Abstract:Ti₃AlC₂ ceramics were fabricated by in-situ reaction in the 2TiC-Ti-1.2Al system. Ti₂AlC/TiAl composites were prepared by spark plasma sintering technology in the 59.2Ti-30.8Al-10Ti₃AlC₂(wt%) system. The phase composition and microstructure of the specimens were analyzed by XRD and SEM methods. The room temperature mechanical properties were also measured. The results revealed that the in-situ Ti₃AlC₂ materials mainly consisted of Ti₃AlC₂ and TiC phases. Ti₃AlC₂ ceramics present layered structure and TiC particles distribute around the grain boundaries. The Ti₂AlC/TiAl composites prepared by SPS mainly consist of TiAl, Ti₃Al and Ti₂AlC phases. Ti₂AlC reinforcements are mainly distributed in the matrix grain boundaries, which show grain-boundary strengthening or intracrystalline strengthening effect. The density, Vickers hardness, fracture toughness and flexural strength of the Ti₂AlC/TiAl composites are 3.85 g/cm₃, 5.37 GPa, 7.17 MPa, 7.17 MPa?m_1/2 and 494.85 MPa respectively.

Abstract:The dissolution and precipitation behaviors of silicides and their influence on the microstructure and tensile properties of Ti-38644 titanium alloy were investigated. Microstructure characteristics and tensile fracture mode were observed by means of OM, SEM and TEM. The results showed that trace impurity Si promote the formation of (TiZr)₆Si₃ silicides. Silicide gradually dissolved when the alloy was solution treated at 700～900 ℃. No silicides were observed after the alloy was solution treated at 950 ℃. The strength of the alloy decreased with increasing solution temperature in the range of 800～950 ℃ due to the dissolution of silicides and the growth of β grians. When the alloy was solution treated at 1100 ℃ and aged at 750～900 ℃ for 1 h, silicides precipitated at grain boundaries. No grain boundary silicides were observed after the alloy was aged at 700 ℃ and 950 ℃. Grain boundary silicides had little influence on the strength, but decreased its plasticity significantly, the tensile fracture mode was mainly intergranular fracture.

Abstract:The effect of aging on superelasticity of TiNi SMA was studied by mechanical property tests. It’s indicated that after aging treatment of 300℃×(60-180min) and aging treatment of 400℃×(10-30min), the tensile strength of TiNi SMA wires is higher than 1000 MPa, and the residual strain is less than 0.31% in loading-unloading tensile tests of 6%. The low clearance TiNi SMA has better mechanical properties and superelasticity after aging treatment.

Abstract:A Ti₂AlNb-base alloy was deposited on a TiAl-base alloy by using micro-beam plasma melting deposition. Optical microscope(OM), scanning electron microscope(SEM), energy-dispersive spectrometer(EDS), X-ray diffraction(XRD) and microhardness testing methods were used to investigate the typical microstructure evolution, phase transformation and the corresponding hardness evolution. Experimental results show that micro-beam plasma melting deposition of Ti₂AlNb-base alloy are mainly composed of β、O andα₂ phases. With the increasing of distance form TiAl-base alloy, a series of phase evolutions along the compositional gradient occurred: γ+α₂/γ→β(solid solution)+O→β₂+O+α₂(widmannstatten structure)→β(solid solution)+O. The microhardness of gradient material shows a wave-like distribution. The phase morphological evolution during forming of micro-beam plasma melting deposition gradient materials was explained based on the effect of the various elements on the phase stability in TiAl/ Ti₂AlNb -base alloy combining with the effects of special thermal cycle and heat accumulation in micro-beam plasma melting deposition forming.

Abstract:This study focused on the hydrogen absorption behavior of high Nb contained titanium alumindies at high temperature, the effect of hydrogen on microstructure evolution and hot deformation behavior the alloy were studied. The results show that hydrogen absorption in titanium aluminides is endothermic reaction, hydrogen contentin the alloy increases with increasing of hydrogenation temperature, hydrogenation time and hydrogen flow rate which is sensitive to hydrogenation temperature.The lamellar space of hydrogenated alloy is coarsened after hydrogenation at 1200℃, the content of B2 phase is more in hydrogenated alloy as hydrogen is beta stabilized element. The interface of lamellar colonies is smoothed when hydrogenation above 1280℃as hydrogen reduces the interface energy. Hydrogen has a great effect on hot deformation of titanium alumnides, the peak stress decreases by 40% after hydrogenated with 0.043wt% hydrogen under strain rate of 0.01s_-1 at 1200℃.Hydrogenation at high temperature is an effective method to improve the hot workability of titanium aluminides

Abstract:The microstructure, tensile and fatigue properties of Ti-6Al-4V alloy made by EBSM were studied. The as-build material exhibited a columnar microstructure in which the prior-β grains grew along the build direction. Within each β grain, Widmanst?tten microstructure is dominant, and colonies of α/b platelets were also present.The tensile strength of as-build material was not affected by defects and the average tensile strength and ductility meet the ASTM standard. HIPpingremoved all defects in the EBSMTi-6Al-4V alloyand increased tensile elongation by ~35%, but the strength was 5% lower due to microstructure coarsening. The fatigue life was also significantly improved by HIPping and the fatigue limit reached 600MPa under 1×10₇ cycle, R=0.1 condition. The large scatter of fatigue life is mailyattributed to the scatter of tensile properties. In most of the samples, crack initiated from the surface. The crack initiation mechanism was proposed base on fracture analysis of typical fatigue specimens.

