Ti-12Mo-6Zr-2Fe钛合金的纳米压入特征

利用纳米压入测量仪测试了Ti-12Mo-6Zr-2Fe钛合金的硬度和模量.测试表明,Ti-12Mo-6Zr-2Fe钛合金的硬度比Ti-6Al-4V ELI高,而模量比后者低,与常规方法得到的规律一致,表明该方法能很好地表征钛合金的力学特性.对测试过程的分析表明这种方法得到的结果不能与传统方法得到的结果互换,表面状态对测量结果有一定影响.     

抗Zr“中毒”Al-Ti-B-C中间合金对7050铝合金力学性能的影响

通过场发射扫描电子显微镜(FESEM),X射线衍射仪(XRD),能量色谱仪(EDS)分析Al-5Ti-1B,Al-4Ti-1C和Al-5Ti-0.8B-0.2C中间合金的微观组织与物相组成,比较研究3种中间合金对7050铝合金晶粒尺寸与力学性能的影响。结果表明:Zr的存在削弱了Al-5Ti-1B和Al-4Ti-1C中间合金的细化效果,而对Al-5Ti-0.8B-0.2C中间合金细化效果影响较小。含掺杂型TiC粒子的Al-5Ti-0.8B-0.2C中间合金具有较好的抗Zr"中毒"能力,加入量为0.2%(质量分数,下同)时,含Zr7050铝合金平均晶粒尺寸由200μm细化至(60±5)μm,室温极限抗拉强度由405MPa提高到515MPa,提高了27.2%,伸长率由2.1%提高到4.1%。而加入0.2%的Al-5Ti-1B或Al-4Ti-1C中间合金时晶粒尺寸较粗大且分布不均匀,表现出明显的细化"中毒"。     

Development of a β-type Ti–12Mo–5Ta alloy for biomedical applications: cytocompatibility and metallurgical aspects

Ti-based biocompatible alloys are especially used for replacing failed hard tissue. Some of the most actively investigated materials for medical implants are the beta-Ti alloys, as they have a low elastic modulus (to inhibit bone resorption). They are alloyed with elements such as Nb, Ta, Zr, Mo, and Fe. We have prepared a new beta-Ti alloy that combines Ti with the non-toxic elements Ta and Mo using a vacuum arc-melting furnace and then annealed at 950 degrees C for one hour. The alloy was finally quenched in water at room temperature. The Ti-12Mo-5Ta alloy was characterised by X-ray diffraction, optical microscopy, SEM and EDS and found to have a body-centred-cubic structure (beta-type). It had a lower Young's modulus (about 74 GPa) than the classical alpha/beta Ti-6Al-4V alloy (120 GPa), while its Vickers hardness remained very high (about 303 HV). This makes it a good compromise for a use as a bone substitute. The cytocompatibility of samples of Ti-12Mo-5Ta and Ti-6Al-4V titanium alloys with various surface roughnesses was assessed in vitro using organotypic cultures of bone tissue and quantitative analyses of cell migration, proliferation and adhesion. Mechanically polished surfaces were prepared to produce unorientated residual polished grooves and cells grew to a particularly high density on the smoother Ti-12Mo-5Ta surface tested.     

Relationships of strength to composition and phase constitution for three aged beta titanium alloys

X-ray diffraction techniques were used to study properties of three beta titanium alloys in the alpha aged condition. The alloys studied were Beta 111 (Ti-11.5 Mo-6 Zr-4.5 Sn), Beta C (Ti-3 Al-8 V-6 Cr-4 Mo-4 Zr), and 8-8-2-3 (Ti-8 V-8 Mo-2 Fe-3 Al). The volume percentage of alpha phase present and the lattice parameters of both the alpha and beta structures were determined for different ageing treatments. Ultimate tensile strength is related to both alpha content and beta unit cell size in these alloys. However, at high strength levels, beta unit cell size is a more sensitive indicator of tensile strength than percentage of alpha phase. The effects of precipitation hardening mechanisms and alloy partitioning on strengthening are discussed.     

