Additive Manufactured Ti 6Al 4V 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

Mechanical Behavior of Additive Manufacturing (AM) and Wrought Ti6Al4V with a Martensitic Microstructure

Processing and microstructure are fundamental in shaping material behavior and failure characteristics. Additively manufactured materials, due to the rapid heating and solidification process, exhibit unique microstructures compared to their as-cast counterparts, resulting in distinct material properties. In this work, the response of the titanium alloy Ti6Al4V has been investigated for different processing conditions through quasi-static testing. AM Ti6Al4V was fabricated by employing Selective Laser Sintering (SLS) and Selective Laser Melting (SLM) techniques. Both materials present a similar microstructure consisting of an acicular martensitic α′-phase. Commercial Ti6Al4V-grade 5 (supplied as bars) was also examined after heat treatment to achieve a microstructure akin to the AM material. The heat treatment involved rapid heating above the β-phase region and water quenching to obtain a full martensite microstructure. A similar constitutive behavior and tensile–compressive asymmetry in strength were noted for the investigated materials. However, AM alloys exhibited a significantly higher deformation at failure, reaching nearly 40%, compared to only 6.1% for the wrought martensitic material, which can be attributed to the dissimilar distribution of both α′ laths and prior-β grain boundaries in the investigated materials. The results indicate that AM can be implemented for the fabrication of martensitic microstructures with mechanical properties superior to those obtained with conventional water-quenching.

Investigation of surface finish and fatigue life of laser Powder Bed fused Ti-6Al-4V

In this fact-pacing world of technological advancement, the rise of additive manufacturing (AM) has found immense applications of metallic alloys such as Ti6Al4V to manufacture key components in automotive, aerospace and healthcare sectors. However, fatigue characteristics of such additively manufactured metal alloys is noticeably weak, and as such requires post-processing. In this study, AM Ti6Al4V manufactured by Laser Powder Bed Fusion (L-PBF) was treated by Hydrodynamic Cavitation Abrasive Finishing (HCAF) and Laser Cavitation Peening (LCP) to observe the improvement in surface roughness as well as fatigue performance. Our investigations revealed a substantial improvement in surface quality post-HCAF processing. Notably, the surface roughness of AM Ti6Al4V specimens showed a significant reduction of about 91.2 %, post surface treatment. However, Laser Cavitation Peening (LCP) treated sample demonstrates a significantly enhanced fatigue strength of 393 ± 22 MPa at 107, which was 1.75 times better than that of as-built one, i.e., 224 ± 16 MPa. This difference can be attributed to the distinct surface modification mechanisms of each technique. LCP, utilizing laser-induced shock waves, likely induces large compressive residual stresses, leading to better fatigue resistance.

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.

High Temperature Oxidation Behavior of Additive Manufactured Ti6Al4V Alloy with the Addition of Yttrium Oxide Nanoparticles.

Titanium alloys face challenges of high temperature oxidation during the service period when used as aircraft engine components. In this paper, the effect of Y2O3 addition on the oxidation behavior and the microstructural change of the Ti6Al4V alloy fabricated by selective laser melting (SLM) was comprehensively studied. The results show that the surface of the Ti6Al4V alloy is a dense oxide layer composed of TiO2 and Al2O3 compounds. The thickness of the oxide layer of the Ti6Al4V increased from 59.55 μm to 139.15 μm. In contrast, with the addition of Y2O3, the thickness of the oxide layer increased from 35.73 μm to 80.34 μm. This indicates that the thickness of the oxide layer formation was a diffusion-controlled process and, therefore, the thickness of the oxide layer increased with an increase in temperature. The Ti6Al4V-1.0 wt.% Y2O3 alloy exhibits excellent oxidation resistance, and the thickness is significantly lower than that of the Ti6Al4V alloy. The oxidation kinetics of the Ti6Al4V and Ti6Al4V-1.0 wt.% Y2O3 alloys at 600 °C and 800 °C follows a parabolic rule, whereas the oxidation of the Ti6Al4V and Ti6Al4V-1.0 wt.% Y2O3 alloys at 1000 °C follows the linear law. The average microhardness values of Ti6Al4V samples after oxidation increased to 818.9 ± 20 HV0.5 with increasing temperature, and the average microhardness values of the Ti6Al4V-1.0 wt.% Y2O3 alloy increases until 800 °C and then decreases at 1000 °C. The addition of Y2O3 shows a significant improvement in the microhardness during the different temperatures after oxidation.

