The Tribological Behavior of a Ti-46Al-2Cr-2Nb Alloy Under Liquid Paraffine Lubrication

The tribological behavior of a Ti-46Al-2Cr-2Nb alloy prepared by hot-pressed sintering was investigated under liquid paraffine lubrication against AISI 52100 steel ball in ambient environment and at varying loads and sliding speeds. For comparison, the tribological behavior of a common Ti-6Al-4V alloy was also examined under the same testing conditions. The worn surfaces of the two alloys were analyzed using a scanning electron microscope. The friction coefficient of the Ti-46Al-2Cr-2Nb alloy in the range of 0.13–0.18 was significantly lower than that of the Ti-6Al-4V alloy (0.4–0.5), but comparable to that under dry sliding, which indicated that TiAl intermetallics could be more effectively lubricated by liquid paraffine than titanium alloys. Applied load and sliding speed have little effect on the friction coefficient of the Ti-46Al-2Cr-2Nb alloy. The wear rate of the Ti-46Al-2Cr-2Nb alloy was about 45–120 times lower than that of Ti-6Al-4V alloy owing to Ti-6Al-4V alloy could not be lubricated effectively. The wear rate of the Ti-46Al-2Cr-2Nb alloy increased with increasing applied load, but decreased slightly at first and then increased with increasing sliding speed. The wear mechanism of the Ti-46Al-2Cr-2Nb intermetallics under liquid paraffine lubrication was dominated by main plowing and slight flaking-off, but that of the Ti-6Al-4V alloy was plastic deformation and severe delamination.     

Fretting wear of Ti-48Al-2Cr-2Nb

An investigation was conducted to examine the wear behavior of gamma titanium aluminide (Ti-48Al-2Cr-2Nb in atomic percent) in contact with a typical nickel-base superalloy under repeated microscopic vibratory motion in air at temperatures from 296–823 K. The surface damage observed on the interacting surfaces of both Ti-48Al-2Cr-2Nb and superalloy consisted of fracture pits, oxides, metallic debris, scratches, craters, plastic deformation, and cracks. The Ti-48Al-2Cr-2Nb transferred to the superalloy at all fretting conditions and caused scuffing or galling. The increasing rate of oxidation at elevated temperatures led to a drop in Ti-48Al-2Cr-2Nb wear at 473 K. Mild oxidative wear was observed at 473 K. However, fretting wear increased as the temperature was increased from 473–823 K. At 723 and 823 K, oxide disruption generated cracks, loose wear debris, and pits on the Ti-48Al-2Cr-2Nb wear surface. Ti-48Al-2Cr-2Nb wear generally decreased with increasing fretting frequency. Both increasing slip amplitude and increasing load tended to produce more metallic wear debris, causing severe abrasive wear in the contacting metals.     

粉末冶金Ti-22Al-25Nb合金的真空热压烧结工艺

以气雾化法获得的Ti-22Al-25Nb（at.%）预合金粉末为初始原料,采用真空热压烧结工艺方法制备组织致密、成分均匀的粉末冶金Ti-22Al-25Nb合金。应用有限元软件MSC.Marc对Ti-22Al-25Nb（at.%）预合金粉末的致密化过程进行数值模拟,分析了温度和压力对Ti-22Al-25Nb粉末致密化过程的影响,揭示了粉末相对密度随温度和压力变化的规律,得到优化的烧结工艺参数,以指导热压实验烧结。通过热压烧结实验制备了组织致密、成分均匀的Ti-22Al-25Nb合金,发现1 050 ℃/35 MPa/1 h条件下烧结的合金具有最优的室温和650 ℃高温综合力学性能。     

Investigations on corrosion resistance behavior in micro-milling of Ti-6Al-4V and Ti-6Al-7Nb alloy: a comparative study

Journal of Mechanical Science and Technology - We compared the corrosion resistance behavior of Ti-6Al-4V and Ti-6Al-7Nb alloy in micro-milling operation. The influence of parameters such as...     

