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Accession Number:
ADA334604
Title:
Transformation Weakening of Ceramic Composite Interfaces
Descriptive Note:
Final rept. 15 Sep 96-31 May 97
Corporate Author:
ILLINOIS UNIV AT URBANA DEPT OF MATERIALS SCIENCE AND ENGINEERING
Report Date:
1997-10-31
Pagination or Media Count:
121.0
Abstract:
A new concept for achieving graceful failure in oxide composites is studied. It is based on debonding of a weak interphase between a matrix and an interphase in a laminated composite. The interphase can be thermally or shear stress induced by transformation weakening, which results from an accompanying significant volume contraction andor unit cell shape change, on cooling from a high temperature to low temperature crystal structure. Mullitecordierite laminates with a beta -- alpha-cristobalite transformation weakened interphase were investigated in order to demonstrate interphase debonding behavior. The laminate showed fracture behavior dependent on a critical size effect. The grain size of polycrystalline beta-cristobalite was controlled by annealing. With increasing annealing time, the strength decreased due to the formation of internal microcracks in the cristobalite layer which occurred spontaneously during thermally-induced transformation. A hot-pressed laminate, annealed for 10 h at 1300 deg C, had an average grain size of 4.2 micrometers and a strength of 131 MPa. Its work of fracture was 2.38 kJsq m with a non-catastrophic fracture behavior. The indentation response indicated crack deflection along the cristobalite debonding interphase.
Distribution Statement:
APPROVED FOR PUBLIC RELEASE
