The role of martensitic transformation in corrosion fatigue failure of Ti-22Nb-6Ta and Ti-22Nb-6Zr (at %) medical alloys

The effect of cyclic dynamic loading on the kinetics of changes in the electrode potentials of Ti-22Nb-6Ta and Ti-22Nb-6Zr (at %) superelastic medical alloys in a model solution simulating the bone tissue environment in a living organism is studied with the use of electrochemical chronopotentiometry. An increase in the applied load from 450 to 780 MPa is found to affect dramatically the character of changes in the electrode potentials of the alloys during exposure. Ti-22Nb-6Ta alloy exhibits higher resistance to corrosion fatigue cracking than does Ti-22Nb-6Zr alloy. It is shown that the superelasticity of the alloys is responsible for the deceleration of the corrosion fatigue cracking due to the blocking effect of martensite crystals formed in the structure during the loading half-cycle, which is confirmed by the low rate of the potential decrease after the nucleation of corrosion fatigue cracks.     

High-Temperature Oxidation Behavior of Ti-22Al-27(Nb, Zr) Alloys

研究了Ti2Al Nb基合金Ti-22Al-(27-x)Nb-x Zr(x=0,1,6,at%)在650~800℃的氧化行为。采用XRD和SEM等测试技术对此温度区间形成的氧化层特征进行了分析。结果表明,相比Ti-22Al-27Nb,含锆合金具有较好的抗氧化性能。Ti-22Al-(27-x)Nb-x Zr合金在650℃氧化100 h,主要氧化产物为Ti O2,而在800℃氧化100 h,Ti O2,Al2O3和Al Nb O4为主要产物,但是在Ti-22Al-21Nb-6Zr合金中还有Zr O2生成。Ti-22Al-26Nb-1Zr合金具有优异抗氧化性能,归因于氧化产物细化形成了致密的氧化层,而Ti-22Al-21Nb-6Zr合金,虽然在800℃也形成了较多Al2O3,但是氧化层中的Zr O2为氧的快速扩散提供通道,进而导致该合金氧化增重明显。     

Electrochemical Behavior of Biomedical Titanium Alloys Coated with Diamond Carbon in Hanks’ Solution

Biomedical implants in the knee and hip are frequent failures because of corrosion and stress on the joints. To solve this important problem, metal implants can be coated with diamond carbon, and this coating plays a critical role in providing an increased resistance to implants toward corrosion. In this study, we have employed diamond carbon coating over Ti-6Al-4V and Ti-13Nb-13Zr alloys using hot filament chemical vapor deposition method which is well-established coating process that significantly improves the resistance toward corrosion, wears and hardness. The diamond carbon-coated Ti-13Nb-13Zr alloy showed an increased microhardness in the range of 850 HV. Electrochemical impedance spectroscopy and polarization studies in SBF solution (simulated body fluid solution) were carried out to understand the in vitro behavior of uncoated as well as coated titanium alloys. The experimental results showed that the corrosion resistance of Ti-13Nb-13Zr alloy is relatively higher when compared with diamond carbon-coated Ti-6Al-4V alloys due to the presence of β phase in the Ti-13Nb-13Zr alloy. Electrochemical impedance results showed that the diamond carbon-coated alloys behave as an ideal capacitor in the body fluid solution. Moreover, the stability in mechanical properties during the corrosion process was maintained for diamond carbon-coated titanium alloys.     

Martensitic transformation of Ti-18Nb(at.%) alloy with zirconium

The addition of 3%～9% Zr on the martensitic transformation of Ti-18Nb(at.%) alloy was investigated. The results of microstructure and X-ray diffraction (XRD) analysis show that the phase constitution of as-quenched Ti-18Nb-9Zr(at.%) alloy consists of the retained matrix and martensite, while that of the other three alloys is single martensite. No trace of athermal phase was found in any of the as-quenched alloys. Unlike the effect of Nb addition on the martensitic transformation start temperature Ms of Ti-1...     

