Electron Beam Melting Specimens Research Articles

Effect of Pore Defects on Very High Cycle Fatigue Behavior of TC21 Titanium Alloy Additively Manufactured by Electron Beam Melting

Titanium alloys additively manufactured by electron beam melting (EBM) inevitably obtained some pore defects, which significantly reduced the very high cycle fatigue performance. An ultrasonic fatigue test was carried out on an EBM TC21 titanium alloy with hot isostatic pressing (HIP) and non-HIP treatment, and the effect of pore defects on the very high cycle fatigue (VHCF) behavior were investigated for the EBM TC21 titanium alloy. The results showed that the S-N curve of non-HIP specimens clearly had a tendency to decrease in very high cycle regimes, and HIP treatment significantly improved fatigue properties. Fatigue limits increased from 250 MPa for non-HIP specimens to 430 MPa for HIP ones. Very high cycle fatigue crack mainly initiated from the internal pore for EBM specimens, and a fine granular area (FGA) was observed at the crack initiation site in a very high cycle regime for both non-HIP and HIP specimens. ΔKFGA had a constant trend in the range from 2.7 MPam to 3.5 MPam, corresponding to the threshold stress intensity factor range for stable crack propagation. The effect of pore defects on the very high cycle fatigue limit was investigated based on the Murakami model. Furthermore, a fatigue indicator parameter (FIP) model based on pore defects was established to predict fatigue life for non-HIP and HIP specimens, which agreed with the experimental data.

On the suitability of applying thermographic methods for the rapid estimation of the fatigue limit of additively manufactured Ti-6Al-4V

The suitability of infrared thermography (IRT) for convenient and rapid estimation of the fatigue limit ofTi-6Al-4V produced by electron beam melting (EBM) under different conditions is assessed. Wrought material is included for comparison purposes. IRT-based methods result appropriate for machined and polished HIPed EBM specimens, as they are for wrought material, but not for other printed material conditions. This is interpreted in terms of the presence of the typical surface (roughness) and internal (lack-of-fusion and gas or keyhole pores) defects that hinder surface thermal manifestation, thus rendering IRT ineffective in non HIP treated EBM produced material.

Abrasive wear resistance of Ti-6AL-4V obtained by the conventional manufacturing process and by electron beam melting (EBM)

Ti–6Al–4V is one of the most used commercial titanium alloys, in part due to properties that are desirable in high value sectors such as the aerospace industry, such as good strength-to-weight ratio and corrosion resistance. These are of importance in gas turbine engines and structural components, where titanium alloys complement heavier steel or nickel alloys. It is also a good candidate to be used in the manufacturing of prostheses, since it has good biocompatibility, but applications in other areas are limited due to its poor bulk wear resistance.Conventionally processed Ti-6AL-4V is typically used, however additive manufacturing (AM) techniques such as electron beam melting (EBM) can also be applied to this alloy. These techniques are increasingly attractive across many industries because of geometrical freedom and control of mechanical properties, both key, for example, to the successful production of highly personalised prostheses and complex thermofluids channels in aerospace and automotive components. Parts produced by EBM are typically denser than those obtained by other AM processes, but still experience increased wear over their traditionally obtained equivalents, particularly in sliding, thus surface treatment is common.This work compares the wear observed when specimens manufactured by either conventionally or EBM were subjected to abrasion via means of a dry sand-rubber wheel tribometer capable of testing to the ASTM G65 test method. The specimens and resulting wear scars were characterised (hardness, grain size, roughness) and details of the wear mechanism(s) identified. The EBM specimens exhibited much greater wear, over twice that of the conventionally obtained specimens, and feature significantly more scratches.Although there are several studies variously considering two-body sliding wear and the efficacy of surface treatments of this type of alloy, this work addresses the paucity of information about the comparative abrasive wear performance of the alloy obtained via the two process routes.

