Comprehensive pore defect analysis for electron beam-powder bed fusion of Ti48Al2Cr2Nb

Despite the unique capabilities of Additive Manufacturing (AM) processes for producing Ti components with complex geometries, the desired properties are only achievable if a holistic scheme is devised, considering the synergistic role of post-processing steps. This work aimed to enhance the applicability of metal AM products by improving the process chain in the manufacturing industry. For this purpose, the current work demonstrates a comprehensive investigation into the hot deformation of Ti-6Al-4 V (Ti64) pre-forms produced via the Electron Beam Powder Bed Fusion (EB-PBF) process focusing on the determination of critical conditions for initiating Dynamic Recrystallization (DRX) in these components. Following a sequential evaluation procedure, hot deformation experiments were carried out at temperatures ranging from 1000 to 1200 °C and strain rates of 0.001–1 s−1 to determine the critical stress and strain required for initiating DRX in Ti64 pre-forms and compare them to their wrought counterparts. In addition, a specific Finite Element Model (FEM) was coupled with DRX kinetics equations to predict the volume percentage of DRX grains during the hot deformation of the pre-forms. The analysis of flow stress curves showed a significant peak stress at low strains, which is then followed by a period of flow softening and eventually transitions into a nearly steady-state flow at higher strains. In addition, compared to their wrought counterparts, the EB-PBF samples exhibited a significantly superior flow softening behavior, as evidenced by a more significant volume fraction of DRX and faster recrystallisation rates. It was also revealed that the normalised strain for DRX initiation in the EB-PBF Ti64 and wrought one was 0.55 and 0.67, respectively. FEM results closely matched the experimental finding, confirming its reliability in providing valuable insights into microstructural evolution and offering a time-efficient alternative for process design and property optimisation, lowering dependence on trial-and-error approaches. Through a combination of experiments, numerical analysis, and finite element simulations, this study sheds light on the macroscopic deformation and microstructural transformations occurring during hot working processes.

High melting point materials such as ceramics and metal carbides are in general difficult to manufacture due to their physical properties, which imposes the need for new manufacturing methods where electron beam powder bed fusion (EB‐PBF) seems promising. Most materials that have been successfully printed with EB‐PBF are metals and metal alloys with good electrical conductivity, whereas dielectric materials such as ceramics are generally difficult to print. Catastrophic problems such as smoking and spattering can occur during the EB‐PBF processing owing to inappropriate physical properties such as lack of electrical, and thermal conductivity and high melting point, which are challenging to overcome by process optimization. Due to these difficulties, a limited level of understanding has been achieved regarding melting ceramics and refractory alloys. Herein, three different substrates of niobium carbide (NbC) are melted using EB‐PBF. The established process parameter window shows a good correlation between EB‐PBF process parameters, surface, and melt characteristics, which can be used as a baseline for a printing process. Melting NbC is proven feasible using EB‐PBF; the work also points out challenges related to arc trips and spattering, as well as future investigations necessary to create a stable printing process.

TiBw reinforced titanium matrix composites (TMCs) are the most promising engineering materials in aerospace and transportation owing to their excellent properties such as lightweight, high strength, wear resistance. The electron beam powder bed fusion (EB-PBF) characterized by its rapid solidification process during the manufacturing, which can effectively controlling the microstructure and mechanical properties of DRTMCs. The state of feedstock used in EB-PBF has a significant influence on the microstructure and mechanical properties of DRTMCs prepared by EB-PBF. However, there is no commercial feedstock available for EB-PBF fabricating DRTMCs. The disadvantages of premixed ball-milled powder are degraded flowability or incomplete reaction and agglomeration of reinforcements, which causes metallurgical defects in the as-fabricated composites. These issues severely affect the stability of mechanical properties of DRTMCs prepared by EB-PBF. The introduction of TiBw led to the formation of melt pool structure. At the boundary of the melt pool, TiBw exhibits an equiaxed continuous network distribution, while at the center of the melt pool, TiBw exhibits a columnar continuous network distribution; Moreover, the introduction of TiBw resulted in a 75% grain refinement, a 40% increase in yield strength, a 54% increase in tensile strength, and a decrease in elongation (13.2%) in the composite material. The improvement in strength of Ti-TiBw composite material prepared by EBM is due to grain refinement and the good load transfer effect generated by high aspect ratio TiBw, while the decrease in plasticity of the composite material is due to the connectivity failure of TiBw on the matrix. Based on the current research of DRTMCs prepared by EB-PBF, the future research trend focus on TiBw reinforced DRTMCs prepared by EB-PBF is discussed.

