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 ...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.展开更多
To overcome the disadvantages of inhomogeneous microstructures and poor mechanical properties of additively manufactured Ti-6Al-4V alloys,a novel technique of hybrid deposition and synchronous micro-rolling is propose...To overcome the disadvantages of inhomogeneous microstructures and poor mechanical properties of additively manufactured Ti-6Al-4V alloys,a novel technique of hybrid deposition and synchronous micro-rolling is proposed.The micro-rolling leads to equiaxed prior β grains,thin discontinuous intergranular α,and equiaxed primary α,in contrast to the coarse columnar prior β grains without the application of micro-rolling.The recrystallization by micro-rolling results in discontinuous intergranular α via the mechanism of strain and interface-induced grain boundary migration.The evolution of α globularization,driven by a solute concentration gradient,starts from the sub-boundary until the formation of equiaxed primary α.Simultaneous strengthening and toughening are achieved,which means an increase in yield strength,ultimate tensile strength,fracture elongation,and work hardening rate.The formation of α recrystallization leads to more fine grain boundaries to strengthen the yield strength,and the improvement of ductility is due to the better-coordinated deformation ability of discontinuous intergranular α and equiaxed primary α.As a result,the fracture mode in micro-rolling changes from intergranular type to transgranular type.展开更多
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 ...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.展开更多
Ti-6Al-4V alloy is extensively used in the manufacture of components in aviation.In the current study,the laser welding process is adopted to joint the Ti-6Al-4V alloy plate which has the thick of 8 mm.A three-dimensi...Ti-6Al-4V alloy is extensively used in the manufacture of components in aviation.In the current study,the laser welding process is adopted to joint the Ti-6Al-4V alloy plate which has the thick of 8 mm.A three-dimensional finite element model is established to simulate the temperature distribution of laser welding process.The thermal cycle curves are produced on the strength of the simulation results.Meanwhile,the microstructure characteristics of the welded joint are investigated combined with simulation results.The results show that weld zone,heat affected zone and based metal experience similar thermal cycles process and the cooling rate has an important influence on the formation of microstructure.Moreover,the simulation results are well matched with experiment results.展开更多
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 10~4–10~6 s^(–1). Flow stresses at high stra...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 10~4–10~6 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.展开更多
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 ...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.展开更多
Laser shock peening(LSP)is an attractive post-processing method to tailor surface microstructure and enhance mechanical performances of additive manufactured(AM)components.The effects of multiple LSP treatments on the...Laser shock peening(LSP)is an attractive post-processing method to tailor surface microstructure and enhance mechanical performances of additive manufactured(AM)components.The effects of multiple LSP treatments on the microstructure and mechanical properties of Ti-6Al-4V part produced by electron beam melting(EBM),as a mature AM process,were studied in this work.Microstructure,surface topography,residual stress,and tensile performance of EBM-manufactured Ti-6Al-4V specimens were systematically analyzed subjected to different LSP treatments.The distribution of porosities in EBM sample was assessed via X-ray computed tomography.The results showed that EBM samples with two LSP treatments possessed a lower porosity value of 0.05%compared to the value of 0.08%for the untreated samples.The strength of EBM samples with two LSP treatments was remarkably raised by 12%as compared with the as-built samples.The grains ofαphase were refined in near-surface layer,and a dramatic increase in the depth and magnitude of compressive residual stress(CRS)was achieved in EBM sample with multiple LSP treatments.The grain refinement ofαphase and CRS with larger depth were responsible for the strength enhancement of EBM samples with two LSP treatments.展开更多
