Ti6Al4V Parts Research Articles

A Novel Hybrid Additive Manufacturing Methodology for the Development of Ti6Al4V Parts

A Novel Hybrid Additive Manufacturing Methodology for the Development of Ti6Al4V Parts

A comparison of fatigue analysis methods for L-PBF net-shape surfaces in Ti6Al4V parts

The fatigue performance of additive manufacturing components is strongly limited by the surface topology, in particular considering the effect of the surface orientation. In the present study, Ti6Al4V laser powder bed fusion (L-PBF) net-shape specimens were printed considering four critical orientations to investigate and compare HCF fatigue properties and two different fatigue assessment methods.Detailed X-ray Computer Tomography (XCT) allowed us to carry out numerical simulations of the 4-Point Bending test samples, by adopting the critical distance method (TCD method). Endurance limit predictions based on the most critical valleys were performed by TCD and compared to predictions made with a Fracture Mechanics model that relies on simple profile roughness parameters.Comparison of the methods show that TCD inherently includes the shielding effect and it can better account for isolated features, while FM is more rapid and conservative.

Comparison between laser and TIG welding of electron beam melted Ti6Al4V parts

Abstract A large number of metal parts specific to the aviation, energy, and biomedical industries are produced by the electron beam melting (EBM) method, which is one of the powder bed additive manufacturing techniques. The limited build volume of EBM machines does not allow the production of parts in the desired dimensions. One way to overcome this limitation is to weld small size additive manufactured parts. In this study, EBMed Ti6Al4V tensile specimens were joined by laser (LBW) and tungsten inert gas (TIG) welding. Welding morphologies, microstructures, and mechanical properties of joints were investigated. The main defects in the samples are pore formation and insufficient penetration. The weld zones of TIG samples contain a higher amount of pores than laser samples, and these pores are distributed over the entire area of the weld. The pores are less than 200 µm in diameter. TIG welded samples exhibited higher mechanical properties than laser welded samples. The highest microhardness was measured in the weld zone. Microhardness of laser welded samples are higher than TIG welded samples. While the welding regions of TIG welded samples consist of coarse and acicular α and α + β structures, laser welded samples consist of thin and acicular α′ structure.

Study of the Effect of Nanosecond Laser Texturing on the Corrosion Behavior of Ti6Al4V and Ti6Al4V Parts Produced by Powder Bed Fusion

Abstract Combining metallic additive manufacturing with laser texturing could be an alternative in obtaining parts with functional hydrophilic surfaces, which improves osteointegration. Careful study of the corrosion behavior of the surfaces obtained is necessary, because the evolution of this phenomenon can influence the osteointegration of the implant, causing the release of metal ions in the body and even the rejection of the component. This study compared the corrosion behavior of laser texturing Ti6Al4V components with components manufactured using laser power bed fusion of the same alloy followed by laser texturing. Their microstructure, roughness, wettability, and electrochemical behavior were analyzed, and different morphologies and microtopographies were observed comparing both samples. The electrochemical tests obtained indicate that Ti6Al4V showed higher corrosion resistance than L-PBF Ti6Al4V after laser texturing. The results suggest that laser texturing can encourage cell proliferation and osseointegration on the surface of Ti6Al4V biomedical implants.

On the structural integrity and fatigue performance of additively manufactured Ti-6Al-4V parts processed using mechanically recycled powders

In light of the steadily increasing importance of resource efficiency, powder recycling represents one of the major prospects in additive manufacturing. The present study focuses on Ti6Al4V parts manufactured by electron beam-based powder bed fusion using blends of virgin and recycled powder. The latter powder was gained by mechanical comminution of support structures and, thus, addresses a novel topic beyond the well-known reuse of un-melted powder. Microstructure analysis is conducted by scanning electron microscopy and micro-computed tomography, mechanical properties are analyzed by quasi-static tensile and fatigue tests. Thereby, the applicability of recycled powder is assessed, eventually revealing that mechanically recycled powder can be qualified to partially substitute virgin powder in powder bed additive manufacturing.

Optimising Surface Roughness and Density in Titanium Fabrication via Laser Powder Bed Fusion.

