Process-induced microstructural features and defect-controlled fatigue mechanisms in laser additive manufactured steels: a mechanistic review

Continuous innovation and breakthroughs in structural steel are the core of the manufacturing, aerospace, and construction industries. Laser-metal additive manufacturing (LAM), an emerging technology highly sought after in various industrial sectors, has paved a new path for the development of high-performance, intricate steel structures. Unlike conventional methods, which are unique in terms of their processing characteristics, LAM often involves materials that behave as a new class of alloys, necessitating tailored solutions and a fresh understanding. Despite significant progress to date, challenges persist, particularly concerning fatigue performance, which is a primary failure mode for structural components. The main objective of this review is to present recent advancements and new findings regarding LAM steels. Furthermore, we focus on the progress in understanding their fatigue behaviors and their influencing factors, which differ from conventional manufactured counterparts. Specifically, we summarize several potential fatigue-related factors, emphasizing the non-equilibrium characteristics of LAM steel in terms of defects and microstructural features. Then, we provide a unique analysis of the effects of process attributes and microstructural features on fatigue properties. Finally, we identify strategies to increase damage tolerance through LAM process optimization, structural and microstructure design, and alloy composition modification while also highlighting research gaps for future exploration. These insights are pivotal for the widespread adoption and robust design of engineered components.