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.     

Precipitation behavior and tensile property of the stress-aged Ti-10Mo-8V-1Fe-3.5Al alloy

A kind of metastable beta titanium alloy, i.e. Ti-10Mo-8V-1Fe-3.5Al, was aged under elastic compressive stress. Transmission electron microscopy (TEM) investigations revealed that, in the stress-aged samples, precipitated alpha plates were parallel to each other. However, in the conventionally aged samples, alpha plates intersected each other. In other words, variant of alpha plate was selected in the stress-aged samples. Tensile tests showed that, at equivalent tensile strength, the stress-aged samples exhibited higher ductility, compared to the conventionally aged ones.     

THE INFLUENCE OF HYDROGEN ON THE FATIGUE BEHAVIOUR OF THE BETA-TITANIUM ALLOY Ti-3Al-8V-6Cr-4Mo-4Zr

In order to characterize the influence of hydrogen on the mechanical properties of β-titanium alloys, monotonic tensile and strain-controlled fatigue tests were performed on samples of the metastable alloy Ti-3Al-8V-6Cr-4Mo-4Zr in uncharged (0.5 at.% hydrogen) and hydrogen-charged (3-4 at.% hydrogen) conditions. The hydrogen was introduced into the material during the last 8 h of an ageing treatment (28 h at 482°C) from the gas phase, whereas the reference (uncharged) specimens were annealed completely in vacuum. The results of the mechanical tests indicate that hydrogen slightly increases the strength of the alloy in monotonic as well as in cyclic loading. Under tensile loading the fracture strain decreases as a result of hydrogen. Under cyclic loading both charged and uncharged conditions show initial softening followed by a saturation state. The cyclic lifetime at a constant total strain amplitude, however, is not reduced by the hydrogen charging. The effect of hydrogen on the mechanical behaviour can be interpreted and understood on the basis of microstructural observations that reveal a hydrogen-induced change in the precipitation state. This indirect influence of hydrogen on the microstructure, which leads to a reduction of the mean size of the α-precipitates, in combination with a slight decrease on the volume fraction of the α-phase, seems to dominate over any direct intrinsic hydrogen effect     

INFLUENCE OF NITRIDING ON MICROSTRUCTURE AND FATIGUE BEHAVIOUR OF A SOLUTE-RICH BETA TITANIUM ALLOY

Abstract— The solute-rich beta titanium alloy Ti-3Al-8V-6Cr-4Mo-4Zr was subjected to 1500 bar nitrogen pressure at elevated temperatures (500–920°C), leading to a diffusion layer with a high surface hardness. Microstructural, crystallographic and compositional analyses indicate that TiN (δ) and Ti₂N (ε) are formed at temperatures exceeding 815°C. The increased concentration of nitrogen, which is a potent α-stabilizer in titanium, also causes α-Ti to form near the surface. The nitriding treatment does not significantly alter the tensile properties or fatigue limit in solution heat treated material. A subsequent ageing treatment of 72 h at 440°C and 16 h at 500°C reduces toughness significantly, allowing cracks induced by nitriding to propagate more easily into the bulk. Tensile ductility and fatigue performance of aged nitrided Ti-3Al-8V-6Cr—4Mo-4Zr are thus significantly lower than in the untreated reference condition.     

Improvement of Ductility of Powder Metallurgy Titanium Alloys by Addition of Rare Earth Element

Ti-4.5Al-6.0Mo-1.5Fe, Ti-6Al-1Mo-1Fe and Ti-6Al-4V alloys were prepared by blended elemental powder metallurgy （PM） process, and the effects of Nd on the microstructures and mechanical properties were investigated by scanning electron microscopy （SEM）, transmission electron microscopy （TEM） and X-ray diffraction （XRD）. It was found out that the addition of Nd increased the density of sintered titanium alloys slightly by a maximum increment of 1% because small amount of liquid phase occurred during sintering. The addition of Nd shows little effect on the improvement of tensile strength, while the elongation is significantly improved. For example, the elongation of Ti-4.SAl-6.0Mo-1.5Fe can be increased from 1% without addition of Nd to 13% at a Nd content of 1.2 wt pct.     