Microtwin formation in the α phase of duplex titanium alloys affected by strain rate

The effect of tensile strain rate on deformation microstructure was investigated in Ti-6-4 (Ti-6Al-4V) and SP700 (Ti-4.5Al-3V-2Mo-2Fe) of the duplex titanium alloys. Below a strain rate of 10⁻² s⁻¹, Ti-6-4 alloy had a higher ultimate tensile strength than SP700 alloy. However, the yield strength of SP700 was consistently greater than Ti-6-4 at different strain rates. The ductility of SP700 alloy associated with twin formation (especially at the slow strain rate of 10⁻⁴ s⁻¹), always exceeded that of Ti-6-4 alloy at different strain rates. It is caused by a large quantity of deformation twins took place in the α phase of SP700 due to the lower stacking fault energy by the β stabilizer of molybdenum alloying. In addition, the local deformation more was imposed on the α grains from the surrounding β-rich grains by redistributing strain as the strain rate decreased in SP700 duplex alloy.     

Effects of the variation in α-phase volume fraction on the thermal stability of TiAl alloys with a lamellar microstructure

The thermal stability of two-phase ( + ) lamellar microstructure in Ti-Al-Mo PST (polysynthetically twinned that has single colony) crystals, containing C or Si, was investigated. In addition, the variation of -phase volume fraction in Ti-Al-Mo-(C,Si) systems was investigated at several temperatures. Ti-46Al-1.5Mo-0.2C and Ti-46Al-1.5Mo-1.0Si alloys did not recrystallized (stable in this paper) during heat treatments at various heating rates and temperatures. Moreover, the -phase volume fractions of Ti-46Al-1.5Mo-0.2C and Ti-46Al-1.5Mo-1.0Si alloys which were stable compositions, changed less than those of Ti-47Al and Ti-46Al-1.5Mo alloys which were unstable compositions. The instability of the latter alloys was caused by their relatively higher variation of -phase volume fraction during heating. Therefore, it is suggested that the variation of -phase volume fraction is an important factor in controlling the thermal stability of lamellar microstructure.     

Structural aspects of corrosion resistance in alloys based on the Fe3Al intermetallic phase in the cast state

This paper presents the results of investigation of four cast alloys based on the Fe₃Al intermetallic phase. Microstructure tests using light microscopy, electron scanning microscopy and X-ray diffraction methods, have been performed. On this basis, a presence of particles rich in zirconium and molybdenum, and in case of the alloy with 28 at.% aluminium and 5 at.% chromium ?? the presence of sigma phase (FeCr), has been found. Also, the results of the study of the microstructure influence on the electrochemical corrosion resistance in the 5 % NaCl solution have been presented. The Fe-26Al-2Cr-1Mo-0.1Zr-0.005B at.% and Fe-26Al-5Cr-1Mo-0.1Zr-0.005B at.% alloys exhibited increased corrosion resistance in comparison to the Fe-23Al-1Mo-0.1Zr-0.005B at.% alloy without chromium addition. The appearance of the sigma phase in the alloy of Fe-28Al-5Cr-1Mo-0.1Zr-0.005B at.% chemical composition resulted in lowering the corrosion resistance of this alloy and a change in corrosion character from the pitting to the intercrystalline one.     

Nucleation and growth of Fe-rich phases in Al-5Ti-1B modified Al-Fe alloys investigated using synchrotron X-ray imaging and electron microscopy

Plate-like Fe-rich intermetallic phases directly influence the mechanical properties of recycled Al alloys;thus,many attempts have been made to modify the morphology of these phases.Through synchrotron X-ray imaging and electron microscopy,the underlying nucleation and growth mechanisms of Fe-rich phases during the solidification of Al-5Ti-1B-modified Al-2Fe alloys were revealed in this study.The results showed that the Al-5Ti-1 B grain refiner as well as the applied pressure both resulted in reduction of the size and number of primary Al3Fe phases and promoted the formation of eutectic Al6Fe phases.The tomography results demonstrated that Al-5Ti-1B changed the three-dimensional (3D) morphology of primary Fe-rich phases from rod-like to branched plate-like,while a reduction in their thickness and size was also observed.This was attributed to the fact that Ti-containing solutes in the melts inhibit the diffusion of Fe atoms and the Al3Fe twins produce re-entrant corner on the twin boundaries along the growth direction.Moreover,the TiB2 provides possible nucleation sites for Al6Fe phases.The nucleation mechanism of Fe-rich phases is discussed in terms of experimental observations and crystallography calculations.The decrease in the lattice mismatch between TiB2 and Al6Fe phases was suggested,which promoted the transformation of Al3Fe to Al6Fe phases.     

