Phase coherence factor-based ultrasonic annular array testing method for coarse-grained materials

Metal materials with coarse-grained structures have the characteristics of coarse grain, acoustic anisotropy, and structural inhomogeneity. When the ultrasonic wave propagates in its interior, the above characteristics will cause strong waveform distortion, acoustic energy attenuation, and structural-acoustic scattering, resulting in a poor signal-to-noise ratio of the ultrasonic echo signal. The annular array ultrasonic transducer has a three-dimensional axisymmetric acoustic field, which is less affected by the grain structure than the linear array ultrasonic transducer. It can realize the focus within the detection range by the total focusing method (TFM) post-processing in the way of the full matrix capture (FMC) and is suitable for ultrasonic non-destructive testing of coarse-grained materials with high acoustic attenuation. In this paper, a TFM C-scan testing method based on the phase coherence factor (PCF) denoising is proposed. The C-scan imaging results of the coarse-grained GH4169 specimen verify the denoising effectiveness of the proposed method. Compared with the TFM of the annular array, the PCF can improve the signal-to-noise ratio of the flat bottom hole defect by up to 14.99 dB.