Non-destructive ultrasonic evaluation and metallographic validation of artificial defects in L-PBF additive manufactured specimens using CAD-seeding

This study investigates the feasibility of ultrasonic testing (UT) for detecting internal defects in laser powder bed fusion (L-PBF) manufactured materials. The suitability of a universal reference test specimen designed for multiple non-destructive tests (NDT) proposed by ISO/ASTM is verified using UT. The star-shaped specimen is used to evaluate the detectability and characterization of artificial defects in 316 L. Each star tip contains spherical or cylindrical defects of varying orientations and sizes (100 – 700 µm). Phased Array Ultrasonic Testing (PAUT) and the Total Focusing Method (TFM) are combined to assess defect detectability, sizing and orientation from multiple probe positions. The results are validated using simulation and microscopic imaging. The results show that PAUT and TFM, when used together, enhance defect detection, identifying flaws as small as 0.1 mm. Detection accuracy depends on probe positioning (top or side surface), beam angle, defect type and orientation. The highest accuracy is achieved from the planar top side of the specimen. The spherical and oriented cylindrical defects proved to be the most challenging to detect. Detectability is mainly influenced by the available sound reflection surface, inner surface roughness and defect filling (loose powder or sintered particles). To improve detectability and promote image-based sizing approaches in ultrasonic testing the inner surface roughness has to be improved. These findings provide a foundation for future research into the detectability of inner defects, sizing approaches and precise seeding of artificial internal defects in L-PBF components using ultrasonic testing.