粉末冶金Ti-22Al-25Nb合金的放电等离子烧结工艺数值模拟与实验研究

选用Ti-22Al-25Nb预合金粉末为实验初始原料,采用放电等离子烧结工艺（SPS）制备组织致密的粉末冶金Ti-22Al-25Nb合金。采用MSC.Marc有限元软件对SPS过程中粉末的致密化过程进行了数值模拟,分析了烧结温度、保温时间和烧结压力对粉末致密化过程的影响,揭示了粉末相对密度随烧结温度、保温时间和烧结压力的变化规律。根据模拟结果,在950~1 200 ℃温度区间、50 MPa烧结压力和10~20 min保温时间的条件下,完成系列SPS烧结实验,制备获得Ti-22Al-25Nb合金。系统分析了50 MPa/10 min烧结条件下温度对Ti-22Al-25Nb合金的相对密度、显微组织和力学性能的影响,揭示了烧结合金的断裂机制。实验结果表明烧结合金在950 ℃/50 MPa/10 min条件下具有最优的综合力学性能,延伸率和屈服强度分别达到8.14%和691.04 MPa。     

Superplastic-like forming of Ti-6Al-4V alloy

Superplastic forming of titanium alloys is used for producing structural components, since it is an effective way to manufacture complex-shaped parts in a one-step operation. An optimized sheet-forming process has been designed incorporating a non-isothermal heating system to establish a fast forming process. This work sought to expand the advantages of the technology to the forming of Ti-6Al-4V alloy at 800 °C and shorter cycle time. The minimum thicknesses area was found at the outward corners, showing a maximum percent thinning of 54 %. In addition to stress variations, the cracks resulting from hot drawing and the oxidation on the sheet surface are the other reasons leading to thickness reduction. From the oxidization behavior of Ti-6Al-4V alloy, it was revealed that the decrease in forming temperature from 900 to 800 °C significantly reduced the formation rate of oxide film on the sheet surface. The study also showed that the main microstructure evolution of Ti-6Al-4V alloy under these conditions was recrystallization.     

Electrochemical corrosion property of nanostructure layer of Ti-5Al-2Sn-2Zr-4Mo-4Cr titanium alloy

Ti-5Al-2Sn-2Zr-4Mo-4Cr titanium alloy was nanocrystallized with supersonic fine particles bombarding (SFPB). The microstructure features of nanocrystalline layer were determined by XRD, TEM, and microhardness tester. The electrochemical corrosion properties of the surface of original sample and the nanocrystallized sample surface were tested by CHI660 tester. That random crystallographic oriented particles (average grain size of 16 nm) were observed in the top surface layer of Ti-5Al-2Sn-2Zr-4Mo-4Cr titanium alloy, which could be attributed to the surface nanocrystallization. The electrochemical corrosion results show that the impedance of the sample nanolayer is reduced after SFPB with 30 min, and the corrosion resistance is lower than the original sample. The residual internal stress from the process of SFPB is one of the main factors to decrease the nanolayer corrosion resistance of Ti-5Al-2Sn-2Zr-4Mo-4Cr titanium alloy. However, the corrosion resistance is significantly recovered after stress relief annealing with 250–350 °C.     

The corrosion-wear behaviour of thermally oxidised CP-Ti and Ti-6Al-4V

The use of commercial purity titanium (CP-Ti) and Ti-6Al-4V alloys in bio-medical implant applications has been limited by their poor resistance to surface degradation processes. In this paper the corrosion-wear behaviour of untreated and thermally oxidised CP-Ti and Ti-6Al-4V have been compared. Oxidation of both alloys at 625 °C for 36 h resulted in the formation of an exterior layer of TiO₂ (rutile) that had a hardness ∼1000 HV. Corrosion-wear tests were made in reciprocation sliding contact with an α-Al₂O₃ ball immersed in physiological saline (0.89% NaCl) at room temperature. The oxidation treatment retarded the corrosion-wear of both CP-Ti and Ti-6Al-4V. For the untreated alloys, surface damage was dominated by micro-asperity shearing which resulted in rapid wear. Corrosion-wear of the oxidised materials was slower but more complex. The exterior TiO₂ layer formed on the oxidised Ti-6Al-4V alloy provided little protection, it was rapidly removed during the first 60 min of testing, by a process involving interfacial fracture. Conversely, the TiO₂ layer, albeit thinner, provided protection for the oxidised CP-Ti. Here, the layer becomes smoothly worn by a process that is proposed to be caused by the mechanical dissociation of the TiO₂-layer. For both oxidised titanium alloys the hardened oxygen diffusion zone (ODZ), formed beneath the TiO₂ layer, provided good protection from corrosion-wear. In both cases the ODZ was smoothly worn by a combination of abrasion and corrosion-wear processes. The latter process, termed Type I corrosion-wear, involves the repetitive mechanical degradation of the passive film that forms through aqueous corrosion. However, this is a relatively slow process.     