This work aims to investigate the effects of hydrogen content(in the range of 0%-0.5%,mass fraction)and stress state (tension and compression)on the room-temperature mechanical properties of Ti-6Al-4V alloy through me...This work aims to investigate the effects of hydrogen content(in the range of 0%-0.5%,mass fraction)and stress state (tension and compression)on the room-temperature mechanical properties of Ti-6Al-4V alloy through mechanical properties tests. The effects of hydrogen content on microstructure evolution of Ti-6Al-4V alloy is also examined by optical microscopy,X-ray diffractometry,transmission electron microscopy and scanning electron microscopy.The results show that hydrogen content and stress state have important effects on the room-temperature mechanical properties of Ti-6Al-4V alloy.Tensile strength and ultimate elongation decrease with increasing the hydrogen content,while compressive strength and ultimate reduction are improved after hydrogenation.The reason is that the intergranular deformation dominates at the state of tension.Hydrogen atoms in solid solution and hydrides at grain boundaries increase with increasing the hydrogen content and they can promote the initiation and propagation of cracks along grain boundaries.While the intragranular deformation dominates at the state of compression.The plastic beta phase and hydrides increase with increasing the hydrogen content and they improve the ultimate reduction and compressive strength.展开更多
Selective laser melting(SLM) is a powerful additive manufacturing(AM) technology, of which the most prominent advantage is the ability to produce components with a complex geometry. The service performances of the SLM...Selective laser melting(SLM) is a powerful additive manufacturing(AM) technology, of which the most prominent advantage is the ability to produce components with a complex geometry. The service performances of the SLM-processed components depend on the microstructure and surface quality. In this work, the microstructures, mechanical properties, and fracture behaviors of SLM-processed Ti-6 Al-4 V alloy under machined and as-built surfaces after annealing treatments and hot isostatic pressing(HIP) were investigated. The microstructures were analyzed by optical microscope(OM), scanning electron microscope(SEM) and transmission electron microscopy(TEM). The mechanical properties were measured by tensile testing at room temperature. The results indicate that the as-deposited microstructures are characterized by columnar grains and fine brittle martensite and the asdeposited properties present high strength, low ductility and obvious anisotropy. After annealing at 800-900°C for 2-4 h and HIP at 920°C/100 MPa for 2 h, the brittle martensite could be transformed into ductile lamellar(α+β) microstructure and the static tensile properties of SLM-processed Ti-6 Al-4 V alloys in the machined condition could be comparable to that of wrought materials. Even after HIP treatment, the as-built surfaces could decrease the ductility and reduction of area of SLM-processed Ti-6 Al-4 V alloys to 9.2% and 20%, respectively. The crack initiation could occur at the columnar grain boundaries or at the as-built surfaces. The lamellar(α+β) microstructures and columnar grains could hinder or distort the crack propagation path during tensile tests.展开更多
Isothermal compression of Ti-6Al-4V alloy was conducted in the deformation temperature range of 1093-1303 K,the strain rates of 0.001,0.01,0.1,1.0,and 10.0 s-1,and the height reductions of 20%-60% with an interval of ...Isothermal compression of Ti-6Al-4V alloy was conducted in the deformation temperature range of 1093-1303 K,the strain rates of 0.001,0.01,0.1,1.0,and 10.0 s-1,and the height reductions of 20%-60% with an interval of 10%.After compression,the effect of the processing parameters including deformation temperature,strain rate,and height reduction on the flow stress and the microstructure was investigated.The grain size of primary α phase was measured using an OLYMPUS PMG3 microscope with the quantitative metallography SISC IAS V8.0 image analysis software.A model of grain size in isothermal compression of Ti-6Al-4V alloy was developed using fuzzy neural net-work(FNN) with back-propagation(BP) learning algorithm.The maximum difference and the average difference between the predicted and the experimental grain sizes of primary α phase are 13.31% and 7.62% for the sampled data,and 16.48% and 6.97% for the non-sampled data,respectively.It can be concluded that the present model with high prediction precision can be used to predict the grain size in isothermal compression of Ti-6Al-4V alloy.展开更多
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 ...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.展开更多