On the characterization of roughness and geometrical irregularities of additively manufactured single titanium-alloy struts

The purpose of this study is to expose data analysis techniques based on X-ray computed microtomography (XCT) for measuring the complex geometric characteristics of millimeter-sized specimens fabricated by additive manufacturing, and their modification induced by surface treatment. A set of Ti-6Al-4V struts was produced by Electron Beam Melting (EBM) at two angles, at 45° and vertically. They were scanned by XCT before and after electropolishing (EP). Extensive analysis allowed for measuring the amount and size of partially melted particles attached to the surface, the cross-section geometry along the axis of the strut, and the roughness over the whole surface at the micrometer scale. The variation of these characteristics was correlated to the EP conditions. The accuracy of the roughness values measured by XCT was validated by Laser Scanning Confocal Microscopy. The as-built 45° specimens showed the usual characteristics of EBM fabricated struts, such as elongated cross-sections, and a smooth overhanging surface. Less expected was the increased roughness on the lateral sides of these specimens, rather than on the underhanging sides. Similarly, the vertically fabricated struts showed a moderate, yet measurable, roughness variation over their circumference. Despite this lack of uniformity, all the specimens fabricated at a given angle were remarkably similar. The average quantities and sizes of attached particles were quantified for all conditions. The amount of removed material after EP correlated well with the total exchanged electric charge related to the formation of tetravalent Ti 4+ ions. Local SEM observations before and after EP put into evidence the removal of partially melted particles. • Novel custom methods for extensive analysis of 3D geometries applied to mm-sized EBM struts: cross-section analysis, surface unfolding, surface granulometry. • Quantitative assessment of attached particles, surface roughness and cross-sectional shape before and after electropolishing and related effects of process parameters. • Relating process parameters to the heterogeneity of attached particles, roughness, and equivalent diameters along the circumferences of full EBM struts. • Precise measurements of surface feature modification during electropolishing on mm-sized EBM specimens and its consequence on surface roughness evolutions. • Documentation of the mechanism of surface particles teared off during electropolishing leaving nanometer sized craters with crystallographic features.

Implant-Abutment Discrepancy Before and After Acrylic Resin Veneering of Complete-Arch Titanium Frameworks Manufactured Using Milling and Electron Beam Melting Technologies.

To assess the implant-abutment discrepancy of complete-arch frameworks manufactured using milling and additive electron beam melting (EBM) technologies, before and after acrylic resin veneering application. A definitive implant cast with six implant replicas was digitized using a laboratory scanner. A software program was used to design an implant-supported framework which was manufactured using milling (M group) and EBM (EBM group) technologies (n = 10). In the M group, titanium milled specimens were fabricated. In the EBM group, titanium EBM specimens were obtained. A coordinate measurement machine (CMM) was used to assess the implant-abutment discrepancy at x-, y-, and z-axed between the specimens and the implant-abutment replicas of the definitive cast. The implant replicas positioned on the lateral incisor positions were not able to be assessed. The 3D gap discrepancy was calculated: . Acrylic resin veneering procedures were finished and the same CMM measurements were completed. Three-way analysis of variance (ANOVA) test was used to analyze the data (α = 0.05). The manufacturing method (df = 1, F = 7.00, p = 0.009) and implant position (df = 3, F = 129.82, p < 0.001) were significant predictors of the x-axis discrepancy. The veneering procedures (df = 1, F = 21.55, p < 0.001) and implant position (df = 3, F = 95.42, p < 0.001) were significant predictors of the y-axis discrepancy. The manufacturing method (df = 1, F = 11.79, p = 0.001) was a significant predictor of the z-axis discrepancy. Lastly, the manufacturing method (df = 1, F = 5.11, p = 0.026), implant position (df = 3, F = 11.36, p < 0.001), and veneering procedures (df = 1, F = 41.56, p < 0.001) were significant predictors of the 3D gap discrepancy in which the manufacturing method explains the 2.37% of variation in the 3D gap discrepancy, the implant position explains the 15.82% of variation in the 3D gap discrepancy, and veneering procedures explain the 19.29% of variation in the 3D gap discrepancy results. The manufacturing methods, veneering procedures, and implant position influenced the linear implant-abutment discrepancy. The milled technique tested obtained lower linear implant-abutment discrepancy compared with the EBM method evaluated. The acrylic resin veneering procedures increased the implant-abutment discrepancy.

