Electron Beam Melting Process Research Articles

Numerical analysis and process optimization of electron beam melting for superalloys

This study aims to determine the optimal parameters for the electron beam melting process by employing a modified transient three-dimensional thermal model. The validity of the thermal model is confirmed through experimental results. Moreover, the proposed method establishes mathematical relationships between the resulting molten pool temperature and process parameters. A broader range of process parameters for a new Ni-Co-based superalloy was achieved by investigating the effects of scanning velocities (10-100 mm/s), scanning radius (20-60 mm), and melting mass (1500-3100 g) on temperature at various electron beam power levels (10-30 kW). Regression models were established between scanning velocities-temperature, and scanning radius-temperature under different electron beam power levels. These models laid the foundation for real-time automatic control of molten pool temperature. Significantly, orthogonal experimental design and response surface method are employed to conduct a multi-objective optimization based on sixteen experiments and three parameters. The results of multi-objective optimization indicate that with a smelting mass of 1.5 kg, an electron beam power of 11 kW, a scanning radius of 60 mm, and a scanning velocity of 75 mm/s, the energy consumption is 34.95 kW·h, and the theoretical mass loss of Ni element is 0.002 kg. The desirability is 91.2 %.

Surface characteristics of additively manufactured γ-TiAl intermetallic alloys post-processed by electrochemical machining

Electron beam melting (EBM) process is the most preferable powder bed fusion process for high melting point alloys. γ-TiAl alloys are intermetallic chemical compounds, which are lightweight and resistant to oxidation and heat, and have low ductility as well. EBM is the best manufacturing process for such alloys to produce aerospace parts, but poor surface quality is the main drawback of this process. Thus, surface post-processing is needed after the EBM process. This study presents the surface characteristics of EBM γ-TiAl alloy surfaces post-processed by electrochemical machining (ECM). The surfaces were ECM and the surface roughness values (Sa, Sq and Sz) have been reduced significantly. The mean reduction values of the experiments are 98.6 %, 98.5 % and 95.3 % for Sa, Sq and Sz, respectively. Additionally, it is observed that the surface roughness is inversely proportional to the electrolyte conductivity up to a limit value (115 mS/cm), and after that the roughness increases via the stray current transition. Sq values decrease with the increased feed rate via the increased current density. However, an increase in feed rate negatively affects the Sku values, which statistically describe the sharpness or spread of surface roughness. Also, XRD results showed that Ti2AlN layer is formed on the surface via the HIP operation. This layer inhibits the electrochemical dissolution of γ-TiAl alloy and caused surface defects.

Impact of Electron Beam Melting process recycling on defects and microstructure of Ti-6Al-4V powders

Metal powders are used as the feedstock material during the Electron Beam Melting processes. The process involves using an electron beam as the energy source to produce intricate parts with complex shapes in a layer-by-layer production system. The electron beam is directed by information from an STL file, and the process takes place in a pre-heated chamber that is maintained under vacuum. Once the production cycle is complete, the process yields the desired components along with a certain amount of residual powders that were not melted.To improve process efficiency and reduce costs associated with powder atomization, it is feasible to reuse the excess powder for subsequent production cycles. Prior to starting a new cycle, the excess powder is initially sieved to ensure a more uniform powder batch, and subsequently, the sieved powder can be mixed with other virgin powder to decrease oxygen content.This study examines the microstructure and defects present in a batch of virgin powders produced through plasma atomization and a batch of powders that were reused five times and mixed with Ti-6Al-4V grade 23 (ELI powders) at each cycle. The ELI powders are characterized by a low oxygen content.The results of the analysis indicate a connection between the powder atomization process and the formation of porosities in virgin powders resulting from trapped gas, as well as surface irregularities, including the presence of satellites. With an increase in the number of reuses, there is a reduction in the number of satellites, potentially due to surface partial melting due to the pre-heating of the EBM chamber, leading to rougher surfaces on the recycled particles.The microstructure of virgin powders is predominantly characterized by a fine acicular α’ phase, known as martensitic, formed due to the rapid cooling rate during the atomization process. Conversely, recycled powder tends to exhibit a coarser grain microstructure due to lower cooling rates. However, it is common to observe particles with a microstructure similar to that of newly manufactured powders, indicating that each individual particle has undergone a distinct thermal history.

