TiH2-based Ti-1Al-8V-5Fe PM alloys with different addition methods of alloying elements

The powder metallurgy high-strength Ti-1Al-8V-5Fe alloy (Ti-185 alloy) was investigated in this paper with different addition methods of alloying elements, Al, V, Fe pure elements powder (EP) or 1Al-8V-5Fe ternary master alloy powder (MAP), based on TiH₂ powders at the sintering temperature from 1150 to 1350°C. The results indicate that the Ti-185 alloy with the 1Al-8V-5Fe master alloy (Ti-185 MAP alloy) possesses the higher relative sintered density, less oxygen content, and less α-phase volume fraction versus the Ti-185 alloy with Al, V, and Fe pure elements (Ti-185 EP alloy). No matter where the sintering temperature is 1150, 1250, or 1350°C, Ti-185 MAP alloy invariably has the higher yield strength and hardness which have a strong relationship to its higher density and less volume fraction of softer α-phase in comparison with Ti-185 EP alloy.     

The sintering densification and microstructure evolutions of Ti-1Al-8V-5Fe alloy with Si additions

The cost-efficient Ti-1Al-8V-5Fe-xSi (denoted Ti-185-xSi hereafter, x = 0, 0.15, 0.3, 0.45, 0.6, 0.75) alloys are synthesized by cold compaction and sintering powder metallurgy (PM) technology using TiH₂ and high-pure FeV₈₀ powders. The sintering densification, microstructural evolutions and mechanical behavior of Ti-185-xSi alloys sintered at 1350°C are investigated. The results show that the Si element is favorable to enhance the sintered density of Ti-185 alloys, which should be limited to ≤0.3%. The amount and average size of precipitate Ti₅Si₃ increase in the Ti-185 alloys with increasing Si content. Meanwhile, the Rockwell hardness of Ti-185 alloy also displays an increasing tendency, suggesting the Si element can improve the hardness of Ti-185. The Ti-185–0.15Si alloy possesses a better comprehensive mechanical property of strength (937 ± 8 MPa) and elongation (3.5%). The high-performance Ti-185 alloy is successfully prepared using low-cost FeV₈₀ master alloy with slight Si impurity instead of costly V.     

Sintering densification behaviors of Ti-1Al-8V-5Fe alloy based on TiH2 and TiH1.5 powders

The sintering densification behaviors of Ti-1Al-8V-5Fe alloys by saturated titanium hydride (TiH₂) and unsaturated titanium hydride (TiH_1.5) powders are investigated. The results show that the TiH₂-185 specimens present better sintering densification ability compared with TiH_1.5–185 specimens, which displays that the titanium hydride with more hydrogen has a stronger densification ability. The TG-MS analysis suggests that the decompositions of TiH₂ and TiH_1.5 powders are accompanied by the H₂O releasing, and the TiH₂ releases more H₂O than that of TiH_1.5. The twice phase transformations can be observed in the TiH₂-185 specimens by DSC, which contribute to the H₂O releasing and dislocations and vacancies. Thus, TiH₂ powder is helpful to obtain higher sintering densification and better mechanical properties for Ti-1Al-8V-5Fe alloy.     

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.     

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。     

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.     

Microstructures and wear properties of in situ formed composite coatings produced by laser alloying technique

Laser-surface alloying of titanium alloy Ti-6Al-4V with C and Si mixed powders has been carried out. The composite coatings, thickness of about 0.7 mm, mainly consisting of titanium carbides and silicides, have a hardness of about 1500 HV_0.1, and the wear resistance is 4 times more than that of the as-received.     

Spine rod straightening as a possible cause for revision

In a previous study, the authors examined the elastic and short-term anelastic springback of Ti6Al4V, CoCrMoC and A316L stainless steel spine rods to observe how the rods mechanically respond in OR contouring. In that study rods were 200?mm long and only the movement at the tip was recorded. The implication of that work was that rods will straighten in-vivo, however, in order for the mechanism of straightening to be determined, the movement of individual bends over time must first be elucidated. Spine rods used were, commercially pure titanium (CP Ti) a primarily α-phase; Ti-6Al-4V; α/β-phase titanium alloy from two different suppliers (denoted by, Ti-6Al-4V (L) and Ti-6Al-4V); β-phase titanium (TNTZ) and CoCrMoC. Following contouring the rods were aged unconstrained, in normal atmosphere or simulated body fluid (SBF) in a CO₂ incubator for up to 288?h. Elastic springback is significantly different between alloys with different microstructures. Both types of Ti6Al4V rods, while meeting the ASTM F136 industry standard, have significantly different properties, most importantly yield strength, flexural modulus, and springback. Environment showed no significant impact on anelasticity. The anelastic response of Ti6Al4V L sample, which has relatively more beta phase than the Ti6Al4V sample, follows the pure beta phase TNTZ in its extended time response. CoCrMoC and CP Ti have a very reduced anelastic response compared to the other alloys. This potentially can have unanticipated effects on the outcome of spine procedures, as the surgeon is reliant on the rods having similar properties to achieve a desired outcome.     