The physically-based internal state variable (ISV) models were used to describe the changes of dislocation density, grain size, and flow stress in the high temperature deformation of titanium alloys in this study. The...The physically-based internal state variable (ISV) models were used to describe the changes of dislocation density, grain size, and flow stress in the high temperature deformation of titanium alloys in this study. The constants of the present models could be identified based on experimental results, which were conducted at deformation temperatures ranging from 1093 K to 1303 K, height reductions ranging from 20% to 60%, and the strain rates of 0.001, 0.01, 0.1, 1.0, and 10.0 s-1. The physically-based internal state variable models were implemented into the commercial finite element (FE) code. Then, a three-dimensional (3D) FE simulation system coupling of deformation, heat transfer, and microstructure evolution was developed for the blade forging of Ti-6Al-4V alloy. FE analysis was carried out to simulate the microstructure evolution in the blade forging of Ti-6Al-4V alloy. Finally, the blade forging tests of Ti-6Al-4V alloy were performed to validate the results of FE simulation. According to the tensile tests, it is seen that the mechanical properties, such as tensile strength and elongation, satisfy the application requirements well. The maximum and minimum differences between the calculated and experimental grain size of primary α phase are 11.71% and 4.23%, respectively. Thus, the industrial trials show a good agreement with FE simulation of blade forging.展开更多
Compound ceramic coatings on Ti-6Al-4V alloy were prepared for different time by pulsed bi-polar micro-plasma oxidation (MPO) in NaAlO2 solution. The phase composition was studied by XRD. And the electrochemical imped...Compound ceramic coatings on Ti-6Al-4V alloy were prepared for different time by pulsed bi-polar micro-plasma oxidation (MPO) in NaAlO2 solution. The phase composition was studied by XRD. And the electrochemical impedance spectra (EIS) of the coatings were measured to study the structure of the coatings, combined with the surface morphology. Using the proper EIS interpreting software, the "equivalent circuit" of the coatings was established, and meanwhile fitting values of equivalent element were obtained. The results show that the coating is composed of Al2 TiO5, α-Al2O3 and rutile TiO2, of which Al2 TiO5 is the main crystalline. Increasing the MPO time, the contents of Al2TiO5, rutile TiO2 and α-Al2O3 in the surface of the coating increase. And the EIS analysis and the surface morphology of the coatings illustrates the double-layer structure of the coatings, and the outer layer is loosen and the inner layer is compact. With the increase of the oxidizing time, the surface coarse degree of the coatings and the porosity of the outer layer of the coating are increased while the compactness of the inner layer of the coating is improved.展开更多
The deformaton behavior of Ti - 6Al - 4V alloy under hot - working condition has been studied by compression testing in the temperature range 750 - 950℃ and strain rate range 0.05 - 15s -1. The flow stress decreases ...The deformaton behavior of Ti - 6Al - 4V alloy under hot - working condition has been studied by compression testing in the temperature range 750 - 950℃ and strain rate range 0.05 - 15s -1. The flow stress decreases with the increase of temperature and with the decrease of strain rate. After a steep initial strain hardening, a flow softening occurs. This softening is mainly ascribed to the temperature rise and dynamic recmptallisation.By a simple extension, a classical sinushyperbolic constitutive equation can be used to describe the flow behavior of Ti - 6Al - 4V alloy. flow stress is described as a function of strain, strain rate and temperature. The parameters Q, n andaare the same at differ- ent deformation conditions, and A is a funciton of strain.展开更多
Differences in wear rate, morphology of the worn surface and debris, and the microstructure in subsurface of the Ti 6Al 4V alloy after wear in air and vacuum were compared. The wear rate of Ti 6Al 4V alloy in air is h...Differences in wear rate, morphology of the worn surface and debris, and the microstructure in subsurface of the Ti 6Al 4V alloy after wear in air and vacuum were compared. The wear rate of Ti 6Al 4V alloy in air is higher than that in vacuum in all the ranges of sliding velocities and applied loads. The wear of Ti 6Al 4V alloy in air is controlled by a combination of abrasion, oxidation and delamination with micro cracks remaining in subsurface. Under the vacuum condition, the surface layer of Ti 6Al 4V alloy experiences a severe plastic deformation on a great scale, which results in an ultra fine microstructure.展开更多
Ti-6 Al-4 V-Si3 N4 composites were effectively fabricated by spark plasma sintering(SPS) technique. The addition of Si_3 N_4 on Ti-6 AI-4 V was varied from 5% to 15%(wt fraction). The effect of Si_3 N_4 addition on th...Ti-6 Al-4 V-Si3 N4 composites were effectively fabricated by spark plasma sintering(SPS) technique. The addition of Si_3 N_4 on Ti-6 AI-4 V was varied from 5% to 15%(wt fraction). The effect of Si_3 N_4 addition on the densification, microstructure, and microhardness and corrosion behaviour of Ti-6 Al-4 V was investigated.An increase in microhardness value was recorded from 325.46 HV_(0.1) to 585.73 HV_(0.1). X-ray diffraction(XRD) analysis showed that the intensity of diffraction peaks of Si3 N4 phase in the composites increased.The sintered Ti-6 Al-4 V reinforced with Si_3 N_4 compacts revealed the non-existence of intermediate phases, such as TiSi_2(titanium silicide) which was expected. SEM analysis of the spark plasma sintered composites revealed a and β phase microstructures in Ti-6 Al-4 V with uniform distribution of Si3 N4 particulates in the matrix. The corrosion resistance property of the material was improved by the addition of Si_3 N_4 from 0.986629 mm/year to 0.030547 mm/year.展开更多
