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- All Subjects: Additive Manufacturing
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Description
Recently, nanostructured metamaterials have attracted lots of attentions due to its tunable artificial properties. In particular, nanowire
anohole based metamaterials which are known of the capability of large area fabrication were intensively studied. Most of the studies are only based on the electrical responses of the metamaterials; however, magnetic response, is usually neglected since magnetic material does not exist naturally within the visible or infrared range. For the past few years, artificial magnetic response from nanostructure based metamaterials has been proposed. This reveals the possibility of exciting resonance modes based on magnetic responses in nanowire
anohole metamaterials which can potentially provide additional enhancement on radiative transport. On the other hand, beyond classical far-field radiative heat transfer, near-field radiation which is known of exceeding the Planck’s blackbody limit has also become a hot topic in the field.
This PhD dissertation aims to obtain a deep fundamental understanding of nanowire
anohole based metamaterials in both far-field and near-field in terms of both electrical and magnetic responses. The underlying mechanisms that can be excited by nanowire
anohole metamaterials such as electrical surface plasmon polariton, magnetic hyperbolic mode, magnetic polariton, etc., will be theoretically studied in both far-field and near-field. Furthermore, other than conventional effective medium theory which only considers the electrical response of metamaterials, the artificial magnetic response of metamaterials will also be studied through parameter retrieval of far-field optical and radiative properties for studying near-field radiative transport. Moreover, a custom-made AFM tip based metrology will be employed to experimentally study near-field radiative transfer between a plate and a sphere separated by nanometer vacuum gaps in vacuum. This transformative research will break new ground in nanoscale radiative heat transfer for various applications in energy systems, thermal management, and thermal imaging and sensing.
anohole based metamaterials which are known of the capability of large area fabrication were intensively studied. Most of the studies are only based on the electrical responses of the metamaterials; however, magnetic response, is usually neglected since magnetic material does not exist naturally within the visible or infrared range. For the past few years, artificial magnetic response from nanostructure based metamaterials has been proposed. This reveals the possibility of exciting resonance modes based on magnetic responses in nanowire
anohole metamaterials which can potentially provide additional enhancement on radiative transport. On the other hand, beyond classical far-field radiative heat transfer, near-field radiation which is known of exceeding the Planck’s blackbody limit has also become a hot topic in the field.
This PhD dissertation aims to obtain a deep fundamental understanding of nanowire
anohole based metamaterials in both far-field and near-field in terms of both electrical and magnetic responses. The underlying mechanisms that can be excited by nanowire
anohole metamaterials such as electrical surface plasmon polariton, magnetic hyperbolic mode, magnetic polariton, etc., will be theoretically studied in both far-field and near-field. Furthermore, other than conventional effective medium theory which only considers the electrical response of metamaterials, the artificial magnetic response of metamaterials will also be studied through parameter retrieval of far-field optical and radiative properties for studying near-field radiative transport. Moreover, a custom-made AFM tip based metrology will be employed to experimentally study near-field radiative transfer between a plate and a sphere separated by nanometer vacuum gaps in vacuum. This transformative research will break new ground in nanoscale radiative heat transfer for various applications in energy systems, thermal management, and thermal imaging and sensing.
ContributorsChang, Jui-Yung (Author) / Wang, Liping (Thesis advisor) / Phelan, Patrick (Committee member) / Wang, Robert (Committee member) / Yu, Hongbin (Committee member) / Hildreth, Owen (Committee member) / Arizona State University (Publisher)
Created2017
Description
Additive manufacturing (AM) describes an array of methods used to create a 3D object layer by layer. The increasing popularity of AM in the past decade has been due to its demonstrated potential to increase design flexibility, produce rapid prototypes, and decrease material waste. Temporary supports are an inconvenient necessity in many metal AM parts. These sacrificial structures are used to fabricate large overhangs, anchor the part to the build substrate, and provide a heat pathway to avoid warping. Polymers AM has addressed this issue by using support material that is soluble in an electrolyte that the base material is not. In contrast, metals AM has traditionally approached support removal using time consuming, costly methods such as electrical discharge machining or a dremel.
