Review of non-destructive evaluation techniques for ex-situ defect detection and characterization in additively manufactured metal components

Additive manufacturing (AM) offers design freedom and the ability to integrate multiple functions into a component. However, AM process-induced defects such as porosity, lack of fusion, cracks, and residual stress remain a major obstacle to its widespread use in safety-critical applications. Advancement in in-situ evaluation during production help minimize this defects. However, reliable ex-situ detection and characterization of the defects are essential for predicting and ensuring quality, reliability, and lifecycle performance of additive manufactured components. This study presents a comprehensive review of non-destructive testing methods for ex-situ defect detection in metal additive manufacturing (MAM). Rather than focusing solely on individual techniques, the review emphasizes the origin of key defect types, including porosity, lack of fusion, cracks, and residual stress while also discussing the detectability using established evaluation method. Finally, current limitations, open challenges, and future research directions are identified to support the development of reliable and industrially deployable non-destructive testing frameworks for MAM.