The diffusion bonding of γ-TiAl alloy to Ti-6Al-4V alloy at different temperatures ranging from 1 073 to 1 173 K under an applied stress of 100 MPa for 2 h was studied. The observation of the microstructure reveals t...The diffusion bonding of γ-TiAl alloy to Ti-6Al-4V alloy at different temperatures ranging from 1 073 to 1 173 K under an applied stress of 100 MPa for 2 h was studied. The observation of the microstructure reveals that sound joints between the γ-TiAl alloy and the Ti-alloy without any pores or cracks can be achieved through diffusion bonding at temperatures over 1 073 K under the applied stress of 100 MPa for 2 h. The bond is composed of two zones, and its width increases with the increase of bonding temperature. The EDS chemical composition profiles indicate that there is a diffusion flux of Al atoms from γ-TiAl alloy towards the Ti alloy and of Ti atoms in the opposite direction. The three point-bending of the joints bonded under different conditions was tested and the fracture mode was analyzed by SEM observation.展开更多
The aim of this work was to study the degradation behavior of Ti-6Al-4V alloys for dental applications in acidic artificial saliva with fluoride ion using electrochemical techniques, optical microscopy, scanning elect...The aim of this work was to study the degradation behavior of Ti-6Al-4V alloys for dental applications in acidic artificial saliva with fluoride ion using electrochemical techniques, optical microscopy, scanning electron microscopy(SEM), and energy dispersive spectrometry(EDS). The experimental results showed that fluoride ion had significant influence on the degradation of Ti-6Al-4V alloys, and there was an obvious critical concentration of fluoride ion(about 0.1wt%). With increasing fluoride ion concentration, the corrosion potential(Ecorr) of alloys moved toward negative and the impedance of alloys decreased, meanwhile, noticeable transformation from minimum corrosion to severe pitting corrosion was observed on alloys surface following the dissolution of TiO_2 passive films, leading to the decrease of the corrosion resistance of alloys. The electrochemical dissolution of TiO_2 passive films involved a nucleophilic attack of fluoride atom to the titanium atom of TiO_2. In addition, Ca^(2+)and Na^+ in acidic saliva may involve the surface reactions and make the reactions more complex.展开更多
Ti-6Al-4V(TC4) alloys were plasma carbonized at different temperatures(900, 950, and 1 000 ℃) for duration of 3 h. Graphite rod was employed as carbon supplier to avoid the hydrogen brittleness which is ubiquitous in...Ti-6Al-4V(TC4) alloys were plasma carbonized at different temperatures(900, 950, and 1 000 ℃) for duration of 3 h. Graphite rod was employed as carbon supplier to avoid the hydrogen brittleness which is ubiquitous in traditional gas carbonizing process. Two distinguished structures including a thin compound layer(carbides layer) and a thick layer with the mixed microstructure of Ti C and the α-Ti in carburing layer were formed during carburizing. Furthermore, it was found that the microstructure and the properties of TC4 alloy were signifi cantly related to the carbonizing temperature. The specimen plasma carbonized at 950 ℃ obtained maximum value both in the hardness and wear resistance.展开更多
Ti-6Al-4V, among the Ti alloys, is the most widely used. In the present work, the behavior of Ti-6Al-4V alloy has beeninvestigated by the uniaxial hot isothermal compression tests and a series of dilatometric experime...Ti-6Al-4V, among the Ti alloys, is the most widely used. In the present work, the behavior of Ti-6Al-4V alloy has beeninvestigated by the uniaxial hot isothermal compression tests and a series of dilatometric experiments were also carried out todetermine the transformation temperatures at different cooling rates. Specimens for hot compression tests were homogenizedat 1050℃ for 10 min and then quickly cooled to different straining temperatures from 1050 to 850℃. Cooling rates were chosenfast enough to prevent high temperature transformation during cooling. Compression tests were conducted at temperaturesfrom 1050 to 850℃ in steps of 50℃ at constant true strain rates of 10-3 or 10-2 s-1. The apparent activation energy forcompression in two-phase region was calculated 420 kJ.mol-1. Partial globularization of α phase was observed in the specimendeformed at low strain rates and at temperatures near the transformation zone and annealed after deformation.展开更多
基金Supported by National Natural Science Foundation of China(Grant Nos.52001142,52005228,51801218,51911530211,51905110)Young Scientists Sponsorship Program by CAST(Grant No.2022QNRC001).
