Effect of electrochemical state on corrosion-wear behaviors of TC4 alloy in artificial seawater

The electrochemical and corrosion?wear behaviors of TC4 alloy in artificial seawater were studied. And the influences of electrochemical state on passive behavior, failure mechanism of passive film and corrosion?wear synergy were emphatically analyzed. The corrosion?wear analysis of the alloy was fulfilled by methods of mass loss, electrochemical testing and scanning electron microscope (SEM). It can be observed that the cathodic shift of open circuit potential and three order of magnitude increase of current density can be obtained during corrosion?wear process. Total corrosion?wear loss increases with increasing applied potential, confirming the synergy between wear and corrosion. High polarisation potential results in low coefficient of friction and high corrosion rate. The relative contribution of pure mechanical wear to total material loss deceases obviously with the increase of potential from open circuit potential to 0.9 V during corrosion?wear. Contributions of wear-induced-corrosion and corrosion-induced-wear are significant especially at higher potentials.

Vacuum diffusion bonding of Ti_(2)AlNb alloy and TC4 alloy

The Ti_(2)AlNb alloy was joined with TC4 alloy by vacuum diffusion bonding.The relationship between bonding parameters,and joint microstructure and shear strength was investigated.The results indicated that the diffusion of Al,Ti,Nb and V elements across bonding interface led to the formation of three reaction layers:B2/βlayer andα2 layer on the TC4 side,andα2+B2/βlayer on the Ti_(2)AlNb side.The bonding temperature determined the atomic activity,thus controlling the growth of reaction layers and influencing the shear strength of the joint.When the Ti_(2)AlNb alloy and TC4 alloy were bonded at 950℃for 30 min under 10 MPa,the shear strength of the joint reached the maximum of 467 MPa.The analysis on the fracture morphology showed that the fracture occurred within the B2/βlayer and the fracture model was ductile rupture.Meanwhile,the formation mechanism of the Ti_(2)AlNb/TC4 joint was discussed in depth.

Influence of hot isostatic pressing on microstructure,properties and deformability of selective laser melting TC4 alloy

The influence of different hot isostatic pressing regimes on microstructure,phase constitution,microhardness,tensile properties and deformability of TC4 alloy fabricated by selective laser melting(SLM)technology was studied.The results show that the microstructure of SLM TC4 alloy is composed of acicular martensiteα’phase,and the sample exhibits high microhardness and strength,but low plasticity.After hot isostatic pressing,acicular martensiteα’phase transforms intoα+βphase,and with the increase of hot isostatic pressing temperature and duration,αphase with coarse lath is gradually refined,and the proportion ofαphase is gradually reduced.Because of the change of phase constitution in SLM TC4 alloy after hot isostatic pressing,the grain refinement strengthening is weakened,the density of dislocation is reduced,so that both microhardness and tensile strength are decreased by around 20%,the elongation is increased by more than about 70%,even over 100%,compared with as-deposited TC4 alloy.When the hot isostatic pressing regime is 940°C/3 h/150 MPa,the tensile strength and the elongation achieve optimal match,which are about890 MPa and around 14.0%in both directions.The fracture mechanism of alloy after 940 oC/3 h/150 MPa HIP is dultile fracture.Hot isostatic pressing causes concave deformation of SLM TC4 alloy thin-walled frames,and the deformation degree increases with the increase of temperature.

Micro electrical discharge machining of small hole in TC4 alloy

Aiming at machining deeply small holes in TC4 alloy,a series of experiments were carried out on a self-developed multi-axis micro electrical discharge machining(micro-EDM)machine tool.To improve machining efficiency and decrease relative wear of electrode in machining deeply small hole in TC4 alloy,many factors in micro-EDM,such as polarity,electrical parameters and supplying ways of working fluid were studied.Experimental results show that positive polarity machining is far superior to negative polarity machining;it is more optimal when open-circuit voltage,pulse width and pulse interval are 130 V,5μs and 15μs respectively on the self developed multi-axis micro-EDM machine tool;when flushing method is applied in micro-EDM,the machining efficiency is higher and relative wear of electrode is smaller.

