TC4/Ta-W合金异种金属电子束焊接

对TC4/Ta-W合金电子束焊接进行了研究,采用偏向钽钨合金一侧进行焊接的方式进行分析.电子束焊接接头成形良好,在一定偏束量时焊缝中Ta和W元素含量较高,焊缝组织为以β钛为基的固溶体组织,无脆性化合物生成,存在富钽区和贫钽区.焊缝中元素分布不均匀,在偏束量为0.6 mm时焊缝中含钛相对较多,约为60%,而钽钨母材熔化相对较少,约占40%.当偏束量为0.4 mm时焊缝的最高抗拉强度达到714MPa,基本与钽钨合金母材等强,断裂发生在焊缝处.钽钨侧热影响区硬度较母材降低,钛侧熔合线处出现硬度最大值.

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.

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.

TC4钛合金环热应力校形的实验研究

TC4钛合金的屈服强度和弹性模量比值高,故其成形后回弹量大,成形后不精确,难以成形出合格零件,需要进行校形,以得到合格零件。因此对钛合金进行了校形实验,得到了感应加热工艺参数对材料校形的影响规律。并运用大型商用模拟软件ANSYS建立了钛合金热应力校形的模型,利用软件中LS-DYNA求解器,对钛合金热应力校形的过程进行了模拟。从而找出钛合金环热应力校形中的一些规律和校形最佳参数,期望能够将其用于指导生产。

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 scanning speeds on electrochemical corrosion resistance of laser cladding TC4 alloy

In order to study the effect of scanning speed on the electrochemical corrosion resistance of laser cladding TC4 alloy in artificial seawater, the x-ray diffraction analysis, microstructure of cross-section, microhardness variation, and impedance spectrum have been studied in comparison with the TC4 titanium alloy. The results show that the main phase of cladding coating is α-Ti, and the change of scanning speed has no obvious effect on it; therefore, the supersaturated α-Ti solid solution is formed, and the acicular α martensite is obtained. As the scanning speed increases, the microstructure of cladding coating is orthogonal basket-weave, the crystal surface spacing decreases, and the average microhardness of laser cladding TC4 alloy slightly increases. When the scanning speed increases to 10 mm/s, the microhardness is about 14.71%higher than that of the substrate, and the electrochemical corrosion resistance of laser cladding TC4 alloy is also improved,which is about 2.48 times more than the substrate. Grain refinement has a great effect on enhancing the anti-electrochemical corrosion.

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.

Numerical simulation on forging process of TC4 alloy mounting parts

In order to eliminate forging defects appearing in production,based on the rigid-viscoplastic FEM principle,the DEFORM3D software package was employed to simulate the forming process of TC4 alloy mounting part and to optimize the process parameters.In this simulation,the temperature dependency of the thermal and mechanical properties of material was considered.Based on the simulation,the metal flow and thermomechanical field variables such as stress and damage are obtained.The simulation results show that the forging defects are caused by improper die dimension and the optimized die dimension was proposed.To verify the validity of simulation results,forging experiments were also carried out in a forging plant.The forging experiments show that the optimized die dimension can ensure the quality of forging part,and it can provide reference to improve and optimize die design process.

Brazing of TiB_w/TC4 composite and Ti60 alloy using TiZrNiCu amorphous filler alloy

TiBw/TC4composite was brazed to Ti60alloy successfully using TiZrNiCu amorphous filler alloy,and the interfacialmicrostructures and mechanical properties were characterized by SEM,EDX,XRD and universal tensile testing machine.The typicalinterfacial microstructure was TiBw/TC4composite/β-Ti+TiB whiskers/(Ti,Zr)2(Ni,Cu)intermetallic layer/β-Ti/Ti60alloy whenbeing brazed at940°C for10min.The interfacial microstructure evolution was influenced strongly by the diffusion and reactionbetween molten fillers and the substrates.Increasing brazing temperature decreased the thickness of brittle(Ti,Zr)2(Ni,Cu)intermetallic layer,which disappeared finally when the brazing temperature exceeded1020°C.Fracture analyses indicated thatcracks were initialized in the brittle intermetallic layer when(Ti,Zr)2(Ni,Cu)phase existed in the brazing seam.The maximumaverage shear strength of joints reached368.6MPa when brazing was conducted at1020°C.Further increasing brazing temperatureto1060°C,the shear strength was decreased due to the formation of coarse lamellar(α+β)-Ti structure.

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.

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.

Microstructure and performance of dissimilar joint QCr0.8/TC4 welded by uncentered electron beam

The mechanical property of dissimilar metal joint between QCr0.8 and TC4 alloy made with centered electron beam is bad and the highest tensile strength of the joint is only about 82.1 MPa.The bad mechanical property is mainly caused by the asymmetric fusion of the two base metals and the generation of the brittle Ti-Cu intermetallic compounds.The finite element analysis shows that the amount of the melted QCr0.8 copper alloy can be added to reduce the amount of the brittle intermetallic compounds.The bias distance to the copper alloy hc has obvious effect on the tensile strength.When hc=0.8 mm,the tensile strength of the joint can reach 270.5 MPa.The reaction layer near the fusion line on the TC4 side consists of the intermetallic compound and the melted base metal which does not react.The joint fractures at the reaction layer and presents quasi-cleavage or transcrystalline rupture in tensile tests.

Effect of undercut defect on deformation behavior TC4 titanium alloy laser welded butt joint under static tensile loading

By measuring and analyzing infrared thermal image of the specimen in static load tensile test process, it was studied that the influence of the undercut defects and double-sided dressing method on the deformation behavior of the laser welded joint specimens of TC4 titanium alloy. The results showed that for the unmodified specimens, the yield phenomenon occurs first in the region of the joint, but the undercut value has an effect on the stress and strain of starting to yield phenomenon, and a great effect on the plastic deformation behavior.When the undercut is less than a certain value, the large plastic deformation occurs in the base metal region and the plasticity of the specimen is comparable to that of the base metal, but the larger undercut defect results in a concentrated plastic deformation in the joint region and rapidly failed in this region. But the double-sided dressing specimen is significantly different. The physical yield is no longer concentrated in the joint region, but at the same time occurs in the several regions including joint and the base metal. And the plastic deformation mainly occurs in the base material area, similar to that of the base material.

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.

Weld shape and microstructure of TC4 laser welding with activating flux of Na_(2)SiF_(6)

Na_(2)SiF_(6) was used as surface activating flux for laser welding of TC4 titanium alloy. The effect of Na_(2)SiF_(6) on TC4 titanium alloy laser welding was determined by observing the weld surface. The morphological characteristics of the high temperature plasma above the workpiece was observed and analyzed by using high-speed digital camera system. The variation of weld depth,width and microstructure were analyzed by optical microscope. The experimental results show that laser weld of TC4 titanium alloy has good appearance with activating flux of Na_(2)SiF_(6), weld penetration increases by about 0.8%–12%, while weld surface width decrease by about 10%–29%, the depth to width ratio is effectively improved. The inhomogeneity of weld microstructure was improved, and the crystallization direction of β columnar crystals on the upper part of the weld was changed, the grain size and microstructure of the weld were refined by Na_(2)SiF_(6).

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.

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.