Optimization of annealing treatment and comprehensive properties of Cu-containing Ti6Al4V-xCu alloys

The Ti6Al4V-Cu alloy was reported to show good antibacterial properties, which was promising to reduce the hazard of the bacterial infection problem. For the purpose of preparing Ti6Al4V-Cu alloy with satisfied comprehensive properties, it’s important to study the heat treatment and the appropriate Cu content of the alloy. In this study, high Cu content Ti6Al4V-x Cu(x = 4.5, 6, 7.5 wt%) alloys were prepared, and firstly the annealing heat treatments were optimized in the α+β+Ti2Cu triple phase region to obtain satisfied tensile mechanical properties. Then the effect of Cu content on the tribological property, corrosion resistance, antibacterial activity and cytotoxicity of the Ti6Al4 V-x Cu alloys were systematically studied to obtain the appropriate Cu content. The results showed that the optimal annealing temperatures for Ti6Al4 V-x Cu(x = 4.5, 6, 7.5 wt%) alloys were 720, 740 and 760℃, respectively, which was resulted from the proper volume fractions of α,β and Ti2Cu phases in the microstructure. The additions of 4.5 wt% and 6 wt% Cu into the medical Ti6Al4 V alloy could enhance the wear resistance and corrosion resistance of the alloy, but the addition of 7.5 wt% Cu showed an opposite effect. With the increase of the Cu content, the antibacterial property was enhanced due to the increased volume fraction of Ti2Cu phase in the microstructure, but when the Cu content was increased to 7.5 wt%, cytotoxicity was presented. A medium Cu content of 6 wt%, with annealing temperature of 740℃ make the alloy possesses the best comprehensive properties of tensile properties, wear resistance, corrosion resistance, antibacterial property and biocompatibility, which is promising for future medical applications.

Corrosion and tribocorrosion behaviors of AISI 316 stainless steel and Ti6Al4V alloys in artificial seawater

The corrosion and tribocorrosion behaviors of AISI 316 stainless steel and Ti6Al4V alloys sliding against Al2O3 in artificial seawater using a pin-on-disk test rig were investigated. And the synergistic effect between corrosion and wear was emphatically evaluated. The results show that the open circuit potentials of both alloys drop down to more negative value due to friction. The corrosion current densities obtained under tribocorrosion condition are much higher than those under corrosion-only condition. Friction obviously accelerates the corrosion of the alloys. The wear loss for both alloys is larger in seawater than that in pure water. Wear loss is obviously accelerated by corrosion. And AISI 316 stainless steel is less resistant to sliding damage than Ti6Al4V alloy. The synergistic effect between wear and corrosion is a significant factor for the materials loss in tribocorrosion. In this surface-on-surface contact geometry friction system, the material loss is large but the ratio of wear-accelerated-corrosion to the total wear loss is very low.

Wear behavior of Ti6Al4V biomedical alloys processed by selective laser melting, hot pressing and conventional casting

The aim of this work was to study the influence of the processing route on the microstructural constituents,hardness andtribological(wear and friction)behavior of Ti6Al4V biomedical alloy.In this sense,three different processing routes were studied:conventional casting,hot pressing and selective laser melting.A comprehensive metallurgical,mechanical and tribologicalcharacterization was performed by X-ray diffraction analysis,Vickers hardness tests and reciprocating ball-on-plate wear tests ofTi6Al4V/Al2O3sliding pairs.The results showed a great influence of the processing route on the microstructural constituents andconsequent differences on hardness and wear performance.The highest hardness and wear resistance were obtained for Ti6Al4Valloy produced by selective laser melting,due to a markedly different cooling rate that leads to significantly different microstructurewhen compared to hot pressing and casting.This study assesses and confirms that selective laser melting is potential to producecustomized Ti6Al4V implants with improved wear performance.