粉末冶金碳化物强化铌合金组织演变及其力学行为

采用机械球磨与热压烧结相结合的粉末冶金法对不同球磨时间Nb-35Ti-6Al-5Cr-8V-5C合金的粉末变形行为,微观组织结构和力学行为进行研究。结果表明:随着球磨时间的增加,Nb-35Ti-6Al-5Cr-8V-5C复合粉末中的块状金属颗粒首先变形为片状后在碰撞挤压作用下破碎成絮状,TiC粉末均匀的分布于片状金属粉末表面;Nb-35Ti-6Al-5Cr-8V-5C合金由Nbss和(Nb,Ti)C两相构成,各合金碳化物体积分数均为11%左右,Ti元素主要分布于Nbss晶界和碳化物内,Al、Cr、V元素主要分布于Nbss晶粒内,Nbss和(Nb,Ti)C相尺寸均随球磨时间增加而尺寸减小;Nbss晶粒细化及强化相碳化物弥散化导致合金的室温压缩力学性能和塑性变形能力显著提高,压缩变形后合金Nbss与碳化物具有良好的界面结合能力,但是碳化物内部存在明显的近似平行分布的裂纹;数据对比表明,粉末冶金法制备Nb-35Ti-6Al-5Cr-8V-5C合金的力学性能优于电弧熔炼法。     

粉末冶金Nb-35Ti-6Al-5Cr-8V合金组织演变及其力学行为

采用粉末冶金法对不同球磨时间的Nb-35Ti-6Al-5Cr-8V合金机械合金化粉末塑变行为,热压烧结材料的微观组织结构和力学行为进行了研究。研究结果表明：塑性良好的Nb-35Ti-6Al-5Cr-8V粉末随着球磨时间增加首先变形为大尺寸的片状、后经持续的加工硬化破碎成絮状;热压烧结能够制备微观组织可控晶粒细化的Nb-35Ti-6Al-5Cr-8V合金,合金由单一的Nbss相构成,Ti、Al、Cr、V元素固溶引起Nb晶格尺寸减小0.0685 ?;随着球磨时间增加合金晶粒明显细化进而显著提高了合金的维氏硬度和室温压缩强度,其变化符合材料硬度和强度的Hall-Petch规律。粉末冶金制备Nb-35Ti-6Al-5Cr-8V合金的各项力学性能明显优于熔铸法制备合金。     

Characterization of the Ti-10Nb-10Zr-5Ta Alloy for Biomedical Applications. Part 1: Microstructure, Mechanical Properties, and Corrosion Resistance

Ti-10Nb-10Zr-5Ta alloy was investigated as possible material candidate for replacing Ti6Al4V in medical applications. The alloy was prepared in a levitation melting furnace and characterized in terms of elemental and phase composition, microstructure, mechanical properties, and corrosion resistance in simulated body fluid and Fusayama Meyer artificial saliva solutions. The characteristics of the new alloy were compared to those of the Ti6Al4V alloy. The Ti-10Nb-10Zr-5Ta system was found to posses of a polyhedral structure consisting in α′ and β phases. X-ray structural analysis revealed a mixture of hexagonal α′ martensite (main phase, with grain size of about 21 nm) and β bcc phase. The Ti-10Nb-10Zr-5Ta alloy exhibited some better mechanical properties (Young modulus, tensile properties) and corrosion resistance (polarization resistance, corrosion current density, and corrosion rate), as compared to Ti6Al4V alloy.     

Tensile behavior of Ti-6Al-4V alloy fabricated by selective laser melting: effects of microstructures and as-built surface quality

Selective laser melting(SLM) is a powerful additive manufacturing(AM) technology, of which the most prominent advantage is the ability to produce components with a complex geometry. The service performances of the SLM-processed components depend on the microstructure and surface quality. In this work, the microstructures, mechanical properties, and fracture behaviors of SLM-processed Ti-6 Al-4 V alloy under machined and as-built surfaces after annealing treatments and hot isostatic pressing(HIP) were investigated. The microstructures were analyzed by optical microscope(OM), scanning electron microscope(SEM) and transmission electron microscopy(TEM). The mechanical properties were measured by tensile testing at room temperature. The results indicate that the as-deposited microstructures are characterized by columnar grains and fine brittle martensite and the asdeposited properties present high strength, low ductility and obvious anisotropy. After annealing at 800-900°C for 2-4 h and HIP at 920°C/100 MPa for 2 h, the brittle martensite could be transformed into ductile lamellar(α+β) microstructure and the static tensile properties of SLM-processed Ti-6 Al-4 V alloys in the machined condition could be comparable to that of wrought materials. Even after HIP treatment, the as-built surfaces could decrease the ductility and reduction of area of SLM-processed Ti-6 Al-4 V alloys to 9.2% and 20%, respectively. The crack initiation could occur at the columnar grain boundaries or at the as-built surfaces. The lamellar(α+β) microstructures and columnar grains could hinder or distort the crack propagation path during tensile tests.     

