High-resolution stress mapping of Al 2O 3/monoclinic ZrO 2 and Al 2O 3/cubic ZrO 2(Y 2O 3) eutectics using scanning near-field optical microscopy

Abstract

Scanning near-field optical microscopy (SNOM) technique was applied to nanometer-scale residual stress mapping for directionally solidified Al 2O 3/monochromic ZrO 2 and Al 2O 3/cubic ZrO 2(Y 2O 3) eutectics, which are ranked as candidates for high-strength materials at high temperatures. These eutectic composites were grown using the micro pulling down (μ-PD) method with a radio frequency heating system. Topographic images and fluorescence spectra of those eutectic composites were measured simultaneously for each pixel on a sample. Its peak intensity, peak position, and peak width, which, respectively, correspond to the abundance of Al 2O 3, stress in the grain, and the anisotropy of that stress, were estimated for each fluorescence spectrum. The distribution of residual stress was observed on a sample surface with spatial resolution of 300 nm; the spatial resolution was constrained by the optical fiber aperture size. Tensile stress was observed in Al 2O 3 of Al 2O 3/mZrO 2 and compressive stress was observed in Al 2O 3 of Al 2O 3/cZrO 2. The stress distributions were visualized within a single Al 2O 3 grain. Considerable stress anisotropy was detected in the grain boundary between Al 2O 3 and ZrO 2 for both eutectics.