Electron Beam Melting Process Research Articles

Effect of Casting and Additive Manufacturing on the Microstructure and Mechanical Property of Al-Cu Composites

The TiB2 reinforced Al-5Cu composites was manufactured by additive manufacturing with two kind of heat sources, i.e., cold metal transfer (CMT) and electron beam melting (EBM). The TiB2 particles were in nano-sized with some submicron-sized particle clusters , and their morphologies were round and near round without sharp angles. It was found that the introduce of TiB2 particles improved the mechanical properties of Al-5Cu alloy obviously. The results demonstrated that both the additive manufacturing methods of cold metal transfer (CMT) and electron beam melting (EBM) could improve the microstructure of the composites significantely. Compared with the traditional casting, Al-5Cu alloy the grain sizes of the TiB2 reinforced Al-5Cu composites decreased from larger than 100 μm to 40 μm with CMT process and 25 μm with EBM process. The hardness of the TiB2 reinforced Al-5Cu composites with EBM after heat treatment could be reached to 153 HV10. The refined grains and high hardness of the TiB2 reinforced Al-5Cu composites with EBM additive manufacturing technique verified that AM technology is a promising way to optimize the microstructure and mechanical properties of Al-Cu composites.

Phase Studies of Additively Manufactured Near Beta Titanium Alloy-Ti55511.

The effect of electron-beam melting (EBM) and selective laser melting (SLM) processes on the chemical composition, phase composition, density, microstructure, and microhardness of as-built Ti55511 blocks were evaluated and compared. The work also aimed to understand how each process setting affects the powder characteristics after processing. Experiments have shown that both methods can process Ti55511 successfully and can build parts with almost full density (>99%) without any internal cracks or delamination. It was observed that the SLM build sample can retain the phase composition of the initial powder, while EBM displayed significant phase changes. After the EBM process, a considerable amount of α Ti-phase and lamella-like microstructures were found in the EBM build sample and corresponding powder left in the build chamber. Both processes showed a similar effect on the variation of powder morphology after the process. Despite the apparent difference in alloying composition, the EBM build Ti55511 sample showed similar microhardness as EBM build Ti-6Al-4V. Measured microhardness of the EBM build sample is approximately 10% higher than the SLM build, and it measured as 348 ± 30.20 HV.

Powder bed irregularity and hot-spot detection in electron beam melting by means of in-situ video imaging

The electron beam melting process has been successfully applied in various sectors to produce high-value-added products. Being a hot process operating in vacuum environment with x-rays and material vaporization among by-products, in-situ sensing and monitoring presents more challenges than in laser powder bed fusion. However, an automated and robust detection of unstable process conditions represents a key capability to meet challenging qualification requirements imposed by industry. This study presents novel in-situ monitoring methods based on high spatial resolution imaging for powder bed homogeneity monitoring and high temporal resolution video-imaging for hot-spot detection, i.e., the detection of anomalous local heat accumulations.

Investigation of the rotating drum technique to characterise powder flow in controlled and low pressure environments

Powder bed fusion, the most popular technique in metal additive manufacturing, utilises two main energy sources: laser or electron beam. The laser powder bed fusion process is typically conducted under inert gas-filled environment, while electron beam melting (EBM) process is operated in vacuum. Regardless of energy source, powder flowability is a major concern as it affects the final product quality. The rotating drum, a tool to characterize flowability and assess powder behavior during recoating, is conducted in ambient air environment, which inaccurately mimics these processes. This work investigated Inconel 625 and Ti6Al4V in atmospheric (air/argon) and low-pressure environments. The gas type did not affect the powders' dynamic flow behavior, however, a systematic difference existed in low-pressure environment especially with smaller particle size. As current research explores finer powder cut in EBM processes, new ways to characterize powder flow in vacuum should be considered to optimise powder spreading in EBM environment.