Superplasticity and Diffusion Bonding of Ti_3AI Intermetallic Compounds

The superplasticity of Ti_3Al intermetallic compounds has been investigated in this paper.TheTi-14Al-21Nb ternary alloy showed 477% elongation at the strain rate of 1.49×10~(-5) s~(-1) and950℃.The elongation of Ti-14Al-21 Nb-3Mo-1V quinary alloy approached to 573% at the strainrate of 4.52×10~(-5) s~(-1) and the same temperature,and it was found that the elongation value in-creased to 1096.4%as temperature was raised up to 980℃ at the same strain rate.Ti_3Al base al-loys were bonded by diffusion bonding technology and good joints were created,the simulatedspecimens were performed by SPF/DB process.     

An investigation of the fatigue and fracture behavior of multicomponent Nb-11Al-41Ti-1.5Mo-1.5Crintermetallic

This paper presents the results of a recent study of the fracture and fatigue crack growth behavior of a newly developed multicomponent niobium aluminide intermetallic Nb-11Al-41Ti-1.5Mo-1.5Cr alloy (compositions quoted in at % unless stated otherwise). The alloy is shown to have attractive combinations of room-temperature tensile ductility (approx. 11%) and fracture toughness (approx. scds 83 MPa ) in the as-forged condition. However, the tensile properties and fracture toughness are degraded somewhat by direct aging at 750 °C for 25 h. The direct aged Nb-11Al-41Ti-1.5Mo-1.5Cr intermetallic is also shown to have comparable fatigue crack growth resistance to pure Nb, IN 718 and mill annealed Ti-6Al-4V at room- and elevated-temperature. Fatigue and fracture mechanisms are elucidated prior to a discussion of the implications of the current results for potential high temperature structural applications.     

Toughening effects of Mo and Nb addition on impact toughness and crack resistance of titanium alloys

Ti-6Al,Ti-6Al-2Mo and Ti-6Al-3Nb alloys were prepared to investigate the toughening effects of β sta-bilizers Mo and Nb on impact toughness and crack resistance of titanium alloys.Instrumented Charpy impact tests showed that the total impact absorbed energy of Ti-6Al-2Mo and Ti-6Al-3Nb (～64J) were two times higher than that ofTi-6Al (～30J),indicating the higher impact toughness of Ti-6Al-2Mo and Ti-6Al-3Nb alloys.Analysis of load-displacement curves revealed the similar crack initiation energy of Ti-6Al,Ti-6Al-2Mo and Ti-6Al-3Nb (15.4J,16.1J and 15.0J,respectively).However,the higher crack propagation energy of Ti-6Al-2Mo and Ti-6Al-3Nb (46.7J and 48.3J,respectively) were about three times higher than that of Ti-6Al (14.4J),indicating the stronger resistance to crack propagation in Ti-6Al-2Mo and Ti-6Al-3Nb.Post-mortem analysis of impact samples demonstrated that the increased dislocation density and deformation twinning were mainly responsible for the stronger resistance to crack propagation in Ti-6Al-2Mo and Ti-6Al-3Nb.Due to the invisibility of dislocation activation and deformation twinning during the Charpy impact process,a mathematical model has been proposed to evaluate the effects of Al,Mo and Nb elements on dislocation mobility based on the Yu Rui-huang electron theory.Addition of Mo and Nb elements significantly improved the dislocation mobility in Ti-6Al-2Mo and Ti-6Al-3Nb compared to that in Ti-6Al alloy.Therefore,more dislocations were activated in Ti-6Al-2Mo and Ti-6Al-3Nb which supplied the larger plastic deformation under impact loading.A dislocation-based model also has been proposed to interpret the nucleation and propagation of deformation twinning under the impact loading.Dislocation pileup at α/β interfaces provided potential sites for nucleation of deformation twinning in Ti-6Al-2Mo and Ti-6Al-3Nb.Furthermore,deformation twinning facilitated the dislocation motion in α grains with hard orientations.The increased dislocation mobility and deformation twinning were responsible for the stronger crack resistance as well as the higher impact toughness of Ti-6Al-2Mo and Ti-6Al-3Nb alloys.     