文摘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.
基金the support of the National Natural Science Foundation of China (No.51971099)the Analytical and Testing Center, HUST。
文摘To overcome the disadvantages of inhomogeneous microstructures and poor mechanical properties of additively manufactured Ti-6Al-4V alloys,a novel technique of hybrid deposition and synchronous micro-rolling is proposed.The micro-rolling leads to equiaxed prior β grains,thin discontinuous intergranular α,and equiaxed primary α,in contrast to the coarse columnar prior β grains without the application of micro-rolling.The recrystallization by micro-rolling results in discontinuous intergranular α via the mechanism of strain and interface-induced grain boundary migration.The evolution of α globularization,driven by a solute concentration gradient,starts from the sub-boundary until the formation of equiaxed primary α.Simultaneous strengthening and toughening are achieved,which means an increase in yield strength,ultimate tensile strength,fracture elongation,and work hardening rate.The formation of α recrystallization leads to more fine grain boundaries to strengthen the yield strength,and the improvement of ductility is due to the better-coordinated deformation ability of discontinuous intergranular α and equiaxed primary α.As a result,the fracture mode in micro-rolling changes from intergranular type to transgranular type.
基金financially supported by the National Natural Science Foundation of China (No.50975234)
文摘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.
文摘Ti-6Al-4V alloy is extensively used in the manufacture of components in aviation.In the current study,the laser welding process is adopted to joint the Ti-6Al-4V alloy plate which has the thick of 8 mm.A three-dimensional finite element model is established to simulate the temperature distribution of laser welding process.The thermal cycle curves are produced on the strength of the simulation results.Meanwhile,the microstructure characteristics of the welded joint are investigated combined with simulation results.The results show that weld zone,heat affected zone and based metal experience similar thermal cycles process and the cooling rate has an important influence on the formation of microstructure.Moreover,the simulation results are well matched with experiment results.
基金Supported by National Natural Science Foundation of China(Grant Nos.51205284,51575384)
文摘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 10~4–10~6 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.
文摘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.
基金financially supported by the Shanghai Science and Technology Committee Innovation Grant(Nos.17JC1400600 and 17JC1400603)the Distinguished Professor Program of Shanghai University of Engineering Science。
文摘Laser shock peening(LSP)is an attractive post-processing method to tailor surface microstructure and enhance mechanical performances of additive manufactured(AM)components.The effects of multiple LSP treatments on the microstructure and mechanical properties of Ti-6Al-4V part produced by electron beam melting(EBM),as a mature AM process,were studied in this work.Microstructure,surface topography,residual stress,and tensile performance of EBM-manufactured Ti-6Al-4V specimens were systematically analyzed subjected to different LSP treatments.The distribution of porosities in EBM sample was assessed via X-ray computed tomography.The results showed that EBM samples with two LSP treatments possessed a lower porosity value of 0.05%compared to the value of 0.08%for the untreated samples.The strength of EBM samples with two LSP treatments was remarkably raised by 12%as compared with the as-built samples.The grains ofαphase were refined in near-surface layer,and a dramatic increase in the depth and magnitude of compressive residual stress(CRS)was achieved in EBM sample with multiple LSP treatments.The grain refinement ofαphase and CRS with larger depth were responsible for the strength enhancement of EBM samples with two LSP treatments.