Abstract:The Ti-22Al-24Nb-0.5Mo electron beam weld was investigated. The FZ is composed of fully collunar B2 grains in the FZ center and the dentritic B2 grains on top and bottom of the weld. Their distribution is symmetrical to the fusion line center. Two post-weld annealing schedules, namely 850_oC/2hr/AC (anneal) and 980_oC/2hr+850_oC/24hr/AC (solution treat + anneal), have been used. The STA weld exhibits a coarser O phase than the annealed weld in the FZ and the α₂ phase reappeared.The tensile strength of the welds for these two annealing conditions are similar at room temperature, while the annealed weld is a little stronger at 650_oC. The creep rupture life of the STA weld is higher, and the fracture mode is intergranular for both annealed and STA welds.

Abstract:1060 pure aluminum and TC4 alloy sheets with a thickness of 0.2 mm were micro resistance spot welded successfully. The effects of the welding current, welding time and electrode force on mechanical properties of the joints were studied. The joining feature and fracture behavior of the joints were analyzed by using scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). Also, the phase compositions of the joints were measured by using micro-X-ray diffraction (micro-XRD). The result shows that: with increasing the welding current, the tensile shear load of the joints increases first and then is steady when the welding current is in the range of 0.3~0.7 kA. However, the welding time has no significant effect on the tensile shear load of the joints when the welding time changes in the range of 2~6 cyc. The tensile shear load of the joints presents an increased first and then decreased trend with increasing of the electrode force in the range of 40~280 N. When the welding current is 0.7 kA, the welding time is 3 cyc and the electrode force is 160 N, the maximum tensile shear load of the joints reaches to 91 N, and the fracture occurs in the heat affected zone. A complete nugget is formed, and the interface on the TC4 side is relatively flat while it is unsmooth on the 1060 side. Inside the nugget, lots of Al₃Ti, Al₂Ti and AlTi₃ compounds are generated. And some needle-like Al₃Ti compounds are found at the interface of the 1060, which plays an important role in the strength of the joints.

Abstract:TC8M-1 titanium alloy was the newly developed hot strength and long life high temperature titanium alloy, which the highest serviceability temperature can be reached at 450 °C. The effect of heat treatment process on microstructure and mechanical properties of TC8M-1 titanium alloy was researched by using solution and aging treatment at different temperatures. The results show that the content of equiaxed primary α phase decreases gradually and the transformed β structure becomes coarse with the increasing of solution temperature. Meanwhile, the equiaxed microstructure transforms into duplex microstructure. Therefore, the room temperature strength presents the decrease trend. However, the content of equiaxed primary α phase changes little with the increasing of aging temperature. The stretch strength at room temperature drops a little, but the ductility increases slightly. After heat treatment at 920 °C/2h, AC+580 °C/1h, AC, the TC8M-1 titanium alloy can be obtain the optimum combination of strength with plasticity.

Abstract:With the development and application of TiNi shape memory alloy, its mechanical properties attract more and more attentions. In order to study the mechanical properties of TiNi alloy, the static tensile stress-strain curves of TiNi alloy under different temperatures has been obtained by using MTS universal testing machine, based on which a detailed analysis was performed. The split Hopkinson pressure bar(SHPB) has been used to get the corresponding stress-strain curves of TiNi alloy under a variety of high strain rates. The improved SHPB system was used to get the dynamic fracture toughness of TiNi alloy by carring out dynamic three-poin bending test. The results showed that the deformation behavior of TiNi alloy was different from those of the general metals.There were two yield platforms, two elastic stages and two non-elastic deformation stages on both static and dynamic stress-strain curves of TiNi alloy. Meanwhile, TiNi alloy was a relatively brittle metal and more easy to be brritle fracture under dynamic impact loading.

Abstract:TC16 titanium alloys with different hydrogen quantity were obtained using a hydrogenating treatment. Effects of the hydrogen quantity on phase transformation temperatures of TC16 titanium alloys were investigated by a continuous heating method. Microstructures of hydrogenated TC16 titanium alloys were studied using OM, deformation behaviours of TC16 titanium alloys were studied using quasi-static compression tests, and the alloy deformation behaviours at high strain rates were investigated using magnetic cold heading. The results have shown that, phase transformation temperature of TC16 titanium alloy decreases with the increasing of hydrogen quantity, when this amount reaches 0.3wt. %, the phase temperature decreases around 150 °C; Microstructures of hydrogenated TC16 titanium alloy changes as well, martensite phase generates for low hydrogen quantity, while equal-axial β phase for high hydrogen quantity; Strain rate sensitivity of hydrogenated TC16 titanium alloy increases, with the increasing of deformation rate, the formability is improved, the limit compression deformation is greater than 86% at a high strain rate. Using cold up-setting tests to manufacture layer board nuts with perfect surfaces, the deformation behaviour was validated.

Abstract:In this study, a new severe plastic deformation method, equal channel angular pressing (ECAP), was applied to strengthen a discontinuously TiB+TiC reinforced titanium alloy. The microstructural evolution mechanism during severe plasitic deformation processing was systematicly studied. Special attention was focused on the grain refinement, the deformation mechnism and formation mechnism in the preparation of ultrafine grain composite. The results indicated that the refinement of TiB fibers and TiC particles could be obtained, as well as the grain size of the matrix alloy. With the increasing of ECAP pass numbers, the clustered long TiB fibers and TiC big particles were also homogenized in the matrix, resulting in the increase of the mechanical properties. The tensile strength is up to 1205MPa, and the elongation improves comparing with the first ECAP pass.

