Ti6Al4V合金在Saline溶液中的微动腐蚀特性

采用液压高精度微动试验机,做了Ti6A l4V/Si3N4摩擦副在干态、蒸馏水和Saline溶液等3种介质中的微动腐蚀试验,用激光共焦扫描显微镜(LCSM)观察了磨痕表面形貌并测量了磨损体积。结果表明:蒸馏水和Saline溶液改变了微动运行区域;空气中的摩擦因数与磨损体积最大,Saline溶液中最小,3种介质中的摩擦因数与磨损体积均随位移增加而增加;载荷增加时,磨损体积增大而摩擦因数减小;较大位移时,腐蚀与磨损交互作用显著地加速了Ti6A l4V的材料流失;微动损伤主要表现为剥落与磨粒磨损共同作用。     

Ti6Al4V的微磨粒磨损研究

研究了医用Ti6Al4V合金在蒸馏水中的微磨粒磨损行为,考察了载荷、滑行距离、料浆浓度和转速对微磨粒磨损规律的影响,并对微磨粒磨损机制进行了讨论。结果表明:随载荷、滑行距离和料浆浓度的增加,Ti6Al4V合金的磨损量增加,磨损机制由三体磨损转变为混合磨损。     

Micro-drilling of Ti–6Al–4V alloy: The effects of cooling/lubricating

This paper presents a series of experimental investigations of the effects of various machining conditions [dry, flooded, minimum quantity lubrication (MQL), and cryogenic] and cutting parameters (cutting speed and feed rate) on thrust force, torque, tool wear, burr formation, and surface roughness in micro-drilling of Ti–6Al–4V alloy. A set of uncoated carbide twist drills with a diameter of 700 μm were used for making holes in the workpiece material. Both machining conditions and cutting parameters were found to influence the thrust force and torque. The thrust force and torque are higher in cryogenic cooling. It was found that the MQL condition produced the highest engagement torque amplitude in comparison to the other coolant–lubrication conditions. The maximum average torque value was obtained in the dry drilling process. There was no substantial effect of various coolant–lubrication conditions on burr height. However, it was observed that the burr height was at a minimum level in cryogenic drilling. Increasing feed rate and decreasing spindle speed increased the entry and exit burr height. The minimum surface roughness values were obtained in the flood cooling condition. In the dry drilling process, increased cutting speed resulted in reduced hardness on the subsurface of the drilled hole. This indicates that the surface and subsurface of the drilled hole were subject to softening in the dry micro-drilling process. The softening at the subsurface of drilled holes under different cooling and lubrication conditions is much smaller compared to the dry micro-drilling process.     

高速切削Ti6Al4V钛合金时切削温度的试验研究

应用硬质合金刀具对Ti6Al4V钛合金材料进行了高速车削和高速铣削试验,研究分析了干切削、空气射流及氮气射流条件下的切削温度变化情况。研究结果表明,氮气射流及空气射流条件下的切削温度明显低于干切削条件下的切削温度,而氮气射流条件下的钛合金高速切削温度则略低于空气射流条件下的切削温度。     

Ti6Al4V激光选区熔化成形悬垂结构的质量研究

为了减小成形误差,提高激光选区熔化成形复杂特征结构件的能力,实验采用Ti6Al4V金属粉末,设计了不同倾斜角度的悬垂结构模型,研究了倾斜角度、扫描策略对悬垂结构SLM成形质量的影响。结果表明：倾斜角度越小,悬垂面的边缘线宽度误差越大（>80μm）,表面粗糙度值越大（>20μm）,翘曲变形越严重;岛形随机扫描策略的整体成形质量要低于Z形正交扫描策略,但对不同角度的悬垂结构影响不同。结合QM-Meltpool监控系统,从熔池的角度分析了倾斜角度和扫描策略的影响,为悬垂结构SLM成形提供了参考依据。     

Ti6Al4V钛合金枪钻加工的切削力试验研究

钛合金在深孔加工过程中存在刀具磨损严重和加工表面质量差等问题。本文采用整体硬质合金单刃枪钻作为深孔加工刀具,通过对刀具结构的分析和对Ti6Al4V钛合金深孔钻削的切削力试验研究,得到工艺参数对切削力的影响规律,结合制孔的表面粗糙度,优化了钛合金枪钻加工工艺参数。同时,通过刀具的磨损分析得到了钛合金枪钻加工过程中刀具的主要磨损形式。     

