Titanium Alloy Ti6Al4V Research Articles

“Evaluation of a method to measure the friction coefficient between vital mandibular bone and biomedical materials”

PurposeThe aim of this study is to evaluate a developed experimental set-up to measure the coefficient of friction between fresh mandibular bone and biomaterials used in oral and maxillofacial surgery including a standardized routine for specimen preparation. Material and methodsFor this purpose, we developed a specialized routine for harvesting and preparation of cortical bone specimen from cadaveric porcine mandibles and modified a ball-plate tribometer. These harvested bone specimen were kept moist all the time. A total of 24 bone cylinders with 8 repetitions per material were examined for their coefficient of friction against stainless steel (1.4404), a titanium alloy (Ti6Al4V) and a cobalt‑chromium‑molybdenum alloy (Biosil F®) and subsequently analyzed by laser-scanning and scanning electron microscopy. ResultsThe lowest coefficients of friction between vital cortical bone and the investigated implant materials were found for Biosil F®, while the highest coefficients of friction were found for the titanium alloy Ti6Al4V. Significant differences for the initial coefficient of friction with p < 0.05 have been proven. Stick-slip effects occurred during the measurement and a layer of debris formed on the metallic samples. EDX analysis of the abrasion marks revealed that this layer consisted of elements contained in hydroxyapatites and carbon. ConclusionThe experimental set-up is suitable to perform reproducible comparative measurements of the coefficient of friction of different material combinations. A significant advantage of the methodology is the flexibility and scalability of harvesting and preparation of the bone specimen, which allows the simulation of realistic situations while measuring the coefficient of friction.

Studi Pengembangan Komponen Implan Paduan Ti6Al4V untuk Aplikasi Biomedis dengan Proses Metal Injection Molding

Titanium alloy Ti6Al4V is a material that has a combination of mechanical properties required for implants such as good ductility, high corrosion resistance and good biocompatibility, so it is widely used as a material for biomedical implant applications. One method that is currently widely used to produce Ti6Al4V implants is by using the metal injection molding (MIM) process. The MIM process is widely used because it can produce parts more effectively, and low-cost production. One of the important factors in the MIM process is the powder loading of metal powders and the binder system used as feedstock material. So, it is necessary to conduct further studies and in-depth literature review related to this matter. Literature search using the ScienceDirect, a digital database and limited to year 2011-2020. The results of the study show that both the binder and powder loading systems have an influence on the mechanical properties of the injection product, the results are evident that the viscosity of the feedstock decreases with the increase in the shear rate.

Functionalization of additive-manufactured Ti6Al4V scaffolds with poly(allylamine hydrochloride)/poly(styrene sulfonate) bilayer microcapsule system containing dexamethasone

Porous titanium alloy Ti6Al4V scaffolds manufactured via electron beam melting (EBM®) reveal broad prospects for applications in bone tissue engineering. However, local inflammation and even implant failure may occur while placing an implant into the body. Thus, the application of drug carriers to the surface of a metallic implant can provide treatment at the inflammation site. In this study, we propose to use polyelectrolyte (PE) microcapsules formed by layer-by-layer (LbL) synthesis loaded with both porous calcium carbonate (CaCO3) microparticles and the anti-inflammatory drug dexamethasone (DEX) to functionalize implant surfaces and achieve controlled drug release. Scanning electron microscopy indicated that the CaCO3 microparticles coated with PE bilayers loaded with DEX had a spherical shape with a diameter of 2.3 ± 0.2 μm and that the entire scaffold surface was evenly coated with the microcapsules. UV spectroscopy showed that LbL synthesis allows the manufacturing of microcapsules with 40% DEX. According to high performance liquid chromatography (HPLC) analysis, 80% of the drug was released within 24 h from the capsules consisting of three bilayers of polystyrene sulfonate (PSS) and poly(allylamine)hydrochloride (PAH). The prepared scaffolds functionalized with CaCO3 microparticles loaded with DEX and coated with PE bilayers showed hydrophilic surface properties with a water contact angle below 5°. Mouse embryonic fibroblast cells were seeded on Ti6Al4V scaffolds with and without LbL surface modification. The surface modification with LbL PE microcapsules with CaCO3 core affected cell morphology in vitro. The results confirmed that DEX had no toxic effect and did not prevent cell adhesion and spreading, thus no cytotoxic effect was observed, which will be further studied in vivo.