On the turning of electron beam melted gamma-TiAl with coated and uncoated tools: A machinability analysis

Abstract Electron beam melting (EBM) is one of the promising technologies with the capability of producing complex near-net shapes from difficult to process materials such as titanium alloys. However, the parts produced from the EBM process suffer from the poor surface quality and machining is required to finish the EBM parts to achieve the necessary surface quality. Unlike the reported studies in the literature, the current study employs both uncoated, and PVD multi-coated (TiAlN/Al2O3/ZrCN) carbide inserts for the finishing of the electron beam melted γ-TiAl (Ti-48Al-2Cr-2Nb) and compares the machinability performance to identify the suitable type of the tool and the corresponding machining conditions. The obtained results indicate that the performance of the uncoated inserts is far superior as compared to the coated inserts in terms of producing lower tool wear and cutting forces, improved surface finish and morphology, and less subsurface microstructural and hardness alterations. The poor performance of the coated inserts is due to the high-temperature accumulation at the tool-workpiece interface due to the thermal shielding effect of the coatings, leading to severe built-up layer formation resulting in cascading effect of higher cutting forces, tool wear and oxidation, and poor workpiece surface integrity.

Effect of Powder Recycling on Defect Formation in Electron Beam Melted Alloy 718

The extent to which powder recycling can be permitted before risking a loss in performance of critical components is a major aspect for the viability of electron beam melting (EBM). In this study, the influence of powder oxidation during multi-cycle EBM processing on the formation of oxide-related defects in Alloy 718 is investigated. The amount of defects and their distribution in samples produced from virgin and re-used powder is studied by means of image analysis and oxygen measurements. Morphological analysis using scanning electron microscopy is performed to understand their origin and formation mechanism. The results indicate a clear correlation between the powder oxygen content and the amount of oxide inclusions present in the investigated samples. The inclusions consist of both molten and unmolten Al-rich oxide which originates from the surface of the recycled powder. Upon interaction with the electron beam, the oxide tends to cluster in the liquid metal and form critical sized defects. Hot isostatic pressing can be successfully used to densify samples produced from virgin powder. However, in the material fabricated from recycled powder, a considerable amount of damage relevant oxide inclusion defects remain after HIP treatment, especially in the contour region. It is suggested that the quality of EBM-processed Alloy 718 is at present dependent on the oxygen level in the powder in general, and on the surface chemistry of the power in particular, which needs to be controlled to maintain a low amount of inclusions.

The effect of geometry on mechanical properties of Ti6Al4V ELI scaffolds manufactured using additive manufacturing technology

Owing to the possibility of direct processing of CAD models into three-dimensional objects, additive manufacturing (AM) is widely used in the production of individualized bone scaffolds that can lead to perfect restoration of anatomical structures of missing bone tissues. In this work, one of the AM technologies was applied, referred to as Electron Beam Melting (EBM), using Ti6Al4V ELI alloy to produce open-cell structures. Scaffold architecture influences its mechanical properties and is important from the point of view of biological considerations. To optimize mechanical properties, designed geometries were subjected to Finite Element Method analysis and experimental static compression tests. Also, geometric CT analysis of manufactured scaffolds was carried out (geometry deviations up to ± 300 µm). Obtained results have shown that AM can be used to produce Ti6Al4V ELI alloy scaffolds displaying mechanical parameters similar to those of bone tissue (E = 0.45–2.88 MPa). The EBM process affects the microstructure and macrostructural properties of manufactured parts, e.g., through internal porosities present in the material by to unmelted powder particles (internal porosity in range of 1.25–2.25%). To assess the quality and suitability of additively manufactured implants, a multidimensional verification of the impact of the manufacturing process on the properties of the final product was performed.

Defect-free laser powder bed fusion of Ti–48Al–2Cr–2Nb with a high temperature inductive preheating system

In the industrial panorama, laser powder bed fusion (LPBF) systems enable the near net shaping of metal powders into complex geometries with unique design features. This makes the technology appealing for many industrial applications, which require high performance materials combined with lightweight design, lattice structures and organic forms. However, many of the alloys that would be ideal for the realisation of these functional components are classified as difficult to weld due to their cracking sensitivity. γ-TiAl alloys are currently processed via electron beam melting (EBM) to produce components for energy generation applications. The EBM process provides crack-free processing thanks to the preheating stages between layers, but lacks geometrical precision. The use of LPBF could provide the means for higher precision, and therefore an easier post-processing stage. However, industrial LPBF systems employ resistive heating elements underneath the base plate which do not commonly reach the high temperatures required for the processing of γ-TiAl alloys. Thus, elevated temperature preheating of the build part and control over the cooling rate after the deposition process is concluded are amongst the features which require further investigations. In this work, the design and implementation of a novel inductive high temperature LPBF system to process Ti–48Al–2Cr–2Nb is presented. Specimens were built with preheating at 800 °C and the cooling rate at the end of the build was controlled at 5 °C min−1. Crack formation was suppressed and apparent density in excess of 99% was achieved.