Deformed microstructure and texture of Ti6Al4V alloy

Microstructure and texture evolution during hot compression of Ti6Al4 V alloy with an initial equiaxed microstructure were studied in the temperature range of 850-930 °C, strain rate range of 0.01-1 s-1 and engineering compressive strain of 70%. The results indicate that when temperature is below 900 °C and strain rate is higher than 0.1 s-1, the microstructure is mainly composed of elongated α grains. While deforming at higher temperatures and lower strain rates, dynamic recrystallization takes place. Electron back scattered diffraction（EBSD） result shows that during dynamic recrystallization, subgrain boundaries absorb dislocations and the recrystallized grains with high angle grain boundary form. At 930 °C dynamic recrystallization has basically completed, and needlelike α phase forms after water quenching. Pole figure analysis indicates that compared with the initial specimen, textures below 930 °C are weaker, while at 930 °C they are stronger.

Analysis on the Wear Performances of Cemented Carbide Tools Containing Ti in the Coatings When Machining Ti⁃6Al⁃4V Alloys

Because of the high affinity of the same element Ti,cemented carbide tools containing Ti seem to be non⁃optimal in machining titanium alloys.However,in practice,cemented carbide tools containing Ti are still widely used in machining titanium alloys.Cutting experiments were conducted in order to systematically explain the contradictions between the practice and theory.The diffusion process between titanium alloys and the cemented carbide tools was analyzed by auger electron spectroscopy detecting the cutting regions.It was also analyzed by Ti/Co diffusion behavior simulated by molecular thermodynamics.The experimental results and the simulation results showed that the mutual diffusion of Ti/Co atoms was the major reason for the diffusion wear.The dissolution⁃diffusion wear was one of the main wear mechanisms for the cemented carbide tools containing Ti in the coatings.Moreover,four types of cemented carbide tools and two other types of cermet tools were used to machine the Ti⁃6Al⁃4V alloys at different cutting speeds to further verify the high affinity of cutting tools containing Ti in the substrate/coating.The verification experiments results showed that the cemented carbide tools containing Ti generally cannot be used for machining titanium alloys,but could show less affinity in the cutting regions with reasonable cutting conditions.

超塑性状态下Ti-6Al-4V钛合金扩散连接研究

根据高温扩散与空洞闭合蠕变理论,对Ti-6Al-4V钛合金在超塑性状态下扩散连接进行理论分析,建立了数学模型,可作为预测工艺参数,诸如温度、压力、时间等对连接质量的影响和选择合适工艺参数的依据。理论分析与试验结果是吻合的。

Advances in titanium alloys and orthopedic implants:new titanium alloys and future research directions

Dear Editor,We read with great interest the article by Tan et al.titled“Accelerated fracture healing by osteogenic Ti45Nb implants through the PI3K-Akt signaling pathway”[1].This research thoroughly examines the bone-forming capabilities of the Ti45Nb alloy.The in vitro studies revealed that the Ti45Nb alloy enhances the osteogenic differentiation of MC3T3-E1 cells more effectively than Ti6Al4V alloy controls,showing no noticeable cytotoxic effects.

Microstructure and mechanical properties of Ti6Al4V alloy prepared by selective laser melting combined with precision forging

To improve the mechanical properties of Ti6Al4V alloy prepared by selective laser melting(SLM)process,the precision forging was conducted at950°C and different strains and strain rates.The microstructure evolution of as-built samples and forged samples in both horizontal and vertical sections was visualized and analyzed by optical microscope and X-ray diffraction.The microstructure was improved by the precision forging and subsequent water quenching.The porosity in each section was accounted.It can be seen that high strain rate and large deformation result in low porosity,consequently contributing to a better fatigue performance.The micro-hardness was lowered after precision forging and water quenching,while the difference of microhardness between the horizontal and vertical sections became smaller,which illustrated that this process can improve the anisotropy of structural components fabricated by SLM.

Tribological behavior of different films on Ti-6Al-4V alloy prepared by plasma-based ion implantation

The tribological behaviors of TiN coating and TiN+TiC+Ti(C, N)/diamond like carbon (DLC), TiN/DLC, TiC/DLC multilayers on Ti 6Al 4V alloy prepared by plasma based ion implantation (PBII) were compared. Under the test conditions of counterbody AISI 52100, load 1 N and speed 0.05 m/s, the tribological properties of the alloy are improved by these films in the order of TiN, TiC/DLC, TiN/DLC and TiN+TiC+Ti(C,N)/DLC. Tribological behavior is affected by the conditions of surface modification and triboexperiments. The appearance of “peaks” in the wear dynamic resistance profiles may be due or correspond to the process of formation and breaking apart of transition films. The breakthrough of the DLC coated samples may start from partially wearing out, and end with joining piece dilamination. There are transition films on all counterbodies AISI 52100. When AISI 52100 counterbody is changed to Ti 6Al 4V, the wear of most modified samples is changed from only disc to both disc and ball abrasive dominated.