Fatigue crack growth in residual stress fields of laser shock peened Ti6Al4V titanium alloy

This study investigates fatigue crack growth behavior in residual stress fields induced by laser shock peening (LSP) and its effect on the fatigue life of Ti6Al4V titanium alloy. The two-dimensional residual stress distribution on the specimen surface prior to and post to fatigue crack growth tests was measured by X-ray diffraction. Laser peening with square spot and circular spot was performed on the fatigue specimens. The fatigue lives of LSPed specimens with square spot and circular spot were 1.68 and 2.38 times those of the unpeened specimens, respectively. The result showed that significant crack retardation was observed in specimens only at high compressive residual stresses levels, which was attributed to the reduction of local stress. The superposition principle combined with the weight function method was used to predict the fatigue crack growth rate in residual stress fields.

Additive manufacturing of functionally graded Ti-Al structures by laser-based direct energy deposition

Two different grading strategies were investigated when manufacturing functionally graded materials (FGMs) by means of laser-based direct energy deposition. The FGMs consist of the aluminum alloys AlMg3 and AlSi10Mg and the titanium alloy TiAl6V4. The transition between the materials was realized in one case by a step transition and in the other case by a graded transition. The local chemical composition, microstructure and mechanical properties in the transition areas were investigated by means of optical micrographs, backscatter electron images, energy dispersive x-ray spectroscopy, a ternary phase diagram and microhardness measurements. In the transition area between the aluminum and titanium alloys, there are several kinds of intermetallic phases in both FGMs. However, the embrittlement due to these intermetallic phases was much less pronounced in the FGM manufactured with step transition.

A contribution to numerical prediction of surface damage and residual stresses on die-sinking EDM of Ti6Al4V

A numerical simulation under plane-strain assumption of residual stresses and damage on titanium alloy Ti6Al4V in die-sinking electrical discharge machining (EDM) process is presented using Johnson–Cook (J–C) model and dynamic explicit temperature-displacement algorithm. A special attention is given to model the damaged thermo-mechanical behavior of EDMed Ti6Al4V alloy while considering the ductile damage evolution via a fully uncoupled damage formulation. A rigorous selection method including analytical and finite-element (FE) computations of tensile fracture behavior with thermal effect is proposed for suitable selection of J–C model parameters for the grade of Ti6Al4V alloy under investigation. The relationships between the machining parameters and both the heat flux density and the available sparking radius are considered for defining sparking analysis input. For a selected set of machining settings, the residual stresses and surface damage profiles were retrieved at the end of a cooling analysis. It has been concluded that J–C constitutive model can be used to describe material damaged thermo-plastic behavior under die-sinking EDM process conditions and thereby forecast temperature distribution, crater cavity shape, thermally induced residual stresses, white layer thickness and EDM thermal cracks formation. Unusually, an approach including damage criterion was proposed for assessment of both the geometry of crater cavity and the thickness of white layer and compared to based-on temperature criterion classical approach. Thus, numerical simulation of damage in die-sinking EDM offers a new insight into the mechanism of surface damage creation and helps to find out such phenomenon very precociously, which is otherwise difficult to access by experiment, such as surface crack formation due to damage mechanism as triggered in sparking phase and which was re-established in cooling. The numerical model yields reliable results for residual stresses profiles when compared with titanium alloy Ti6Al4V experimental results available in literature in the same machining conditions.

Enhanced interfacial bonding strength between metal and polymer via synergistic effects of particle anchoring and chemical bonding

To enhance the performance of metal-polymer joint, surface modification is normally applied. Different from the common methods of increasing roughness or manufacturing complicated patterning, a new strategy of microscale morphology design of low roughness surface was introduced in this work, for improving the interfacial bonding strength between Ti6Al4V titanium alloy (TC4) and polyethylene terephthalate (PET) joined by hot pressing method. Low-roughness (R a = 0.18 μm) surface achieved by HF etching can also significantly enhance the interfacial bonding strength of TC4-PET joint by 133%, from 4.5 MPa (as-polished) to 10.5 MPa, as high as the joint strength achieved by sandblasting (11 MPa) with much higher roughness (R a = 3.7 μm). The bonding mechanisms in joints with different surface treatments were investigated and compared, showing that a new effect of surface particle anchoring played a key role in enhancing the interfacial bonding. Based on the characterization results and analyses, the crack propagation paths of HF and HNO 3 -HF treated samples were clarified and illustrated. This study indicated that roughness is not the only decisive factor of joint strength and demonstrated a new effective strategy via synergistic effects of surface particle anchoring and chemical bonding to improve interfacial bonding of metal and polymer from both theoretical and practical points of view.