Rapid Solidification Microstructure and Carbide Precipitation Behavior in Electron Beam Melted High-Speed Steel

The solidified microstructure and carbide precipitation behavior in an S390 high-speed steel processed by electron beam melting (EBM) have been fully characterized. The as-EBM microstructure consists of discontinuous network of very fine primary carbides dispersed in auto-tempered martensite matrix together with a limited amount of retained austenite. The carbide network consists of M2C/M6C and MC carbides. Both the columnar and near-equiaxed grain structures were found in as-EBM microstructure and the presence of inter-dendritic eutectic carbides assisted in revealing the dendritic solidification nature. The top-layer microstructure observation confirmed that the columnar dendritic structured grains were located adjacent to the micro-melt pool boundary, indicating an epitaxial growth with the average growth direction parallel to the maximum thermal gradient. At the center of the micro-melt pool, the near-equiaxed grains were developed by dendritic growth parallel to the beam traveling direction. The carbide decomposition was revealed by scanning transmission electron microscopy and confirmed by transmission Kikuchi diffraction. The MC carbides (rich in V followed by W) nucleated at the interface between M2C (W, Fe, Mo, and Co in the order of significance) and the matrix and then grew from the outside inward, but their nucleation might occur from the M2C carbide itself. The thermal effect induced by the adjacent scan lines seems to trigger a solid-state phase transformation of MC → M2C + γ-Fe. The elemental migration was theoretically calculated and compared with the experimental results. The high hardness of ~ 65 HRC and good transverse rupture strength of ~ 2500 MPa in as-EBM S390 means that EBM processing can be used to fabricate highly alloyed tool steels. With the help of the post-processing heat treatment, the best Rockwell hardness of 73.1±0.2 HRC and transverse rupture strength of 3012±34 MPa can be obtained.

Unit process energy consumption analysis and models for Electron Beam Melting (EBM): Effects of process and part designs

Electron Beam Melting (EBM) has the potentiality of being an effective system in terms of time and energy consumption. Among the different additive manufacturing processes that are available, the EBM process has shown the lowest Specific Energy Consumption (SEC) and the highest average Deposition Rate (DRa). However, there appears to be a lack of literature on the correlation between SEC and DRa. Moreover, all the literature studies have only an analysis of energy efficiency during the melting of the bulk material phase and have adopted a fixed job design. Therefore, the aim of this study has been to fill this gap. The EBM process is decomposed into small substeps and a bottom-up approach is adopted to provide models that can be used to evaluate the energy of each process subphase and to perform an energy characterisation at the unit process level. A black-box approach is applied to provide a new model for the energy efficiency of the EBM process. Different jobs have been designed to analyse the effect of a part and of manufacturing designs. Bulk material, support and lattice structures have been included. The design has therefore been aimed at investigating the effect of the building height, melted area and process themes on energy efficiency. The jobs have been produced using Arcam A2X and Standard Arcam Ti6Al4V powders. According to this research, the architecture of the machine and its control of the process have the main impact on the relationship between SEC and DRa. The design features of the part and of the job influence the position of the job on this curve and thus the relative energy and time efficiency. Additionally, the empirical approach applied to the machine subunits has highlighted that only a small part of the total energy demand is needed to power the electron beam during the melting phase, while the remaining part guarantees the good machine working conditions.