The Ti6Al4V alloy has many advantages, such as being lightweight, formal, and resistant to corrosion. This makes it highly desirable for various applications, especially in the aerospace industry. Laser Powder Bed Fusion (LPBF) is a technique that allows for the production of detailed and unique parts with great flexibility in design. However, there are challenges when it comes to achieving high-quality surfaces and porosity formation in the material, which limits the wider use of LPBF. To tackle these challenges, this study uses statistical techniques called Design of Experiments (DoE) and Analysis of Variance (ANOVA) to investigate and optimise the process parameters of LPBF for making Ti6Al4V components with improved density and surface finish. The parameters examined in this study are laser power, laser scan speed, and hatch space. The optimisation study results show that using specific laser settings, like a laser power of 175 W, a laser scan speed of 1914 mm/s, and a hatch space of 53 µm, produces Ti6Al4V parts with a high relative density of 99.54% and low top and side surface roughness of 2.6 µm and 4.3 µm, respectively. This promising outcome demonstrates the practicality of optimising Ti6Al4V and other metal materials for a wide range of applications, thereby overcoming existing limitations and further expanding the potential of LPBF while minimising inherent process issues.

Mass finishing of additively manufactured Ti6Al4V parts: An investigation of surface finish dependency on build orientation and processing conditions

Poor surface finish of as-built metal Additive Manufacturing (AM) remains a key challenge in fabricated parts. Metal AM parts typically require postprocessing to improve surface finish before application. Furthermore, different surface orientations and scanning strategies in Powder-Bed-Fusion (PBF) metal AM are prone to result in non-uniform surface roughness across different surfaces of a part. In recent years, Mass Finishing (MF) technologies, such as Centrifugal Disc Finishing (CDF), are gaining popularity in improving AM surfaces due to its fixture-free, batch-processing, and relatively low costs. There is a critical need to study the surface finish dependency on AM build orientation and MF processing conditions. In this study, Ti6Al4V ASTM-E8b tensile bars were fabricated in 45⁰ and 90⁰ orientation via Laser Powder Bed Fusion (L-PBF) to investigate the effects of CDF processing conditions on upward facing surface (up-skin), downward facing surface (down-skin), and side facing surface (side-skin). The surface roughness evolution on each type of surface were collected via laser scanning profilometry. It was found that both processing speed and processing time of CDF were statistically significant factors in improving AM surface roughness, however, processing time had higher impact. Furthermore, different build orientation demonstrated different surface roughness reduction rate and material removal rate. It was found that side-skin had the highest average roughness reduction, and the down-skin exhibited the least roughness reduction. In addition, this study found that the surface with the highest initial surface roughness (down-skin) had the least material removal rate, and that the highest material removal rate was observed in surface with higher periodicity (side-skin). Findings from this study will help the AM community in decision-making of CDF conditions to prevent over-finishing and under-finishing. In addition, the investigation of surface evolution dependency on AM build orientation can further improve the understanding of key mechanisms of AM + MF hybrid manufacturing system.

Preliminary investigation on tensile and fatigue properties of Ti6Al4V manufactured by selected laser melting

Selective laser melting (SLM) is a promising additive manufacturing method that falls under the category of powder bed fusion (PBF) technology. It has many advantages such as material versatility, efficiency, and the ability to print complex parts without additional machining. However, its surface quality and fatigue properties have been found to be inferior to traditional manufacturing methods. Process-related defects such as pores, incomplete fusion, and un-melted powders give rise to areas of stress concentrations, which lead to mechanical inferiority such as poor fatigue strength. This study aims to investigate and optimize the printing process parameters for Ti6Al4V fabricated by SLM to reduce process-related defects and to investigate their relative density, tensile, and fatigue properties. Ti6Al4V specimens were printed in both 30- and 130-μm layer thicknesses using SLM280 and subjected to tensile and fatigue testing according to ASTM standards. The relative density of Ti6Al4V samples built by 30-µm layer thickness is 99.97 ± 0.02 % (n = 8). The relative density of Ti6Al4V samples built by 130-µm layer thickness is 99.96 ± 0.02 % (n = 8). The average ultimate tensile strength (UTS) of specimens with 30-μm layer thickness is 1152.8 ± 23.8 MPa (n = 4). The average UTS of specimens with 130-μm layer thickness is 1075.5 ± 46.8 MPa (n = 4). S/N curve of the fatigue performance of Ti6Al4V samples printed by 30-μm layer thickness was also obtained. Possible factors impacting the tensile property of SLM-produced parts, such as layer thickness, build orientation, and post-process, are discussed in this paper. Furthermore, crack propagation and surface quality were observed using optical microscopes, laser scanning microscopes, and scanning electron microscopes. The findings of this study will contribute to the improvement of SLM-printed Ti6Al4V parts, which can be potentially applied in the aerospace industry, where fatigue strength is critical to ensuring safety.

