Titanium Alloy Ti6Al4V Research Articles

Modeling of the thermal softening of metals under impact loads and their temperature–time correspondence

The thermal softening related to the stress relaxation, i.e. a reduction in the internal resistance to deformation, due to the increasing bulk temperature is theoretically studied using the incubation time approach. The plastic deformation at high-loading rates is often accompanied by an obvious adiabatic temperature rise. Phenomenological constitutive models describing these thermo-mechanical responses of metals are generally developed by assuming empirical rate-dependent and temperature-dependent components into existing conventional bases originally proposed for quasi-static cases. This work aims to model the thermal softening of metals subjected to high-rate loads using the incubation time approach and examine the temperature–time correspondence, i.e. temperature-dependence of the incubation time, by introducing the relative stress (RS) factor over a wide range of strain, strain rate and temperature. The incubation time approach considers the strain-rate sensitivity as a manifestation of the time sensitivity of materials. Additionally, we conduct a comprehensive analysis of the developed relaxation model of plasticity (RP model) and conclude that this model may be derived by the time-dependent yield surface equation using the incubation time framework. Based on experimental facts for HSLA–65 steel, 93W–4.9Ni–2.1Fe Tungsten-based composite and titanium alloy Ti–6Al–4V, the descriptive abilities of the developed RP model are compared with other constitutive models (phenomenological and micromechanism-based ones) and the artificial neural networks (ANN) model. The advantages and disadvantages of various models are discussed, and the main differences between the ANN model and other constitutive models are examined.

Influence of niobium and hafnium doping on the wear and corrosion resistance of coatings based on ZrN

The properties of coatings based on the ZrN system with the introduction of hafnium and zirconium (ZrN, (Zr,Nb)N and (Zr,Hf)N), deposited on a Ti6Al–4V titanium alloy substrate are compared. Coatings are deposited by controlled accelerated arc-physical vapor deposition, and the structure of the coatings is studied using a transmission electron microscope. A comparison is made of both the mechanical (hardness, wear resistance, scratch strength) and anticorrosion (in a 3 % solution of NaCl) properties. The (Zr,Hf)N coating (22 at% Hf and 78 at% Zr) has the maximum hardness (HV, 3225 ± 73) and wear resistance. This coating also exhibits higher corrosion resistance. In contrast, introducing Nb into the coating composition reduces the corrosion resistance. This combination of beneficial properties makes the (Zr,Hf)N coating useful for conditions in which the surfaces of parts must simultaneously have high wear resistance, strength, and corrosion resistance.

Comparison of low-cycle fatigue properties of two kinds of high energy beam welded joints of TC4 alloy

The low-cycle fatigue properties of 30 mm Ti6Al4V titanium alloy joints welded by vacuum electron beam welding and laser wobble welding with filler wire were compared. The test results show that the low-cycle fatigue performance of the electron beam welding joint is close to that of the base meal, while the low-cycle fatigue performance of the laser wobble welding with a filler wire joint is clearly inferior to that of the electron beam welding joint and base meal. An examination of the microhardness of the base metal, heat-affected zones and weld area of the two joints found that the microhardness of the weld area of the electron beam welding joint is close to that of the base meal, but is lower than that of the heat-affected zones on both sides. The weld area of the laser wobble welding with the filler wire joint is significantly weakened.

Functionality and Mechanical Performance of Miniaturized Non-Assembly Pin-Joints Fabricated in Ti6Al4V by Laser Powder Bed Fusion.

In this work, additively manufactured pin-joint specimens are analyzed for their mechanical performance and functionality. The functionality of a pin-joint is its ability to freely rotate. The specimens were produced using laser powder bed fusion technology with the titanium alloy Ti6Al4V. The pin-joints were manufactured using previously optimized process parameters to successfully print miniaturized joints with an angle to the build plate. The focus of this work lies in the influence of joint clearance, and therefore all specimens were manufactured with a variety of clearance values, from 0 µm up to 150 µm, in 10 µm steps. The functionality and performance were analyzed using torsion testing and tensile testing. Furthermore, a metallographic section was conducted to visually inspect the clearances of the additively manufactured pin-joints with different joint clearance values. The results of the torsion and tensile tests complement each other and emphasize a correlation between the joint clearance and the maximal particle size of the powder utilized for manufacturing and the mechanical behavior and functionality of the pin-joints. Non-assembly multibody pin-joints with good functionality were obtained reliably using a joint clearance of 90 µm or higher. Our findings show how and with which properties miniaturized pin-joints that can be integrated into lattice structures can be successfully manufactured on standard laser powder bed fusion machines. The results also indicate the potential and limitations of further miniaturization.