文摘This work aims to investigate the effects of hydrogen content(in the range of 0%-0.5%,mass fraction)and stress state (tension and compression)on the room-temperature mechanical properties of Ti-6Al-4V alloy through mechanical properties tests. The effects of hydrogen content on microstructure evolution of Ti-6Al-4V alloy is also examined by optical microscopy,X-ray diffractometry,transmission electron microscopy and scanning electron microscopy.The results show that hydrogen content and stress state have important effects on the room-temperature mechanical properties of Ti-6Al-4V alloy.Tensile strength and ultimate elongation decrease with increasing the hydrogen content,while compressive strength and ultimate reduction are improved after hydrogenation.The reason is that the intergranular deformation dominates at the state of tension.Hydrogen atoms in solid solution and hydrides at grain boundaries increase with increasing the hydrogen content and they can promote the initiation and propagation of cracks along grain boundaries.While the intragranular deformation dominates at the state of compression.The plastic beta phase and hydrides increase with increasing the hydrogen content and they improve the ultimate reduction and compressive strength.
基金financially supported by the National Program on Key Basic Research Project of China(973 Program)under Grant(No.613281)the National Natural Science Foundation of China(No.51505451)+3 种基金the Natural Science Foundation of Beijing(No.3172042)supported by EMUSIC which is part of an EU-China collaborationthe European Union’s Horizon 2020 research and innovation programme under Grant Agreement No.690725MIIT under the programme number MJ-2015-H-G-104
文摘Selective laser melting(SLM) is a powerful additive manufacturing(AM) technology, of which the most prominent advantage is the ability to produce components with a complex geometry. The service performances of the SLM-processed components depend on the microstructure and surface quality. In this work, the microstructures, mechanical properties, and fracture behaviors of SLM-processed Ti-6 Al-4 V alloy under machined and as-built surfaces after annealing treatments and hot isostatic pressing(HIP) were investigated. The microstructures were analyzed by optical microscope(OM), scanning electron microscope(SEM) and transmission electron microscopy(TEM). The mechanical properties were measured by tensile testing at room temperature. The results indicate that the as-deposited microstructures are characterized by columnar grains and fine brittle martensite and the asdeposited properties present high strength, low ductility and obvious anisotropy. After annealing at 800-900°C for 2-4 h and HIP at 920°C/100 MPa for 2 h, the brittle martensite could be transformed into ductile lamellar(α+β) microstructure and the static tensile properties of SLM-processed Ti-6 Al-4 V alloys in the machined condition could be comparable to that of wrought materials. Even after HIP treatment, the as-built surfaces could decrease the ductility and reduction of area of SLM-processed Ti-6 Al-4 V alloys to 9.2% and 20%, respectively. The crack initiation could occur at the columnar grain boundaries or at the as-built surfaces. The lamellar(α+β) microstructures and columnar grains could hinder or distort the crack propagation path during tensile tests.
基金financially supported by the National Natural Science Foundation of China (No.50975234)
文摘Isothermal compression of Ti-6Al-4V alloy was conducted in the deformation temperature range of 1093-1303 K,the strain rates of 0.001,0.01,0.1,1.0,and 10.0 s-1,and the height reductions of 20%-60% with an interval of 10%.After compression,the effect of the processing parameters including deformation temperature,strain rate,and height reduction on the flow stress and the microstructure was investigated.The grain size of primary α phase was measured using an OLYMPUS PMG3 microscope with the quantitative metallography SISC IAS V8.0 image analysis software.A model of grain size in isothermal compression of Ti-6Al-4V alloy was developed using fuzzy neural net-work(FNN) with back-propagation(BP) learning algorithm.The maximum difference and the average difference between the predicted and the experimental grain sizes of primary α phase are 13.31% and 7.62% for the sampled data,and 16.48% and 6.97% for the non-sampled data,respectively.It can be concluded that the present model with high prediction precision can be used to predict the grain size in isothermal compression of Ti-6Al-4V alloy.
文摘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.
