Measurement of Stresses Using Fluorescence in an Optical Microprobe: Stresses around Indentations in a Chromium‐Doped Sapphire

Abstract

A technique for measuring stress (positive and negative) with a lateral spatial extent of approximately 2 pm is introduced. The technique, implemented using a Raman microprobe, is demonstrated with measurements of. the frequency shift of the sharp, R-luminescence lines (2A and E to 4A2 radiative transitions) in, and around, a hardness indentation in a 0.06-wt%-chromium doped sapphire. From the observed frequency shifts the stresses in regions sampled in the hardness impression, in the complex stress field surrounding it, and at the tip of a crack are measured. [

Review: Coefficients for Stress, Temperature, and Composition Effects in Fluorescence Measurements of Alumina

“…Hence, the linear variation of shift with applied stress (up to a few hundred megapascals; one unverified exception) and the numerical agreement with the non-polycrystal coefficient determinations surveyed above further support the observations. It is noted that the applied stress range of the polycrystal experiments was about an order of magnitude less than the single-crystal or fiber experiments (previous sections) and comparable to the intrinsic microstructural stresses expected and observed in bulk polycrystals [38][39][40][41][42][58][59][60][61][62][63][64][65][66][67]. Table 3 gives the first author, year published, citation, R-line coefficients (R1 or R2), and notes for original works that (experimentally) determined the temperature coefficients β (1) and β (2) ; see Eq.…”

“…Fiber measurements were compared with the predicted polycrystalline average values, e.g., Refs. [82,88], as were the uniaxial or bending polycrystal measurements [42,43,90]. These tests were good measures of the sum (which is well known; Table 1), but could not distinguish individual piezospectroscopic components.…”

“…(12). One of the simplest examples is the simple bending of a polycrystalline beam, in which the fluorescent measurement encompasses many grains [42]. In this case, 11 = u = / , and 22 = 33 = 0, where here is the bending moment applied to the beam, is the beam moment of inertia, is the distance from the neutral axis, and u is the resulting uniaxial stress at .…”

“…Molis and Clarke [42] /GPa. The R1 data were similar but exhibited slightly different coefficients in tension and compression.…”

“…At least part of the motivation for the polycrystalline research was to investigate the stress fields arising in polycrystalline alumina responsible for microcracking-the spontaneous localized cracking that occurs in polycrystalline alumina on cooling as a consequence of the anisotropic structure and thermal expansion of corundum [39][40][41]. From the 1990s onward, although there were many notable fundamental studies of the phenomenon [42][43][44][45][46][47][48][49][50][51][52][53][54][55][56][57][58], the shift in energy of R lines with stress was largely confined to the applied domain, detailed in numerous works, such as: measurement of stress in bulk Al2O3 polycrystals [42,[58][59][60][61][62][63][64][65][66][67]; in bulk Al2O3-ZrO2 composites [68][69][70][71][72][73][74][75][76][77][78]; in sapphire or composite fibers, free or in matrices [79][80]…”