High-resolution 3-D characterization and detection of subsurface defects in metal additive manufacturing using laser ultrasonic.

With the advancement of metal additive manufacturing, components fabricated by this technique are being increasingly adopted across various industries. However, due to the influence of fabrication parameters, components tend to develop defects during the manufacturing process. Timely detection of defects in the heat-affected zone (the subsurface region) is crucial, as process parameters can be adjusted and reprocessing can be performed to eliminate such defects. As a non-contact, high-resolution technique, laser ultrasonic offers a powerful tool for defect detection in manufacturing processes. In this study, laser ultrasonic was employed to perform off-line detection of subsurface defects in additively manufactured specimens. Three sub-millimeter horizontal blind holes were fabricated at a depth of 1 mm below the surface of laser powder bed fusion manufactured TI-6AL-4 V specimens to simulate typical subsurface defects. The total focusing method was utilized for high-resolution planar imaging of the defects, while an optimized elliptical localization method was applied for accurate defect localization and sizing in the depth direction. By integrating the results from these two methods, 3-D mapping and reconstruction of the defects were achieved, enabling high-precision characterization of sub-surface defects.