基金supported by the National Natural Science Foundation of China (No.50975234)China Postdoctoral Science Foundation (No.20110491685)
文摘The physically-based internal state variable (ISV) models were used to describe the changes of dislocation density, grain size, and flow stress in the high temperature deformation of titanium alloys in this study. The constants of the present models could be identified based on experimental results, which were conducted at deformation temperatures ranging from 1093 K to 1303 K, height reductions ranging from 20% to 60%, and the strain rates of 0.001, 0.01, 0.1, 1.0, and 10.0 s-1. The physically-based internal state variable models were implemented into the commercial finite element (FE) code. Then, a three-dimensional (3D) FE simulation system coupling of deformation, heat transfer, and microstructure evolution was developed for the blade forging of Ti-6Al-4V alloy. FE analysis was carried out to simulate the microstructure evolution in the blade forging of Ti-6Al-4V alloy. Finally, the blade forging tests of Ti-6Al-4V alloy were performed to validate the results of FE simulation. According to the tensile tests, it is seen that the mechanical properties, such as tensile strength and elongation, satisfy the application requirements well. The maximum and minimum differences between the calculated and experimental grain size of primary α phase are 11.71% and 4.23%, respectively. Thus, the industrial trials show a good agreement with FE simulation of blade forging.
基金Project (50171026) supported by the National Natural Science Foundation of China
文摘Compound ceramic coatings on Ti-6Al-4V alloy were prepared for different time by pulsed bi-polar micro-plasma oxidation (MPO) in NaAlO2 solution. The phase composition was studied by XRD. And the electrochemical impedance spectra (EIS) of the coatings were measured to study the structure of the coatings, combined with the surface morphology. Using the proper EIS interpreting software, the "equivalent circuit" of the coatings was established, and meanwhile fitting values of equivalent element were obtained. The results show that the coating is composed of Al2 TiO5, α-Al2O3 and rutile TiO2, of which Al2 TiO5 is the main crystalline. Increasing the MPO time, the contents of Al2TiO5, rutile TiO2 and α-Al2O3 in the surface of the coating increase. And the EIS analysis and the surface morphology of the coatings illustrates the double-layer structure of the coatings, and the outer layer is loosen and the inner layer is compact. With the increase of the oxidizing time, the surface coarse degree of the coatings and the porosity of the outer layer of the coating are increased while the compactness of the inner layer of the coating is improved.
文摘The deformaton behavior of Ti - 6Al - 4V alloy under hot - working condition has been studied by compression testing in the temperature range 750 - 950℃ and strain rate range 0.05 - 15s -1. The flow stress decreases with the increase of temperature and with the decrease of strain rate. After a steep initial strain hardening, a flow softening occurs. This softening is mainly ascribed to the temperature rise and dynamic recmptallisation.By a simple extension, a classical sinushyperbolic constitutive equation can be used to describe the flow behavior of Ti - 6Al - 4V alloy. flow stress is described as a function of strain, strain rate and temperature. The parameters Q, n andaare the same at differ- ent deformation conditions, and A is a funciton of strain.
文摘Differences in wear rate, morphology of the worn surface and debris, and the microstructure in subsurface of the Ti 6Al 4V alloy after wear in air and vacuum were compared. The wear rate of Ti 6Al 4V alloy in air is higher than that in vacuum in all the ranges of sliding velocities and applied loads. The wear of Ti 6Al 4V alloy in air is controlled by a combination of abrasion, oxidation and delamination with micro cracks remaining in subsurface. Under the vacuum condition, the surface layer of Ti 6Al 4V alloy experiences a severe plastic deformation on a great scale, which results in an ultra fine microstructure.
基金financial support from National Research Foundation(NRF), Pretoria, South Africa
文摘Ti-6 Al-4 V-Si3 N4 composites were effectively fabricated by spark plasma sintering(SPS) technique. The addition of Si_3 N_4 on Ti-6 AI-4 V was varied from 5% to 15%(wt fraction). The effect of Si_3 N_4 addition on the densification, microstructure, and microhardness and corrosion behaviour of Ti-6 Al-4 V was investigated.An increase in microhardness value was recorded from 325.46 HV_(0.1) to 585.73 HV_(0.1). X-ray diffraction(XRD) analysis showed that the intensity of diffraction peaks of Si3 N4 phase in the composites increased.The sintered Ti-6 Al-4 V reinforced with Si_3 N_4 compacts revealed the non-existence of intermediate phases, such as TiSi_2(titanium silicide) which was expected. SEM analysis of the spark plasma sintered composites revealed a and β phase microstructures in Ti-6 Al-4 V with uniform distribution of Si3 N4 particulates in the matrix. The corrosion resistance property of the material was improved by the addition of Si_3 N_4 from 0.986629 mm/year to 0.030547 mm/year.