In-situ observation of microstructurally small fatigue crack initiation and growth behaviors of additively-manufactured alloy 718

To reveal the effects of microstructural features on fatigue property, microscopic fatigue crack initiation and growth behavior were successively observed for rolled plate and additively-manufactured nickel base 718 alloy. Three types of additive manufacturing (AM) methods: powder bed Electron Beam Melting (EBM), Selective Laser Melting (SLM), and wire-fed Electron Beam Additive Manufacturing (EBAM) were adopted for specimen preparation to create various microstructures for comparison. The results showed that the fatigue lives of the EBM and EBAM specimens, which have a robust (001) texture, were shorter than those of the rolled plate and SLM specimens. This fatigue life difference could not be explained by the defects, because the fatigue cracks in the part of EBAM specimen were initiated along a slip plane. On the other hand, acceleration of the early stage fatigue crack growth rate (FCGR) was found in the EBM and EBAM specimens. Cross-sectional electron back scatter diffraction (EBSD) observations also showed that early stage cracks initiated and grew along the {111} slip plane; but in the EBAM specimens, the cracks continuously propagated straight to an adjacent grain due to their (001) texture. It thus appears that the low-angle grain boundaries which tend to be generated as a result of the (001) texture do not act as barriers to the penetration of dislocations; instead, they accelerate the shear mode fatigue crack growth rate in the early stages and decrease fatigue life.

Systematic evaluation of selective fusion additive manufacturing based on thermal energy source applied in processing of titanium alloy specimens for medical applications

In this study, two selective metal fusion additive manufacturing (AM) technologies, electron-beam melting (EBM) and selective laser melting (SLM), were used to fabricate Ti6Al4V test specimens for a comprehensive evaluation, including physical-chemical properties and biological properties. The results indicated that the mechanical behaviors, for instance tensile strength and yield strength, of the processed metal devices could exhibit different outcomes with the use of fusion approaches with different thermal energies. Moreover, the relationship between mechanical properties and the crystal structure, α:β-phase ratio, was characterized systematically to evaluate the samples produced via these two powder bed methods. The corrected β-phase fractions of the EBM and SLM specimens were 0.12 and 0.10, respectively, which corresponded to a slight difference in mechanical strength. Furthermore, the EBM- and SLM-fabricated specimens presented excellent biocompatibility in an in vitro cellular evaluation. Consequently, our findings demonstrated that the AM-fabricated Ti6Al4V parts conformed to all of the international standard requirements, particularly in terms of the mechanical properties, chemical composition, and non-corrosiveness. Thus, we believe that our study can contribute to the further development of additive manufacturing processes.

Effect of Various Peening Methods on the Fatigue Properties of Titanium Alloy Ti6Al4V Manufactured by Direct Metal Laser Sintering and Electron Beam Melting.

Titanium alloy Ti6Al4V manufactured by additive manufacturing (AM) is an attractive material, but the fatigue strength of AM Ti6Al4V is remarkably weak. Thus, post-processing is very important. Shot peening can improve the fatigue strength of metallic materials, and novel peening methods, such as cavitation peening and laser peening, have been developed. In the present paper, to demonstrate an improvement of the fatigue strength of AM Ti6Al4V, Ti6Al4V manufactured by direct metal laser sintering (DMLS) and electron beam melting (EBM) was treated by cavitation peening, laser peening, and shot peening, then tested by a plane bending fatigue test. To clarify the mechanism of the improvement of the fatigue strength of AM Ti6Al4V, the surface roughness, residual stress, and surface hardness were measured, and the surfaces with and without peening were also observed using a scanning electron microscope. It was revealed that the fatigue strength at N = 107 of Ti6Al4V manufactured by DMLS was slightly better than that of Ti6Al4V manufactured by EBM, and the fatigue strength of both the DMLS and EBM specimens was improved by about two times through cavitation peening, compared with the as-built ones. An experimental formula to estimate fatigue strength from the mechanical properties of a surface was proposed.

