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Title Thermal Processing of Injection-Molded Silicon Carbide
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Publication Date
Date Available
Date Accessioned
Degree PhD
Discipline/Department Materials Science
Degree Level doctoral
University/Publisher Oregon State University
Abstract Silicon carbide is an important and versatile nonoxide ceramic. Powder injection molding (PIM) is a method of high-speed fabrication of complex near-net shapes of SiC and other powders. Green micro-machining (GMM) is used to extend the shaping capability of green ceramics and powder metallurgy to smaller feature sizes. Debinding – removal of organic additives – is the rate-limiting step in PIM. Sintering aids enable densification of sintered powders, especially in the absence of applied pressure during sintering. Thermal Processing of Injection-Molded Silicon Carbide presents a study of the effects of GMM, debinding, sintering aids and sintering on two size distributions of PIM α-SiC with 5% each of Y₂O₃ and AlN as sintering aids. The use of 10% 20-nm particles, i.e., a bimodal size distribution, to increase the packing density of the green bodies was found to have a small effect on the rate of debinding, the liquid-phase sintering (LPS) precipitates, the microstructural development and the mechanical properties of SiC compared to the conventional monomodal size distribution, where D₅₀ = 0.7 μm. The nanoparticles and debinding methods did have a strong effect on the feasibility of GMM on SiC. The nanoparticles, debinding methods and GMM in combination significantly affected the sinterability of SiC. The rates and effects of solvent debinding and thermal debinding were measured and compared by various kinetic models. The catalytic effect of the bimodal SiC, if any, was small compared to PIM SiC with monomodal particles. The activation energy for thermal debinding was similar to that of solvent debinding. Too rapid of debinding by either method was detrimental to sintering in the form of fracture in the green body by residual stress. The debinding mechanism shifted from surface dissolution to bulk diffusion as the solvent debinding progressed. Changes in thermal debinding mechanisms were also noted as a function of heating rate. Thermal debinding was problematic in PIM bars with a large characteristic diffusion path length ψ, which led to fractures during sintering. Weak particle bonding and uncontrolled grain growth were observed in some cases after thermal debinding, and attributed to dissolution of aluminum in SiC, excess oxidation of the SiC and premature decomposition of polypropylene. Solvent debinding was less stressful, but not without fractures in some instances due to the swelling of the wax as it dissolved. Monomodal SiC was much more amenable to GMM than bimodal, whether solvent or thermally debound. The GMM swarf adhered to the monomodal more than to bimodal, even after the wax holding the swarf to the substrate was dissolved. The bimodal SiC had about one percentage point better densification than the monomodal. The grain size, precipitate content and Knoop hardness were about the same for monomodal and bimodal, whether solvent or thermally debound, with or without GMM, except in the case of thermally dewaxed bimodal SiC.
Subjects/Keywords silicon carbide; Silicon carbide
Contributors Atre, Sundar V. (advisor); Malhotra, Rajiv (committee member)
Language en
Rights Attribution-ShareAlike 3.0 United States
http://creativecommons.org/licenses/by-sa/3.0/us/ [Always confirm rights and permissions with the source record.]
Country of Publication us
Record ID handle:1957/56310
Repository oregonstate
Date Indexed 2017-03-17
Grantor Oregon State University
Issued Date 2015-06-15 00:00:00
Note [] Graduation date: 2016; [peerreview] no;

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…and 6. TABLE OF CONTENTS Chapter Page 1 General Introduction ........................................................................................................ 1 2 Powder Injection Molded Silicon Carbide

…18 The Effects of Nanoparticle Addition on Binder Removal from Injection Molded Silicon Carbide ........................................................................................................................23 4 3.1 Introduction…

…39 3.5 References ...............................................................................................................40 Kinetics of Thermal Debinding of Injection Molded Silicon Carbide ............................43 TABLE OF CONTENTS…

…61 4.5 References ...............................................................................................................62 The Effects of Sintering Additives on the Properties of Silicon Carbide, Part I: Pressureless Sintering…

…108 The Effects of Sintering Additives on the Properties of Silicon Carbide, Part II: Pressure-Assisted Sintering ..................................................................................................119 6.1 Introduction…

…159 Microstructural Development of Green Micro-Machined, Injection-Molded Silicon Carbide ..................................................................................................................................163 7.1 Introduction…

…185 Green Micro-Machining and Sintering of Injection Molded Silicon Carbide .............190 8.1 Introduction ...........................................................................................................191 8.2 Experiment…

…carbides, boron, silicon and metals; sintering parameters and properties of pressureless-sintered silicon carbide. .....................................................89 Table 5.5: Oxides additives, sintering parameters and properties of pressureless…

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