Numerical analysis of machinability and surface alterations in cryogenic machining of additively manufactured Ti6Al4V alloy

Metal additive manufacturing (AM) technology has been utilized in many industries including automotive, aerospace, and medical. AM Ti6Al4V (Ti64) alloy is highly noticed for production of medical instruments such as dental implants and the machining process is mostly needed during the production or post-processing of these components. Numerical model, as a powerful tool, can be efficiently used for analyzing the machining process. A customized model was employed using a user-written subroutine in this work to evaluate machinability and microstructural changes in cryogenic machining of AM Ti64 alloy. For this purpose, the microstructural changes were simulated as the new numerical outputs. The numerical results of cutting forces, temperature, nano-hardness, and alpha lamellae thickness (grain size) were successfully verified by corresponding experiments from literature. Then, the impact of tool geometry (including rake and clearance angles, cutting edge radius, and nose radius) on the machinability performance was examined. It was found that, the variation of clearance and rake angles were more effective on depth of the hardened layer compared to the other parameters. Thickness of alpha lamellae phase near the machined surface and depth of the affected layer by nano-hardness changes were changed from 0.9 to 1.58 µm, and from 18 to 40 µm, respectively. Overall, it was concluded that the variation of insert positioning made by tool holder (change in rake and clearance angles) was an effective parameter on the process outputs when machining AM Ti64 alloy.

Low-temperature creep performance of additive manufactured Ti–6Al–4V

Abstract Additive manufacturing enables the fabrication of versatile and cost-effective metallic-alloy components from a digital data model. This study explores the prospects of selective laser melting (SLM), an additive manufacturing technique, for fabricating Ti6Al4V alloy components from Ti6Al4V alloy powders. Selective laser melting parameters, such as laser power, scanning speed, powder thickness, hatching space, and scanning strategy, are carefully selected through a series of experiments. The metallurgical characteristics (microstructure, grain orientation, and phase composition), microhardness, and creep performance of the as-fabricated specimens are tested and analyzed. The kinetics of phase transformation and rupture mechanism are determined using advanced instrumental characterization tools, such as field emission scanning electron microscope, energy dispersive X-ray spectroscope, X-ray diffractometer, and transmission electron microscope.

Flash plasma electrolytic oxidation and electrochemical behaviour in physiological media of additive manufacturing Ti6Al4V alloy

The objective of this work is to understand the plasma electrolytic oxidation (PEO) treatment and electrochemical behaviour of a Ti6Al4V alloy manufactured by a laser powder bed fusion additive manufacturing (AM) technique known as direct metal laser sintering (DMLS). Ca and P-containing coatings were produced with short time (<120 s) PEO treatments (also termed as Flash-PEO) obtaining 3–10 μm-thick coatings on both the AM alloy and a conventional counterpart. Subsequently, the electrochemical behaviour of the bare and treated alloys was assessed in a modified α-MEM solution via potentiodynamic polarization and electrochemical impedance spectroscopy (EIS). The fine α-lamellar microstructure of the AM alloy with small β-phase particles at the interlamellar spaces was seen to advance the onset of sparking promoting faster growth of PEO coating in comparison to the conventional alloy. Flash-PEO coatings enhanced the corrosion protection of both conventional and AM alloys, the thinnest (<3 μm) coatings providing up to three times greater protection. AM Ti6Al4V was found to be susceptible to localized crevice corrosion which could be assigned to the high grain boundary density. Flash-PEO treatments, even as short as 35 s, were sufficient to successfully prevent it.

