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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- Creators: Mobasher, Barzin
- Creators: Seetharaman, Sridhar
Description
High-temperature mechanical behaviors of metal alloys and underlying microstructural variations responsible for such behaviors are essential areas of interest for many industries, particularly for applications such as jet engines. Anisotropic grain structures, change of preferred grain orientation, and other transformations of grains occur both during metal powder bed fusion additive manufacturing processes, due to variation of thermal gradient and cooling rates, and afterward during different thermomechanical loads, which parts experience in their specific applications, could also impact its mechanical properties both at room and high temperatures. In this study, an in-depth analysis of how different microstructural features, such as crystallographic texture, grain size, grain boundary misorientation angles, and inherent defects, as byproducts of electron beam powder bed fusion (EB-PBF) AM process, impact its anisotropic mechanical behaviors and softening behaviors due to interacting mechanisms. Mechanical testing is conducted for EB-PBF Ti6Al4V parts made at different build orientations up to 600°C temperature. Microstructural analysis using electron backscattered diffraction (EBSD) is conducted on samples before and after mechanical testing to understand the interacting impact that temperature and mechanical load have on the activation of certain mechanisms. The vertical samples showed larger grain sizes, with an average of 6.6 µm, a lower average misorientation angle, and subsequently lower strength values than the other two horizontal samples. Among the three strong preferred grain orientations of the α phases, <1 1 2 ̅ 1> and <1 1 2 ̅ 0> were dominant in horizontally built samples, whereas the <0 0 0 1> was dominant in vertically built samples. Thus, strong microstructural variation, as observed among different EB-PBF Ti6Al4V samples, mainly resulted in anisotropic behaviors. Furthermore, alpha grain showed a significant increase in average grain size for all samples with the increasing test temperature, especially from 400°C to 600°C, indicating grain growth and coarsening as potential softening mechanisms along with temperature-induced possible dislocation motion. The severity of internal and external defects on fatigue strength has been evaluated non-destructively using quantitative methods, i.e., Murakami’s square root of area parameter model and Basquin’s model, and the external surface defects were rendered to be more critical as potential crack initiation sites.
ContributorsMian, Md Jamal (Author) / Ladani, Leila (Thesis advisor) / Razmi, Jafar (Committee member) / Shuaib, Abdelrahman (Committee member) / Mobasher, Barzin (Committee member) / Nian, Qiong (Committee member) / Arizona State University (Publisher)
Created2022
Description
The purpose of this study was to comprehend the global warming potential (GWP), cost variability, and competitiveness of steel with rising carbon taxes. Aluminum, glass fiber composite, and carbon fiber composite were chosen as competing materials. In order to compare the aforementioned factors, the GWP of several processes to produce steel, aluminum, and fiber composites was examined. Cost analyses of various methods were also carried out to determine their viability. Energy consumption data for each of the paths under consideration were taken from the literature for the study. To get the consistent GWP for traditional and decarbonized scenarios, the required energy is multiplied with corresponding energy source (natural gas or electricity). Even after accounting for the carbon tax and the weight-reduction factor, the results show that steel still has the lowest production costs, followed by aluminum, while fiber composites remain the most costly. EAF- steel and secondary aluminum has least GWP followed by H2-DRI (Hydrogen- Direct Reduced Iron)steel and NG-DRI (Natural Gas- Direct Reduced Iron) steel with carbon capture and storage (CCS). The state of art technology for glass fiber reinforced composite also emits less carbon dioxide but the cost of production is still high. Carbon fiber reinforced composite emits most carbon dioxide and is least economical.
ContributorsRajulwar, Vaishnavi Vijay (Author) / Seetharaman, Sridhar (Thesis advisor) / Emady, Heather (Committee member) / Nian, Qiong (Committee member) / Arizona State University (Publisher)
Created2023