Ultrasonic testing of austenitic stainless steel overlay structures using Voronoi tessellation and phase coherence imaging

Abstract Austenitic stainless steel overlay structures typically cause significant scattering and energy attenuation of ultrasonic waves due to their coarse-grained microstructure. This leads to problems such as low signal-to-noise ratio (SNR) and blurred imaging in traditional ultrasonic testing methods. This study presents an optimized ultrasonic testing method based on Voronoi tessellation modeling and phase coherence imaging . First, a uniform Voronoi grain model was generated using the Lloyd algorithm. The effect of grain anisotropy on sound attenuation was then analyzed with a finite element simulation model, which confirmed the model’s effectiveness in predicting scattering distortions. Second, a full matrix capture acquisition model for overlay structures was built. Total focusing method (TFM) imaging was performed for both the grain and non-grain structures. A phase-coherent algorithm was applied to reduce noise. Spatially adaptive weighting of the circular coherence factor and sign coherence factor (SCF) was used to suppress grain noise. Experimental results show that, compared to conventional TFM, SCF-TFM improves the SNR of flat-bottom hole defect detection at the interface from 31.9 dB to 57.2 dB (a 79% improvement). Both simulation and experimental results demonstrate that the method is effective in suppressing grain noise and improving the imaging quality of flat-bottom hole defects, providing an effective optimization approach for enhancing the resolution of nondestructive testing in high attenuation coarse-grained materials.