A study on the tribological characteristics of duplex-treated Ti–6Al–4V alloy under oil-lubricated sliding conditions

The tribological characteristics of the polished, dimpled and over-coated dimpled specimens were investigated. Dimples were produced on a Ti–6Al–4V alloy specimen using a laser surface texturing (LST). A Cr-doped diamond-like carbon (DLC) film was deposited on a dimpled specimen using an unbalanced magnetron sputtering (UBMS). The effects of dimples and over-coated Cr-doped DLC film on the tribological characteristics were investigated by performing the friction tests against a Cr-plated steel pin. The test results showed that the over-coated dimpled specimen exhibited a lower friction coefficient and wear compared to those of the polished and dimpled specimens, which may be attributed to the storage of wear debris and high hardness. A model of the wear reduction mechanism of the specimens was discussed.     

Experimental Study on Cutting Forces and Surface Integrity in High-Speed Side Milling of Ti-6Al-4V Titanium Alloy

This article is concerned with the cutting forces and surface integrity in high-speed side milling of Ti-6Al-4V titanium alloy. The experiments were conducted with coated carbide cutting tools under dry cutting conditions. The effects of cutting parameters on the cutting forces, tool wear and surface integrity (including surface roughness, microhardness and microstructure beneath the machined surface) were investigated. The velocity effects are focused on in the present study. The experimental results show that the cutting forces in three directions increase with cutting speed, feed per tooth and depth of cut (DoC). The widths of flank wear VB increases rapidly with the increasing cutting speed. The surface roughness initially decreases and presents a minimum value at the cutting speed 200 m/min, and then increases with the cutting speed. The microstructure beneath the machined surfaces had minimal or no obvious plastic deformation under the present milling conditions. Work hardening leads to an increment in micro-hardness on the top surface. Furthermore, the hardness of machined surface decreases with the increase of cutting speed and feed per tooth due to thermal softening effects. The results indicated that the cutting speed 200 m/min could be considered as a critical value at which both relatively low cutting forces and improved surface quality can be obtained.     

选择性激光熔化成形TC4钛合金开裂行为及其机理研究

裂纹是选择性激光熔化(Selective laser melting, SLM)成形Ti6-Al-4V(TC4)钛合金过程中最常见、破坏性最大的一种缺陷。采用逐行交替的扫描策略制备TC4钛合金试样,利用扫描电子显微镜及X射线能谱分析等检测方法,研究SLM成形TC4钛合金过程中裂纹的开裂行为及其形成机理。结果表明,SLM成形TC4钛合金所产生的裂纹为冷裂纹,具有典型的穿晶开裂特征。采用逐行交替扫描策略成形的TC4钛合金,其组织为网篮状马氏体组织。SLM成形过程中高温度梯度导致制件内部存在较高的残余应力,抗裂强度较差的马氏体组织在残余应力的作用下而产生裂纹,粗大的裂纹最终分解为较小的裂纹而终止扩展。进一步分析认为,通过调整成形工艺参数,可以改变制件组织,同时削弱残余应力,从而达到减弱或消除裂纹的目的。     

Ti6Al4V合金整体零件的两步热等静压近净成形工艺探究

针对热等静压整体成形高温合金零件容易产生部分区域致密度较低、整体性能不均一的问题,提出了热等静压两步成形方法,在较低的温度和压力作用下成形为不带连通孔隙的原始零件,去除控形模具后用合适的温度压力作用使不致密区域致密,提高零件均一性。以Ti6Al4V粉末材料为例,使用有限元模拟和实验测试相结合的方法,确定了两步成形法的工艺参数,并成形了叶盘零件。SEM结果显示：热等静压两步法成形的零件组织由板条状α+β相组成,原始颗粒边界消失,不连通孔隙闭合。断口形貌显示:在合适的两步成形工艺参数加载下,粉末颗粒冶金结合牢固, 不再成为裂纹起始处,拉伸强度提高。两步法拉伸性能略优于常规热等静压拉伸性能,性能达到同规模锻件水平。     

硬质合金刀具高速切削Ti6Al4V合金时扩散磨损的数值模拟

应用通用商业有限元软件Deform-2D,对航空用钛合金Ti6Al4V进行了不同冷却润滑条件下的正交切削有限元模拟。在参考已有刀具扩散磨损率模型的基础上,利用有限元模拟出的刀具/工件接触区的切削温度与相对滑动速度等基本变量,对高速切削钛合金Ti6Al4V时的WC-Co类硬质合金刀具前刀面的扩散磨损率进行了预测,进而分析了切削介质的冷却与润滑作用对刀具扩散磨损率的影响。研究结果表明:切削介质的润滑作用对刀具前刀面的扩散磨损率具有较大影响,而切削介质的冷却作用则对刀具前刀面扩散磨损率无显著影响。     