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.     

Toughening of titanium alloys by twinning and martensite transformation

Two kinds of titanium alloys, titanium alloy (Ti-10V-2Fe-3Al) and titanium alloy (Ti-5Al-2.5Sn) were used to investigate the toughening mechanisms with new approaches. The results show that Ti-5Al-2.5Sn alloy possesses good combination of strength and ductility as well as satisfied low-cycle fatigue life both at 293 K and 77 K. As for Ti-10V-2Fe-3Al alloy, the microstructure with metastable phase shows lower strength and ductility but higher threshold stress intensity factor (K _th) than solution treated and aged microstructure composed of and phases. The microstructures also show that twinning occurs in deformation of Ti-5Al-2.5Sn alloy at 77 K. Twinning seems to be helpful for improving the low-cycle fatigue life to a great extent at cryogenic temperature. It's also found that owing to stress-assisted martensite transformation in metastable Ti-10V-2Fe-3Al alloy, the fatigue crack propagation path shows a very tortuous way, which decrease the effective stress intensity factor (K _eff) at crack tip, and increase threshold stress intensity factor (K _th).     

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.     

Investigation of three-body wear behavior and hardness of experimental titanium alloys for dental applications in oral environment

The aim of this study was to investigate the three-body wear resistance and hardness of commercially pure titanium and titanium alloys containing zirconium and tantalum (cp-Ti, Ti-5Zr and Ti-5Ta). Each titanium test group, were subjected to wear tests under 10⁵ wear cycles, 50 N mechanical force, 2.0 Hz wear frequency, 6 mm diameter Al₂O₃ antagonist ball, 5 °C/55 °C thermal change conditions immersed in poppy seed slurry as third-body medium. The mean wear volume loss and depth of all test specimens after the three-body wear tests was determined with use non-contact 3D profilometer and also Vicker's hardness was measured. Wear area of microstructures were evaluated using scanning electron microscopy (SEM) and x-ray diffraction (XRD) analysis. The hardness of Ti-5Zr material was significantly greater than the other alloy material and cp-Ti. However, for the test materials in this study considered, correlations between the three-body wear resistance and hardness were found to be insignificant. It was concluded, the three-body wear resistance of the alloy formed with the adding of zirconium and tantalum to the pure titanium is increased after wear tests.     

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.     

Influence of noble metals alloying additions on the corrosion behaviour of titanium in a fluoride-containing environment

Titanium alloys exhibit excellent corrosion resistance in most aqueous media due to the formation of a stable oxide film, and some of these alloys (particularly Ti-6Al-7Nb) have been chosen for surgical and odontological implants for their resistance and biocompatibility. Treatment with fluorides (F⁻) is known to be the main method for preventing plaque formation and dental caries. Toothpastes, mouthwashes, and prophylactic gels can contain from 200 to 20,000 ppm F⁻ and can affect the corrosion behaviour of titanium alloy devices present in the oral cavity. In this work, the electrochemical corrosion behaviour of Ti-1M alloys (M = Ag, Au, Pd, Pt) was assessed in artificial saliva of pH = 3.0 containing 910 ppm F⁻ (0.05 M NaF) through open circuit potential, E_OC, and electrochemical impedance spectroscopy (EIS) measurements. The corrosion behaviour of the Ti-6Al-7Nb commercial alloy was also evaluated for comparison. E _OC measurements show an active behaviour for all the titanium alloys in fluoridated acidified saliva due to the presence of significant concentrations of HF and HF₂ ⁻ species that dissolve the spontaneous air-formed oxide film giving rise to surface activation. However, an increase in stability of the passive oxide layer and consequently a decrease in surface activation is observed for the Ti-1M alloys. This behaviour is confirmed by EIS measurements. In fact, the Ti-6Al-7Nb alloy exhibits lower impedance values as compared with Ti-1M alloys, the highest values being measured for the Ti-1Au alloy. The experimental results show that the corrosion resistance of the studied Ti-1M alloys is similar to or better than that of Ti-6Al-7Nb alloy currently used as biomaterial, suggesting their potential for dental applications.     

Hot deformation behavior of Cu-bearing antibacterial titanium alloy

We investigated the deformation behavior of a new biomedical Cu-bearing titanium alloy (Ti-645 (Ti-6.06Al-3.75V-4.85Cu, in wt%)) to optimize its microstructure control and the hot-working process. The results showed that true stress–true strain curve of Ti-645 alloy was susceptible to both deformation temperature and strain rate. The microstructure of Ti-645 alloy was significantly changed from equiaxed grain to acicular one with the deformation temperature while a notable decrease in grain size was recorded as well. Dynamic recovery (DRV) and dynamic recrystallization (DRX) obviously existed during the thermal compression of Ti-645 alloy. The apparent activation energies in (α?+?β) phase and β single phase regions were calculated to be 495.21?kJ?mol^?1 and 195.69?kJ?mol^?1, respectively. The processing map showed that the alloy had a large hot-working region whereas the optimum window occurred in the strain rate range of 0.001–0.1?s^?1, and temperature range of 900–960?°C and 1000–1050?°C. The obtained results could provide a technological basis for the design of hot working procedure of Ti-645 alloy to optimize the material design and widen the potential application of Ti-645 alloy in clinic.     

