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The inlet casing inner has manufactured using Ti-6Al-4V alloy through a closed die-forging route. It undergoes cyclic loads in addition to operating in extreme conditions in high-temperature environments. The demanding mission requirement of these engines necessitates the inlet casing inner to be flawless throughout its life cycle while retaining its structural integrity. It makes the qualification for airworthiness of the casing, a daunting task. In addition, the qualification tests also help to evaluate the design and manufacturing processes (closed die forging) of the inlet casing inner. The tests also provide data for further improvement of the inlet casing inner in terms of strength and fatigue life. It helps to ensure that the inlet casing inner will be able to perform as expected throughout its operational life. All the batch and consolidated test results comply with the relevant ASTM, MIL standards, and test schedule requirements. [ABSTRACT FROM AUTHOR]

Recently, the use of orthodontic mini-screws as an anchorage for orthodontic treatment is increasing, and the degree of osseointegration of the mini-screws affects the performance of orthodontic treatment. This study aimed to evaluate the biocompatibility and osseointegration of Titanium 6Aluminum 4Vanadium (Ti-6Al-4V) alloy orthodontic mini-screws with an ibandronate-loaded TiO2 nanotube (TNT) layer. The TNT layer was formed on the surface of the Ti-6Al-4V alloy orthodontic mini-screws and loaded with ibandronate. The TNT formed by anodic oxidation formed a completely self-organized and compact structure and was stably released for 7 days after loading with ibandronate. Mini-screws loaded with ibandronate were implanted into both tibias of rats, confirming rapid initial bone regeneration. We demonstrate that the release of stable ibandronate from the TNT layer of Ti-6Al-4V alloy orthodontic mini-screws can effectively improve biocompatibility and osseointegration. [ABSTRACT FROM AUTHOR]

In this research, hydroxyapatite powder particles were coated on a Ti-6Al-4V alloy substrate by the plasma spraying method to create bone implants by benefitting from titanium's mechanical properties and hydroxyapatite's biological properties. Hydroxyapatite prepared by the plasma spraying method suffers from decomposition, formation of other calcium phosphate phases, weak adhesion to the substrate, and microcrack formation in the coating due to residual stresses initiated by the high temperature of the coating process. To improve the hydroxyapatite coating properties, the Ti-6Al-4V alloy was preheated, and then hydroxyapatite coating took place. The results showed that residual stress in the interface decreased, and adhesion improved by preheating the substrate. However, formation of an amorphous phase on coating was observed, resulting in a higher dissolution rate in the biological environment and weak mechanical properties compared to crystalline hydroxyapatite. Experimental results showed that heat treatment after the coating process decreased the amount of this amorphous phase and heightened the crystallinity of the coating by up to more than 60%. [ABSTRACT FROM AUTHOR]

• Dry machining of Ti-6Al-4V alloy using novel duel-textured inserts reduces the cutting forces and friction experienced. • Machining with textured inserts can produce chips with significant variations in segment size, shape, and geometry. • Quantitative analysis revealed that the textured inserts produce chips with high shear angle and low segment strain. • The microstructure in the chip produced with textured inserts show differences in strain hardening. • An increase in cutting velocity beyond a critical value could undermine the performance of textured tools. Cutting tool surface texturing is emerging as an eco-friendly alternative to improve the tribological aspects and enhance machining performance. Despite several studies on the merits of textured cutting tools, limited information is available on their effect on chip segmentation. This study presents a quantitative analysis of the chip segmentation characteristics in dry machining of Ti-6Al-4V alloy using duel-textured carbide inserts. The optical and scanning electron microscopy analyses were performed to characterise the chip morphology. The effects of rake surface textures on segment width, shear angle, and chip thickness ratio were assessed and compared with the conventional inserts. In addition, the influence of surface textures on the microstructure of chip roots and the surface roughness of the workpiece was investigated. It appears that the textures on the rake face help reduce the spacing between the segments and the extent of fracture along the shear plane, ultimately reducing the segment strain and surface roughness. Therefore, this study facilitates the understanding of chip morphology and its evolution in turning operation using textured inserts and brings its industrial implementation a step closer. [ABSTRACT FROM AUTHOR]

Compared with the gas metal arc welding (GMAW), the cold metal transfer technology can significantly reduce the welding heat input owing to obtain the output current of almost zero in the droplet detaching, which has a greater advantage in additive manufacturing. In this work, the cold metal transfer was employed to study the law of appearance and mechanical behavior of additively manufacturing of Ti–6Al–4V alloy. The results showed that the continuous and uniform weld appearance could be obtained when the current of 120 A–130 A was used. In the top layer, middle layer and bottom layer of thin-walled components, the same microstructure was obtained with the different parameters, which were mainly consisted of the columnar original β grains and acicular martensite α'. The max-hardness was obtained in the bottom zone (BZ) of thin-walled component. With the increase of welding current, the hardness values in BZ were decreased. With the increases of current, the tensile strength was reduced, which caused by the grain growth. [ABSTRACT FROM AUTHOR]