Correlation between real geometry and tensile mechanical behaviour for Ti6Al4V electron beam melted thin specimens

The Electron Beam Melting (EBM) is an Additive Layer Manufacturing (ALM) technique used to directly manufacture 3D functional parts from metal powder, selectively melted, layer by layer, by an electron beam according to a geometry defined by a CAD model. The EBM technology allows benefitting from countless advantages: material waste reduction, easy manufacturing of complex shapes, lead time reduction, etc; on the other hand the EBM process is typically associated with lower resolutions and higher surface roughness (Ra = 25–30 μm) compared to similar laser based powder bed metal processes.Therefore the surface morphology may be a critical issue for the structural integrity of components made in EBM and used in-service in their “as built” condition, i.e. with the characteristic surface released by the process.This study evaluates surface morphology and tensile properties of Ti6Al4V specimens of varying nominal thickness (1–5.0 mm), made by using EBM process with a layer thickness of 50 μm. The aim is therefore to investigate how the surface morphology and the tensile properties are affected by the nominal thickness of the component.

Comparison of wear properties of Ti6Al4V fabricated by wrought and electron beam melting processes in simulated body fluids

PurposeThis paper aims to study the wear properties of electron beam melted Ti6Al4V (EBM-Ti6Al4V) in simulated body fluids for orthopedic implant biomedical applications compared with wrought Ti6Al4V (Wr-Ti6Al4V).Design/methodology/approachWear properties of EBM-Ti6Al4V compared with Wr-Ti6Al4V against ZrO2 and Al2O3 have been investigated under dry friction and the 25 Wt.% newborn calf serum (NCS) lubricated condition using a ball-on-disc apparatus reciprocating motion. The microstructure, composition and hardness of the samples were characterized using scanning electron microscopy (SEM), x-ray diffraction and a hardness tester, respectively. The contact angles with 25 Wt.% NCS were measured by a contact angle apparatus. The wear parameters, wear 2D and 3D morphology were obtained using a 3D white light interferometer and SEM.FindingsEBM-Ti6Al4V yields a higher contact angle than the Wr-Ti6Al4V with the 25 Wt.% NCS. EBM-Ti6Al4V couplings exhibit lower coefficients of friction compared with the Wr-Ti6Al4V couplings under both conditions. There is only a slight difference in the wear resistance between the Wr-Ti6Al4V and EBM-Ti6Al4V alloys. Both Wr-Ti6Al4V and EBM-Ti6Al4V suffer from similar friction and wear mechanisms, i.e. adhesive and abrasive wear in dry friction, while abrasive wear under the NCS condition. The wear depth and wear volume of the ZrO2 couplings are lower than those of the Al2O3 couplings under both conditions.Originality/valueThis paper helps to establish baseline bio-tribological data of additively manufactured Ti6Al4V by electron beam melting in simulated body fluids for orthopedic applications, which will promote the application of additive manufacturing in producing the orthopedic implant.

Effect of Compositional Variation Induced by EBM Processing on Deformation Behavior and Phase Stability of Austenitic Cr-Mn-Ni TRIP Steel

Electron beam melting (EBM) is an established powder bed-based additive manufacturing process for the fabrication of complex-shaped metallic components. For metastable austenitic Cr-Mn-Ni TRIP steel, the formation of a homogeneous fine-grained microstructure and outstanding damage tolerance have been reported. However, depending on the process parameters, a certain fraction of Mn evaporates. This can have a significant impact on deformation mechanisms as well as kinetics, as was previously shown for as-cast material. Production of chemically graded and, thus, mechanically tailored parts can allow for further advances in terms of freedom of design. The current study presents results on the characterization of the deformation and strain-hardening behavior of chemically tailored Cr-Mn-Ni TRIP steel processed by EBM. Specimens were manufactured with distinct scan strategies, resulting in varying Mn contents, and subsequently tensile tested. Microstructure evolution has been thoroughly examined. Starting from one initial powder, an appropriate scan strategy can be applied to purposefully evaporate Mn and, therefore, adjust strain hardening as well as martensite formation kinetics and ultimate tensile strength.

