Grain Size Estimation using phased array ultrasound attenuation

Abstract

Grain size is a key parameter for polycrystalline material affecting the mechanical properties. Ultrasonic attenuation method can be used to evaluate the grain size efficiently and accurately, but it is still a challenge for phased array ultrasound. This study develops a phased array ultrasound method for grain size estimation by incorporating the diffraction loss correction. The phased array sound field model of back-wall echoes is established, allowing for calculating the diffraction loss coefficients with different steering angles and focusing depths. The Weaver's classical scattering model is used to inversely solve the grain size. Experimental testing on a steel testing piece is performed to acquire the phased array ultrasound data. The developed method is employed to estimate the grain size with the measured attenuation, and the results are compared with metallography results. The influences of the steering angle and the focusing depth are investigated in detail. It is shown that a low focal depth and a relatively smaller sweeping angle can achieve reliable results.