Design and Characterization of New Ti-Nb-Hf Alloys

Three new Ni-free Ti alloys Ti-16.2Hf-24.8Nb-1Zr, Ti-5.2Hf-31.2Nb-0.4Zr, and Ti-16Hf-36.2Nb-1Zr (wt.%), were designed and produced in order to obtain shape memory and/or low elastic modulus materials for the use in the load transfer implant field. For that, a method based on the molecular orbital theory was implemented to design the three new Ti-Nb-Hf system alloys. A vacuum arc-melted button of each alloy was treated at 1100 °C for 1.5 h and quenched in a mixture of ethanol/water at 0 °C. Finally, the alloys were microstructurally and mechanically characterized. Special attention on studying the elastic modulus and the thermoelastic martensitic transformation was given by means of nanoindentation tests using a Berkovich and a spherical tip, respectively. X-ray diffraction results showed the presence of β-phase in the three studied alloys. Moreover, one of the alloys exhibited reversible phase transformation due to the presence of thermoelastic martensitic α′′-plates inside the β-grains observed by transmission electron microscopy. Results showed a low elastic modulus in all the studied alloys with values between 70 and 90 GPa, which are lower than those of the commercial alloys used in load transfer bone implants.     

Effects of Sn and Zr on the Microstructure and Mechanical Properties of Ti-Ta-Based Shape Memory Alloys

Ti-Ta binary shape memory alloys have attracted much interest due to the absence of toxic element and the low Young??s modulus. However, the effects of the third element on the microstructure and mechanical property had not been well understood. In the present study, the effect of Sn and Zr additions on the microstructure and mechanical property of Ti-35Ta (at.%) alloys has been investigated. The results show that the microstructure of the solution treated Ti-Ta-based alloys compose of equiaxial grains. The alloys consist of ??-phase and ???? martensite phase at room temperature, except for the Ti-30Ta-5Sn alloy which consists of only ??-phase. This is possibly due to the presence of Sn which provides a stronger ??-stabilized effect on quenching compared to Zr addition. The lattice parameter of the ??-phase increased with the increase in Sn and Zr content. The addition of Sn and Zr had caused obvious increase in the tensile strength. The corrosion resistance of Ti-Ta-based alloys was also improved by adding Sn.     

生物医用钛合金的研究进展

钛合金具有较低的弹性模量、优异的耐腐蚀性能和生物相容性,是理想的生物医用材料.综述了医用钛合金的发展过程及新型医用β钛合金的研究现状,以及开发的新合金系列.目前开发的医用钛合金中,Ti-35Nb-7Zr-5Ta和Ti-29Nb-13Ta-7.1Zr合金的弹性模量为55 GPa,与致密骨的弹性模量很接近,与人体骨有较好的...     

Effects of minor yttrium addition on hot deformability of lamellar Ti-45Al-SNb alloy

The effects of 0.3%（molar fraction, the same below） yttrium addition on hot deformability of lamellar Ti-45Al-5Nb alloy were investigated by simulated isothermal forging tests. The ingots with the nominal compositions of Ti-45Al-5Nb and Ti-45Al-5Nb-0.3Y were prepared by induction skull melting. Simulated isothermal forging tests were conducted on Gleeble 1500D thermo-simulation machine using a 6 mm in diameter and 10 mm in length compressive specimen at the deformation temperatures of 1 100, 1 150, 1 200 ℃ and strain rates of 1.0, 0.1, 0.01 s^-1. The results show that yttrium addition remarkably improves hot deformability of Ti-45Al-5Nb alloy. An appropriate hot deformation processing parameter of Ti-45Al-5Nb-0.3Y alloy is determined as 1 200 ℃, 0.01 s^-1. The flow stresses are decreased by yttrium addition under the same compressive conditions. The activation energies of deformation Q are calculated as 448.6 and 399.5 kJ/mol for Y-free and Y-containing alloys, respectively. The deformed microstructure observation under 1 200 ℃, 0.01 s^-1 condition indicates that Ti-45Al-5Nb-0.3Y alloy shows more dynamic recrystallization. The improvement of hot deformability of Ti-45Al-5Nb-0.3Y alloy induced by yttrium addition should be attributed to that the smaller the original lamellar colonies, the lower the deformation resistance and activation energy of deformation are, and the more the dynamic recrystallization is.     

