Electron Beam Freeform Fabrication Research Articles

Optimizing for IC10 single crystal Ni3Al-based alloy joint by electron beam welding with chemical composition controlling

Due to severe cracking tendency in IC10 single crystal Ni3Al-base alloy jointed by electron beam welding, the solidification crack in the IC10 alloy weldment is detrimental for crucial applications in industry. In this paper, the cracking mechanism in the IC10 alloy joint was investigated, and a perfect joint without any crack is obtained by controlling chemical composition in weld, which microhardness is equivalent to the IC10 alloy and tensile strength is up to 900 MPa reaching 1.5 times of the IC10 alloy. The cracking initiation is derived from the liquid film of low melting point precipitated phase-Ta2C along grain boundary under welding stress during solidification. With chemical composition controlling that a 0.4 mm Inconel718 alloy layer is deposited by electron beam freeform fabrication on the welding path before welding, the finer high melting point NbC phases replacing Ta2C phases is precipitated along grain boundary, and the preferred orientation slender columnar grain containing with a multitude of deformation twins is formed in weld, which can reduce the number and proportion of high angle grain boundary, attributing to the elimination of solidification cracks and the enhancement of tensile strength.

Microstructure and mechanical properties of Ti-52 at% Al alloy synthesized in-situ via dual-wires electron beam freeform fabrication

The in-situ synthesized Ti-52 at% Al alloy was additively manufactured for the first time by electron beam freeform fabrication (EBF3) with pure Ti and Al wires. The chemical compositions, microstructure, crystal orientation and mechanical properties of the Ti-52 at% Al walls were investigated. The results show that the actual Al content was lower than that the designed content due to the evaporation of elements. The microstructure of the as-fabricated walls was composed of γ dendrite which was oriented along the <111> direction. The solidification path was L→ γ phase due to the high cooling rate during EBF3 process. The primary dendrite spacing and the width of the secondary dendrite increased with the building height indicating that the cooling rate decreased. The dendrite disappeared in layer bands due to the repeating thermal cycles. Based on the orientation analysis, the epitaxial growth of the γ phase was found between the dendritic and interdendritice regions and between layers. The microhardness of the dendrite was higher than that of the interdendritic regions. The compressive tests at ambient temperature indicated anisotropic mechanical properties due to the dendrite structure. The compressive strength along the building direction was higher than that along the deposited direction.

Development of a material model for predicting extreme deformation and grain refinement during cold spraying

Fusion-based additive manufacturing techniques such as selective laser melting, electron beam freeform fabrication cause solidification problems such as grain coarseness and high porosity. As a new technique, cold spraying (CS) can overcome such melting-induced drawbacks. In this study, a material model using dislocation dynamics was developed specifically for the CS process for describing the following five nanosecond-scale physical phenomena: strain hardening, normal-range strain rate hardening, ultra-high strain rate hardening, thermal softening and grain size evolution. A single Cu microparticle impact test was conducted, and a good agreement between experimental and model-predicted microparticle deformations was observed, indicating high model accuracy. The corresponding finite element model was established, and the individual effects of the above phenomena were discussed in detail to show that material deformation is mainly controlled by ultra-high strain rate hardening while jetting is controlled by thermal softening. Additionally, both simulated and actual grain size distributions indicated that grain refinement occurs only near the microparticle-substrate interface (mainly at the interface edge). Thus, the newly developed model could accurately reproduce the dynamic deformation behaviors of impacting particles and correctly predict grain refinement (particularly due to dynamic recrystallization).

Wire-Based Additive Manufacturing of Ti-6Al-4V Using Electron Beam Technique.