Abstract:TC16 titanium alloys have good mechanical properties and cold forming performance, widely used in the production field of aerospace fasteners. To study hexagon bolt heading behaviors of TC16 titanium alloy wire, hexagon bolt heading behaviors of TC16 titanium alloy wire was simulated by MSC.Marc finite element simulation software. The simulation results show that friction coefficient has great effects on the deformation degree and the temperature increasing distribution in different zone, initial temperature has little effect on the deformation degree but has greater effect on the temperature increasing in different zone. The mould can not be fully filled when friction coefficient is lower. However, prone flash will be produced when friction coefficient is higher. A better hexagonal head shape can be got when friction coefficient is 0.1. A good fit between simulation results and real testing can be found by contrasting the simulation results with real hexagonal head bolt microstructure and micro-hardness.

Abstract:A combination of transmission electron microscopy and scanning electron microscopy was used to study deformation and fracture behavior of Ti-55531 alloy with bimodal microstructure (donated by BM Ti-55531 alloy) during tensile and torsion tests at room temperature. Results indicate that loading modes have a significant influence on deformation and fracture failure of BM Ti-55531 alloy. First of all, the tension strength is more about 300 MPa than torsion strength of BM Ti-55531 alloy, and its ductilty of tension is also higher. BM Ti-55531 alloy is more sensitive to tensile stress than torsion shear stress.Secondly, deformation mechanism of both tensile and torsion test are a mix mode which combines dislocation slip and shear, while deformation of torsion test was predominantly controlled by shear. These interfaces between net-like grain boundary α, primary α and retained β phases were easly filled with high density dislocations.Thirdly, fractographs of tensile and torsion tested specimens seem to possess different morphologies. Fractographs of tensile specimens are cliffier than torsion specimens. The tensile sample shows a ductile failure, including microvoid coalescence and inter-granular fracture mechanisms. The fracture of torsion specimen is still a mix mode type but with more shear dimples.

Abstract:Thermal stability of SiC_f/Ti-60 composites under thermal exposure at different temperature was studied. Interfacial reaction layer and element diffusion of SiC_f/Ti-60 composites after HIP and thermal exposure were also investigated. The results showed that the mainly product of reaction layer was TiC. The interdiffusion of C or Si in SiC fiber and Ti or other elements in matrix occurred. TiC was formed at the interface and in the matrix due to the high diffusion rate of C. TiC mainly existed on the grain boundaries of matrix. The growth behavior of SiC_f/Ti-60 composites reaction layer was influenced by diffusion and followed an Arrhenius law. The preexponential factor and the activation energy of SiC_f/Ti-60 composites were 2.27×10_-4 m/s_1/2 and 118 kJ/mol respectively.

Abstract:The TiCN coatings were deposited on Ti6Al4V alloy by arc ion plating technique. Inorder to improve the adhesion of TiCN coating, the buffer layer of Ti and TiN was prepared between titanium substrate and TiCN coating. It is studied on effect of buffer layer on dynamic wear resistance of TiCN coating on titanium alloy in artificial seawater. It shows that The all TiCN films have dense structure with a total thickness of about 2μm. The TiN/TiCN coatings have a higher hardness of 30 GPa. The TiN buffer layer has a higher adhesion for the TiCN coating and Lc1 and Lc2 are 60N and 80N respectively. The TiN/TiCN coatings have a excellent wear resistance with a lower friction coefficient and wear rate.

Abstract:Effects of annealing temperature, cooling mode and isothermal annealing process on microstructure and mechanical properties of TC6 titanium alloy bars were studied in this paper. The results show that when specimens were annealed at 800~840 ℃ with air cooling,equiaxed microstructure formed and strength decreased slightly with increasing annealing temperature. Bimodal microstructure formed due to secondary α phase precipitated in β matrix after annealing at 880 ℃ with air cooling, which led to the maximum strength and little decrease in plasticity. With annealing temperature further increasing, microstructure was coarsend obviously, so strength and plasticity decreased. Fine acicular Widmanstatten structure was obtained above the β transus, which led to increase in strength but significantly decrease in plasticity. When specimens were annealed at 800~1000 ℃ with furnace cooling, there are two obvious microstructure evolution differences between air-cooled and furnace-cooled specimens. Firstly, compared with air-cooled specimens, the annealing temperature of forming bimodal microstructure is higher and secondary α phase did not obviously precipitate in β matrix below the β transus. Secondly, lamellar Widmanstatten was obtained above the β transus. The strength of furnace-cooled specimens decreased with temperature increasing, and the change of plasticity was not significant. In addition, the maximum value of impact toughness occurred after annealing at 880 ℃ with furnace cooling. The excellent matching of strength, plasticity and impact toughness was obtained after isothermal annealing (880 ℃, 2 h, FC to 650 ℃, 2 h, AC), which was similiar to furnace-cooled specimen annealed at 880 ℃.

