| Résumé | Laser-ultrasonics is a technique to remotely generate and detect acoustic waves using lasers. Being a truly remote technique, it is especially well suited for ultrasonic measurements at high temperatures, where conventional ultrasonic methods are impractical. Shear and longitudinal acoustic wave velocities were simultaneously measured in SiC reinforced alumina samples of varying porosity in the temperature range of 20°C to 1800°C. The temporal evolution of the velocities was also measured. Knowing the mass density and thermal expansion behavior of the samples, the measured velocities can be related to the average bulk elastic moduli. At room temperature, the elastic moduli vary linearly by one order or magnitude with mass density (porosity). At temperatures of up to 1300°C, the elastic moduli decrease linearly and independently of mass density (porosity). Above 1300°C, the elastic moduli may either increase or decrease depending on the sample mass density. Some time-dependence measurements at high temperatures were obtained. However, the samples sublimated and the condensate eventually blocked the furnace's optical ports, thus eliminating the time window to a few hours. |
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