Analysis of Geometric Surface Structure and Surface Layer Microhardness of Ti6Al4V Titanium Alloy after Vibratory Shot Peening.

This article presents an analysis of the impact of vibratory shot peening on the surface roughness and physical properties of the Ti6Al4V titanium alloy surface layer after milling. The elements of machine parts and structures made of titanium alloys are often exposed to variable loads during operation. Therefore, it is advisable to apply methods that enhance functional properties and increase the durability of interacting components. Increasing the operational durability of such elements can be achieved by vibratory shot peening. Variable amplitudes A = 24; 33; 42; 51; 60 mm and times t = 1; 7; 13; 19; 25 min were applied. It has been demonstrated that it is possible to achieve a threefold reduction in the roughness parameter, Sa = 0.344 µm, compared with milling, Sa = 0.95 µm. An increase in Smr(c) areal material ratio was observed after vibratory shot peening compared with milling. It has been shown that amplitude has a greater impact on the increase in hardening of the surface layer gh compared with time. The highest rate of change in surface roughness and thickness of the hardened layer was achieved at a vibratory shot-peening time of t = 13 min. The greatest thickness of the hardened layer, exceeding 200 µm, was obtained after shot peening with an amplitude of A = 60 mm.

Exploring wide-parametric range for tool electrode selection based on surface characterization and machining rate employing powder-mixed electric discharge machining process for Ti6Al4V ELI

The titanium alloy Ti6Al4V ELI (grade 23) is widely used in biomedical industry because of its engineering attributes. However, it requires surface modifications and has processing challenges because it is difficult to machine nature. Therefore, powder-mixed electric discharge machining process is commonly applied to simultaneously machine the material and carry out surface treatment. The performance of the process is limited by both low cutting efficiency and the formation of a rough surface. In this regard, the current study evaluates SiC powder-mixed electric discharge machining of Ti6Al4V ELI using a range of tool materials such as copper, brass, graphite, and aluminum along with a comprehensive list of process parameters. The surface roughness parameters involving arithmetic roughness, the average peak-to-valley distance, and the highest peak-to-deepest valley distance along with material removal rate are comprehensively studied. Taguchi design of experiments L16 orthogonal array is used to study the process performance with parametric effect analysis, parametric significance analysis, and surface morphological analysis with a scanning electron microscope. Furthermore, the experimental results are optimized against a multi-response optimization matrix using grey relational analysis approach. An optimal compromise between surface attributes and cutting efficiency is identified by Al electrode, pulse current of 14 A, pulse on time of 75 µs, pulse off time of 75 µs, and negative polarity parametric conditions.

Microstructural Transformation and Enhanced Strength of Wire‐Feed Electron‐Beam Additive Manufactured Ti–6Al–4V Alloy Induced by High‐Pressure Torsion

For the first time, the present study demonstrates the influence of high‐pressure torsion (HPT) on microstructural refinement and mechanical strength of Ti–6Al–4V titanium alloy produced by wire‐feed electron‐beam additive manufacturing. This technology has attracted an increasing interest presently from manufacturers of products with complex shapes and it allows for producing a titanium alloy with a unique microstructure that consists of martensitic α′ phase, separated by thin interlayers of residual β phase. Further processing of the alloy by HPT results in the formation of an ultrafine‐grained (UFG) structure with an average grain size of about 25 ± 10 nm, significantly increasing its microhardness up to 448 ± 5 HV. Microscopic studies reveal that the attained UFG structure consists predominantly of the grains of α and β phases in the ratio of 92.8% and 7.2%, respectively. This article also considers the nature of the high strength of Ti–6Al–4V subjected to HPT.

