激光高速应变对双态组织近α型Ti-6Al-3Nb-2Zr-1Mo合金组织与性能的影响

利用激光冲击强化使Ti-6Al-3Nb-2Zr-1Mo(Ti80)合金表面产生严重塑性变形,借助SEM、TEM和XRD等方法深入研究了表面严重塑性变形对Ti80合金显微组织、力学性能以及耐腐蚀性能的影响。结果表明:激光冲击强化使Ti80合金表面产生无相变的严重塑性变形层,表层晶粒内部产生大量位错胞、位错墙、位错缠结等晶体缺陷。此外,通过位错间的相互作用,表面粗大晶粒细化至纳米级。晶粒细化和晶粒内高密度位错严重阻碍了位错的运动,从而增加了样品的硬度和强度。与原始试样相比,LSP处理试样的表面显微硬度提高了16.5%,产生了386.4 MPa的高幅残余压应力,在不牺牲延展性的前提下提高了强度。电化学和静态浸泡实验结果表明,LSP处理后试样的自腐蚀电位增加了77.7 mV vs.SCE,腐蚀电流密度和腐蚀速率分别降低了1.358μA·cm^(-2)、0.08 mm·year^(-1),点蚀和晶间腐蚀现象减弱。这是由于LSP处理后样品晶粒得到细化,增强了表面结构的稳定性并提供了更多钝化膜的形核位点,从而提高了Ti80合金的耐腐蚀性能。

Electrochemical Hydrogen Charging on Corrosion Behavior of Ti-6Al-4V Alloy in Artificial Seawater

This study employs advanced electrochemical and surface characterization techniques to investigate the impact of electrochemical hydrogen charging on the corrosion behavior and surface film of the Ti-6Al-4V alloy.The findings revealed the formation ofγ-TiH andδ-TiH_(2) hydrides in the alloy after hydrogen charging.Prolonging hydrogen charging resulted in more significant degradation of the alloy microstructure,leading to deteriorated protectiveness of the surface film.This trend was further confirmed by the electrochemical measurements,which showed that the corrosion resistance of the alloy progressively worsened as the hydrogen charging time was increased.Consequently,this work provides valuable insights into the mechanisms underlying the corrosion of Ti-6Al-4V alloy under hydrogen charging conditions.

Tribocorrosion behaviors of Ti-6Al-4V and Monel K500 alloys sliding against 316 stainless steel in artificial seawater

The tribocorrosion behaviors of Ti-6Al-4V and Monel K500 alloys sliding against 316 stainless steel were investigated using a ring-on-block test rig in both artificial seawater and distilled water. It is found that friction coefficients are in general larger in distilled water compared with seawater. The wear losses of Ti-6Al-4V and Monel K500 alloys are larger in seawater compared with distilled water. The mechanical action can destroy the passive film and increase the corrosion rate. The synergism effect between corrosion and wear occurs. The synergism action between corrosion and wear is related to the corrosion rate and with the increase of corrosion rate, the synergism becomes more important. 316 stainless steel suffers severe wear sliding against Monel K500 alloy compared with sliding against Ti-6Al-4V alloy in both distilled water and seawater.

Corrosion and antimicrobial property of TiO_(2)/Cu_(2)O and TiO_(2)/Cu_(2)O@CeO_(2)micro-arc oxidation coatings on Ti-6Al-4V alloys in natural seawater

Microarc oxidation is an effective surface treatment for improving certain properties of metals and their alloys.In this paper,TiO_(2)/Cu_(2)O and TiO_(2)/Cu_(2)O@CeO_(2)coatings were prepared on Ti-6Al-4V by microarc oxidation.Thecoatings exhibited good corrosion resistance and antimicrobial properties.X-ray diffraction(XRD),scanning electronmicroscopy(SEM),and 3D laser confocal were used to characterize the coatings.The properties of TiO_(2)/Cu_(2)O and TiO_(2)/Cu_(2)O@CeO_(2)coatings were analyzed,including microstructure,surface roughness,corrosion resistance,andantimicrobial properties.The electrochemical results showed that the coatings prepared by microarc oxidation hadenhanced corrosion resistance compared to the substrate.The antibacterial properties of TiO_(2)/Cu_(2)O and TiO_(2)/Cu_(2)O@CeO_(2)coating against Pseudomonas aeruginosa were evaluated by fluorescence microscopy and plate counting.The antibacterial rate of TiO_(2)/Cu_(2)O@CeO_(2)coating was up to 99.70%.In summary,the TiO_(2)/Cu_(2)O and TiO_(2)/Cu_(2)O@CeO_(2)coatings prepared by microarc oxidation have a potential application background in the field of marine corrosionprotection and biofouling.