Friction welding of electron beam melted Ti-6Al-4V

Ti-6Al-4V samples produced by electron beam melting (EBM) are welded using solid-state friction welding (FW) process. The microstructure of the weld sample shows the presence of fine equiaxed α grains with irregular β phase. Microstructural investigations reveal a pronounced change in the shape and size of the α phase in the weld metal as-compared to the base material along with the disappearance of columnar prior β grains. Such variations in the microstructure significantly change the mechanical properties of the FW material. The hardness in the weld zone increases and a decrease of hardness is observed along the heat affected zone (HAZ) with respect to the base metal as expected. Similarly, the room temperature tensile tests show an improvement of ductility in the welded EBM samples. However, the yield and the ultimate strength show a marginal drop in the welded samples compared to the as-prepared EBM specimens. The present work demonstrates that solid-state FW process not only permits successful joining of additively manufactured materials, but also helps in improving their ductility.

Micro-CT Evaluation of Defects in Ti-6Al-4V Parts Fabricated by Metal Additive Manufacturing

In this study, micro-computed tomography (CT) is utilized to detect defects of Ti-6Al-4V specimens fabricated by selective laser melting (SLM) and electron beam melting (EBM), which are two popular metal additive manufacturing methods. SLM and EBM specimens were fabricated with random defects at a specific porosity. The capability of micro-CT to evaluate inclusion defects in the SLM and EBM specimens is discussed. The porosity of EBM specimens was analyzed through image processing of CT single slices. An empirical method is also proposed to estimate the porosity of reconstructed models of the CT scan.

Mechanical and corrosion properties of CoCrFeNiTi-based high-entropy alloy additive manufactured using selective laser melting

The effectiveness of applying selective laser melting (SLM) to a CoCrFeNiTi-based high-entropy alloy was compared with that of using electron beam melting (EBM). The higher solidification rate during SLM promoted a fine uniform microstructure with no visible segregation, which led to superior tensile properties (yield strength: 773.0 ± 4.2 MPa, ultimate tensile strength: 1178.0 MPa, elongation: 25.8 ± 0.6%) and a higher pitting potential (0.88 ± 0.03 V versus Ag/AgCl in a 3.5% NaCl solution at 353 K) in comparison to the EBM specimens (743.4 ± 11.6, 932.2 ± 4.8 MPa, 4.0 ± 0.2%, and 0.50 ± 0.04 V versus Ag/AgCl, respectively). The effect of a solution treatment on the tensile properties and pitting-corrosion resistance of the SLM specimens was then examined. The effect of the solution treatment on these properties depended on the cooling method used during the treatment. In particular, the tensile properties and pitting-corrosion resistance improved as a result of water quenching. On the other hand, the properties of the solution-treated specimens depended on the size and volume fraction of very fine-ordered particles, with diameters of tens of nanometers that contained Ni and Ti. The as-built and solution-treated SLM specimens exhibited excellent tensile strength and exceptional pitting-corrosion resistance; they had higher tensile strength and pitting-corrosion resistance than the conventional high-corrosion-resistant alloys.

Effect of Hot Isostatic Pressure treatment on the Electron-Beam Melted Ti-6Al-4V specimens

The main advantages of additive manufacturing (AM), including fabrication of complex geometry lightweight objects, lattice structures, chain and gear mechanisms, better environment saving materials and resources and energy, better tool life of component, etc. are already well known. The main challenge in AM of metals is to achieve proper mechanical properties and performance, especially for safety critical parts. Thus, post-processing procedures for AM come to the front.In the framework of this research were prepared specimens by Electron Beam Melting (EBM). In case of the EBM, the greatest problem is porosity, which is especially critical for airspace components. One of the procedures recommended for decreasing porosity is Hot Isostatic Pressure (HIP) treatment, and its effect should be thoroughly studied to widespread its application.To investigate this aspect, Ti-6Al-4V cylinder parts were printed on the ARCAM EBM A2X machine using a 210×210 mm building platform. The microstructure and mechanical properties of the EBM specimens were tested before and after the HIP treatment. High cycle fatigue tests (HCFT), fracture surface examination, as well as micro-CT evaluation were performed.