基金Project(50371072) supported by the National Natural Science Foundation of China
文摘The diffusion bonding of γ-TiAl alloy to Ti-6Al-4V alloy at different temperatures ranging from 1 073 to 1 173 K under an applied stress of 100 MPa for 2 h was studied. The observation of the microstructure reveals that sound joints between the γ-TiAl alloy and the Ti-alloy without any pores or cracks can be achieved through diffusion bonding at temperatures over 1 073 K under the applied stress of 100 MPa for 2 h. The bond is composed of two zones, and its width increases with the increase of bonding temperature. The EDS chemical composition profiles indicate that there is a diffusion flux of Al atoms from γ-TiAl alloy towards the Ti alloy and of Ti atoms in the opposite direction. The three point-bending of the joints bonded under different conditions was tested and the fracture mode was analyzed by SEM observation.
基金Funded by the National Natural Science Foundation of China(No.50801057)the National Basic Research Priorities Program of China(No.2005DKA10400-CT-1-08-06)+1 种基金the Special Fund for Basic Scientific Research of Central Colleges,China University of Geosciences(Wuhan)(No.007-G1323521109)the National Natural Science Fundation of China(81641035 and 81401524)
文摘The aim of this work was to study the degradation behavior of Ti-6Al-4V alloys for dental applications in acidic artificial saliva with fluoride ion using electrochemical techniques, optical microscopy, scanning electron microscopy(SEM), and energy dispersive spectrometry(EDS). The experimental results showed that fluoride ion had significant influence on the degradation of Ti-6Al-4V alloys, and there was an obvious critical concentration of fluoride ion(about 0.1wt%). With increasing fluoride ion concentration, the corrosion potential(Ecorr) of alloys moved toward negative and the impedance of alloys decreased, meanwhile, noticeable transformation from minimum corrosion to severe pitting corrosion was observed on alloys surface following the dissolution of TiO_2 passive films, leading to the decrease of the corrosion resistance of alloys. The electrochemical dissolution of TiO_2 passive films involved a nucleophilic attack of fluoride atom to the titanium atom of TiO_2. In addition, Ca^(2+)and Na^+ in acidic saliva may involve the surface reactions and make the reactions more complex.
基金Funded in part by National Natural Science Foundation of China(No.51301023)the Fundamental Research Funds for the Central Universities,Chang'an University(No.CHD2011JC126,2013G1311054 and 310831151079)
文摘Ti-6Al-4V(TC4) alloys were plasma carbonized at different temperatures(900, 950, and 1 000 ℃) for duration of 3 h. Graphite rod was employed as carbon supplier to avoid the hydrogen brittleness which is ubiquitous in traditional gas carbonizing process. Two distinguished structures including a thin compound layer(carbides layer) and a thick layer with the mixed microstructure of Ti C and the α-Ti in carburing layer were formed during carburizing. Furthermore, it was found that the microstructure and the properties of TC4 alloy were signifi cantly related to the carbonizing temperature. The specimen plasma carbonized at 950 ℃ obtained maximum value both in the hardness and wear resistance.
文摘Ti-6Al-4V, among the Ti alloys, is the most widely used. In the present work, the behavior of Ti-6Al-4V alloy has beeninvestigated by the uniaxial hot isothermal compression tests and a series of dilatometric experiments were also carried out todetermine the transformation temperatures at different cooling rates. Specimens for hot compression tests were homogenizedat 1050℃ for 10 min and then quickly cooled to different straining temperatures from 1050 to 850℃. Cooling rates were chosenfast enough to prevent high temperature transformation during cooling. Compression tests were conducted at temperaturesfrom 1050 to 850℃ in steps of 50℃ at constant true strain rates of 10-3 or 10-2 s-1. The apparent activation energy forcompression in two-phase region was calculated 420 kJ.mol-1. Partial globularization of α phase was observed in the specimendeformed at low strain rates and at temperatures near the transformation zone and annealed after deformation.