Evaluation of tribological interactions and machinability of Ti6Al4V alloy during finish turning under different cooling conditions

The titanium alloy Ti6Al4V has several applications and is considered as a difficult-to-machine material. This study evaluates some tribological interactions in finish turning of Ti6Al4V titanium alloy, including the tool wear, and coefficient of friction in tool-chip interface. Subsequently, the machinability of Ti6Al4V titanium alloy has been investigated, considering the chip geometry, chip thickness ratio, as well as changes in the total cutting force components. The turning process was carried out over a wide range of the feed rate (f) and depths of cut (ap) using hard carbide, GC1115 grade, inserts with double-layer PVD coating. The finish turning tests were conducted under the dry, flood, and MQL (minimum quantity lubrication) cutting conditions. It was found that favorable chip shapes (arc loose) were obtained in the range ap = 0.9–1.2 mm and f = 0.25–0.4 mm/rev. Increasing the f clearly affects the formation of a serrated chip. In addition, the intensity of tool wear, as well as the variations of cutting forces and chip thickness ratios were strongly affected by the applied cooling/lubricating condition. Compared to wet conditions, the Kh values decrease by ∼22 % with dry machining and by ∼12 % with MQL. Compared to wet conditions, for dry machining the cutting forces decrease to 70 % and with MQL to 8 %. The cumulative wear rate under dry machining increases by 18 % compared to wet conditions, and with MQL reduces by 19 %.

Effect of Ultrasonic Impact Treatment on Microstructure and Fatigue Life of 3D Printed Ti–6Al–4V Titanium Alloy

Effect of Ultrasonic Impact Treatment on Microstructure and Fatigue Life of 3D Printed Ti–6Al–4V Titanium Alloy

The Effect of Rotary Friction Welding Conditions on the Microstructure and Mechanical Properties of Ti6Al4V Titanium Alloy Welds.

The main task that the article introduces is the experimental study of how the geometry of contact surfaces affects the quality and mechanical properties of a rotary friction weld (RFW), as well as the findings of whether the RFW technology is suitable for the titanium alloy Ti6Al4V. The experiments were carried out for specimens with a diameter of 10 mm and were performed at 900 RPM. Three types of geometry were proposed for the RFW process: flat on flat, flat on 37.5° and flat on 45°. Based on these results, the best tested flat geometry was selected from the perspective of quality and economic efficiency. The welded joints were subjected to microstructural analysis, tensile testing, microhardness testing, and fractography, as well as spectral analysis of the fracture surface and EDS map analysis of oxygen. The flat geometry of the contact surface resulted in the least saturation with interstitial elements from the atmosphere. Fracturing in the RFW zone led to a brittle fracture with a certain proportion of plastic deformation. A pure ductile fracture occurred in specimens fractured in the HAZ region, where the difference in UTS values compared to specimens fractured by a brittle fracture mechanism was not significant. The average UTS value was 478 MPa.

Adhesion and Activation of Blood Platelets on Laser-Structured Surfaces of Biomedical Metal Alloys.

The laser surface modification of metallic implants presents a promising alternative to other surface modification techniques. A total of four alloyed metallic biomaterials were used for this study: medical steel (AISI 316L), cobalt-chromium-molybdenum alloy (CoCrMo) and titanium alloys (Ti6Al4V and Ti6Al7Nb). Samples of metallic biomaterials after machining were subjected to polishing or laser modification in two different versions. The results of surface modification were documented using SEM imaging and roughness measurement. After modification, the samples were sterilized with dry hot air, then exposed to citrate blood, washed with PBS buffer, fixed with glutaraldehyde, sputtered with a layer of gold and imaged using SEM to enable the quantification of adhered, activated and aggregated platelets on the surface of biomaterial samples. The average total number, counted in the field of view, of adhered platelets on the surfaces of the four tested biomaterials, regardless of the type of modification, did not differ statistically significantly (66 ± 81, 67 ± 75, 61 ± 70 and 57 ± 61 for AISI 316L, CoCrMo, Ti6Al4V and Ti6Al7Nb, respectively) and the average number of platelet aggregates was statistically significantly higher (p < 0.01) on the surfaces of AISI 316L medical steel (42 ± 53) and of the CoCrMo alloy (42 ± 52) compared to the surfaces of the titanium alloys Ti6Al4V (33 ± 39) and Ti6Al7Nb (32 ± 37). Remaining blood after contact was used to assess spontaneous platelet activation and aggregation in whole blood by flow cytometry. An in-depth analysis conducted on the obtained results as a function of the type of modification indicates small but statistically significant differences in the interaction of platelets with the tested surfaces of metallic biomaterials.