Coatings on Ti6Al4V as palliatives for fretting fatigue in cryogenic environment

Fretting, also known as small oscillatory sliding motion, can lead to catastrophic failure in industrial applications. To reduce the damage caused by fretting increasing use has been made of surfaces treatments. These treatments result in multilayer solids (coating, diffusion layer…). The understandings of fretting fatigue have enabled us to evaluate the fretting resistance of homogeneous and coated materials. The experimental part is associated to a numerical one to obtain cracking threshold of the coated materials to obtain lifetime evaluation. This present study seeks to compare the behaviour of bare substrate and coated substrate submitted to fretting and evaluates the improvement of the fretting fatigue strength.     

FE modeling of burr size in high- speed micro-milling of Ti6Al4V

This article is focused on the finite element modeling of burr formation in high speed micromilling of Ti6Al4V. Studies show that the burr produced at the up milling side at the exit of the micromilling tool is the biggest among burrs at other locations. Therefore, side exit burr at the up milling side has been modeled through finite element modeling. Johnson cook material constitutive model has been implemented in the formulation of burr formation. Experimental work has been performed to validate the developed model. It is found that the burr height and width obtained from the simulation has been validated experimentally with a maximum error of 15%. It was found from the literature review that the cutting speed is the factor, which influences the burr formation. Therefore, the model has been further extended to study the effect of cutting speed on the burr size. A maximum tool rotation of 200,000 rpm was considered with a tool diameter of 500 μm. It is predicted from the simulation that, the burr size was reduced by 96% (both height and width) if cutting tool speed was increased from 10,000 to 200,000 rpm. Therefore, it is concluded that the cutting speed is the major factor to reduce the burr size in micromilling of Ti6Al4 V. This study shows that the high speed micromachining center can be helpful in producing the micro parts with less or no burrs. It is expected that further extension of the burr formation model can minimize the burr size to zero/near zero size.     

Ti6Al4V钛合金枪钻加工轴线直线度误差试验研究

针对某大型飞机轴类零件深孔加工粗糙度差、轴线偏差和切屑不易控制等问题,进行了Ti6Al4V钛合金枪钻加工试验,测试了枪钻加工深孔的轴线偏差、孔径误差和加工表面完整性,并分析了产生偏差的主要原因。从而优化了Ti6Al4V钛合金枪钻加工工艺参数,得到了Ti6Al4V钛合金17深孔枪钻加工最佳工艺参数,最终实现了860mm深孔的枪钻加工,使得最终综合误差控制在0.2mm以内,表面粗糙度Ra小于1.6μm。     

New insights into wear of Ti6Al4V by ultra-high molecular weight polyethylene under water lubricated conditions

Laboratory studies indicate that sliding Ti6Al4V against soft ultra-high molecular weight polyethylene (UHMWPE) pins produces severe damage to the titanium and the lubricant (water) changes colour suggesting chemical change. Blackening of periprosthetic tissues associated with titanium wear debris was also observed in clinical investigations. To increase scientific understanding of the mechanism involved, systematic characterisation work has been conducted employing grow discharge spectrometry (composition), scanning electron microscopy (wear morphology) and cross-sectional transmission electron microscopy (phase identification). Experimental results show that hydrogen may play an important role in promoting the formation of abrasive particles in the Ti6Al4V/UHMWPE tribosystem under water lubricated conditions. The observed abnormal wear of Ti6Al4V by soft UHMWPE can be to a large extent attributed to hydrogen evolution and formation of titanium hydride. Based on experimental results and discussion, a hydrogen-assisted wear mechanism is proposed.     

