Titanium Alloy Ti6Al4V Research Articles

The influence of laser texturing on the tribological behavior of titanium alloy Ti6Al4V in medical applications

This paper analyzes the tribological behavior of the Ti6Al4V ELI alloy subjected to laser texturization for medical purposes. Laser texturing enables one to observe specific patterns of the material surface at established depths. Microtexturing of the samples was performed using a 355 nm picosecond laser. The influence of the microtexturing process (depending on the process parameters) on the geometric parameters of the proposed laser texturing pattern was evaluated. Selected samples were subjected to tribological testing using the ball-on-plate technique in dry and lubricant-sliding methods (in Ringer solution). The wear properties were evaluated by comparing the coefficient friction, wear volumes, and wear ratio. A scanning electron microscope characterized the morphologies of the wear scar and the wear mechanism. The experimental results show that the surface texturing and the changes in microgrooves can reduce wear. The results indicate, that samples after laser texturing were characterized by 15% higher microhardness, compared to those in the initial state. It was found, a 26% reduction in friction coefficient and 29% in the wear volume compared to the smooth, untextured surface samples under lubricated conditions. The decrease in value of the coefficient friction and wear volume for the samples after the laser texturing process is an effect of synergistic of entrapped wear debris in micro-grooves and increased hardness for samples after laser textured.

Effect of heat treatment on microstructures and properties of vacuum laser welding Ti–6Al–4V titanium alloy

Vacuum laser welding of titanium alloys is currently being explored for use in UAVs and military-related fields, but the impact of post-weld heat treatment has been seldom studied. In this paper, the Ti–6Al–4V titanium alloy was welded by vacuum laser welding(VLW)with IPG 50 kW fiber laser, and analyze the microstructure and properties of the welds in as-welded state and post-welding heat treatment (850 °C/2h/FC(FC:furnace cooling)and 980 °C/10min/FC+720 °C/2h/FC).The results show that the microstructure of the as-welded weld is composed of primary columnar crystal (primary β phase) and grain boundary martensite (α′), and the microstructure of primary columnar crystal is composed of α'+ (α'+β). The proportion of high-angle grain boundary(HAGB) is 92.3%. The tensile strength is 1009 MPa, and the elongation is 9.3%. The average impact toughness at room temperature is 13J. The weld microstructure at 850 °C/2h/FC is composed of the acicular α phase and the α+β between the acicular α phases, the primary columnar crystals basically disappear, and the acicular α phases criss-cross weave into the net basket structure.The proportion of HAGB is 97.4%.The tensile strength is 988.3 MPa,and the elongation is 14.8%. The average impact toughness is 17J. The microstructure of the weld at 980 °C/10min/FC+720 °C/2h/FC is composed of the coarser acicular α phase and the (α+β) between the coarser acicular α phases. The proportion of HAGB is about 83.2%. The tensile strength is 586 MPa, and the elongation is 1.6%. The average impact toughness is 1.4J.

The oil lubricated fretting wear behavior under different sliding displacements and frequencies of Ti6Al4V titanium alloy as affected by micro-shot peening

The fretting wear behavior under oil lubricants is of great practical significance since oil is usually used to regulate fretting regime for minimizing wear. In this study, micro-shot peening (MSP) was performed on Ti6Al4V titanium alloy, in which 0.6 MPa injection air pressure, 60 s shot time and high-speed steel particles with an average diameter of 50 μm were used. Surface topography, microstructure, hardness and compression residual stress of test samples were examined. Oil lubricated fretting wear tests were then conducted between titanium alloy sample and GCr15 counterbody under different sliding displacements and frequencies. The test results show that the surface structure of MSP treated samples experienced severe plastic deformation, the surface hardness was increased from 310.8 HV to 433.5 HV, and a compression residual stress of −303.5 MPa was introduced within surface layer. Moreover, MSP treatment reduced the coefficients of friction through producing a micro-dimpled surface. Thereby, the fretting wear resistance of MSP treated sample under oil lubricated condition was improved. By comparison, at higher sliding displacement and frequency, the ability of MSP treatment to resist fretting wear was improved more significantly since more better lubricating effect can be obtained. Fretting damage of untreated sample under oil lubrication was mainly attributed to fatigue wear, delamination wear, abrasive wear and oxidation wear, while that of MSP treated sample was mainly regional peeling off and abrasive wear.

