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Over the past several decades, metal Additive Manufacturing (AM) has transitioned from a rapid prototyping method to a viable manufacturing tool. AM technologies can produce parts on-demand, repair damaged components, and provide an increased freedom of design not previously attainable by traditional manufacturing techniques. The increasing maturation of metal AM is attracting high-value industries to directly produce components for use in aerospace, automotive, biomedical, and energy fields. Two leading processes for metal part production are Powder Bed Fusion with laser beam (PBF-LB/M) and Directed Energy Deposition with laser beam (DED-LB/M). Despite the many advances made with these technologies, the highly dynamic nature of the process frequently results in the formation of defects. These technologies are also notoriously difficult to control, and the existing machines do not offer closed loop control. In the present work, the application of various Machine Learning (ML) approaches and in-situ monitoring technologies for the purpose of defect detection are reviewed. The potential of these methods for enabling process control implementation is discussed. We provide a critical review of trends in the usage of data structures and ML algorithms and compare the capabilities of different sensing technologies and their application to monitoring tasks in laser metal AM. The future direction of this field is then discussed, and recommendations for further research are provided.

Powder bed fusion of copper has been extensively investigated using both laser-based (PBF-LB/M) and electron beam-based (PBF-EB/M) additive manufacturing technologies. Each technique offers unique benefits as well as specific limitations. Near-infrared (NIR) laser-based LPBF is widely accessible; however, the high reflectivity of copper limits energy absorption, thereby resulting in a narrow processing window. Although optimized parameters can yield relative densities above 97%, issues such as keyhole porosity, incomplete melting, and anisotropy remain concerns. Green lasers, with higher absorptivity in copper, offer broader process windows and enable more consistent fabrication of high-density parts with superior electrical conductivity, often reaching or exceeding 99% relative density and 100% International Annealed Copper Standard (IACS). Mechanical properties, including tensile and yield strength, are also improved, though challenges remain in surface finish and geometrical resolution. In contrast, Electron Beam Powder Bed Fusion (EB-PBF) uses high-energy electron beams in a vacuum, eliminating oxidation and leveraging copper’s high conductivity to achieve high energy absorption at lower volumetric energy densities (~80 J/mm3). This results in consistently high relative densities (>99.5%) and excellent electrical and thermal conductivity, with additional benefits including faster scanning speeds and in situ monitoring capabilities. However, EB-PBF processes in general face their own limitations, such as surface roughness and powder smoking. This paper provides a comprehensive review of the current state of laser-based (PBF-LB/M) and electron beam-based (PBF-EB/M) powder bed fusion processes for the additive manufacturing of copper, summarizing key trends, material properties, and process innovations. Both approaches continue to evolve, with ongoing research aimed at refining these technologies to enable the reliable and efficient additive manufacturing of high-performance copper components.

Aluminum alloys are key materials in additive manufacturing (AM) technologies thanks to their low density that, coupled with the possibility to create complex geometries of these innovative processes, can be exploited for several applications in aerospace and automotive fields. The AM process of these alloys had to face many challenges because, due to their low laser absorption, high thermal conductivity and reduced powder flowability, they are characterized by poor processability. Nowadays mainly Al-Si alloys are processed, however, in recent years many efforts have been carried out in developing new compositions specifically designed for laser based powder bed AM processes. This paper reviews the state of the art of the aluminum alloys used in the laser powder bed fusion process, together with the microstructural and mechanical characterizations.

The main objective of this research is to investigate the capability of laser powder bed fusion (LPBF) to manufacture complex heat exchangers with gyroid-shaped channels. First, the gyroid’s geometric features are investigated including the network type, thickness, unit cell size, and aspect ratio. Computational fluid dynamics (CFD) were used to screen these designs based on their thermal and fluid dynamics performance. Then, the manufacturability of various AlSi10Mg gyroid designs is tested using the LPBF, and the microstructure was investigated for defects. Finally, five heat exchanger prototypes were manufactured using LPBF; four of them were based on gyroid designs, and the fifth one was a conventional design for comparison. A heat transfer analysis is performed to compare the performance of the heat exchangers using conjugate heat transfer (CHT) methods. It was found that manipulating the sheet gyroid thickness and aspect ratio can result in a reasonable tradeoff between air side and coolant side pressure drops while maintaining the same heat rejection value. The suggested process parameters were able to successfully print the gyroid heat exchanger cores with thicknesses higher than 0.2 mm successfully. The LPBF-fabricated gyroid heat exchangers outperformed the conventional design. This study paves the road to a new generation of crossflow heat exchanger designs.