Effect of ultrasonic rolling on crack propagation behavior of Ti6Al4V titanium alloy laser welded joints

This study investigated the effect of ultrasonic rolling on the fatigue resistance of Ti6Al4V titanium alloy laser welded joints, with an emphasis on crack growth rate. Multiple analyses were conducted on samples subjected to different numbers of rolling passes, including analysis of surface roughness, morphology, cross-section structure, hardness, fatigue fracture, and residual stress. Ultrasonic rolling was found to considerably enhance the life cycle of the sample. One, three, and five rolling passes resulted in fatigue life increases of 17.14%, 46.38%, and 66.61%, respectively, when compared with untreated samples. Treated samples exhibited rough and intricate crack propagation paths on fracture surfaces, along with numerous secondary cracks. Fatigue striation width decreased by 48.6%, 62.5%, and 69.4% for samples receiving one, three, and five rolling passes, respectively. These fatigue striations, which were narrower and more densely distributed, indicate that ultrasonic rolling effectively increases fatigue life. The ultrasonic rolling treatment enhanced fatigue performance and reduced the rate of crack propagation due to changes in surface compressive residual stress, microstructure, microhardness, and improved surface quality. Crack retardation primarily occurred in initial stage of crack propagation and stable propagation stages, whereas inhibitory effects weakened during the final fracture stage due to superposition and offset of the higher driving force with compressive residual stress. In summary, the study demonstrates that treatment via ultrasonic rolling is an effective method for improving fatigue life and fracture toughness in Ti6Al4V titanium alloy laser-welded joints.

Evaluation of tool wear during turning of Ti6Al4V alloy applying MQL technique with Cu nanoparticles diversified in terms of size

In case of hard-to-cut materials, as titanium alloy Ti6Al4V, eco-friendly cooling methods or their modifications are still being developed. Therefore, various types of nanofluids are applied in the cutting process to reduce friction in the cutting zone and thus heat accumulation in the tool corner. This paper presents an analysis of the selected tool wear indicators, as well as the wear mechanisms, after turning with various cooling/lubricating techniques, including: MQL with the addition of copper nanoparticles (CuNPs), dry machining and the MQL technique without nanoparticles. Four sizes of CuNPs were applied: 22 nm, 35 nm, 65 nm and 80 nm. Analysis of SEM images and maps of elemental distributions on the cutting edge working surfaces allowed to determine that the smallest sizes of copper nanoparticles introduced in the cutting fluid result in reduced tool flank wear, as well as the reduced width and depth of the crater wear on the rake face. With the smallest size of copper nanoparticles, a “ball bearing” and tribofilm formation effects were obtained, which prevented intense adhesive and abrasive wear. Turning, applying MQL + CuNPS 22 nm method resulted in a decrease of selected tool wear rates from 25.7% to 55% compared to effects reached during dry machining, and from 11.7% to 39.2% compared to effects of MQL turning without addition of nanoparticles to the cutting fluid.

Tribocorrosion Susceptibility and Cell Viability Study of 316L Stainless Steel and Ti6Al4V Titanium Alloy with and without DLC Coatings

Stainless steel (SS316L) and titanium alloy (Ti6Al4V) exhibit suitable properties for biomedical applications; however, the tribocorrosion of these materials, which is associated with metallosis, is still a significant concern. This work investigates the effectiveness of DLC smoothing coatings applied to the metals to reduce tribocorrosion and improve cell viability. The study was motivated by many reports of metallosis caused by metal debris in the soft tissues of the body. DLC coatings were produced using the plasma-enhanced chemical vapor deposition (PECVD) technique. The cytotoxicity, genotoxicity, and cell viability of metallic samples with and without DLC coatings were analyzed, considering the chemical composition of the coating and metallic components. The results show that the DLC coatings presented suitable interaction properties and no cytotoxicity or genotoxicity when exposed to the cellular environment, compared with the control group (p &lt; 0.0001). They also demonstrated cell viability, low friction representing a reduction of 80%, and hardness 23–26 GPa, making them ideal for use on fixed implants. It is necessary to control the thickness and roughness of the coating to avoid pinholes and increase the corrosion protection of implants. These DLC coatings with low friction coefficients could facilitate the fixation of implantable pins and screws, including Kirschner wires.

