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High Performance Thermal Barrier Coatings on Additively Manufactured Nickel Base Superalloy Substrates
(2023-08) Dube, Tejesh Charles; Zhang, Jing; Jones, Alan S.; Koo, Dan Daehyun; Yang, Shengfeng
Thermal barrier coatings (TBCs) made of low-thermal-conductivity ceramic topcoat, metallic bond coat and metallic substrate, have been extensively used in gas turbine engines for thermal protection. Recently, additive manufacturing (AM) or 3D printing techniques have emerged as promising manufacturing techniques to fabricate engine components. The motivation of the thesis is that currently, application of TBCs on AM’ed metallic substrate is still in its infancy, which hinders the realization of its full potential. The goal of this thesis is to understand the processing-structure-property relationship in thermal barrier coating deposited on AM’ed superalloys. The APS method is used to deposit 7YSZ as the topcoat and NiCrAlY as the bond coat on TruForm 718 substrates fabricated using the direct metal laser sintering (DMLS) method. For comparison, another TBC system with the same topcoat and bond coat is deposited using APS on wrought 718 substrates. For thermomechanical property characterizations, thermal cycling, thermal shock (TS) and jet engine thermal shock (JETS) tests are performed for both TBC systems to evaluate thermal durability. Microhardness and elastic modulus at each layer and respective interfaces are also evaluated for both systems. Additionally, the microstructure and elemental composition are thoroughly studied to understand the cause for better performance of one system over the other. Both TBC systems showed similar performance during the thermal cycling and JETS test but TBC systems with AM substrates showed enhanced thermal durability especially in the case of the more aggressive thermal shock test. The TBC sample with AM substrate failed after 105 thermal shock cycles whereas the one with wrought substrate endured a maximum of 85 cycles after which it suffered topcoat delamination. The AM substrates also demonstrated an overall higher microhardness and elastic modulus except for post thermal cycling condition where it slightly underperformed. This study successfully demonstrated the use of AM built substrates for an improved TBC system and validated the enhanced thermal durability and mechanical properties of such a system. A modified YSZ TBC architecture with an intermediate Ti3C2 MXene layer is proposed to improve the interfacial adhesion at the topcoat/bond coat interface to improve the thermal durability of YSZ TBC systems. First principles calculations are conducted to study the interfacial adhesion energy in the modified and conventional YSZ TBC systems. The results show enhanced adhesion at the bond coat/MXene interface. At the topcoat/MXene interface, the adhesion energy is similar to the adhesion energy between the topcoat and bond coat in a conventional YSZ TBC system. An alternative route is proposed for the fabrication of YSZ TBC on nickel base superalloy substrates by using the SPS technology. SPS offers a one-step fabrication process with faster production time and reduced production cost since all the layers of the TBC system are fabricated simultaneously. Two different TBC systems are processed using the same heating protocol. The first system is a conventional TBC system with 8YSZ topcoat, NiCoCrAlY bond coat and nickel base superalloy substrate. The second system is similar to the first but with an addition of Ti3C2 MXene layer between the topcoat and the bond coat. Based on the first principles study, addition of Ti3C2 layer enhances the adhesion strength of the topcoat/bond coat interface, an area which is highly susceptible to spallation. Further tests such as thermal cycling and thermal shock along with the evaluation of mechanical properties would be carried out for these samples in future studies to support our hypothesis.
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The “White Ocean” Hypothesis: A Late Pleistocene Southern Ocean Governed by Coccolithophores and Driven by Phosphorus
(Frontiers Media, 2012-07-02) Flores, José-Abel; Filippelli, Gabriel M.; Sierro, Francisco J.; Latimer, Jennifer; Earth Sciences, School of Science
Paleoproductivity is a critical component in past ocean biogeochemistry, but accurate reconstructions of productivity are often hindered by limited integration of proxies. Here, we integrate geochemical (phosphorus) and micropaleontological proxies at millennial timescales, revealing that the coccolithophore record in the Subantarctic zone of the South Atlantic Ocean is driven largely by variations in marine phosphorus availability. A quantitative micropaleontological and geochemical analysis carried out in sediments retrieved from Ocean Drilling Program Site 1089 (Subantarctic Zone) reveals that most of the export productivity in this region over the last 0.5 my was due to coccolithophores. Glacial periods were generally intervals of high productivity, with productivity reaching a peak at terminations. Particularly high productivity was observed at Termination V and Termination IV, events that are characterized by high abundance of coccolithophores and maxima in the phosphorus/titanium and strontium/titanium records. We link the increase in productivity both to regional oceanographic phenomena, i.e., the northward displacement of the upwelling cell of the Antarctic divergence when the ice-sheet expanded, and to the increase in the inventory of phosphorus in the ocean due to enhanced transfer of this nutrient from continental margins during glacial lowstands in sea level. The Mid-Brunhes interval stands out from the rest of the record, being dominated by the small and highly calcified species Gephyrocapsa caribbeanica that provides most of the carbonate in these sediments. This likely represents higher availability of phosphorus in the surface ocean, especially in mesotrophic and oligotrophic zones. Under these condition, some coccolithophore species developed an r-strategy (opportunistic species; growth rate maximized) resulting in the bloom of G. caribbeanica. These seasonal blooms of may have induced “white tides” similar to those observed today in Emiliania huxleyi.
