Ti6Al4V Sheets Research Articles

Controlled surface modification of Ti6Al4V using biomimetic mineralization via thermo-chemical route improves bioactivity

Ti alloy (Ti6Al4V) sheets were bio-activated by a two-step thermo-chemical treatment followed by biomimetic mineralization. The samples were then characterized by standard techniques and evaluated of their mechanical properties, electrochemical corrosion potential and biological performance. The intermediate layer corresponding to thermo-chemical treatment displayed anatase TiO2 peaks and the final bio-mineralization resulted in a globular hydroxyapatite (HAP) layer. Thermo-chemical treatment yielded a two-fold increase (98.79% increment) in microhardness value, whereas, the biomimetically activated samples showed a very small decrease in the same owing to their ceramic behavior. The surface hydrophobicity of the bio-activated surface was found reduced significantly, might assist to facilitate improved cell adhesion. Electrochemical corrosion measurements exhibited an increase in corrosion potential and decrease in current density of the samples, suggested increased corrosion resistant. The surface coating on the Ti6Al4V sheet also demonstrated enhanced cytocompatibility as no toxic effect of the samples could be perceived to human keratinocyte cell line (HaCaT). Similarly, the samples showed higher hemocompatibility and enhanced bactericidal activity. Our study concluded that the surface coating of Ti6Al4V sheets significantly improved corrosion resistance and bioactivity of the substrates, which can be applied for various biomedical applications.

The effect of aluminum interlayer on weld strength, microstructure analysis, and welding parameters optimization in resistance spot welding of stainless steel 316L and Ti6Al4V titanium alloy

Stainless steel (SS) and Titanium alloy (Ti) are the most commonly used materials in many industrial fields such as the automotive and aerospace industry. Stainless steel has good corrosion resistance and titanium alloy has an extremely lightweight characteristic. The combination of both materials has become a tremendous innovation in the industrial sector. Resistance spot welding which has commonly applied in many industrial fields is a good consideration to join these two dissimilar materials due to the high efficiency that could be achieved by using this method. However, the way of joining these dissimilar materials should be carefully considered due to the significant difference in mechanical properties between SS and Ti. In the present study, 3 mm of SS316L and Ti6Al4V sheets were joint under the resistance spot welding method with an aluminum interlayer. The optimized welding parameters were provided under the Taguchi method L9 orthogonal array along with the mechanical properties’ investigation. The optimum welding parameters were 11 kA of weld current, 30 Cycles of welding time, and 5 kN of electrode force which produced 8.83 kN tensile-shear load of the joint. The mechanical structure analysis shows the different morphology between stainless steel and titanium interfaces and the intermetallic compound layer was formed on the SS/Al and Al/Ti interfaces. The EDX analysis shows the atomic diffusion-reaction on the application of aluminum as an interlayer on the SS/Ti joint.

Low-velocity impact perforation response of titanium/composite laminates: analytical and experimental investigation

The low-velocity impact perforation behavior of fiber-metal laminates (FMLs) is evaluated by analytical modeling. Four different FML layups consisting of glass fiber/epoxy layers and titanium alloy Ti–6Al–4V sheets are fabricated, exhibiting the same thickness of total metal layers. The perforation behavior, threshold, and energy absorption mechanisms of FMLs are assessed using a mass-spring system. The results indicate that the elastic–plastic force history of FMLs up to maximum force predicted by both membrane and bending strain energy (M & B) and membrane strain energy only (M only) is found to be in good agreement with experiments, with M only matches closely than both M & B. The principal part of the total energy absorption of FMLs with both M & B and M only accounts for the energy absorption associated with global deformation of titanium and glass/epoxy layers, which is 67–71% and 65–69%, respectively. Here, a higher percentage of energy is absorbed by FML 4/3–0.3, succeeding by FMLs 3/2–0.3(O), 3/2–0.4, and 2/1–0.6. The predicted perforation threshold and overall energy absorption by various damage mechanisms of FMLs are in good comparison with experiments. The perforation response has also been predicted for aluminum-based FMLs, agreeing well with experiments. This insists on the robustness of the offered model. Also, the perforation resistance seems to be higher for titanium-based FMLs than aluminum-based FMLs. The overall energy absorption seems to be higher for titanium-based FMLs under low-velocity impact than high-velocity impact. This is also observed in the case of aluminum-based FMLs.