The present study reports on the identification of an adequate process window for electron beam powder bed fusion (E-PBF) of AISI 4140 steel. For characterization, only miniature samples were used. It is clearly revealed that, for comparison and evaluation of different conditions, the use of such small samples is absolutely sufficient, even under fatigue loading. The initial E-PBF as-built condition is compared with conventionally heat-treated conditions (i.e., normalized as well as quenched and tempered). Based on the results obtained, the advantages of E-PBF in comparison to other additive manufacturing routes, such as laser powder bed fusion (L-PBF), are discussed. In E-PBF, a very ductile material behavior results from the prevailing process conditions. Furthermore, an as-built condition almost free of residual stresses is established by E-PBF. Microstructural as well as fracture surface analyses were conducted and further supported by three-dimensional defect characterization applying X-ray computed tomography. It was found that the microstructural appearance of the as-built condition is affected most severely by the relatively sluggish cooling after the uppermost layer is finished. Thus, many issues related to L-PBF processing of carbon steels such as AISI 4140 do not prevail in E-PBF. The results obtained by mechanical testing clearly reveal that the remaining process-related volume defects can be compensated to a certain extent in the ductile as-built state. Consequently, the non-heat-treated, as-built condition is characterized by fatigue properties similar to those of post-treated AISI 4140. The latter, however, is characterized by superior strength under monotonic loading.

Effects of the higher accelerating voltage on electron beam powder-bed based additive manufacturing of Ti6Al4V alloy

Electron beam-powder bed fusion (EB-PBF), a high-temperature additive manufacturing (AM) technique, shows great promise in the production of high-quality metallic parts in different applications such as the aerospace industry. To achieve a higher build efficiency, it is ideal to build multiple parts together with as low spacing as possible between the respective parts. In the EB-PBF technique, there are many unknown variations in microstructural characteristics and functional performance that could be induced as a result of the location of the parts on the build plate, gaps between the parts and part geometry, etc. In the present study, the variations in the microstructure and corrosion performance as a function of the parts location on the build plate in the EB-PBF process were investigated. The microstructural features were correlated with the thermal history of the samples built in different locations on the build plate, including exterior (the outermost), middle (between the outermost and innermost), and interior (the innermost) regions. The cubic coupons located in the exterior regions showed increased level (~ 20 %) of defects (mainly in the form of shrinkage pores) and lower level (~ 30-35 %) of Nb-rich phase fraction due to their higher cooling rates compared to the interior and middle samples. Electrochemical investigations showed that the location indirectly had a substantial influence on the corrosion behavior, verified by a significant increase in polarization resistance (Rp) from the exterior (2.1 ± 0.3 kΩ.cm2) to interior regions (39.2 ± 4.1 kΩ.cm2).

Additive manufacturing (AM) technologies continuously evolve in materials and operational processes. However, challenges related to energy consumption, material reuse efficiency, and the integration of Circular Economy (CE) principles may impede the overall sustainability of AM processes. As many industrial sectors adopt AM technologies, there is a growing need for innovative tools, methods, and frameworks that guide companies toward more sustainable and circular production practices. This shift involves improving resource efficiency and fostering new Circular Business Models that emphasize material recovery, product lifecycle extension, and waste minimization. This study assesses current and future trends in the development of sustainable AM technologies for processing metal feedstock, based on a comprehensive patent analysis covering the period from 2004 to 2024. We specifically focus on the sustainability impacts of Electron and Laser Beam Powder Bed Fusion (PBF-EB, PBF-LB) and Direct Energy Deposition (DED), given their widespread industrial applications. Patents were categorized into three groups: materials, processes, and components. Furthermore, AM technologies were analyzed according to their role within the production cycle: materials preparation, pre-processing, manufacturing, and post-processing. This categorization allows for a detailed understanding of how innovations in AM contribute to more sustainable production and consumption practices by improving energy efficiency, material usage, circularity, and overall environmental impact.

