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New Mechanism for Toughening Ceramic Materials
Final rept. 15 Mar 1989-15 Jul 1993
CERAMATEC INC SALT LAKE CITY UT
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Ferroelastic toughening was identified as a viable mechanism for toughening ceramics. Domain structure and domain switching was identified by x- ray diffraction, transmission optical microscopy, and transmission electron microscopy in zirconia, lead zirconate titanate and gadolinium molybdata. Switching in compression was observed at stresses greater than 600 MPa and at 400 MPa in tension for polycrystalline t-zirconia. Domain switching contributes to toughness, as evidenced by data for monoclinic zirconia, t-zirconia, PZT and GMO. The magnitude of toughening varied between 0.6 MPa.ml2 for GMO to 2-6 MPa- ml2 for zirconia. Polycrystalline monoclinic and t-zirconias, which showed no transformation toughening, had similar toughness values as Y-TZP which exhibits transformation. Coarse-grained monoclinic and tetragonal t zirconia samples could be cooled to room temperature for mechanical property evaluation since fine domain size, not grain size, controlled transformation for t-zirconia and minimized stress for m-ZrO2. LnAlO3, LnNbO4, and LnCrO3 were among the materials identified as high temperature ferroelastics.
APPROVED FOR PUBLIC RELEASE