Surface modification through sustainable micro-EDM process using powder mixed bio-dielectrics

ABSTRACT In this research, both eco-friendly and commercially available dielectric liquid (EDM oil, EDM oil + MoS2 powders (EDP), Sunflower oil (SF), and Sunflower oil + MoS2 powders (SFP)) was adopted to carry out the small area surface modification on Ti6Al4V sheet through the micro-EDM process. Brass rod (diameter: 0.95 mm) was used as the micro-tool electrode. The quality (surface roughness (Ra, Rq, Rz), recast layer (or coating) thickness (RLT), and the micro-hardness (MH)) of the coated surfaces was tested and compared with the change of input process parameters and dielectrics. The results indicate that the maximum micro-hardness of the coated layer for differently used dielectric mediums such as EDM oil, SF oil, EDP oil, and SFP oil is 495.9 HV, 619.05 HV, 665.42 HV, and 694.02 HV, respectively. Similarly, the coated layer thickness varies within the range of 4.56 to 24.42 μm (EDM oil), 7.24 to 28.31 μm (SF oil), 5.42 to 26.84 μm (EDP oil), and 4.66 to 32.75 μm (SFP oil). EDX plots suggest transfer of tool and the dielectric material (Ti, V, Al, C, Cu, Zn, Mo, S) to the substrate surface.

Extended anisotropy yield criteria applied to Ti6Al4V at a high range of temperatures and considerations on asymmetric behavior

Heat assisted-forming processes are essential for Ti6Al4V sheet metal forming due to the poor formability of this alloy at room temperature. Although there exist works on the stress-strain response at high temperature, there is a lack of data in the literature on the yield criteria. The present paper presents an efficient experimental methodology to determine significant stress states at high temperature. Both plane strain data and compressive anisotropy values at high temperature allowed obtaining a more complete definition of the mechanical behavior of the Ti6Al4V, being the novel contribution of this research. Yield loci up to 900 °C were built according to different yield criteria that are fitted to the experimental data. Thus, Barlat1989 and CPB2006 were selected as the most suitable yield criteria to predict Ti6Al4V behavior. These criteria were extended to contemplate the anisotropy evolution under a wide range of working conditions. The formulated extended criteria for the entire range of conditions were close to the equivalent traditional ones applied to only a particular condition, which demonstrates the advanced made in the comprehensive modeling of Ti6Al4V alloy for all conditions applied in forming industries.

Parametric Analysis of Laser Beam Percussion Drilling for Thin Titanium Alloy Sheet Using Yb: Yag Fiber Laser

Laser beam percussion drilling (LBPD) can create high density holes in aerospace materials with the repeated application of laser pulses at a single spot. In this study, one-parameter-at-a-time approach has been used to investigate the individual effect of peak power, pulse width and pulse frequency on geometrical accuracy and metallurgical distortion during LBPD of 0.85[Formula: see text]mm thick Ti–6Al–4V sheet using 200[Formula: see text]W Yb:YAG fiber laser. It has been found that the output parameters behave differently at the higher and lower values of a particular input process. The increase of pulse width from 1 to 1.50[Formula: see text]ms increases hole taper by 20% whereas the same corresponding change from 1.50 to 2.00[Formula: see text]ms reduces the taper by 20%. The increase of pulse frequency from 10 to 50[Formula: see text]Hz reduces hole circularity by 40% but the same proportionate change from 50 to 90[Formula: see text]Hz reduces circularity by 79%. Increase of peak power from 1.70 to 2.0[Formula: see text]kW increases hole taper by 8% but the corresponding increase from 2 to 2.30[Formula: see text]kW is 143%.

