Grain size evaluation in polycrystalline materials using the interference effect of bounded ultrasonic beams at the...

Non-destructive evaluation of grain size is crucial for characterizing the mechanical properties of polycrystalline materials. We present a novel ultrasonic methodology for evaluating mean grain size based on the interference effect of bounded ultrasonic beams at the Rayleigh critical angle. We analyzed and overviewed the reflected field of a bounded ultrasonic beam at a liquid-solid interface and the relationship between single-crystal and polycrystal elastic constants. Numerical simulations and experimental measurements were conducted to validate the effectiveness of the proposed method. Results show that when a bounded ultrasonic beam is obliquely incident on the liquid-solid interface at the Rayleigh critical angle, the acoustic pressure amplitude captured by the specular receiver exhibits a monotonic relationship with, and high sensitivity to, different mean grain sizes of polycrystalline materials. In contrast, only minor variations are observed at either the longitudinal or transverse wave critical angle. The smaller the deviation of the incident angle from the Rayleigh critical angle, the higher the sensitivity of the proposed method to variations in grain size. Furthermore, the results indicate that by optimizing the bandwidth of the excitation signal while keeping other parameters constant, maximum sensitivity to variations in grain size can be achieved. These findings demonstrate that the proposed method achieves high sensitivity in evaluating the mean grain size of polycrystalline materials, further enriching the ultrasonic measurement techniques for the mean grain size of polycrystalline materials.