Design of Si/SiC hybrid structures for elevated temperature micro-turbomachinery

thermal softening behavior at temperatures above 900 K. This thermal softening behavior limits the turbine inlet temperature, which in turn significantly degrades the overall engine efficiency. Previous studies have shown that hybrid structures of silicon and silicon carbide have good potential for improved engine performance. Detailed design of Si/SiC hybrid structures for high temperature micro-turbomachinery, however, has been hampered by the relatively poor performance of single crystal Si at elevated temperatures and high stresses and by the unavailability of accurate material properties data for both Si and SiC at the temperatures of interest. From previous work, the critical structures and materials issues to be resolved, in order to proceed with the design of high temperature Si/SiC hybrid structures, were identified as follows: 1. the safety margin of the Si/SiC hybrid structures based on the upper yield strength of Si 2. reliable estimation of the service life of the Si/SiC hybrid structures 3. structural instabilities caused by the combination of stress concentrations and strain softening. In the course of this thesis, these issues provided the key motivations of the work, and have been substantially resolved. As a first step, it is critical to obtain a better understanding of the mechanical behavior of this material at elevated temperatures in order to properly exploit its capabilities as a structural material. Creep tests in simple compression with n-type single crystal silicon, with low initial dislocation density, were conducted over a temperature range of 900 K to 1200 K and a stress range of 10 MPa to 120 MPa. The compression specimens were machined such that the multi-slip <100> or <111> orientations were coincident with the compression axis.

Department dc:contributor.department

Massachusetts Institute of Technology. Dept. of Mechanical Engineering.

Grantor dc:publisher

Massachusetts Institute of Technology

Year dc:date.issued

2002

Author dc:creator

• Moon, Hyung-Soo, 1969-

Advisor dc:contributor.advisor

• S. Mark Spearing and Lallit Anand.

• Mechanical Engineering.

Statement dc:rights

• 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.

Licence dc:rights.uri

• http://dspace.mit.edu/handle/1721.1/7582

Language dc:language.iso

eng

Handle dc:identifier.uri

http://hdl.handle.net/1721.1/29222

OAI identifier oai:identifier

oai:dspace.mit.edu:1721.1/29222