Selective Electron Beam Melting Research Articles

Hot deformation behavior of a layered heterogeneous microstructure TiAl alloy prepared by selective electron beam melting

TiAl-based alloys are known for their exceptional high-temperature properties but suffer from low hot workability. The emergence of additive manufacturing (AM) technology significantly decreases the workability requirement, while the microstructure heterogeneities in AMed TiAl are troublesome. This paper explores the hot deformation behavior and microstructure evolution of a layered heterogeneous microstructure TiAl alloy prepared by selective electron beam melting. The Arrhenius constitutive model with strain compensation was established, and hot processing maps were constructed. The microstructure showed that at the initial stage of deformation, a large number of dislocation slips occur preferentially in the soft coarse-grained layers. With the increase of strain, dislocation accumulation in heterogeneous interfaces, and dynamic recrystallization (DRX) occurs. Eventually, the coarse-grained region is constantly occupied by fine DRX grains. A high density of deformation twins at high strain rates further promotes the formation of tiny DRX grains. When the hot compression temperature reaches 1200 °C, the initial alternative fine-grained and coarse-grained hetero-structure transforms into duplex (DP) and near-lamellar (NL) microstructure, and microstructure heterogeneity is eliminated. The results enhance understanding of the hot deformation behavior of heterogeneous microstructure TiAl alloys.

Mechanical and Electrochemical Properties Comparison of Additively Manufactured Ti-6Al-4V Alloys by Electron Beam Melting and Selective Laser Melting

Mechanical and Electrochemical Properties Comparison of Additively Manufactured Ti-6Al-4V Alloys by Electron Beam Melting and Selective Laser Melting

Effect of Heat Treatment on the Structure and Properties of Titanium Aluminide Alloy Ti–Al–V–Nb–Cr–Gd Produced by Selective Electron Beam Melting

Effect of Heat Treatment on the Structure and Properties of Titanium Aluminide Alloy Ti–Al–V–Nb–Cr–Gd Produced by Selective Electron Beam Melting

Creep behavior and creep-oxidation interaction of selective electron beam melted Ti–48Al–2Cr–2Nb alloy at different temperatures

In this work, creep behavior and creep-oxidation interaction behavior of Ti–48Al–2Cr–2Nb alloy fabricated by selective electron beam melting at different temperatures were investigated in detail. This alloy exhibits a near-γ microstructure composed of coarse/fine mixed equiaxed grains. Creep test results show that creep behavior of this alloy is sensitive to temperature. This is mainly manifested in that creep life reduces significantly by 84.8 % as temperature increases from 800 °C to 850 °C. During creep, discontinuous dynamic recrystallization characterized by grain nucleation and growth and continuous dynamic recrystallization characterized by strain gradient and orientation accumulation occur simultaneously. The formation of mechanical twins plays an important role in stimulating dynamic recrystallization. Meanwhile, creep deformation and fracture mechanisms of this alloy at different temperatures were also discussed. On the other hand, oxidation test results reveal that the applied tensile stress has a positive effect on the oxidation behavior of this alloy: the growth of TiO2 oxide is inhibited and the oxidation rate is slowed down. However, under creep-oxidation interaction, the intergranular cracking of the oxide film occurs along with the necking of the alloy matrix during creep.

Anomalous strain rate dependence of ultra-low temperature strength and ductility of an electron beam additively manufactured near alpha titanium alloy

The strain rate (ε˙) dependence of ultra-low temperature strength and ductility was investigated systematically on a cryogenic near alpha titanium alloy Ti-3Al-3Mo-3Zr-0.2Y additively manufactured by electron beam selective melting (EBSM). As ε˙ increases under quasi-static tension at 77 and 20 K, ductility monotonically decreases when yield strength (YS) keeps ascending. As ε˙ increases from 5.6 × 10–4 s−1 once by one order of magnitude, elongation-to-fracture declines from 20.0 % to 16.5 % and 15.7 % at 20 K. However, unlike the regular monotone increase at 298 and 77 K, ultimate tensile strength (UTS) at 20 K rises to 1460 MPa first then drops to 1320 MPa. This study further examined how strain rate affects slipping, twinning and strain hardening behavior. The monotone increase in YS is primarily attributed to the increased CRSS for slips and the enhanced tendency of pyramidal 〈a〉 and 〈c + a〉 slipping and <101¯0 > 34° twinning at 20 K. On the other hand, the monotone decrease of ductility is essentially ascribed to the intensified deformation localization characterized by micro shear bands, multiple necking and single necking. More importantly, the mechanisms of abnormal UTS variation and disappearance of serration flow at 20 K are discussed in terms of strain hardening levels, degree of shear deformation localization and the interaction of slips and twins. This study provides deep insights into strain rate effect on cryogenic mechanical behavior of EBSM-built titanium alloy.