Corrosive Wear and Mechanical Properties of Ni/Al2O3 Micro- and Nanoparticulates-Reinforced Coatings on Ti-6Al-4V Alloy

Nanocomposite coatings can endow a plated surface with various properties such as wear resistance, high-temperature corrosion protection, oxidation resistance, and self-lubrication. This work studies the corrosion and corrosive wear resistance of electroplated nickel nanocomposite coatings on Ti-6Al-4V alloy in a Hank's solution, adding various concentrations of an Al₂O₃ powder in plating solution, with particle diameters of 20–30 nm and 1 μm for comparisons. The experimental results showed that the content of Al₂O₃ incorporated into the electroplated nickel composite coating increased with the concentration of Al₂O₃ powder in the electroplating solution, and increasing the surface hardness, corrosion, and corrosive wear resistance of electroplated nickel micro- and nanocomposite coatings caused smearing of the nodule boundary and elimination of voids in the deposits. The Al₂O₃ nanoparticulates were embedded and distributed more uniformly than the Al₂O₃ microparticulates in the nickel matrix after a heat treatment of 400°C, producing a more continuous and dense coated composite layer on the Ti-6Al-4V substrate. This phenomenon is responsible for the Ni/Al₂O₃ composite coating with superior surface hardness, providing high corrosion resistance and corrosive wear protection to the Ti-6Al-4V alloy substrate in Hank's solution.     

Tribological Behaviour of Orthopaedic Ti-13Nb-13Zr and Ti-6Al-4V Alloys

The aim of this study is to compare the tribological behaviour of novel orthopaedic implant alloy Ti-13Nb-13Zr with that of the standard Ti-6Al-4V ELI alloy, available in four different microstructural conditions produced by variations in the heat treatments. The friction and wear tests were performed by using a block-on-disc tribometer in Ringer’s solution at ambient temperature with a normal load of 20–60 N and sliding speed of 0.26–1.0 m/s. It was found that variations in microstructures produced significant variations in the wear resistance of Ti-6Al-4V ELI alloy. The wear losses of materials solution treated (ST) above the β transus temperature are significantly lower compared with those of materials ST in the (α + β) phase field and are almost insensitive to applied load and sliding speed. Wear loss of the (α + β) ST Ti-6Al-4V ELI alloy continuously increased as applied load was increased and was highest at the highest sliding speed. The Ti-6Al-4V ELI alloy in all microstructural conditions possesses a much better wear resistance than cold-rolled Ti-13Nb-13Zr alloy. Friction results and morphology of worn surfaces showed that the observed behaviour is attributed to the predominant wear damage mechanism.     

基于变弹性模量的Ti-6Al-4V板材五点弯曲回弹预测

Ti-6Al-4V钛合金材料在弯曲成形过程中会产生较大的回弹,其弹性模量对回弹影响较大,但以往研究均未考虑材料塑性应变变化过程中弹性模量的变化。以Ti-6Al-4V钛合金为对象,进行了材料的单轴拉伸实验和循环加载-卸载实验,以揭示材料各向异性参数及材料弹性模量随塑性应变变化的规律,在此基础上建立了Ti-6Al-4V钛合金变弹性模量数学模型。基于YLD2000-2D屈服准则及变弹性模量和Mises各向同性两种不同的本构模型,对常温下Ti-6Al-4V钛合金板材的五点弯曲过程进行了数值模拟,为了验证数值模拟结果,进行了常温下Ti-6Al-4V板材的五点弯曲实验,结果显示,前者显著提高了Ti-6Al-4V钛合金弯曲回弹预测精度,预测精度相比后者提高了31.18%。     