This work introduces dissolvable supports to single- and multi-material metals AM. The multi-material approach uses material choice to design a functionally graded material where corrosion is the functionality being varied. The single-material approach is the primary focus of this thesis, leveraging already common post-print heat treatments to locally alter the microstructure near the surface. By including a sensitizing agent in the ageing heat treatment, carbon is diffused into the part decreasing the corrosion resistance to a depth equal to at least half the support thickness. In a properly chosen electrolyte, this layer is easily chemically, or electrochemically removed. Stainless steel 316 (SS316) and Inconel 718 are both investigated to study this process using two popular alloys. The microstructure evolution and corrosion properties are investigated for both. For SS316, the effect of applied electrochemical potential is investigated to describe the varying corrosion phenomena induced, and the effect of potential choice on resultant roughness. In summary, a new approach to remove supports from metal AM parts is introduced to decrease costs and further the field of metals AM by expanding the design space.
This work introduces dissolvable supports to single- and multi-material metals AM. The multi-material approach uses material choice to design a functionally graded material where corrosion is the functionality being varied. The single-material approach is the primary focus of this thesis, leveraging already common post-print heat treatments to locally alter the microstructure near the surface. By including a sensitizing agent in the ageing heat treatment, carbon is diffused into the part decreasing the corrosion resistance to a depth equal to at least half the support thickness. In a properly chosen electrolyte, this layer is easily chemically, or electrochemically removed. Stainless steel 316 (SS316) and Inconel 718 are both investigated to study this process using two popular alloys. The microstructure evolution and corrosion properties are investigated for both. For SS316, the effect of applied electrochemical potential is investigated to describe the varying corrosion phenomena induced, and the effect of potential choice on resultant roughness. In summary, a new approach to remove supports from metal AM parts is introduced to decrease costs and further the field of metals AM by expanding the design space.
ContributorsLefky, Christopher (Author) / Hildreth, Owen (Thesis advisor) / Chawla, Nikhilesh (Committee member) / Azeredo, Bruno (Committee member) / Rykaczewski, Konrad (Committee member) / Nian, Qiong (Committee member) / Arizona State University (Publisher)
Created2018
Description
Additive Manufacturing and 3D printing are becoming important technologies in the manufacturing sector. The benefits of this technology include complex part geometry, short lead-times, low waste, and simple user interface. However, the technology does not come without its drawbacks: mainly the removal of support structures from the component. Traditional techniques that involve sawing and cutting can be expensive and take a long time, increasing the overall price of 3D printed metal components. This paper discusses two approaches taken for dissolvable support structures in 3D printed stainless steel (17-4 PH). For the first time in powder bed fusion components, with the help of Christopher Lefky and Dr. Owen Hildreth, dissolvable support capabilities are achieved in metal prints. The first approach, direct dissolution, involves direct corrosion of the entire part, leading to support removal. This approach is not self-terminating, and leads to changes in final component geometry. The second approach involves a post-build sensitization step, which physically alters the microstructure and chemical stability of the first 100-200 microns of the metal. The component is then etched at an electric potential that will readily corrode this sensitized surface, but not the underlying base metal. An electrolytic solution of HNO3/KCl/HCl paired with an anodic bias was used for the direct dissolution approach, resulting in a loss of about 120 microns of material from the components surface. For the self-limiting approach, surface sensitization was achieve through a post build annealing step (800 C for 6 hours, air cooled) with exposure to a sodium hexacynoferrate slurry. When the slurry decomposes in the furnace, carbon atoms diffuse into the surface and precipitate a chromium-carbide, which reduces the chemical stability of the stainless steel. Etching is demonstrated in an anodic bias of HNO3/KCl. To determine proper etching potentials, open circuit potential and cyclic voltammetry experiments were run to create Potentiodynamic Polarization Curves. Further testing of the self-terminating approach was performed on a 316 stainless steel interlocking ring structure with a complex geometry. In this case, 32.5 hours of etching at anodic potentials replaced days of mechanical sawing and cutting.
