Browsing by Subject "Infiltration"
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Item Additively manufactured Si-SiC combustion devices : the role of heat recirculation in counter-flowing reactors(2021-07-24) Radyjowski, Patryk Pawel; Ellzey, Janet L.; Bourell, David; Kovar, Desiderio; Belmont, Erica LThe importance of energy efficiency demands novel approaches to combustion of fossil fuels. Significant research has focused on increasing efficiency, reducing emissions, and improving fuel flexibility. One approach of recycling energy from the flame to the reactants, called excess enthalpy combustion, offers all of these potential advantages. A variety of heat recirculating reactor designs exist, but they are all characterized by small pores or channels to maximize the exposure of hot walls to the flowing reactants. This requires a material that can withstand the combustion environment without constraining possible geometries. Standard materials such as ceramics and superalloys are limited in either one or the other of these criteria. A potential solution is an additively manufactured ceramic-metal composite, siliconized silicon carbide (Si-SiC) cermet. It can be fabricated in the desired shape and withstands temperatures up to 1400°C. This work examines the fabrication of Si-SiC parts by a multi-step process including laser sintering, transient binder processing, and metal infiltration. Modifications in the process improved intermediate handling and part quality. Future material science development of manufacturing method could lead to a 1900°C capable material. The newly developed material was investigated under a lean methane-air combustion environment. Flame compatibility and good thermal oxidation above 1200°C were confirmed in the isolated exposure tests. Using the AM process above, three counter-flow combustors were manufactured with different channel geometries such that the surface area to volume ratio was varied. The relationship between the resulting change in heat transfer and the stable operating range was investigated. Higher heat recirculation increased internal temperatures and improved flame stability. The role of heat recirculation was crucial under high speed, high firing rate conditions. Experimental findings were supported by analytical modeling and previous research in the field. CO and NO [subscript x] emissions registered at exits were low, substantially below equilibrium. The material degradation of Si-SiC was tracked over an entire 80-hour period. The operation near 1400°C resulted in partial melting and protrusions of infiltrating metal. Otherwise, passive oxidation was observed to happen in-line with the literature. The new material system for high-temperature applications shows significant potential for the development of new combustor designs.Item Characterization of the swelling potential of expansive clays using centrifuge technology(2010-05) Kuhn, Jeffrey Albin; Zornberg, Jorge G.; Gilbert, Robert B.; Scanlon, Bridget R.; Folliard, Kevin J.; DiCarlo, DavidThe characterization of the swell potential of expansive clay is complicated by the fact that traditional swell testing methods require an excessive amount of time for specimens to swell to their maximum heights. As a result, the practicing engineer has typically referred to correlations between swell potential and index properties rather than directly measuring swelling in a laboratory experiment. The purpose of this study is to evaluate an alternate testing method using a geotechnical centrifuge in an attempt to decrease the time required to evaluate the swell potential of expansive clays so that expermientally obtained swelling properties may be obtained within a reasonable time period. This study includes an experimental program involving a series of tests in which compacted clay specimens are flown in a cetrifuge and their heights are monitored as water infiltrates into them.Item Electrochemical deposition of metal ions in porous laser sintered inter-metallic and ceramic preforms(2010-12) Goel, Abhishek, 1986-; Bourell, David Lee; Beaman Jr., Joseph J.Selective laser sintering (SLS) is a commercial, powder-based manufacturing process that produces parts with complicated shape and geometry based on a computer solid model. One of the major drawbacks of SLSed inter-metallic and ceramic parts is their high porosity because of the use of binder system. High porosity results in poor mechanical, electrical and thermal properties of the preform and hence renders it unsuitable for various applications. This thesis attempts to infiltrate SLSed preforms by carrying out electrochemical deposition of metal ions inside the interconnected pore network. One of the major benefits of carrying out this novel process is low processing temperature as opposed to existing methods such as melt infiltration. Low temperature reduces both energy consumption and associated carbon-footprint and also minimizes undesirable structural changes. Both conductive and non-conductive preforms may be electrochemically infiltrated, and MMCs produced by this method have potential for use in structural applications.Item Homogeneous Metal Parts by Infiltration(2001) Lorenz, Adam M.; Sachs, Emanuel M.; Allen, Samuel M.; Cima, Michael J.Infiltration of powdered metal parts made by SFF processes enables densification with negligible dimensional change, but typically uses a dissimilar infiltrant material resulting in poor corrosion resistance, machinability, and a heterogeneous composition inconducive to certification for critical applications. A new approach called transient liquid-phase infiltration is described using an infiltrant composition similar to that of the powder skeleton, but containing a melting point depressant. Upon infiltration, the liquid undergoes diffusional solidification at infiltration temperature and eventually the composition becomes homogeneous. Parts over 20 cm tall have been fabricated through careful selection of skeleton and infiltrant compositions, skeleton powder size, and infiltration technique. The work presented in this paper uses a nickelsilicon alloy to infiltrate a skeleton of pure nickel powder.Item Selective laser sintering and post-processing of fully ferrous components(2011-05) Vallabhajosyula, Phani Charana Devi; Bourell, David Lee; Beaman, Joseph J.; Kovar, Desiderio; Taleff, Eric M.; Juenger, Maria G.Indirect additive processing of ferrous metals offers the potential to freeform fabricate parts with good surface finish and minimal dimensional variation from the computer solid model. The approach described here is to mix a ferrous powder with a transient binder followed by selective laser sintering (SLS) in a commercial polymer machine to create a “green” part. This part is post-processed to burn off the transient binder and to infiltrate the porous structure with a lower melting point metal/alloy. Commercially available SLSed ferrous components contain copper-based infiltrant in a ferrous preform. The choice of copper alloy infiltrant has led to inferior mechanical properties of these components limiting their use in many non-injection-molding structural applications, particularly at elevated temperature. In the present work, an attempt has been made to replace the copper-based infiltrant considering cast iron as a potential infiltrant because of its fluidity, hardness and stability at comparatively high temperature. A critical consideration is loss of part structural integrity by over-melting after infiltration as chemical diffusion of alloying elements, principally carbon, occurs resulting in a decrease in the melting temperature of tool steel preform. A predictive model was developed which defines the degree of success for infiltration based on final part geometry and depending on the relative density of the preform and infiltration temperature. The processing regime is defined as a function of controllable process parameters. An experimental program was undertaken using commercially available LaserForm[superscript tm] A6 tool steel that was infiltrated with ASTM A532 white cast iron. Guided by Ashby densification maps, pre-sintering of the A6 tool steel SLS part was performed to increase the part initial relative density prior to infiltration. The final infiltrated parts were analyzed for geometry, microstructure and hardness. The model may be extended to other ferrous powder and infiltrant compositions in an effort to optimize the properties and utility of the final infiltrated part.