Additive Manufacturing Ti Research Articles

Comparative Study of Room and Cryogenic Deformation Behavior of Additive Manufactured Ti–6Al–4V Alloy

Comparative Study of Room and Cryogenic Deformation Behavior of Additive Manufactured Ti–6Al–4V Alloy

Effect of manganese on grain morphology and microstructure of Ti-6Al-4V alloy by laser wire deposition

The addition of growth restricting elements in additive manufacturing of Ti and Ti-based alloys can result in the formation of equiaxed structures. However, an excessive incorporation of these elements frequently impairs the mechanical properties. Obtaining the minimum necessary amount of addition is crucial to achieve the transition from columnar to equiaxed microstructure. This ensures that the desired equiaxed structure is obtained while minimizing any potential negative effects on the material's properties. Here manganese was taken as the potential grain refiner in Ti alloy. Then, evolutions of grain morphologies and microstructures as well as the mechanical properties various of Ti-6Al-4V alloy in laser wire deposition additive manufacturing with the growth restriction factors of 26, 32, 39 were explored respectively. And the average hardness of the deposits were 495 HV, 512 HV, and 530 HV, respectively, showing an increase of approximately 15%, 19% and 23%. When the growth restricting factor value reached 39, the columnar prior β grains underwent a complete transformation into equiaxed grains. Mn elements promoted the decomposition of β→α+Mn2Ti during the multi-pass deposition and the microhardness of the deposits were significantly increased. Additionally, Mn elements were expelled outwards during the β→α transition. Nevertheless, the diffusion rate of Mn elements was low and thereby there was a low growth rate of α phases, thus refining α phases.

Novel bainitic Ti alloys designed for additive manufacturing

Novel ternary titanium alloys with a bainitic microstructure have been designed specifically for additive manufacturing (AM). The Ti-xCu-yFe alloys take advantage of constitutional supercooling to suppress the growth of large columnar grains usually associated with AM Ti alloys. In the as-built condition the bainitic microstructure consists of a refined α-phase within a matrix of β-phase. The intermetallic phase, Ti2Cu, forms predominantly on the interface of the α- and β-phase and within the β matrix. The high strength of these materials is attributed to the refined α-phase and Ti2Cu particles as well as significant solid solution hardening. This work demonstrates a viable way to fabricate structural components with unique and excellent properties using low-cost elemental powders with AM.

Comparative Study of Room and Cryogenic Deformation Behavior of Additive Manufactured Ti–6Al–4V Alloy

The microstructural evolution and underlaying deformation behavior of Ti–6Al–4V alloy fabricated by laser powder bed fusion (LPBF‐Ti64) during room (RT) and cryogenic (CT: −150 °C) temperature are systematically investigated. LPBF‐Ti64 exhibits significantly higher strength at CT (yield strength [YS]: 1339 MPa, ultimate compressive strength [UCS]: 1982 MPa) as compared to RT (YS: 1013 MPa, UCS: 1690 MPa) with reduction in fracture strain. To probe the deformation mechanisms responsible for exceptionally higher strength at CT, LPBF‐Ti64 alloy is compressed to 10% strain at both temperatures and the underlaying strengthening mechanisms are investigated. Dislocation strengthening is emphasized to be the major strengthening mechanisms (1166/1359 MPa for RT‐10 and CT‐10, respectively). The significantly higher dislocation density at CT (3.73 1016 m−2 for CT‐10 and 2.9 1016 m−2 for RT‐10) is attributed to the restricted dislocation movement at low temperature, whereas dislocation nucleation during further deformation will multiply the dislocations interlocking and pinning, hence resulting in higher strength.

Understanding the fatigue behaviour of Ti–6Al–4V manufactured via various additive processes

Additive Manufacturing (AM) is receiving widespread attention from both industry and academia who are looking to benefit from the numerous advantageous possibilities that AM processes have to offer, such as the potential to design and produce highly complex bespoke geometries with minimal material wastage. Yet, despite this, AM also has some drawbacks. Some of the most significant include the presence of process-induced defects and the inherent surface roughness of an AM built component, both of which can have a considerable influence on the mechanical properties of the final product. This research will investigate the role of an as-built surface on the fatigue properties of AM Ti–6Al–4V manufactured by electron beam melting (EBM), laser powder bed fusion (L-PBF) and laser metal deposition with wire (LMD-w). Fatigue results have been generated alongside advanced surface profilometry, microstructural, defect and fractographic analyses that have revealed that whilst the surface roughness in the majority of instances is the primary factor impacting the fatigue performance on AM material, it cannot be considered alone. It was found that the inherent as-built (AB) surface finish was significantly different across the various AM processes, inducing a range of effective stress concentrations and thus, a contrasting impact on the resulting fatigue performance. Results from each variant have been compared against a machined and polished equivalent, to provide a further consideration as to whether the as-built surface would be suffice from a time and economical viewpoint. Statistical analysis of the generated results also allowed for an extrapolation of predicted fatigue lives in the very high cycle regime for the alternative AM Ti–6Al–4V variants.