ANN modeling and multiobjective genetic algorithm optimization of pulsed laser welding of Ti6Al4V alloy sheets with various thicknesses

According to the high cost and time-consuming nature of laser welding experiments, repetition of one experiment in a wide range of data is not feasible; so, achieving unexperimented data can be interesting. Hence, the high precision predictability of artificial neural networks (ANN) seems useful. ANN is an intelligent approach to solve different problems. In this study, the experimental data belonging to the pulsed laser welding of two Ti6Al4V sheets, one of them with 1 mm thickness and the other with 1, 1.5, and 3 mm thicknesses, were used to predict the dimensions of the heat-affected zone (HAZ) and the maximum temperature. Moreover, 12 learning methods of a backpropagation network was utilized to select the best one. The Levenberg–Marquardt method had the best performance by considering the mean square error. According to the ANN results, when the laser focus is at the vicinity of workpiece’s surface, the maximum temperature and HAZ width are achieved. It should be also mentioned that increasing thickness and welding speed results in decreasing width of HAZ. By comparing the ANN and experimental results, the maximum relative error for the temperature and HAZ width was obtained equal to 8.62% and 8.22%, respectively. Therefore, ANN can be employed as a tool to develop experimental results and predict indeterminate values in unexperimented ranges with very high precision. Furthermore, in order to optimize the parameters of laser welding, the multiobjective genetic algorithm was used to reduce the HAZ width. The genetic algorithm specified that the HAZ width can be reduced to 0.24 mm by increasing the velocity and thickness.

Bioinspired oil‐soluble polymers based on catecholamine chemistry for reduced friction

AbstractReduction of friction and wear contributes significantly to energy saving for mechanical system as considerable energy has been consumed in various forms of friction worldwide. In the present study, two kinds of dopamine‐based oil‐soluble polymers were synthesized by atom transfer radical polymerization (DOPA‐BiBB‐pLMA) and photopolymerization (DOPA‐I2959‐pLMA), and modified onto the Ti6Al4V sheet by the “grafting to” method. The characterizations of nuclear magnetic resonance, Fourier transform infrared spectrum, water contact angle, and X‐ray photoelectron spectroscopy confirmed that the polymers were successfully grafted onto the Ti6Al4V surface. Additionally, a series of tribological tests were performed in oil environment using a universal materials tester under different experimental conditions. It was shown that the coefficient of friction using the Ti6Al4V sheets grafted by the dopamine‐based polymers was reduced by 23.5–46.2% compared with bare Ti6Al4V sheet. Furthermore, the wear depth and wear volume were also greatly decreased with the introduction of the dopamine‐based polymers. DOPA‐I2959‐pLMA showed slightly better lubrication enhancement than that of DOPA‐BiBB‐pLMA, which may be attributed to the relatively higher polymerization degree. In summary, a universal “grafting to” surface modification approach was proposed bioinspired by catecholamine chemistry, which remarkably reduced friction and wear of the tribopairs with the introduction of oil‐soluble polymers.

An experimental design of spot welding of Ti6Al4V sheets and numerical modeling approach

In this study, the traditional α–β titanium alloy Ti6Al4V sheets were joined by the resistance spot welding (RSW) process. RSW method was modeled numerically and investigated experimentally by using different welding parameters. In numerical modeling, material properties and process parameters were modeled with the finite element method (FEM), and simulations were realized in experimentally performed parameters. In order to validate and calibrate the developed numerical model, preliminary experiments were carried out and then Taguchi L9 orthogonal experimental design was determined to examine the effect of different parameters that are thought to be suitable for this process. The signal/noise (S/N) ratio was used to interpret the results in the determined experimental setup. The experimental study aims to validate the established numerical model and to obtain information such as the unpredictable strength of the welded joint through the numerical model. The experimental results were analyzed by using the Taguchi technique with the help of the Minitab software. In this study, electrode force, welding current, and welding time parameters were determined as the control factors, and the effect of these factors on the results was found using analysis of variance (ANOVA). Lastly, verification tests were performed, and it was determined that optimization was applied successfully.

Deformation and Microstructural Analysis of Fiber Laser and TIG Welding of Thin Ti6Al4V Sheet by Coordinate Measurement Machine (CMM)

This paper reports on a study to compare the mechanical and deformation properties of Ti6Al4V titanium alloy joints between a pulsed fiber laser source and a tungsten inert gas (TIG) welding. Ti6Al4V alloy sheets - 0.8 mm thick-deformation modifications were investigated via a 3D laser scanner integrated to a portable-arm Coordinate Measurement Machine (CMM) and PC-DMIS software. Deformation pattern, residual distortions, weld geometry, microstructure and microhardnes properties of the joints produced with fiber laser source and tungsten inert gas welding were compared. Compared with the TIG, the welded by fiber laser has narrow heat affected zone (HAZ), small overall residual distortion, fine microstructure, high Vickers hardness. It can be concluded that fiber laser welding is more suitable for welding the thin Ti6Al4V titanium alloy plate than TIG welding; due to the small beam focus characteristics of fiber lasers enabiling deep penetration welding.

