High temperature shear modulus determination using a laser-ultrasonic surface acoustic-wave device

For radioactive thin specimens in high pressure or high temperature environments, the conventional approach for high precision elastic modulus measurements is not easy. Radiation damage to transducer’s bonds or the substantial changes in specimen dimensions induced by temperature, pressure, and phase transitions, reduce the intrinsic accuracy of the time-of-flight acoustic measurements. We describe here an alternative approach in which the surface acoustic-wave (SAW) velocity is measured directly with a fixed propagation distance, independent of specimen dimensions. Then, using the known relationship between SAW and shear velocities, it is possible to obtain the shear modulus with a high accuracy without measuring the bulk shear wave. Laser ultrasonics was used combining a pulsed laser source with a heterodyne interferometer. The proposed technique is validated for Al, Au, Ta, and Pb 0.8% Ca, TA6V4 without phase transitions, and for Sn and Co through the phase transitions.