Abstract:The fluidity of in-situ synthesized (TiB+La₂O₃)/Ti composite is investigated by using a vacuum fluidity test. The cast ingots were prepared in consumable vacuum arc-melting furnace. Spiral fluidity test was carried out in vacuum consumable electrode condensing furnace. The microstructures and reinforcements are examined by means of optical microscopy. The big β grain and Laminar α are observed on root of spiral fluidity specimen. The big β grain and Laminar α are smallest on top of spiral fluidity specimen. TiB reinforcements are evenly distributed in the matrix. The addition of reinforcements would enlarge the crystallization and solidification region of the TMCs. The termination mechanism of the melt flow is attributed to the continuous growth of equiaxed grains. Specifically, the decrease in the diameter of pores in between grains would reach a critical value that finally stops the flowing, due to a sufficient friction between the melt and equiaxed grains.

Abstract:Phase transformations and microstructure evolution of high Nb-TiAl alloy after solution treating were investigated using differential scanning calorimetry (DSC), backscattered electron microscopy (BSEM), X-ray diffraction (XRD) and microhardness tester during aging process from 1000 °C to 1300 °C. The results indicated that the microstructure segregation of high Nb-TiAl alloy after solid solution treatment was not completely eliminated and metastable α₂ phase still existed. Two phase transformations, ordered α₂ → disorder α and tetragonal γ → hexagonal α, took place between 1192 °C and 1331 °C during continuous heating. The microstructure of the alloy was lamellar when the sample was aging treated at 1200 °C, while it was clustered at 1300 °C. The microhardness of high Nb-TiAl alloy decreased firstly and then increased with the time increasing when the alloys were aging treated between 1000 °C and 1100 °C; conversely, the hardness increased firstly and then decreased as time went on when the treating temperature ranged from 1200 °C to 1300 °C.

Abstract:The objective of this study is to find a suitable heat treatment for below T_α extruded TiAl alloy with balanced tensile property. The Ti-47Al-2Cr-2Nb-0.15B(at%) alloy rod was fabricated by near isothermal canned hot extrusion at 1300℃ with a 3:1 extrusion ratio. With less refined microstructure including small equiaxed grain belt, remnant lamellar and coarse γ grains in the band shape, the extrusion rod was heat-treated at 900℃, 1150℃ and 1310℃ respectively. The tensile results at room temperature and elevated temperature show that the samples by heat-treatment at 900 ℃ have the superior tensile properties with 3.3% elongation at room temperature. For those samples heat treated at 1150 ℃ with microstructure of near γ and heat treated at 1310℃ with microstructure of near lamellar, their yield strength and ultimate tensile strength are lower than those heat treated at 900℃. The remnant lamellar limits the γ grain growth freely and keeps the extrusion morphology at 900 ℃.

Abstract:Titanium alloy Ti5Al2.5Sn ELI is an important structural material in the field of aerospace and others. Microstructure and mechanical properties of the alloy are studied in the paper by methods of TEM, XRD, and etc. The results indicate that microstructure of Ti5Al2.5Sn ELI alloy is consist of single α phase which is distributed in platelet. After HIP treated, there is no obvious change in the microstructure but the recrystallization on the position of defects closed. The alloy has moderate strength, good plasticity and toughness. The fatigue crack growth rate of the alloy is low, and the accurate value of K_Ic cannot get by testing fracture toughness with specimens of 25 mm in thickness, just the condition value K_q can be gotten. The ability of anti-fracture and crack propagation of ELI grade titanium alloy is higher than non-ELI grade alloy.

Abstract:For the precision preparation of complex shape of pure titanium,powder injection molding technology was used.Several different powders were used to prepare defatted type feeding.Then they were burned into products after powder injection molding.The effect of sintering process parameters on sintering density, carbon and oxygen content, microstructure and mechanical properties was studied.The result shows that P3 sample has a better comprehensive performance .The density of P3 reaches 96.7% after 2h vaccum sintering under 1250 _oC.the content of C and O is respectively 0. 14% and 0. 46%, the tensile strength is 968 MPa, the bending strength is 1141MPa, the tensile strength is 720 MPa and the elongation is 4.5%. It possesses uniform small grain size and presents ductile fracture characteristics.

Abstract:The microstructures and mechanical properties of d300 mm large size Ti₂AlNb alloy bars prepared by forging process which was forged in reducing temperature gradually were investigated. The results show that the near-surface region exhibits more sufficient deformation than the interior region. Accordingly, a more homogeneous microstructure is found at the near-surface region. While at the interior region, more unbroken grain boundaries are found. This phenomenon will be passed down to the corresponding the heat-treated microstructure. By comparing mechanical properties after heat treatment at different positions of the bar, it can be found that the difference of tensile properties at the different locations is not so apparent. Also, the strength at the interior region is less than the surface region, the plastic is opposite. This can be attributed to the difference between the volume fraction and size of the primary α₂ phases.