The Effect of Welding Parameters on Static and Dynamic Behaviors of Spot Welded Ti6Al4V Sheets

In this study, the traditional α-β titanium alloy Ti6Al4V sheets were joined by the resistance spot welding process (RSW). RSW method was modeled statistically and investigated experimentally by using different welding parameters. After a literature survey, possible test parameters were determined, and experimental design was made. The objective of this study is to choose the optimum spot-welding parameters in both static and dynamic loading cases. In order to validate and calibrate the developed model, preliminary experiments were carried out, then Taguchi L9 orthogonal experimental design was determined to examine the effect of different parameters that are thought to be suitable for this process. The Signal/Noise (S/N) ratio was used for the interpretation of the results in the determined experimental setup. The experimental study aims to show the responses of spot welds created with different process parameters. In this study, electrode force, welding current, and welding time parameters were determined as the control factors, and the effect of these factors on the results was found using variance analysis (ANOVA). Additionally, a characterization study was conducted on spot-welded joints. Lastly, verification tests were performed and it was determined that optimization was applied successfully. It was determined that process parameters have a significant effect on failure mode and joint strength. The highest strength is obtained in both static and dynamic conditions at the control group.

Experimental and numerical studies on gas tungsten arc welding of Ti–6Al–4V tailor-welded blank

The effect of gas tungsten arc welding (GTAW) process parameters and its impact on the titanium TWB was studied experimentally as well as using numerical simulation. Bead characteristics of BoP trials (bead on plate) were analyzed based on Taguchi L27 orthogonal array by taking welding current (115 A, 125 A, 135 A), welding speed (4.1 mm/s, 5.8 mm/s, 7.5 mm/s) and arc length (3 mm, 4 mm, 5 mm) as process parameters. The bead width and depth of penetration for all trials were measured by using the weld expert system. Based on the bead characteristics, optimized GTAW process parameters (135 A, 4.1 mm/s and 3 mm) were identified for making the TWB by joining 2–1.6-mm-thick Ti–6Al–4V sheets. The tensile test of the prepared Ti–6Al–4V TWB was conducted in the universal testing machine. The COMSOL and ABAQUS software packages were used for the numerical simulation of TWB to assess the bead profile and tensile properties. The prediction made from the temperature distribution curve related to phase change near weld zone, exactly matched with the experimental work. The joint strength of TWB observed to be around 982 MPa and 1005 MPa was evaluated experimentally and conducting ABAQUS simulation work. The tensile test results were comparable with each other within the acceptable error level.

Experimental investigation of plasma arc welded Ti–6Al–4V sheets

In the present work, experimental trials were conducted with Ti–6Al–4V sheet. The influence of process parameters on the weld bead geometry of bead on joint welding and butt joint configuration was studied. It was concluded that at high current and low travel speed, the heat input was found to be maximum. This led to a higher linear heat input over the base metal that subsequently yielded a full depth of penetration. The strength and integrity of the welded butt joint configuration were ascertained by tensile and bend tests. The microhardness values of the fusion and heat-affected zones were concluded to be higher compared to the base metal. In addition, an Erichsen cupping test ensured that the formability of the welded specimen was comparable to that of the base metal.

Influence of laser heat input on weld zone width and fatigue performance of Ti-6Al-4V sheet

During this study, the fatigue life of laser welded Ti6Al4V sheet was evaluated as a function of process heat input. Heat input was varied by manipulating laser power and welding travel speed and was categorised into three heat input ranges (Low = 40–60 J/mm; Medium = 65–120 J/mm and High = 160–230 J/mm). Fatigue data was acquired from as-welded and polished specimens in order to study the effect of weld geometry resulting from a change in process parameters. Results showed that there was an increase in fatigue life for low heat input welds, mainly derived from the associated higher traverse speeds, demonstrating that laser power variation was not the sole determinant in fatigue life. A higher fatigue life and lower heat input relationship is related to the occurrence of a narrower fusion zone and increased weld zone hardness that corresponds with a lower heat input obtained from higher traverse speeds. Two predominant crack initiation mechanisms were observed; internal initiation from discontinuities that is related to inadequate optimisation of welding process parameters for the polished samples, while surface initiation occurred in the welded specimens, due to the stress concentration effect of the weld bead geometry. An increase in welding speed or decrease in laser power both led to a reduction in weld undercut or a lower stress concentration at the weld toe. As expected, the fatigue data for the polished samples showed a marked improvement in life and a reduction in scatter compared to the as-welded data.