Multi-Response Optimization of Additively Manufactured Ti6Al4V Component Using Grey Relational Analysis Coupled with Entropy Weights

Due to its near-net-shape manufacturing and ability to treat challenging-to-manufacture materials such as titanium alloys, Additive manufacturing (AM) is growing in popularity. However, due to the poor surface quality of AM components, finishing processes such as machining are required. One of the most difficult aspects of finishing AM components is the fact that even when using the same machining parameters, the surface roughness can vary significantly depending on the orientation of the part. In this study, electron beam melting (EBM) Ti6Al4V parts are subjected to the finishing (milling) process in three potential orientations relative to the direction of the tool feed. The impact of the feed rate, radial depth of cut, and cutting speed on the surface roughness and cutting force of the Ti6Al4V EBM part is studied while taking the orientations of the EBM components into consideration. It is found that the machined surface changes in noticeable ways with respect to orientation. A factorial design is used for the experiments, and analysis of variance (ANOVA) is used to evaluate the results. Furthermore, the grey relational analysis (GRA) method coupled with entropy weights is utilized to determine the optimal process variables for machining a Ti6Al4V EBM component. The results show that the feed rate has the greatest impact on the multi-response optimization, followed by the cutting speed, faces, and radial depth of cut.

Tailoring microstructure with special bimodal structure to improve the ductility and fatigue life of laser powder bed fused Ti6Al4V alloy

Achieving the high strength and ductility, as well as the excellent fatigue life, was the primary consideration for aerospace application of the additively manufactured (AM) titanium alloys, but it was limited to the high residual stress, huge columnar β grains arising from the severe directional heat flow and temperature gradient. To address these challenges and then improve the comprehensive mechanical properties, this work newly designed heat treatment schedules to tailor the microstructure to improve tensile/fatigue properties in the laser-powder bed fusion (L-PBF) of Ti6Al4V. The optimized schedule (920 °C/1 h/water cooling + 800 °C/2 h/furnace cooling) obtained the special bimodal structure, including the thin lamellar α+β phases (thickness of 1.8 μm) and the discontinuous equiaxed grain boundary α phases (GB-α) (diameter in ∼6 μm), achieving the good combination of tensile strength (1025 MPa) and ductility (17.2%). The heated-treated Ti6Al4V parts with thickness of 2∼10 mm exhibited the good stability of strength and eliminated the strength anisotropy. The dimensional effect of specimen resulted in the significant discrepancy in ductility. The tailored Ti6Al4V exhibited the superior low-cycle fatigue life equivalent to the wrought counterpart due to the refined α phases, whereas presenting the relatively low stability in the high cycle fatigue life. The fracture morphology showed the crack initiation and propagation resulting from the aligned pores and uncontrollable defects.

Effect of Surface Modifications on Surface Roughness of Ti6Al4V Alloy Manufactured by 3D Printing, Casting, and Wrought.

This work aimed to comprehensively evaluate the influence of different surface modifications on the surface roughness of Ti6Al4V alloys produced by selective laser melting (SLM), casting and wrought. The Ti6Al4V surface was treated using blasting with Al2O3 (70-100 µm) and ZrO2 (50-130 µm) particles, acid etching with 0.017 mol/dm3 hydrofluoric acids (HF) for 120 s, and a combination of blasting and acid etching (SLA). It was found that the optimization of the surface roughness of Ti6Al4V parts produced by SLM differs significantly from those produced by casting or wrought processes. Experimental results showed that Ti6Al4V alloys produced by SLM and blasting with Al2O3 followed by HF etching had a higher surface roughness (Ra = 2.043 µm, Rz = 11.742 µm), whereas cast and wrought Ti6Al4V components had surface roughness values of (Ra = 1.466, Rz = 9.428 m) and (Ra = 0.940, Rz = 7.963 m), respectively. For Ti6Al4V parts blasted with ZrO2 and then etched by HF, the wrought Ti6Al4V parts exhibited higher surface roughness (Ra = 1.631 µm, Rz = 10.953 µm) than the SLM Ti6Al4V parts (Ra = 1.336 µm, Rz = 10.353 µm) and the cast Ti6Al4V parts (Ra = 1.075 µm, Rz = 8.904 µm).