ABSTRACTThe high cycle fatigue (HCF) behaviors of an additively manufactured (AM) Ti–6Al–4V alloy with fully lamellar microstructures processed electron beam powder bed fusion (EB‐PBF) and wire‐fed electron beam directed energy deposition (Sciaky) routes were compared. Ultrasonic fatigue (USF) testing at the stress ratio of R = −1 was applied to monitor the growth of small cracks initiated at surface micronotches. Crack growth rates lower than 10−8 (m/cycle) at ΔK = 6 MPa·m1/2 were measured in samples processed by both methods. The finer α lath thickness (~1 μm) of the Sciaky samples resulted in a slower fatigue crack growth rate than the EB‐PBF samples with coarser laths. The interaction of cracks with the lamellar microstructures was characterized by electron backscatter diffraction. Crack propagation largely followed the lath interfaces in the Sciaky samples, whereas cracks cut across colonies in the EB‐PBF samples. Different fatigue fracture surface characteristics were observed for the EB‐PBF and Sciaky samples.

The purpose of this work is to identify the principle of electron beam powder bed fusion (EB-PBF) and the performance of this AM method in the processing of copper components. This review details the experimentally reported properties, including microstructural, mechanical and physical properties of pure copper made by EB-PBF. The technical challenges and opportunities of EB-PBF are identified to provide insight into the influence of process parameters on observed mechanical properties as well as a roadmap for strategic research opportunities in this field. These insights allow optimisation of EB-PBF parameters, as well as comparison of the relative merits of EB-PBF over LB-PBF in the processing of copper components. This review details the microstructure and mechanical properties of EB-PBF of copper and identifies the technical opportunities and challenges. In addition, this report characterises the influence of process parameters, and subsequent energy density, on the associated mechanical properties. The discussions showed that the chance of pollution in copper processing by EB-PBF is less than laser-based powder bed fusion (LB-PBF) due to the high vacuum environment for electron beam. Oxygen content in the EB-PBF of copper powder is a vital factor and significantly affects the mechanical properties and quality of the specimen including physical density. The produced Cu2O due to the existence of oxygen content (in powder and bulk material) can improve the mechanical properties. However, if the Cu2O exceeds a certain percentage (0.0235%wt), cracks appear and negatively affect the mechanical properties. In copper printing by this method, the process parameters have to be tuned in such a way as to generate low build temperatures due to the high thermal conductivity of this alloy and the high sintering tendency of the powder.

Ti-6Al-4V alloy fabricated by laser powder bed fusion (L-PBF) and electron beam powder bed fusion (EB-PBF) techniques have been studied for applications ranging from medicine to aviation. The fabrication technique is often selected based on the part size and fabrication speed, while less attention is paid to the differences in the physicochemical properties. Especially, the relationship between the evolution of α, α’, and β phases in as-grown parts and the fabrication techniques is unclear. This work systematically and quantitatively investigates how L-PBF and EB-PBF and their process parameters affect the phase evolution of Ti-6Al-4V and residual stresses in the final parts. This is the first report demonstrating the correlations among measured parameters, indicating the lattice strain reduces, and c/a increases, shifting from an α’ to α+β or α structure as the crystallite size of the α or α’ phase increases. The experimental results combined with heat-transfer simulation indicate the cooling rate near the β transus temperature dictates the resulting phase characteristics, whereas the residual stress depends on the cooling rate immediately below the solidification temperature. This study provides new insights into the previously unknown differences in the α, α’, and β phase evolution between L-PBF and EB-PBF and their process parameters.

Additive manufacturing (AM) is a modern way of manufacturing structures, which tends to have fewer design limitations than those manufactured by conventional processes such as casting or forging. A combination of high-strength materials and small and complex structures opens up a wide range of potential applications, especially in the fields of medicine and aerospace. Titanium and its alloys show a very beneficial combination of density and mechanical properties. One of these alloys is the metastable β titanium alloy Ti– 5Al–5Mo–5 V–3Cr (Ti-5553), which is currently used mainly for large forged structures like landing gears of airplanes. In this study, for the first time the fatigue behavior of electron beam powder bed fused (PBF-EB) Ti-5553 was investigated with a focus on the defects created by the layer wise manufacturing. To understand the defect structure and its respective influence on the fatigue behavior, all specimens were scanned prior to fatigue testing using a state-of-the-art µ-focus CT. The specimens were subjected to two heat treatment procedures commonly used in technical applications, which were aiming for high strength (solution treated and aged—STA) as well as high ductility (beta annealed, slow cooled and aged—BASCA). Results indicate that the fatigue strength of PBF-EB manufactured Ti-5553 is significantly reduced compared to conventionally manufactured Ti-5553. The main reason for this are defects, which have varying critical effects depending on the heat treatment of the specimen and the defect size, shape, location and type.