Fretting fatigue crack initiation and propagation in Ti6Al4V sheets under tribocorrosive conditions of artificial seawater and physiological solutions

The interaction of mechanical components experiencing relative movements and cyclic loads in a corrosive environment is known as fretting corrosion or tribocorrosion. In the current work, the mechanism of crack initiation and propagation in dovetail slots of Ti6Al4V samples (in contact with carbide rods) under fretting corrosion conditions was investigated. A newly developed test rig installed on a universal testing machine was used to conduct tests at 20 Hz frequency under 5 and 7.5 kN fretting loads. Tests were conducted at room temperature in 3.5% NaCl and phosphate-buffered saline solutions. Crack propagation in all samples was examined by a metallurgical microscope, and the detailed analysis of fractured samples was carried out by a scanning electron microscope. In comparison to dry conditions, early crack initiation and faster crack propagation were observed in salt and physiological solution environments. Colored spots and large amounts of chlorine, sodium, and oxygen were found around cracks, and plastically deformed regions in the 3.5% NaCl environment provided the evidence of a corrosive attack. Large amounts of oxygen, phosphorous, chlorine, potassium, and sodium were detected in the phosphate-buffered saline environment.

Uni-axial tensile response and failure of glass fiber reinforced titanium laminates

Abstract Layers of thin metallic sheets and fiber-reinforced composite layers bonded together is known as fiber metal laminates (FMLs). In the current study, titanium Ti–6Al–4V sheets are used with thicknesses 0.2 mm, 0.4 mm and, 0.6 mm along with layers of unidirectional glass-fiber reinforced composite to produce FMLs and the tensile response of these laminates are examined. Four different stacking sequences of FMLs have been considered exhibiting the same thickness for the total metal layer and the hand layup process is used to prepare these laminates. An orthotropic plasticity theory of macro mechanical type and classical laminated plate theory are considered to model the elastic-plastic type of behavior of titanium-based FMLs. A plastic potential function based on three parameters is used to the model the orthotropic plasticity. Behavior with linearly elastic and orthotropic elastic-plastic types is assumed for the layers of glass composite and titanium, respectively in the laminated plate theory. The results show that the initial modulus of FMLs has not been influenced by the sequence of the layup, while this sequence of layup does considerably affect the response of FMLs following ultimate strength. The properties of FMLs such as failure strain and toughness which are important parameters from a design point of view of FMLs can be altered to absorb energy at dissimilar rates, i.e., by insulating the composite layers from each other by metallic layers in case of FMLs 3/2–0.4, 4/3–0.2(O) and 4/3–0.4(O). The model with orthotropic plasticity is found to be precise up to the total strain level of 2.1%, i.e., close to the failure of composite layers within FMLs, when compared with results measured from experiments. The behavior with stress-strain predicted by laminated plate theory also finds realistic up to the total strain of 2.1% to describe the corresponding behavior obtained from experiments.

Investigation of Microstructure, Mechanical Properties, and Numerical Modeling of Ti6Al4V Joints Produced by Friction Stir Spot Welding

In this work, lap-joined titanium alloy sheets have been successfully spot welded using friction stir spot welding (FSSW). Fully consolidated spot welds of thin Ti6Al4V sheets were obtained with a convex scrolled polycrystalline cubic boron nitride probe. The influence of processing parameters on FSSW was evaluated through a finite element analysis (FEA). Numerical results showed that von Mises stress and strain distributions were non-symmetric in the stir zone, whereas higher temperatures were observed in the region next to the tool pin. The welding microstructures showed different effects due to temperature gradients and material flow. The tool configuration played a significant role when determining the spot weld quality, since it directly influences the flow behavior of FSSW. It was observed that, in the stir zone, the microstructure suffered a transformation from α to β. The effect of welding parameters and the development of a FEA for the friction stir spot process were explored in the current investigation.