Abstract:In this paper, in-situ synthesized titanium matrix composites (TMCs) reinforced with TiB whisker plus La₂O₃ particle were successfully fabricated by the laser beam welding (LBW) process with a Nd:YAG laser source. The evolution behavior of TiB was investigated during laser welding. Optical microscope (OM), X-ray diffractometry (XRD) analysis, scanning electron microscopy (SEM) and Transmission electron microscopy (TEM) were used to analyze the phase, distribution and morphology characteristics of TiB whisker reinforcements in the laser weld seam, and the interface between TiB whiskers (or La₂O₃ particles) and titanium matrix was also discussed. Research results show that TiB is still retained in the welding joints, and no harmful substances are found. TiB is significantly refined and redistributed at b grain boundaries, a novel network structure forms in the fusion zone and the heat-affected zone near the fusion zone. Relatively, only some TiB whiskers in the heat-affected zone far away from the fusion zone change their sizes through intensi?ed diffusion of boron, and TiB near the base metal exhibits no changes and similar morphological features with that in the base metal. Further examination by TEM proves that interfaces between the reinforcements and the titanium matrix are very clean, and TiB maintains good bonding relationship with the matrix. There is no interfacial reaction which explains that interfacial microstructures between the reinforcements and the matrix are very stable during welding.

Abstract:The influence of the forging technical(methods) on the microstructure and dynamic properties of TC4 titanium fan blade is investigated in this paper. The results show that with the increase of primary αphase proportion the adiabatic shear susceptibility of TC4 fan blade is decreased and the absorbed impact energy is increased apparently. When the billet forge temperature higher than the moulding forge temperature, produce two different size primary αphase which reducing the uniform plastic defromationability of the material. Therefore, the impact resistance ability is reduced. So, for the sake of better dynamic properties should adopt lower moulding forge temperature at the same time ensure the billet forge temperature higher than the moulding forge temperature for the TC4 titanium fan blade.

Abstract:Titanium alloys have a dwell fatigue failure mode during service in the aircraft engine, which is manifested by a significant reduction in fatigue life when comparing with normal continuous cycling. In contrast to normal fatigue, dwell fatigue has distinct failure characteristics. Through a systematic experimental research, this paper summarized the characteristics of dwell fatigue failure from three aspects, including the fatigue fracture, secondary crack and strain accumulation. The research objects covered from highly susceptible to unsusceptible titanium alloys. According to the summarized failure characteristics, a methodology for identifying the dwell fatigue failure and assessing the dwell sensitivity has been given, which could provide guidance for the experimental research and engineering failure investigation.

Abstract:TB9 alloy has superior strength effect through heat treatment and high corrosion resistance as metastableβtitanium alloy. The effects of solution treatment and solution followed by aging treatment on mechanical properties and microstructure of TB9 alloy were studied in this paper. The results indicate that the strength gradually decreased and the change of ductility was not obvious after solution treatment between 800℃and 900℃. The βgrains size quickly increased with the solution treatment temperature above 820℃. The influence on strength of TB9 alloy was not distinct after solution between 800℃and 900℃ and aging treatment, while the ductility obviously droped with the solution treatment temperature increasing,the elongation droped from 15% to 10% and the reduction of area droped from 37.5% to below 20%.The α phase adequately precipitated and the mechanical properties was steady after solution and aging treatment (820℃/30min、WQ+520℃/8h、AC)

Abstract:Two kinds of titanium foams with different pore structures were prepared by slurry method. The pore structure and morphology of titanium foam were observed by digital camera and scanning electron microscope. The mechanical properties and energy absorption properties of titanium foam were investigated by the static compression tests. The results show that the titanium foam prepared by slurry method inherits the structure of precursor, and has 3D net structure. The edge of titanium foam is not compact, on which there are many fine pores. Titanium foam is not sensitive to the strain rates, and the yield strength is in the range of 1.00MPa-2.38MPa at strain rate of 3×10_-4s_-1-1×10_-2s_-1.Titanium foam has the properties of absorbing energy, and the titanium foam of fine pore and coarse pore reaches can absorb the max energy of 0.78MJ/m₃ and 0.22MJ/m₃ respectively.

Abstract:SPF process for titanium semi-annular part had been researched in this article. A direct-reverse SPF process was intended for controlling the thickness of the semi-annular part after forming,and the SPF forming die which is the key for the thickness control had been designed and optimized by numerical simulation method.Verification experiment was preceeded for a TC4 semi-annular part,the results show that the actual thickness distribution of the part can be well predicted by the numerical simulation,the thickness of the part was homogenized by using optimized SPF forming die.This process can not only improve material utilization ratio and efficiency of subsequent processing,but also reduce total manufactuting costs.

Abstract:In this study, porous Ti-6Al-4V alloy was prepared by diffusion bonding method using Ti6Al4V mesh. The microstructure, tensile and fatigue properties were studied after various heat treatment methods, i.e., 780℃/2h, FC; 950℃/2h, FC; 950℃/2h, FC + 540/4h, FC. The results showed that the elastic modulus and tensile strength of porous Ti-6Al-4V alloy, can be adjusted in the range of 9.5 ~ 12.2GPa and 360 ~ 505MPa, respectively. The fatigue strength can reach 40 ~ 80MPa at R = -1, f = 10Hz and N = 5′10₆ under cyclic loading conditions. In addition, it was found that the heat treatments have a greater effect on tensile strength than for elastic modulus.

Abstract:The paper mainly studied the strength variation and microstructure of the biomedical Ti-15Mo titanium alloy after the solution and aging treatments. And the hardness variation of the alloy in different aging conditions also was studied. Through analysis of the relationship of the alloy strengthening effect and microstructure, the alloy strengthening effect would be discussed due to the different transformation and microstructure, and reveals the Ti-15Mo titanium alloy strengthening process and its formation mechanism. The study on the mechanism of the alloy systematically, will be use for provide good theoretical basis for material evaluation and the application.