Machining distortion caused by residual stresses is one of the major challenges in the production of thin-walled monolithic parts. One reason for the distortion is the relaxation of the initial residual stresses within the raw part due to the material removal during the machining process. The initial residual stresses mainly depend on the manufacturing process of the raw part and the subsequent heat treatment. This paper presents the results from a set of experimental and computational studies of the influence of heat treatment on residual stress-related machining distortion of Ti-6Al-4V alloy monolithic parts. A thermo-mechanical simulation of the heat treatment process is developed for the prediction of the initial residual stresses. For experimental validation, the contour method is used to quantify the initial residual stresses. Finally, machining tests are conducted to measure the final part distortion for two different residual stress states. [ABSTRACT FROM AUTHOR]

The change in the spectra of elastically and discretely scattered electrons in Ti–6Al–4V alloy subjected to radial shear rolling at T = 1000°C was studied in comparison with the initial state. Interatomic bonds in the equilibrium α phase of the alloy are formed by Al sp electrons, and their contribution is small. Quenching after radial shear rolling at T = 1000°C causes the formation of a nonequilibrium αʹ phase in the α phase. The resulting αʹ phase contains vanadium atoms whose d electrons are part of the interatomic bond. As a result, the α phase is strengthened and the low-temperature toughness of the alloy is enhanced. At the same time, sp electrons are strongly scattered by vanadium ions and therefore their contribution to the interatomic bond is weakened. This generates localized plastic flows in the lattice curvature zones, which develop in the field of Coulomb repulsion of electrons and govern a high relaxation ability of the alloy at low temperatures. Very high strengthening is found to be fundamentally related to a very high relaxation factor. The results are explained by the effect of structural transformation. [ABSTRACT FROM AUTHOR]

Ti-6Al-4V alloy is used as biomaterials for dental and orthopedic implants because of their excellent biocompatibilities and mechanical properties. However, it is unclear that electron cyclotron resonance (ECR) plasma oxidation can create the oxide films on Ti-6Al-4V alloy surface, and this technique improves the ability of its osseointegration. The purpose of this study was to investigate the characteristics and calcification ability of the oxide films. X-ray diffraction (XRD) peaks of rutile phase were intensified with increasing the temperature. Scanning electron microscopy (SEM) images showed a crater-like structure, and bonding strengths between the substrate and oxide film reached a maximum at 400°C. Calcium phosphate (CaP) compounds after calcification process were identified as octacalcium phosphate (OCP) and precipitation amount was maximized at 400°C. The results suggested that the altered surface of Ti-6Al-4V alloy by ECR plasma oxidation might have the potential of accelerating the ability of its osseointegration through enhancement of OCP. [ABSTRACT FROM AUTHOR]

The paper studies the effect of the temperature of helical rolling, which creates nanoscale mesoscopic structural states in lattice curvature zones, on the low-temperature impact toughness of Ti–6Al–4V alloy. The polymorphic transformation temperature Tс = 950°C is shown to play the decisive role in this effect. The impact toughness is very high at helical rolling temperatures above Tс, while in the low-temperature range up to T = –70°C it decreases monotonically. This is a very important aspect of the technology. Starting from the helical rolling temperature T = 950°C, the toughness sharply decreases at T = –70°C. At T = 900°C, it decreases sharply already at T = –20°C. At T = 850°C, the level of the entire toughness curve of the alloy is low. The high level of impact toughness at T > Tс is found to be due to a two-stage transformation of the bcc β phase into a mixture of (α + β) phases. The first stage involves nonequilibrium microscopic decomposition into the α and β phases. At the second stage, the nonequilibrium β phase decomposes into (α + β) subbands in accordance with the interstitial structural states associated with lattice curvature. In helical rolling at T < Tс, the formation of martensite phases in the close-packed lattice of the α phase of titanium reduces its impact toughness. The fatigue life of Ti–6Al–4V alloy helically rolled at T = 1000°C remains unchanged. [ABSTRACT FROM AUTHOR]

The study of laser cladding of 90Ti-10Al2O3, 90Ti-8Al2O3-2Zn and 90Ti-4Al2O3-6Zn coatings onto Ti-6Al-4V alloy, with intention to produce defect-less, high microhardness and wear resistant coating was carried out. The coatings were deposited onto Ti-6Al-4V alloy at 900 W laser power and 0.6 m/min laser scan speed. Microstructures and phase constituents of the developed coatings were investigated by using a scanning electron microscope (SEM) and X-ray diffractometer correspondingly. Vickers microhardness tester and pin-on-disk tribometer were employed to characterize microhardness and wear behaviour of the Ti-Al2O3/Zn coatings respectively. SEM was also used to examine the worn track. It was observed that 90Ti-10Al2O3 coating yielded optimal microhardness along with maximal wear resistance in comparison to the other coatings and Ti-6Al-4V alloy. It has been established that laser cladding of Ti-Al2O3 coating with Zn contents on Ti-6Al-4V alloy alleviates the formation of cracks, however, microhardness and wear properties are negatively affected. [ABSTRACT FROM AUTHOR]

