Session: 19-02: Material Characterization by Ultrasonic waves

Paper Number: 98238

98238 - Characterization of Polycrystalline Microstructures by Wavenumber-Filtering of Ultrasonic Field Data 

Polycrystalline components composed of grains with different crystal orientations have been widely used. In polycrystals, each grain is locally anisotropic, with its elastic properties varying according to the crystal orientation. In this work, we present a characterization technique based on ultrasonic surface waves that reveals the microstructures using grain-boundary-reconstruction and surface-velocity-mapping. The surface waves are generated from a single location in the sample and the wave field is measured with high spatial resolution. To reconstruct grain boundaries, evanescent waves, which only exist close to the grain boundary, are extracted from the acquired field data by applying a high-pass wavenumber filter. To indicate the crystal orientation of the grain, the velocity map of Rayleigh waves can be used. The components of the surface waves propagating along specific direction are separated from the field data using a directional filter, so that the velocity map can be reconstructed by calculating its phase gradient. Finite element simulations and experiments are carried out to validate the method in a polycrystalline sample from additive manufacturing. The reconstructed velocity map agrees well with that obtained from electron backscatter diffraction (EBSD). Sub-wavelength resolution can be achieved by the proposed method if sufficient data is captured spatially within one wavelength of the surface wave.

Presenting Author: Zeqing Sun Nanyang Technological University