The influence of quenching on fatigue life of Ti6Al4V alloy

Titanium Ti6Al4V alloy falls into the α+β category alloy system. It is widely used due to its unique mechanical and physical properties which can be modified by applied heat-treatment. The α-phase is considered to be the main phase influencing mechanical properties of an alloy such as ultimate tensile strength or ductility. However, it has also influence on the fatigue life where the form and presence of α-phase in prior β grains may increase or decrease fatigue life. The length and width of α-lamellae influence on fatigue life is well-known. A lot of authors have done their experiments on alloys with Widmanstätten or acicular α-phase structures. Our goal was to obtain an α’-martensitic structure in prior p grains and investigate its influence on fatigue life. To fulfil this goal the heat-treatment consisted of heating near above β-transus temperature 1050°C for a dwell time of 3 hours followed by water quenching was applied. After heat-treatment, the set of specimens with dimensions 10 mm x 9 mm x 55 mm were subjected to three-point bending fatigue test with the parameter of cycles asymmetry R < 1 and test frequency f = 69 Hz. The S-N curve of fatigue life was plotted after the fatigue test and SEM fractography analysis of fractured surfaces was done as well. Our results were compared to previous fatigue test done on alloy with α-lamellae structure.

Characterization of Titanium Alloy Ti6Al4V-ELI Components made by Laser Powder Bed Fusion Route for Space Applications

Characterization of Titanium Alloy Ti6Al4V-ELI Components made by Laser Powder Bed Fusion Route for Space Applications

Revealing tensile behaviors and fracture mechanism of Ti–6Al–4V titanium alloy electron-beam-welded joints using microstructure evolution and in situ tension observation

This study aimed to systematically investigate the microstructure evolution of the nail-shaped weld on electron beam welded joint of Ti–6Al–4V alloy. The microstructure evolution demonstrated that the needle martensitic α′ phases constituted the microstructure in the fusion zone, in which the grain size decreased in the depth direction, and the Widmannstätten structure lamellar α phases covered the base metal. The fusion zone got the strongest tensile strength that reached 980 MPa due to the smallest grain size and the largest number of low angle grain boundary, whereas the tensile strength of the base metal was the lowest in the whole butt joint. The best plastic deformation capacity in the base metal in which the strain approached 13 % was attributed to the largest number of high angle grain boundary in the Widmannstätten structure. Moreover, there were many deformation twins and faults in fusion zone to enhance the resistance to deformation. The tip of the nail-shaped weld was the brittlest location in the entire joint. The experiment also explored the fracture mechanism by in situ observation of tension and fractography, which involved the following three processes: the nucleation and growth of microvoids, the formation of microcracks produced by microvoids, and the occurrence of fracture caused by the growth and propagation of microcracks.

Effect of temperature and cyclic loading on stress relaxation behavior of Ti–6Al–4V titanium alloy

The effect of temperature and cyclic loading on stress relaxation (SR) behavior of Ti–6Al–4V titanium alloy was studied by uniaxial tensile test. SR limit and rate vary with increasing the temperature and cyclic loading times. The microstructural variations were observed by scanning and transmission electron microscopes. Unstable SR behavior happens at 450–550 °C, which becomes obvious with the increase of cyclic loading times or the decrease of relaxation temperature. The stress instability maybe attributes to the activation energy improvement. Based on dislocation distribution and morphology as well as stress exponent values varying from 1.8 to 2.4, SR mechanism of the alloy is dislocation creep in the tested temperature range. The mechanical properties of the alloy at room temperature almost maintains invariable after SR process. However, the discontinuous yielding in as-received alloy changes to continuous yielding in relaxed ones.