ContributorsZucker, Brian Nicholas (Co-author) / Lefky, Christopher (Co-author) / Hildreth, Owen (Co-author, Thesis director) / Hsu, Keng (Committee member) / Materials Science and Engineering Program (Contributor) / Barrett, The Honors College (Contributor)
Created2016-12
Description
The removal of support material from metal 3D printed objects is a laborious necessity for the post-processing of powder bed fusion printing (PBF). Supports are typically mechanically removed by machining techniques. Sacrificial supports are necessary in PBF printing to relieve thermal stresses and support overhanging parts often resulting in the inclusion of supports in regions of the part that are not easily accessed by mechanical removal methods. Recent innovations in PBF support removal include dissolvable metal supports through an electrochemical etching process. Dissolvable PBF supports have the potential to significantly reduce the costs and time associated with traditional support removal. However, the speed and effectiveness of this approach is inhibited by numerous factors such as support geometry and metal powder entrapment within supports. To fully realize this innovative approach, it is necessary to model and understand the design parameters necessary to optimize support structures applicable to an electrochemical etching process. The objective of this study was to evaluate the impact of block additive manufacturing support parameters on key process outcomes of the dissolution of 316 stainless steel support structures. The parameters investigated included hatch spacing and perforation, and the outcomes of interests included time required for completion, surface roughness, and effectiveness of the etching process. Electrical current was also evaluated as an indicator of process completion. Analysis of the electrical current throughout the etching process showed that the dissolution is diffusion limited to varying degrees, and is dependent on support structure parameters. Activation and passivation behavior was observed during current leveling, and appeared to be more pronounced in non-perforated samples with less dense hatch spacing. The correlation between electrical current and completion of the etching process was unclear, as the support structures became mechanically removable well before the current leveled. The etching process was shown to improve surface finish on unsupported surfaces, but support was shown to negatively impact surface finish. Tighter hatch spacing was shown to correlate to larger variation in surface finish, due to ridges left behind by the support structures. In future studies, it is recommended current be more closely correlated to process completion and more roughness data be collected to identify a trend between hatch spacing and surface roughness.
ContributorsAbranovic, Brandon (Author) / Hildreth, Owen (Thesis director) / Torres, Cesar (Committee member) / Chemical Engineering Program (Contributor) / Barrett, The Honors College (Contributor)
Created2018-05
Description
Material extrusion based rapid prototyping systems have been used to produceprototypes for several years. They have been quite important in the additive manufacturing field, and have gained popularity in research, development and manufacturing in a wide field of applications. There has been a lot of interest in using these technologies to produce end use parts, and Fused Deposition Modeling (FDM) has gained traction in leading the transition of rapid prototyping technologies to rapid manufacturing. But parts built with the FDM process exhibit property anisotropy. Many studies have been conducted into process optimization, material properties and even post processing of parts, but were unable to solve the strength anisotropy issue. To address this, an optical heating system has been proposed to achieve localized heating of the pre- deposition surface prior to material deposition over the heated region. This occurs in situ within the build process, and aims to increase the interface temperature to above glass transition (Tg), to trigger an increase in polymer chain diffusion, and in extension, increase the strength of the part. An increase in flexural strength by 95% at the layer interface has been observed when the optical heating method was implemented, thereby improving property isotropy of the FDM part. This approach can be designed to perform real time control of inter-filament and interlayer temperatures across the build volume of a part, and can be tuned to achieve required mechanical properties.
