Influence of microstructural grain-size distribution on ultrasonic scattering

Ultrasonic attenuation and diffuse scattering result from the interaction of ultrasound with the microstructure of polycrystalline samples. Researchers are now using these effects to quantify mean grain size with good success and progress is being made with respect to more complex grain morphologies and macroscopic texture. However, theoretical models of such microstructures can become untenable because the scattering theory requires the two-point spatial statistics of the microstructure. For this reason, computational models of polycrystals are often considered for which grain spatial statistics can be calculated directly. In this study, the influence of grain-size distribution is examined using such an approach with three-dimensional (3D) realizations of polycrystalline materials. Representative material volumes are created using DREAM.3D with lognormal grain-size distributions, with fixed means but six different widths. These realizations are then used to calculate the relevant grain statistics which are then used to determine ultrasonic attenuation. The use of thirty realizations for each grain-size distribution allows the variation of the ultrasonic scattering to be quantified. The results show that the correlation between attenuation and distribution width can be modeled with a power law. Additionally, the frequency dependence of attenuation is shown to depend strongly on the distribution width. These results are expected to aid in the development of simplified models to quantify the grain-size distribution.