Measurement of Stress Due to Thermal Expansion Anisotropy in Al ₂ O ₃

Abstract

The stress due to thermal expansion anisotropy in polycrystalline Al 2 O 3 was measured. The broadening of spectroscopic R lines (692 and 693 nm, due to Cr 3+ impurities) was used to measure the stresses (at 77 K) in samples with grain sizes of 50 to 150 μm that had been cooled, from 2150 K, at constant rates from 0.1 to 100 K/min. The maximum stress was found to vary from 80 to 100 MPa, depending on the thermal history of the sample. The results are compared to the predictions of a model based on stress relaxation by diffusional creep and are in good agreement for the dependence on cooling rate. No effect due to grain‐size changes was observed due to the limited range of grain sizes accessible in this study.