Electron beam freeform fabrication is a wire feed direct energy deposition additive manufacturing process, where the vacuum condition ensures excellent shielding against the atmosphere and enables processing of highly reactive materials. In this work, this technique is applied for the α + β-titanium alloy Ti-6Al-4V to determine suitable process parameter for robust building. The correlation between dimensions and the dilution of single beads based on selected process parameters, leads to an overlapping distance in the range of 70–75% of the bead width, resulting in a multi-bead layer with a uniform height and with a linear build-up rate. Moreover, the stacking of layers with different numbers of tracks using an alternating symmetric welding sequence allows the manufacturing of simple structures like walls and blocks. Microscopy investigations reveal that the primary structure consists of epitaxial grown columnar prior β-grains, with some randomly scattered macro and micropores. The developed microstructure consists of a mixture of martensitic and finer α-lamellar structure with a moderate and uniform hardness of 334 HV, an ultimate tensile strength of 953 MPa and rather low fracture elongation of 4.5%. A subsequent stress relief heat treatment leads to a uniform hardness distribution and an extended fracture elongation of 9.5%, with a decrease of the ultimate strength to 881 MPa due to the fine α-lamellar structure produced during the heat treatment. Residual stresses measured by energy dispersive X-ray diffraction shows after deposition 200–450 MPa in tension in the longitudinal direction, while the stresses reach almost zero when the stress relief treatment is carried out.

Microstructure and mechanical properties of electron beam freeform fabricated TiB2/Al-Cu composite

TiB2/ZL205 composite thin wall component was built with electron beam freeform fabrication by feeding TiB2 /Al-Cu wire. The microstructure and mechanical properties were tested and studied. The main existed phases were α-Al, Al2Cu phases and TiB2 particles. The eutectic Al2Cu phase and TiB2 particles distributed mainly along the grain boundaries in α-Al matrix. The composite exhibited equiaxed grains, and the average grain size was 13.3 μm. The hardness was about 71.8 HV. The ultimate tensile strength, yield strength and elongation of the samples in horizontal direction were 198 MPa, 88 MPa and 12.9%, respectively. The properties in vertical direction were slightly lower.

The effect of B doping on the oxidation resistance of Ti6Al4V by EBF3

The role of boron doping on the oxidation behavior of the electron beam free form fabrication (EBF3) Ti6Al4V alloys are investigated and compared to the forged alloy. The oxidation resistance of Ti6Al4V (EBF3) is inferior to forged sample, and the diffusion rate is about 1.52×10-5 cm2/s. Doping B can enhance the oxidation resistance of Ti6Al4V (EBF3) due to the effects of breaking the boundary α, disordering and shortening α and β lathes. Among doping B samples, oxidation resistance of 50 mA is better than 80 mA due to the different microstructure and finer oxide particles. And the mechanism of oxidation behavior has been discussed.

A new coating method with potential for additive manufacturing: Premelting electron beam-assisted freeform fabrication

Premelting electron beam-assisted freeform fabrication, as a new method to avoid the direct coupling of wire-beam-molten pool during electron beam freeform fabrication, is proposed for the first time. The three factors referring to wire, beam and molten pool, are decomposed into two factors as wire and beam. The liquid metal is formed in the diversion nozzle, as the wire is heated and melted inside it by an electron beam, and, subsequently, is transferred to the substrate with solidification process. Finally, a continuous and stable process of premelting electron beam-assisted freeform fabrication is achieved. When an aluminum alloy was deposited on a TC4 substrate by premelting electron beam-assisted freeform fabrication, the TC4 base metal did not melt because the electron beam did not directly act on the TC4 substrate. There is no stirring of the electron beam inside the liquid deposition body, and the dissolution and diffusion of elemental Ti exists, which ensures the effective connection between the deposition and the TC4 substrate. Although TiAl3 intermetallic compounds were generated in the deposition, the interface between TiAl3 and the Al matrix was coherent, as (101) TiAl3//(020) Al was clearly detected in the center of the deposition. There are no cracks or other defects in the deposition. The acicular TiAl3 intermetallic compounds are dispersed in the deposition, which improves the wear resistance of the deposition.

Closed-Loop Control of Droplet Transfer in Electron-Beam Freeform Fabrication.

