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.

Stitch welding of Ti-6Al-4V titanium alloy by fiber laser

Stitch welding of plate covered skeleton structure of Ti-6Al-4V titanium alloys has a variety of applications in aerospace vehicle manufacture. The laser stitch welding of Ti-6Al-4V titanium alloys was carried out by a 4 kW ROFIN fiber laser. Influences of laser welding parameters on the macroscopic geometry, porosity, microstructure and mechanical properties of the stitch welded seams were investigated by digital microscope, optical microscope, scanning electron microscope and universal tensile testing machine. The results showed that the three-pipe nozzle with gas flow rate larger than 5 L/min could avoid oxidization, presenting better shielding effect in comparison with the single-pipe nozzle. Porosity formation could be suppressed with the gap between plate and skeleton less than 0.1 mm, while the existing porosity can be reduced with remelting. The maximum shear strength of stitch welding joint with minimal porosity was obtained by employing laser power of 1700 W, welding speed of 1.5 m/min and defocusing distance of ＋8 ram.

Development of processing windows for diffusion bonding of Ti-6Al-4V titanium alloy and 304 stainless steel with silver as intermediate layer

As titanium alloy is chemically reactive,it is very difficult to join by conventional welding techniques.Titanium alloys can easily pick up nitrogen and oxygen from the atmosphere.In the fusion welding method,brittle intermetallic compounds are formed when joining titanium alloy and stainless steel,which decrease the mechanical behavior of the couples.Hence,for joining of titanium alloy,diffusion bonding is recommended.This work dealt with the measurement of feasible process parameters for diffusion bonding of Ti-6Al-4V and AISI 304 stainless steel with silver as an intermediate layer.The quality of the bonds was confirmed by the lap shear test and microstructural analysis.With the experimental results obtained,diffusion bonding windows were constructed and this will act as reference maps to identify the process parameters for obtaining defect free bond.Bonding was successful in the temperature range of 750-800 °C.Maximum lap shear strength was achieved under a bonding pressure of 5 MPa and holding time of 90 min.

Identification and evolution of interfacial structure of SiO2 glass ceramic/Ti-6AI-4V alloy joint bonded with AgCu/Ni interlayer

AgCu/Ni composite interlayer was utilized to join SiO2 glass ceramic （74. 52% SiO2-23. 40% Al2 03 -2. 08 % K2 O, wt. % ） and Ti-6Al-4V alloy by eutectic reaction. Interface structures of the joints were identified by means of TEM analysis. This joining method contains three characteristic processes, which are the melting of AgCu eutectic alloy, eutectic reaction between interlayer and Ti-6Al-4V base material and active reaction of element Ti to SiO2 glass ceramic. It is different from traditional active brazing because active element Ti totally dissolves from Ti-6Al-4 V and reacts with SiO2 glass ceramic. SiO2 glass ceramic can be joined suecessfuUy to Ti-6Al-4 V alloy by this novel bonding method and the joint exhibits high shear strength, up to 110 MPa.

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.

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.

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.

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.

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.

Dynamic fracture of Ti-6Al-4V alloy in Taylor impact test

The dynamic fracture behaviors of Ti-6Al-4V alloy at high strain rate loading were investigated systemically through Taylor impact test, over the range of impact velocities from 145 m/s to 306 m/s. The critical impact velocity of fracture ranges from 217 m/s to 236 m/s. Smooth surfaces and ductile dimple areas were observed on the fracture surfaces. As the impact velocity reached 260 m/s, the serious melting regions were also observed on the fracture surfaces. Self-organization of cracks emerges when the impact velocity reaches 260 m/s, while some special cracks whose ＂tips＂ are not sharp but arc and smooth, and without any evidence of deformation or adiabatic shear band were also observed on the impact end surfaces. Examination of the sections of these special cracks reveals that the cracks expand along the two maximum shear stress directions respectively, and finally intersect as a tridimensional ＂stagger ridge＂ structure.

TI-6AI-4V裂纹缺陷荧光渗透检测研究

阐述了荧光渗透检测TI-6AI-4V裂纹缺陷的原理,给出了缺陷宽度和缺陷深度公式。研究了荧光渗透检测的工艺过程,通过对TI-6AI-4V裂纹缺陷的试验分析,表明结构曲率变化过大处是产生裂纹缺陷的区域。对TI-6AI-4V裂纹缺陷的产生原因做了理论、模拟分析和试验研究,表明在加工TI-6AI-4V过程中,切削用量是造成应力集中的重要因素,其中切削深度过大会造成裂纹缺陷。

Quasi-static and dynamic tensile behaviors in electron beam welded Ti-6Al-4V alloy

The quasi-static and dynamic tensile behaviors in electron beam welded（EBW） Ti-6Al-4V alloy were investigated at strain rates of 10-3 and 103 s-1,respectively,by materials test system（MTS） and reconstructive Hopkinson bars apparatus.The microstructures of the base metal（BM） and the welded metal（WM） were observed with optical microscope.The fracture characteristics of the BM and WM were characterized with scanning electronic microscope.In Ti-6Al-4V alloy joint,the flow stress of WM is higher than that of BM,while the fracture strain of WM is less than that of BM at strain rates of 103 and 10-3 s-1,respectively.The fracture strain of WM has apparent improvement when the strain rate rises from 10-3 to 103 s-1,while the fracture strain of BM almost has no change.At the same time,the fracture mode of WM alters from brittle to ductile fracture,which causes improvement of the fracture strain of WM.