Effects of artificial embedded defect size and position on the fatigue lives of additive manufacturing Ti–6Al–4V alloy

Additive manufacturing (AM) components usually contain various defects with different positions and sizes inside, resulting in the great change of fatigue performance with the defect location and sizes. Therefore, in the evaluation of numerous structural factors, the defect size effect is one of the most typical problems in the AM components. This study for the first time investigated the effects of sizes and positions of the artificial embedded defects on the high-cycle fatigue (HCF) lives of the most widely studied AM Ti–6Al–4V alloy. Samples with artificially embedded defects of two sizes (300 μm and 500 μm) and three positions (center, 1.5 mm from the center and 0.5/0.2 mm from the center) for fatigue tests. The result show that the larger the defect size and the closer it is to the surface, the lower the fatigue life. Through fractographic observations, fatigue lives analysis, and defects statistics, the influences of defect size and position on the HCF lives were discussed. It is found that the Murakami formula can well describe the HCF lives distribution of the AM Ti–6Al–4V alloy with different artificial embedded defects.

Alternative Reagent for Revealing the Entire Microstructure of Additive Manufactured Ti–6Al–4V Alloy

Alternative Reagent for Revealing the Entire Microstructure of Additive Manufactured Ti–6Al–4V Alloy

Effect of V Content on the Corrosion Resistance of Wire Arc Additive Manufactured Ti–6Al–xV Alloys

Effect of V Content on the Corrosion Resistance of Wire Arc Additive Manufactured Ti–6Al–xV Alloys

Microstructural Transformation and Enhanced Strength of Wire‐Feed Electron‐Beam Additive Manufactured Ti–6Al–4V Alloy Induced by High‐Pressure Torsion

For the first time, the present study demonstrates the influence of high‐pressure torsion (HPT) on microstructural refinement and mechanical strength of Ti–6Al–4V titanium alloy produced by wire‐feed electron‐beam additive manufacturing. This technology has attracted an increasing interest presently from manufacturers of products with complex shapes and it allows for producing a titanium alloy with a unique microstructure that consists of martensitic α′ phase, separated by thin interlayers of residual β phase. Further processing of the alloy by HPT results in the formation of an ultrafine‐grained (UFG) structure with an average grain size of about 25 ± 10 nm, significantly increasing its microhardness up to 448 ± 5 HV. Microscopic studies reveal that the attained UFG structure consists predominantly of the grains of α and β phases in the ratio of 92.8% and 7.2%, respectively. This article also considers the nature of the high strength of Ti–6Al–4V subjected to HPT.

Numerical Analysis and Experimental Investigation of High Cycle Fatigue Behavior in Additively Manufactured Ti–6Al–4V Alloy

Additive Manufacturing (AM) of the Ti–6Al–4V alloy has gained significant importance across various industries, including biomedical, aerospace, cellular, and land vehicle applications, due to its numerous benefits. The certification of performance and reliability of AM materials, particularly for critical applications, heavily relies on evaluating fatigue strength. In this study, a numerical analysis based on the finite element method is presented to predict the High Cycle Fatigue (HCF) behavior of AM Ti–6Al–4V alloy. The investigation focuses on exploring the sensitivity of material fatigue life to surface roughness and Ultimate Tensile Strength (UTS). Uniaxial tensile and High Cycle Fatigue (HCF) tests were conducted on Ti–6Al–4V alloy samples extracted from rectangular walls manufactured using the Laser Metal Deposition (LMD) process. The walls were surface machined prior to sample extraction. Porosity and surface roughness measurements were performed on the samples. Numerical simulations of the HCF tests were carried out, considering various surface roughness ranges and UTS values. The numerical results were then compared to experimental data. The findings consistently demonstrated that higher surface roughness led to a shorter fatigue life, while higher UTS values resulted in a longer fatigue life. The numerical solutions aligned with the experimental results, indicating the efficacy of the finite element method in predicting the fatigue behavior of AM Ti–6Al–4V alloy. These insights contribute to a better understanding of the relationship between surface roughness, UTS, and fatigue life of Ti–6Al–4V alloys manufactured by AM.

