Mode-converted ultrasonic scattering in polycrystals with elongated grains

Abstract

Elastic wave scattering is used to study polycrystalline media for a wide range of applications. Received signals, which include scattering from the randomly oriented grains comprising the polycrystal, contain information from which useful microstructural parameters may often be inferred. Recently, a mode-converted diffuse ultrasonic scattering model was developed for evaluating the scattered response of a transverse wave from an incident longitudinal wave in a polycrystalline medium containing equiaxed single-phase grains with cubic elastic symmetry. In this article, that theoretical mode-converted scattering model is modified to account for grain elongation within the sample. The model shows the dependence on scattering angle relative to the grain axis orientation. Experimental measurements were performed on a sample of 7475-T7351 aluminum using a pitchcatch transducer configuration. The results show that the mode-converted scattering can be used to determine the dimensions of the elongated grains. The average grain shape determined from the experimental measurements is compared with dimensions extracted from electron backscatter diffraction, an electron imaging technique. The results suggest that mode-converted diffuse ultrasonic scattering has the potential to quantify detailed information about grain microstructure.

Comparison of Experimental Measurements of Material Grain Size Using Ultrasound

“…The present results from the SSR and DSR models are closer to the short side of grain than the equivalent diameter, where the short side of the grains was re-measured as 54.5 ± 2.4 µm from the microstructure image. Although the backscattering models for elongated grains have been built [22,23], they would be cumbersome to perform in the industrial application. It is suggested that at least 2 scans from orthogonal planes of the specimen are necessary to define an unknown elongated microstructure meanwhile there might be only one plane could be scanned for some large plates.…”

Generalized ultrasonic scattering model for arbitrary transducer configurations

“…7(b), the response most resembles the mode-converted scattering response dependence on angle of incidence. 28 The decrease in amplitude is gradual after the maximum near, h I . Note that the grain orientation angles depicted are w g ¼ 45 ; 90 , and 135 because the symmetry in the response for this transducer configuration is about w g ¼ 45 rather than w g ¼ 0 or 90 as shown later in Fig.…”

“…Multiple authors have explored the applicability of this solution for extraction of microstructural features of polycrystalline media. [25][26][27][28] Ghoshal and Turner 25 provided a solution for the longitudinal backscatter response through a curved interface. Hu et al extended the model to in-plane mode-converted 26 and shear-to-shear 27 scattering, which are advantageous for thinner samples and detection of defects in the transverse direction.…”

“…Hu et al extended the model to in-plane mode-converted 26 and shear-to-shear 27 scattering, which are advantageous for thinner samples and detection of defects in the transverse direction. Arguelles et al 28 then considered the mode-converted scattering model in the presence of grain elongation. In all these studies, [25][26][27][28] the authors were successful at inverting ultrasonic data to obtain characteristic grain sizes.…”

“…Arguelles et al 28 then considered the mode-converted scattering model in the presence of grain elongation. In all these studies, [25][26][27][28] the authors were successful at inverting ultrasonic data to obtain characteristic grain sizes.…”