Microfabricated refractory ceramic structures for micro turbomachinery
Name
43584020-MIT.pdf
Description
Full printable version
Size
6.68 MB
Format
Adobe PDF
Checksum (MD5)
949c286461c01273453a3f4f4a5ce123
Author(s)
Lohner, Kevin Andrew, 1974-
Advisor(s)
S. Mark Spearing.
Date Issued
1999
Publisher
Massachusetts Institute of Technology
Abstract
The MIT Microengine Project was initiated in 1995 as a joint effort between the Gas Turbine Laboratory (GTL) and Microsystems Technology Laboratory (MTL) to develop a MEMS-based micro-gas turbine engine. The thermodynamic requirements of power-generating turbomachinery drive the design towards high rotational speeds and high temperatures. To achieve the specified performance requires materials with high specific strength and creep resistance at elevated temperatures. The thermal and mechanical properties of silicon carbide make it an attractive candidate for such an application. Silicon carbide as well as silicon-silicon carbide hybrid structures are being designed and fabricated utilizing chemical vapor deposition of relatively thick silicon carbide layers (10-100 [mu]m) over time multiplexed deep etched silicon molds. The silicon can be selectively dissolved away to yield high aspect ratio silicon carbide structures with features that are hundreds of microns tall. Positive mold, negative mold, and hybrid Si/SiC processing techniques appear to be feasible microfabrication routes with potential for increasing microengine performance. Research has been performed to characterize the capabilities of these processes. Specimens fabricated in the course of this research show very good conformality and step coverage with a fine (~0.1 [mu]m diameter) columnar microstructure. Surface roughness (Rq) of the films is on the order of 100 nm, becoming rougher with thicker deposition. Residual stress limits the achievable thickness, as the strain energy contained within the compressive film increases its susceptibility to cracking. Room temperature biaxial mechanical testing of CVD silicon carbide exhibits a reference strength of 724 MPa with a Weibull modulus, m =16.0. This thesis documents the design trades that led to the selection of CVD SiC as the primary candidate refractory material for the microengine, and the initial experiments performed to assess its suitability and guide future material and process development.
Description
Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 1999.
Includes bibliographical references (p. 103-109).
Subjects
Aeronautics and Astronautics
MIT Department
Massachusetts Institute of Technology. Department of Aeronautics and Astronautics
Terms of Use
M.I.T. theses are protected by copyright. They may be viewed from this source for any purpose, but reproduction or distribution in any format is prohibited without written permission. See provided URL for inquiries about permission.
Persistent DSpace Link