PERSPECTIVES AND DEVELOPMENT TRENDS FOR APPLICATION OF ADDITIVE TECHNOLOGIES IN MODERN DENTISTRY IN THE LIGHT OF INDUSTRY 4.0

Additive manufacturing technologies (AMTs) offer a new approach for cost-effective production of goods and services and are therefore quite rightly included as part of the Fourth Industrial Revolution, Industry 4.0. Last years great attention is paid to the AMTs as technologies of the future development in many countries all over the world including the European Union. Depending on the availability of a good base of installed 3D printers and intellectual potential, the countries are divided into two groups: 1) leaders in the field of 3D printing technology and 2) countries with large bases of equipment, but lack of trained and qualified labor force. The aim of the present paper is to analyze the perspectives and development trends for application of additive technologies in modern dental medicine in the light of Industry 4.0. The constant development of AMTs will accelerate their implementation in various fields and in particular in medicine/dentistry. The 3D printing technologies are first applied in dentistry, due to the possibility for fabrication of individual dental constructions. Currently, almost all worldrenowned companies for production of dental materials and machines develop additive technologies and manufacture the corresponding equipment. According to the forecasts, the 3D printing is expected to be widely used in dental clinics and laboratories in the next 5-10 years. The additive technologies most often applied in dentistry include stereolithography, fused deposition modeling, selective electron beam melting, selective laser melting/sintering and ink-jet printing. The great variety of materials used in these processes allow constructions with different purposes to be made for all areas of dental medicine - surgery, oral implantology, conservative dentistry, orthodontics and prosthetic dentistry.

Mechanical properties characterization of Ti-6Al-4 V grade 5 (recycled) additively manufactured by selective electron beam melting (EB-PBF)

Additive manufacturing, a rapidly expanding technology, enables the production of intricate parts through the successive layering of materials. However, there remains a dearth of research on the viability of incorporating recycled powder into this process, with the potential to decrease expenses and enhance sustainability. This study's objective is to investigate the ramifications of employing recycled Titanium Ti-6Al-4 V alloy powder, for up to ten cycles, without the addition of virgin powder, in the context of additive manufacturing. The findings reveal that the mechanical properties of the material experience an approximate 40 % degradation in comparison to virgin powder. In ultrasonic very high-cycle fatigue tests (VHCF), the failure stress in the Z direction for additive manufacturing EB-PBF equals or surpasses 245 MPa. This research makes a significant contribution to the sustainable advancement of additive manufacturing, as it demonstrates the potential for recycling Titanium Ti-6Al-4 V grade 5 powder for the production of new items. This not only reduces costs but also serves the environment by circumventing unnecessary material disposal. Consequently, the outcomes of this investigation underscore the promising prospects of additive manufacturing with recycled powder, ushering in fresh opportunities for the industry, especially with regards to sustainability and environmental responsibility.

Comparing the Cold, Warm, and Hot Deformation Flow Behavior of Selective Laser‐Melted and Electron‐Beam‐Melted Ti–6Al–2Sn–4Zr–2Mo Alloy

The cold, warm, and hot deformation flow behavior and mechanical properties of the Ti‐6242 alloy produced by selective laser melting (SLM) and electron beam melting (EBM) are compared. Hot compression tests are conducted over a wide temperature range (100–1000 °C) at a constant strain rate of 0.001 s−1. The yield and overall strength levels of the SLMed specimens are higher than those of the EBMed specimens at all temperatures. A thermally stable region is observed for SLMed specimens in the temperature range of 100–700 °C, but the strength level drops significantly (approximately 300–500 MPa) at above 700 °C. The stability region shifts to the lower temperature range of 100–600°Cfor the EBMed specimens, and strength starts to decrease at 600 °C. Both specimens experience fracture in a cold‐temperature regime but exhibit a high strain tolerance of approximately 0.4. The SLMed samples display a completely brittle behavior at a warm temperature regime, whereas, the EBMed specimens demonstrate better formability, tolerating higher compressive strains. The softening fraction substantially increases at high temperatures, indicating safe domains for thermomechanical processing of additively manufactured Ti6242 alloy.