Microstructural effects and constitutive modelling of cyclic softening behaviour in Ti–6Al–4V titanium alloys

Cyclic softening in Ti–6Al–4V titanium alloy significantly influences the reliability and performance of critical engineering components. This study addresses the lack of a comprehensive understanding of cyclic softening in different microstructures of Ti–6Al–4V titanium alloys. Microstructures with bimodal and lamellar morphologies were prepared by heat treatment of Ti–6Al–4V titanium alloy at various temperatures. Interrupted low-cycle fatigue tests revealed a larger cyclic softening for the bimodal microstructures than the lamellar microstructures. Finite element analysis (FEA) captured the cyclic softening by incorporating the Voce isotropic hardening model with the Chaboche kinematic hardening model. Two nonlinear kinematic hardening terms, along with the Voce isotropic hardening model whose parameters were calculated using the variation in cyclic yield strength and cyclic stress amplitude resulted in good prediction for bimodal and lamellar microstructures, respectively. The accuracy of the model is further improved when a linear kinematic term is added to it. Transmission electron microscope, electron backscatter diffraction, and energy dispersive spectroscopy analysis revealed that the extensive softening in the bimodal microstructure is associated with the dislocation localization in the primary alpha (αp) leading to a considerable plastic strain accumulation and subsequent crystal re-orientation. The alloying element partitioning, lamella width, and the ease of slip transmission at the secondary alpha (αs) and beta (β) interface also play essential roles in the cyclic softening.

Electrochemical Studies of The Corrosion Resistance of Bismuth Titanate Thin Films Deposited by RF Sputtering

Thin films of bismuth titanate were grown on stainless steel (316L) and titanium alloy (Ti6Al4V) substrates using the magnetron sputtering technique. The surface morphology of these films was observed with a scanning electron micrograph (SEM). The electrochemical studies used to evaluate the corrosion resistance of the substrate-coating set were the potentiodynamic polarization (Tafel) tests and electrochemical impedance spectroscopy (EIS), both done in a solution of NaCl (3%) as an electrolyte. The SEM showed that the morphology of the coatings grown on a titanium alloy Ti6Al4V substrate was generally homogeneous with a smooth surface but with unmelted material in some regions, while the morphology of the thin films grown on stainless steel 316L was mainly granular, with the presence of a few holes or craters. The potentiodynamic polarization curves showed that the corrosion resistance of the coated samples was better than that of the bare substrate because the corrosion current obtained from the coated samples was lower by two orders of magnitude than that exhibited by the uncoated substrates, and in addition, the corrosion potential of the coated samples was greater than that of the bare substrate. The EIS test showed the presence of a passive thin film of titanium oxide on the titanium alloy substrate.

Microstructure and mechanical properties of Ti6Al4V/W bimetallic structure via selective laser melting

The titanium alloy Ti–6Al–4V (TC4) and tungsten (W) possess excellent complementary properties that would be useful for a wide range of industrial applications if they could be suitably combined. Selective laser melting was applied to prepare TC4/W specimens with a bimetallic structure. A strong bond without interfacial macrocracks was obtained by adjusting the laser line energy density to <0.75 J/mm. The bond interface of the bimetallic structure reached a microhardness of 503 ± 20 HV, which was harder than that of the two base materials, and the transverse and longitudinal ultimate compressive strengths were 1510 ± 40 MPa at strains of 20%–22.5%. Three-point bending experiments showed that when TC4 was used as the base material, the flexural strength of the specimen was 2210.5 ± 44.5 MPa. The high strength of the bond interface was attributed to sufficient agitation of the molten pool and reinforcement by fine crystalline grains. The agitation was provided by the melting and elemental diffusion of TC4 owing to the high energy input during the formation of W, and the fine crystalline grains were obtained by the dispersed W particles providing multiple nucleation sites for liquid TC4. The bimetallic structure retained the strength of W and toughness of TC4, which bodes well for its industrial application.

