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Ti6Al4V alloy–CoCrMo alloy pair is commonly applied for modular head–neck interfaces for artificial hip joint. Unfortunately, the fretting corrosion damage at this interface seriously restricts its lifespan. This work studied the fretting corrosion of Ti6Al4V–CoCrMo pair in calf serum solution. We established this material pair's running condition fretting map (RCFM) regarding load and displacement, and revealed the damage mechanism of this material pair in various fretting regimes, namely partial slip regime (PSR), mixed fretting regime (MFR), and gross slip regime (GSR). The damage mechanism of Ti6Al4V alloy was mainly abrasive wear induced by CoCrMo alloy and tribocorrosion. Adhesive wear (material transfer) also existed in MFR. The damage mechanism of CoCrMo alloy was mainly abrasive wear induced by metal oxides and tribocorrosion in GSR and MFR, while no apparent damage in PSR. Furthermore, a dense composite material layer with high hardness was formed in the middle contacting area in GSR, which reduced the corrosion and wear of Ti alloys and exacerbated damage to Co alloys. Finally, the ion concentration maps for Ti and Co ions were constructed, which displayed the transition in the amount of released Ti and Co ions under different displacements and loads. [ABSTRACT FROM AUTHOR]

Investigation into the post-processing machinability of Ti6Al4V alloy is increasingly crucial in the manufacturing industry, particularly in the machining of additively manufactured (AM) Ti6Al4V alloy to ensure effective machining parameters. This review article summarizes various AM techniques and machining processes for Ti6Al4V alloy. It focuses on powder-based fusion AM techniques such as electron beam melting (EBM), selected laser melting (SLM), and direct metal deposition (DMD). The review addresses key aspects of machining Ti6Al4V alloy, including machining parameters, residual stress effects, hardness, microstructural changes, and surface defects introduced during the additive manufacturing (AM) process. Additionally, it covers the qualification process for machined components and the optimization of cutting parameters. It also examines the application of finite element analysis (FEA) in post-processing methods for Ti6Al4V alloy. The review reveals a scarcity of articles addressing the significance of post-processing methods and the qualification process for machined parts of Ti6Al4V alloy fabricated using such AM techniques. Consequently, this article focuses on the AM-based techniques for Ti6Al4V alloy parts to evaluate and understand the performance of the Johnson–Cook (J–C) model in predicting flow stress and cutting forces during machining of the alloy. [ABSTRACT FROM AUTHOR]

Titanium is a highly operational alloy for use in dental implants. Surface inertness of the titanium alloy surfaces reduces osseointegrate, raising concerns about implant loosening. Hydroxyapatite (HA)-rich porous titanium surfaces with moderated surface roughness have better osteoconductivity. This study focused on the surface alteration of Ti6Al4V via hydroxyapatite mixed electric discharge-assisted centerless turning (HA-mixed-EDCLT) to find the optimum surface. The experiments were planned based on a four-factor, three-level Box-Behnken design. HA-powder concentration (Cp), revolutions per minute (RPM), duty factor and impulse current (IP) were the input parameters. The Ra value of machined surfaces ranged from 1.12μm to 1.63μm, which is in the bone growth supportive implants range. The average hardness reached 415.8–962.7HV, where untreated surfaces’ hardness was 340±6HV. Porous, hydrophilic coating with a high Ca, P, and O content deposited on the implant surfaces supports the biocompatibility of implants. Analysis of the elements and compounds shows that the machined surface layer is rich with Ca3(PO4)2 and TiO2,which improves the bioactivity of the alloy. [ABSTRACT FROM AUTHOR]

This work presents a systematic investigation of the corrosion behavior of two materials, 316 stainless steel (316), and Ti6Al4V alloy (Ti6Al4V), in simulated seawater (3.5wt.% NaCl solution). This includes electrochemical tests, immersion experiments, scanning electron microscopy (SEM), energy disperse spectroscopy (EDS) analyses. The polarization curves demonstrate that passivation occurs in both alloys. The lower self-corrosion and passivation current densities of Ti6Al4V indicate that its corrosion resistance is superior to that of 316. However, the impedance spectrum of the 316 shows a larger capacitive arc radius, which is indicative of the presence of a more robust passivation film on its surface. The results of the immersion experiments demonstrate that 316 exhibits a high-corrosion rate under static conditions, which can be attributed to the instability of the passivation film and environmental factors. However, under dynamic conditions, the corrosion rate is lower due to the effect of scouring. In contrast, Ti6Al4V demonstrated superior corrosion resistance in a variety of environmental conditions. In the context of simulated seawater, both 316 and Ti6Al4V exhibited varying degrees of corrosion behavior. Consequently, when selecting corrosion-resistant materials, it is imperative to select suitable materials according to the specific use environment and requirements. [ABSTRACT FROM AUTHOR]

The development and characterization of bioactive surfaces based on chitosan-polyethylene glycol coatings modified with hydroxyapatite on Ti6Al4V alloy were conducted to enhance bioactivity. Characterization techniques such as scanning electron microscopy, X-ray diffraction, infrared spectroscopy, atomic absorption spectroscopy, and electrochemical impedance spectroscopy were used to evaluate coating properties, apatite formation after immersion in simulated body fluid, and electrochemical stability. Results demonstrated apatite deposition due to the bioactivity of the polymer-ceramic composite, with calcium accumulation observed on the substrate surface after 5 days of immersion. Electrochemical impedance spectroscopy revealed a highly capacitive layer in the 50:50 chitosanpolyethylene glycol coating with 0.05% w/v hydroxyapatite, indicating increased interaction with the biological medium while preserving the protective resistive properties of the Ti6Al4V alloy. These findings suggest that this coating composition is a promising material for bone tissue regeneration applications. [ABSTRACT FROM AUTHOR]