Recently, the production of well-defined patterned surfaces with random or regular micro and nano-features has brought new opportunities for research and development in the field of tissue engineering and regenerative medicine. Among advanced micro and nano processing technologies, laser surface texturing (LST) stands out due to its simplicity, flexibility, precision, reproducibility and relatively low cost. This work studies the development of patterned surfaces controlled by of LST into biomedical grade V titanium, Ti–6Al–4V–alloy. We present different cross-hatched micropatterns followed by the characterisation of surface morphology and topography. Structural integrity of the produced patterns is evaluated by friction tests against bone, mimicking the insertion of an implant. Wettability is studied as it is crucial for protein adsorption and cell adhesion. The results show that the surface topography obtained using different patterning plans influences the wetting behaviour and the coefficient of friction against bone. [ABSTRACT FROM AUTHOR]

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In the present work, inter-diffusion of nickel and titanium and formation of Ni-Ti intermetallic compounds on Ti-6Al-4V substrate have been studied. Initially, nickel was electrodeposited on the alloy using a modified Watts bath solution at a current density of 2 A dm−2 for 1 h. The coated specimens were then heat treated for different durations at 750, 800 and 850 °C under argon atmosphere. The effects of temperature and time on the characteristics, hardness and wear resistance of intermetallic phases were investigated. The results showed that a multilayer structure was formed after heat treatment, an outer layer of residual nickel, an area of intermetallic layers with different compositions followed by a solid solution of Ni-Ti. It was also observed that an increase in time or temperature at first led to the formation of thicker intermetallic layers; however, after passing a critical point, the intermetallic layers seem to dissolve into the substrate. Furthermore, the wear rates of the diffusion treated samples were four times lower compared to Ti-6Al-4V alloy when sliding against AISI 52100 hardened steel. [ABSTRACT FROM AUTHOR]

In this paper, inorganic phosphate bonded coatings (IPBCs) via embedding reduced graphene oxide (rGO) modified with heptadecafluoro-1,1,2,2-tetradecyl trimethoxysilane (FAS) were prepared through sol-gel method. Aim of this paper is to research the corrosion resistance of IPBCs with the addition of rGO modified with FAS. Firstly, the Fourier transform infrared spectroscopy (FT-IR), Raman spectroscopy (Raman) and surface morphology of GO and rGO modified with and without FAS were characterized. Results indicated that the hydrophobic –CF 2 – and –CF 3 groups were successfully introduced into GO and rGO after modification. And IPBCs with rGO-FAS exhibited higher hydrophobicity and corrosion resistance than IPBCs with the addition of GO or GO-FAS. That is because the hydrophobicity and the introduction of low surface energy material is conducive to overcoming the interaction of rGO itself, thus rGO can be better utilized and played, which resulting the excellent corrosion performance of IPBC@rGO-FAS. [ABSTRACT FROM AUTHOR]

Abstract The effects of process parameters of laser additive manufacturing (laser power, scanning speed, scanning direction) and heat treatment on the microstructure and properties of Ti-6Al-4V titanium alloy forming parts were studied under coaxial powder feeding. The results show that the columnar crystals of the Ti-6Al-4V forming parts made by laser material are all wechsler structure, and there are obvious layers in the layer; the strength of laser reinforced Ti-6Al-4V titanium alloy parts exceeds the requirements of national standard for as cast and forged Ti-6Al-4V titanium alloy; With the increase of laser power, the tensile strength and yield strength of Ti-6Al-4 V titanium alloys tend to increase first and then decrease, and the maximum value is obtained when the laser power is 500 W; when the scanning speed increased from 0.12 m/min to 0.60 m/min, the tensile strength and yield strength of the Ti-6Al-4V titanium alloy showed a gradual decrease, but the elongation gradually increased; when the laser scanning mode is changed from single sweep to round-trip scanning, the tensile strength and yield strength of Ti-6Al-4V titanium alloy have been improved, but the elongation has decreased significantly. Through the solution and aging heat treatment at 950 °C/AC/1 h + 540 °C/AC/4 h, the original wechsler structure can be improved and the high performance net basket organization can be obtained, this is the fundamental reason for improving the comprehensive performance of the forming parts. [ABSTRACT FROM AUTHOR]

