Hot isostatic pressing for powder-based additive manufacturing of metals: State-of-the-art review and future perspectives

Additive manufacturing (AM), commonly known as 3D printing, is defined by ISO/ASTM 52900:2021 as “process of joining materials to make parts from 3D model data, usually layer upon layer, as opposed to subtractive manufacturing and formative manufacturing methodologies”. Powder-based AM is a subcategory of AM technology in which metal powders are sintered or melted using a high-power heat source, such as laser or electron beam. Despite various advantages of this manufacturing process widely applied for metals, powder-based AM often results in metallurgical defects. These defects, particularly in low-density metal parts, necessitate post-processing techniques to improve the mechanical properties and ensure the structural integrity of as-built metal parts. Among post-processing techniques, hot isostatic pressing (HIP) has emerged as an effective thermal post-processing technique for densifying metal parts to mitigate or eliminate metallurgical defects such as, porosity and cracking, not only for AM parts but also for casted parts. The HIP process involves subjecting materials to high-pressure isostatic compression in a pressurised chamber at elevated temperatures, typically using an inert gas such as argon. Although there have been several promising developments and emerging trends in the field of HIP, very few review papers on HIP as a post-processing technique for metals produced by powder-based AM has been published to date. Therefore, this paper provides a comprehensive review of the state of the art in such topic, detailing challenges and considerations, recent advancements and innovations, as well as future directions and market trends in the field of HIP.