In this study, recycled Ti6Al4V alloy powder was utilized as a reinforcement to enhance the mechanical and modal properties of polyurethane foam (PUF) core-based sandwich composites. Sandwich composite having carbon fiber reinforced polymer (CFRP) composite face sheets and Ti6Al4V powder-reinforced PUF cores were manufactured. The PUF cores were reinforced with two different variants of Ti6Al4V powder based on particle sizes from 1 to 3 wt.%. The dispersion quality was investigated using scanning electron microscopy (SEM). A detailed experimental modal analysis was conducted to evaluate the modal properties in terms of the natural frequencies and damping ratios of the sandwich specimens. A comprehensive mechanical study was also conducted in terms of compression, buckling, flexural, and impact tests according to the relative ASTM standards. The experimental results demonstrated that the Ti6Al4V reinforced sandwich specimens exhibited superior mechanical and modal properties with enhanced PUF cores. Improvements in excess of 21%, 37%, and 24% were recorded in the compression, buckling, and flexural response of the reinforced specimens, respectively, compared to those of their neat counterparts. Similarly, remarkable improvements were also observed in the experimental modal and impact properties of the Ti6Al4V alloy powder-reinforced sandwich composites. [ABSTRACT FROM AUTHOR]

This research paper presents an innovative approach to fabricating enhanced-quality hierarchical surface micro-textures on Ti6Al4V alloy by synergistically employing in situ electrical discharge machining (EDM) and electrochemical machining (ECM) processes. The hierarchical structure encompasses three levels: a primary level at a few hundred micrometers, a secondary level at a few tens of micrometers, and a ternary level at sub-micrometer scales. Despite the precision achieved in generating the primary-level texture through EDM using a chemically patterned tool, inherent thermal damages and surface defects, such as micro-craters and irregularities, pose challenges. Unlike usual ex situ chemical or electrochemical post-processing methods, this study introduces in situ ECM post-processing (ECM) with the same patterned tool. This approach enhances the quality of EDMed surfaces without compromising geometrical accuracy, offering anisotropic dissolution along the feature depth. To ensure geometrical accuracy, an experimentally validated finite element method-based transient numerical simulation model is developed. This model accurately predicts the evolution of the feature profile during the ECM operation. Furthermore, ECM with a fluoride ion–containing electrolyte introduces additional secondary and ternary levels of hierarchical textures. Fluoride ions play a pivotal role in augmenting material removal during ECM, particularly in areas around micro-crevices and pores, shaping the secondary-level texture. [ABSTRACT FROM AUTHOR]

Ti-Ta coatings were deposited on titanium alloy by electrospark deposition in the anode mixture of titanium granules and tantalum powder in an argon atmosphere. The cathode weight gain kinetics, tantalum concentration, structure, oxidation resistance, microhardness, and tribotechnical properties of the coatings were studied. It was shown that, with increasing tantalum concentration in the anode mixture, the net cathode gain during 10 min of treatment increased monotonically. The average thickness of the deposited coatings varied in the range from 30.9 to 39.1 µm. The concentration of tantalum in the coating composition increased with increasing tantalum powder concentration in the anode mixture. The coating structure was dense without longitudinal and transverse cracks. With an excess of tantalum powder in the anode mixture, the discharge energy was not enough to completely melt it. The phase composition included α-Ti and a bcc tantalum solid solution in β-Ti. With increasing powder concentration in the anode mixture, the intensity of the bcc-phase peaks increased relative to the α-Ti peaks. The surface hydrophobicity of Ti-Ta coatings was higher than that of uncoated Ti6Al4V titanium alloy. The developed method can be used to produce Ti-Ta coatings with up to 5.9 times higher oxidation resistance compared to Ti6Al4V alloy. The high oxidation resistance of Ti-Ta coatings is explained by the formation of a dense and durable TiO2 layer. The surface microhardness of Ti-Ta coatings ranged from 4.72 to 4.91 GPa. The friction coefficient was in the range of 0.87–0.97. The wear resistance was 23 to 36 times higher as compared to the titanium alloy. [ABSTRACT FROM AUTHOR]

Laser powder bed fusion (LPBF) is the most widely used metal additive manufacturing technology, but it still faces challenges in manufacturing efficiency. To address the issue, high-power LPBF (HP-LPBF) which employs kilowatt-level lasers emerges in recent years. In this study, a 4 kW Flat-top laser was used for the HP-LPBF of Ti6Al4V alloy. The samples in as-built state and annealed states (750 °C/2h, 850 °C/2h, 950 °C/2h, 1050 °C/2h) were investigated in terms of defects, microstructure, and mechanical properties. Results show that keyhole mode melting is avoided by adopting the Flat-top laser, so the relative density of as-built Ti6Al4V is generally positively correlated with the employed laser energy density. The minimum laser energy density to obtain the high-density (≥99.9%) sample is 50.0 J/mm3, and the highest build rate is 288 cm3/h. The microstructure in as-built state exhibits a unique alternating pattern of ''bright bands/dark bands''. The dark bands consist of needle-shaped α′ martensite, while the bright bands consist of needle-shaped α+β, which results from the decomposition of α′ under the in-situ annealing effect of the 4 kW Flat-top laser. After annealing at 750 °C, most of the residual α′ decomposes into needle-shaped α+β. As the annealing temperature increases from 750 °C to 1050 °C, the microstructure undergoes an evolution from needle-shaped α+β to lamellar α+β then to lamellar α+β with some globular α and finally to duplex α+β. An optimum strength-ductility balance is achieved after annealing at 850 °C, both the tensile strength and the elongation exceed the standard values of Ti6Al4V forgings.

