredo, Bruno
Description
In recent years, the scientific community around the synthesis and processing of nanoporous metals is striving to integrate them into powder metallurgy processes such as additive manufacturing since it has a potential to fabricate 3D hierarchical high surface area electrodes for energy applications. Recent research in dealloying – a versatile method for synthesizing nanoporous metals – emphasized the need in understanding its process-structure relationships to independently control the relative density, ligament and pore sizes with good process reproducibly. In this dissertation, a new understanding of the dealloying process is presented for synthesizing (i) nanoporous gold thin-films and (ii) nanoporous Cu spherical powders with an emphasis on understanding variability in their process-structure relationships and process scalability. First, this work sheds the light on the nature of the dealloying front and its percolation along the grain boundaries in nanocrystalline gold-silver thin films by studying the early stages of ligament nucleation. Additionally, this work analyses its variability by investigating new process variables such as (i) equilibration time and (ii) precursor aging and their impacts in achieving process reproducibility. The correlation of relative density with ligament size is contextualized with state-of-the-art data mining research. Second, this work provides a new methodology for large scale production of nanoporous Cu powder and demonstrates its integration with powder casting to fabricate porous conductive electrode. By understanding the influence of etching solution concentration and titration methodology on the structure and composition of nanoporous Cu, it was possible to fabricate precipitate-free powders at high throughputs. Further, the nature of oxygen incorporation into porous Cu powder was studied as a function of surface-to-volume ratio of powder in atmospheric conditions. To consolidate powders into parts via open-die casting, this work harvests Ostwald Ripening phenomena associated with thermal coarsening in nanoporous metals to weld them at low temperatures (approximately one-third of its melting temperature). This work represents a major step towards the integration of nanoporous Cu feedstocks into additive manufacturing.
ContributorsNiauzorau, Stanislau (Author) / Azeredo, Bruno (Thesis advisor) / Sieradzki, Karl (Committee member) / Song, Kenan (Committee member) / Chawla, Nikhilesh (Committee member) / Arizona State University (Publisher)
Created2022
Description
Corrosion is one of the key failure modes for stainless steel (SS) piping assets handling water resources managed by utility companies. During downtime, the costs start to incur as the field engineer procures its replacement parts. The parts may or may not be in stock depending on how old, complex, and common the part model is. As a result, water utility companies and its resilience to operate amid part failure are a strong function of the supply chain for replacement piping. Metal additive manufacturing (AM) has been widely recognized for its ability to (a) deliver small production scales, (b) address complex part geometries, (c) offer large elemental metal and alloy selections, (d) provide superior material properties. The key motive is to harvest the short lead time of metal AM to explore its use for replacement parts for legacy piping assets in utility-scale water management facilities. In this paper, the goal was to demonstrate 3D printing of stainless steel (SS) 316L parts using selective laser melting (SLM) technology. The corrosion resistance of 3D printed SS 316L was investigated using (a) Chronoamperometry (b) Cyclic Potentiodynamic Polarization (CPP) and Electrochemical Impedance Spectroscopy (EIS) and its improved resistance from wrought (conventional) part was also studied. Then the weldability of 3D printed SS 316L to wrought SS 316L was illustrated and finally, the mechanical strength of the weld and the effect of corrosion on weld strength was investigated using uniaxial tensile testing. The results show that 3D printed part compared to the wrought part has a) lower mass loss before and after corrosion, (b) higher pitting potential, and (c) higher charge transfer resistance. The tensile testing of welded dog bone specimens indicates that the 3D printed parts despite being less ductile were observed to have higher weld strength compared to the wrought part. On this basis, metal AM holds great value to be explored further for replacement piping parts owing to their better corrosion resistance and mechanical performance.
ContributorsSampath, Venkata Krishnan (Author) / Azeredo, Bruno (Thesis advisor) / Torres, Cesar (Committee member) / Mu, Bin (Committee member) / Arizona State University (Publisher)
Created2021