In the process of electron-beam freeform fabrication deposition, the surface of the deposit layer becomes rough because of the instability of the feeding wire and the changing of the thermal diffusion condition. This will make the droplet transfer distance change in the deposition process, and the droplet transfer cannot always be stable in the liquid bridge transfer state. It is easy to form a large droplet or make wire and substrate stick together, which makes the deposition quality worsen or even interrupts the deposition process. The current electron-beam freeform fabrication deposition is mostly open-loop control, so it is urgent to realize the real-time and closed-loop control of the droplet transfer and to make it stable in the liquid bridge transfer state. In this paper, a real-time monitoring method based on machine vision is proposed for the droplet transfer of electron-beam freeform fabrication. The detection accuracy is up to ± 0.08 mm. Based on this method, the measured droplet transfer distance is fed back to the platform control system in real time. This closed-loop control system can stabilize the droplet transfer distance within ± 0.14 mm. In order to improve the detection stability of the whole system, a droplet transfer detection algorithm suitable for this scenario has been written, which improves the adaptability of the droplet transfer distance detection method by means of dilatation/erosion, local minimum value suppression, and image segmentation. This algorithm can resist multiple disturbances, such as spatter, large droplet occlusion and so on.

A new method for distortion calculations in additive manufacturing: Contact analysis between a workpiece and clamps

For the first time, contact theory is incorporated into the deformation calculation of additive manufacturing. Compared with the traditional boundary constraints of pure rigidity or elasticity, the model in this study considers the contact between a workpiece and clamps. The Coulomb friction law is utilized to solve the contact problems. A penalty function method is used to solve the Coulomb friction problems, and the tangential and normal behaviors of the contact parts are analyzed in detail. For both rigid and contact constraints, the deformation trend is consistent with the measured results; however, the deformation distribution of the contact constraints is closer to the real distribution. The maximum deformation that is obtained with the rigid constraints is only 60.6% of the actual measured value, compared to 90.4% with the contact constraints. The mean square error of multiple points between the results by rigid constraints and the measurement is 0.23, while it is 0.14 with contact constrains. Therefore, the incorporation of contact theory can improve the accuracy of deformation simulations for additive manufacturing. Relative motion analysis of the contact part between the workpiece and the clamp during electron beam freeform fabrication demonstrates that the dominant role of the transverse deformation of the substrate decreases with the increase in the number of deposition layers, and warping deformation gradually increases to become the main component of the contact force.

Effect of beam power on the distribution statues of aligned TiBw and tensile behavior of trace boron-modified Ti6Al4V alloy produced by electron beam freeform fabrication

Trace boron-modified Ti6Al4V walls were prepared by electron beam freeform fabrication (EBF3), and the role of beam power in the distribution statues of aligned TiB whiskers (TiBw) and tensile behavior was investigated. The results show that the studied beam power has a remarkable effect on the interval, number density and size of aligned TiBw, while the orientation remains unchanged. High-density and fine TiBw are achievable at a decreased beam power, and play a great role in the increment in strength. With an increase in the beam power, the interval between the aligned TiBw enlarges. It allows the vertical direction to tolerate a large amount of elongation before failure by reducing the crack-propagation rate, blunting and deflecting the cracks. Due to the presence of highly orientated TiBw, the transverse direction of all deposits suffers from a premature failure. This study provides a new route to obtain a desirable mechanical performance by tailoring the distribution statues of TiBw during additive manufacturing of such materials.

Role of trace boron in the microstructure modification and the anisotropy of mechanical and wear properties of the Ti6Al4V alloy produced by electron beam freeform fabrication

This study focused on the effects of trace boron on the microstructure of the electron beam freeform fabricated (EBF3-ed) Ti6Al4V alloy. The anisotropic compression properties and wear behave or were systematically studied, and results indicate that TiB whiskers align in parallel in the longitudinal (Z) direction with trace boron addition. The boron addition enhances the compression strength of Ti6Al4V alloy but the highly directional TiB whiskers lead to the anisotropy of compressive strength. The higher compressive strength can be obtained when the orientation of TiB whiskers is parallel to the load. Besides, trace boron addition improves the wear resistance of Ti6Al4V. Because of the unidirectional alignment of TiB whiskers, the Ti6Al4V-0.07B samples show anisotropy in their wear properties. This study reveals the effect of trace boron on the compression and wear anisotropy of boron-modified Ti6Al4V alloy prepared by EBF3, which is beneficial to its practical application.