A V-shaped stirring mixing method was utilised to prepare SiCw/Ti6Al4V composite powder, followed by selective laser melting (SLM) to fabricate SiCw/Ti6Al4V matrix composites. Then, the thermal compression behaviour of the Ti6Al4V-SiCw composites and Ti6Al4V alloy were analysed at a deformation of 60%, temperature of 900 °C, and strain rate of 1 s−1. The flow stress of Ti6Al4V-SiCw composites was always higher than that of Ti6Al4V alloys throughout the deformation stage and the high-temperature compressive resistance improved mainly due to the in-situ generation of TiC reinforcing phases during the forming process leading to grain refinement and dislocation reinforcement, thereby enhancing the composite's high-temperature compressive resistance. The composites showed flow softening behaviour after the peak of flow stress during hot pressing attributed to the presence of nanoscale TiC to enhance the composite recrystallisation. Moreover, microstructural analysis after hot pressing showed that the bonding between the TiC reinforcing phase in the composites and the matrix was still strong, and the matrix remains intact without any visible cracks. These results revealed that the in-situ introduction of reinforcing phases increased the dislocation density of the composites and refined the grain size ,which is the main reason for the improvement of the mechanical properties of the composites.

The effects of heat treatment on the microstructure, mechanical properties and wear resistance of Selective Laser Melting Ti6Al4V alloy were systematically studied. The results show that the as-built part has an acicular α ′ martensite structure. The increase in heat treatment temperature causes the decomposition of acicular α ′ martensite, which leads to the decrease of the hardness of Ti6Al4V alloy. When the heat treatment temperature is 800∘C, the alloy forms an α ′ / α structure, which increases the tensile strength and elongation of the alloy by 12% and 23%, respectively. When the heat treatment reaches above 900∘C, the mechanical properties of the alloy decrease sharply due to the disappearance of the α ′ / α structure, the coarse grains of the α phase, and the increase of the content of the β phase. The tensile strength decreased from 935 MPa to 815 MPa, and the elongation decreased from 8.7% to 3.1%. With the increase of heat treatment temperature, the friction coefficient and wear rate increase linearly, which is opposite to the changing trend of hardness, and the wear mechanism is changed from single abrasive wear to abrasive wear and oxidative wear. This is attributed to the increase in the grain size of the alloy and the increase in the content of the β phase, resulting in a decrease in the overall hardness of the alloy. [ABSTRACT FROM AUTHOR]

MgAl 2 O 4 and Ti6Al4V, the greatly suitable materials for industrial application, are rarely explored to realize reliable bonding in current research. In this study, the transparent MgAl 2 O 4 and Ti6Al4V were successfully bonded by innovative use of ultrashort pulse laser with ultra-high peak power. The high energy near the laser focus makes MgAl 2 O 4 and Ti6Al4V mix and react with each other after absorbing the laser energy, thus realizing the bridge between them. The homogeneous mixing of all phases was observed in the joint and the newly generated Ti 6 O phase was identified at the interface. In addition, the effects of laser power and scanning speed on the microstructure and mechanical properties of the joint have been thoroughly clarified. This study creatively used femtosecond laser welding as a new mean to realize ceramic-metal joining, which shows great advantages in superior efficiency and precision compared with other welding methods. [ABSTRACT FROM AUTHOR]

In order to improve the wear and corrosion resistance of Ti6Al4V alloy, a Ti-N compound layer was formed on the alloy by plasma nitriding at a relatively low temperature (750 °C) and within an economical processing duration (4 h), in a mixture of NH3 and N2 gases with varying ratios. The influence of the gas mixture on the microstructure, phase composition, and properties of the Ti-N layer was investigated. The results indicated that the thickness of the nitrided layer achieved in a mixed atmosphere with optimal proportions of NH3 and N2 (with a ratio of 1:2) was substantially greater than that obtained in an atmosphere of pure NH3. This suggests that appropriately increasing the proportion of N2 in the nitriding atmosphere is beneficial for the growth of the nitrided layer. The experiments demonstrated that the formation of the surface nitrided layer significantly enhances the corrosion and wear resistance of the titanium alloys. [ABSTRACT FROM AUTHOR]

This study aims to optimize the performance of CrN coatings deposited on WC cutting tools for machining Ti6Al4V alloy, where the formation of built-up edge (BUE) is a prevalent and critical issue. In-house CrN coatings were developed using the PVD (Physical Vapor Deposition) process, with variations in deposition parameters including nitrogen gas pressure, bias voltage, and coating thickness. A comprehensive experimental approach encompassing deposition, characterization, and machining performance evaluation was employed to identify the optimal deposition conditions. The results indicated that CrN coatings deposited at a nitrogen gas pressure of 4 Pa, a bias voltage of −50 V, and a thickness of 1.81 µm exhibited superior performance, significantly reducing BUE formation and tool wear. These optimized coatings demonstrated enhanced properties, such as a higher elastic modulus and a lower coefficient of friction, which contributed to improved tool life and machining performance. Comparative studies with commercial CrN coatings revealed that the in-house developed coatings outperformed the commercial variants by approximately 65% in tool life, owing to their superior mechanical properties and reduced friction. This research highlights the potential of tailored CrN coatings for advanced machining applications and emphasizes the importance of optimizing deposition parameters to achieve high-performance tool coatings. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Titanium alloys are widely applied in the aerospace field owing to their exceptional properties, but coarse grains can easily form during the welding process, seriously diminishing the mechanical properties of the welded joint. To address this problem, a pulsed current was introduced to refine the grain structure of titanium alloy welds. In this study, we investigated the effect of varying the pulsed current frequency on grain refinement in titanium alloy welds and explored the mechanism of grain refinement using the "overlap welding" method. The results showed that the grain refinement improved with increasing pulse current frequency, particularly at the original β and α grain boundaries. Compared to non-pulsed welding, the original β grain boundary decreased from 305 to 158 μm, and the maximum α grain size decreased from 93.236 to 46.693 μm when the pulse frequency was 100 Hz. Moreover, dendrite fragmentation was identified as the primary mechanism of grain refinement in pulsed plasma arc welding of the Ti6Al4V alloy. The repeated heating of the molten pool by application of the pulsed current caused the dendrite tip to remelt in the pasting region, promoting dendrite fragmentation. [ABSTRACT FROM AUTHOR]