Corrosion resistance characteristics of a Ti-6Al-4V alloy scaffold that is fabricated by electron beam melting and selective laser melting for implantation in vivo

The purpose of this study is to determine the corrosion resistance of Ti-6Al-4V alloy fabricated with electron beam melting and selective laser melting for implantation in vivo. Ti-6Al-4V alloy specimens were fabricated with electron beam melting (EBM) and selective laser melting (SLM). A wrought form of Ti-6Al-4V alloy was used as a control. Surface morphology observation, component analysis, corrosion resistance experimental results, electrochemical impedance spectroscopy, crevice corrosion resistance experimental results, immersion test and metal ions precipitation analysis were processed, respectively. The thermal stability of EBM specimen was the worst, based on the result of open circuit potential (OCP) result. The result of electrochemical impedance spectroscopy indicated that the corrosion resistance of the SLM specimen was the best under the low electric potential. The result of potentiodynamic polarization suggested that the corrosion resistance of the SLM specimen was the best under the low electric potential (<1.5V) and EBM specimen was the best under the high electric potential (>1.5V).The crevice corrosion resistance of the EBM specimen was the best. The corrosion resistance of SLM specimen was the best, based on the result of immersion test. The content of Ti, Al and V ions of EBM, SLM and wrought specimens was very low. In general, the scaffolds that were fabricated with EBM and SLM had good corrosion resistance, and were suitable for implantation in vivo.

Fatigue life of additively manufactured Ti–6Al–4V in the very high cycle fatigue regime

The present study reports on the impact of two different additive manufacturing routes, i.e. selective electron beam melting (EBM) and selective laser melting (SLM) on the fatigue life of the titanium alloy Ti–6Al–4V in the high cycle fatigue (HCF) and in the very high cycle fatigue (VHCF) regime. Cylindrical fatigue specimens were manufactured by EBM and SLM and tested in differently post-treated conditions. The EBM specimens were tested in the as-built condition, SLM manufactured specimens were heat treated at 800°C and hot isostatically pressed, respectively. The type, size and location of every crack initiating discontinuity was determined and thoroughly investigated by scanning electron microscopy. Three main findings were derived from the present investigation. Fatigue properties of as-built EBM and stress relieved SLM specimens in the HCF and VHCF regimes are very similar. Defect types and defect sizes of similar nature were observed in both conditions. In consequence, stress relieving heat treatment has not to be conducted in EBM processed Ti–6Al–4V. The shape of the discontinuities, however, currently is not considered by traditional approaches for estimation of fatigue strength. The fatigue performance of the SLM processed and subsequently hot isostatically pressed condition is superior to its two additively manufactured counterparts and similar to conventionally processed material. Duplex S–N behavior with a clear transition area was observed in case of the Ti–6Al–4V specimens tested.

Evaluation of Titanium Alloys Fabricated Using Rapid Prototyping Technologies-Electron Beam Melting and Laser Beam Melting.

This study characterized properties of Ti-6Al-4V ELI (extra low interstitial, ASTM grade 23) specimens fabricated by a laser beam melting (LBM) and an electron beam melting (EBM) system for dental applications. Titanium alloy specimens were made into required size and shape for each standard test using fabrication methods. The LBM specimens were made by an LBM machine utilizing 20 µm of Ti-6Al-4V ELI powder. Ti-6Al-4V ELI specimens were also fabricated by an EBM using 40 µm of Ti-6Al-4V ELI powder (average diameter, 40 µm: Arcam AB®) in a vacuum. As a control, cast Ti-6Al-4V ELI specimens (Cast) were made using a centrifugal casting machine in an MgO-based mold. Also, a wrought form of Ti-6Al-4V ELI (Wrought) was used as a control. The mechanical properties, corrosion properties and grindability (wear properties) were evaluated and data was analyzed using ANOVA and a non-parametric method (α = 0.05). The strength of the LBM and wrought specimens were similar, whereas the EBM specimens were slightly lower than those two specimens. The hardness of both the LBM and EBM specimens was similar and slightly higher than that of the cast and wrought alloys. For the higher grindability speed at 1,250 m/min, the volume loss of Ti64 LBM and EBM showed no significant differences among all the fabrication methods. LBM and EBM exhibited favorable results in fabricating dental appliances with excellent properties as found for specimens made by other fabricating methods.