Surface morphology influences of PBF-LB manufactured Ti6Al4V parts on adhesive bond strength—investigation of as-built and surface-treated conditions

Additive manufacturing in combination with adhesive bonding enables high lightweight potential in structural design. A decisive factor for high adhesive bond performance are the surface properties. In the present work, the surface morphology of laser powder bed fusion (PBF-LB) processed Ti6Al4V parts was investigated in the as-built condition for the build orientations 0°, 45°, 90°. Furthermore, subsequent surface treatment by grit blasting or laser treatment allowed to modify the surface morphology and examine its effect on the bond strength. The surface characteristics were assessed using scanning electron microscopy, laser confocal microscopy and contact angle measurements. Evaluating the bond strength was done for tensile loading by centrifugal adhesion testing. The lowest bond strength was found for 0° oriented specimens, while the 45° and 90° oriented samples showed similar strengths. Fracture surface analysis of the as-built surfaces showed that the partially melted particles remain attached and cause mechanical interlocking. Furthermore, surface treatment by grit blasting allowed a minor improvement of the bond strength, while with laser treatment a significant increase was possible.

A 3D Multiscale Model for Prediction of the Microstructure Evolution in Ti6Al4V Components Produced by Laser Powder Bed Fusion

A transient 3D multiscale model has been created to simulate the evolution of solidification microstructures rapidly and effectively in Ti6Al4V parts produced through Laser Powder Bed Fusion (LPBF). The microstructure simulation tool has been enhanced to account for rapid solidification conditions in Ti6Al4V alloys during processing of multi-layer multi-track LPBF parts. The simulation tool can evaluate the impact of part geometry, lase power input, laser speed, and laser beam shape on the formation of the microstructure in LPBF-processed Ti6Al4V alloy. The multiscale model considers several factors, including preferential crystallographic growth direction, isomorphism, epitaxy, melt pool motion, and temperature gradients to generate the observed texture and morphology of the microstructure in Ti6Al4V components. The model can evaluate various microstructure characteristics, such as grain size and texture. Consequently, it could aid in controlling the formation of solidification microstructures in Additive Manufacturing (AM) processed parts. The simulation tool has been previously validated by using IN625 laser remelting experiments made by National Institute of Standards and Technology. The 3D simulation tool can also be utilized to predict the microstructure formation in Ti6Al4V components produced by the Electron Beam AM processes.

Numerical Simulation of the Taylor Impact Test for Laser Powder Bed Fusion Parts Based on Microstructural Internal State Variables

The response of any engineering design components to stresses should be predictable, While the response of a material to complex loading, such as high strain rates experienced during service, is difficult to represent with simple tests, the Taylor impact test is one of a number of tests devised for high strain rate complex loading. To expedite the acceptance of LPBF Ti6Al4V (ELI) for use in demanding structural applications, there is a need to develop numerical models based on the internal microstructural state variables to predict the performance of the alloy over a wide range of high strain rates using such complex tests. This paper documents the numerical simulation of Taylor impact tests for direct metal laser-sintered and post-processed Ti6Al4V (ELI—Extra Low Interstitial) alloy. A microstructural variable-based constitutive model was used to predict the mechanical properties (stresses and evolution of plastic strains) of the material. The corresponding material parameters of the model were based on the specific microstructure obtained upon post-process heat treatment. The model was first implemented as a user material subroutine in the explicit finite element program ABAQUS using the VUHARD subroutine. Subsequently, the symmetrical Taylor impact tests of Laser Powder Bed Fusion (LPBF) Ti6Al4V (ELI) parts were numerically simulated using the VUHARD subroutine at different impact velocities. The equivalent von Mises stress and plastic strain obtained from numerical simulations were compared with the analytical solutions based on the strain rates obtained. It was shown that the instantaneous and average absolute errors between the numerical and analytical values of the model were generally less than 5%. The mushroom end, commonly observed in a Taylor test specimen, was also seen in the numerical model.