Effect of Technological Parameters of Selective Electron Beam Melting on Chemical Composition, Microstructure, and Porosity of a TiAl-Alloy of Ti-Al-V-Nb-Cr-Gd System

Effect of Technological Parameters of Selective Electron Beam Melting on Chemical Composition, Microstructure, and Porosity of a TiAl-Alloy of Ti-Al-V-Nb-Cr-Gd System

Compressive creep behavior of selective electron beam melted high Nb containing TiAl alloy

In this study, the compressive creep behavior of Ti–45Al–8Nb alloy fabricated by selective electron beam melting technology at 800 °C and 850 °C was investigated. This alloy is mainly composed of equiaxed γ grains, and minor α2 and B2 grains. Creep results show that compressive creep behavior of this alloy is dependent on temperature, which is manifested in the significant increase of creep strain and creep rate with the increase of temperature. Through a multi-step creep test, the stress exponent n (2.65 at 800 °C and 3.65 at 850 °C) and activation volume V* (36.49 b3 at 800 °C and 53.51 b3 at 850 °C) were measured. Combined with kinetic analysis based on n and V* and TEM observation, compressive creep deformation of this alloy at 800 °C and 850 °C is dominated by dislocation motion, including dislocation slip and climb. Additionally, mechanical twinning also plays an important role in creep deformation. Driven by dislocation pile-ups or mechanical twins, discontinuous dynamic recrystallization (DDRX) occurs during creep. The degree of DDRX at 850 °C is greater. Sufficient DDRX greatly softens the alloy and accelerates creep rate, resulting in no steady-state creep stage at 850 °C.

Tensile properties of Ti6.5Al2Zr1Mo1V titanium alloy fabricated via electron beam selective melting at high temperature

Here, near α titanium alloy TA15 (Ti-6.5Al–2Zr–1Mo–1V) samples were fabricated by electron beam selective melting (EBSM) and their high-temperature tensile deformation behaviors were studied at 773K–1023K. The results show that the tensile strength decreases gradually with the deformation temperature while the yield ratio increases as temperature increases from 773K to 923K, and then decreases gradually with further increasing the temperature. The deformation mechanism of EBSM-built TA15 samples at elevated temperatures can be ascribed to work hardening caused by the increase of dislocation density, and softening caused by the recovery and recrystallization. The studied TA15 alloy exhibits obvious work hardening behaviors at both 773K and 823K, dynamic recovery occurs during tensile deformation at 873K, and dynamic recrystallization plays a dominant role at 923K–1023K. The EBSM-built TA15 samples have excellent mechanical properties at medium temperatures, and the present results are helpful for the industrial applications of EBSM-built titanium alloy components in the aerospace fields.

The cylindrical mechanical metamaterial with high-level thermal-mechanical stabilities and high dynamic stiffness

Mechanical metamaterials with high-level thermal-mechanical stabilities are attracting increasing interest in aerospace. Although numerous configuration designs have been proposed, few of them can satisfy the demands of space explorations, mainly considering the inevitable geometric errors during the assembling process of the metamaterial using a number of parts. To address this issue, the design strategy of cylindrical mechanical metamaterials based on the building block assembly method is proposed here to achieve high-level thermal-mechanical stabilities and high dynamic stiffness. The mechanical and thermal properties of the metamaterial have been systematically studied in terms of theoretical predictions, Finite Element Analysis (i.e., FEA), and experimental measurements. The theoretical model proposed here has accurately predicted the thermal-mechanical behaviors of the metamaterial and demonstrated the capabilities of the metamaterial in achieving combined attributes of the good loading capability (i.e., 2.30 × 106 kN mm/kg for the specific compression modulus, 1.02 × 106 kN mm/kg for the specific shear modulus), the experimentally high thermal-mechanical stabilities (i.e., 0.037 ppm/°C), the high-level dynamic stiffness (i.e., 1013.84 Hz). Notably, the selective electron beam melting and the unique assemble method realize the feasibility of structurally integrated preparation of the metamaterial and achieve the reusability capability even once fabricated.

