Surface integrity and fatigue performance in metal additive manufacturing: a review on surface mechanisms, advanced characterization, and post-processing-induced evolution

Purpose This study aims to critically examine the role of surface and near-surface integrity in governing the fatigue performance and surface integrity of metal additive manufacturing (AM) components, with emphasis on surface-driven failure mechanisms. Design/methodology/approach The study investigates recent literature on metal AM surface science by organizing developments around governing surface and subsurface mechanisms rather than individual processing routes. Advances in three-dimensional topography analysis, residual stress characterization and subsurface microstructural evaluation are assessed alongside the influence of post-processing techniques, including machining, heat treatment and mechanical surface treatments. Findings Metal AM processes inherently generate non-equilibrium surface conditions characterized by high roughness, defect populations, residual stress gradients and heterogeneous microstructures, which critically control fatigue crack initiation. Post-processing strategies significantly modify these surface states by reducing defects, strain hardening and redistributing stress, thereby enhancing fatigue resistance. However, limitations remain in quantitatively linking surface metrics to long-term structural performance. Originality/value This review provides a mechanism-oriented and transdisciplinary perspective that integrates AM, surface engineering and fatigue mechanics. By reframing surface integrity as a controlling design variable rather than a secondary outcome of processing, it offers a structured framework for predictive, performance-based surface engineering in AM metals.