Electric hot incremental forming of Ti-6Al-4V titanium sheet

Electric hot incremental forming of metal sheet is a new technique that is feasible and easy to control to form hard-to-form sheet metals. In the present study, Ti-6Al-4V titanium sheet was studied because it was wildly used in the aeronautics and astronautics industries. Although Ti-6Al-4V titanium can be well-formed in high temperature, the surface quality is a problem. In order to enhance the surface quality, it is very important to select the proper lubricant. At the same time, because Ti-6Al-4V titanium has a lively chemical property, it is very important to choose a processing temperature range in order to acquire excellent plastic property and to prevent oxidation. Various lubricants were selected in processing to compare the effect, and some workpieces were formed at different temperatures to find the best forming temperature. The results show that using the lubricant film of nickel matrix with MoS₂ self-lubricating material, Ti-6Al-4V titanium workpiece was formed with high surface quality, and the optimum thickness of composite coating is 20 μm for Ti-6Al-4V titanium sheet of 1.0-mm thickness. In fact, the lubricant film also does help to prevent oxidation of Ti-6Al-4V titanium sheet. The appropriate temperature range of Ti-6Al-4V forming with slightly oxidized is 500–600°C in processing, and the maximum draw angle formed in this range was 72°.     

Comparative study on tribology and microhardness of laser synthesized Ti-Al2O3/Zn coatings on Ti-6Al-4V alloy

ABSTRACT

The study of laser cladding of 90Ti-10Al₂O₃, 90Ti-8Al₂O₃-2Zn and 90Ti-4Al₂O₃-6Zn coatings onto Ti-6Al-4V alloy, with intention to produce defect-less, high microhardness and wear resistant coating was carried out. The coatings were deposited onto Ti-6Al-4V alloy at 900 W laser power and 0.6 m/min laser scan speed. Microstructures and phase constituents of the developed coatings were investigated by using a scanning electron microscope (SEM) and X-ray diffractometer correspondingly. Vickers microhardness tester and pin-on-disk tribometer were employed to characterize microhardness and wear behaviour of the Ti-Al₂O₃/Zn coatings respectively. SEM was also used to examine the worn track. It was observed that 90Ti-10Al₂O₃ coating yielded optimal microhardness along with maximal wear resistance in comparison to the other coatings and Ti-6Al-4V alloy. It has been established that laser cladding of Ti-Al₂O₃ coating with Zn contents on Ti-6Al-4V alloy alleviates the formation of cracks, however, microhardness and wear properties are negatively affected.     

Enhanced wear resistance of Ti-5Al-2Nb-1Ta orthopaedic alloy by nitrogen ion implantation

The tribological properties of nitrogen implanted Ti-5Al-2Nb-1Ta orthopaedic alloy was studied by performing lubricated pin on disc tests against ultra high molecular weight polyethylene pins. The results were interpreted on the basis of friction coefficient, wear volume loss and by characterising the wear debris to understand the wear mechanism. The results indicated a decrease in wear rate for implanted samples. Detailed investigations of the dose dependence on wear performance were carried out. The friction and wear data show a clear transition in wear modes between implanted and unimplanted alloys. The wear debris confirms the presence of titanium oxide and titanium oxynitride phases for untreated and nitrogen implanted alloy.     

Investigation on diffusion wear during high-speed machining Ti-6Al-4V alloy with straight tungsten carbide tools

During high-speed machining Ti-6Al-4V alloy, high-temperature at the tool–chip interface and the concentration gradient of chemical species between tool material and workpiece material support the activation of diffusion process, and therefore the crater wear forms on the rake surface of the cutting tool at a short distance from the cutting edge. In this paper, the diffusion analysis was theoretically proposed. The constituent diffusion at the contact interface between tool material and Ti-6Al-4V alloy at high-temperature environment, the crater wear on the rake surface of the tool, and the chips collected from high-speed milling Ti-6Al-4V alloy with straight tungsten carbide tools were analyzed by the scanning electron microscope with energy dispersive X-ray spectroscopy. The constituents inside the tool could diffuse into the workpiece and the diffusion layer was very thin and close to the interface. Compared with the diffusion of tungsten and carbon atoms, the pulling out and removing of the tungsten carbide (WC) particles due to cobalt diffusion dominated the crater wear mechanism on the rake surface of the cutting tool.     