Crystallographic texture and mechanical properties by electron beam freeform fabrication of copper/steel gradient composite materials

Copper/stainless steel gradient material was preparated by electron beam freeform fabrication. With the increase of deposition layers, the interfaces between them become smooth. Crystallographic textures at the first, third and fifth copper layers were determined by means of electron backscatter diffraction analysis. The results yielded clear information that grain growth was significantly affected by heat dissipation. The grain gradually altered from competitive growth to epitaxial growth with the increase of the layers. A strong crystallographic texture in <0 0 1> direction is produced on the top of the deposition, but weak at the bottom of the deposition. Cracks and shrinkages were found in the deposition, which are attributed to the liquid copper. The average shear strength of the depositions exceeds 240 MPa. The fracture is primarily characterized by a ductile mode.

Online Measurement of Deposit Surface in Electron Beam Freeform Fabrication

In the process of electron beam freeform fabrication (EBF3), due to the continuous change of thermal conditions and variability in wire feeding in the deposition process, geometric deviations are generated in the deposition of each layer. In order to prevent the layer-by-layer accumulation of the deviation, it is necessary to perform online geometry measurement for each deposition layer, based on which the error compensation can be done for the previous deposition layer in the next deposition layer. However, the traditional three-dimensional reconstruction method that employs structured laser cannot meet the requirements of long-term stable operation in the manufacturing process of EBF3. Therefore, this paper proposes a method to measure the deposit surfaces based on the position information of electron beam speckle, in which an electron beam is used to bombard the surface of the deposit to generate the speckle. Based on the structured information of the electron beam in the vacuum chamber, the three-dimensional reconstruction of the surface of the deposited parts is realized without need of additional structured laser sensor. In order to improve the detection accuracy, the detection error is theoretically analyzed and compensated. The absolute error after compensation is smaller than 0.1 mm, and the precision can reach 0.1%, which satisfies the requirements of 3D reconstruction of the deposited parts. An online measurement system is built for the surface of deposited parts in the process of electron beam freeform fabrication, which realizes the online 3D reconstruction of the surface of the deposited layer. In addition, in order to improve the detection stability of the whole system, the image processing algorithm suitable for this scene is designed. The reliability and speed of the algorithm are improved by ROI extraction, threshold segmentation, and expansion corrosion. In addition, the speckle size information can also reflect the thermal conditions of the surface of the deposited parts. Hence, it can be used for online detection of defects such as infusion and voids.

Obtaining the bimetallic composition by the electron beam freeform fabrication

This paper is devoted to obtaining the multimaterials using the electron-beam wire-feed additive manufacturing technology. The sample of titanium alloy Ti-6Al-4V and stainless steel 321 composition was obtained. It was found that steel and Ti-alloy form a transitional intermediate layer between themselves. The Ti-alloy layer does not undergo major changes, while the layer of stainless steel undergoes significant cracking.

Temperature distribution simulations during electron beam freeform fabrication process based on the fully threaded tree

PurposeThe purpose of this study is to simulate the temperature distribution during an electron beam freeform fabrication (EBF3) process based on a fully threaded tree (FTT) technique in various scales and to analyze the temperature variation with time in different regions of the part.Design/methodology/approachThis study presented a revised model for the temperature simulation in the EBF3 process. The FTT technique was then adopted as an adaptive grid strategy in the simulation. Based on the simulation results, an analysis regarding the temperature distribution of a circular deposit and substrate was performed.FindingsThe FTT technique was successfully adopted in the simulation of the temperature field during the EBF3 process. The temperature bands and oscillating temperature curves appeared in the deposit and substrate.Originality/valueThe FTT technique was introduced into the numerical simulation of an additive manufacturing process. The efficiency of the process was improved, and the FTT technique was convenient for the 3D simulations and multi-pass deposits.