Surface structure evolution and measurement analysis of Ti6Al4V titanium alloy by electric arc electrochemical machining

In this study, a theoretical model about the conversion mechanism of material removal by electric arc electrochemical machining (EAECM) was derived. The limiting conversion rate of ECM-EAECM was measured on this basis. The current waveform, surface integrity, shape accuracy and process indexes during machining were measured and evaluated. The results showed that when the limiting conversion rate of ECM was exceeded, the material removal consisted of alternating effects of electric arc machining (EAM) and ECM. The proportion of EAM increased and the surface structure evolved into discharge defects, verifying the correctness of the theory. In addition, parametric crossover experiments were performed to clarify the degree of parametric response to EAECM modulation. Finally, the optimal combination of parameters resulted in a material removal rate of up to 5452 mm3/min, a relative electrode wear rate of 1.39 %, and a surface roughness of only 4.62 μm.

The residual stress state in meso- and micro-milling processes with a ball-end mill in Ti–6Al–4V titanium alloy

An experimental investigation and comparative analysis of the residual stress state between micro- and meso-milling processes with a ball-end mill on the Ti–6Al–4V titanium alloy were carried out. A methodology to study the characteristic kinematics of a five‑axis machining process in a three-axis vertical machining centre was proposed. The study considers the chip formation process according to the lead and tilt angles of the tool axis concerning the normal vector of the surface. When using the up‑milling cutting strategy, the defect of smeared/adhered material to the surface occurs in both the micro- and meso-milling levels, associated with the build-up edge and build-up layer phenomenon. The residual stress tensor of the surface was obtained through the X-ray diffraction technique. The down-milling cutting strategy produced the best surface finish and higher compressive residual stresses. The experiments showed higher compressive residual stresses in the feed direction than in the cross-feed direction. The micro-milling process produced higher compressive residual stresses than those observed in the meso-milling process.

Electron-Beam Welding of Titanium and Ti6Al4V Using Magnetron-Sputtered Nb, V, and Cu Fillers

In this work, the results of an investigation of electron-beam-welded samples of commercially pure titanium (CP-Ti) and the titanium alloy Ti6Al4V (Ti64) using fillers of various beta-stabilizing elements (Nb, V, Cu) are presented. The fillers were in the form of deposited layers on each of the two specimens via DC magnetron sputtering. The specimens were then subjected to electron-beam welding (EBW) under the same technological conditions. The structure of the obtained welded joints was investigated by scanning electron microscopy (SEM). X-ray diffraction (XRD) was used to investigate the phase composition of the fusion zone (FZ). The study of the mechanical properties of the samples was carried out via tensile tests and microhardness measurements. The results showed a different influence of the used fillers on the structure and properties of the obtained joints, and in all cases, the yield strength increased compared to the samples welded using the same technological conditions without the use of filler material. In the case of using Nb and V as a filler, the typical transformation of titanium welds into elongated αTi particles along with α’-Ti martensitic structures was observed. The addition of a Cu filler into the structure of the welds resulted in a unification and refining of the structure of the last, which resulted in the improvement of the mechanical properties of the weld, particularly its ductility, which is a known issue where electron-beam welding is concerned.

The numerical simulation of a new biomimetic silicone layer component of total knee prosthesis

The knee osteoarthritis requires the latter joint replacement by a total knee prosthe-sis (TKP). Generally, this prosthesis consists of three parts; a femoral component in CoCrMo cobalt alloy, a tibial insert in polyethylene, and a tibial tray in titanium alloy Ti6AL4V. This type of prosthesis is not 100 % comfortable, after years of implantation, the tibial insert (polyethylene) degrades and gives more wear debris, which affects the bio-functionality of this prosthesis and the patient life. In this study, two models of total knee prosthesis are designed and analyzed using SolidWorks and Ansys software, the first model is the existing three-part prosthesis, and the second model is based on the theory of Mooney – Rivlin method prosthesis with a new layer of silicone component. In this paper, shock simulation of a free fall from a height of 75 cm is studied. The results of the displacement comparison between the first model 0.039 mm, and the second model 1.41 mm. In comparison with the contraction of the biological knee joint show that the second model has a contraction closer to the biological knee. It can be deduced that this total knee prosthesis has a hyper-elastic behavior closer to the behavior of a biological knee as well, which gives more stability and provides a cushioning role for the knee compared to the existing TKP.