Unlubricated gross slip fretting wear of metallic plasma-sprayed coatings for Ti6Al4V surfaces

Plasma-sprayed Al–bronze or CuNiIn coatings are often applied to protect against fretting wear and extend the operational life of Ti-alloy compressor blades in turbine engines. In order to develop a fundamental understanding of how these coating systems perform under gross slip fretting conditions, bench level fretting wear tests were conducted at room temperature to simulate cold engine startup. Alternative coatings such as plasma-sprayed molybdenum and nickel were also evaluated because of their potential for reducing fretting wear under certain simulated engine conditions. The combination of scanning electron microscopy (SEM), surface profilometry, surface chemistry (EDS), and friction analysis were used to study coating performance and evaluate the interfacial wear mechanisms. In this study, it was determined that all coatings caused significant damage to the mating Ti6Al4V surfaces and that the wear mechanisms were all similar to those of the uncoated baseline case.     

Several plasma diffusion processes for improving wear properties of Ti6Al4V alloy

Different kinds of diffusion processes, plasma nitriding, oxidizing and oxynitriding as of a combination of other two, have been applied to Ti6Al4V alloy to evaluate the effect of treatment times (1 and 4 h) and temperatures (650 and 750 °C) on wear properties of the alloy. It was observed that a hard modified layer was produced on the surface of the alloy after each diffusion process. While TiN and Ti₂N phases form in the modified layer with plasma nitriding, mainly TiO₂ phase forms after plasma oxidizing treatment. The wear tests performed at different normal loads showed that all treated samples, except for nitrided and oxidized at 650 °C for 1 h, exhibited higher wear resistance than untreated Ti6Al4V alloy. The plasma nitrided samples showed adhesive wear. On the other hand, while the plasma oxidizing samples displayed adhesive wear at lower loads, wear mechanism changed to abrasive wear as the load increased because the oxide film which covers the surface was broken during the sliding at higher loads.     

航空钛合金Ti6Al4V微细铣削加工数值模拟与试验研究

根据实际微细铣削加工方法,采用DEFORM软件建立螺旋立铣刀铣削加工分析模型,利用该模型分析硬质合金刀具铣削加工航空用钛合金Ti6Al4V过程中的铣削力变化,在相同条件下进行铣削加工试验。试验结果表明:随着铣削的进行,刀具与切屑逐步接触,各个铣削方向切削力逐渐增加;随着铣削的进行,切削厚度逐渐减小、铣削温度升高、工件材料力学性能和铣削力开始降低;铣削深度、单齿进给量及铣削速度对铣削力均有不同程度的影响,其中单齿进给量影响最大。     

Fretting of CoCrMo and Ti6Al4V alloys in modular prostheses

Implantation of a total hip replacements (THR) is an effective intervention in the management of arthritis. Modularity at the taper junction of THR was introduced in order to improve the ease with which the surgeon could modify the length of the taper section and the overall length of the replacement. Cobalt chromium (Co–28Cr–6Mo) and titanium (Ti–6Al–4V) alloys are the most commonly used materials for the device. This study investigates the fretting behaviour of both CoCr–CoCr and CoCr–Ti couplings and analyses their damage mechanisms. A reciprocating tribometer ball on plate fretting contact was instrumented with in situ electrochemistry to characterise the damage inflicted by tribocorrosion on the two couplings. Fretting displacements amplitudes of 10, 25 and 50?μm at an initial contact pressure of 1?GPa were assessed. The results reveal larger metallic volume loss from the CoCr–CoCr alloy compared to the CoCr–Ti alloy, and the open circuit potential indicates a depassivation of the protective oxide layer at displacement amplitudes >25?μm. In conclusion, the damage mechanisms of CoCr–CoCr and CoCr–Ti fretting contacts were identified to be wear and fatigue dominated mechanisms respectively.     

Slurry abrasion response of surface engineered Ti6Al4VELI

Titanium alloys, by virtue of their outstanding combination of properties, continue to evolve as direct replacements for steels in offshore production systems to meet the challenging offshore application conditions. However, the wider use of titanium and its alloys is frequently retarded by their reputation for poor tribological behaviour. It is because of this simple engineering scenario that comparative tribological behaviour of surface engineered Ti6Al4VELI in abrasive slurry has been evaluated to identify treatments capable of improving its wear behaviour. To best simulate potential application conditions, sliding wear tests were carried out using a block-on-wheel test configuration in abrasive mud slurry. The wear volumes lost from the surface engineered Ti6Al4VELI test blocks ranged from negligibly small for substrates plasma sprayed with either WC–Co, Ni–Cr or Mo, to approximately twice that measured for a steel test block in the cases of untreated, shot peened, electroless Ni plated and anodised Ti6Al4VELI. Hard chrome plated material and thermochemically treated material demonstrated a certain degree of wear, which however, was significantly less than that found for the steel block.