Experimental analysis of additively manufactured component and design guidelines for lightweight structures: A case study using electron beam melting

Powder bed fusion additive manufacturing (AM) technology, such as electron beam melting (EBM) and selective laser melting, has attracted tremendous academic and industrial interests because of its capacity to fabricate components with greater complexity compared with traditional processes, without significantly increasing the cost. It provides significantly higher design freedom to the designers and can make the built components closer to the optimum design in theory when compared with traditional processes. However, the mechanical performance of the new design fabricated by AM has not been clarified yet. Here, we report the fabrication and tensile deformation behavior of the EBM-built lightweight car suspension double wishbone for both conventional and optimized designs. EBM process is an effective method to produce a highly-dense Ti-6Al-4V lightweight design component with good reproducibility and fine α/β duplex microstructure. A poor mechanical performance in the optimized design is observed, which results from the build thickness-dependent mechanical performance that is caused by both various microstructures and rough surfaces in the Ti-6Al-4V parts. Notably, the rough surface plays a dominant role in premature failure when the build thickness is below 2 mm. Based on these findings, the degraded mechanical performance in the optimized design is discussed. The experimental results and analyses provide a guideline for the design of lightweight structures that are mainly comprised of thin walls and/or struts.

Tantalum Bone Implants Printed by Selective Electron Beam Manufacturing (SEBM) and Their Clinical Applications

Tantalum is a refractory metal with a melting point of 2996°C but it offers outstanding biocompatibility for bone implant applications. In this study, the selective electron beam melting (SEBM) process was used for the first time to fabricate both dense and fine lattice tantalum structures. The use of 90-ppm-oxygen Ta powder for SEBM ensured excellent ductility of the as-printed fine Ta lattice implants with strut diameter of just 350 μm. The as-printed dense Ta samples (99.90%) achieved tensile ductility of 45% compared with the minimum requirement of 25% by ISO 13782 and the reported 2% fabricated by SLM using 1800-ppm-oxygen Ta powder. Since 2016, 27 clinical applications have been achieved in China using the custom-designed and SEBM-printed Ta implants by the authors of this study. All these Ta implants (mostly Ta lattice structures) have performed satisfactorily in patients’ bodies so far. Three selected clinical applications, Ta lattice hip, fibula and femur implants, are briefly discussed in this article.

Microstructure and Mechanical Performance of Ti–6Al–4V Lattice Structures Manufactured via Electron Beam Melting (EBM): A Review

Electron beam melting (EBM) process is an additive manufacturing process largely used to produce complex metallic components made of high-performance materials for aerospace and medical applications. Especially, lattice structures made by Ti–6Al–4V have represented a hot topic for the industrial sectors because of having a great potential to combine lower weights and higher performances that can also be tailored by subsequent heat treatments. However, the little knowledge about the mechanical behaviour of the lattice structures is limiting their applications. The present work aims to provide a comprehensive review of the studies on the mechanical behaviour of the lattice structures made of Ti–6Al–4V. The main steps to produce an EBM part were considered as guidelines to review the literature on the lattice performance: (1) design, (2) process and (3) post-heat treatment. Thereafter, the correlation between the geometrical features of the lattice structure and their mechanical behaviour is discussed. In addition, the correlation among the mechanical performance of the lattice structures and the process precision, surface roughness and working temperature are also reviewed. An investigation on the studies about the properties of heat-treated lattice structure is also conducted.

Correlations of cracking with scan strategy and build geometry in electron beam powder bed additive manufacturing

The extension of metal additive manufacturing (AM) to non-weldable Ni-based superalloys remains a challenge for the electron beam melting process. Various cracking mechanisms, including solidification, liquation, strain-age, and ductility dip cracking, make it difficult to fabricate traditionally non-weldable Ni-based superalloys using the AM process. Because airfoil geometries are highly complicated, the correspondingly complex thermal signatures lead to various types of cracking in geometries that are under severe mechanical restraints during the printing process. This work aims to understand the correlations between cracking, scan strategy, and part geometry in airfoil geometries. Crack locations were monitored via an in-situ near-infrared camera during printing. A part-scale finite element method (FEM) was used to reveal cracking mechanisms. New scan strategies that avoided cracking were utilized in an FEM simulation. The present work demonstrates the potential for scan strategy optimization to manipulate stress distribution and the resultant microstructure of parts for industrial applications.