Ti6Al4V alloy has become the preferred material for key components in machinery due to its many excellent mechanical properties, however, the defects of Ti6Al4V alloy such as low hardness and poor wear resistance limit its wider application in the mechanical field. In view of this, the laser texture technology was used to prepare a streamlined symmetrical texture on the surface of Ti6Al4V alloy, and the effects of laser streamline texture with different parameters on the wear resistance of Ti6Al4V alloy material were studied by friction test system under oil lubrication conditions. SEM and LICHEN electronic balance equipment were used to characterize the wear scar morphology and wear amount on different sample surfaces. The experimental results show that when the texture length is 400 μm and the depth is 600 μm, the friction coefficient and wear of the sample are smaller, and the friction reduction effect is better. In addition, ANSYS Workbench software was used to simulate the flow characteristics of lubricating oil on the texture surface, and it was found that the decrease of friction coefficient in the experiment was mainly caused by the increase of oil film pressure caused by the change of flow velocity and flow direction of lubricating oil under the action of texture. The increase of oil film pressure can improve the bearing capacity of the oil film and effectively reduce the friction coefficient of the friction pair. [ABSTRACT FROM AUTHOR]

Residual stress is a key factor affecting the properties of ceramic/metal brazed joints. In this work, the residual stress of sapphire/Ti6Al4V alloy joints brazed with CuTi+B composite filler after cooling and reheated to 400 °C was calculated by finite element numerical simulation method. The effect of the B content in the filler and the filler thickness on the residual stress distribution of brazed joints after cooling was studied. The results show that the residual stress is mainly concentrated in the area near the filler layer. The maximum von Mises stress is located in the filler layer and a large Z-axial (the direction perpendicular to the brazed surface) tensile stress is on the sapphire near the filler layer. The B content and the filler thickness have no significant effect on the distribution of residual stress, but they have a certain effect on the value of residual stress of the sapphire near the filler layer. The von Mises stress and the Z-axial stress of this area increase with the increase of B content, and they decrease first and then increases with the increase of filler thickness. When the sapphire/Ti6Al4V joint is reheated to 400 °C, its residual stress significantly reduces and the residual stress on the periphery of the filler layer changes from compressive stress to tensile stress. As the B content is 1 and 3 wt%, the sapphire/Ti6Al4V joint with a smaller residual stress can be obtained. The microstructure observation and shear tests of the joints show that cracks appear in the high stress concentration area and the fracture starts from the area with maximum axial tensile stress, which verifies the accuracy of the simulation results. [ABSTRACT FROM AUTHOR]

Niobium Nitride (NbN) film deposition has emerged as a pivotal process in modifying the surface properties of the Ti6Al4V alloy, a material widely recognized for its excellent mechanical properties and biocompatibility. This innovative approach not only enhances the alloy's suitability for various medical applications but also paves the way for future advancements in biomedical technology. By applying NbN films to the surface of Ti6Al4V, researchers are addressing critical challenges in medical device performance, particularly in the areas of wear resistance and corrosion resistance, which are essential for the longevity and reliability of implants. The microstructural morphologies of the thin films were assessed through field emission scanning electron microscopy, highlighting the significant impact of NbN nanoparticles on the surface characteristics of the nanocoated Ti6Al4V. Electrochemical studies conducted through cyclic polarization measurements indicated a decreased corrosion rate of 4.02 × 10-4 mmpy for the sputter-deposited samples compared to 4.79 × 10-1 mmpy for the uncoated sample. In vitro biocompatibility characterization in simulated body fluid demonstrated the growth of a hydroxyapatite layer on the NbN-coated Ti6Al4V surface, with its relative thickness increasing at higher sputtering power and substrate deposition temperature. These findings underscore the superior biocompatibility and enhanced corrosion protection of nanostructured NbN coatings over Ti6Al4V compared to uncoated Ti6Al4V specimens. [ABSTRACT FROM AUTHOR]

The non-equilibrium solidification process in the additive manufacturing of titanium alloy leads to special microstructures, and the resulting changes in corrosion behavior are worthy of attention. In this paper, the microstructure and electrochemical corrosion behavior of Ti6Al4V alloys prepared using laser powder bed melting (LPBF) and casting are systematically compared. The results show that the LPBF-processed Ti6Al4V alloy is composed of dominant acicular α′ martensite within columnar prior β phase, and less β disperses have also been discovered, which is significantly different from the α + β dual-phase structure of cast Ti6Al4V alloy. Compared to the as-cast Ti6Al4V alloy, LPBF-processed Ti6Al4V alloy has a thinner and unstable passive film, and exhibits slightly poorer corrosion resistance, which is mainly related to its higher porosity, a large amount of acicular α′ martensite and less β phase compared to as-cast Ti6Al4V alloy. This result proves that suitable methods should be taken to control the relative density and phase composition of LPBF-processed Ti6Al4V alloys before application. [ABSTRACT FROM AUTHOR]