Trapped powder removal from sheet-based porous structures based on triply periodic minimal surfaces fabricated by electron beam powder bed fusion

Additive manufacturing (AM), as an advanced manufacturing technology, enables the production of personalized orthopedic implant devices with complex geometries that closely resemble bone structures. Titanium and its alloys are extensively employed in biomedical fields like orthopedics and dentistry, thanks to the excellent compatibility with the human body and high corrosion resistance due to the existence of a thin protective oxide layer known as TiO2 upon exposure to oxygen on the surface. However, in joint inflammation, reactive oxygen species like hydrogen peroxide and radicals can damage the passive film on Ti implants, leading to their deterioration. Although AM technology for metallic implants is still developing, advancements in printing and new alloys are crucial for widespread use. This work aims to investigate the corrosion resistance of in-situ alloyed Ti536 (Ti5Al3V6Cu) alloy produced through electron beam powder bed fusion (EB-PBF) under simulated peri-implant inflammatory conditions. The corrosion resistance was evaluated using electrochemical experiments conducted in the presence of 0.1% H2O2 in a physiological saline solution (0.9% NaCl) to replicate the conditions that may occur during post-operative inflammation. The findings demonstrate that the micro-environment surrounding the implant during peri-implant inflammation is highly corrosive and can lead to the degradation of the TiO2 passive layer. Physiological saline with H2O2 significantly increased biomaterial open circuit potential up to 0.36 mV vs. Ag/AgCl compared to physiological saline only. Potentiodynamic polarization (PDP) plots confirm this increase, as well. The PDP and electrochemical impedance spectroscopy (EIS) tests indicated that adding Cu does not impact the corrosion resistance of the Ti536 alloy initially under simulated inflammatory conditions, but prolonged immersion leads to enhanced corrosion resistance for all biomaterials tested, indicating the formation of an oxide layer after the reduction of the solution oxidizing power. These results suggest that modifying custom alloys by adding appropriate elements significantly enhances corrosion resistance, particularly in inflammatory conditions.

Electron beam powder bed fusion/hot isostatic pressing (E-PBF/HIP), also known as in-situ shelling, is an emerging technology that produces components by only forming their shells whilst retaining sintered powder at the core, and then using HIP to consolidate the entire structure. E-PBF/HIP can boost additive manufacturing productivity, however, the fundamental understanding of the process-microstructure-property correlations remains unclear. Here, we systematically investigate the microstructural evolution of E-PBF/HIP Ti-6Al-4V parts as a function of hatch melting parameters. All HIPped samples achieve full densification, however, their microstructures are significantly different from one another. Using X-ray computed tomography (XCT) and optical microscopy, our results show that the HIPped Ti-6Al-4V microstructure can be controlled by varying the porosity, P (%), pore surface areas and morphology in the as-built parts with a single set of HIP parameters. The HIPped microstructures still exhibit the as-built columnar grains when the as-built porosity, P < 3 % with mainly spherical micro-pores; a mixture of columnar and equiaxed grains when the 3 % < P ≤ 5 % with a tortuous and interconnected pore network; and equiaxed grains when P > 5 % with a highly dense pore network. This work suggests two main drivers for the grain morphology transitions during HIP: (1) a dramatic increase in pore volume increases the localised applied pressure up to 4 times at the core region of the sample and (2) minimise lack-of-fusion pores with high surface energies, promoting dynamic recrystallisation. This study provides a fundamental insight into the E-PBF/HIP technology, showing the feasibility to tailor microstructural properties of E-PBF built parts whilst boosting additive manufacturing productivity.

To fully exploit the benefits of additive manufacturing (AM), an understanding of its processing, microstructural, and mechanical aspects, and their interdependent characteristics, is necessary. In certain instances, AM materials may be desired for applications where impact toughness is a key property, such as in gas turbine fan blades, where foreign or direct object damage may occur. In this research, the impact energy of a series of Ti-6Al-4V specimens produced via electron beam powder bed fusion (EBPBF) was established via Charpy impact testing. Specimens were produced with five different processing parameter sets, in both the vertical and horizontal build orientation, with microstructural characteristics of prior β grain area, prior β grain width, and α lath width determined in the build direction. The results reveal that horizontally oriented specimens have a lower impact energy compared to those built in the vertical orientation, due to the influence of epitaxial grain growth in the build direction. Relationships between process parameters, microstructural characteristics, and impact energy results were evaluated, with beam velocity displaying the strongest trend in terms of impact energy results, and normalised energy density exhibiting the most significant influence across all microstructural measurements.