Finite element analysis of temperature and residual stress profiles of porous cubic Ti-6Al-4V titanium alloy by electron beam melting

The temperature and stress profiles of porous cubic Ti-6Al-4V titanium alloy grids by additive manufacturing via electron beam melting (EBM) based on finite element (FE) method were investigated. Three-dimensional FE models were developed to simulate the single-layer and five-layer girds under annular and lateral scanning. The results showed that the molten pool temperature in five-layer girds was higher than that in single-layer grids owing to the larger mass and higher heat capacity. More energies accumulated by the longer scanning time for annular path than lateral path led to the higher temperature and steeper temperature gradient. The thermal stress drastically fluctuated during EBM process and the residual stress decreased with the increase of powder layer where the largest stress appeared at the first layer along the build direction. The stress under lateral scanning was slightly larger but relatively more homogeneous distribution than those under annular scanning. The stress distribution showed anisotropy and the maximum Von Mises stress occurred around the central node. The stress profiles were explained by the temperature fields and grids structure.

Energy modeling and eco impact evaluation in direct metal laser sintering hybrid milling

This paper presents an analytical model of energy consumption for Direct metal laser sintering hybrid milling (DMLS-HM) additive manufacturing (AM) of stainless steel 316L. The model is used to quantify energy consumption during production of a defined geometry with DMLS-HM process and compared with energy consumption in electron beam melting (EBM) and conventional machining (CM). The solid-envelope ratio (α) was used to quantify energy consumption and eco impact of the three manufacturing processes on three different geometry models. The Gabi database and other published literature were used to establish energy consumption during primary metal production and material shaping processes. It was found that solid-envelope ratio (α) has more impact on the energy model of the additive processes than on the subtractive machining. On average, the percentage change in α is equal to the percentage change in energy consumed by DMLS-HM and EBM. The CM process had very little average change of 1.5% compared to the major changes in α. The DMLS-HM process showed dominant energy consumption during the part production stage with an average 84% more than EBM and CM processes. However, the CM was dominant in energy consumption during the primary production stage with an average 70% more energy than DMLS-HM and EBM processes. The novel outcomes of this research will contribute to the understanding of basic physics of energy consumption in AM and can be used in setting sustainable manufacturing goals. Moreover, energy consumption in metal AM also influences mechanical properties and microstructure of produced parts, so this work will further enhance prediction of their quality and service life. DMLS-HM is recently being introduced for industrial applications such as mold and tool manufacturing due to its capabilities in building free form and complex shapes that are otherwise challenging to manufacture by conventional methods.

Influence of Conventional Machining on Chemical Finishing of Ti6Al4V Electron Beam Melting Parts

Additive manufacturing is feeding great hopes for future developments in fields such as aeronautical, biomedical and rapid tooling industrssssies. However, limitations are still restricting its use to make prototypes and hampering mass production. In the case of titanium alloy printing (e.g. Ti6Al4V) with the EBM (Electron Beam Melting) process, the major obstacle to use parts directly after printing is their roughness (Arithmetic Roughness (Ra) ~25 µm). Even if the parts are better regarding residual stresses than parts coming from other 3D printing processes, the high roughness decreases their fatigue resistance. A set of parts were manufactured in Ti6Al4V by EBM process. Their characteristics in terms of dimension (cylindricity and diameter) and surface (Arithmetic Roughness Ra and Total Roughness Rt) were evaluated directly after printing. The average Rt stands at 96 µm e.g. The parts endorsed then a first chemical etching to remove the peaks and valleys on their surface. The average Rt decreased at 90 µm e.g. Afterwards, a robotic machining was performed to remove a layer of 400 µm to reach the core material of the part. The average Rt obtained was 5 µm e.g. Finally, a second chemical etching with the same parameters as the first was done. The average Rt increased finally to 9 µm e.g. The same set of dimensional and surface measurements were made after each step of the experimental setup. The succession of operations and measurements allows to compare the influence of conventional machining on the chemical finishing performed on the parts. Furthermore, the machining emphasizes the apparition of surface defects due to the use of a robot (tessellation). Finally, a Rt degradation and a surface finish change have been recorded after the second chemical etching. Perspectives can be focused on assessing these last observations by repeating the experimental setup with more parts.