Microstructure and fracture behavior of SiO_2 glass ceramic and TC4 alloy joint brazed with TiZrNiCu alloy

Vacuum brazing of SiO2 glass ceramic and TC4 alloy using a commercially available TiZrNiCu foil was investigated. The interfacial microstructure and the fractures were examined with an optical microscope （OM） and an S-4700 scanning electron microscope （SEM） equipped with an energy dispersive spectrometer （EDS） and an electron probe X-ray microanalyzer （EPMA）. The structure of joint interface was identified by XRD （JDX-3530M）. Meanwhile, the fracture paths of the joints were comprehensively studied. The results show that processing parameters, especially the brazing temperature, have a significant effect on the microstructure and mechanical properties of joints. The typical interface structure is SiO2/Ti2O＋Zr3Si2＋Ti5Si3/（Ti,Zr）＋Ti2O＋ TiZrNiCu/Ti（s.s）/TiZrNiCu＋Ti（s.s）＋Ti2（Cu,Ni）/TC4 from SiO2 glass ceramic to TC4 alloy side. Based on the mechanical property tests, the joints brazed at 880 ℃ for 5 rain has the maximum shear strength of 23 MPa.

Three Dimensional FE Analysis on Flange Bending for TC4 Alloy during Shear Spinning

In this paper, the 3D elastic-plastic simulation was carried out by using finite element （FE） code according to the phenomena of flange keeping straight, bending towards headstock and bending towards tailstock in the shear spinning experiments for TC4 alloy. The simulation results for the three kinds of deformations of the flange agree well with the experimental results. So it is possible to explain the reason of flange bending by analyzing the strain vectors in the flange for the three kinds of deformation, which shows that it is important to apply the FE simulation technology for predicting the defects and optimizing the spinning process of TC4 alloys.

Laser-induced combustion joining of C_(f)/Al composites and TC4 alloy

The C_(f)/Al composites were joined to the TC4 alloy via the laser-induced combustion joining method.The exothermic reaction of the interlayer provided the required energy for the joining process.By combining the theoretical calculation and experiment,the chemical composition of the Ni−Al−Zr interlayer was designed.The microstructure and mechanical properties of the joint were investigated.The results show that the addition of Zr slightly weakened the combustion reaction of exothermic interlayer but played a key role in the successful joining.Ni−Al−Zr interlayer reacted with substrates,forming a TiAl_(3)layer adjacent to TC4 alloy and NiAl_(3),Ni_(2)Al_(3)layers adjacent to the C_(f)/Al composites.Zr content dominated the microstructure and shear strength of the joint.When the Zr content was 5 wt.%under the joining pressure of 2 MPa,the joint had a maximum shear strength of 19.8 MPa.

Effect of low temperature thermo-mechanical treatment on microstructures and mechanical properties of TC4 alloy

The effects of low temperature thermo-mechanical treatment （LTTMT） on microstructures and mechanical properties of Ti-6Al-4V （TC4） alloy were studied by optical microscopy （OM）, tensile test, scanning electron microscopy （SEM） and transmission electron microscopy （TEM）. The experimental results confirm that the strength of TC4 alloy can be improved obviously by LTTMT processing, which combines strain strengthening with aging strengthening. The effect of LTTMT on the alloy depends on the microstructure of the refined and dispersed a＋fl phase on the basis of high dislocation density by pre-deformation below recrystallization temperature. The tensile strength decreases with the increase of pre-deformation reduction. The optimal processing parameters of LTTMT for TC4 alloy are as follows： solution treatment at 900 ℃ for 15 min, pre-deformation in the range of 600-700 ℃ with a reduction of 35%, finally aging at 540 ℃ for 4 h followed by air-cooling.