Structural characteristics and high-temperature tribological behaviors of laser cladded NiCoCrAlY−B_(4)C composite coatings on Ti6Al4V alloy

In order to improve the hardness and tribological performance of Ti6Al4V alloy,NiCoCrAlY-B_(4)C composite coatings with B_(4)C of 5%,10%and 15%(mass fraction)were fabricated on its surface by laser cladding(LC).The morphologies,chemical compositions and phases of obtained coatings were analyzed using scanning electronic microscope(SEM),energy dispersive spectrometer(EDS),and X-ray diffraction(XRD),respectively.The effects of B_(4)C mass fraction on the coefficient of friction(COF)and wear rate of NiCoCrAlY-B_(4)C coatings were investigated using a ball-on-disc wear tester.The results show that the NiCoCrAlY-B_(4)C coatings with different B_(4)C mass fractions are mainly composed of NiTi,NiTi_(2),α-Ti,CoO,AlB_(2),TiC,TiB and TiB_(2)phases.The COFs and wear rates of NiCoCrAlY-B_(4)C coatings decrease with the increase of B_(4)C content,which are contributed to the improvement of coating hardness by the B_(4)C addition.The wear mechanisms of NiCoCrAlY-B_(4)C coatings are changed from adhesive wear and oxidation wear to fatigue wear with the increase of B_(4)C content.

Microstructure and electrochemical corrosion behavior of selective laser melted Ti−6Al−4V alloy in simulated artificial saliva

Ti−6Al−4V alloy was fabricated via selective laser melting(SLM)to improve its corrosion resistance for implant.The microstructure and electrochemical corrosion behavior were investigated using scanning electron microscopy(SEM),electron backscatter diffraction(EBSD),transmission electron microscopy(TEM),electrochemical test and contact angle test.It can be found that the as-selective laser melted(as-SLMed)Ti−6Al−4V alloys showβcolumnar microstructure in building direction and nearly circular checkerboard microstructure in scanning direction,while the wrought and wrought+HT samples exhibit equiaxed microstructure.The as-SLMed Ti−6Al−4V alloy exhibits better corrosion resistance than the wrought and wrought+HT samples due to hydrophobicity,high grain boundary density and uniform distribution of alloying elements in simulated artificial saliva at 37℃.

Preparation of micro/nano-structured ceramic coatings on Ti6Al4V alloy by plasma electrolytic oxidation process

In order to improve the osseointegration and antibacterial activity of titanium alloys,micro/nano-structured ceramic coatings doped with antibacterial element F were prepared by plasma electrolytic oxidation(PEO)process on Ti6Al4V alloy in NaF electrolyte.The influence of NaF concentration(0.15-0.50 mol/L)on the PEO process,microstructure,phase composition,corrosion resistance and thickness of the coatings was investigated using scanning/transmission electron microscopy,energy dispersive spectroscopy,atomic force microscopy,X-ray diffractometer,and potentiodynamic polarization.The results demonstrated that Ti6Al4V alloy had low PEO voltage(less than 200 V)in NaF electrolyte,which decreased further as the NaF concentration increased.A micro/nano-structured coating with 10-15μm pits and 200-800 nm pores was formed in NaF electrolyte;the morphology was different from the typical pancake structure obtained with other electrolytes.The coating formed in NaF electrolyte had low surface roughness and was thin(<4μm).The NaF concentration had a small effect on the phase transition from metastable anatase phase to stable rutile phase,but greatly affected the corrosion resistance.In general,as the NaF concentration increased,the surface roughness,phase(anatase and rutile)contents,corrosion resistance,and thickness of the coating first increased and then decreased,reaching the maximum values at 0.25 mol/L NaF.