Effects of cutting conditions on the cutting forces in machining additively manufactured Ti6Al4V alloy

Machining of additive manufacturing (AM) process results in excessive consumption of the cutting power due to the high strength and hardness of the material produced that led to high cutting forces and short tool life during machining process. This paper aims to investigate the effect of cutting conditions and coefficient of friction on the cutting forces, during finite element analysis (FEA) of an orthogonal cutting of AM Ti6Al4V alloy bar. The FEA simulation considers three different experiments at low, medium, and high cutting conditions. The result shows that as the depth of cuts gets deeper and the cutting speed increases, the cutting forces were found to increase, leading to serrated or segmented chips formation. A cutting force of 1300.36N was observed at a cutting speed of 150 m/min and a coefficient of friction of 0.9. The cutting force was found to be weaker at the higher shear plane angle of 42.2o and higher at a smaller angle of 37.57o. The coefficient of friction was observed to be insignificant at lower value of 0.09 and was seemed to affect the cutting force at value around 1.

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

Biocompatibility screening of Mo–Si–Ta glassy alloy films sputtered on additive manufactured Ti–6Al–4V implant prototypes and PCL scaffolds

A ternary system of amorphous alloy with the components Mo, Ti, and Si with the composition Mo54Si33Ta13 has been chosen as the surface coating for the implantable materials to improve Ti6Al4V bioactivity. Ti6Al4V alloy metal powders were used to create the implant prototypes with the 3D metal printer. With the aid of a DC magnetron, the films are sputtered onto the implant prototypes. Elemental composition, amorphous nature, surface chemistry and topography of the as-fabricated microstructure films were comprehensively analysed using X-ray diffraction analysis, X-ray photoelectron spectroscopy and electron/atomic force microscopic techniques. The mechanical properties were studied from Nano indentation method. The coatings were confirmed to be cytocompatible determined from the in-vitro biocompatibility investigations using human osteosarcoma cells. The electrochemical corrosion studies carried out in SBF showed the higher corrosion resistance for the thin film metallic glass (TFMG)-coated customized 3D printed Ti-alloy implants than the pristine specimen.

Alloying strategies for additive manufacturing of Ti6Al4V based alloys, composites and functionally graded materials: Microstructure and phase evolution of intra and inter-layer

The further developments of additive manufacturing (AM) provides a possibility for Ti6Al4V and its functionally graded materials (FGMs), but limits further applications due to its low ductility, low microhardness and poor wear resistance. The key lies in the presence of microstructures such as epitaxial columnar β-grain orientation and heterogeneous phase distribution in AM Ti6Al4V, as well as the interfacial bonding problems (intermetallic phases, delamination, cracking) in AM Ti6Al4V FGMs. In order to address these fundamental intra and inter-layer problems, firstly the microstructure and phase evolution process of AM Ti6Al4V columnar-to-equiaxed transformation (CET) promoted by some alloying strategies was summarized in this paper according to alloying elements and reinforcing particle types. Subsequently, controlled changes in the composition and microstructure of AM Ti6Al4V FGMs were achieved by adding interlayers/introducing gradient interfaces, and the metallurgical reactions and phase transformation mechanisms that inhibit the formation of intermetallic compounds and interfacial defects were explored. Finally, the difficulties and future research directions for alloying strategies to achieve high strength and ductility of AM Ti6Al4V were presented. This review aims to improve the reliability of AM Ti6Al4V and its FGMs for applications in critical load-bearing structures through in-situ alloying and multi-material for the microstructure design of AM Ti6Al4V.

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 and Experimental Analysis of Dual-Beam Laser Polishing Additive Manufacturing Ti6Al4V.