Characterization of friction behavior under cryogenic conditions: Ti–6Al–4V

Friction phenomena at the chip/tool/workpiece interfaces during machining of material impacts significantly the cutting process. In this article, the effect of friction conditions (dry, emulsion, cryogenic) on the tribological performance of uncoated tungsten carbide tools is investigated when machining titanium alloy Ti–6Al–4V. Friction tests were conducted to analyze the impact of sliding speed and cooling on the evolution of the friction coefficient. To determine the real friction coefficient (adhesive friction coefficient), a numerical simulation using the Lagrangian method was employed. After a comparative study of various simulation methods (“Lagrangian”, “CEL”, and “ALE”), the Lagrangian method was identified as the most relevant. The obtained results reveal that an increase of sliding velocity significantly influences the friction coefficient. Additionally, the application of cryogenic fluid (LN2) reduces the friction coefficient compared to both dry and emulsion-based friction. Adhesion phenomena play a crucial role in the nature of the contact, especially at high sliding velocities.

Optimization of laser-texturing process parameters of Ti6Al4V alloys using metaheuristic algorithms

Manufacturing microscale textures can reduce friction and wear compared with smooth surfaces. In laser surface texturing, the resulting texture geometry is directly affected by laser parameters such as laser power, scanning speed and overlap rate. Therefore, finding the optimal parameter settings to improve the process performance is crucial. One of the biggest challenges encountered during the optimization stage is accurately determining the functional relationship between surface quality and process parameters. Another significant problem is solving the nonlinear equation system. This study aims to investigate the effect of laser-textured surfaces on the tribological behavior of titanium Ti6Al4V. Optimization of laser texture process parameters using metaheuristic algorithms is a hot topic. The first contribution of this study is the modeling of the contact angle, kurtosis and skewness quality parameters of Ti6Al4V titanium alloy based on the polynomial curve fitting method as a function of laser power, laser speed and overlap rate. Another significant contribution is to optimize the proposed nonlinear regression models using metaheuristic approaches such as genetic algorithm, particle swarm optimization, whale optimization algorithm, gray wolf optimization, equilibrium optimizer, teaching-learning-based optimization, student psychology-based optimization (SPBO), slime mould algorithm and social network search. The reason for using many metaheuristics is to test the effectiveness of different metaheuristic methods in solving this problem. Analysis of variance was performed to evaluate experimental data and compare the success of optimization methods. The results revealed that the proposed metaheuristic methods can be applied to the related problem. It has been observed that the methods give identical results. Among these methods, the SPBO method provided the best performance in the optimization of all laser output parameters.

Mechanical properties and microstructure evolutions of deposited Ti–6Al–4V titanium alloy under short-term stress relaxation at elevated temperatures

This study investigates the stress relaxation behavior and associated microstructure evolution in laser melted deposited Ti–6Al–4V alloy under various temperature and pre-strain conditions for the first time. A set of stress relaxation and tensile tests has been performed to characterize the stress and strength evolution properties of the as-deposited alloy, and microstructural analysis has also carried out for mechanisms identification. It is found that the as-deposited alloy exhibits a lower threshold stress (less than 10 MPa), faster relaxation rate, and a more significant decrease in strength (9.9%∼15.8%) when compared with the same testing conditions of conventionally extruded alloy. Based on the microstructural evolutions, as well as the stress exponent analysis, the stress relaxation mechanisms have been identified: at low pre-strain and temperature (700 °C and 0.5%), diffusion creep plays the dominant role, while with the increasing pre-strains and temperatures, the mechanism transits to dislocation climb, and eventually to grain boundary sliding, at 750 °C and 10%. It is observed that the fine lamellae in the as-deposited alloy are susceptible to morphological changes during relaxation, including dislocation rearrangement, lamellae spheroidization and coarsening. These microstructural evolutions lead to the creep mechanism transitions, as well as the noticeable reduction in yield strength after relaxation. The results could provide insights into designing appropriate stress relaxation parameters for deposited alloys in hybrid additive manufacturing processes.