Effect of martensitic phase formation on the nano-mechanical attributes during the electron beam melting process of Ti-6Al-4V

Electron Beam Melting based Ti-6Al-4V parts plays a predominant role in the field of bio medical and aerospace applications, especially in the aero due to its sustainability. However, there were not enough studies on nano-mechanical properties that looked at how phase changes during the heat and cooling process affected the printing process. With the assistance of OM and FESEM with EDX, the EBM Ti64 coupons were analysed for the grain orientation and phase transformation studies. The FESEM with EDX supported the existence of columnar grains and orthogonally oriented martensitic needles. Additionally, both XRD and TEM confirmed the presence of vanadium-rich precipitates and the HCP α-Ti and BCC β-Ti phases. EBSD analysis was adopted to further investigate the orientation of grains. The nano-hardness and elastic reduced modulus mapping confirmed the phase transformation to martensitic phase. The strong “martensitic” phase had a maximum reduced modulus of 183.5 GPa and a hardness value of 7.31 GPa. However, the EBM based Ti64 possesses an average nano-hardness and reduced modulus of 4.26 GPa and 118.3 GPa under the applied load of 2500μN. In addition, topographic wear and scratch tracks confirmed the soft nature of α colonies by forming more piles of materials, while nano-wear and scratch analysis predicted the functions caused by the presence of hard martensitic phases. The SR sensitivity of the Ti64 specimens was investigated using three different quasi-static strain rates. It was determined that the EBM Ti64 parts have a considerable effect over the strain rate, whereas, a quasi-static strain rate allowed for the achievement of the highest possible Ultimate Tensile Strength (UTS) and ductility.

Microstructure evolution and mechanical properties of H13 steel produced by Selective Electron Beam Melting

As one of the additive manufacturing technologies, the Selective Electron Beam Melting (SEBM) process several advantages over Selective Laser Melting (SLM), including faster scanning velocity, higher energy utilization and higher preheating ability of up to 1100 °C. Thus, it is particularly advantageous for the production of high melting point and brittle metals, like the medium carbon high-alloy H13 steel. This study presents a systematic investigation of the microstructural evolution and mechanical properties of H13 steel fabricated using Selective Electron Beam Melting (SEBM) with varying deposition heights. The manufactured samples were examined using high-tech measuring instruments to evaluate different properties such as phase composition, microstructure, microhardness and grain morphology. The results reveal that the microstructure of the as-built SEBM-H13 sample consists of martensite, bainite, and residual austenite with a typical cellular/dendritic structure. As the deposition height decreases, the grain morphology degrades, and the grain boundary undergoes carbide precipitation ((Cr, Fe)7C3) and growth. Consequently, the sample exhibits a gradient hardness structure in the building direction with the highest hardness of 565.6 (±5.8) HV0.5 at the top surface, followed by a distinct decrease in hardness to approximately 506.7 (±3.3) HV0.5 at increased distances from the surface. This study provides a fundamental understanding of fabricating high-performance H13 steel using SEBM.

Microstructural evolution and tribological properties of M2 high-speed steel fabricated under various selective electron beam melting processing parameters

In the current study, crack-free M2 high-speed steel (HSS) was produced by selective electron beam melting (SEBM) under different volumetric energy densities (VED, 40–56.3 J mm−3) and high powder bed preheating temperatures (PBPT, 750 °C and 820 °C). Results show that fully dense M2 HSS can be achieved under the VED of 43.6–47.9 J mm−3 and PBPT of 820 °C. Moreover, SEBM M2 HSS mainly consists of less than 7 µm α-Fe matrix grain as well as fine carbide, which were induced by high cooling rate of the molten pool. The fully dense sample presents ultra-high hardness (∼70 HRC) and excellent tribological properties. Its wear rate is 13.7 % lower than that of quenched and tempered wrought bulk counterpart.

Mechanical Properties and in Vivo Assessment of Electron Beam Melted Porous Structures for Orthopedic Applications

Electron beam melting (EBM) is an additive manufacturing technique with the ability to produce porous implants with desired properties for orthopedic applications. This paper systematically investigated the mechanical properties and in vivo performance of two commonly used stochastic porous structures (the Voronoi structure and the randomized structure) fabricated by the EBM process. The pore geometries of two porous structures were characterized through micro-computed tomography (μCT). In addition, clinically relevant mechanical performances were evaluated for both structures, including tensile testing, shear testing and abrasion resistance testing. In vivo assessment of the two porous structures was further conducted in a dog model for three different follow-up periods. It was found that the Voronoi structures showed a higher mechanical strength compared to the randomized structures, even though both structures exhibited similar pore geometries. Further analysis revealed that the non-uniform stress distribution caused by the sample size and boundary effects led to a decrease in strength in the randomized structures. The in vivo assessments revealed the Voronoi structure exhibited a higher bone ingrowth ratio compared to the randomized structure due to its radially oriented pore geometry and homogenous pore size distribution. This study suggested that the EBM Ti-6Al-4V Voronoi porous structure has favorable mechanical performance and good osseointegration properties for orthopedic implants.