Hybrid manufacturing process combining laser powder-bed fusion and forging for fabricating Ti–5Al–5V–5Mo–3Cr–1Zr alloy with exceptional and isotropic mechanical properties

The metal additive manufacturing (AM) technology offers a unique advantage for production of complex and unconventional parts. However, the thermal history during the AM process often leads to anisotropy in the mechanical properties and inherent porosity of the deposits, which limits their performance compared to traditional forgings. To overcome these limitations, laser powder bed fusion (LPBF) technology was employed to produce single-step die-forging preforms. This innovative approach used coarse powder with a wide distribution of particle sizes to create a variety of molten pool structures, preventing the growth of columnar β grains in AM Ti–5Al–5V–5Mo–3Cr–1Zr (Ti-55531) alloys. The subsequent die-forging process eliminated inherent defects and regulated grains to be near-equiaxed, significantly improving the mechanical properties and reducing anisotropy. With proper post-heat treatment, the strength-ductility trade-off of the Ti-55531 alloy was adjusted to meet standards. This unconventional process route produced parts with isotropic and excellent mechanical properties, overcoming the defects and anisotropic properties of AM parts. This supplement to the traditional manufacturing process of high-performance titanium alloy parts holds great promise for future applications.

Strong and ductile titanium via additive manufacturing under a reactive atmosphere

Pure metals tend to have a superior malleability compared to alloys. However, the applicability of pure metals is limited by their low strengths and hardness properties. In this study, strong and ductile pure Ti was synthesized via an approach involving powder modification and additive manufacturing (AM) under a reactive atmosphere. Specifically, pure Ti was processed by laser powder bed fusion in an environment containing a mixture of argon and nitrogen gases. In-situ high-energy synchrotron X-ray diffraction analysis reveals that in-situ nitrogen strengthening of the pure Ti occurs during the reactive AM of Ti. Furthermore, the presence of a nitrogen solid solution leads to the formation of high-strength pure Ti (yield strength of ∼979 MPa and ultimate tensile strength of ∼1058 MPa, respectively). This material exhibits excellent uniform elongation (11%) due to strong work hardening caused by the interaction of interstitial elements and submicrostructure. The proposed reactive AM approach paves the way for in-situ strengthening of pure metals and alloys.

Mechanism of ultrahigh ductility obtained by globularization of αGB for additive manufacturing Ti–6Al–4V

In the present work, two post-processes, the 800 °C and 950 °C for 4 h annealing below β transus, were designed to improve the performance of selective laser melted (SLM) Ti–6Al–4V (Ti64) alloy. The results show that 800 °C annealing raises the ductility to 18%, while 950 °C annealing raises the ductility high up to 26%. Although the residual stress relief and martensite decomposition fully accomplished in both annealed samples, there is still a noticeable difference in ductility. The difference is due to that 950 °C annealing induce noticeable globularization which further alters the fracture mode. Further study indicates that with globularization of αGB phase (α phase along prior β grain boundary), the transgranular fracture replaces the detrimental intergranular fracture. Particularly, the high angle grain boundary (HAGB) between equiaxed αGB phase effectively inhibits the initiation and propagation of crack, when comparing to the low angle grain boundary (LAGB) in α lamella. The reason for globularization in 950 °C annealing could be concluded as the boundary splitting model. The β phase grow along the LAGB in α lamella and form thermal grooving. With the groove deepening, the lamella was separated into equiaxed α phase. In this process, high temperature annealing promotes sufficient bulk diffusion, which is a necessary condition for globularization of lamellar α phase in SLM Ti64 alloy.

Hybrid Electron Beam Powder Bed Fusion Additive Manufacturing of Ti\u20136Al\u20134V: Processing, Microstructure, and Mechanical Properties

Processing, microstructure, and mechanical properties of the hybrid electron beam powder bed fusion (E-PBF) additive manufacturing of Ti–6Al–4V have been investigated. We explore the possibility of integrating the substrate as a part of the final component as a repair, integrated, or consolidated part. Various starting plate surface conditions are used to understand the joining behavior and their microstructural properties in the bonding region between the plate and initial deposited layers. It is found that mechanical failures mainly occur within the substrate region due to the dominant plastic strains localized in the weaker Ti–6Al–4V substrate. The hybrid concept is successfully proven with satisfactory bonding performance between the E-PBF build and substrate. This investigation improves the practice of using the hybrid E-PBF additive manufacturing technique and provides basic understanding to this approach.