Titanium and its alloys are widely used in the biomedical sector. In this field, titanium and its alloys are the material of choice for biomedical devices such as hip and knee replacements. Usually, a Total Hip Replacement (THR) is based on four components, made out of different materials due to the material properties associated with the functional performance. One approach to lower the overall manufacturing costs and enhance the reliability of THR’s is to manufacture the prosthesis out of one material. The titanium alloy Ti-6Al-4V is, therefore, feasible as it exhibits better osseous integration compared to other metallic materials used as orthopedic devices. The sole use of Ti-6Al-4V alloy requires improvements of surface integrity (SI) and characteristics that are sensitive to SI. One possible way to improve the tribological properties of the THR and the biocompatibility of Ti-6Al-4V alloy is to deliberately decrease the material grain size in the surface layer from the micron scale (> 1 µm) to the region of nano-sized grains (< 100 nm). The objective of this paper is to study and prove the formation of nano-sized grains within the surface as well as the characterization of surface integrity when machining Ti-6Al-4V alloy. Therefore, different cryogenic cooling strategies are used where liquid nitrogen (LN 2 ) is applied to the flank and rake face, and just to the flank face respectively. To compare the effect of cryogenic machining, conventional flood cooling was applied as third cooling strategy. As cutting tool, a roughing tool, having a large cutting edge radius, was used, since severe plastic deformation (SPD) has shown to be capable to produce nano-sized grains in the surface. The results showed, that cryogenic machining using a large cutting edge radius tool is able to decrease the materials grain size to the region of nano-sized grains. [ABSTRACT FROM AUTHOR]

Titanium alloys stand out primarily due to their high specific strength and excellent corrosion resistance, they have higher mechanical strength to weight ratio but are 40% lighter than steel. It is widely used in aero-engines, gas turbines and aero-space structures and titanium products increased during the last decade. However, it is well known that titanium alloy is difficult to be formed at room temperature. Therefore, hot stretch bending (HSB) process was developed to create bent parts of extruded Ti-6Al-4V titanium alloy profile, thus reducing the cost impact of raw material and finished machining. In the present paper, a new force-controlled electric heating rotary stretch bending (HRSB) process was developed. In order to obtain the precise bending of titanium alloys extrusion, experimental investigations for extruded Ti-6Al-4V Alloy profile with T-section are carried out. Firstly, experimental method of HRSB and electric heating tension are proposed. Secondly, the HRSB process of Ti-6Al-4V Alloy extrusion at different forming temperatures and tension forces was investigated. Lastly, microstructures of Ti-6Al-4V Alloy formed in different conditions are investigated using SEM, TEM and EBSD method. The results show that: (1) When initial temperature of Ti-6Al-4V titanium alloy profile ranges from 700 to 750 ° C, and temperature of die surface ranges from 100 to 200 ° C, the forming quality and precision are higher. (2) Increasing post-stretching force can reduce the angle springback of Ti-6Al-4V titanium alloy profile. The results may help to provide the basis for the determination and optimization of hot stretch bending of Ti-6Al-4V titanium alloy profile. [ABSTRACT FROM AUTHOR]

The mechanical properties are impacted by the surface condition of metals. Titanium alloy is oxidized and diffused oxygen into substrate, leading to phase transition in an atmosphere with oxygen. The alpha-case kinetics and tensile behavior of Ti-6Al-4V alloy by high temperature oxidized in different phase regions were investigated by static oxidation test over the temperature range of 850-1100 °C and tensile tests over the temperature range of 830-950 °C. The relationship between high temperature plasticity, oxidation and microstructural transformation of titanium alloy was analyzed by metallographic method, hardness measurements and scanning electron microscopy. The results showed that the inward diffusion of oxygen was the reason of alpha-case generation, which modified the different effects at the surfaces of titanium in different phase regions. The cracks were observed at the surface of the specimens whose depths were greater at higher temperatures. The thickness of this alpha-case was increasing with elevated temperature. Under the high strain rate, the lower stress value of the thermally oxidized Ti-6Al-4V alloy in the vicinity of yielding point was observed compared with that unoxidized. The fractographic appearances of specimens oxidized were brittle and sharp type, while the fracture mode of specimens was ductile fracture without alpha-case. The higher amount of oxygen in α phase both stabilized α phase forming a microstructure and strengthened the α phase via solid solution strengthening. The existence of alpha-case led to easier surface crack initiation and propagation under the tension stress state. [ABSTRACT FROM AUTHOR]

Generally, torsion deformation has been recognized as a method of severe plastic deformation (SPD) to obtain a higher shear strain. The effect of strain reversal on the microstructure and mechanical properties was investigated using commercially Ti-6Al-4V alloy by twisting the rods with different effective strain amplitude, such as 180#x00B0;, 270#x00B0;, 360#x00B0; and 450#x00B0; per half cycle. In this work, the microstructure evolution and fracture morphology were carried out by a scanning electron microscope (SEM) and transmission electron microscope (TEM). An Instron 3382 was used for determining ultimate compression strength (UCS). The results show that UCS is very sensitive to cyclic forward-reverse torsion (CFRT) processing and increase distinctly after pre-CFRT. And the value of UCS reaches maximum at 180#x00B0; per half cycle. Besides, monotonic torsion (MT) by twisting the rods in one direction until the fracture occurs was also compared with CFRT. It is found that the ability of work hardening and accumulation of plastic strain is higher for CFRT as compared to MT, which is due to the latticed dislocation in the interior of the grains under CFRT deformation. Grain refinement and fracture feature were discussed to reveal the deformation mechanism of CFRT and MT. The discussion of microstructure evolution and strengthening mechanisms will provide a view to extrapolation to larger strains, finer structures and larger stresses. [ABSTRACT FROM AUTHOR]