Low-Cycle Fatigue Behavior of Wire and Arc Additively Manufactured Ti-6Al-4V Material.

Additive manufacturing (AM) techniques, such as wire arc additive manufacturing (WAAM), offer unique advantages in producing large, complex structures with reduced lead time and material waste. However, their application in fatigue-critical applications requires a thorough understanding of the material properties and behavior. Due to the layered nature of the manufacturing process, WAAM structures have different microstructures and mechanical properties compared to their substrate counterparts. This study investigated the mechanical behavior and fatigue performance of Ti-6Al-4V fabricated using WAAM compared to the substrate material. Tensile and low-cycle fatigue (LCF) tests were conducted on both materials, and the microstructure was analyzed using optical microscopy and scanning electron microscopy (SEM). The results showed that the WAAM material has a coarser and more heterogeneous grain structure, an increased amount of defects, and lower ultimate tensile strength and smaller elongation at fracture. Furthermore, strain-controlled LCF tests revealed a lower fatigue strength of the WAAM material compared to the substrate, with crack initiation occurring at pores in the specimen rather than microstructural features. Experimental data were used to fit the Ramberg-Osgood model for cyclic deformation behavior and the Manson-Coffin-Basquin model for strain-life curves. The fitted models were subsequently used to compare the two material conditions with other AM processes. In general, the quasi-static properties of WAAM material were found to be lower than those of powder-based processes like selective laser melting or electron beam melting due to smaller cooling rates within the WAAM process. Finally, two simplified estimation models for the strain-life relationship were compared to the experimentally fitted Manson-Coffin-Basquin parameters. The results showed that the simple "universal material law" is applicable and can be used for a quick and simple estimation of the material behavior in cyclic loading conditions. Overall, this study highlights the importance of understanding the mechanical behavior and fatigue performance of WAAM structures compared to their substrate counterparts, as well as the need for further research to improve the understanding of the effects of WAAM process parameters on the mechanical properties and fatigue performance of the fabricated structures.

Ti–48Al–2Cr–2Nb alloys prepared by electron beam selective melting additive manufacturing: Microstructural and tensile properties

Here, an electron beam selective melting (EBM) technique was employed to shape Ti–48Al–2Cr–2Nb alloy to combat its intrinsic brittleness and insufficient hot workability. Through process optimization, high-density samples (4.2327 g/cm3) were produced. First, the mechanism of interaction between phase transformation and microstructural evolution of EBM-formed Ti–48Al–2Cr–2Nb alloy was investigated using scanning electron microscopy (SEM), X-ray diffraction (XRD), and electron backscattering diffraction (EBSD). And then, the mechanism of interaction between tensile properties and microstructural evolution of EBM-formed Ti–48Al–2Cr–2Nb alloy was discussed. Based on the results, the microstructure consists of coarse equiaxed grains and fine lamellar grains, which gradually coarsen from upper to bottom. As the thickness of the layer increases from upper to bottom, the content of the B2 phase increases continuously, with a predominant component of TiAl and a small amount of Ti3Al and B2 phases. The majority of the γ-TiAl phase does not exhibit significant texture, while the α2-Ti3Al phase shows a texture of (0001) with 19.32 times the random intensity, and its c-axis is parallel to the deposition direction. Benefiting from its unique structure features, the maximum room temperature tensile strength of as-deposited Ti–48Al–2Nb–2Cr alloy reaches 854.6 MPa with an elongation of over 2%. And the maximum high-temperature tensile strength of EBM-formed Ti–48Al–2Nb–2Cr alloy reaches 707 MPa at 650 °C with an elongation over 3.5%. According to these results, the mechanical properties of our EBM Ti–48Al–2Cr–2Nb alloy are superior to those previously reported.

