Transformation Weakening of Ceramic Composite Interfaces
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 and/or unit cell shape change, on cooling from a high temperature to low temperature crystal structure. Mullite/cordierite 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 kJ/sq m with a non-catastrophic fracture behavior. The indentation response indicated crack deflection along the cristobalite debonding interphase.
Document Details
- Document Type
- Technical Report
- Publication Date
- Oct 31, 1997
- Accession Number
- ADA334604
Entities
People
- Waltraud M. Kriven
Organizations
- University of Illinois Urbana–Champaign