When the Ti-6Al-4V alloy is overaged at 500-600°C, nanometer-sized α (TiAl) particles can be homogeneously precipitated inside a phases, thereby leading to strength improvement. Widmanstätten and equiaxed microstructures containing fine α (TiAl) particles were obtained by overaging the Ti-6Al-4V alloy. Precipitation of α (TiAl) particles was monitored using thermoelectric power measurements for different aging conditions in the Ti-6Al-4V alloy. Overaging heat treatments were conducted at 515, 545 and 575°C for different aging times. In addition, overaging samples were examined by optical microscopy, scanning electron microscopy and hardness measurements. It was found that the thermoelectric power is very sensitive to the aging process in the two studied Ti-6Al-4V structures. [ABSTRACT FROM AUTHOR]

Plasma arc additive manufacturing (PAM) is a novel additive manufacturing (AM) technology due to its big potential in improving efficiency, convenience and being cost-savings compared to other AM processes of high energy bea\m. In this research, several Ti-6Al-4V thin walls were deposited by optimized weld wire-feed continuous PAM process (CPAM), in which the heat input was gradually decreased layer by layer. The deposited thin wall consisted of various morphologies, which includes epitaxial growth of prior β grains, horizontal layer bands, martensite and basket weave microstructure, that depends on the heat input, multiple thermal cycles and gradual cooling rate in the deposition process. By gradually reducing heat input of each bead and using continuous current in the PAM process, the average yield strength (YS), ultimate tensile strength (UTS) and elongation reach about 877 MPa, 968 MPa and 1.5%, respectively, which exceed the standard level of forging. The mechanical property was strengthened and toughened due to weakening the aspect ratio of prior β grains and separating nano-dispersoids among α lamellar. Furthermore, this research demonstrates that the CPAM process has a potential to manufacture or remanufacture in AM components of metallic biomaterials without post-processing heat treatment. [ABSTRACT FROM AUTHOR]

In this paper numerical analysis of hip replacement implant behaviour from a fracture mechanics perspective is presented. It is necessary to understand the fatigue crack initiation and propagation characteristics in order to prevent catastrophic failure of the implant. For the simulation of crack propagation extended finite element method (XFEM) was used, as being one of the most advanced modeling techniques for this type of problem. Short theoretical background information on the XFEM is provided, as well as the representation of crack and the stress intensity factors computation. For chosen titanium alloy hip implants numerical modeling and analysis were done in ABAQUS software. It is shown that is possible to assume hip implant mechanical behaviour to the existence of defects such as cracks by application of numerical simulation crack behaviour. The numerical results illustrate that XFEM is efficient for the simulation of crack propagation in complicated biomedical structures, without the need to re-mesh during the propagation if the finite element mesh is well defined. [ABSTRACT FROM AUTHOR]

In this paper a numerical investigation of replacement implant for partial hip arthroplasty is presented. The long-term stability of hip implants depends, among other things, on the loads acting across the joint. Forces occurring in vivo can be much greater than the recommended test values, because a typical gait cycle generates forces up to 6–7 times the body weight in the hip joint. A finite element analysis (FEA) was performed using 3-dimensional models to examine the mechanical behaviour of the femoral component at forces ranging from 2.5 to 6.3 kN. This implant design was chosen for numerical analysis because stress concentration in femoral component lead to implant fracture. Results show that the force magnitudes acting on the implant are of interest, and that they can cause implant stress field changes and implant stability problems, which can lead to implant failure. [ABSTRACT FROM AUTHOR]

The present study reports the corrosion fatigue of the Ti–6Al–4V alloy using cyclic deformation test in a simulated body fluid under cell culturing for the first time. Cyclic deformation tests were carried out using three types of specimens to reveal the effects of proteins and cells on the corrosion fatigue of the alloy. For the 1-day-immersed and 1-week-immersed specimens, tensile specimens were soaked in a simulated body fluid for 1 day and 1 week, respectively, before cyclic deformation test, whereas for the cell-cultured specimen, MC3T3-E1 osteoblast-like cells were seeded and then cultured on tensile specimens for 1 week. The incubation period for crack initiation was longer for the cell-cultured and 1-week-immersed specimens compared to that for the 1-day-immersed specimen. On the other hand, crack propagation period for the cell-cultured and 1-week-immersed specimens was shorter than that for the 1-day-immersed specimen. These results indicate that proteins and cells adhered on the alloy surface inhibit metal dissolution at newly created surface emerged by cyclic deformation to suppress crack initiation, whereas they accelerate crack propagation because dissolution at crack tip is accelerated in the occluded space formed under proteins and cells. [ABSTRACT FROM AUTHOR]