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Geochemical legacies and the future health of cities: A tale of two neurotoxins in urban soils
(University of California Press, 2015) Filippelli, Gabriel M.; Risch, Martin; Laidlaw, Mark A. S.; Nichols, Deborah E.; Crewe, Julie
The past and future of cities are inextricably linked, a linkage that can be seen clearly in the long-term impacts of urban geochemical legacies. As loci of population as well as the means of employment and industry to support these populations, cities have a long history of co-locating contaminating practices and people, sometimes with negative implications for human health. Working at the intersection between environmental processes, communities, and human health is critical to grapple with environmental legacies and to support healthy, sustainable, and growing urban populations. An emerging area of environmental health research is to understand the impacts of chronic exposures and exposure mixtures—these impacts are poorly studied, yet may pose a significant threat to population health. Acute exposure to lead (Pb), a powerful neurotoxin to which children are particularly susceptible, has largely been eliminated in the U.S. and other countries through policy-based restrictions on leaded gasoline and lead-based paints. But the legacy of these sources remains in the form of surface soil Pb contamination, a common problem in cities and one that has only recently emerged as a widespread chronic exposure mechanism in cities. Some urban soils are also contaminated with another neurotoxin, mercury (Hg). The greatest human exposure to Hg is through fish consumption, so eating fish caught in urban areas presents risks for toxic Hg exposure. The potential double impact of chronic exposure to these two neurotoxins is pronounced in cities. Overall, there is a paradigmatic shift from reaction to and remediation of acute exposures towards a more nuanced understanding of the dynamic cycling of persistent environmental contaminants with resultant widespread and chronic exposure of inner-city dwellers, leading to chronic toxic illness and disability at substantial human and social cost.
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From the warm Pliocene to the cold Pleistocene: A tale of two oceans
(Geological Society of America, 2009) Filippelli, Gabriel M.; Flores, José-Abel
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Examining primary care provider experiences with using a clinical decision support tool for pain management
(Oxford University Press, 2023-08-09) Mazurenko, Olena; McCord, Emma; McDonnell, Cara; Apathy, Nate C.; Sanner, Lindsey; Adams, Meredith C. B.; Mamlin, Burke W.; Vest, Joshua R.; Hurley, Robert W.; Harle, Christopher A.; Health Policy and Management, School of Public Health
Objective: To evaluate primary care provider (PCP) experiences using a clinical decision support (CDS) tool over 16 months following a user-centered design process and implementation. Materials and methods: We conducted a qualitative evaluation of the Chronic Pain OneSheet (OneSheet), a chronic pain CDS tool. OneSheet provides pain- and opioid-related risks, benefits, and treatment information for patients with chronic pain to PCPs. Using the 5 Rights of CDS framework, we conducted and analyzed semi-structured interviews with 19 PCPs across 2 academic health systems. Results: PCPs stated that OneSheet mostly contained the right information required to treat patients with chronic pain and was correctly located in the electronic health record. PCPs used OneSheet for distinct subgroups of patients with chronic pain, including patients prescribed opioids, with poorly controlled pain, or new to a provider or clinic. PCPs reported variable workflow integration and selective use of certain OneSheet features driven by their preferences and patient population. PCPs recommended broadening OneSheet access to clinical staff and patients for data entry to address clinician time constraints. Discussion: Differences in patient subpopulations and workflow preferences had an outsized effect on CDS tool use even when the CDS contained the right information identified in a user-centered design process. Conclusions: To increase adoption and use, CDS design and implementation processes may benefit from increased tailoring that accommodates variation and dynamics among patients, visits, and providers.