Enhancement of a quasi-analytical solution for modelling additive manufacturing processes

Numerical modelling methods (e.g. finite element) can provide accurate descriptions of long-range temperature fields in laser or electron-beam melting processes, however the high computational costs at part-scale make them unsuitable for process modelling in additive manufacturing (AM). Alternative methods such as semi-analytical solutions based on a moving heat source reduce the computational expense but at the cost of unrealistic assumptions. Radiation, temperature-dependent physical properties and latent heat are not considered in the semi-analytical approach but can have a significant effect on the thermal history. In this study, the error associated with each of these contributions are assessed against the conduction-only semi-analytical solution for a range of processing parameters for surface melting on solid Ti-6Al-4V. The semi-analytical model is then “enhanced” using results from finite element simulations to better account for the heat transfer in the AM process.

A feasibility study of promoting osseointegration surface roughness by micro-milling of Ti-6Al-4V biomedical alloy

The reliability of a prosthetic implant needs durability, biocompatibility, and osseointegration capability. Accomplishing these characteristics, Ti-6Al-4V alloy is the main used material for implant fabrication. Moreover, it can be processed by additive manufacturing technique, permitting to meet the needs of patience-tailored, often complex shaped, prosthesis topologies. Once an implant is realized, it is finished by machining operations and its osseointegration capability is heavily influenced by the resulting surface roughness. Consequently, the assessment of this latter is mandatory to evaluate the prosthesis durability. This paper presents the analysis of surface roughness of Ti-6Al-4V micro-milled specimens produced by plastic deformation, selective laser melting, and electron beam melting processes. A central composite design was employed for planning the cutting tests. The comparison between surface roughness results and its values for enhancing osseointegration, firstly permitted to individuate the range of micro-milling suitable applications, which have been individuated as ball joints, bone plates, and screws. Next, the statistical analysis of the experimental measurements allowed the identification of the most influential micro-milling parameters together with the determination of the mathematical models of surface roughness by response surface methodology. The good comparison among calculated and experimental results revealed the reliability of the model, allowing the prediction of achievable surface roughness once micro-machining parameters are selected, or their optimization as a function of a desired surface roughness value.

An Innovative Method to Analyse the Geometrical Accuracy of Ti6Al4V Octet-Truss Lattice Structures.

Metal lattice structures manufactured utilising additive techniques are attracting increasing attention thanks to the high structural efficiency they can offer. Although many studies exist on the characterisation of massive parts in Ti6Al4V processed by Electron Beam Melting (EBM), several investigations are necessary to characterise the Ti6Al4V lattice structures made by the EBM process. The objective of this paper is to develop a measurement method to assess the dimensional accuracy of Ti6Al4V octet truss lattice structures manufactured by EBM technology. Beam specimens with a 2 mm diameter and different growth orientations with respect to the build direction were analysed. The geometry differences between the designed and the manufactured beam specimens were highlighted. Two effects were identified: (i) The EBM-manufactured beams are generally thinner than the designed ones, and (ii) the shape of the section was found to be almost circular for the beam specimens oriented at 45° and 90°; on the contrary, the section of the horizontal beam (0°) cannot be considered circular.

Parametric optimization of multi-pass electron beam melting for molybdenum alloy containing 47.5 wt% rhenium

In this study, the effects of multi-pass electron beam melting (EBM) processes under vacuum condition on microstructure and mechanical behavior of a molybdenum alloy containing 47.5 wt% rhenium were systematically investigated. Nine experimental designs were performed to improve the surface quality and minimize the defects. Results showed that beam power, scan speed, processing step and penetration depth played a critical role in the specific energy density function, which would further influence the porosity and microhardness. Meanwhile, specific energy density was significantly influenced by beam power at higher scan speed (e.g. 15 mm/s) whereas it was mainly related to scan speed under lower beam power (e.g. 2 kW). With a processing step of 0.5 mm (half of the beam diameter), a continuous melt morphology and less porosity were obtained, indicating that a significant overlap between the scan tracks was beneficial for the optimization of microstructure. Microhardness results showed that mechanical performance can be improved with the reduction of porosity together with the increased specific energy density. Thus, a combination of 10 kW beam power, 2 mm/s scan rate and 0.5 mm processing step can realize surface optimization in melted plates through multi-pass EBM technique.

