Transformation Toughening of Composite Ceramics
Annual rept. 1 Mar 1989-30 Sep 1990,
ILLINOIS UNIV AT URBANA DEPT OF MATERIALS SCIENCE AND ENGINEERING
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Research is underway into the application of martensitic transformations in ceramics to toughen a variety of ceramic-ceramic composites, i.e., to reduce their brittleness. The toughening agents of interest and their volume changes are dicalcium silicate Ca2SiO4, 12, nickel sulfide NiS, 4, lanthanide sesquioxides Ln2O3, 8 and lutentium borate LuBO3, 8. Ceramic processing routes have been developed to fabricate different types of toughened composites, viz., either by using a dispersed second phase microstructure or as a fine grained, single phase material. Specifically, Ca2SiO4 has been dispersed in CaZrO3 and the mechanical properties measured by bend tests. The critical importance of matrix toughness and grain size, as well as role of intergranular microcracking has been established. Dense pellets of fine grained, pure beta- Ca2SiO4 have been sintered and their transformability by grinding established. Their microstructures were examined by TEM and preliminary micromechanical studies made on it, and on Gd2O3, by indentation and SEM techniques. NiS inclusions in glass were examined by TEM and EDS and a sol gel processing route to precipitate NiS in glass has been identified. Composites of Dy2O3 in SiC and powders of LuBO3 in B2O3 have been fabricated.
- Ceramics, Refractories and Glass