Piezospectroscopic study of residual stresses in Al2O3-ZrO2 directionally solidified eutectics

The residual thermoelastic stresses were studied in Al2O3-ZrO2 (monoclinic zirconia, m-ZrO2) and Al2O3-ZrO2(Y2O3) (tetragonal zirconia, t-ZrO2) fibrou s eutectics that were produced ria the laser floating zone method, using di fferent piezospectrosocopic probes. The luminescence of the R-lines of ruby (Cr3+ in Al2O3 phase) was used to determine the stresses in the Al2O3 matr ix, assuming that the stress state in the fibers was transversally isotropi c. The sapphire matrix was subjected to tensile stresses in the Al2O3-m-ZrO 2 eutectics, The hydrostatic stress component attained a value of 1.13 GPa in well-ordered regions, In contrast, sapphire was in compression in the Al 2O3-ZrO2(Y2O3) fibers, and the hydrostatic stress was -0.37 GPa in both ord ered and disordered regions. The influence of the microstructure in the res idual stresses was explained through thermoelastic analyses, based on a sel f-consistent method. In addition, the Raman spectra of m-ZrO2 and the 417 c m(-1) Raman mode of Al2O3 were measured in samples that showed different mi crostructures and thermoelastic stresses. An approximate linear dependence was observed in the tension- compression range between frequency shifts of the Al2O3 R-lines and those of the 417 cm(-1) Raman mode.