Influence of anions in phosphate and tetraborate electrolytes on growth kinetics of microarc oxidation coatings on Ti6Al4V alloy

The growth kinetics of microarc oxidation(MAO)coatings on Ti6Al4V alloy was studied by designing an electrolyte with low PO_(4)^(3−)content and high B_(4)O_(7)^(2−)content,using scanning electron microscopy,transmission electron microscopy,X-ray diffraction,and potentiodynamic polarization.The results showed that B_(4)O_(7)^(2−)increased the spark intensity and dissolved most of the oxides at high temperatures.Then,a thicker barrier layer at the coating/substrate interface was produced,which increased the polarization resistance of the coating.PO_(4)^(3−)at a low concentration also promoted the uniform growth of the MAO coating and the formation of hat-shaped holes in the outer deposition layer.The thickness of the MAO coatings obtained in Na_(2)B_(4)O_(7) electrolytes exhibited an exponential increase with time at spark discharge stage,while that of the MAO coating obtained in phosphate–tetraborate electrolytes showed a linear trend as the PO_(4)^(3−)content increased.

Effects of hot isostatic pressing temperature on casting shrinkage densification and microstructure of Ti6Al4V alloy

The Ti6Al4V alloy castings were produced by the investment casting process, and the hot isostatic pressing(HIP) was used to remove shrinkage from castings. The processing pressure and holding time for HIP were 150 MPa and 20 min, respectively. Four different HIP temperatures were tested, including 750 ℃, 850 ℃, 920 ℃ and 950 ℃. To evaluate the effects of temperature on densification and microstructure of Ti6Al4V alloy treated by HIP, non-destructive testing and metallographic observation was performed. The experimental results show that the shrinkage was completely closed at 920 ℃ and 950 ℃. The densification of Ti6Al4V alloy increased as the HIP temperature increased below 920 ℃. The lamel ae were more uniform, the thickness of lamel ae was obviously broadened and the structure was coarsen. Besides, the Norton creep equation was used to simulate the effect of different temperatures on the densification of Ti6Al4V alloy during HIP. The simulation results were in good agreement with the experimental results. It was also found that 920 ℃ is a suitable temperature for HIP for Ti6Al4V alloy.

Effect of Fe content on microstructures and properties of Ti6Al4V alloy with combinatorial approach

A combinatorial approach was applied to investigating the influence of Fe content on the microstructures and properties of Ti6Al4V alloy.A diffusion couple was manufactured with Ti6Al4V and Ti6Al4V20Fe alloys and annealed at 1000°C for 600 h to obtain a wide range of compositions.By combining electron probe micro-analysis(EPMA),scanning electron microscopy(SEM)and nanoindentation,the relationships between composition and microstructure as well as hardness were determined.It is found that after aging the Ti6Al4V5Fe sample contains reasonable(about 55%)volume fraction of fineαphase and shows the peak hardness among the Ti6Al4VxFe alloys.Therefore,it is a promising candidate for the development of titanium alloys.HAADF-STEM and XRD reveal that after quenching from the singleβphase field,the metastableα''lamellae form in the Ti6Al4V5Fe alloy,and on subsequent isothermal aging,theα''lamellae become coarse and act as precursors/preferential nucleation sites for the stableαphase.

Effect of strain rate difference between inside and outside groove in M-K model on prediction of forming limit curve of Ti6Al4V at elevated temperatures

The influence of initial groove angle on strain rate inside and outside groove of Ti6Al4V alloy was investigated.Based on the evolution of strain rate inside and outside groove,the effect of strain rate difference on the evolution of normal stress and effective stress inside and outside groove was also analyzed.The results show that when linear loading path changes from uniaxial tension to equi-biaxial tension,the initial groove angle plays a weaker role in the evolution of strain rate in the M-K model.Due to the constraint of force equilibrium between inside and outside groove,the strain rate difference makes the normal stress inside groove firstly decrease and then increase during calculation,which makes the prediction algorithm of forming limit convergent at elevated temperature.The decrease of normal stress inside groove is mainly caused by high temperature softening effect and the rotation of groove,while the increase of normal stress inside groove is mainly due to strain rate hardening effect.