Tailoring the Microstructure and Mechanical Properties of Titanium Alloy Ti6Al4V Forgings with Different Combinations of Thermo-Mechanical Processing and Heat Treatment Cycles

Tailoring the Microstructure and Mechanical Properties of Titanium Alloy Ti6Al4V Forgings with Different Combinations of Thermo-Mechanical Processing and Heat Treatment Cycles

“Peel cutting” – A new cutting method for difficult-to-cut workpieces with hard oxide surfaces

A new cutting method named “peel cutting” is proposed in this research to suppress notch wear in machining of metals with hard oxide surfaces. In general, metals are produced by hot deformation processes like rolling, forging, and extrusion, which cause hard oxide surfaces called scales on their surfaces. These hard scales need to be removed first in machining of precision parts. However, the machining causes the severe notch wear at the depth-of-cut position, where the tool contacts the hard scale. To solve this problem, the proposed peel cutting avoids this direct contact between the tool and the scale by inclining the end cutting edge at an extremely large inclination (oblique) angle. This extremely oblique cutting changes the material flow and generates a “burr-like chip”. In the proposed cutting method, the tool contacts only soft non-oxide metal under the scale during cutting. Cutting of titanium alloy Ti–6Al–4V is conducted by modifying commercial tools to provide extremely large inclination angles, and it is clarified that an inclination angle of 70 deg or greater is required to realize the proposed cutting. Tool wear in the proposed cutting of the alloy with a hard scale is also observed in comparison with the ordinary cutting, and the result verifies that the notch wear can be suppressed successfully by the proposed peel cutting.

Experimental study on the reduction of process-induced deformation when milling a low stiffness structure made of Ti6Al4V titanium alloy

Large-scale slender beam structures with low stiffness are widely used in the aviation field. There will be a great deformation problem in machining because the overall stiffness of slender beam parts is lower. Firstly, the cutting mechanism and stability theory of the Ti6Al4V material are analyzed, and then the auxiliary support is carried out according to the machining characteristics of the slender beam structure. The feasibility of the deformation suppression measures for the slender beam is verified by experiments. The experimental analysis shows that on the basis of fulcrum auxiliary support, the filling of paraffin melt material is capable of increasing the damping of the whole system, improving the overall stiffness of the machining system, and inhibiting the chatter effect of machining. This method is effective to greatly improve the accuracy and efficiency during machining of slender beam parts. On the premise of the method of processing support with the combination of fulcrum and paraffin, if the tool wear is effectively controlled, the high precision machining of large-scale slender beams can be realized effectively, and the machining deformation of slender beams can be reduced.

Multi response optimization of PMEDM of Ti6Al4V using Al2O3 and SiC powder added de-ionized water as dielectric medium using grey relational analysis

In the present work, surface characteristics of powder mixed electro-discharge machining (PMEDM) process are investigated using alumina and carborundum abrasive powder added dielectric fluid for titanium alloy Ti6Al4V. Deionized water is utilized as dielectric to accomplish an environmentally safe machining climate, and limit the emanation of harmful substances. Pulse ON/OFF time (TON/TOFF), discharge current (IP), and powder concentration (PC) are selected as process variables to reconnoiter characteristics of performance like surface finish, rate of material removal, and tool wear. The multi-response optimization has been performed using grey relational analysis (GRA) to establish the optimal parametric combination of process variables that gives the finest surface quality and minutest tool wear. The investigation results divulge that discharge current (IP) and powder concentration (PC) have the most significant effect on material removal rate (MRR), tool wear rate (TWR), and surface finish. The surface characteristics were evaluated by scanning electron microscope for the optimal parameters combination. The minutest value of surface roughness and tool wear rate is achieved at IP: 06 amps, TON: 05 µS, TOFF: 96 µS, and PC: 0.50 g/L. The optimized set of parameters would help process engineers to attain improved machining performance of PMEDM, economically along with desired surface characteristics.

Sonotrodes for Ultrasonic Welding of Titanium/CFRP-Joints—Materials Selection and Design

Ultrasonic welding of titanium alloy Ti6Al4V to carbon fibre reinforced polymer (CFRP) at 20 kHz frequency requires suitable welding tools, so called sonotrodes. The basic function of ultrasonic welding sonotrodes is to oscillate with displacement amplitudes typically up to 50 µm at frequencies close to the eigenfrequency of the oscillation unit. Material properties, the geometry of the sonotrode, and the sonotrode tip topography together determine the longevity of the sonotrode. Durable sonotrodes for ultrasonic welding of high-strength joining partners, e.g., titanium alloys, have not been investigated so far. In this paper, finite element simulations were used to establish a suitable design assuring the oscillation of a longitudinal eigenmode at the operation frequency of the welding machine and to calculate local mechanical stresses. The primary aim of this work is to design a sonotrode that can be used to join high-strength materials such as Ti6Al4V by ultrasonic welding considering the longevity of the welding tools and high-strength joints. Material, sonotrode geometry, and sonotrode tip topography were designed and investigated experimentally to identify the most promising sonotrode design for continuous ultrasonic welding of Ti6AlV4 and CFRP. Eigenfrequency and modal shape were measured in order to examine the reliability of the calculations and to compare the performance of all investigated sonotrodes.

