Shape and size evaluations of elongated grains using phased array ultrasound and directional backscattering method

Elongated grain is a typical grain morphology and influences the mechanical properties of polycrystalline materials. Directional ultrasonic backscattering signal is sensitive to the grain shape, and the phased array ultrasound provides an effective and efficient means to collect the directional backscattering signals. In this study, the theoretical backscattering model is modified to allow for phased array detection. The model shows that the backscattering amplitude is dependent on the direction of the ultrasound propagation. Experimental testing on an aluminum sample is performed to acquire phased array ultrasound data with multiple steering angles and rotation angles. The experimental directional backscattering ratios are fitted by the theoretical ratios using the least-squares method. The results show that the phased array directional backscattering method can be used to measure the size and shape of elongated grains. The size and shape quantifications of elongated grains obtained using the developed method are comparable to those obtained via metallography.