Abstract
Analytical electron microscopy has been used to study the precipitation reactions in sintered samples of 9 mol% La2O3-Y2O3 samples upquenched from the single phase cubic region into the cubic and hexagonal phase field. Samples annealed just inside the two-phase cubic-cubic and hexagonal solvus exhibited predominantly grain boundary precipitation. Small La2O3 rich second phases formed within the first ten minutes and developed into strained, facetted precipitates after 300 min. Intergranular and intragranular precipitation occurred in samples annealed further into the two-phase field. Strained, lathlike La2O3-rich monoclinic precipitates, exhibiting a preferrred orientation in the matrix, appeared as the dominant morphology for long times at temperature. Chemical microanalyses of the strained structures obtained in samples annealed for 300 min revealed La2O3 matrix concentrations in agreement with phase diagram predictions. However, the La2O3 concentrations in the second-phase precipitates were found to be far in excess of the cubic and hexagonal-hexagonal solvus. This discrepancy is believed to arise from a re-equilibration of the second phase in the cubic and monoclinic phase field during quenching.
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Horvath, S.F., Harmer, M.P., Williams, D.B. et al. Analytical transmission electron microscopy of La2O3-doped Y2O3 . J Mater Sci 24, 863–872 (1989). https://doi.org/10.1007/BF01148769
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DOI: https://doi.org/10.1007/BF01148769