Effect of cyclic heat treatment on microstructure and mechanical properties of laser aided additive manufacturing Ti–6Al–2Sn–4Zr–2Mo alloy

Globular α phases can significantly improve the ductility of titanium alloys. Cyclic heat treatment (CHT) has been proved to be an effective way to induce the formation of globular α phases in α+β titanium alloy Ti–6Al–4V fabricated by laser aided additive manufacturing (LAAM). However, there is no prior research reporting methods for obtaining globular α phases in LAAM-built near-α titanium alloys. This work investigated the cyclic heat treatment (CHT) procedures suitable for the LAAM-built near-α titanium alloy Ti–6Al–2Sn–4Zr–2Mo (Ti6242) to attain the globular α phases. The results show that 980 ​°C is the most suitable upper temperature limit for CHT. However, it is difficult to achieve a high volume fraction of the globular α phases in the LAAM-built Ti6242 alloys through CHT, which is ascribed to the low composition gradient caused by more α-stabilizing elements and fewer β-stabilizing elements. The as-built sample demonstrated elongation of 6.3%, which is lower than the AMS 4919J standard (elongation ≥10%). After 980 ​°C CHT and 980 ​°C CHT with solution heat-treatment, the formation of the globular α phases significantly increased the elongation to 13.5% and 12.9%, respectively. Although the mechanical strength is reduced after heat-treatment, the room-temperature tensile properties still exceed the AMS 4919J standard. Fractography examination showed that the as-built sample exhibited a mixed brittle and ductile fracture behavior, while the 980 ​°C CHT and 980 ​°C CHT with solution heat-treated samples displayed ductile fracture.

Localized Corrosion Resistance on Additively Manufactured Ti Alloys by Means of Electrochemical Critical Localized Corrosion Potential in Biomedical Solution Environments.

This study proposes a new method, electrochemical critical localized corrosion potential (E-CLCP), in order to evaluate localized corrosion resistance of biomedical additive manufacturing (AM) titanium (Ti) alloys. The procedures for determining E-CLCP are completely different from that of the electrochemical critically localized corrosion temperature (E-CLCT) method (ISO 22910:2020). However, its application should be limited to pH and temperature of the human body because of the temperature scan. E-CLCP displays the localized corrosion resistance of AM Ti alloys based on the human body’s repassivation kinetics, whereas E-CLCT displays the localized corrosion resistance of the alloys based on passive film breakdown in much harsher corrosive environments.

Architectural bone parameters and the relationship to titanium lattice design for powder bed fusion additive manufacturing

Additive manufacturing (AM) of titanium (Ti) and Ti-6Al-4V lattices has been proposed for bone implants and augmentation devices. Ti and Ti-6Al-4V have favourable biocompatibility, corrosion resistance and fatigue strength for bone applications; yet, the optimal parameters for Ti-6Al-4V lattice designs corresponding to the natural micro- and meso-scale architecture of human trabecular and cortical bone are not well understood. A comprehensive review was completed to compare the natural lattice architecture properties in human bone to Ti and Ti-6Al-4V lattice structures for bone replacement and repair. Ti and Ti-6Al-4V lattice porosity has varied from 15% to 97% with most studies reporting a porosity between 50% and 70%. Cortical bone is roughly 5–15% porous and lattices with 50–70% porosity are able to achieve comparable stiffness, compressive strength, and yield strength. Trabecular bone has a reported porosity range from 70% to 90%, with trabecular thickness varying from 120 to 200 μm. Existing powder bed fusion technologies have produced strut and wall thicknesses ranging from 200 to 1669 μm. This suggests limited overlap between current AM of Ti and Ti-6Al-4V lattice structures and trabecular bone architecture, indicating that replicating natural trabecular bone parameters with latticing is prohibitively challenging. This review contributes to the body of knowledge by identifying the correspondence of Ti and Ti-6Al-4V lattices to the natural parameters of bone microarchitectures, and provides further guidance on the design and AM recommendations towards addressing recognized performance gaps with powder bed fusion technologies.