New Partially Water-Soluble Feedstocks for Additive Manufacturing of Ti6Al4V Parts by Material Extrusion.

In this work, a process chain for the realization of dense Ti6Al4V parts via different material extrusion methods will be introduced applying eco-friendly partially water-soluble binder systems. In continuation of earlier research, polyethylene glycol (PEG) as a low molecular weight binder component was combined either with poly(vinylbutyral) (PVB) or with poly(methylmethacrylat) (PMMA) as a high molecular weight polymer and investigated with respect to their usability in FFF and FFD. The additional investigation of different surfactants' impact on the rheological behaviour applying shear and oscillation rheology allowed for a final solid Ti6Al4V content of 60 vol%, which is sufficient to achieve after printing, debinding and thermal densification parts with densities better than 99% of the theoretical value. The requirements for usage in medical applications according to ASTM F2885-17 can be fulfilled depending on the processing conditions.

Toward a sustainable laser powder bed fusion of Ti 6Al 4 V: Powder reuse and its effects on material properties during a single batch regime

Titanium alloy Ti6Al4V is the most used titanium alloy due to its high specific strength, ductility, corrosion resistance, and weldability. Currently, this alloy is produced with a density above 99% with laser welding-based additive manufacturing processes. However, the costs of titanium powder are high, and for critical components, the excess powder is usually not reused. In this work, we characterized the powder and additively manufactured Ti6Al4V parts by reusing the powder of a single batch to determine the impact on morphology, chemical composition, melt pool viscosity, density, microstructure, and tensile and impact strength. We aimed to determine the limits of powder reuse to increase sustainability and reduce the carbon footprint of Laser Powder Bed Fusion (L-PBF). We found that the powders pick up oxygen after each cycle to form an oxide layer up to 20 nm, causing a change in the optical and thermal properties of the titanium powders. This change affected the laser absorption and, with this, the melt pool properties. The powders reused after 18 cycles were responsible for a drop in the relative density of 0.1%. However, the tensile properties remained unchanged. The reused powders also presented a small shift in particle size distribution that did not affect the sphericity and increased flowability. In this work, we proved that the powders of Ti6Al4V alloys could be reused up to 18 cycles without any modification to the tensile properties but with a decrement in the impact strength of 30% for vertical- and 12% for horizontal stress-relieved specimens and 19% and 16% for furnace-annealed specimens, respectively.

A New Approach to Empirical Optimization of Laser Powder Bed Fusion Process for Ti6Al4V Parts

Optimization of all the process parameters for laser powder bed fusion (L-PBF), considering the effects of individual parameters on Ti6Al4V fabricated parts, can be complex and challenging. Therefore, for the first time, the effects of three main variable process parameters (laser power, scan speed, and hatch spacing) on three outcomes parameters (surface roughness, bulk porosity, and production rate of parts) were studied in this work. Then, the combination of above-mentioned process parameters in the form of volumetric energy density (VED) was investigated in order to establish a practical method for optimization of process parameters for making Ti6Al4V parts with the desired quality targets, i.e., the smoothest surface, the lowest bulk porosity and a higher production rate. It was revealed that although VED is a reliable metric for the optimization of process parameters, some thresholds and ranges should be considered for all three parameters of laser power, scan speed, and hatch spacing. It was demonstrated that by employing an optimum laser power of 180 W or 270 W and changing the scan speed and hatch spacing to keep VED in the range of 50-100 J/mm3, fabrication of samples with micro-roughness Ra < 10 µm and bulk porosity less than 0.15% is achievable. In addition, the surface of the L-PBF fabricated parts may appear in two categories of surface morphology; wavy surface classified “meso-roughness topography” and non-wavy surface termed “micro-roughness”. Since there was not any correlation between the value of roughness of samples with meso-rough surface and their bulk porosity, and besides, their process parameters were far from optimized parameters, the samples with meso-rough surface were not included in the final results. However, it was realized in the samples with micro-rough surfaces, the value of their micro-roughness could accurately indicate the porosity content of Ti6Al4V samples.