Fast simulation for powder bed fusion process based on thermal field pattern repetitions: application on electron beam melting process

Fast simulation for powder bed fusion process based on thermal field pattern repetitions: application on electron beam melting process

Influence of linear energy on side surface roughness in powder bed fusion electron beam melting process: Coupled experimental and simulation study

Influence of linear energy on side surface roughness in powder bed fusion electron beam melting process: Coupled experimental and simulation study

Electron Beam Based Additive Manufacturing of Alloy 247 for Turbine Engine Application: From Research towards Industrialization

In this contribution it will be shown how the metal powder bed fusion technology electron beam melting (EBM) enables a successful crack- and defect-free processing of the non-weldable Ni-based superalloy Alloy 247. Besides a defect-free processing, EBM process capabilities offer unique opportunities to tailor the microstructure according to material requirements for high-temperature applications. It could be demonstrated that EBM material properties are comparable or even better than traditionally casted Alloy 247 material. Tailored polycrystalline and columnar microstructures were achieved by process parameter adoption for solidification control. The EBM as-built microstructure was characterized by conventional metallography techniques and the results were used to define an adopted HIP + heat-treatment cycle which was applied prior to mechanical testing. Thus, corresponding mechanical and microstructural properties in different conditions will be presented and discussed to show EBM material capabilities. As a result, directionally solidified (DS) EBM material can achieve similar creep performance as DS cast material, despite an observed fine-grained “micro-DS” structure in EBM.Graphical

Effect of mechanical ball milling on the electrical and powder bed properties of gas-atomized Ti–48Al–2Cr–2Nb and elucidation of the smoke mechanism in the powder bed fusion electron beam melting process

Smoke is unexpected powder-splashing caused by electrostatic force and is one of the main problems hindering the process stability and applicability of the powder bed fusion electron beam (PBF-EB) technology. In this study, mechanical stimulation was suggested to suppress smoke of gas-atomized (GA) Ti–48Al–2Cr–2Nb powder using Al2O3 and WC ball milling. The deformation mechanism of the GA powder depending on the ball milling media was discussed based on the developed particle morphology distribution map and contact mechanics simulation. It was revealed that the rapid decrement of flowability and packing density after WC ball milling owing to the formation of angular fragments by the brittle fracture. The variation of surface and electrical properties by mechanical stimulation was investigated via XPS, TEM, Impedance analysis. The electrical resistivity of the ball-milled powders gradually decreased with increasing milling duration, despite the increased oxide film thickness, and the capacitive response disappeared in Al-60 and WC-30 via metal–insulator transition. This could be due to the accumulation of strain and defects on the oxide film via mechanical stimulation. The smoke mechanism of ball-milled powders was discussed based on the percolation theory. In the smoke experiment, smoke was more suppressed for WC-10 and WC-20 than that for Al-40 and Al-50, respectively, despite the longer charge dissipation time. This could be due to the high probability of contact with conductive particles. For the Al-60 and WC-30 powders, smoke was further restricted by the formation of a percolation cluster with metal-like electrical conductivity. We believe that this study will contribute to a better understanding of the smoke mechanism and process optimization of the PBF-EB.

Effect of Powder Characteristics on Relative Density and Porosity Formation During Electron Beam Selective Melting of Al2024 Aluminum Alloy

Abstract Defects, such as pores and cracks, can be found in parts fabricated by powder-bed additive manufacturing techniques. The origin of certain defects, such as some voids, can be linked to initial powder quality, which makes it an important factor in the process. Powders used in additive manufacturing processes are produced by different methods such as gas atomization (GA), plasma atomization (PA), and plasma rotating electrode process (PREP); each gives different powder quality. In this study, two different Al2024 powders, produced by electrode induction GA and PREP techniques, were used to investigate the effect of powder characteristics on defect formation during electron beam melting process (EBM). Powders were first characterized by using Hall flowmeter funnel and scanning electron microscope (SEM); then, the EBM process was carried out, and finally, samples were examined by density measurement using Archimedes method, SEM analysis, and tensile test. PREP powder showed higher levels of sphericity and surface smoothness without attached satellites. Consequently, a higher apparent density and decreased flowing time were achieved in PREP powder. Moreover, gas-induced internal pores were observed in GA particles. The results also revealed the average relative density of 96.7% and 99.4% for the parts built by GA and PREP powders, respectively. SEM micrographs confirmed the results of density measurement of the fabricated parts and showed higher degrees of both spherical and irregular-shaped pores in samples built by GA powder. Additionally, they showed deprived mechanical properties due to the higher porosity contents which can form stress-concentrated areas.