Laser polishing is an emerging efficient technique to remove surface asperity without polluting the environment. However, the insufficient understanding of the mechanism of laser polishing has limited its practical application in industry. In this study, a dual-beam laser polishing experiment was carried out to reduce the roughness of a primary Ti6Al4V sample, and the polishing mechanism was well studied using simulation analysis. The results showed that the surface roughness of the sample was efficiently reduced from an initial 10.96 μm to 1.421 μm using dual-beam laser processing. The simulation analysis regarding the evolution of material surface morphology and the flow behavior of the molten pool during laser the polishing process revealed that the capillary force attributed to surface tension was the main driving force for flattening the large curvature surface of the molten pool at the initial stage, whereas the thermocapillary force influenced from temperature gradient played the key role of eliminating the secondary roughness at the edge of the molten pool during the continuous wave laser polishing process. However, the effect of thermocapillary force can be ignored during the second processing stage in dual-beam laser polishing. The simulation result is well in agreement with the experimental result, indicating the accuracy of the mechanism for the dual-beam laser polishing process. In summary, this work reveals the effect of capillary force and thermocapillary force on molten pool flows during the dual-beam laser polishing processes. Moreover, it is also proved that the dual-beam laser polishing process can further reduce the surface roughness of a sample and obtain a smoother surface.

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.

The response of human macrophages to 3D printed titanium antibacterial implants does not affect the osteogenic differentiation of hMSCs.

Macrophage responses following the implantation of orthopaedic implants are essential for successful implant integration in the body, partly through intimate crosstalk with human marrow stromal cells (hMSCs) in the process of new bone formation. Additive manufacturing (AM) and plasma electrolytic oxidation (PEO) in the presence of silver nanoparticles (AgNPs) are promising techniques to achieve multifunctional titanium implants. Their osteoimmunomodulatory properties are, however, not yet fully investigated. Here, we studied the effects of implants with AgNPs on human macrophages and the crosstalk between hMSCs and human macrophages when co-cultured in vitro with biofunctionalised AM Ti6Al4V implants. A concentration of 0.3g/L AgNPs in the PEO electrolyte was found to be optimal for both macrophage viability and inhibition of bacteria growth. These specimens also caused a decrease of the macrophage tissue repair related factor C-C Motif Chemokine Ligand 18 (CCL18). Nevertheless, co-cultured hMSCs could osteogenically differentiate without any adverse effects caused by the presence of macrophages that were previously exposed to the PEO (±AgNPs) surfaces. Further evaluation of these promising implants in a bony in vivo environment with and without infection is highly recommended to prove their potential for clinical use.

Effect of Zr on microstructure and properties of TC4 alloy fabricated by laser additive manufacturing

In this paper, the effect of Zr on the microstructure of laser additive manufactured Ti–6Al–4V (TC4) alloy is studied by adding different contents of Zr (0%, 15%, 30%, 45%), and the mechanisms of strengthening and corrosion passivation are also discussed. The results show that the stability of β phase increases with increasing Zr content, when Zr content reaches 45%, the β phase is completely retained to room temperature. The microstructure of TC4 can be refined by Zr (when the content of Zr is less than or equal to 30%), and the ultra-fine martensite with twinning substructure can be formed. With the increase of Zr content to 45%, the strength of the alloy increases from 1044 MPa to 1360 MPa. The elongation decreases from 10.8% to 7.7% with the increase of Zr content to 30%. However, as the content of Zr increases to 45%, the elongation increases to 12.5%. The abnormal phenomenon of elongation is mainly due to the change of deformation mechanism from dislocation slip to stress-induced martensite transformation with the content of Zr increasing to 45%. The corrosion resistance of TC4-Zr alloys increases significantly with the increase of Zr content, which is mainly attributed to the better corrosion resistance of Zr and the better protection of ZrO2 formed in passivation film.

Blast response of additive manufactured Ti–6Al–4V sandwich panels

Blast response of additive manufactured Ti–6Al–4V sandwich panels