Realizing in-situ preparation of ZnAl layered double hydroxide film on titanium alloy through one-step hydrothermal reaction

A hydrothermal process was proposed for in-situ preparation of ZnAl layered double hydroxides with nitrate (ZnAl-NO3-LDHs) on a Ti6Al4V titanium alloy. To destroy the dense and stable TiO2 film on the titanium alloy, mild NH4F instead of strong HF was used as a F− ion source in the growth solution of the hydrothermal reaction, and ammonia water instead of urea was used to adjust the pH value, both of which helped to realize in situ growth of ZnAl-LDHs films on titanium alloys. The structure and morphology of the LDHs films were characterized using X-ray diffraction and scanning electron microscopy. The corrosion resistance and stability of the LDHs films were evaluated using potentiodynamic polarization curves and immersion tests. The results show that a uniform ZnAl-NO3-LDHs film was formed in situ on the titanium alloy with the help of NH4F and NH3·H2O. The formation mechanism of ZnAl-NO3-LDHs on the TC4 titanium alloy was determined. The ZnAl-NO3-LDHs film improved the corrosion resistance of the titanium alloys and has the potential to improve anti-fouling properties by loading anti-fouling substances; however, the laminates of the LDHs fell off after long-term immersion in marine environments.

Elasto-plastic bending behavior of Ti–6Al–4V alloy under coupling conditions of elevated temperature and combined tension-bending

Overload failure under coupling conditions of elevated temperature and combined tension-bending (CTB) is one of the typical failure modes of aero-engine low-pressure compressor blade materials, which is commonly occurring in fighter engines performing low-altitude high-speed penetration missions. In this study, the elasto-plastic deformation behavior and fracture mechanism of Ti–6Al–4V titanium alloy under coupling conditions of elevated temperature and CTB were investigated by experiments and finite element analysis (FEA). CTB tests were conducted on Ti–6Al–4V alloy in the pre-tension ratio range of 0.60–0.90 and in the temperature range of 298 K–573 K. The results show that the maximum bending load, effective bending modulus, and total energy dissipated for the Ti–6Al–4V alloy at room temperature increase with the increase of the pre-tension ratio. The maximum bending load and the energy dissipated are significantly higher at elevated temperatures compared to that of room temperature, due to the elevated temperature induced deformation mode change from bending-dominated to tensile-dominated. The FEA results are in good agreement with the experimental results. SEM fractography indicated that the Ti–6Al–4V alloy fracture at elevated temperature showed only equiaxed dimples, which exhibited a tensile fracture mode. This study is valuable for the in-depth understanding of the deformation behavior and fracture mechanism of blade materials under elevated temperature and complex loads.

Machining Temperature, Surface Integrity and Burr Size Investigation during Coolant-Free Hole Milling in Ti6Al4V Titanium Alloy

Modern Aircraft structures use titanium alloys where the processing of holes becomes essential to assemble aerospace parts. Considering the limitations of drilling, the study evaluates the helical milling for hole processing in Ti6Al4V. The experimental evaluation was conducted by considering burr size, surface roughness, machining temperature, and microhardness under coolant-free conditions. The axial feed and cutting speed were varied at three levels, and nine experiments were conducted. The results exhibit a lower machining temperature during helical milling than during drilling. In addition, the helical milling helped to lower the surface roughness and size of the exit burrs. However, helical-milled holes showed higher subsurface microhardness than conventionally drilled holes. The process variables were influential on machining temperature magnitude. The highest recorded temperature of 234.7 °C was observed at 60 m/min of cutting speed and 0.6 mm/rev feed. However, the temperature rise did not affect the microhardness. Strain hardening associated with mechanical deformation was the primary mechanism driving the increase in microhardness. Helical-milled holes exhibited an excellent surface finish at lower axial feeds, while chatter due to tool deformation at higher feeds (0.6 mm/rev) diminished the surface finish. The surface roughness increased by 98% when the cutting speed increased to 60 m/min from 20 m/min, while a moderate increment of 28% was observed when the axial feed increased to 0.6 mm/rev from 0.2 mm/rev. Furthermore, the formation of relatively smaller burrs was noted due to significantly lower thrust load and temperature produced during helical milling.