选区激光熔化Ti-6Al-4V合金在模拟乏燃料后处理环境中的腐蚀行为

研究选区激光熔化(SLM)制备的Ti-6Al-4V合金在乏燃料后处理环境中的腐蚀行为。借助光学显微镜、X射线衍射、扫描电子显微镜、电子背散射衍射以及电化学测试等手段研究SLMTi-6Al-4V合金的显微组织及耐蚀性。结果表明,相较于铸造合金,SLM Ti-6Al-4V合金在含氧化性离子的6 mol/L热硝酸溶液中的耐腐蚀性更好。进一步分析表明,SLMTi-6Al-4V合金具有α'+β的微观结构,β-Ti相含量较高且分布均匀,同时其晶粒尺寸较小、晶界密度较高,这种微观结构可提高其在含氧化性离子的硝酸中的钝化能力以及耐腐蚀性。SLM Ti-6Al-4V合金有望在乏燃料后处理过程中得到广泛应用。

激光选区熔化Ti-6Al-4V合金的微纳压痕尺寸效应

目的研究不同状态激光选区熔化Ti-6Al-4V合金的纳米压痕尺寸效应。方法对原始态合金分别进行600、700、800、900℃退火处理,利用扫描电子显微镜观察原始态和4种退火态合金的显微组织。基于纳米压痕技术测量原始态及4种退火态合金的纳米硬度和弹性模量。基于比例试样阻力模型、Nix-Gao模型和Meyer定律对纳米硬度进行函数拟合。结果随着退火温度的升高,原始态组织从魏氏体逐渐演变为网篮组织。5种形态的Ti-6Al-4V合金的硬度和弹性模量均出现随压入深度的增加而减小的现象,表现出典型的压痕尺寸效应,基于试验测得的原始态及4种退火态合金的纳米硬度分别为3.66、4.36、3.96、3.88、4.77 GPa,弹性模量分别为113.1、125.2、102.1、100.3、108.7 GPa;基于比例试样阻力模型计算的纳米硬度分别为3.53、4.34、3.92、3.52、4.04 GPa;基于Nix-Gao模型计算的纳米硬度分别为3.68、3.94、4.07、3.85、4.47 GPa;基于Meyer定律拟合出的迈耶指数分别为1.75、1.86、1.82、1.80、1.81,均小于2,均表现为正压痕尺寸效应。结论激光选区熔化Ti-6Al-4V合金的硬度及弹性模量均有典型的压痕尺寸效应;3种模型均能较好地描述原始态和退火态合金的压痕尺寸效应,Nix-Gao模型直接建立了纳米硬度和压痕深度的关系,其拟合结果更接近于试验结果,计算的硬度值也最为准确。

Constitutive Modeling for Ti-6Al-4V Alloy Machining Based on the SHPB Tests and Simulation

A constitutive model is critical for the prediction accuracy of a metal cutting simulation. The highest strain rate involved in the cutting process can be in the range of 104-106 s 1. Flow stresses at high strain rates are close to that of cutting are difficult to test via experiments. Split Hopkinson compression bar （SHPB） technology is used to study the deformation behavior of Ti-6Al-4V alloy at strain rates of 10 -4-10 4s- 1. The Johnson Cook （JC） model was applied to characterize the flow stresses of the SHPB tests at various conditions. The parameters of the JC model are optimized by using a genetic algorithm technology. The JC plastic model and the energy density-based ductile failure criteria are adopted in the proposed SHPB finite element simulation model. The simulated flow stresses and the failure characteristics, such as the cracks along the adiabatic shear bands agree well with the experimental results. Afterwards, the SHPB simulation is used to simulate higher strain rate（approximately 3 × 10 4 s -1） conditions by minimizing the size of the specimen. The JC model parameters covering higher strain rate conditions which are close to the deformation condition in cutting were calculated based on the flow stresses obtained by using the SHPB tests （10 -4 - 10 4 s- 1） and simulation （up to 3 × 10 4 s - 1）. The cutting simulation using the constitutive parameters is validated by the measured forces and chip morphology. The constitutive model and parameters for high strain rate conditions that are identical to those of cutting were obtained based on the SHPB tests and simulation.