ContributorsKurapatti Ravi, Abinesh (Author) / Hao Hsu, Keng (Thesis advisor) / Hildreth, Owen (Committee member) / Wang, Liping (Committee member) / Arizona State University (Publisher)
Created2016
Description
The use of nanoparticle-in-matrix composites is a common motif among a broad range of nanoscience applications and is of particular interest to the thermal sciences community. To explore this morphological theme, crystalline inorganic composites were synthesized by mixing colloidal CdSe nanocrystals and In2Se3 metal chalcogenide complex (MCC) precursor in hydrazine solvent and then thermally transform the MCC precursor into a crystalline In2Se3 matrix. The volume fraction of CdSe nanocrystals was varied from 0 to ~100% .Rich structural and chemical interactions between the CdSe nanocrystals and the In2Se3 matrix were observed. The average thermal conductivities of the 100% In2Se3 and ~100% CdSe composites are 0.32 and 0.53 W/m-K, respectively, which are remarkably low for inorganic crystalline materials. With the exception of the ~100% CdSe samples, the thermal conductivities of these nanocomposites are insensitive to CdSe volume fraction.This insensitivity is attributed to competing effects rise from structural morphology changes during composite formation.
Next, thermoelectric properties of metal chalcogenide thin films deposited from precursors using thiol-amine solvent mixtures were first reported. Cu2-xSeyS1-y and Ag-doped Cu2-xSeyS1-y thin films were synthesized, and the interrelationship between structure, composition, and room temperature thermoelectric properties was studied. The precursor annealing temperature affects the metal:chalcogen ratio, and leads to charge carrier concentration changes that affect Seebeck coefficient and electrical conductivity. Incorporating Ag into the Cu2-xSeyS1-y film leads to appreciable improvements in thermoelectric performance. Overall, the room temperature thermoelectric properties of these solution-processed materials are comparable to measurements on Cu2-xSe alloys made via conventional thermoelectric material processing methods.
Finally, a new route to make soluble metal chalcogenide precursors by reacting organic dichalcogenides with metal in different solvents was reported. By this method, SnSe, PbSe, SnTe and PbSexTe1-x precursors were successfully synthesized, and phase-pure and impurity-free metal chalcogenides were recovered after precursor decomposition. Compared to the hydrazine and diamine-dithiol route, the new approach uses safe solvent, and avoids introducing unwanted sulfur into the precursor. SnSe and PbSexTe1-x thin films, both of which are interesting thermoelectric materials, were also successfully made by solution deposition. The thermoelectric property measurements on those thin films show a great potential for future improvements.
Next, thermoelectric properties of metal chalcogenide thin films deposited from precursors using thiol-amine solvent mixtures were first reported. Cu2-xSeyS1-y and Ag-doped Cu2-xSeyS1-y thin films were synthesized, and the interrelationship between structure, composition, and room temperature thermoelectric properties was studied. The precursor annealing temperature affects the metal:chalcogen ratio, and leads to charge carrier concentration changes that affect Seebeck coefficient and electrical conductivity. Incorporating Ag into the Cu2-xSeyS1-y film leads to appreciable improvements in thermoelectric performance. Overall, the room temperature thermoelectric properties of these solution-processed materials are comparable to measurements on Cu2-xSe alloys made via conventional thermoelectric material processing methods.
Finally, a new route to make soluble metal chalcogenide precursors by reacting organic dichalcogenides with metal in different solvents was reported. By this method, SnSe, PbSe, SnTe and PbSexTe1-x precursors were successfully synthesized, and phase-pure and impurity-free metal chalcogenides were recovered after precursor decomposition. Compared to the hydrazine and diamine-dithiol route, the new approach uses safe solvent, and avoids introducing unwanted sulfur into the precursor. SnSe and PbSexTe1-x thin films, both of which are interesting thermoelectric materials, were also successfully made by solution deposition. The thermoelectric property measurements on those thin films show a great potential for future improvements.
ContributorsMa, Yuanyu (Author) / Wang, Robert (Thesis advisor) / Newman, Nathan (Committee member) / Wang, Liping (Committee member) / Hildreth, Owen (Committee member) / Arizona State University (Publisher)
Created2016