摩擦速度对Ti-6Al-4V合金腐蚀磨损的影响

采用腐蚀摩擦磨损试验机,进行了Ti合金/Al2O3摩擦副在林格溶液介质中的腐蚀磨损试验。试验在改变摩擦速度时对材料的耐腐蚀性能及钝化膜的再生能力进行了探讨。结果表明:摩擦破坏了Ti合金表面的钝化膜使电流密度上升。电流密度随摩擦速度的增大而增大。但是,钝化膜再生能力随摩擦速度的增大而减小。摩擦速度影响到磨损形态,速度小时主要以磨粒磨损形态为主,随着速度的增大磨损形态将过渡为腐蚀磨损和粘着磨损。     

Finite element modeling of machining of hydrogenated Ti-6Al-4V alloy

The present study is undertaken to investigate the effect of hydrogen on the cutting performance of Ti-6Al-4V alloy by FEM. Mechanical behaviors of hydrogenated Ti-6Al-4V alloy are studied at elevated temperatures and high strain rates with split Hopkinson pressure bar. The Johnson–Cook model was developed combined with quasi-static experimental data. A numerical model is developed to simulate the cutting process. The results of the experiments and simulations agreed well. The results demonstrate that the presence of hydrogen has a significant effect on the cutting forces and temperature, and the cutting forces and temperature increase first and then decreased gradually with the increasing of hydrogen contents. The simulation results show that titanium alloys with 0.3% hydrogen have better machinability at high cutting speed.     

Tribological behaviour of plasma nitrided Ti-5Al-2Nb-1Ta alloy against UHMWPE

A detailed study has been made on the wear behaviour of untreated and plasma nitrided Ti-5Al-2Nb-1Ta orthopaedic alloy against ultra high molecular weight polyethylene (UHMWPE) using pin on disc tribometer under lubricated conditions. The effects of nitriding temperature and nitriding time on the basis of the evolution of the wear volume loss and friction coefficient were investigated. The wear resistance of the plasma nitrided alloys increased considerably when compared to the untreated alloy. The wear debris identified using X-ray diffraction measurements indicated the formation of titanium oxide and titanium oxynitride particles. The wear rate was found to increase with increase in load and sliding velocity.     

Assessment of the machinability of Ti-6Al-4V alloy using the wear map approach

The high strength to density ratio of titanium alloys coupled with excellent corrosion resistance even at elevated temperatures make them ideal for aerospace applications. Moreover, the biocompatibility of titanium also enables its widespread use in the biomedical and food processing industries. However, the difficulty in machining titanium and its alloys along with the high cost of its extraction from ore form presents a major economic constraint. In the context of machining economics, the wear map approach is very useful in identifying the most suitable machining parameters over a feedrate–cutting velocity plane. To date, wear maps have only been prepared for the machining of ferrous alloys. In this article, a review of the machinability of Ti-6Al-4V alloy is presented with emphasis on comparing the wear performance of various tool materials. In addition, a new wear map for Ti-6Al-4V alloy is presented based on unified turning tests using H13A grade carbide inserts. This wear map can be used as a guide in the selection of cutting variables that ensure the least tool wear rates. This article contrasts the occurrence of a safety zone in the case of machining steels to that of an avoidance zone for Ti-6Al-4V alloy.     

Ti-6Al-4V钛合金板与304L不锈钢网的扩散焊

分别在800℃、825℃、850℃焊接温度、30 m in保温时间,3 MPa焊接压力下,进行Ti-6A l-4V钛合金板与304L不锈钢网的真空扩散焊接。对接头组织结构与化学元素扩散进行了扫描电镜与能谱分析,并测试了接头的剪切强度。结果表明:不添加中间过渡层金属,可以成功地实现钛合金板与不锈钢网的扩散焊接,并使接头的剪切强度达到90 MPa以上。不锈钢网中的Fe、N、iCr扩散并固溶到钛合金中,稳定了β相,使钛合金在一定深度上,其组织由原来的α+β双相结构转变为单相的β相。不锈钢中的Cr,由于钛合金中Ti的扩散进入,而在界面发生了上坡扩散现象。这种Cr在不锈钢一定深度内的富集,形成窄长的富Cr区域,冷却后转变为硬脆的σ相。但在焊接接头中没有发现明显其它的金属间化合物或氧化物相的生成,使得接头的机械性能得到了很好的保证。