This work aims at reducing abrasion between titanium alloy parts, such as drive shafts and support pairs used in aviation. Three different NiCrBSi coatings, Ni40, Ni50, and Ni60, are prepared on surfaces of Ti6Al4V by laser cladding. The microstructural and mechanical properties of these coatings are analyzed by scanning electron microscope (SEM) and a microhardness tester. The tribological properties of the NiCrBSi coatings undergoing friction with Ti6Al4V are tested using a wear testing machine. The results show that the Vickers hardnesses of the Ni40, Ni50, and Ni60 coatings are 490 HV0.3, 609 HV0.3, and 708 HV0.3, respectively. For the above NiCrBSi coatings, more hard phases are produced with increases in the amounts of Cr in the powders, resulting in increases in the coatings' hardnesses. The wear test results show that the NiCrBSi coatings could reduce the friction coefficients, which gradually decreased with increases in the coatings' hardnesses. Both the coating-specific wear rates and the friction pair wear losses initially decreased and then increased. The Ni50 coating and the Ti6Al4V friction pair undergoing friction with the Ni50 coating showed the best wear performance, with a specific wear rate and wear loss of 0.51 × 10−7 mm3/(N·m) and 7.8 mg, respectively. The specific wear rates for Ni50 were only 8.4%, 35.4%, and 37.0% of the Ti6Al4V, Ni40, and Ni60, respectively. In addition, the friction pair wear loss was only 36.4%, 52.5%, and 55.3% of that while undergoing friction with Ti6Al4V, Ni40, and Ni60, respectively. The NiCrBSi coatings prepared on the surface of Ti6Al4V show excellent antifriction and wear resistance properties, providing a viable solution for the design of wear-resistant coatings on load-bearing and non-load-bearing titanium alloy parts. [ABSTRACT FROM AUTHOR]

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The development and characterization of bioactive surfaces based on chitosan-polyethylene glycol coatings modified with hydroxyapatite on Ti6Al4V alloy were conducted to enhance bioactivity. Characterization techniques such as scanning electron microscopy, X-ray diffraction, infrared spectroscopy, atomic absorption spectroscopy, and electrochemical impedance spectroscopy were used to evaluate coating properties, apatite formation after immersion in simulated body fluid, and electrochemical stability. Results demonstrated apatite deposition due to the bioactivity of the polymer-ceramic composite, with calcium accumulation observed on the substrate surface after 5 days of immersion. Electrochemical impedance spectroscopy revealed a highly capacitive layer in the 50:50 chitosan-polyethylene glycol coating with 0.05% w/v hydroxyapatite, indicating increased interaction with the biological medium while preserving the protective resistive properties of the Ti6Al4V alloy. These findings suggest that this coating composition is a promising material for bone tissue regeneration applications.

In this study, the electrophoresis-assisted milling (EAM) method, an alternative method to the conventional milling (CM) method, was proposed to increase the machinability of Ti6Al4V alloy, which is difficult to machine. The nanoparticles in the electrophoresis solution generated an electric field. This electric field collected abrasive particles around the cutting tool, and the machining quality was improved. The impacts of different cutting parameters on the performance characteristics were examined using both EAM and CM methods. The experimental results demonstrate that the proposed EAM method significantly improves these performance characteristics. In addition, increasing spindle speed increased tool wear and cutting temperature for both machining methods; It was observed that it reduced cutting force and surface roughness. It was concluded that as the feed rate increased, tool wear, cutting temperature, cutting force, and surface roughness increased. The experimental results showed that feed rate, machining method, and spindle speed affect machining quality. In conclusion, the experimental results significantly impact improving the machining performance of the EAM method.

The Ti2Cu intermetallics compound possessing an ability to release Cu2+ ions has promising antibacterial properties. This research integrates experimental and computational techniques to delve into the interfacial intermetallic (IMC) formation within the Ti6Al4V/Cu system. Heat transfer analysis is performed to numerically outline the thermal history within the microstructure during laser surface alloying (power = 1000 W and scan speed = 200 mm/s), while the phase field method is employed to describe the Ti2Cu IMC grain growth in the Ti6Al4V matrix. As the IMC and the matrix phases respectively have free energy minima of -68.52 and -61.35 kJ/mol at Taverage=1250.0 K, the growth of Ti2Cu IMC grains at the Ti6Al4V matrix located around the depth of 5 μm from the top surface is thermodynamically favorable. Laser processing can cause the nucleation of IMC precipitates of irregular sizes and curvature profiles, in which case the curvature driven effects between the adjacent grains can additionally affect their growth kinetics. Furthermore, microbiological assays underscore the superior antibacterial efficacy of the Ti6Al4V+Ti2Cu heterostructures as compared to the control (Ti6Al4V) counterpart.

Laser powder bed fusion (LPBF) is a cutting-edge metal additive manufacturing technology with promising applications in aerospace, biomedicine, and industrial automation. Its ability to fabricate intricate geometric shapes, achieve high surface precision, and deliver comprehensive results renders it highly advantageous. In LPBF process, several factors such as the interference of laser processing fluctuations, rapid cooling rate, and environmental gas, contribute to the initiation and expansion of defects including pores and cracks, limiting the application of LPBF components. Laser ultrasonic testing (LUT) is a promising non-destructive evaluation method that can accurately detected defects in LPBF manufactured components by non-contact generation and detection. In this paper, a multi-physical field LUT model for the pores and cracks in LPBF additively manufactured Ti6Al4V alloy is proposed. The interaction of ultrasound with defects produces defect reflection echo wave, diffracted wave, and transmission wave. The transmission and diffraction phenomena occur in the longitudinal sound waves at defects. Furthermore, the echo wave reflected at crack exhibited enhanced prominence and an irregular shape. Clear differences were observed in the effects of laser ultrasonic detection on different defect types, pore depths and sizes. Finally, the LUT technology achieved the detection of 90 μm pore defects in LPBF manufactured Ti6Al4V alloy.