Recoater-Induced Distortions and Build Failures in Selective Laser Melting of Thin-Walled Ti6Al4V Parts

Additively manufactured thin-walled structures through selective laser melting (SLM) are of great interest in achieving carbon-neutral industrial manufacturing. However, residual stresses and warpages as well as recoater crashes often occur in SLM, leading to the build failure of parts, especially for large-scale and lightweight geometries. The challenge in this work consists of investigating how the recoater affects the warpage and (sometimes) causes the failure of different thin-walled Ti6Al4V parts (wall thickness of 1.0 mm). All these parts are printed on the same platform using a commercial SLM machine. After the loose powder removal and before the cutting operation, a 3D-scanner is used to obtain the actual warpage of each component. Next, an in-house coupled thermo-mechanical finite element model suitable for the numerical simulation of the SLM process is enhanced to consider the recoater effects. This numerical framework is calibrated to predict the thin-walled warpage as measured by the 3D-scanner. The combination of numerical predictions with experimental observations facilitates a comprehensive understanding of the mechanical behavior of different thin-walled components as well as the failure mechanism due to the recoater. The findings show that the use of a higher laser energy input causes larger residual stresses and warpage responsible for the recoater crashes. Finally, potential solutions to mitigate the warpage and the recoater crashes in the SLM of lightweight structures are assessed using the validated model.

Effect of post-processing methods on the surface quality of Ti6Al4V fabricated by laser powder bed fusion

Ti6Al4V is widely used in aerospace and medical applications, where high demands on dimensional accuracy and surface quality require the application of post-processing to achieve optimal performance. However, the surface quality of parts fabricated by LPBF is inferior due to the inherent defects of LPBF. Therefore, it is important to investigate the effect of post-processing on the surface quality of Ti6A14V parts fabricated by LPBF. In this work, the effect of post-processing methods (i.e., sandblasting, electrolytic polishing, chemical polishing, and abrasive flow polishing) on the surface quality of Ti6Al4V fabricated by laser powder bed fusion (LPBF) additive manufacturing was investigated. The changes in surface roughness and morphology of the 45° inclined square and curved pipe Ti6Al4V samples processed with post-processing were observed, and the weight and elemental changes of the parts were also analyzed. The result reveals that sandblasting, electrolytic polishing, chemical polishing, and abrasive flow polishing are all effective in improving the surface quality of Ti6Al4V parts fabricated by LPBF. The effect of sandblasting is mainly caused by sharp-edged grit driven by high-speed airflow, resulting in the lowest surface roughness and the least influence on the weight, but may contaminate the surface with residual brown corundum. Electrolytic polishing and chemical polishing achieve surface quality improvement through different corrosion patterns without changing the surface composition. The surface smoothness of parts processed with chemical polishing is the best, while the weight loss rate of the sample processed with electrolytic polishing is the most at about 7.47%. Abrasive flow polishing presents a remarkable effect on polishing the internal surface of the Ti6Al4V sample by the extrusion scratching, extrusion deformation, and micro-cutting effects of abrasive on the surface. The findings can provide important engineering references for the post-processing of precision Ti6Al4V parts fabricated by LPBF and further promote the engineering applications of Ti6Al4V parts.

Study on Surface Roughness Improvement of Selective Laser Melted Ti6Al4V Alloy

To improve the surface quality of Ti6Al4V parts formed by selective laser melting (SLM), this paper systematically studies the effects of laser power, scanning speed and inclination angle on the different surface morphology and roughness of parts. On this basis, the effect of surface remelting and multi-layer profile scanning process strategies on improving the surface quality of parts is explored. The upper surface roughness varies parabolically with increasing line energy density, the line energy density value that minimizes the upper surface roughness is around 0.22 J/mm, and the minimum Ra value is 4.41 μm. The roughness of upper and lower sides increases significantly with the increase in scanning speed. As the inclination angle increases, the roughness of the upper and lower sides gradually decreases, which is caused by the combined influence of powder adhesion and step effect. The surface remelting process strategy can reduce the upper surface roughness by 35.68% and reduce its Ra value to 2.65 μm. The multi-layer profile scanning process strategy can reduce the upper side and vertical side roughness by more than 50%, down to Ra 5.10 μm and Ra 4.61 μm, respectively.