Influence of material models on theoretical forming limit diagram prediction for Ti-6Al-4V alloy under warm condition

Forming limit diagram (FLD) is an important performance index to describe the maximum limit of principal strains that can be sustained by sheet metals till to the onset of localized necking. It offers a convenient and useful tool to predict the forming limit in the sheet metal forming processes. In the present study, FLD has been determined experimentally for Ti?6Al?4V alloy at 400 °C by conducting a Nakazima test with specimens of different widths. Additionally, for theoretical FLD prediction, various anisotropic yield criteria (Barlat 1989, Barlat 1996, Hill 1993) and different hardening models viz., Hollomon power law (HPL), Johnson?Cook (JC), modified Zerilli–Armstrong (m-ZA), modified Arrhenius (m-Arr) models have been developed. Theoretical FLDs have been determined using Marciniak and Kuczynski (M?K) theory incorporating the developed yield criteria and constitutive models. It has been observed that the effect of yield model is more pronounced than the effect of constitutive model for theoretical FLDs prediction. However, the value of thickness imperfection factor (f0) is solely dependent on hardening model. Hill (1993) yield criterion is best suited for FLD prediction in the right hand side region. Moreover, Barlat (1989) yield criterion is best suited for FLD prediction in left hand side region. Therefore, the proposed hybrid FLD in combination with Barlat (1989) and Hill (1993) yield models with m-Arr hardening model is in the best agreement with experimental FLD.

Use of a Laser/TIG Combination for Surface Modification of Ti-6Al-4V Alloy

The surface modification of materials such as Ti-6Al-4V is necessary to improve their wear resistant properties for use in tribological applications. In this paper it is shown that a laser with low power and tungsten inert gas (TIG) can be combined together for surface modification of Ti-6Al-4V alloy, and when performed in a controlled atmosphere of pure nitrogen or a mixture of nitrogen and argon, can produce a wear-resistant surface alloy. Compared with laser processing, a cheaper surface modification process has been developed involving a shorter processing time, which is free of stringent requirements such as a vacuum system.

Effect of wet shot peening on Ti-6Al-4V alloy treated by ceramic beads

Ti-6Al-4V alloy was processed by wet shot peening with ceramic beads. The effects of the shot peened intensity on the microstructure, surface morphology, and residual stress were investigated. A tensile-tensile fatigue test was performed and the fracture mechanism was proposed. The results demonstrate that the surface roughness after wet shot peening is obviously lower than that after dry shot peening. With the increase of the shot peened intensity, the depth of the residual stress layer increases to 250 ktrn, and the maximum stress in this layer increases to -895 MPa. The fatigue strength also increases by 12.4% because of the wet shot peening treatment. The dislocation density of the surface layer is significantly enhanced after the wet shot peening with ceramic beads. The microstructure of the surface layer is obviously refined into ultra-fine grains.

Thermomechanical Behavior of Ti-6Al-4V Alloy

Ti-6AI-4V, among the Ti alloys, is the most widely used. In the present work, the behavior of Ti-6AI-4V alloy has been investigated by the uniaxial hot isothermal compression tests and a series of dilatometric experiments were also carried out to determine the transformation temperatures at different cooling rates. Specimens for hot compression tests were homogenized at 1050℃ for 10 min and then quickly cooled to different straining temperatures from 1050 to 850℃. Cooling rates were chosen fast enough to prevent high temperature transformation during cooling. Compression tests were conducted at temperatures from 1050 to 850℃ in steps of 50℃ at constant true strain rates of 10-3 or 10-2 s-1. The apparent activation energy for compression in two-phase region was calculated 420 kJ·mol-1. Partial globularization of a phase was observed in the specimen deformed at low strain rates and at temperatures near the transformation zone and annealed after deformation.