The titanium alloys are widely used in aeronautical engineering and medical device materials due to exceptional mechanical properties such as tensile resistance and toughness of fractures. High thermo-mechanical loads occur in metal cutting of Titanium alloy Ti6Al4V, which can decrease life of cutting tool and increase cost of part production. In this paper, the coolant effects on the cutting temperature, surface roughness and tool wear are investigated by using the developed virtual machining system. The cutting forces during turning operations of Ti6Al4V alloy are accurately calculated in order to be used in calculation of cutting temperature and tool wear. The modified Johnson–Cook methodology is utilized to obtain the cutting temperatures along machining paths. Then, the Coupled Eulerian-Lagrangian (CEL) approach is investigated to predict and evaluate the effects of coolants on the cutting temperature in turning operations of Ti6Al4V alloy. The finite element approach is employed to predict tool wear by using the Takeyama–Murata analytical model and modifying the cutting tool geometry during the chip production process. To verify the developed methodology in the study, the results of experiments for the measured cutting temperatures, surface quality and wear rate are compared to the results of virtual machining system obtained by the finite element simulation. Thus, utilizing the proposed virtual machining system in the study, cutting temperatures, surface quality and tool wear during the turning operations of Ti6Al4V alloys with and without coolant can be accurately predicted to enhance the accuracy as well as productivity in the CNC machining operations. [ABSTRACT FROM AUTHOR]

Achieving 3D-printed Ti6Al4V alloy with customized microstructures and mechanical characteristics remains challenging, wherein the processing efficiency mainly depends on the laser energy, mass deposition rate, and duration. Based on these factors, a simple and eco-friendly direct laser metal deposition approach was followed to get 3D-printed Ti6Al4V alloys at various laser powers (300–500 W). Herein, a 1.5-kW continuous fiber laser with a wavelength of 1080 nm was used to create a stable and dense alloy. The obtained 3D-printed specimens were characterized to assess the laser power–dependent microstructures, compositions, microhardness, grain sizes, color filling, and dimensional stability in terms of height/width. FESEM micrographs of the obtained alloys revealed the existence of porous spherical grains of mean size in the range of 50–81 μm. The alloy deposited at 300 W and 0.495 mm/s scan speed displayed the maximum hardness (excellent bong strength) value of 859.2 HV0.5 devoid of any crack and porosity. XRD patterns of the alloy revealed the existence of α + β martensitic phase transformation which is responsible for the marginal increase of hardness. It is asserted that the proposed 3D-printed Ti6Al4V alloy can be beneficial for the development of efficient structural parts desired for diverse applications. [ABSTRACT FROM AUTHOR]

Electrolytic plasma polishing (EPPo) is an advanced metal surface finishing technology with high quality and environmental protection that has broad application prospects in the biomedical field. However, the effect of EPPo on surface properties such as corrosion resistance and the wettability of biomedical titanium alloys remains to be investigated. This paper investigated the changes in surface roughness, surface morphology, microstructure, and chemical composition of Ti6Al4V alloy by EPPo and their effects on surface corrosion resistance, wettability, and residual stress. The results showed that Ra decreased from 0.3899 to 0.0577 μm after EPPo. The surface crystallinity was improved, and the average grain size increased from 251 nm to more than 800 nm. The oxidation behavior of EPPo leads to an increase in surface oxygen content and the formation of TiO2 and Al2O3 oxide layers. EPPo can significantly improve the corrosion resistance and wettability of titanium alloy in simulated body fluid and eliminate the residual stress on the sample surface. The surface properties are enhanced not only by the reduction in surface roughness but also by the formation of a denser oxide film on the surface, changes in the microstructure, an increase in surface free energy, and the annealing effect developed during EPPo. This study can provide guidance and references for applying EPPo to biomedical titanium alloy parts. [ABSTRACT FROM AUTHOR]

Controlling the surface roughness of materials manufactured by laser powder bed fusion (L-PBF) is critical for achieving functional performance of components and improving their mechanical properties. This is important for components whose surfaces cannot be post-treated using subtractive methods. In this study, the surface roughness has been investigated by applying different laser power and scanning speed combinations. Furthermore, potential effects of different locations on the build platform have been considered as well. The regression models have been developed using significant predictor variables, with their levels defined using face-centered central composite design. The analysis of variance (ANOVA) procedure has been used to evaluate the statistical significance of factors and model performances for each prediction variable. It has been found that the average surface roughness of L-PBF Ti6Al4V alloy can be described with high fitting accuracy using laser power and scanning speed as predictor variables. The position of specimens on the build platform showed no statistically significant effect on the average surface roughness. The experimental research and statistical analysis reported in this paper will contribute to a better understanding of how position, laser power, and scanning speed influence the average surface roughness of L-PBF Ti6Al4V alloy. [ABSTRACT FROM AUTHOR]

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This article explains development of high strength and lightweight Ti6Al4V5Cr alloy by μ-plasma powder additive manufacturing (μ-PPAM) process for automotive, aerospace, military, dies and moulds, and other similar applications. Microstructure, formation of phases, porosity, microhardness, tensile properties, abrasion resistance, and fracture toughness of multi-layer deposition of Ti6Al4V5Cr alloy are studied and compared with Ti6Al4V alloy. Results reveal that the presence of chromium in Ti6Al4V5Cr alloy refined the grains of its β-Ti and α-Ti phases, increased volume % of β-Ti phase, and promoted formation of its equiaxed grains. It also increased tensile strength, microhardness, abrasion resistance, and fracture toughness of Ti6Al4V5Cr alloy. It enhanced solid solution strengthening and formed higher hardness imparting intermetallic Cr2Ti phase and changed fracture mode to mixed ductile and brittle mode with larger size dimples, cleavage facets, and micropores. But it decreased formation temperature of β-Ti phase and % elongation as compared to Ti6Al4V alloy. Chromium and vanadium content in β-Ti phase of Ti6Al4V5Cr alloy is 7 % and 2.1 % more than its α-Ti phase. This study demonstrates that inclusion of limited amount of chromium content to Ti6Al4V5Cr alloy by μ-PPAM process is very beneficial to enhance microstructure, mechanical properties, crack propagation resistance, and abrasive wear resistance of the Ti6Al4V5Cr alloy. It makes Ti6Al4V5Cr alloy very useful in many commercial applications that require higher strength than Ti6Al4V alloy along with lightweight requirement.