Fatigue Improvement of Additive Manufactured Ti–TiB Material through Shot Peening

In this work, fatigue improvement through shot peening of an additive manufactured Ti–TiB block produced through Plasma Transferred Arc Solid Free-Form Fabrication (PTA-SFFF) was investigated. The microstructure and composition were explored through analytical microscopy techniques such as scanning and transmission electron microscopy (SEM, TEM) and electron backscatter diffraction (EBSD). To investigate the isotropic behavior within the additive manufactured Ti–TiB blocks, tensile tests were conducted in longitudinal, diagonal, and lateral directions. A consistent tensile behavior was observed for all the directions, highlighting a nearly isotropic behavior within samples. Shot peening was introduced as a postmanufacturing treatment to enhance the mechanical properties of AM specimens. Shot peening led to a localized increase in hardness at the near-surface where stress-induced twins are noted within the affected microstructure. The RBF-200 HT rotating-beam fatigue machine was utilized to conduct fatigue testing on untreated and shot-peened samples, starting at approximately 1/2 the ultimate tensile strength of the bulk material and testing within low- (<105 cycles) to high-cycle (>105 cycles) regimes. Shot-peened samples experienced significant improvement in fatigue life, increasing the fitted endurance limit from 247.8 MPa for the untreated samples to 318.3 MPa, leading to an increase in fatigue resistance of approximately 28%.

Correction to: Evaluating Corrosion Resistance of Biomedical Ti‑6Al‑4V Alloys Fabricated via Additive Manufacturing Using Electrochemical Critical Localized Corrosion Potential

Titanium (Ti) and its alloys have attractive properties like high strength-to-weight ratio, excellent formability, biocompatibility, and corrosion resistance. These alloys are conventionally produced via subtractive manufacturing (SM) method, but recently new additive manufacturing (AM) method has been developed and can fabricate desired products by melting and stacking powders using a laser, electron beam, or a plasma arc. From a mechanical perspective, the strength and ductility of AM Ti alloys are comparable to or above those fabricated via SM because of their unique microstructure. However, AM Ti alloys corrosion resistance is still unknown, because of their defects and formation of martensite phase resulting from rapid solidification, hence new strategies were developed to evaluate localized corrosion resistance Consequently, a measurement method based on electrochemical critical localized corrosion temperature (E-CLCT) was adopted as ISO 22,910:2020 but its application should be limited at normal ranges of pH and temperatures corresponding to the human body because of the temperature scan during the E-CLCT testing. Therefore, electrochemical critical localized corrosion potential (E-CLCP) was introduced and proposed in this paper as a new criterion in evaluating the resistance against localized corrosions in biomedical AM Ti alloys in human body environments. AM Ti alloy samples without a hole and crevice former as well as an electrochemical polarization cell were used in the artificial physiological fluids. This study explores how to efficiently evaluate the localized corrosion resistance of AM Ti alloys such as Ti-6Al-4 V by measuring E-CLCP values in the artificial physiological fluids.

Osseointegration of additive manufacturing Ti–6Al–4V and Co–Cr–Mo alloys, with and without surface functionalization with hydroxyapatite and type I collagen

The introduction of additive manufacturing (AM) technologies has profoundly revolutionized the implant manufacturing industry, with a particularly significant impact on the field of orthopedics. Electron Beam Melting (EBM) and Direct Metal Laser Sintering (DMLS) represents AM fabrication techniques with a pivotal role in the realization of complex and innovative structure starting from virtual 3D model data. In this study, Ti–6Al–4V and Co–Cr–Mo materials, developed by EBM (Ti-POR) and DMLS (Co-POR) techniques, respectively, with hydroxyapatite (Ti-POR + HA; Co-POR + HA) and type I collagen (Ti-POR-COLL; Co-POR-COLL) coatings, were implanted into lateral femoral condyles of rabbits. Osseointegration process was investigated by histological, histomorphometrical and microhardness evaluations at 4 and 12 weeks after implantation. Both Ti–6Al–4V and Co–Cr–Mo implants, with or without HA and COLL coatings, demonstrated good biocompatibility. As expected, HA coating hastened bone-to-implant contact (BIC) process, while collagen did not significantly improved the osseointegration process in comparison to controls. Regarding newly trabecular bone formation (B.Ar/T.Ar), Co-POR presented the highest values, significantly different from those of Co-POR-COLL. Over time, an increase of BIC parameter and a decrease of B.Ar/T.Ar were detected. Higher mineral apposition rate was observed for Ti-POR and Co-POR in comparison to Ti-POR-COLL and Co-POR-COLL, respectively, at 12 weeks. The same behavior was found for bone formation rate between Co-POR and Co-POR-COLL at 12 weeks. In conclusion, the AM materials guarantee a good osseointegration and provide a suitable environment for bone regeneration with the peculiarity of allowing personalized and patient-specific needs customization to further improve the long-term clinical outcomes.