The present investigation mainly focuses on effects of centrifugal forces and casting modulus on structures and mechanical properties of Ti-6Al-4V alloy formed under different vertical centrifugal casting conditions in graphite molds. Mold rotating rates of 0, 110 and 210 r/min were adopted in the experiment. Results show that grain size and lamellar thickness decrease with the decreasing of casting modulus or the increasing of centrifugal force, while tensile strengths are considerably enhanced, but the elongation of the casting shows the opposite changing trend. The quantitative relationships among gravity coefficient, casting modulus and structures or mechanical properties of Ti-6Al-4V alloy have been obtained. As the comparison of Ti-6Al-4V alloy cast in graphite mold under gravity field, the structures of stepped casting in metal mold were also investigated. It is found that the grain size or lamellar thickness in the two molds shows the same changing trend with the cooling rate, and the quantitative relationships between structures and cooling rates have been obtained. [ABSTRACT FROM AUTHOR]

The influence of cold plastic deformation on passivity of Ti-6Al-4V alloy (UNS R56400) was investigated by means of potentiodynamic polarization, Mott-Schottky analysis, atomic force microscopy, and scanning Kelvin probe force microscopy. The results showed that the cold working increased the passive current density. Mott-Schottky analysis revealed the n-type semiconducting behavior of the passive film. The donor density of the passive film was declined by increasing the film formation potential. On the other hand, work hardening increased the density of defects within the passive film, regardless of the applied potential. The Volta potential maps showed that a phase possesses lower surface potential compared to the β, i.e., 38.6 mV. The plastic deformation decreased the surface potential of both phases; however, the relative nobility of the constituent phases had been slightly affected by cold working, i.e., 5 mV. The topographic results after immersion of the alloy in an aggressive acidic environment revealed that the Volta potential difference between a and β was sufficient to make a more vulnerable to corrosion attacks. [ABSTRACT FROM AUTHOR]

To understand the relationship among the processes, mechanical properties and microstructures of the Ti-6Al-4V alloy processed by the different combinations of ring rolling, bulging and different heat treatments, the correlation between the α- and β-phase morphologies, the strength and plasticity properties of tensile tests at ambient temperature and elevated temperature were investigated. Researches indicate that adding the second procedure, bulging, is necessary after the rolling process under the condition of the appropriate heat treatment. The tensile properties are closely related to the size and the volume fraction of the primary α-phase, the size and the thickness of the secondary α-phase. Furthermore, the bulging after heat treatment mainly affects firstly the size of primary α-phase, and the compositions of α- and β-phase, secondarily the size and the quantity of the secondary platelet α-phase. The elongation decreases when the primary α-phase transforms from the small equiaxed to the thick multilateral shape. As the volume fraction of the primary α-phase decreases and the proportions of both untransformed β structure and the dispersed secondary α-phase increase, the alloy strength increases. Fracture modes of the elevated temperature tensile fracture samples were determined as the ductile fracture. Poor plastic deformation ability is attributed to the casting micro-defects on the fracture surface. [ABSTRACT FROM AUTHOR]

Crevice corrosion behavior of commercial pure titanium (CP Ti), Ti-6Al-4V alloy and Ti-Ni Shape Memory Alloy (SMA) were investigated through an electrochemical methods in Ringer's artificial body fluids. The results indicate that the crevice corrosion occurs for all alloys in Ringer's artificial body fluids at potential of 400 mV. The crevice corrosion for all alloys increases with the increase of corrosion solution temperature. The corrosion potential of Ti-6Al-4V alloy is more positive than that of CP Ti and Ti-Ni SMA, manifesting that the anodic polarization characterization of Ti-6Al-4V is better than those of both CP Ti and Ti-Ni SMA. So its crevice corrosion resistance is enhanced. The dynamic equations of crevice corrosion for CP Ti, Ti-6Al-4V and Ti-Ni SMA are as follows: i T, CPTi =0.028 e −2×10 −4 t , i T, Ti-6Al-4V =0.0149 e −3×10 −4 t , i T, Ti-Ni SMA =0.4712 e −7×10 −4 t , which indicate that the process of the crevice corrosion is controlled by the dissolution of chloride salt film on its surface. [ABSTRACT FROM AUTHOR]

The diffusion kinetics of hydrogen in Ti-6Al-4V alloy was investigated by the gaseous hydrogen charging at the initial hydrogen pressures of 0.012, 0.04 and 0.07 MPa and the temperatures of 800, 850 and 900 °C. The results show the variation of the average hydrogen concentration in the alloy with hydrogen charging time exhibits an exponential characteristic relationship at different initial hydrogen pressures or hydrogen charging temperatures. The hydrogen charging process is controlled by the diffusion of hydrogen atoms in Ti-6Al-4V alloy. Based on the solution of diffusion equation, the apparent activation energy of hydrogen diffusion in Ti-6Al-4V alloy is estimated to be 32.80 kJ/mol. This energy is the activation energy of hydrogen diffusion in β phase of Ti-6Al-4V alloy. [ABSTRACT FROM AUTHOR]

