Matching Items (2)
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
Intermittent social defeat stress produces vulnerability to drugs of abuse, a phenomena known as cross-sensitization, which is proceeded by a corresponding upregulation of ventral tegmental area (VTA) mu-opioid receptors (MORs). Since VTA MORs are implicated in the expression of psychostimulant sensitization, they may also mediate social stress-induced vulnerability to drugs of abuse. Social stress and drugs of abuse increase mesolimbic brain-derived neurotrophic factor (BDNF) signaling with its receptor, tropomyosin-related kinase B (TrkB). These studies examined whether VTA MOR signaling is important for the behavioral and cellular consequences of social stress. First, the function of VTA MORs in the behavioral consequences of intermittent social defeat stress was investigated. Lentivirus-mediated knockdown of VTA MORs prevented social stress-induced cross-sensitization, as well as stress-induced social avoidance and weight gain deficits. Next it was examined whether VTA MOR expression is critical for stress-induced alterations in the mesocorticolimbic circuit. At the time cross-sensitization was known to occur, lentivirus-mediated knockdown of VTA MORs prevented stress-induced increases in VTA BDNF and its receptor, TrkB in the nucleus accumbens (NAc), and attenuated NAc expression of delta FosB. There was no effect of either stress or virus on BDNF expression in the prefrontal cortex. Since social stress-induced upregulation of VTA MORs is necessary for consequences of social stress, next activity dependent changes in AKT, a downstream target of MOR stimulation associated with sensitization to psychostimulant drugs, were investigated. Using fluorescent immunohistochemical double labeling for the active form of AKT (pAKT) and markers of either GABA or dopamine neurons in the VTA, it was determined that social stress significantly increased the expression of pAKT in GABA, but not dopamine neurons, and that this effect was dependent on VTA MOR expression. Moreover, intra-VTA inhibition of pAKT during stress prevented stress-induced weight gain deficits, while acute inhibition of VTA pAKT blocked the expression of cross-sensitization in subjects that had previously exhibited sensitized locomotor activity. Together these results suggest that social stress upregulates MORs on VTA GABA neurons, resulting in AKT phosphorylation, and that increased VTA MOR-pAKT signaling may represent a novel therapeutic target for the intervention of substance abuse disorders.
ContributorsJohnston, Caitlin (Author) / Hammer, Ronald P. (Thesis advisor) / Nikulina, Ella M. (Thesis advisor) / Neisewander, Janet L. (Committee member) / Wu, Jie (Committee member) / Olive, Michael F. (Committee member) / Arizona State University (Publisher)
Created2015