Microstructure and mechanical properties of Ti–6Al–4V alloy fabricated using electron beam freeform fabrication

Electron beam freeform fabrication (EBF3) has drawn increasing attention over the past decade due to its potential for time and cost savings. The microstructure and mechanical properties of EBF3- fabricated Ti–6Al–4V block have been investigated and discussed in this work. The microstructure of the as-fabricated block was found to be dominated by columnar grains and equiaxed grains. The phase constitutions were identified by X-ray diffraction and transmission electron microscopy. The results reveal that the as-fabricated Ti–6Al–4V samples consist of lamellar structure, basketweave structure and Widmanstätten structure. The graded Ti–6Al–4V microstructure was observed which mainly arise from the complex thermal cycles. The average width of lamellar α phase and element content of Al are decreased with the increasing of the building height. Graded mechanical properties of Ti–6Al–4V with microhardness and tensile strength were found. The microhardness and ultimate tensile strength increase while decreasing elongation as the increasing of build height. This work provides a better understanding of microstructural evolution during the EBF3 process, which will be conducive process control, improvement, and optimization.

Microstructure and mechanical behaviour of additive manufactured Ti–6Al–4V parts under tension

Metal-based additive manufacturing technologies using electron or laser beams as a heat source for melting a metal powder or wire have been the subject of keen interest in recent years. At present paper a comparative analysis of the microstructure, strain response during tensile test and mechanical properties of Ti–6Al–4V samples produced by selective laser melting, electron beam melting or electron beam free-form fabrication were performed. A microstructural study using transmission electron microscopy revealed columnar prior β grains transformed into a lamellar α-morphology in the samples. According to X-ray diffraction study, the volume fractions of the β-Ti phase in the samples were equal to 2, 4 and 6 % respectively. It has been shown that the Vickers microhardness of SLM and EBM Ti–6Al–4V samples was similar (~5.4 GPa) while the hardness of EBF3 parts was significantly lower (4.5 GPa). The uniaxial stress-strain response of the Ti–6Al–4V samples fabricated by different additive manufacturing technologies were compared. Crystallographic (dislocation motion) and non-crystallographic (shear banding) deformation mechanisms of the loaded samples were studied by scanning electron microscopy and optical profilometry.

Structural evolution of 321 stainless steel in electron beam freeform fabrication

The study of the structural evolution in the specimens of austenitic steel 321 manufactured by an additive method through the melting of a wire material by an electron beam in a vacuum chamber has been carried out using optical metallography, scanning electron microscopy and EBSD analysis. Tensile properties were determined on standard dumbbell specimens. The studies of the structure and properties showed that the 3D-printed samples have a pronounced dendritic structure with a sharp fusion boundary between the substrate and the printed material. The mechanical properties of the specimens are at the level of those cast austenitic steel 321.

On the problem of formation of articles with specified properties by the method of electron beam freeform fabrication

The obtained results show that using an electron beam wire feed process makes it possible to manufacture axially symmetric articles which metal strength is close to this of conventionally made ones. However, it is necessary to optimize the process parameters and thus provide forming the desired microstructure with or without the anisotropy.

A new 3D printing method based on non-vacuum electron beam technology

Electron beam freeform fabrication (EBF3) is one the of rapid manufacturing methods, which produces metal parts using an electron beam and wire feed unit in a layer additive fashion without need of mold or jigs. The main disadvantage of EBF3 is that the process is carried out in a chamber, which not only takes a lot of time to evacuate but also limits the size of the part being printed. Non-vacuum electron beam (NVEB) welding is widely used in industry field as a reason for its high production volumes. So a NVEB 3D printing device based on a non-vacuum electron beam welding machine from SST is designed. A serial of experiments is carried out to get a deep understand of 3D printing processing procedure using non-vacuum electron beam system and find a suitable process window. Result shows that droplet transfer mode is one of the most important parameters which determines the quality of the deposition.