The topological optimization of components by means of lattice structures allows to reduce their weight avoiding a loss in the mechanical performance. Often the lattice parts are integrated in a more complex geometry, and they present an interface with a solid part. In the present paper, the mechanical and microstructural characterization of Ti6Al4V lattice structures with body-centered cubic unit cell was carried out. Samples with and without an external solid shell were designed and produced with electron beam powder bed fusion in order to investigate the behavior of these complex structures, especially at the interface between the solid and lattice parts. The microstructure and defects were analyzed, and compression tests were performed on the samples with and without solid shell to understand the influence of the solid part and its interaction with the lattice structure. After the fracture and detachment of the shell, the same behavior for both set of samples was observed. Finally, a finite element model was defined to better understand the mechanical behavior of the investigated structures. The nominal sample stiffness was significantly higher than the experimental one. This discrepancy can be attributed to local defects, both in terms of porosities and deviations from ideal geometry. [ABSTRACT FROM AUTHOR]

In this paper, the influences of two post-heat treatments on the structural, mechanical and corrosion resistance properties of additively manufactured Ti6Al4V alloys were discussed in detail. The materials were produced using the laser engineering net shaping (LENS) technique, and they were subjected to annealing without pressure and hot isostatic pressing (HIP) under a pressure of 300 MPa for 30 min at temperatures of 950 °C and 1050 °C. Annealing without pressure led to the formation of a thin plate structure, which was accompanied by decreasing mechanical properties and increasing elongation and corrosion resistance values. For the HIP process, the formation of a thick plate structure could be observed, resulting in the material exhibiting optimal mechanical properties and unusually high elongation. The best mechanical and corrosion resistance properties were obtained for the material subjected to HIP at 950 °C. [ABSTRACT FROM AUTHOR]

The phenomenon of hydrogen embrittlement (HE) in metals and alloys, which determines the performance of components in hydrogen environments, has recently been drawing considerable attention. This study explores the interplay between strain rates and solute hydrogen in inducing HE of Ti6Al4V alloy. For the hydrogen-charged sample, as the strain rate was decreased from 10−2/s to 10−5/s, the ductility decreased significantly, but the HE effect on mechanical strength was negligible. The low strain rate (LSR) conditions facilitated the development of high-angle grain boundaries, providing more pathways for hydrogen diffusion and accumulation. The presence of solute hydrogen intensified the formation of nano/micro-voids and intergranular cracking tendencies, with micro-crack occurrences observed exclusively in the LSR conditions. These factors expanded the brittle hydrogen-damaged region more deeply into the interior of the lattice. This, in turn, accelerated both crack initiation and intergranular crack propagation, finally resulting in a considerable HE effect and a reduction in ductility at the LSR. The current study underscores the influence of strain rate on HE, enhancing the predictability of longevity and improving the reliability of components operating in hydrogen-rich environments under various loading conditions. [ABSTRACT FROM AUTHOR]

While titanium nitride (TiN) coatings are well known for their biocompatibility and excellent mechanical properties, their wear particle and debris release in orthopedic implants remains a matter of active investigation. This study addresses the efficacy of TiN coatings on CoCrMo and Ti6Al4V alloys to enhance wear resistance and reduce ion release from prosthetic implants. Three different coating variants were utilized: one variant deposited using arc evaporation (Arc) followed by post-treatment, and two variants deposited using high-power impulse magnetron sputtering (HiPIMS) with or without post-treatment. The coatings' performance was assessed through standard wear testing against ultra-high-molecular-weight polyethylene (UHMWPE) in bovine serum lubricant, and in the presence of abrasive PMMA bone cement particles in the lubricant. The results indicated that Arc and HiPIMS with post-treatment significantly reduced wear and eliminated detectable metal ion release, suggesting that these coatings could extend implant longevity and minimize adverse biological responses. Further long-term simulator and in vivo studies are recommended to validate these promising findings. [ABSTRACT FROM AUTHOR]

In the present work, a hybrid modular machining technology was designed for machining of Ti6Al4V alloy. Ultrasonic machining was integrated with vortex tube based spot cooling system with CO2 gas as working fluid for achieving the cumulative advantage of both, which is termed as Spot Cooled Vibration Assisted Turning (SCVAT). Its performance is evaluated and compared with Conventional turning, Vibration Assisted Turning and Vortex tube based spot cooling under constant machining conditions. The vibration and cooling parameters were also kept constant wherever applicable. The results showed a significant reduction in cutting temperature (30.98%), surface roughness (65.97%), and tool wear (75.03%); however, cutting forces are increased slightly compared to dry cutting. Compressive surface residual stresses were generated on the machined surface in SCVAT. [ABSTRACT FROM AUTHOR]

Additive manufacturing, particularly the laser powder bed fusion (LPBF) technique, has ushered in a new era of intricate metallic component fabrication, leveraging the exceptional performance of the Ti6Al4V alloy. However, the intricate mechanical behavior of additively manufactured Ti6Al4V, particularly its anisotropic attributes stemming from non-equilibrium microstructures, presents a formidable challenge. In this study, we embark on a comprehensive exploration of the anisotropic mechanical properties exhibited by LPBFed Ti6Al4V alloy. The interplay between microstructure and tensile response is unraveled by integrating experimental investigations with crystal plasticity finite element (CPFE) simulations. The acquired empirical data with CPFE model predictions are harmonized through systematic tensile tests along distinct processing orientations. The results unveil the genesis of plastic anisotropy within the LPBFed Ti6Al4V alloy, ascribed to the emergence of columnar grains meticulously aligned along the building direction, despite the intricate material microstructure inherent to additive manufacturing. These findings collectively furnish a holistic comprehension of the intricate nexus between material attributes and the mechanical manifestations intrinsic to metal components realized through additive manufacturing modalities. [ABSTRACT FROM AUTHOR]