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.

Heat-treated microstructure and mechanical properties of laser solid forming Ti-6Al-4V alloy

The effects of heat treatment on the microstructure and mechanical properties of laser solid forming （LSF） Ti-6Al-4V alloy were investigated The influences of the temperature and time of solution treatment and aging treatment were analyzed. The results show that the microstructure of LSFed samples consists of Widmanstatten α laths and a little acicular in columnar prior β grains with an average grain width of 300 μm, which grow epitaxiaUy from the substrate along the deposition direction （27）. Solution treatment had an important effect on the width, aspect ratio, and volmne fraction of primary and secondary a laths, and aging treatment mainly affects the aspect ratio and volume fraction of primary α laths and the width and volume fraction of secondary a laths. Globular a phase was first observed in LSFed samples when the samples were heat treated with solution treatment （950℃, 8 h/air cooling （AC）） or with solution treatment （950℃, 1 h/AC） and aging treatment （550℃, above 8 h/AC）, respectively. The coarsening and globularization mechanisms of a phase in LSFed Ti-6Al-4V alloy during heat treatment were presented. To obtain good integrated mechanical properties for LSFed Ti-6Al-4V alloys, an optimized heat treatment regimen was suggested.

Improving impact wear resistance of Ti-6Al-4V alloy treated by laser shock peening

The effects of laser shock peening (LSP) on the impact wear behavior of Ti-6Al-4V alloys were investigated by a homemade impact wear test rig. The microstructure and mechanical properties of the peened samples were studied. During the impact wear test, the energy absorption, impact force, wear contact time and wear mechanism of all the test samples were investigated in terms of the influence of the impact kinetic energy. The results showed that microhardness, elastic modulus and residual compressive stress of the treated samples were markedly improved. The wear resistances of both treated samples were highly improved after LSP, and a higher pulse energy corresponded to a more obvious effect. Besides, the wear in all test samples involved a combination of abrasive and oxidation wear and fatigue spalling.

Hot deformation behavior of Ti-6Al-4V-0.1Ru alloy during isothermal compression

The hot deformation behavior of Ti-6 Al-4 V-0.1 Ru titanium alloy was investigated by isothermal compression tests on a Gleeble-3500 thermal simulator over deformation temperature range of 1023-1423 K and strain rate of 0.01-10 s-1.Arrhenius-type constitutive models were developed for temperature ranges of bothα+βdual phase andβsingle phase at strain of 0.1.Afterwards,a series of material constants(including activation energy Q,material constants n,αand ln A)as polynomial functions of strain were introduced into Arrhenius-type models.Finally,the improved Arrhenius-type models in temperature field ofα+βandβphase were constructed.The results show that the improved Arrhenius-type models contribute to the calculation of Zener-Hollomon(Z)parameter,and the microstructural evolution mechanism is uncovered by combining microstructure observations with Z-parameter.Furthermore,the improved Arrhenius-type models are also helpful to improve the accuracy of finite element method(FEM)simulation in the deformation process of Ti-6 Al-4 V-0.1 Ru titanium alloy.

Variation effect of strain rate on microstructure in isothermal compression of Ti-6Al-4V alloy

Isothermal compression of the Ti-6Al-4V alloy at the deformation temperatures of 950 and 980℃,height reductions of 30% and 60%,and strain rates of 0.001,0.010,0.100 and 1.000 s-1 was conducted,wherein the variations of microstructure with strain rate were investigated.The experimental results showed that the variation of the microstructure with the strain rate under one condition was significantly different from that under another condition,which meaned that the interaction between the processing parameters was great.The optimization of the strain rate under one condition was not suitable for another condition.Therefore,selecting the forging equipment and optimizing the strain rate should be based on simultaneously considering the deformation temperature and height reduction.

In situ laser deposition of NiTi intermetallics for corrosion improvement of Ti-6Al-4V alloy

NiTi intermetallic coatings were fabricated on the surface of Ti-6Al-4V alloy by melting Ni and Ti powders using laser metal deposition（LMD） process.The effects of NiTi reinforcement content on the microstructure,hardness and corrosion properties of the coatings were examined.The results show that the deposited coatings are characterized by NiTi,NiTi2 and NiTi3 intermetallic phases.An appreciable increase in corrosion resistance is obtained for all the coatings,and Ti55Ni45 coating shows the highest corrosion resistance;while coatings Ti50Ni50 and Ti45Ni55 follow in that succession.The reinforcement materials are proven to be corrosion resistant in the tested environment,and the effect of Ti is more dominant.

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.