Piezospectroscopic Study of Residual Stresses in Al ₂ O ₃ –ZrO ₂ Directionally Solidified Eutectics

Abstract

The residual thermoelastic stresses were studied in Al 2 O 3 –ZrO 2 (monoclinic zirconia, m ‐ZrO 2 ) and Al 2 O 3 –ZrO 2 (Y 2 O 3 ) (tetragonal zirconia, t ‐ZrO 2 ) fibrous eutectics that were produced via the laser floating zone method, using different piezospectrosocopic probes. The luminescence of the R ‐lines of ruby (Cr 3+ in Al 2 O 3 phase) was used to determine the stresses in the Al 2 O 3 matrix, assuming that the stress state in the fibers was transversally isotropic. The sapphire matrix was subjected to tensile stresses in the Al 2 O 3 – 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 2 O 3 –ZrO 2 (Y 2 O 3 ) fibers, and the hydrostatic stress was −0.37 GPa in both ordered and disordered regions. The influence of the microstructure in the residual stresses was explained through thermoelastic analyses, based on a self‐consistent method. In addition, the Raman spectra of m ‐ZrO 2 and the 417 cm −1 Raman mode of Al 2 O 3 were measured in samples that showed different microstructures and thermoelastic stresses. An approximate linear dependence was observed in the tension–compression range between frequency shifts of the Al 2 O 3 R ‐lines and those of the 417 cm −1 Raman mode.