Characterizing polycrystalline microstructures by reconstructing grain boundaries and velocity map from ultrasonic surface wave field

An ultrasonic material characterization method is proposed to reconstruct the polycrystalline microstructures from the field-measurement of ultrasonic surface waves. Two wavenumber–frequency domain filters are developed to extract specific wave components for the reconstructions. One is the evanescent-pass filter that can be used to reconstruct the grain boundaries. The other is the directional filter to map the surface wave velocity along a specific direction. The method is validated by numerical simulations, as well as by experiments, on an additively manufactured sample. Sub-wavelength resolution can be achieved by the proposed method if sufficient data is captured spatially within one wavelength of the surface wave. •Polycrystals are characterized using ultrasonic surface waves. Wavenumber–frequency domain filters are used for signal processing.•Grain boundaries and wave velocity map are reconstructed simultaneously.•Sub-wavelength information can be revealed from Rayleigh waves.