New developments and open challenges in defect mechanisms in Selective Laser Melting (SLM)

Selective Laser Melting (SLM), also known as Laser Powder Bed Fusion (LPBF), has emerged as a key additive manufacturing technology for high-performance applications in the aerospace, medical, and energy sectors. However, defect formation remains a central barrier to achieving consistent part reliability and large-scale industrial adoption. While conventional reviews have extensively addressed classical defects such as porosity, cracking, and balling, recent studies reveal additional, less-explored mechanisms, including oxide and slag inclusions from powder reuse, microsegregation-driven degradation, near-surface defects induced by recoater interactions, and the impact of powder aging. This review provides a critical synthesis of recent advances (2018–2024), integrating defect mechanisms with emerging monitoring, simulation, and AI-driven control strategies. Unlike previous studies that treat defect formation and mitigation separately, this work establishes connections between process physics, material evolution, and data-driven approaches. By systematically comparing defect types, mitigation strategies, and current limitations across different material systems, this paper identifies key research gaps, including the lack of standardized defect characterization, insufficient cross-alloy benchmarking, and the fragmented understanding of less-studied defects. The findings highlight a paradigm shift toward integrated defect management frameworks, combining in situ monitoring, multiphysics modeling, and machine learning for predictive and adaptive process control. Ultimately, this review outlines the critical challenges and future directions required to transition SLM from a defect-limited process toward a reliable and scalable manufacturing technology.