This study presents a methodology to fabricate Ti6Al4V cylindrical compacts with a highly porous core and dense shell with the aim to mimic the bone microstructure. Compacts with different core diameters were obtained via conventional pressing and sintering. Large pores were created with the aid of pore formers. Dilatometry was used to determine the sintering kinetics, while X-ray computed tomography was used for characterization. Also, the permeability was evaluated on the 3D microstructure, and the mechanical strength was evaluated via compression tests. The results indicated that sintering was constrained by the different densification rates of the porous and dense layers. However, defect-free compacts were obtained due to neck bonding between the Ti6Al4V particles. Large pores were located in the designed core with a similar pore size distribution. The permeability increased following a power law as a function of the pore volume fraction. The porous core drove the stiffness of the bilayer components, while the combination of both layers increased their strength. The bilayer materials showed permeability (1.36 × 10−10 m2), mechanical properties (E = 6.83 GPa and σy = 299 MPa), and admissible strain (σy/E = 43 × 10−3) similar to those of human bones. [ABSTRACT FROM AUTHOR]

In this study, selective laser melting (SLM) technology was utilized to fabricate Ti6Al4V and TiC/Ti6Al4V composites. We then investigated the effect of the solution heat treatment temperature and aging time on the microstructural and mechanical properties of both the Ti6Al4V alloy and the TiC/Ti6Al4V composites. The findings showed that with an increase in the solution heat treatment temperature, the acicular martensite in the matrix of the Ti6Al4V alloy and the composites progressively transitioned into the plate-bar α phase. Concurrently, there was a distinct irregularity in the morphology of the β columnar grain boundaries, accompanied by an evenly enhanced and distributed β phase. With respect to hardness, the microhardness of Ti6Al4V initially displayed a slight drop with an increase in the solution temperature, followed by a significant increase, reaching a peak of 430 HV. In contrast, the composite materials exhibited an initial minor increase in microhardness followed by a substantial surge, with a maximum value of 607 HV. Post the aging treatment, the microhardness of the composite samples was observed to decrease from 463.2 HV to 362.7 HV. The aging time had a notable influence on the α + β structure, where the size of the martensitic α phase was constrained by the size of the β phase. This study revealed that an extension in the aging time resulted in an increased size of the strengthening phase, subsequently leading to a substantial reduction in the composite’s microhardness. This underscored the pivotal role of aging time in defining the mechanical properties of the composites.

Laser-directed energy deposition (L-DED) utilizes a high-power laser and coaxial powder feed to rapidly fabricate high-quality components with intricate structures. However, the complex interaction between the powder stream and laser beam is not yet fully understood. Particularly, the morphological evolution of the droplets after powder melting is closely related to the quality of component formation. In this study, the dynamical mechanism of the aggregation and evolution of molten powder after laser–powder interaction was investigated. The Ti6Al4V powder flow was observed at various laser powers using a high-speed camera. Imaging of the molten droplets at approximately 50,000 frames·s−1 was conducted, depicting the aggregation of molten powder into droplets of different sizes and shapes, mainly consisting of spherical and ribbon droplets, after laser–powder interaction. A transient numerical model was established with consideration of the mutual influence of gravity, recoil pressure, and surface tension, depicting the temporal evolution of the temperature field and droplet morphology. The simulation results indicated that the balance between the surface tension, gravity, and recoil pressure determined the morphological evolution of the molten droplets. When spherical and ribbon droplets fell into the molten pool, the maximum velocities within the pool increased by 24 % and 69 %, respectively. This phenomenon reduced the stability of the molten pool to a certain extent and affected the print quality of the part. This study deepens our comprehension of the dynamic mechanisms of Ti6Al4V alloy powder melting evolution, providing invaluable insights for optimizing L-DED processes.

Titanium alloys are broadly used in the medical and aerospace sectors. However, they are categorized within the hard-to-machine alloys ascribed to their higher chemical reactivity and lower thermal conductivity. This aim of this research was to study the impact of the dry-end-milling process with an uncoated tool on the produced surface roughness of Ti6Al4V alloy. This research aims to study the impact of the dry-end milling process with an uncoated tool on the produced surface roughness of Ti6Al4V alloy. Also, it seeks to develop a new hybrid neural model based on the training back propagation neural network (BPNN) with swarm optimization-gravitation search hybrid algorithms (PSO-GSA). Full-factorial design of the experiment with L27 orthogonal array was applied, and three end-milling parameters (cutting speed, feed rate, and axial depth of cut) with three levels were selected (50, 77.5, and 105 m/min; 0.1, 0.15, and 0.2 mm/tooth; and 1, 1.5, and 2 mm) and investigated to show their influence on the obtained surface roughness. The results revealed that the surface roughness is significantly affected by the feed rate followed by the axial depth. A 0.49 µm was produced as a minimum surface roughness at the optimized parameters of 105 m/min, 0.1 mm/tooth, and 1 mm. On the other hand, a neural network having a single hidden layer with 1–20 hidden neurons, 3 input neurons, and 1 output neuron was trained with both PSO and PSO–GSA algorithms. The hybrid BPNN–PSO–GSA model showed its superiority over the BPNN–PSO model in terms of the minimum mean square error (MSE) that was calculated during the testing stage. The best BPNN–PSO–GSA hybrid model was the 3–18–1 structure, which reached the best testing MSE of 3.8 × 10−11 against 2.42 × 10−5 of the 3–8–1 BPNN–PSO hybrid model.

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.