On interaction between laser and Ti6Al4V titanium alloy

On interaction between laser and Ti6Al4V titanium alloy

Synthesis and characterization of poly (methyl methacrylate)/ silver-doped hydroxyapatite dip coating on Ti6Al4V

This study intends to analyze the properties and potential applications of a novel composite coating composed of poly (methyl methacrylate) (PMMA) and silver-doped hydroxyapatite (HAPAg) produced from waste eggshells, which was dip-coated onto Ti6Al4V substrates. Medical implants frequently made of the titanium alloy Ti6Al4V can benefit greatly from surface coatings in terms of biocompatibility and performance. In order to add antibacterial and osteoconductive characteristics, silver-doped hydroxyapatite nanoparticles were dispersed within a PMMA matrix to create the PMMA/HAPAg composite coating. The coated samples report an average contact angle (CA) between 70 and 750 and total surface free energy (SFE) between 35 and 50 mJ/m2, which signifies its improved wettability. The 7.03% change in hydrophilicity was observed between PMMA/H0 (75.270 ± 1.690) and PMMA/H20 (700 ± 1.440) coated samples. The increase in adhesion strength and coating thickness with the increase in HAPAg reinforcement was observed. The surface morphology of the defective zones was examined using scanning electron microscopy (SEM), and information on the elemental composition of synthesized was obtained using Inductively Coupled Plasma Mass Spectroscopy (ICPMS), Fourier Transform Infrared spectroscopy (FTIR) and X-ray diffractogram (XRD). Atomic force microscopy (AFM) reveals the surface roughness; root mean square roughness, roughness profile, skewness and kurtosis of the coated samples. The contact angle reports the hydrophilicity and SFE. Finally, the results conclude that the composite coating had a consistent distribution of HAPAg nanoparticles incorporated within the PMMA matrix. The minimal presence of Ag ions on the surface indicates the coating's potential antibacterial properties, and it is highly recommended for dental applications.

Parameters Influencing the Fatigue Behavior of Ti6Al4V

The fatigue strength of components is affected by loading and environmental conditions, their geometry, the material and the manufacturing process adopted for their production. As a consequence of local stress concentrations, fatigue cracks can propagate to failure from the defects created by the manufacturing processes or introduced during the service life, as occurs in impact-damage. Ti6Al4V titanium alloy is commonly used in the aeronautical sector and other engineering applications due to its high specific strength. The study of the fatigue behavior of Ti6Al4V is therefore critical for designing reliable and durable structures. The work reports a synthesis of the results present in the literature for the fatigue behavior of Ti6Al4V in inert and aggressive environments, in the presence of a deposited coating, in the case of impact-damage, when components are produced by additive manufacturing and in the absence of solution treatment and over-aging.

Study of the Influence of Coating Roughness on the Properties and Wear Resistance of Electrospark Deposited Ti6Al4V Titanium Alloy

The present work is concerned with studying surface parameters of coatings deposited to titanium alloy Ti6Al4V by electrospark deposition (ESD) with hard alloy depositing electrodes based on WC, TiC and TiCN. The variation of roughness parameters, composition, structure and tribological characteristics of coatings as a function of ESD mode parameters was investigated. The influence of the mode parameters on the main coating roughness parameters (Ra, Rz, Rmax, Rpk, Rk, Rs, Rsk, Rku (ISO 21920-2:2021) was analysed, the values of which can be used to determine the load bearing capacity and wear resistance. The results of the tribological tests showed that within the test range, the roughness of the coatings has a controversial influence on their frictional wear performance. As the roughness parameters increase to Ra=3÷3.5 µm, the relative wear resistance of the coated surfaces also increases, reaching values up to 4÷5 µm for the electrodes used and no significant changes in the wear mechanism were observed. However, increasing coating roughness above Ra=3.5 to 5 µm results in a monotonic decrease in relative wear resistance to 2.5÷3 times. Possible ways to reduce the surface roughness and increase the wear resistance of coatings were presented.