Corrosion resistance improvement of Ti-6Al-4V alloy by anodization in the presence of inhibitor ions

Colorful thin oxide films were synthesized by galvanostatic anodization on Ti−6Al−4V alloy.Three different aqueous solutions containing corrosion inorganic inhibitors(Na_(2)MoO_(4),NaH_(2)PO_(4) and NH4VO3)were employed for the anodization treatment.The effect of inhibitor anions on the corrosion behavior of the alloy in Ringer solution was studied.Open circuit potential(OCP),Tafel polarization,linear sweep voltammetry(LSV)and chronoamperometry(CA)were performed to evaluate the corrosion performance of the treated electrodes.The incorporation of the inhibitor ions was detected by the release of Mo,V and P through ICP-AES technique.The formed oxides were characterized by scanning electron microscopy(SEM),X-ray diffraction(XRD)and X-ray photoelectron spectroscopy(XPS).The results show that compact,amorphous oxides without pores or cracks were obtained independently of the solution used.The sample anodized in Na_(2)MoO_(4) solution registered the lowest corrosion current density(0.11μA/cm^(2)),and it was able to protect the alloy even after 168 h of immersion in Ringer solution.No cracks or corrosion products were detected.The XPS analysis reveals the incorporation of molybdenum to the oxide film in the form of Mo^(6+) and Mo^(4+).

Electrochemical dissolution and passivation of laser additive manufactured Ti6Al4V controlled by elements segregation and phases distribution

The electrochemical dissolution and passivation of laser additive manufactured Ti6Al4V were investigated through Tafel polarization,potentiostatic polarization and AC impedance measurements.The results show that the solution treatment−aging(STA)process aggravates the element micro-segregation compared to the annealing process,leading to varied Al and V contents of the phases from different samples.It is proven that either Al-rich or V-rich condition can highly affect the electrochemical dissolution behaviors due to thermodynamical instability caused by element segregation.The dissolution rate in the metastable passivation process is controlled by the stability of the produced film that is affected by phases distribution,especially the difficult-to-dissolve phase.And then,the dissolution rate of the phases in the transpassivation region is consistent with the rank in the activation process because the dense film is not capable of being produced.Compared to the annealed sample,the higher dissolution rate of the STA sample is beneficial to the electrochemical machining(ECM)of Ti6Al4V.

Compatibility research of laser additive repairing TA15 forgings with Ti6Al4V-xTA15 alloy

The application of mixed powders with different mass fraction on laser additive repairing(LAR)can be an effective way to guarantee the performance and functionality of repaired part in time.A convenient and feasible approach is presented to repair TA15 forgings by employing Ti6Al4V-xTA15 mixed powders in this paper.The performance compatibility of Ti6Al4V-xTA15 powders from the aspects of microhardness,tensile property,heat capacity,thermal expansion coefficient and corrosion resistance with the TA15 forgings was fully investigated.The primaryαlaths were refined and the volume fraction of the secondaryαphase was increased by increasing the mass fraction of TA15 in the mixed Ti6Al4V-xTA15 powders,leading to varied performances.In conclusion,the mixed Ti6Al4V-70%TA15(x=70%)powders is the most suitable candidate and is recommended as the raw material for LAR of TA15 forgings based on overall consideration of the compatibility calculations of the laser repaired zone with the wrought substrate zone.

Effect of cryogenic and aging treatments on low-energy impact behaviour of Ti-6Al-4V alloy

The objective of this study is to examine the effects of cryogenic and aging treatments on the impact strength andmechanical properties of Ti?6Al?4V alloy.To accomplish that objective,cryogenic treatment(CT),aging treatment(AT)andcryogenic treatment followed by aging treatment(CAT)were conducted on Ti?6Al?4V alloy.Impact tests were performed onheat-treated and untreated samples using different impactor nose geometries(hemispherical,60°and90°conical)to determine theeffect of impactor nose geometry on the damage characteristic.The findings showed that energy absorption increased and areas ofdamage decreased as a result of heat treatment in all treated samples.The highest energy absorption was observed in the CATsamples,due to the increase in energy absorption,the smallest damaged area occurred in the CAT sample,and the largestdeformation was seen in the untreated samples.Additionally,it was seen that the damaged area and deflection were stronglydependent on impactor nose geometry.The maximum deflection and narrowest deformation area were seen with60o conical nosegeometry.The deformation area increased with increasing impactor nose angle.