Spatter is an inherent, unpreventable, and undesired phenomenon in laser powder bed fusion (L-PBF) additive manufacturing. Spatter behavior has an intrinsic correlation with the forming quality in L-PBF because it leads to metallurgical defects and the degradation of mechanical properties. This impact becomes more severe in the fabrication of large-sized parts during the multi-laser L-PBF process. Therefore, investigations of spatter generation and countermeasures have become more urgent. Although much research has provided insights into the melt pool, microstructure, and mechanical property, reviews of spatter in L-PBF are still limited. This work reviews the literature on the in situ detection, generation, effects, and countermeasures of spatter in L-PBF. It is expected to pave the way towards a novel generation of highly efficient and intelligent L-PBF systems.

WE43 parts with favorable forming quality are fabricated by laser-beam powder bed fusion and the interaction between laser beam and powder is revealed. After suitable heat treatment, the anisotropic microstructure is eliminated, with nano-scaled Mg 24 Y 5 particles homogeneously precipitated. The yield strength and ultimate tensile strength are improved to (250.2  ± 3.5)  MPa and (312  ± 3.7)  MPa, respectively, while the elongation still maintains at high level of 15.2%. Homogenized microstructure inhibits the micro galvanic corrosion and promotes the development of passivation film, thus decreasing the degradation rate by an order of magnitude. The porous WE43 scaffolds offer a favorable environment for cell growth. Magnesium (Mg) alloys are considered to be a new generation of revolutionary medical metals. Laser-beam powder bed fusion (PBF-LB) is suitable for fabricating metal implants with personalized and complicated structures. However, the as-built part usually exhibits undesirable microstructure and unsatisfactory performance. In this work, WE43 parts were firstly fabricated by PBF-LB and then subjected to heat treatment. Although a high densification rate of 99.91% was achieved using suitable processes, the as-built parts exhibited anisotropic and layered microstructure with heterogeneously precipitated Nd-rich intermetallic. After heat treatment, fine and nano-scaled Mg 24 Y 5 particles were precipitated. Meanwhile, the α -Mg grains underwent recrystallization and turned coarsened slightly, which effectively weakened the texture intensity and reduced the anisotropy. As a consequence, the yield strength and ultimate tensile strength were significantly improved to (250.2  ± 3.5)  MPa and (312  ± 3.7)  MPa, respectively, while the elongation was still maintained at a high level of 15.2%. Furthermore, the homogenized microstructure reduced the tendency of localized corrosion and favored the development of uniform passivation film. Thus, the degradation rate of WE43 parts was decreased by an order of magnitude. Besides, in-vitro cell experiments proved their favorable biocompatibility.

Additive manufacturing (AM) technologies have gained considerable attention in recent years as an innovative method to produce high entropy alloy (HEA) components. The unique and excellent mechanical and environmental properties of HEAs can be used in various demanding applications, such as the aerospace and automotive industries. This review paper aims to inspect the status and prospects of research and development related to the production of HEAs by AM technologies. Several AM processes can be used to fabricate HEA components, mainly powder bed fusion (PBF), direct energy deposition (DED), material extrusion (ME), and binder jetting (BJ). PBF technologies, such as selective laser melting (SLM) and electron beam melting (EBM), have been widely used to produce HEA components with good dimensional accuracy and surface finish. DED techniques, such as blown powder deposition (BPD) and wire arc AM (WAAM), that have high deposition rates can be used to produce large, custom-made parts with relatively reduced surface finish quality. BJ and ME techniques can be used to produce green bodies that require subsequent sintering to obtain adequate density. The use of AM to produce HEA components provides the ability to make complex shapes and create composite materials with reinforced particles. However, the microstructure and mechanical properties of AM-produced HEAs can be significantly affected by the processing parameters and post-processing heat treatment, but overall, AM technology appears to be a promising approach for producing advanced HEA components with unique properties. This paper reviews the various technologies and associated aspects of AM for HEAs. The concluding remarks highlight the critical effect of the printing parameters in relation to the complex synthesis mechanism of HEA elements that is required to obtain adequate properties. In addition, the importance of using feedstock material in the form of mix elemental powder or wires rather than pre-alloyed substance is also emphasized in order that HEA components can be produced by AM processes at an affordable cost.