Abstract:Sharp texture in large sizing integration of titanium alloy forgings, which were more easily formed by heterogeneity of stress field and temperature field during forging, is harmful for safety and reliability of products application. By use of EBSD techniques this paper observed the microstructure and texture of TC18 titanium bars at center layer and surface layer, and analyzed the evolution regularity of microstructure and texture after forging and annealing process under different temperature. Results show that after α+β region annealing, most β grains were recovered, some α grains recrystallized, and the grains size and texture of β phases were scarcely changed. When annealed near phase transformation temperature, large sized recovery β grains grew by grains size advantage; some α grains, particularly the lamellar α grains in β grain boundaries, grew by the combination of near oriented α grains; some special oriented α grains trended to transform, the transformed α grains would not create new β phase nuclei. After β region annealing, β phase texture were weakened obviously because β grains recrystallized and grew up without orientation preference.

Abstract:Spraying WC10Co4Cr coatings by HVOF on typical aerial material TC18 Alloy is one of most important method to improve its wear. In this paper, oxygen flow rate, kerosene, spray distance and powder feed rate were as main parameters and L9_3_4 orthogonal experiments were set up. Comparing with influences of parameters on porosity and W₂C content each other, optimized parameters were found. The optimized parameter is as follows: O₂, 873NLPM, Kerosene, 22LPH, Spray distance, 380mm, powder feed rate, 60g/min. The optimized WC10Co4Cr coatings’ performance is as follows: its porosity is less than 1%, its micro-hardness is HV_0.31204.8, its bonding strength is 74.5MPa, no spalling after bending test. All of these have met with AMS 2447 standard. Under the test conditions, the wear of WC10Co4Cr coatings is 3.371×10_-7mm₃/ N.m and that of TC18 is 3.371×10_-7 2.095×10_-3mm₃/Nm. The wear resistance of TC18 was improved greatly.

Abstract:Microstructural evolution and mechanical properties of the election beam weldments of different thickness Ti60 titanium alloy plates were investigated in this study. Metallographic examination of as-welded Ti60 electron beam welds showed that there exhibited three zones in the EBW weldments, the fusion zone (FZ), heat affected zone (HAZ), and base metal (BM). The fusion zone was consisted of columnar grains. Effect of plate thickness on the microstructure of columnar grains is small. So the microstructure of columnar grains of different thickness plate was similar and was consisted of fine α plates and a small amount of β phase. The micro-hardness and the strength of the fusion zone was higher than the base metal. For the fusion zone, a large number of silicide precipitated in the boundary of α phase after the post weld heat treatment (PWHT) at 700℃.

Abstract:Ti6321 alloy wire with a diameter of Ф2.9mm was produced by hole die drawing process, and the evolution of microstructure and mechanical properties in the forming process of Ti6321 alloy wire was studied in the paper. The results show that the average grain size of primary α phase decreases from 10.5μm to about 2.1μm, and the tensile strength increased from 1035MPa to 1250MPa. The tensile fracture surface with a typical ductile fracture of the wire was observed by scanning electron microscope,. And the texture in the wire was analyzed by EBSD, and found that there are (0001) ⊥ axial texture and {0001} <10-10> texture. It can be concluded that grain refinement and texture are the main cause for wire reinforcement.

Abstract:In this article, the effect of two typical microstructures (equiaxed and basket-waved microstructure) on the fracture morphylogy of high cycle fatigue is investigated. The results show that the macro-fracture surface of the samples with both microstructures is charactered by brittle fracture and the fatigue crack initiates at the sample surface. The difference of the fractograph between the two microstructures is significant. On macro level, fractograph of equiaxed microstructure is quite smooth, and the fatigue crack area has a very large fraction of the whole facture surface. While fractograph of basket-waved microstructure is rough, and the fraction of fatigue crack area is relatively small. On micro level, the fatigue striation in equiaxed microstructure has a similar size with the primary α grain. While in basket-waved microstructure, basket-waved structure can be clearly seen in the fatigue fracture surface. Secondary cracks are more pervasive than in equiaxed microstructure. The fatigue striation also has a different morphylogy with than in equiaxed microstructure.

Abstract:In this paper, the effect of Fe content on microstructure evolution and mechanical properties of as-cast Ti-xFe-B(x = 1 ~ 5 wt%) alloy was investigated by means of optical microscopy (OM), scanning electron microscopy (SEM), X-ray diffraction (XRD), vickers hardness tester and electronic tensile testing machine. The results show that when the Fe content is below 3 wt%, the structure of as-cast Ti-xFe-B alloy is mainly α lamellar. With the increase of Fe content, the β phase increases significantly, Meanwhile, with increasing Fe content from 1 wt% to 5 wt%, the precipitation of Fe content in compound increase, grain size of α-phase decreased by 56.5%; It is found that mechanical properties of as-cast alloy are significantly improved by the addition of Fe into TiB alloy. With the increase of Fe content, Vickers hardness of as-cast alloy increased by 45.7%, and the tensile strength increased from 502 MPa to 834 MPa. However, the ductility of Ti-xFe-B alloy decreased significantly, reduction rate decreased from 30.4% to 9.5%, elongation at break long rate fell 19.4% to 7.9%. The results show that when the Fe content is in the range of 3 ~ 4 wt%, the alloy can achieve the best match strength and plasticity and greater potential for development.