Effect of mold temperature and casting dimension on microstructure and tensile properties of counter-gravity casting Ti-6Al-4V alloys

The cast Ti-6Al-4V alloy bars with different section sizes were fabricated by investment casting at counter-gravity condition with the mold temperatures of 300 ℃ and 650 ℃, respectively. The microstructure of the alloy was observed by means of OM and SEM, and the effect of mold temperature and casting dimension on tensile properties was studied. Results show that equiaxed grains are obtained regardless of the casting dimension. 13 grain size tends to increase with an increase in mold temperature. Hot isostatic pressing of the alloy was carried out for tensile properties＇ comparison. Room temperature tensile test results show that Ti-6Al-4V alloy produced via counter-gravity casting has good balance of strength and ductility after hot isostatic pressing （HIP）. The alloy shows higher ductility due to the elimination of porosity. In both cast and HIP status, the tensile strength is inclined to decrease with an increase in mold temperature, while the ductility is prone to slightly increase. Both the strength and ductility tend to decrease with an increase in the casting dimension.

Effect of electropulsing on deformation behavior of Ti-6Al-4V alloy during cold drawing

Electron backscattered diffraction （EBSD） and transmission electron microscopy （TEM） were used to investigate effect of electropulsing on microstructure and texture evolution of Ti-6Al-4V during cold drawing. Research results demonstrate that the electropulsing treatment （EPT） can enhance the deformability of the grains with unfavorable orientations, which makes the compatibility of deformation among grains much better. A comparison in texture evolution between conventional cold drawing and EPT cold drawing indicates that the EPT promotes prismatic 〈a〉 slip moving, restricts pyramidal 〈c＋a〉 slip occurring and accommodates the deformation with c-component by grain boundary sliding. The fraction decrease of low-angle grain boundaries for samples deformed with EPT reveals that the application of electropulsing restricts the formation of the incidental dislocation boundaries and the geometrically necessary boundaries.

Mechanical properties of strengthened surface layer in Ti-6Al-4V alloy induced by wet peening treatment

A modified surface layer was formed on Ti-6Al-4V alloy by wet peening treatment. The variations of the residual stress,nano-hardness and microstructure of the modified layer with depth from surface were studied using X-ray diffraction analysis,nano-indentation analysis, scanning electron microscopy and transmission electron microscopy observations. The results show thatboth the compressive residual stress and hardness decrease with increasing depth, and the termination depths are 160 and 80 μm,respectively. The microstructure observation indicates that within 80 μm, the compressive residual stress and the hardness areenhanced by the co-action of the grain refinement strengthening and dislocation strengthening. Within 80–160 μm, the compressiveresidual stress mainly derives from the dislocation strengthening. The strengthened layer in Ti-6Al-4V alloy after wet peeningtreatment was quantitatively analyzed by a revised equation with respect to a relation between hardness and yield strength.

Adiabatic shear fracture in Ti-6Al-4V alloy

Separated specimens of Ti-6Al-4V alloy were dynamically loaded at a strain rate of 3 900 s-1 using a split Hopkinson pressure bar（SHPB） apparatus.The fracture features of the separated specimens were investigated by a scanning electron microscope.The results show that adiabatic shear failure occurs in the tested specimens,and two typical areas（dimple and smooth areas） with different features are alternatively distributed on the whole fracture surface.The dimple areas originate from voids generation and coalescence,exhibiting ductile fracture characteristics.Simultaneously,ultrafine grains（UFGs） and microcracks among grains are observed on the smooth areas,indicating that the emergence of UFG areas is caused by the propagation of microcracks along grain boundaries and exhibits brittle fracture characteristics.Fracture occurring in adiabatic shear bands is not uniform and ultimate rupture is resulted from ductile and brittle fracture modes.

