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Materials Science at Oregon State University

Microstructural Development of Green Micro-Machined, Injection-Molded Silicon Carbide

Date: Thursday, May 4th
Presenter: Dr. Richard Chinn, National Energy Technology Laboratory


The talk begins with an introduction to silicon carbide processing and properties, and its many applications. The second half is on a research project where SiC was injection molded, micro-machined and sintered to full density. Silicon carbide in two particle size distributions with 5% AlN and 5% Y2O3 was extruded with a paraffin-polypropylene binder. The extruded feedstock was pelletized and injection-molded into 10-gm bars. The bars were dewaxed by solvent or pyrolysis, green micro-machined (GMM) before or after dewaxing, and sintered at 2000°C for 2 hr in argon at atmospheric pressure. High-temperature x-ray diffraction indicated the beginning of the Al-Y-O liquid phase at ~1200°C for both size distributions. Dilatometry showed the large thermal expansion associated with dewaxing, and the onset of sintering, also at ~1200°C for both size distributions. The monomodal bars withstood the stresses of GMM well, but the waxy swarf had a tendency to adhere to the workpiece and bond to the workpiece during sintering. The bimodal bars were much less resilient to GMM, whether dewaxed before or after GMM. All bars were at least 95% densified. The effects of particle size distribution at each step were compared.

Richard Chinn, a Colorado native, earned a B.Sc. in Metallurgical Engineering and an M.Sc. in Materials Science at the Colorado School of Mines, and a Ph.D. in Materials Science at Oregon State University. He was an engineer at CoorsTek and Coors Brewing Company near Denver, a chromium and manganese smelter in Ohio, and the ATI Wah Chang zirconium smelter in Albany before joining NETL in 2000. He is the author of a book, Ceramography, published jointly by ASM International and the American Ceramic Society in 2002, and is working on a second edition. His research specialties are primarily related to processing and properties of high-performance alloys and ceramics, especially microstructural development. Chinn is a registered Professional Engineer in Colorado and Oregon, and an ASQ Certified Quality Engineer.