3D打印医用钛合金的抗菌性能和体外生物相容性

应用选择性激光熔融技术(SLM)制备出3D打印医用钛合金Ti-6Al-4V和Ti-6Al-4V-5Cu,用平板共培养法研究测定其抗菌性能,用CCK8细胞增殖测定法、鬼笔环肽细胞骨架染色法和Annexin-V/PI流式细胞术研究了这种合金的抗菌性能和对小鼠胚胎成骨前体细胞(MC3T3-E1)的体外生物相容性影响。结果表明,3D打印Ti-6Al-4V-5Cu合金具有较高的抗菌性能,对金黄色葡萄球菌的抗菌率达到(57.03±1.55)%。在CCK8细胞增殖毒性测定、细胞骨架鬼笔环肽染色实验和Annexin-V/PI双标记法流式分析三种研究中Ti-6Al-4V-5Cu表现的优越,具有更好的体外生物相容性。     

The effect of hydrogen on the strength and superplastic deformation of beta-titanium alloys

The effect of hydrogen on mechanical properties and superplastic deformation of two commercial titanium alloys, Ti-4Al-7Mo-10V-2Fe-1Zr (Ti-471021) and Ti-10V-2Fe-3Al (Ti-1023), was studied in the range of hydrogen concentration up to 1.3 wt%. The elevated temperature hardness of Ti-471021 alloy increased with hydrogen concentration. The stress levels during the superplastic deformation in both alloys increased with increasing concentrations of hydrogen in the -phase region. X-ray diffraction results and examination of the microstructure with TEM revealed that no hydrides had formed up to hydrogen concentrations of 1.3 wt%. The increase in flow stress was mainly due to the solid solution strengthening by hydrogen during the superplastic deformation.     

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.     

Microstructural evolution during fabrication of ultrafine grained alpha+beta titanium alloy

Abstract

In this work, several important problems related to the fabrication of ultrafine grained UFG alpha+beta titanium alloys have been investigated, taking Ti-6.5Al-3.3Mo-1.8Zr-0.26Si wt- as the model material. It has been shown that UFG titanium alloys can be produced by deformation at relatively low temperatures or high strain rates. There were different Zenner-Holloman parameter-grain size relationships in the relatively high temperature region 750-920C and the relatively low temperature region 650-750C for the present titanium alloy. During the compression of a martensite microstructure at 890C, both the alpha and beta phases were dynamic recrystallised and the lamellae were broken up by means of grain boundary sliding and phase penetration along the subgrain boundaries. During compression at 650C, alpha phases were dynamically recrystallised, and beta phases precipitated and grew in the matrix of alpha phases. It was suggested that the martensite microstructure should be preferred to other lamellar microstructures for the fabrication of UFG Ti alloys. The UFG Ti alloy demonstrated good superplasticity at relatively high strain rates and low temperatures.     

Thermal stability of Ti-V-Cr burn-resistant alloys

Ti-35V-15Cr, Ti-25V-15Cr and Ti-25V-15Cr-0.4Si alloys were exposed to different temperatures in air (450–600°C) for aging times between 0 and 200 h and subsequently tensile tested at room temperature with the surface oxide retained or removed. The influence of an applied tensile stress (50–200 MPa) during thermal exposure was also investigated. The results showed that post-exposure tensile properties deteriorated with the increase in exposure temperature and time. The decrease in tensile properties resulted from the combination of surface oxidation and microstructural changes. The main change of the microstructure during thermal exposure is the heterogeneous precipitation of phase on beta grain boundaries. Both increased vanadium content in the alloy and the addition of silicon have shown an adverse effect on alloys' thermal stability.     

Fabrication of low-cost Ti-1Al-8V-5Fe by powder metallurgy with TiH2 and FeV80 alloy

The low-cost Ti-1Al-8V-5Fe (Ti-185) alloy with a high strength is prepared by cold-compaction-and-sintering powder metallurgy process with low-cost titanium hydride (TiH₂) powders and FeV₈₀ master alloy powders. The use of simple technique process and cheap alloying elements can lead to the cost reduction for titanium alloys. The thermal decomposition of TiH₂-1Al-8V-5Fe is analyzed by thermal gravimetric analyses and differential scanning calorimetry simultaneous thermal analyzer. The shrinkage behavior of TiH₂-1Al-8V-5Fe during the sintering process is employed by the high-sensitivity dilatometer system. The microstructure of sintered Ti-185 consists of β-phase and lamellar α-phase. The results show that the sintered Ti-185 alloys have the relative density of 97.8%, homogeneous composition, and fine grains. The yield strength and the hardness are 1461?MPa and 40.1?±?1.0 HRC (unit of Rockwell hardness), which are better than that of as-cast Ti-185.     