Effects of Ni,Co, B,and Ge on the microstructures and mechanical properties of Nb-Ti-Si ternary alloys

Nb-Si in situ composites with a nominal composition of Nb-22Ti-12Si-X (at.%, X represents Ni, Co, B, or Ge) are prepared using non-consumable arc melting technology. The effects of the alloying elements on the microstructures and mechanical properties are investigated. The Nb-22Ti-12Si ternary alloy consists of Nbss and Nb₃Si. A new phase of Ti₂Ni or Ti₂Co is introduced into the ternary system after adding Ni or Co. The addition of 6% Ge promotes the formation of Nb₅Si₃ and creates significantly finer microstructures. The values of the high temperature strength and room temperature fracture toughness of Nb-22Ti-12Si-6Ge are 566.33MPa and 12.81 MPa·m^1/2, respectively, which are approximately 88.2% and 18.5% higher than those of Nb-22Ti-12Si (300.98 MPa and 10.81 MPa·m^1/2). The addition of 3% B changed the morphological features and induced the appearance of large fine rosettes, which is favorable for restraining the crack propagation, and it also leads to a 22.3% increase in room temperature fracture toughness compared with the Nb-22Ti-12Si ternary alloy.     

新型医用钛合金Ti-12．5Zr-2．5Nb-2．5Ta的研究

按照临床上对外科植入材料的要求和现有医用钛合金存在的问题，制定了新合金设计的原则。确定了新合金添加合金化元素为Zr，Nb，Ta，合金的名义成分为Ti-12．5Zr-2．5Nb-2．5Ta，对新合金进行了组织结构分析与机械性能的测试。实验结果表明：该新型医用钛合金，满足了设计原则中对机械性能的要求。     

Effects of V and Zr Additions on Microstructures and Mechanical Properties of Nb-Ti-Al-Base Alloys

Microstructures and mechanical properties of Nb-32Ti-7Al alloys containing different V and Zr contents were investigated. The microstructures were characterized using optical microscopy and scanning electron microscopy (SEM). The alloy with V and Zr presents single phase Nb solid solution (Nbss). Tensile testing was carried out at room temperature and 1373 K. The results show that these alloys have good ductility at room temperature. The strengths at room and high temperature increase with the addition of V...     

Effect of surface treatment on electrochemical behavior of CP Ti, Ti-6Al-4V and Ti-13Nb-13Zr alloys in simulated human body fluid

The effect of an alkaline surface treatment on the electrochemical behavior of CP titanium, Ti-6Al-4V and Ti-13Nb-13Zr has been investigated by potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) techniques. Experiments were performed in Hank’s solution as a function of immersion time. The electrochemical behavior of untreated alloys was also studied. Potentiodynamic polarization experiments conducted after 1 and 168 h of immersion in Hank’s solution indicated minimal change in passive current density for the untreated alloys. EIS data obtained after 1, 24, 72 and 168 h for untreated alloys also indicated minimal change in passive film resistance. In the case of surface-treated alloys, EIS revealed the formation of one additional layer on CP Ti and two additional layers on Ti-6Al-4V and Ti-13Nb-13Zr alloys after surface treatment and immersion in Hank’s solution. Some ideas about the nature of these layers have been obtained by fitting the EIS data to equivalent electrical circuit models. The surfaces of the treated Ti-alloys were also characterized using X-ray diffraction and scanning electron microscopy. The first additional layer has been identified as a sodium titanate hydrogel layer and the second layer, as an apatite layer. The apatite nucleation and growth on the surface occurred after immersion in Hank’s solution. Ti-6Al-4V and Ti-13Nb-13Zr alloys exhibited higher apatite film resistance compared to CP Ti.     