Influence of high pulsed magnetic field on tensile properties of TC4 alloy

The tensile tests of TC4 alloy are carried on electronic universal testing machine in the synchronous presence of high pulsed magnetic field（HPMF） parallel to the axial direction.The effects of magnetic induction intensity（5 = 0,1 T,3 T,and 5 T） on elongation（5） of TC4 alloy are investigated.At 3 T,the elongation arrives at a maximum value of12.41%,which is enhanced by 23.98%in comparison with that of initial sample.The elongation curve shows that 3 T is a critical point.With B increasing,the volume fraction of α phase is enhanced from 49.7%to 55.9%,which demonstrates that the HPMF can induce the phase transformation from β phase to α phase.Furthermore,the magnetic field not only promotes the orientation preference of crystal plane along the slipping direction,but also has the effect on increasing the dislocation density.The dislocation density increases with the enhancement of magnetic induction intensity and the 3-T parameter is ascertained as a turning point from increase to decrease tendency.When B is larger than 3 T,the dislocation density decreases with the enhancement of B.The influence of magnetic field is analyzed on the basis of magneto-plasticity effect.The high magnetic field will enhance the dislocation strain energy and promote the state conversion of radical pair generated between the dislocation and obstacles from singlet into triplet state,in which is analyzed the phenomenon that the dislocation density is at an utmost with B = 3 T.Finally,the inevitability of optimized 3-T parameter is further discussed on a quantum scale.

Flat jet electrochemical milling of TC4 alloy with tailoring backward parallel flow

In flat jet electrochemical milling, the electrolyte forms a backward parallel flow after impacting the workpiece, resulting in a weak current density distribution on the workpiece. Poor surface quality usually occurs on the machined titanium alloy surface because it inevitably suffers from the weak current density. In this study, a method of flat jet electrochemical milling with tailoring the backward parallel flow was proposed to eliminate the negative effects caused by the weak current density. Multiphysics simulations are carried out to comprehend the mechanism of flat jetEC milling with tailoring backward parallel flow and better construct the novel tool electrode.Experiments on flat jet electrochemical milling of TC4 alloy with and without tailoring backward parallel flow are conducted. The results reveal that, compared with flat jet electrochemical milling without tailoring backward parallel flow, the recommended tool reduces the surface roughness by86% to 93%, and improves the material removal rate by 93% to 163% with different feed rates.Additionally, the recommended tool is more conducive to maintaining the inherent hardness of the material. Finally, a surface with low Sa of 0.37 μm is obtained.

Synthesis of Y_2O_3 particle enhanced Ni/TiC composite on TC4 Ti alloy by laser cladding

A Y2O3 particle enhanced Ni/TiC composite coating was fabricated in-situ on a TC4 Ti alloy by laser surface cladding. The phase component, microstructure, composition distribution and properties of the composite layer were investigated. The composite layer has graded microstructures and compositions, due to the fast melting followed by rapid solidification and cooling during laser cladding. The TiC powders are completely dissolved into the melted layer during melting and segregated as fine dendrites when solidified. The size of TiC dendrites decreases with increasing depth. Y2O3 fine particles distribute in the whole clad layer. The Y2O3 particle enhanced Ni/TiC composite layer has a quite uniform hardness along depth with a maximum value of HV1380, which is 4 times higher than the initial hardness. The wear resistance of the Ti alloy is significantly improved after laser cladding due to the high hardness of the composite coating.

Microstructure characterization and mechanical properties of TC4-DT titanium alloy after thermomechanical treatment

Influence of thermomechanical treatments （mill annealing, duplex annealing, solution treatment plus aging and triple annealing） on microstructures and mechanical properties of TC4-DT titanium alloy was investigated. Results showed that thermomechanical treatments had a significant influence on the microstructure parameters and higher annealing and aging temperature and lower cooling rate led to the decrease of the volume fraction of primaryαand the size of prior-βand the increase of the width of grain boundary αand secondary α. The highest strength was obtained by solution treatment and aging due to a large amount of transformedβand finer grain boundaryαand secondaryαat the expense of slight decrease of elongation and the ultimate strength, yield strength, elongation, reduction of area were 1100 MPa, 1030 MPa, 13%and 53%separately. A good combination of strength and ductility has been obtained by duplex annealing with the above values 940 MPa, 887.5 MPa, 15%and 51%respectively. Analysis between microstructure parameters and tensile properties showed that with the volume fraction of transformedβphase and the prior-βgrain size increasing, the ultimate strength, yield strength and reduction of area increased, but the elongation decreased. While the width of grain boundary α and secondary α showed a contrary effect on the tensile properties. Elimination of grain boundaryαas well as small prior-βgrain size can also improve ductility.