钎缝间隙对TC4与Ti_3Al-Nb合金钎焊接头组织的影响

采用50Ti-20Zr-20Ni-10Cu粉末钎料对Ti3Al-Nb(Ti-13Al-24Nb)(质量分数)合金与TC4合金(Ti-6Al-4V)进行真空钎焊,通过SEM、EDS电子探针及拉伸试验,研究不同钎缝间隙的钎焊接头的显微组织及性能特征。结果表明,钎缝间隙对钎焊接头的组织及性能有较大影响,当钎缝间隙增大时,钎焊接头的组织变得复杂,在接头中既形成了共晶组织又形成了化合物带,这种组织特征会显著降低接头的强度。     

Microstructural Evolution of Ti-5.6Al-4.8Sn-2Zr-1Mo-0.35Si-0.7Nd Titanium Alloy with Carbon Additions

The effect of carbon addition on microstructural evolution was studied in a near-α titanium alloy(Ti-5.6Al-4.8Sn-2Zr-1Mo-0.35Si-0.7Nd). It was found that flake and ribbon titanium carbides with a NaCl crystal structure formed in the as-cast alloys with carbon additions of over 0.17 wt pct. Flake carbide particles are the product of eutectic transformation and precipitate from the high-temperature β phase. The ribbon carbide particles are primary phases formed prior to the nucleation of any metallic phases. The as-cast alloys with carbide precipitation after heat-treatment atβt-30℃ followed by water quenching showed the spheroidization of α lamellae and partial dissolution of carbide particles. After annealing at βt 15℃, carbide particles are mostly distributed at the grain boundary and spheroidized through mixed grain boundary plus bulk diffusions.     

A New Approach for Manufacturing a High Porosity Ti-6Al-4V Scaffolds for Biomedical Applications

Titanium and its alloys are currently considered as one of the most important metallic materials used in the biomedical applications, due to their excellent mechanical properties and superior biocompatibility. In the present study, a new effective method for fabricating high porosity titanium alloy scaffolds was developed. Porous Ti-6Al-4V scaffolds are successfully fabricated with porosities ranging from 30% to 70% using spaceholder and powder sintering technique. Based on its acceptable properties, spherical carbamide particles with different diameters （0.56, 0.8, and 1mm） were used as the space-holder material in the present investigation. The Ti-6Al-4V scaffolds porosity is characterized by using scanning electron microscopy. The results show that the scaffolds spherical-shaped pores are depending on the shape, size and distribution of the space-holder particles. This investigation shows that the present new manufacturing technique is promising to fabricate a controlled high porosity and high purity Ti-6Al-4V scaffolds for hard tissue replacement.     

Microstructure and Mechanical Properties of Mg-Al-Ca-Nd Alloys Fabricated by Gravity Casting

The aims of this study are to investigate the effects of Nd addition in the Mg-Al-Ca alloys on microstructure and mechanical properties.Microstructure of as-cast Mg-5Al-3Ca alloy containing Nd consists ofα-Mg matrix, eutectic phase and Al-Nd rich intermetallic compound.As Nd addition was increased,α-Mg matrix morphology was changed from dendritic to equiaxed grains and average value of grain size was decreased.Nd addition to Mg-5Al-3Ca based alloys resulted in the formation of Al-Nd rich intermetallic compounds at grain boundary andα-Mg matrix grains.And these Al-Nd rich intermetallic compounds were dispersed homogeneously.In these alloys,two kinds of eutectic phases were observed,i.e.coarse irregular-shape structure at grain boundary and fine needle-shape structure in theα-Mg matrix grain.It is found that the ultimate strength showed the maximum value of 271 MPa at Mg-5Al-3Ca-2Nd alloy and elongation was decreased as the addition of Nd was increased.     

Effect of hydrogen charging on microstructural evolution and corrosion behavior of Ti-4Al-2V-1Mo-1Fe alloy

The effect of hydro gen charging on microstructural evolution and corrosion behavior of a Ti-4Al-2V-1Mo-1Fe alloy in a 3.5 wt.% NaCl solution was investigated.The results showed that the hydrogen charging induced the formation and growth of γ-TiH and δ-TiH₂ phases,leading to the initiation and propagation of hydrogen-induced cracks.It was also found that hydrogen charging can change the passivity of this alloy and increase its pitting corrosion susceptibility.The main reason for these was attributed to the fo rmation of hydrides in α phase in the Ti-4Al-2V-1Mo-1Fe alloy,leading to the preferential dissolution of the α phase and thus the deterioration in the protective ability of passive film.     