Effects of recycling on defects and microstructure in Ti-6Al-4V powder particles and samples fabricated by Electron Beam Melting process

Effects of recycling on defects and microstructure in Ti-6Al-4V powder particles and samples fabricated by Electron Beam Melting process

Powder Bed Fusion of Multimaterials

Powder bed fusion (PBF) process has been used successfully to produce 3D structures using single material properties. The current industrial demand is to use the technology to produce 3D structures of multimaterial properties. An electron beam melting (EBM) process has been used to produce 3D structures of multimaterial properties. However, due to the large beam size, the EBM process lacks geometrical accuracy, requiring a large machining allowance. A laser powder bed fusion (LPBF) process could be used to produce multimaterials with geometrical precision. However, the thermal gradient within the molten pool and the thermophysical difference between the multimaterials leads to defects (weak interfacial bonds, interlayer and intralayer cracks). Other challenges such as poor powder delivery system, powder cross-contamination, and lack of appropriate data processing software for producing 3D multimaterial structures are not yet fully resolved. Nonetheless, there have been encouraging results for producing the next generational multimaterial 3D components of intricate geometrical characteristics.

Improvement in the high temperature mechanical properties of additively manufactured Ti–48Al–2Cr–2Nb alloy using heat treatment

Gamma Ti–48Al–2Cr–2Nb (Ti4822) alloy, which is manufactured by an electron beam melting (EBM) process, has excellent ductility but poor high-temperature strength, because it has a near gamma structure. The objective of this study was to control the microstructure of Ti4822 by considering various forms of heat treatment to improve the mechanical properties at room and high temperatures. The heat treatment conditions were varied to create nearly lamellar (NL) and fully-lamellar (FL) structures. First, the EBM-built NL-Ti4822 exhibited a lamellar structure with an average layer thickness of about 92 nm and equiaxed γ-phase particles with a size of several tens of micrometers. On the other hand, the EBM-built FL-Ti4822 had an average lamellar thickness of about 347.2 nm, but in this case the equiaxed γ phase was not observed. The results of the room- and high-temperature compression test showed that the mechanical properties of the two heat-treated materials were significantly superior to those of the as-built Ti4822 across all temperature ranges. Moreover, both materials were highly ductile at room and high temperature despite having a lamellar structure, and exhibited intensified yield stress anomaly and dynamic recrystallization as the fraction of lamellar structure increased. Based on the above results obtained by subjecting the materials to different heat treatment methods, the effects of the microstructures of the two materials on the mechanical properties and deformation mechanisms at room and high temperatures were investigated.

Excellent compression strength and energy absorption of additively manufactured porous titanium with trapezo-rhombic dodecahedron cell

Porous metals with excellent properties for lightweight structural applications and energy absorption are manufactured via additive manufacturing (AM). The 3D-Voronoi division method generates trapezo-rhombic dodecahedron cells as a new cell structure. Porous titanium specimens with trapezo-rhombic dodecahedron cells were prepared using the electron beam melting process. The normalized first maximum compressive strength of the [0001] direction was determined to be the highest, while the normalized first maximum compressive strength of the [ 2 ̅ 110 ] direction was the lowest. The bending moment of cell struts could be used to explain the anisotropic compressive strength. In addition, AM porous titanium with trapezo-rhombic dodecahedron cells had higher normalized first maximum compressive strength and energy absorption than AM porous titanium with truncated octahedron and rhombic dodecahedron cells. Porous titanium with trapezo-rhombic dodecahedron cells exhibits significantly larger anisotropy than truncated octahedron and rhombic dodecahedron cells. • Trapezo-rhombic dodecahedron cell is a new cell structure similar to rhombic dodecahedron. • Porous titanium specimens with trapezo-rhombic dodecahedron cells have excellent first maximum compressive strength and energy absorption. • Porous titanium consisting of trapezo-rhombic dodecahedron cells exhibited large anisotropy.