PSI - Issue 54

Daniel F.O. Braga et al. / Procedia Structural Integrity 54 (2024) 631–637

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2 Daniel F.O. Braga et al. / Structural Integrity Procedia 00 (2023) 000–000 novative, lightweight, and complex components. Among the various metal AM techniques, Selective Laser Melting (SLM), Laser Metal Deposition (LMD), and the fusion of these technologies stand out as transforma tive processes that have found applications across a multitude of industries, from aerospace and automotive to healthcare and beyond. However, the evolution of metal AM has brought with it an intensified focus on a critical aspect—structural integrity.

Nomenclature AM Additive Manufacturing EBM Electron Beam Melting FCG Fatigue Crack Growth HAZ Heat Affected Zone HIP Hot Isostatic Pressing

LMD Laser Melting Deposition SLM Selective Laser Melting PDT Probabilistic Damage Tolerance

In metal AM, where intricate parts are built layer by layer through the precise application of energy, ensuring structural integrity is paramount. The components produced must meet rigorous performance, reliability, and safety standards, reflecting the industries they serve. As these industries increasingly turn to metal AM for the fabrication of critical components, understanding and addressing the challenges related to structural integrity have become central to harnessing the full potential of this disruptive technology. This review centers on structural integrity in metal additive manufacturing, with a particular emphasis on SLM, LMD, and the integration of these techniques. It explores the critical considerations and methodologies employed in assessing the structural integrity of parts manufactured through these advanced processes. Furthermore, it delves into the impact of material properties, microstructural characteristics, defects, and post-processing procedures on the integrity of metal AM components. The increasing interest in adoption of metal additive manufacturing processes in safety critical and complex loaded components is accompanied by and increase in studies regarding structural integrity issues with these manufacturing processes. Gorelik (2017) reviewed metal additive manufacturing in the context of structural integrity. The author states that casting factors as defined in Civil Air Regulations, may not be completely suited to the adoption of manufacturing technologies, such as, metal additive manufacturing, due to the risks of "unknown unknowns", due to process variability. A zone-based probabilistic damage tolerance (PDT) framework is suggested to be developed jointly by industry and governing authorities, to address this challenge. As these manufacturing processes involve complex thermal cycles and rapid solidification, which can in troduce microstructural variations and defects, ensuring consistent process parameters, such as laser power, scan speed, and powder feed rates, is pivotal in maintaining the desired mechanical properties and metalog raphy. However, process variability still arises from inconsistencies in the raw material, machine-to-machine variability, work environment inconsistency and others, which given the geometrical complexity of compo nents manufactured with these processes, makes the process qualification challenging, Frazier (2010). This process variability is and added challenge in structural integrity point of view. Although powder-bed based technologies like SLM enable optimized, high geometric complexity parts to be manufactured, low build-up rates and systems print volumes limit component sizes and feasibility of many applications. One approach to dealing with these limitations is to manufacture with a combination of SLM and LMD, in the same process chain (see schmatics of SLM and LMD in Fig. 1). Graf et al. (2015), demonstrated the feasibility of a process chain including both technologies to manufacture Inconel 718 turbine blades. Microstructural analysis was conducted, on a specimen prior to demonstrator manufacturing in Ti-6Al-4V, showing good metallurgical bonding between LMD single layers and to the SLM part, with no visible cracks at the boundary and in the adjacent microstructure. By employing the combined process chain, a significant decrease in manufacturing time was achieved ( ≈ 61.4 %), but temperature and part