Determining the influence of technological parameters of electron beam surfacing process on the microstructure and microhardness of Ti-6Al-4V alloy

This paper reports the devised technology and equipment for manufacturing parts and assemblies with pre-defined properties by 3D printing methods. Underlying the technology is the application of a high-power electron beam to fuse metal powder in a vacuum chamber with the formation of successive layers that repeat the contours of the digital model of the product. The object of research is the process of surfacing products made of Ti6Al4V titanium alloy powder. The influence of technological parameters (speed and power of the electron beam) on the formation of the structure of the deposited metal and its mechanical properties was investigated. 3 samples printed under 3 modes were studied: beam speed, 270, 540, and 780 mm/s; power, 240, 495, and 675 W, respectively. The beam energy density was 44.5 J/mm3; the trajectory displacement step was 0.2 mm; the dynamic focusing current Idf was –0.31 A; and the powder layer thickness was 0.1 mm. The samples were examined by conventional methods. The structures were studied using an optical microscope, images were recorded with a camera. The Vickers hardness was measured with a microhardness meter in the direction from the technological supports to the surface of the sample, as well as along the surface of the product, and in the layers of the middle part of the sample. It was established that the articles had a dense cast structure of surfaced metal. On all samples, large crystallites with a uniform lamellar-acicular structure of α´-phase with a small amount of β-phase are formed along the height, mostly without defects with uniform microhardness both along the height and along the surface. It was determined that the surfacing mode at beam speed, 240 mm/s; power, 270 W is the most rational for practical use. Under this mode, a stronger structure is formed when it is crushed, reducing the width of the crystallites by 1.55 and 1.17 times compared to other modes

Influence of bonding time during diffusion bonding of Ti–6Al–4V to AISI 321 stainless steel on metallurgical and mechanical properties

Diffusion bonding was employed to join AISI 321 stainless steel to Ti–6Al–4V titanium alloy via Cu–Zn foil as the interlayer. The influence of bonding time (30, 45 and 60 min) at 900 °C temperature with the pressure of 2 MPa on the microstructural and mechanical behaviors of the joints is evaluated. The optical and scanning electron microscopes were utilized to examine the microstructural characteristics of the Ti–6Al–4V/Cu–Zn/AISI 321 stainless steel joints. Results displayed that three distinct reaction layers have been created as a result of the brazing process at all joints. It was also found that a longer bonding time led to the widening/expanding of the reaction/diffusion layers. The attained data also showed that bonding time affected the formation of brittle IMCs including CuTi2, CuTi, FeTi, Fe22Zn78 and TiZn3 phases within the interface as a result of the increased diffusivity of reaction elements and subsequently resulted in the reduction of the shear strength of the diffusion bonded joints from 281 MPa for bond made at 30 min to about 174 MPa for bond made at 60 min. Decreasing the shear strength by rising the bonding time can be a sign of expanding the level of interfacial reaction at the joints.

Effects of Shot Peening and Electropolishing Treatment on the Properties of Additively and Conventionally Manufactured Ti6Al4V Alloy: A Review.

This literature review indicates that the basic microstructure of Ti6Al4V is bimodal, consisting of two phases, namely α + β, and it occurs after fabrication using conventional methods such as casting, plastic forming or machining processes. The fabrication of components via an additive manufacturing process significantly changes the microstructure and properties of Ti6Al4V. Due to the rapid heat exchange during heat treatment, the bimodal microstructure transforms into a lamellar microstructure, which consists of two phases: α' + β. Despite the application of optimum printing parameters, 3D printed products exhibit typical surface defects and discontinuities, and in turn, surface finishing using shot peening is recommended. A literature review signalizes that shot peening and electropolishing processes positively impact the corrosion behavior, the mechanical properties and the condition of the surface layer of conventionally manufactured titanium alloy. On the other hand, there is a lack of studies combining shot peening and electropolishing in one hybrid process for additively manufactured titanium alloys, which could synthesize the benefits of both processes. Therefore, this review paper clarifies the effects of shot peening and electropolishing treatment on the properties of both additively and conventionally manufactured Ti6Al4V alloys and shows the effect process on the microstructure and properties of Ti6Al4V titanium alloy.