The melt pool characteristics in terms of size and shape and the porosity development in laser powder bed fusion–processed Inconel 718 were investigated to determine how laser power and scan speed influence the porosity in the microstructure. The melt pool characteristics developed with both single-track and multilayer bulk laser deposition were evaluated. It was found that the melt pool characteristic is critical for the porosity development. It is shown that the porosity fraction and pore shape change depending on the melt pool size and shape. This result is explained based on the local energy density of a laser during the process. High-density (> 99%) Inconel 718 samples were achieved over a wide range of laser energy densities (J/mm 2 ). A careful assessment shows that the laser power and scan speed affect differently in developing the pores in the samples. The porosity decreased rapidly with the increase in laser power while it varied linearly with the scan speed. A proper combination, however, led to fully dense samples. The study reveals an optimum condition in terms of laser power and scan speed that can be adopted to fabricate high-density Inconel 718 parts using laser powder bed fusion–based additive manufacturing process.

Laser powder bed fusion (L-PBF) and direct laser deposition (DLD) are the two main processes currently used in the additive manufacturing (AM) of metals. For both methods, metal powders are used as feedstock, and they must present specific physical and chemical properties to ensure optimal processing and reliable and reproducible printing results. Particle morphology, size distribution, and flowability, among other factors, depend on the powder production process and directly influence the processing parameters and physical characteristics of the parts built by AM. This systematic review presents different concepts involving L-PBF and DLD manufacturing and the application of metal powders. The methods used to produce and characterize metal powders and the modification techniques to improve their processability by AM are detailed and discussed. Environmental and health risks are also presented, and safety measures that must be considered while handling metal powders. Some key topics requiring attention for further development are highlighted. Graphical abstract

The printability, microstructural characteristics, phase transformation behaviors, and mechanical properties of LPBF-fabricated NiTi alloys are reviewed. Several common structures for LPBF-fabricated NiTi alloys are considered and their various fields of application are illustrated. The technical challenges, limitations, and development tendencies of LPBF-fabricated NiTi alloys are put forward. NiTi alloys have drawn significant attentions in biomedical and aerospace fields due to their unique shape memory effect (SME), superelasticity (SE), damping characteristics, high corrosion resistance, and good biocompatibility. Because of the unsatisfying processabilities and manufacturing requirements of complex NiTi components, additive manufacturing technology, especially laser powder bed fusion (LPBF), is appropriate for fabricating NiTi products. This paper comprehensively summarizes recent research on the NiTi alloys fabricated by LPBF, including printability, microstructural characteristics, phase transformation behaviors, lattice structures, and applications. Process parameters and microstructural features mainly influence the printability of LPBF-processed NiTi alloys. The phase transformation behaviors between austenite and martensite phases, phase transformation temperatures, and an overview of the influencing factors are summarized in this paper. This paper provides a comprehensive review of the mechanical properties with unique strain-stress responses, which comprise tensile mechanical properties, thermomechanical properties (e.g. critical stress to induce martensitic transformation, thermo-recoverable strain, and SE strain), damping properties and hardness. Moreover, several common structures (e.g. a negative Poisson’s ratio structure and a diamond-like structure) are considered, and the corresponding studies are summarized. It illustrates the various fields of application, including biological scaffolds, shock absorbers, and driving devices. In the end, the paper concludes with the main achievements from the recent studies and puts forward the limitations and development tendencies in the future.