Prediction model for flow stress during isothermal compression in α+β phase field of TC4 alloy

Isothermal compression of TC4 alloy was performed on a Thermecmaster-Z simulator at the deformation temperatures ranging from 1093 to 1243 K, the strain rates ranging from 0.001 to 10.000 s^-l and a maximum strain of 0.8. The experimental results show that the flow stress increases with the decrease in the deformation temperature and the increase in the strain rate. The apparent activation energy for deformation is much lower at lower strain rates than that at higher strain rates. The flow stress model considering strain compensation was established. The average relative error between the calculated flow stress and experimental results is about 7.69%, indicating that the present model could be used to accurately predict the flow stress during high temperature in α＋β phase field of TC4 alloy.

COMPOSITION AND PROPERTY OPTIMIZATION FOR TC4 Ti ALLOY

The optimization study of the compositions and properties of TC4 alloy has been conducted by using KCYH pattern recognition optimization dedicated system. Taking 92 groups of the production tesing data as the primary samples, the influence of Ti, Al, V, Fe, N H, O, C in the TC4 on 3 target values, i.e. tensil strength, yield strength and elongation has been quantitatively analysed. Based on the principle of the Pattern Recognition and other related analysing techniques, the tag extract and variable screen on the 92 groups of data have carried out to seek the optimum design area. Although these groups of data did affect the determination of the optimum area for lack of processing parameters or stability in the production procedure, by various means of the Pattern Recognition, the optimum design area for some no basic elements and the properties, which are under the national standard, has been obtained: 5.95<Al<6.315, 4.09< V<4.2, 0. 011<N<0.025, 0. 128< O<0.171. This result has a significance to guide the research and production of TC4 alloy.

Self-propagating synthesis joining of C_(f)/Al composites and TC4 alloy using AgCu filler with Ni-Al-Zr interlayer

The successful joining of carbon fiber-reinforced aluminum matrix(C_(f)/Al)composites and TC4 alloy can produce composite structure and meet the demands of lightweight in aerospace field.Up to now,few experimental researches have been reported on the joining of C_(f)/Al composites and TC4 alloy.In this study,the AgCu foils and Ni-Al-Zr compact were designed for the self-propagating high-temperature synthesis joining of these two materials.C_(f)/Al composites were joined with a reactive Ti plated on its joining surface.The typical microstructure of TC4/(AgCu/Ni-Al-Zr/AgCu)/Ti/C_(f)/Al joint was analyzed,and the effects of joining condition on microstructural evolution of the SHS joint were investigated.A thin reaction layer of Ni-Al-Ti intermetallic compounds was formed adjacent to the TC4 alloy.As a result,AgCu foils could reduce the effect of reaction heat on the substrates and improve the joint shear strength.When the thickness of AgCu foils reaches 150 lm,the Ni-Al-Zr interlayer mainly acts as auxiliary heat source.High joining pressure caused the active elements to diffuse into C_(f)/Al composites and weakened the shear strength of the joint.Finally,the joint shear strength could reach 36.4 MPa when the AgCu foils were 50 lm and the joining pressure was 2 MPa.

Significance and interaction of bonding parameters with bonding ratio in press bonding of TC4 alloy

The variation of bonding ratio in the press bonding of TC4 alloy at temperatures from 850 to 900℃,pressures from 10 to 30 MPa,and time from 5 to 15 min was investigated.The bonding ratio increases with the increase of temperature,time and pressure.The maximum bonding ratio,i.e.98 %,can be obtained at 900℃,30 MPa and 15 min.The significance and interaction of bonding parameters with the bonding ratio were investigated.The results demonstrate that the effect of pressure on the bonding ratio is the most effective and the effect of temperature is secondary,while the effect of time is not very powerful.The interaction of bonding parameter on the bonding ratio exists but that is distinguishing in different bonding parameter ranges.It is concluded that increasing pressure can be considered as the primary method to increase the bonding ratio.