Mechanism of surface modification of a porous-coated Ti-6Al-4V implant fabricated by electrical resistance sintering

A porous-coated Ti-6Al-4V implant was fabricated by electrical resistance sintering, using 480 F capacitance and 1.5 kJ input energy. X-ray photoelectron spectroscopy (XPS) was used to study the surface characteristics of the implant material before and after sintering. There were substantial differences in the content of O and N between as-received atomized Ti-6Al-4V powders and the sintered prototype implant, which indicates that electrical resistance sintering alters the surface composition of Ti-6Al-4V. Whereas the surface of atomized Ti-6Al-4V powders was primarily TiO₂, the surface of the implant consisted of a complex of titanium oxides as well as small amounts of titanium carbide and nitride. It is proposed that the electrical resistance sintering process consists of five stages: stage I – electronic breakdown of oxide film and heat accumulation at the metal-oxide interface; stage II – physical breakdown of oxide film; stage III – neck formation and neck growth; stage IV – oxidation, nitriding, and carburizing; and stage V – heat dissipation. The fourth stage, during which the alloy repassivates, is responsible for the altered surface composition of the implant.     

Processing of nanocrystalline FeAlX (X = Ni, Mn) intermetallics using a mechanical alloying and hot pressing techniques

Fe-40Al-40Ni-20 and Fe-40Al-40Mn-20 (all in at.%) intermetallics were mechanically alloyed for 40 h and followed by hot-pressing at 650°C under 450 MPa for 1 h. As resulted from the X-ray diffraction studies, the ordered B2 structure was formed in the Fe-40Al-40Ni-20 alloy while in the case of Fe-40Al-40Mn-20 alloy, the disordered Fe(Al) solid solution was observed. The chemically homogenous rounded particles of size of about 5 μm were identified using scanning analytical electron microscopy in alloys after 40 h of milling. TEM studies of milled powders revealed a nanostructure in both alloys with grain size of about 20 nm. The hot pressing process of milled powders allowed to obtain compacts with the density of about 87 and 89% of the theoretical one for Fe-40Al-40Mn-20 and Fe-40Al-40Ni-20 alloys, respectively. The micro-hardness measurements have shown that the alloy with the Ni addition possesses the hardness of about 1200 HV₂₀, whereas in the alloy with the Mn addition it is 1100 HV₂₀. The TEM investigations allowed to identify a nanocrystalline structure of compacts with a mean grain size below 50 nm, with B2 ordered structure in both alloys.     

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.     

Investigation of the effects of microstructure on creep deformation in α2-based titanium aluminide intermetallics

The results of a systematic investigation of the effects of microstructure/substructure on the secondary creep behaviour of α2-based titanium aluminide alloys are presented. This includes a study of the effects of heat treatment on the steady-state creep behaviour of α2+β-processed Ti-24Al-11Nb and Ti-25Al-10Nb-3V-1Mo at 540, 650 and 760°C, and an investigation of the effects of creep deformation on dislocation substructures in Ti-24Al-11Nb. The parameters that control secondary creep deformation are identified for both alloys, and the results are compared with data obtained for conventional high-temperature near-α titanium alloys and β-forged Ti-24Al-10Nb-3V-1Mo. This revised version was published online in November 2006 with corrections to the Cover Date.     

Synthesis of high-energy-density Pr2Fe14−x Co x B,x⩽3, magnets for practical applications

Stable magnetic powders, of 1–2μm particle size, of partially Co-substituted, Pr₂Fe_14−x Co _x B,x⩽3, alloys together with 2–4 at% excess Pr were prepared by rapidly quenching the associated melts into thin ribbons and then mechanical attriting the ribbons in the refined particle sizes. The saturation magnetizationM _s, remanent magnetizationJ _r, intrinsic coercivityH _ci and Curie temperatureT _c were studied in characterizing the powders for fabricating into sintered or polymer bonded magnets. It is found that the smallx=0·4–0·8 substitution of the Co on Fe sites in this series sensitively leads to an increase in the value ofH _ci, by as much as 40%, with the optimum value of 21 kOe atx ∼ 0·55, together with an improvement in theT _c from 292°C to 325°C, without significantly diluting theM _s∼150 emu/g andJ _r∼8·0 kG values. The Co-substituted Pr₂Fe₁₄B alloy particles are better stable and corrosion resistant in ambient atmosphere. The results are discussed with the microstructure and comparison with the data for Nd₂Fe₁₄B powders processed under the same conditions. Paper presented at the poster session of MRSI AGM VI, Kharagpur, 1995