Ultrasonic Signal Response from Internal Manufactured Defects in Laser- Based Powder Bed Fusion (PBF-LB) Manufactured superalloys

Abstract

Additive manufacturing (AM) is an advanced technology reshaping global product fabrication by enabling lightweight and complex structures directly from CAD models [1]. While AM provides design freedom and material efficiency, challenges remain in ensuring consistent quality, as defects such as porosity, microcracks, and lack of fusion (LOF) voids can degrade mechanical performance [7–9]. Non-destructive testing (NDT) methods are therefore critical, with X-ray Computed Tomography (XCT) and Ultrasonic Testing (UT) emerging as the most promising despite limitations of cost, speed, and geometry sensitivity [16,20]. UT, in particular, enables early detection of internal flaws without damaging the component, and recent advances such as phased array and laser-based techniques are expected to further enhance inspection capability [2,24,25]. This study evaluates the ultrasonic signal response from intentionally introduced defects in PBF-LB manufactured Alloy 247 and Inconel 939 samples. Both immersion UT and PAUT were applied to investigate the influence of defect morphology, orientation, and surface finish. Results showed that defects down to 0.4 mm could be reliably detected when oriented perpendicular to the scanning surface. Machined surfaces significantly improved defect detectability, while partially melted powder around defects increased scattering and reduced signal clarity. Among probes, the 3.25" transducer provided the most consistent response due to its larger aperture, which enhanced beam focus, signal strength, and defect detectability across varied geometries and surface conditions. Defect morphology strongly influenced detectability, with angled and roof-shaped defects showing reduced visibility compared to cylindrical or spherical ones. Comparison of inspection methods demonstrated that PAUT enhanced sensitivity and imaging in geometrically complex regions, whereas XCT provided more accurate defect characterization but with slower scan speed and higher cost. These findings highlight the importance of probe selection, surface condition, and defect morphology for developing robust in-situ inspection strategies and support the integration of PAUT and XCT as complementary methods for standardized quality control in metal additive manufacturing.