TENSÕES RESIDUAIS AO REDOR DE INDENTAÇÕES EM VIDROS SODA-CAL E BOROSSILICATO

Abstract

Residual stress measurements by fluorescence microscopy is a well-established technique which uses the R1 and/or R2 fluorescence peaks of Cr+3 ions in Al2O3. These peaks are sensitive to the distortion of the lattice and their position changes if the crystal is stressed. Borosilicate (BS) and soda-lime (SL) sintered samples with 10 vol. % Al2O3 were produced mixing the glass and alumina powders, uniaxial compressed and sintered at high temperature. Surface morphology and microstructure were characterized by optical and scanning electron microscopies. The porosity obtained was less than 2%. 10 N Vickers indentations were performed and the stresses around the indentations were measured by fluorescence microscopy. Measurements of residual stresses due to thermal expansion mismatch between the glass matrix and the Al2O3 were 163 MPa and -35 MPa for BS and SL composites samples, respectively, in agreement with Hseuh & Becher’s model. The probe response function was fitted to the fluorescence data taking into account the iteraction of the laser beam within the sample and effects of light absorption, refraction and scattering by alumina particles and pores and stresses gradients. The experimental fluorescence shift as a function of the distance from the indentations was compared with Yoffe’s model and the PRF function. It was found that the experimental blister field strength is a factor of 10 smaller than that predicted by Yoffe´s model, taking into account the densification of the glass underneath the indenter. Indentation residual stresses were also measured for SL glass using the Zeng and Rowcliffe’s model. Stress profiles were measured around 50 N and 100 N Vickers indentations performed between -196 °C to 400 °C. The blister field strength increased with temperature and it could be explained by the variation of the 𝐸𝐸/𝐻𝐻 ratio with temperature. This work contributes for the understanding of the mechanisms responsible for the indentation residual stresses in glasses.