Comprehensive in vitro comparison of cellular and osteogenic response to alternative biomaterials for spinal implants

A variety of novel biomaterials are emerging as alternatives to conventional metals and alloys, for use in spinal implants. These promise potential advantages with respect to e.g. elastic modulus compatibility with the host bone, improved radiological imaging or enhanced cellular response to facilitate osseointegration. However, to date there is scarce comparative data on the biological response to many of these biomaterials that would give insights into the relative level of bone formation, resorption inhibition and inflammation. Thus, in this study, we aimed to evaluate and compare the in vitro biological response to standard discs of four alternative biomaterials: polyether ether ketone (PEEK), zirconia toughened alumina (ZTA), silicon nitride (SN) and surface-textured silicon nitride (ST-SN), and the reference titanium alloy Ti6Al4V (TI). Material-specific characteristics of these biomaterials were evaluated, such as surface roughness, wettability, protein adsorption (BSA) and apatite forming capacity in simulated body fluid. The activity of pre-osteoblasts seeded on the discs was characterized, by measuring viability, proliferation, attachment and morphology. Then, the osteogenic differentiation of pre-osteoblasts was compared in vitro from early to late stage by Alizarin Red S staining and real-time PCR analysis. Finally, osteoclast activity and inflammatory response were assessed by real-time PCR analysis. Compared to TI, all other materials generally demonstrated a lower osteoclastic activity and inflammatory response. ZTA and SN showed generally an enhanced osteogenic differentiation and actin length. Overall, we could show that SN and ST-SN showed a higher osteogenic effect than the other reference groups, an inhibitive effect against bone resorption and low inflammation, and the results indicate that silicon nitride has a promising potential to be developed further for spinal implants that require enhanced osseointegration.

Three-dimensional finite element simulation of high speed milling of titanium alloy Ti6Al4V

In this paper, ABAQUS finite element simulation software was used to establish a more reliable three-dimensional milling titanium alloy Ti6Al4V finite element simulation model. This model sets up important links such as the material constitutive model, the tool-chip contact friction model, and the chip separation criterion. And the accuracy of the model is verified by experiments. Based on this model, orthogonal experiment was used to explore the effects of axial cutting depth, tool speed and feed speed on the milling force. And the morphology of the chip and the surface morphology of the machined workpiece were investigated. The results show that the influence of cutting parameters on milling force from high to low is as follows: axial cutting depth > tool speed > feed rate. The change of cutting parameters has different influence on milling force in all directions, and has the largest influence on milling force in X direction.

Finite Element Analysis of the Milling of Ti6Al4V Titanium Alloy Laser Additive Manufacturing Parts

This study aimed to analyze the defects of large residual stress in laser additive manufacturing metal parts by establishing a milling numerical simulation of Ti6Al4V titanium alloy thin-walled parts based on the Johnson-Cook constitutive model of Ti6Al4V titanium alloy, a modified Coulomb friction stress model, the physical chip separation criterion and other theories, combined with the finite element software ABAQUS. The influences of milling depth, initial temperature and milling speed on the forming quality of the formed part were analyzed. The results show that milling changes the residual stress distribution of the deposition layer, which can reduce or even change the residual tensile stress on the surface of the deposition layer produced by the additive manufacturing process into compressive stress, and the equivalent Mises stress decreases by 47% compared with the original forming surface. When the initial temperature increases from 20 °C to 400 °C, the maximum equivalent Mises stress of the milling surface decreases by 26%.

Effects of laser shock peening on the hot corrosion behaviour of the selective laser melted Ti6Al4V titanium alloy

The effects of laser shock peening (LSP) on the hot corrosion behaviour of the selective laser melted (SLMed) Ti6Al4V titanium alloy were investigated. The results indicated that the SLMed specimen exhibited a significantly lower hot corrosion resistance in comparison to the SLM-LSPed specimen. In addition, high-density dislocations and a large number of nano-twins were generated after LSP treatment, which contributed to the grain boundary effect in the surface layer. The coupling effect of LSP-induced grain boundary effect and plastic deformation effectively improved the hot corrosion resistance of the SLMed Ti6Al4V.