Abstract:In this paper, a near-α titanium alloys reinforced with different volume fraction of TiCwere prepared by vacuum induction melting technology. The addition of TiC_p was 1, 2.5, 5, 7.5, 10, 15 vol.% respectively. The effect of TiC content on microstructure and mechanical properties of near-α titanium alloys was systematically investigated by XRD, OM, SEM and Instron universal testing machine. The XRD result confirms that in-situ casting process is feasible to fabricate the composite. As TiC content increases, the morphologies of TiC are transformed from long strip-like to equiaxed shape and then to dendritic characteristic, which is closely related to the solidification paths. The addition of TiCpromotes the ultimate compression strength (UCS) and yield strength(YS) of the alloy. However, as the TiC content reaches to a certain degree, the strength decreases in different degree. The increased UCS and YS is accompanied by the rapid decreasing in fracture strain.

Abstract:The refractory oxide coating includes Y₂O₃, Al₂O₃, and CaZrO₃ were coated on the inner surface of graphite mold, to study the effect of coating composition on the interface reaction of pure titanium and its microstructure and properties. The results show that the coating can effectively overcome the chilling effect of graphite casting mould. No chemical reactions occur between Y₂O₃ and molten titanium liquid, and Y₂O₃ coating only physically adhere to the surface, so the stability of Y₂O₃ coating and titanium liquid is best. Al₂O₃ and CaZrO₃ coating have interface reaction with molten titanium liquid, and Ti-Al-O and Ca-Ti-O phase form during the interface reaction, respectively. The interface reaction between Al₂O₃ coating and molten titanium liquid is most severe. After the coating, the gain size of the surface layer, the thickness of coarse grain layer and the microhardness all increase. And these changes degree with the coating type from the small to large is Al₂O₃, CaZrO₃, Al₂O_3, respectively.

Abstract:Graded Ti-6Al-4V reticulated meshes with different porosities in Materialise software were fabricated by additive manufacturing using the electron beam melting (AM-EBM) and the effects of annealing temperature on the microstructure and mechanical properties of these samples were studied. The results show that the strut microstructure is dominated by thinα’martensiteplatelets and minimal β phase. The effective modulus and strength are theweighted average of the moduli and strengthof each constituent. There is stressdiscontinuity along the interface between thetwo different layers,which causesthe reduction of strength. Annealed in the temperature of 950_oC for 1 h, α platelets are thickerand the plastic of struts is improved, at the same time, the effective elastic modulus and compressive strength are slightly reduced. After annealing treatment, the graded Ti-6Al-4V meshes achieve the optimal mechanical performance.

Abstract:The study focused on the evolution of equiaxed microstructural and its effect on the tensile properties in Ti-22Al-25Nb alloy. During the solution in O+B2 phase region, the primary lath O phase in microstructures obtained in isothermal forging in α₂+O+B2 phase region coarsened and became shorter and fine lath O dissolved into B2 matrix phase, while equiaxedα₂/O phase did not change significantly. A part of equiaxed O phase dissolved and rim O phase became thinner with higher solution temperature. During the aging in O+B2 phase region, aboundant of secondary fine lath O phase precipitate from B2 phase, and a little of α₂phase surronded with rim O transformed to O phase. Higher aging temperature resulted in coaser but less secondary lath O phase and thicker rim O phase, as well as lower tensile strength and higher ductility.

Abstract:Hot deformation behavior of two kinds of TC4-xFe alloys has been investigated by using a Gleeble 3800 thermal simulator at strain rates range of 1~10 s_-1 and deformation temperature range of 800~950℃ with height reduction of 60%. Based on the analysis of the stress-strain curve behaviors, two constitutive equations have been obtained, which represented as a function of deformation temperature, strain rate and flow stress.The calculated apparent activation energies are 550.77kJ/mol for TC4-0.18Fe alloy and 420.57kJ/mol for TC4-0.55Fe alloy, respectively.In order to evaluate of the flow instability areas and optimize relevant processing parameters, two processing maps were constructed at the true strain of 0.92 based on dynamic material model. The results show that the optimal processing condition with peaks in power dissipation of 0.52 and 0.47 is at the temperature of 950℃ and the strain rate of 5~10 s_-1.

Abstract:Considering the characteristics of the actual spinning of Ti₂AlNb alloy, a three-dimensional elastic-plastic FE (finite element) model of power spinning of thin-walled Ti₂AlNb alloy shell was established based on the dynamic, explicit module of FE software. Stress concentration and the inhomogeneous deformation during simulation was dealt with reasonably. The process parameters were optimized and the distribution of strss and strain of workpiece with different passes were studied based on this model. Results showed that stressconcentration is found with increase of passes, meanwhile strain increases. This will lead to the deformation of workpiece is inhomogeneous. To solve this problem, stress-relief annealing between pass and pass was adopted. The reliability of model was validated by comparing the results of simulation and actual production.

Abstract:Instability mechanism of lamellar structures of Ti-48Al alloy solidified under high pressure was investigated. The results indicate that after 1100 ℃/12 h air cool, α₂ phase particles can hardly be seen in normal pressure solidified Ti-48Al alloy. Howerver, α₂ phase has been found in high pressure solidified Ti-48Al alloy. Incresaing the temperature to 1280 ℃, the high pressure solidified Ti-48Al alloy is easier to decomposite than normal pressure. This research has provided the basis of further studying on the microstructures and phase transformation of high pressure solidified Ti-Al intermetallics and enriched the theory of high pressure solidification.