Optimum condition of hot processing parameter with the premise of achieving the desired mechanical properties is often carried out from the corresponding references and checked subsequently using the trial-and-error approach, which consequently costs large amount of time and is highly associated with the experience and skills of the materials scientists. As the key branch of soft computing, the technique of combined artificial neural network (ANN) and genetic algorithm (GA) has been widely utilised to predict and optimise the processing parameter. In this work, the forging and heat treatment experiments of Ti-6Al-4V alloy were conducted with various experimental parameters, including forging temperature, deformation degree and heat treatment. The mechanical properties including the ultimate tensile strength, yield strength, elongation and reduction in area of this alloy were obtained by the tensile tests at room temperature. On the basic of obtained experimental data, the optimal model of hot processing parameters of Ti-6Al-4V alloy was established with the help of the combination of ANN and GA. It was found that the final research result is consistent with the actual experimental value, suggesting the fact that the developed optimisation model is an available and powerful tool to deal with multiple variables and nonlinear relationship problems, and can be widely utilised in the area of materials science and engineering. [ABSTRACT FROM AUTHOR]

The effect of cryogenic treatment on wear resistance of Ti–6Al–4V alloy for biomedical applications was experimentally investigated in this paper. Cryogenic treatments with the same soaking time of 24h at different temperatures of −80°C, −140°C and −196°C were conducted and the treatments at the same temperature of −196°C were then further given different soaking time of 3h, 48h and 72h to be investigated. After cryogenic treatment, the Vickers hardness of specimens was measured. Wear resistance of Ti–6Al–4V alloy was measured by pin-on-disk wear test under dry sliding condition. The results demonstrated that the Vickers hardness increased slightly with the reduction of temperature while it increased obviously with the elongation of soaking time at −196°C. The friction coefficients of specimens cryo-treated at −196°C were lower than those of untreated and of cryo-treated at −80°C and −140°C. And the longer the soaking time is during the cryogenic treatment, the higher the friction coefficient reduction can be achieved. The obvious reduction of mass loss can be obtained at −196°C with 72h soaking. The X-ray diffraction (XRD) and scanning electron microscopy (SEM) were used to detect the microstructure and worn surface of specimens. By cryogenic treatment, the plowing in the worn surface was smoothed and shallowed, and the degree of plastic deformation in the subsurface was decreased. There was no obvious phase transformation which can be detected in the microstructure after cryogenic treatment. However, the tendency of refinement in grain size can be detected by XRD which improved the wear resistance of Ti–6Al–4V alloy. [ABSTRACT FROM AUTHOR]

Abstract: In the case of sheet metal characterization, compression tests at normal direction of the sheet can be done by means of the layer compression test. Circular cylinder specimens are commonly used for compression test but the complicated layer alignment is time consuming and may induce a wrong anisotropy characterization. This final goal explains the interest of working on elliptic shape. In this article, an elliptical cylinder specimen is proposed and tested for bulk Titanium alloy. Full-field optical technique (3D Digital Image Correlation) is used for displacement measurements by means of three camera systems (Limess), which allows out-of-plane displacement/strain fields on around 300° of the specimen. The use of this technique easily provides accurate barreling profile used to compute Coulomb friction coefficient by using inverse method. In addition, stress-strain curves computations are more accurate than conventional method, and plastic anisotropy characterization can be obtained by using the measured shape evolution of the specimen and local strain distribution. [Copyright &y& Elsevier]

Abstract: Hydrogenation of Ti-6Al-4V titanium alloys was carried out in a special furnace through the accumulated flux method, and OM, XRD and TEM techniques were used to investigate the microstructure evolution of the hydrogenated Ti-6Al-4V titanium alloy. The hydrogenation of the Ti-6Al-4V titanium alloy with the hydrogen content of 0.30 wt% makes the α phase fraction decrease compared with that of the as-received Ti-6Al-4V titanium alloy, but it makes the β phase fraction increase. The δ hydride (TiH2 phase) occurs in the hydrogenated Ti-6Al-4V titanium alloy when the hydrogen content is more than 0.3 wt%. The shear deformation is main pattern in the transformation processes from β-Ti(H) phase to α-Ti phase and δ hydride (TiH2 phase). The phase transformation temperature of the hydrogenated Ti-6Al-4V titanium alloy decreases by 180 °C compared with that of the as-received Ti-6Al-4V titanium alloy, and it is related to the phase fraction and phase transformation. [Copyright &y& Elsevier]

Abstract: The effect of the deformation temperature, deformation degree, strain rate and their interaction on the microstructure and mechanical properties in the high temperature deformation of Ti-6Al-4V alloy was investigated. The experimental results show that the deformation degree and strain rate have significant influence on the microstructure and mechanical properties, in which finer microstructure and higher tensile strength can be obtained at a middle deformation degree and a higher strain rate. The interactions between the deformation temperature and the deformation degree or the strain rate in the high temperature deformation of Ti-6Al-4V alloy are significant, especially being deformed at the temperature just under the β transus, the ductility and tensile strength are sensitive to all of processing parameters including their interactions. So the interactions should be considered to optimize the processing parameters in order to meet the requirements of the mechanical properties. [Copyright &y& Elsevier]