Impacts of laser cladding residual stress and material properties of functionally graded layers on titanium alloy sheet

Laser cladding induces high tensile residual stress (RS), which can compromise the quality of a specimen. Therefore, it is critical to accurately predict the RS distribution in cladding and understand its formation mechanism. In this study, functionally graded material (FGM) layers were successfully deposited on the surface of a titanium alloy Ti6Al4V sheet by laser cladding technology. A corresponding thermo-mechanical coupling simulation model of the laser cladding process was developed to investigate the formation mechanism of RS in the laser cladding FGM layers. The results show that high tensile RS forms in cladding components. Subsequent cladding can effectively alleviate the RS in cladding components although the position of maximum RS remains unchanged. The measurement results of the longitudinal RS on the top and bottom surfaces of cladding components by the X-ray diffraction (XRD) method agreed with the simulation results, thereby proving the accuracy of the simulation. In addition, the formation mechanism of RS in the laser cladding FGM layers was revealed by discussing the individual impact of each material property on RS. It was indicated that the RS distribution in the laser cladding FGM layers was significantly affected by material properties (in particular, coefficient of thermal expansion and Young’s modulus), except for the temperature gradient induced by the laser cladding process.

Correlation of microstructural, textural characteristics and hardness of Ti–6Al–4V sheet β-cooled at different rates

In this work, a hot-rolled Ti–6Al–4V (Ti-64) sheet was annealed at 1050 °C (β field) and then subjected to different coolings (in water, air and furnace). Electron backscatter diffraction, electron channeling contrast imaging, energy-dispersive spectroscopy and X-ray diffraction techniques were jointly utilized to comprehensively reveal microstructural and textural characteristics of the specimens following various β-cooling rates. Hardness measurements were also performed to probe the hardness variation associated with the β-cooling rates and were further rationalized based on the revealed microstructures. Results show that the β-cooled specimens in water, air and furnace exhibited twinned martensite, basket-weave and parallel-plate Widmanstatten structures, respectively. The Burgers orientation relationship is always obeyed during the β → α transformation at all cooling rates. After phase transformation, major α texture components ((0°, 60°, 0°), (90°, 30°, 30°) and (90°, 90°, 30°)) are completely different from those of the as-received material ((0°, 90°, 0°) and (90°, 30°, 0°)). Slow cooling facilitates preferable nucleation of α phases at prior β boundaries and strengthens α-variant selection, leading to greatly intensified transformation texture (the maximum density from 9.5 to 31.1 times of random). Hardness values of the β-cooled specimens drop from 416.8 ± 4.3 HV for water cooling to 329.2 ± 23.6 HV for furnace cooling. Quantitative calculations suggest such hardness variation can be more related to differences in grain size between them, as compared to specific contributions from other microstructural and textural characteristics.

Characterization and correlation of microstructure and hardness of Ti–6Al–4V sheet surface-treated by pulsed laser

A hot-rolled Ti–6Al–4V (Ti-64) sheet was surface-treated by pulsed laser at two different powers (100 and 200 W), with microstructural features and hardness before and after the laser surface treatment (LST) systematically investigated. Results show that after the LST at both powers there are two modification zones with distinct microstructural characteristics: melted zone (MZ) near the laser beam center, completely composed of fine martensitic plates with dense {10–11} nanotwins inside them; heat-affected zone (HAZ) far away from the laser beam center, comprised of mixed structures of short-rod β particles, martensitic plates and untransformed bulk α grains. Hardness measurements reveal that the hardness of the Ti-64 sheet can be markedly increased (especially in the MZ) after the LST. In-depth analyses suggest that the hardness increase in the MZ can be ascribed to combined contributions from grain refinement, presence of nanotwins and solid solution of alloying elements, while only the structural refinement by fine plate structures contributes to hardening in the HAZ. Comparisons between both the LSTed specimens reveal that increasing the laser power from 100 W to 200 W can effectively enlarge the laser-modified zones (both the MZ and the HAZ) and simultaneously refine plate structures, leading to further hardness increase.