Investigating the self-lubricating properties of novel TiSiVN coating during dry turning of Ti6Al4V alloy

The machining of titanium alloys like Ti6Al4V has been challenging owing to their low thermal conductivity, making them highly difficult-to-cut. Many techniques have been adopted to improve machinability of Ti6Al4V titanium alloy and the durability of the cutting tools during its machining. Thus, to improve their machinability, the current work investigates the applicability of TiSiVN self-lubricating coating deposited on Al2O3–SiC ceramic cutting tools during continuous turning of Ti6Al4V alloy under dry cutting environment. The TiSiVN coating accounted for lower surface roughness and cutting temperatures under all conditions. Due to the formation of V2O5 at high temperatures that were observed during oxidation and machining tests in EDS and Raman spectroscopy, the TiSiVN coating helped in reducing friction and, thus, retained the crater wear area. In contrast, the worn area on the crater surface reduced for uncoated and TiSiN coated cutting tools due to a significant increase in nose depth decrement with increasing cutting speed. Furthermore, increased nose depth decrement resulted in the drop of machining forces when using TiSiN coated and uncoated cutting tools. However, the coating delamination due to oxidation was apparent which reduced the effectiveness of lubricious phases present in the cutting zone for TiSiVN coated tool.

Selection of the numerical formulation for modeling the effect of tool cutting edge microgeometries in machining of Ti6Al4V titanium alloy

The Finite-element method (FEM) is often used to simulate the metal machining process. Currently, several formulations are used in metal cutting simulation, such as Lagrangian (LAG), Eulerian (EUL), Arbitrary Lagrangian–Eulerian (ALE), and Coupled Eulerian–Lagrangian (CEL). The selection of the numerical formulation that better reproduces the material separation in machining to form the chip is a critical issue. This is quite important when the ratio between the uncut chip thickness and the cutting edge microgeometry, often represented by a cutting edge radius, is very low. In this study, orthogonal cutting of Ti6Al4V titanium alloy using different tool edge microgeometries is investigated using LAG and CEL approaches. In the case of LAG approach, two types of cutting models were develop: one using a sacrificial layer (hereby called LAG-SL), and another without sacrificial layer (hereby called LAG-nSL). The cutting models have included a constitutive model (both plasticity and damage) considering the effects of strain, strain rate, temperature, and state of stress, which have proved to be accurate enough to represent the mechanical behavior of the Ti6Al4V alloy in machining. Comprehensive comparisons between CEL and LAG-based cutting models and experimental results are carried out in terms of chip morphology, forces, and residual stresses. When compared to the experimental results, LAG-nSL model gives the best predictions of the maximum chip compression ratio (CCRm) with an error of 9.5%, cutting force (12.8%) and thrust force (9.3%) than the other two models. In the case of the of residual stress profiles, LAG-SL offers good predictions of the maximum compressive residual stress by a preference ratio of 75%. Although CEL yields the worst predictions of chip morphology and forces, it is preferred from the perspective of the thickness of the layer affected by residual stress.

Influence of Ball Burnishing on Lubricated Fretting of the Titanium Alloy Ti6Al4V

Ball burnishing is a very promising alternative to grinding because of it produces little environmental pollution. It can cause improvement of the functional properties of machine parts, such as friction and wear. The connection between the ball burnishing and the lubricated fretting has not been analysed yet. In this study, it was found that ball burnishing discs from titanium alloy Ti6Al4V caused a decrease in the height of the roughness up to 84% and an increase in the microhardness up to 26% compared to the turned surface. Tribological experiments were carried out under lubricated fretting conditions. Ceramic balls from WC material co-acted with the burnished discs. Ball burnishing resulted in significant improvement in the tribological behaviour of the ball-on-disc sliding pair. Due to ball burnishing, the friction coefficient decreased up to 45% and the volumetric wear of the disc decreased up to 50% compared to the turned disc. The smallest friction and disc wear were achieved for the sample burnished with a pressure of 30 MPa; this sample was characterised by a low roughness height and great microhardness. The turned disc sample corresponded to high friction and wear. Wear losses of the balls were negligible due to the large difference between the hardness values of the balls and discs.