Abstract:The residual stress was measured by X-ray diffraction method (XRD) for large-size and middle-thick TA15 Ti alloy plate. By scanning the (213) plane of TA15 titanium alloy by X-ray diffraction, we observed the changes in peak shape, and usedthesin₂ymethod to calculate the residual stress. Residual stresses at some different locations on the plate surface have the larger deviation under the normal diffraction conditions,so that the test results are not reliable. On thebasis of the range 30 °～85 ° diffraction scans on samples,it is regarded that big deviation of stress is resulted from the coarse grain. So we propose that increasing theX-ray irradiating area is an appropriate way to decrease the deviation of the residual stress.After improvement, the results show that the surface of TA15 titanium alloy plate exists compressive stress after hot rolling. The surface residual stress range is from -250 MPa to -450Mpa,and measuring deviations were within ± 50MPa, which is highly reliable. The further analysis of the formation mechanism is conducted on TA15 plate residual stress.A theoretical basis and experimental data are supplied to eliminate the residual stress.

Abstract:Comparison Study on DC PAW、high-frequency pulse PAW(HF-PAW) and one keyhole per pulse PAW procedure on TC4,the weld joint appearance of the high-frequency pulse PAW and one keyhole per pulse PAW are better than DC PAW,and the mechanical properties and processing properties of the three procedure measure up to the standard. As the High-frequency pulse,the high-frequency pulse PAW reinforce the arc force,bring down the probability of undercut,and raise the travel speed. The weld joint appearance of one keyhole per pulse PAW is smooth and uniform,the front of the weld joint is not subside at all,the mechanical properties test and the SEM test show that one keyhole per pulse PAW procedure is superior than traditional DC PAW,and this procedure is more suitable for TC4 PAW.

Abstract:This paper investigates the oxidation behavior and microstructure evolution of Ti-6Al-4V alloy at 900_oC, 930_oC and 960_oC. The thickness of surface oxide layer increases during 0.5-24h and the closer to the surface, the more porous of the oxide. There is a sharp decrease of O level at the boundary of oxide layer and a-case. The O level decreases gradually inside the a-case to a stable level in the Ti-6Al-4V base material. The oxide layer is maily composed of TiO₂, and there is also small amount of Al₂O₃. The volume fraction of a in much higher in the a-case and the grain size is also larger. The relationship between a-case depth and thermal exposure time can be fitted using log-log function. Linear regression analysis shows that the activation energy of O diffision in a case is 206 kJ/mol.

Abstract:Consecutive thermal cycling at 920_oC, 800_oC, 850_oC, 900_oC was performed onthe Ti-6Al-4V alloy for investigatingmicrostructure,texture evolution, tensile and rotating bending fatigue properties. After four cycles, the elongated grains in the as-received alloy disappeared due to recrystallization andthe microstructure was homogenized. Equiaxedgrains grew a little larger, from ~12mm to ~16mm, while the volumnfractionremained stable. The as-received Ti-6Al-4V alloy exhibited a transverse texture, and formed microzones parallel to the rolling direction.The rotating bending fatigue limit in the rolling direction was higher than that of the transverse direction, which was 497MPa/474MPa, respectively. The intensity of the transverse texture was weakenedafter each thermal cycle and (0001) basal texture appeared. Both the ultimateStensileSstrength and yield strength decreased for about 20MPa after four thermal cycles due to a grain coarsening. The fatigue limit of transverse/longitudinal directions decreased to441MPa/441MPa, respectively.

Abstract:In this work, a Ti₂AlNb based intermetallic alloy with the composition of Ti-22Al-24Nb-0.5Mo (at. %) pre-alloyed powder was produced by gas atomization, then fully dense powder metallurgy (PM) Ti₂AlNb alloy was fabricated by a hot isostatic pressing (HIPing) route. Powder size distribution obviously affected the porosity distribution of PM Ti₂AlNb alloys. The weld porosity and inclusion were not found in the as-HIPed Ti₂AlNb rings to be electron beam welded according to the X-ray radiographic inspection. The microstructure of as-HIPed Ti₂AlNb compacts was characterized by optical microscopy (OM), scanning electron microscopy (SEM), X-ray diffraction(XRD) and so on.From the fusion zone to the parent material, the microstructure changed from the single phase (B2) to duplex (α₂ B2 O phase). The microhardness of fusion zone and heat affected zone were higher thanparent material.

Abstract:Titanium alloysfind wide applications in aerospace industry for its high specific strength and good corrosion resistance. However, limited creep resistance may restrict their applications at high temperature. Experiments have demonstrated that the steady creep activation energy is close to the effective diffusion activation energy, indicating that the atomic diffusiontakesan important effect on the creep resistance. In the present work, a first-principles method is employed to study the migration energy of various alloying atoms ina-titanium. We show that, for the atoms migrating through vacancy mechanism, the in-basal-plane migration energy decreases in the order of Al, V, Ti,Sn, Ta, Mo,Nb,Zr, whereas the out-plane migration energy decreases in the order of Al, Sn, V, Ti, Ta, Mo,Nb,Zr. For the atoms (Fe, Co, Ni) migrating through interstitial mechanism, the migration energies are quite low.