As the global trauma fixation devices market expands rapidly, it is imperative to improve the production of fixation devices through enhanced design accuracy and fit for best performance and maximum patient comfort. Selective laser melting (SLM) is one of the mature additive manufacturing methods, which provides a viable route for the rapid production of such devices. In this work, the ability of SLM to produce near-net-shape parts, as desired for medical implants, was utilized for the fabrication of bone plates from Ti-6Al-4V alloy powder. Martensitic microstructure obtained after the printing of alloy resulted in poor ductility, limiting its application in the field of orthopedics. A specially designed repeated cyclic heating and cooling close to but below the β-transus was used to transform from acicular to a bimodal microstructure without the need for plastic deformation prior to heat treatment for improving the ductility. Bone plates subjected to this heat treatment were mechanically tested by means of tensile and 3-point bend tests and demonstrated large improvement in ductility, and the values were comparable to those similar plates prepared from wrought alloy. Other important properties required for implants were assessed, such as corrosion resistance in simulated body fluid and cytocompatibility in vitro using MC3T3-E1 cells. These results for the bone plate after heat treatment were excellent and similar to those of the additively manufactured and wrought plates. Taken together, the performance of the additively manufactured bone plates after subjecting to heat treatment was similar to those of bone plate manufactured using wrought alloy. These results have important implications for the fabrication of patient-specific metallic orthopedic devices using SLM without compromising their biomechanical performance by subjecting them to a tailored heat treatment. [ABSTRACT FROM AUTHOR]

The grain structure and surface morphology of bio-implants act as a pivotal part in altering cell behavior. Titanium alloy bone screws, as common implants, are prone to screws loosening and complications threat in the physiological environment due to their inferior anti-wear and surface inertia. Manufacturing bone screws with high wear resistance and ideal biocompatibility has always been a challenge. In this study, a series of overlapping morphologies inspired by the hierarchical structure of fish scales and micro bulges of shrimp were structured on Ti–6Al–4V implant by laser texturing. The results indicate that the textured patterns could improve cell attachment, proliferation, and osteogenic differentiation. The short-term response of human bone marrow-derived mesenchymal stem cells (hBMSCs) on the textured surface are more sensitive to the microstructure than the surface roughness, wettability, grain size and surface chemical elements of the textured surfaces. More importantly, the friction-increasing and friction-reducing type overlapping structures exhibit excellent friction stability at different stages of modified simulated body fluid (m-SBF) soaking. The overlapping structure (Micro-smooth stacked ring: MSSR) is more beneficial to promote the formation of apatite. Deposited spherical-like apatite particles can act as a "lubricant" on the MSSR surface during the friction process to alleviate the adhesion wear of the surface. Meanwhile, apatite particles participate in the formation of friction film, which plays an effective role in reducing friction and antiwear in corrosion solution (m-SBF) for a long time. These features show that the combination of soaking treatment in m-SBF solution with laser-textured MSSR structure is expected to be an efficient and environmentally friendly strategy to prolong the service life of bone screws and reducing the complications of mildly osteoporotic implants. • The overlapping structure exhibits a promotion in the short term response of hBMSCs and apatite deposition ability. • The main factors influencing the frictional stability and hBMSCs behaviors on the textured surface are revealed. • Soaking treatment can further improve the tribological properties of the textured surface with overlapping structures. • The formation process and lubrication mechanism of apatite on the textured surface are proposed. [ABSTRACT FROM AUTHOR]

• Effects of laser power and track overlapping in selective laser melting are studied. • The scanning speed also varied to keep the energy density at the obtained best value. • Density, porosity and microstructural features of Ti6Al4V are observed and analyzed. • Laser power and track overlapping affected keyhole and melting defects respectively. • Laser power, speed and track overlapping varied α′ size and another microstructure. The improvement of the density with functional microstructure is still a challenge in the Selective Laser Melting process considering the laser processing parameters. In this study, the pore formation mechanisms and microstructural changes caused by the effects of laser power and track overlap during the manufacturing process in selective laser melting were examined. Laser power played a crucial role in the geometry and quantity of keyhole pore formation and thus in improving density and quality. In contrast, a slightly higher track overlap led to a significant reduction in porosity, resulting in the production of fully dense samples of a Ti-6Al-4V alloy. The gradual variations in the solid-state phase transformation architecture occurred with variations in laser power and track overlap due to the use of different thermal mechanisms. The associated scanning speeds also significantly affected the microstructural architectures in some states. The melt pool dynamics and thermal properties that influenced the metallurgical properties of the samples are analyzed and interpreted. The analysis of the presented consequences can help the engineers to produce high density products together with functionally graded materials. [ABSTRACT FROM AUTHOR]