Dissociation of super-dislocations and the SISF energy in γ-TiAl based alloy with Nb-doping, as studied by HRTEM

The dissociation of super-dislocations in γ-TiAl in Nb-doped Ti-48 at.% Al-5 at.% Nb has been studied by high resolution transmission electron microscopy (HRTEM). The SISF energy in γ-TiAl in Ti-48 at.% Al-5 at.% Nb was calculated to be 35 mJ/m² according to the dissociation width. It is concluded that Nb addition may affect the electronic structure of TiAl and furthermore decrease SF energies in TiAl alloys, which is partly responsible for the strengthening effect of Nb-doping.     

The effect of interfaces on mechanical and superplastic properties of titanium alloys

The effect of volume fraction of the β-phase on the mechanical and superplastic properties of ultrafine-grained titanium alloys with grain size d of ~0.2 µm was investigated by transmission and scanning electron microscopy, X-ray diffraction analysis, and tensile test experiments. The ultrafine-grained structure of the materials was formed by the multi-directional pressing technique. The structure in question is shown to improve the mechanical properties by 30–50 % and to lower down to 823 K, the temperature at which superplastic flow starts as compared to coarse-grained analogs, no matter what the phase composition and concentration of the alloying elements used. The reduced temperature is attributable to the activation of diffusion-controlled grain boundary sliding in the case of nonequilibrium interfaces of materials produced by severe plastic deformation. The fraction of the β-phase and its precipitation pattern are found to have significant influence on the temperature range in which superplastic flow occurs and on the maximum elongation to failure. A near-β Ti-5Al-5Mo-5V-1Cr-1Fe alloy with a large fraction of the β-phase (>34 %) under superplastic conditions exhibits record-breaking strains (>1300 %) that do not cause fracture of the material and extremely low flow stresses. This is associated with the activation of the grain boundary sliding due to an increase in the diffusivity along the phase boundaries in a case of microduplex structure.     

基于气体捕捉法的泡沫Ti-6Al-4V等温发泡规律研究

为了确定气体捕捉法制备泡沫Ti-6Al-4V等温发泡过程中孔隙率和微观孔洞的变化规律,在不同发泡温度及发泡时间下制备了泡沫Ti-6Al-4V.运用阿基米德原理对泡沫Ti-6Al-4V的孔隙率进行测量,通过OM和SEM对其微观特征进行观察.研究表明:泡沫Ti-6Al-4V的孔隙率及孔径均随等温发泡温度升高而增加;但当发泡温度大于950℃时,孔隙率和孔径均减小,且孔洞形态由球形变成多边形,这是由于基体内生成大尺寸β相造成的.增加发泡时间能以促进孔洞长大的方式提高泡沫Ti-6Al-4V的孔隙率,球形孔洞数量随着发泡时间的增加逐渐增多.经950℃/10 h发泡得到了孔隙率34.2%、孔径平均值156μm、孔洞为球形且分布弥散的泡沫Ti-6Al-4V.     

In-situ microstructural investigations of the TRIP-to-TWIP evolution in Ti-Mo-Zr alloys as a function of Zr concentration

Aiming at overcoming the strength-ductility trade-off in structural Ti-alloys,a new family of TRIP/TWIP Ti-alloys was developed in the past decade(TWIP:twinning-induced plasticity;TRIP:transformationinduced plasticity).Herein,we study the tunable nature of deformation mechanisms with various TWIP and TRIP contributions by fine adjustment of the Zr content on ternary Ti-12 Mo-xZr(x=3,6,10)alloys.The microstructure and deformation mechanisms of the Ti-Mo-Zr alloys are explored by using in-situ electron backscatter diffraction(EBSD)and transmission electron microscopy(TEM).The results show that a transition of the dominant deformation mode occurred,going from TRIP to TWIP major mechanism with increasing Zr content.In the Ti-12 Mo-3 Zr alloy,the stress-induced martensitic transformation(SIM)is the major deformation mode which accommodates the plastic flow.Regarding the Ti-12 Mo-6 Zr alloy,the combined deformation twinning(DT)and SIM modes both contribute to the overall plasticity with enhanced strain-hardening rate and subsequent large uniform ductility.Further increase of the Zr content in Ti-12 Mo-10 Zr alloy leads to an improved yield stress involving single DT mode as a dominant deformation mechanism throughout the plastic regime.In the present work,a set of comprehensive in-situ and ex-situ microstructural investigations clarify the evolution of deformation microstructures during tensile loading and unloading processes.