Ti-10Mo-XNb合金铸态组织和机械性能的研究

为了研究Nb元素对Ti-10Mo合金组织和性能的影响,采用钨电极熔化、离心浇注工艺制备了4种钛合金(Ti-10Mo-XNb,X=0,3,7,10),分析并测试了Nb元素对Ti-10Mo合金铸态组织和力学性能的影响.研究结果表明:随着Nb含量的增加,3种Ti-Mo-Nb合金的铸态组织和相组成发生了改变,Ti-10Mo-3Nb合金由等轴的α+β晶粒组成,Ti-10Mo-7Nb合金由等轴的β晶粒组成,Ti-10Mo-10Nb合金由少量等轴和大量枝状的β晶粒组成.另外,随着Nb含量的增加,3种Ti-Mo-Nb合金的维氏硬度、压缩强度、弹性模量降低,压缩率和抗弯强度升高,压缩断口和弯曲断口由脆性断裂向韧性断裂转变.Ti-Mo-Nb合金有望成为新型的生物医用材料.     

Effect of chromium content on structure and mechanical properties of Ti-7.5Mo-xCr alloys

The present work is a study of a series of Ti-7.5Mo-xCr alloys with the focus on the effect of chromium content on the structure and mechanical properties of the alloys. Experimental results show that low hardness, strength and modulus binary Ti-7.5Mo alloy is comprised primarily of fine, acicular martensitic phase. When 1 wt % Cr is added, a small amount of phase is retained. With 2 wt % or more chromium added, the entire alloy becomes equi-axed phase with bcc crystal structure. The average grain size decreases with Cr content. When the alloy contains about 2–4 wt % Cr, a metastable phase is present. In Ti-7.5Mo-2Cr alloy appears the highest intensity accompanied with high microhardness, bending strength and modulus. The -induced embrittling effect is most profound in Ti-7.5Mo-2Cr alloy that exhibits a terrace type fracture surface covered with numerous micron-sized dimples. The alloys with higher Cr contents show normal ductile type fractography with much larger deformation dimples. The present results indicate that Ti-7.5Mo-(4–6)Cr alloys seem to be potential candidates for implant application.     

Comparison of fatigue strengths of biocompatible Ti-15Zr-4Nb-4Ta alloy and other titanium materials

The fatigue strength of an annealed Ti-15Zr-4Nb-4Ta alloy at 1 × 10⁸ cycles was approximately 730 MPa. The fatigue strength of its alloy was much improved following an ageing treatment after a solution treatment. The tension-to-tension fatigue strengths of annealed Ti-6Al-4V, V-free Ti-6Al-7Nb, Ti-6Al-2Nb-1Ta, and Ti-15Mo-5Zr-3Al alloys at 1 × 10⁸ cycles were approximately 685, 600, 700, and 350 MPa, respectively. The ratios of fatigue strength at 1 × 10⁸ cycles to ultimate tensile strength for the α- and (α + β)-type Ti materials were higher than 65%.     