Effect of Technological Parameters of Selective Electron Beam Melting on Chemical Composition, Microstructure, and Porosity of a TiAl-Alloy of Ti-Al-V-Nb-Cr-Gd System

Effect of Technological Parameters of Selective Electron Beam Melting on Chemical Composition, Microstructure, and Porosity of a TiAl-Alloy of Ti-Al-V-Nb-Cr-Gd System

Effect of different hydrogen Fugacities on the microstructure of additively manufactured Ti-6Al-4V

In this study we compared the microstructural changes in the presence of hydrogen of Ti-6Al-4V alloy prepared by two different additive manufacturing (AM) methods: electron beam melting (EBM) and selective laser melting (SLM). Cathodic hydrogenation of AM Ti-6Al-4V resulted in significant expansion of β Ti phases due to the solute hydrogen, increasing of micro-strains, and α → titanium hydride/βH transformation. It was shown that SLM Ti-6Al-4V with acicular martensitic structure is more prone to hydrogen-induced phase transformation and hydrogen-assisted damage, compared to EBM. Moreover, it was revealed that different hydrogen charging environments cause different microstructural changes in EBM Ti-6Al-4V. Unlike cathodic hydrogen charging, gaseous hydrogen charging at elevated temperature reduced the process-induced micro-strains and promoted Al redistribution within the EBM Ti-6Al-4V. This resulted in massive precipitation of brittle α2-Ti3Al intermetallic compound, which act as a strong hydrogen trapping site aside from the Ti hydride phase.

Effect of in-situ post-heating on the microstructure and tensile performance of TiAl alloys produced via selective electron beam melting

Selective electron beam melting (SEBM) is an additive manufacturing technique commonly used to fabricate TiAl alloys. Changing the process parameters to adjust the alloy structure for enhanced mechanical performance is an effective means in this field. Herein, we investigated the effects of the in-situ post-heating process on the microstructure and tensile performance characteristics of SEBM Ti–48Al–2Cr–2Nb alloys. Two processes were designed: without and with post-heating after melting under identical melting process and total energy input conditions. The tensile strength of the samples with the post-heating process reached 707 ± 12 MPa and strain reached 1.8 ± 0.1%. Compared with the other process, the strain increases by 50%, and the strength decreases by 4.8%. This phenomenon was mainly caused by the more precipitation of γ-phase during the phase transformation of TiAl via an in-situ post-heating process. Even with the same energy input, different heating strategies still significantly affect the tensile performance of TiAl alloy, showing that post-heating is an effective way to improve mechanical properties of additive manufactured material.

High-temperature mechanical behaviors of a WTaRe refractory alloy manufactured by selective electron beam melting

Refractory alloys with their brilliant high-temperature tolerance earn a place for applications in extremely harsh environments. Recent development in additive manufacturing technologies speeds up these alloys' design and forming processes before entering the market. However, the desire for better microstructures and superior high-temperature mechanical behaviors has never been fed up. As was wished, in this study, an additively manufactured WTaRe alloy with compressive strength, ultimate compressive strength, and strain of 356 ± 15 MPa, 731 ± 15 MPa, and > 40% at 1600 °C is herein developed. Composition characterization after deformation of the as-deposited WTaRe alloy suggests the super high thermal stability of this alloy. Considering the excellent high-temperature mechanical behaviors, the printable WTaRe refractory alloy may serve as an alternative in a high-temperature environment.

Statistical Analysis of Surface Roughness of Ti–6Al–4V Products Manufactured by Selective Electron Beam Melting

Statistical Analysis of Surface Roughness of Ti–6Al–4V Products Manufactured by Selective Electron Beam Melting

Efficacy of 3D-printed customized titanium implants and its clinical validation in foot and ankle surgery

&amp;nbsp;In foot and ankle surgery, internal fixation was crucial to maintain the stability of bony structure, and bone grafting material is commonly used to treat bone defects. With rapid development of three-dimensional (3D) printing technology, new advances were made in these two aspects. In this study, digital image correlation method (DICM) data of the patient&amp;rsquo;s ankle via computed tomography (CT) examination were obtained and imported into a series of software. The engineer cooperated with the surgeon to design the customized implants. Ti-6Al-4V spherical metal powder was chosen as raw material and fused together by selective electron beam melting (SEBM), a type of 3D printing technology, to prepare the implant. The implants were sterilized with ethylene oxide. The customized 3D-printed implants were successfully utilized in tibiotalocalcaneal (TTC) arthrodesis to maintain the bony structures at the functional position. In another case, the 3D-printed fusion cage was applied in subtalar arthrodesis to treat bone defects. In these clinical cases, 3D-printed customized titanium implants helped improve the surgical operation flow, and no obvious tissue reaction was observed. The successful implementation suggested that the application of 3D printing technology to prepare customized titanium implants would play an important role in future foot and ankle surgery.