Additive manufacturing and post-processing needs: an analysis of defect mitigation and performance enhancement

Abstract

Additive manufacturing (AM) has revolutionised the production of complex metallic components by enabling unprecedented geometric freedom; however, the layer-by-layer fabrication process inherently generates a complex landscape of defects, including extreme residual stresses, internal porosity, microstructural anisotropy, and high surface roughness. These structural anomalies significantly degrade the fatigue life and operational reliability of as-built parts, rendering them unsuitable for direct structural applications and necessitating a comprehensive, highly engineered post-processing workflow. This necessity is further amplified as the industry scales towards Large Area Additive Manufacturing (LAAM), where macroscopic distortion and severe residual stress accumulation in massive, metre-scale components require unprecedented levels of thermal and mechanical intervention. This manuscript systematically reviews the genesis of manufacturing defects at the thermodynamic and microstructural levels, detailing the kinetic mechanisms of melt-pool instability and rapid solidification. It explores the synergistic application of support-structure removal, thermal treatments for microstructural homogenisation, and Hot Isostatic Pressing (HIP) for internal void closure, highlighting phenomena such as pore regrowth in titanium, aluminium, and nickel-based alloys. Furthermore, advanced surface-finishing techniques – including Abrasive Flow Machining (AFM) and Plasma Electrolytic Polishing (PEP) – are evaluated for their efficacy in complex internal geometries, such as novel heat exchangers. By integrating these post-processes in accordance with evolving ISO/ASTM qualification standards, the synergistic effects on mitigating crack growth and maximising fatigue performance are elucidated, demonstrating the absolute imperative of post-processing for transitioning AM into a certified engine for high-performance industrial production.