Phenomena of nanotube nucleation and growth on new ternary titanium alloys

Ti-30Nb-xZr and Ti-30Ta-xNb alloys have been investigated using various methods of surface nanotube formation. Ternary Ti-30Nb-xZr (x = 3 and 15 wt%) and Ti-30Ta-xNb (x = 3 and 15 wt%) alloys were prepared by using high-purity sponge Ti (Grade 4, G&S Titanium, USA), Ta, Zr and Nb spheres. The two groups of ternary Ti alloys were prepared using a vacuum arc melting furnace. Nanotube formation was carried out with a conventional three-electrode configuration with the Ti alloy specimen, a platinum counterelectrode, and a saturated calomel (SCE) reference electrode. Experiments were performed in 1 M H3PO4 with small additions of NaF (0.1-0.8 wt%), using a potentiostat. Nanotubes formed on the surfaces of the two ternary Ti alloys were examined by field emission scanning electron microscopy, EDS and XRD. The Ti-30Ta-xZr alloys had microstructure with entirely needle-like constituents; the thickness of the needle-like alpha-phase increased as the Zr content increased. The Ti-30Nb-xZr alloys had equiaxed microstructures of the beta-phase, and increasing amounts of the needle-like alpha phase appeared at the grain boundaries of the beta-phase as the Zr content increased. The nanotubes were nucleated and grew mainly on the beta phase for the Ti-30Ta-3Zr and Ti-30Nb-3Zr alloys, which had nanotubes with uniform shape, but the nanotubes were nucleated at the alpha phase for the Ti-30Ta-15Zr and Ti-30Nb-15Zr alloys, which had nanotubes with irregular shape and diameters of two sizes. The diameter and depth of the nanotubes could be controlled, depending upon the alloy composition and composition of the surface oxide films (TiO2, Nb2O5, Ta2O5, and ZrO2). It is concluded that this research that selection of the appropriate alloying element can allow significant control of the nanotopography of these Ti alloy surfaces and that it is possible to control the surface nanotube size to promote long-term osseointegration for clinical dental or orthopedic use.     

Microstructural investigation of a rapidly solidified Ti-6Al-4V-1B-0.5Y alloy

A Ti-6Al-4V-1B-0.5Y (wt%) alloy has been prepared by consolidation of the melt-spun alloy fibres. The microstructures of the melt-spun fibre and the consolidated alloy were examined by different techniques. It was found that in the consolidated alloy, titanium boride and yttrium oxide particles have a refined particle size and a uniform distribution in the (+) matrix compared with the microstructure of the same alloy obtained by conventional ingot metallurgy. The boride phase in the consolidated alloy mainly has a needle-shaped morphology and has been identified by electron diffraction to be orthorhombic TiB with a B27 structure, while the yttrium oxide has a cuboidal morphology and has been identified as bcc Y₂O₃. Detailed TEM examination also revealed that yttrium addition has a strong influence on the TiB morphology by comparing the microstructures of Ti-6Al-4V-1B alloys with and without yttrium addition. Under similar processing conditions, the TiB phase in the consolidated alloys without yttrium addition mainly has a nearly equiaxed morphology with a finer particle size, while the TiB phase in the consolidated alloy with yttrium addition will mainly have a needle-shaped morphology. This effect of yttrium addition on the TiB morphology has been discussed in terms of heterogeneous nucleation and the reduced undercooling.     

固溶温度对Ti-4Al-6Mo-2V-5Cr-2Zr钛合金的组织和拉伸性能的影响

研究了固溶温度对一种亚稳β钛合金(Ti-4Al-6Mo-2V-5Cr-2Zr)的锻态组织和室温拉伸性能的影响。结果表明,固溶温度低于相变点时大量的α相在β基体中析出并聚集在滑移带附近,随着固溶温度接近相变点α相的数量减少且部分滑移带消失。固溶温度高于相变点时显微组织为单一的β相且滑移带完全消失,随着固溶温度继续升高β晶粒聚集且长大。这种合金经750℃×1 h固溶处理后达到良好的强度塑性匹配,气抗拉强度、屈服强度和伸长率分别为957 MPa、887 MPa和11.7%。     

Subzero tensile properties of 7010 aluminium alloy and Ti-6A1-4V and IMI550 titanium alloys in sheet form

Tensile properties are reported for Al-6Zn-2.5Mg-1.7Cu-0.12Zr (7010), Ti-6Al-4V and Ti-4Al-4Mo-2Sn-0.5Si (IMI550) alloy sheet, 1.7 mm thick tested at 293, 223, 173 and 77 K. The strength of these alloys increased and the reduction of area decreased with decreasing test temperature. The Young's Modulus (E), 0.1% proof stress (σ_0.1) and true tensile strength ($\text{σ}{}_{\mathrm{TS}}$) were related to temperature T in degrees absolute (in the range 293-173 K for E and 293-77 K for σ_0.1 and $\text{σ}$_TS) by     

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.     

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.