Ti-6Al-4V六槽深浅腔动静压轴承刚度数值分析

针对传统材料制造的动静压轴承刚度较差的问题,提出一种基于Ti-6Al-4V材料制造六槽深浅腔交错分布的动静压轴承。利用ANSYS有限元软件建立六槽深浅腔动静压轴承流固耦合模型,研究轴径间隙、转速以及偏心率对QSn4-3轴承和Ti-6Al-4V轴承刚度的影响规律。结果表明:钛合金材料制成的轴承刚度优于传统锡基合金材料制造的轴承,各工况参数中,轴径间隙对轴承刚度的影响最为显著,其次是偏心率。该研究可为钛合金滑动轴承的数值模拟和设计提供参考。

Process parameters optimization of Ti-6Al-4V alloy sheet during hot stretch-creep forming

Hot stretch-creep forming （SCF） is a novel technique to produce hard-to-form thin-walled metal components. Comprehensively considering the analysis results of the springback angle, yield strength and microstructure, four hot SCF process parameters including temperature, stretch velocity, post stretch percentage and dwelling time of a Ti-6Al-4V alloy sheet were optimized using an orthogonal experiment. The results reveal that temperature is the most important factor on springback angle. The yield strength of the deformed material in 0° direction increases, while those in directions of 45° and 90° fluctuate around the original value. After hot SCF, the shape of some a phases changes from short thin grains to long slender ones, and the microhardness changes very little. The optimized parameters with temperature of 700 ℃, stretch velocity of 5 mm/min, post stretch percentage of 2% and dwelling time of 8 min are achieved finally.

Influence of hydrogen content on room temperature compressive properties of Ti-6Al-4V alloy at high strain rate

Electromagnetic forming tests were done at room temperature to reveal the influence of hydrogen content on the compressive properties of Ti-6Al-4V alloy at high strain rate. Microstructure was observed to reveal the mechanism of hydrogen-enhanced compressive properties. The experimental results indicate that hydrogen has favorable effects on the compressive properties of Ti-6Al-4V alloy at high strain rate. Compression of Ti-6Al-4V alloy first increases up to a maximum and then decreases with the increase of hydrogen content at the same discharge energy under EMF tests. The compression increases by 47.0% when 0.2% (mass fraction) hydrogen is introduced into Ti-6Al-4V alloy. The optimal hydrogen content for cold formation of Ti–6Al–4V alloy under EMF was determined. The reasons for the hydrogen-induced compressive properties were discussed.

A modified Johnson-Cook model for NC warm bending of large diameter thin-walled Ti-6Al-4V tube in wide ranges of strain rates and temperatures

Numerical control（NC） warm bending is a proven strategy to form the large diameter thin-walled（LDTW） Ti-6 Al-4 V tubes, which are typical light-weight and high-performance structural components urgently required in many industries. In virtue of unveiling the thermo-mechanical coupled deformation behaviors, uniaxial tensile tests were conducted on Ti-6 Al-4 V tube within wide ranges of temperatures（25-600 ℃） and strain rates（0.00067-0.1 s～（-1））. Moreover, a modified Johnson-Cook（JC） model is proposed with a consideration of nonlinear strain rate hardening and the interaction between strain hardening and thermal softening. Resultantly, the present model gives more accurate predictions for flow stress over the entire deformation ranges and the maximum error decreases by about 90%. By employing proposed model to NC warm bending, preferable precision is obtained in predicting forming defects including fracture, wrinkling and over thinning. The present work lays foundation for the forming limit prediction and process optimization in NC warm bending of LDTW Ti-6 Al-4 V tubes.

Effect of grain size of primary α phase on bonding interface characteristic and mechanical property of press bonded Ti-6Al-4V alloy

The effect of grain size of primary α phase on the bonding interface characteristic and shear strength of bond was investigated in the press bonding of Ti-6Al-4V alloy. The quantitative results show that the average size of voids increases from 0.8 to 2.6 μm and the bonding ratio decreases from 90.9% to 77.8% with an increase in grain size of primary α phase from 8.2 to 16.4 μm. The shape of voids changes from the tiny round to the irregular strip. The highest shear strength of bond can be obtained in the Ti-6Al-4V alloy with a grain size of 8.2 μm. This is contributed to the higher ability of plastic flow and more short-paths for diffusion in the alloy with smaller grain size of primary α phase, which promote the void closure process and the formation of α/β grains across bonding interface.