Transformation Toughening of Ceramics
Annual rept. no. 2, 15 Jan 1990-11 Jan 1991
ROCKWELL INTERNATIONAL CORP THOUSAND OAKS CA SCIENCE CENTER
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The transformation strains responsible for toughening of Zro2 materials have been measured directly using Moire interferometry and a high resolution strain mapping technique based on digital image correlation. Results were correlated with Raman spectroscopy and finite element calculations. Calculations of the crack tip shielding in Ce-Zr02 indicated that the fracture toughness could be increased by a factor of 2 by modifying the microstructure to change the shape of the transformation zone ahead of the crack tip. Layered composites of Ce-ZrO2 and Al203Ce-Zr02 have been explored as a means of achieving such zone modifications. Using a colloidal technique, multilayered composites with layer thickness as small as 10 microns have been fabricated. These layered structures have been observed to interact much more strongly than expected with the transformation zones, causing widening of the zone to the side of cracks as well as modification of the frontal region. The potential exists for extremely high fracture toughness in such systems.
- Ceramics, Refractories and Glass
- Laminates and Composite Materials