Ultrasonic Signal Response from Internal Manufactured Defects in PBF-LB Manufactured Superalloys

Abstract

In the emerging field of Additive Manufacturing (AM), the promise of unparalleled design flexibility, resource efficiency, and rapid prototyping has captivated both industry and academia. While AM techniques offer a wide range of manufacturing possibilities, they also present unique challenges in ensuring structural integrity and material properties. Non-Destructive Testing (NDT) methods, including Ultrasonic Testing (UT), have emerged as invaluable tools for evaluating the internal structure of AM components without compromising their integrity. By employing NDT techniques, it is possible to detect flaws such as porosities, cracks, and other inhomogeneities early in the manufacturing process, thereby improving reliability, extending the lifespan, and reducing the overall environmental footprint of AM products. While the occurrence of defects from processes such as welding is well-established, documented and standardized with regards to NDT, a knowledge gap exists for defects in the field of AM. Specifically, reference reflectors commonly used in the industry, such as side-drilled holes and flat bottom holes, are well understood when machined into components using traditional (subtractive) means. AM offers more flexibility, e.g., adding closed internal reference reflectors directly from the build-process. Twelve straight blocks were manufactured using Laser Powder Bed Fusion (PBF-LB) with carefully selected artificial defects. All defects were created by CAD (Computer Aided Design) seeding, i.e., introducing voids into the CAD-model. The blocks were inspected using Phased Array Ultrasonic Testing as well as conventional ultrasonic testing. It was shown that the as-built surface of PBF-LB has an adverse impact on the ultrasonic testing signal response, and the detectability of defects was quantified under the different conditions (machined surface compared to as-built). It was shown that the build direction has an impact on the morphology and the UT signal response from internally seeded defects.