Hot deformation behavior and microstructure evolution of TC4 titanium alloy

The hot deformation behavior of Ti-6Al-4V （TC4） titanium alloy was investigated in the temperature range from 650℃ to 950℃ with the strain rate ranging from 7.7×10^-4 s^-1 to 7.7×10^-2 s^-1. The hot tension test results indicate that the flow stress decreases with increasing the deformation temperature and increases with increasing the strain rate. XRD analysis result reveals that only deformation temperature affects the phase constitution. The microstructure evolution under different deformation conditions was characterized by TEM observation. For the deformation of TC4 alloy, the work-hardening is dominant at low temperature, while the dynamic recovery and dynamic re-crystallization assisted softening is dominant at high temperature.

Surface modification of TC4 Ti alloy by laser cladding with TiC+Ti powders

Laser surface cladding was applied on a TC4 Ti alloy to improve its surface properties. Mixed TiC and Ti powders with a TiC-to-Ti mass ratio of 1：3 were put onto the TC4 Ti alloy and subsequently treated by laser beam. The microstructure and composition modifications in the surfaee layer were carefully investigated by using SEM, EDX and XRD. Due to melting, liquid state mixing followed by rapid solidification and cooling, a layer with graded microstructures and compositions formed. The TiC powders were completely dissolved into the melted layer during melting and segregated as fine dendrites when solidified. The inter-dendritic areas were filled with fine a＇ phase lamellae enrich in A1. Mainly due to the reduced TiC volume fraction with increasing depth, the hardness decreases with increasing depth in the laser clad layer with a maximum value of HV1400, about 4.5 times of the initial one.

Effect of grain size on high-temperature stress relaxation behavior of fine-grained TC4 titanium alloy

In order to analyze the effect of grain size on stress relaxation(SR) mechanism,the SR tests of TC4 alloy with three kinds of grain size were performed in a temperature range of 650-750℃.A modified cubic delay function was used to establish SR model for each grain size.A simplified algorithm was proposed for calculating the deformation activation energy based on classical Arrhenius equation.The grain size distribution and variation were observed by microstructural methods.The experimental results indicate that smaller grains are earlier to reach the relaxation limit at the same temperature due to lower initial stress and faster relaxation rate.The SR limit at 650℃ reduces with decreasing grain size.While the effect of grain size on SR limit is not evident at 700 and 750℃ since the relaxation is fully completed.With the increase of grain size,the deformation activation energy is improved and SR mechanism at 700℃ changes from grain rotation and grain boundary sliding to dislocation movement and dynamic recovery.

Corrosion and wear properties of micro-arc oxidation treated Ti6Al4V alloy prepared by selective electron beam melting

In order to analyze the effect of voltage during micro-arc oxidation(MAO)on corrosion and wear properties of Ti6Al4V(TC4),the MAO technology was employed to treat TC4 samples fabricated by selective electron beam melting(SEBM)at the voltages of 400,420 and 450 V.The results show that the metastable anatase phase gradually transforms to rutile phase with oxidation time and temperature increasing.The surface morphology of coating contains numerous micropores with uniform size distribution.Cracks and pores over 10μm are found on MAO-TC4 sample with applied voltage of 450 V.The thickness of MAO coating is positively correlated with the voltage.The corrosion resistance and wear resistance are related to phase composition,micropore size distribution on the surface and film thickness.When the voltage is 420 V,the coating shows the smallest corrosion current density(0.960×10^-7 A/cm^2)and the largest resistance(7.17×10^5Ω·cm^2).Under the same load condition,the coating exhibits larger friction coefficient and wear loss than the TC4 substrate.With the increase of voltage,the wear mechanism of the coating changes from abrasive wear to adhesive wear,and the adhesive wear is intensified at applied voltage of 450 V,with a maximum friction coefficient of 0.821.