Mechanical properties and corrosion resistance of low rigidity quaternary titanium alloy for biomedical applications

Electrochemical corrosion of Ti-35Nb-5Ta-7Zr alloy fabricated by arc melting and heat treatment process was studied in 0.9% NaCl at (37±1) °C. Phase and microstructure of the fabricated alloy were investigated using X-ray diffractometer and scanning electron microscope. Mechanical properties such as yield strength and elastic modulus of the alloy were determined by tensile test. Potentiodynamic polarization technique and impedance spectroscopy were employed to study the corrosion behavior. The results of the study were compared with those obtained for Ti-6Al-4V commercial alloy. The result of the study supports feasibility of Ti-35Nb-5Ta-7Zr alloy for implant applications.     

Characterization of the Ti-10Nb-10Zr-5Ta Alloy for Biomedical Applications. Part 2: Wettability, Tribological Performance and Biocompatibility

The Ti-10Nb-10Zr-5Ta alloy, prepared in a levitation melting furnace, was investigated as a possible candidate for replacing Ti6Al4V alloy in medical applications. The sessile drop method, pin-on-disc and in vitro tests were used to analyze wettability, wear resistance, and biocompatibility of the new alloy. The characteristics of the Ti-10Nb-10Zr-5Ta alloy were assessed in comparison to those of the Ti6Al4V alloy. The Ti-10Nb-10Zr-5Ta system was found to have hydrophilic characteristics with similar contact angle as the Ti6Al4V alloy. In all environments (deionized water, simulated body fluid and Fusayama Meyer artificial saliva), the friction coefficient showed a stable evolution versus sliding distance, being similar for both alloys. On overall, the wear resistance of Ti-10Nb-10Zr-5Ta alloy was lower than that of Ti6Al4V for all testing environments. The Ti-10Nb-10Zr-5Ta alloy exhibited good biocompatibility characteristics at in vitro test compared to Ti6Al4V alloy. The cell viability on Ti-10Nb-10Zr-5Ta surfaces was higher than the one observed on Ti6Al4V samples, regardless the number of days spent in osteoblast-like cells culture. A high degree of cell attachment and spreading was observed on both alloys.     

Ni含量对Cu-xNi-3Ti-0.1Zr合金组织和性能的影响

采用真空熔炼并经均匀化退火、热轧、固溶、冷轧和时效处理工艺制备Cu-xNi-3Ti-0.1Zr(x=2、4、6)合金,通过X射线衍射仪、光学显微镜和扫描电镜对合金的析出相进行表征和分析。结果表明,Ni的加入能够显著提高合金的导电率,且对其硬度的影响也同样显著。Ni在Cu-xNi-3Ti-0.1Zr合金中主要以CuNiTi相存在;Ni的加入导致合金中大量CuNiTi相的析出,降低了基体中Ti的固溶度,使合金的晶格畸变程度降低,从而提高了合金的导电率。但随着Ti的析出,Ti对合金的强化效果减弱,从而导致合金的硬度降低。在本试验工艺下,Cu-xNi-3Ti-0.1Zr(x=2、4、6)合金在500 ℃时效的峰值硬度分别为295、231、201 HV0.5。     

Electrochemical Behavior of Novel Superelastic Biomedical Alloys in Simulated Physiological Media Under Cyclic Load

The aim of the present work was to study corrosion and electrochemical behavior of Ti-22Nb-6Ta and Ti-22Nb-6Zr (at.%) superelastic alloys under conditions which imitate the performance mode of target devices (bone implants), i.e., under cyclic load in simulated physiological solutions. Open circuit potential (OCP) measurements were carried out on wire specimens in Hank’s solution and artificial saliva at 37 °C with various strain values up to 1.5%. It is shown that at clinically relevant strain values (about 0.2%) the alloys exhibit OCP growth indicating their high stability and resistance to corrosion fatigue under these cycling conditions. At much higher strains (about 1%), fatigue crack initiation and propagation take place, however, the corresponding OCP variation indicates that the fracture process is significantly restrained by reversible martensitic transformation during cycling.