The use of nickel graphite composite coatings for the mitigation of gross slip fretting wear on Ti6Al4V interfaces

In metallic contacts, surface oxides, adhesion, and material transfer play a primary role in the initial stages of fretting wear degradation. Given this behavior, the focus of this study was to mitigate fretting wear within Ti6Al4V contacts at room temperature and 450 °C with the use of thermally sprayed nickel graphite composite coatings with 5–20% graphite. The results show that the embedded graphite particles reduced the friction of the nickel thermal sprayed coatings during both low and high temperature fretting wear experiments. Friction and wear mechanisms are discussed with correlations of contact chemistry, morphology, and mechanical performance. Wear on the mated Ti6Al4V surfaces was reduced by the formation of uniform transfer films that were identified as graphitic based at room temperature and NiO based at 450 °C.     

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.     

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.     

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。     

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.     

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。     

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.     

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.     

Ti6Al4V/WC-Co干摩擦性能研究

利用Optimal SRV高温摩擦磨损试验机,研究干摩擦条件下钛合金(Ti6Al4V)对硬质合金(WC-Co)的摩擦学性能.研究了载荷、温度与滑动速度对摩擦过程的影响,通过磨损区微观形貌表征分析了磨损机理.结果表明:Ti6Al4V与WC-Co的摩擦系数波动剧烈,产生了严重的黏滑摩擦,且随着载荷、温度与滑动速度的增加,黏...     

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。     

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.     

电场对WC-Co/Ti6Al4V摩擦磨损性能的影响

为了研究电场对摩擦副摩擦磨损性能的影响,在自行设计的高速摩擦磨损试验装置上,进行了WC-Co/Ti6Al4V摩擦副的摩擦磨损试验。结果表明：断开摩擦副热电回路可以有效地减小热电流对WC-Co/Ti6Al4V摩擦副摩擦磨损的影响,静电冷却环境下形成的强电场的效果更加明显,在抑制摩擦副磨损的同时还可以改善
Ti6Al4V磨损表面质量。通过扫描电镜及EDS能谱分析可知,静电冷却条件下的列宾捷尔效应削弱了钛合金的黏着能力,从而有效地减小了WC-Co的黏着磨损;WC-Co在高速摩擦时主要以黏着磨损、氧化磨损为主,同时伴有微裂纹的产生。
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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。     

Fretting behavior of shot peened Ti-6Al-4V under slip controlled mode

Fretting tests of shot peened Ti-6Al-4V were conducted under slip controlled mode using a dual actuator test setup which could apply an independent pad displacement at a given applied bulk stress. Fretting regime was identified based on the hysteresis loop of tangential force versus relative slip range and the evolution of tangential force. Fretting regime changed from partial slip to mixed slip and then to gross slip with increasing relative slip range, and the transition from mixed to gross slip occurred at a relative slip range of ∼50 μm regardless of the applied bulk stress magnitude for both shot peened and unpeened specimens. Fretting fatigue life initially decreased as the relative slip range increased and reached to a minimum value, and then increased with an increase of the relative slip range due to the transition in fretting regime from mixed slip to gross slip. Shot peened specimens had longer fatigue life than unpeened specimens at a given relative slip range, but the minimum fatigue life was at the same value of the relative slip range for both shot peened and unpeened specimens. The relationship between relative slip and fatigue life was also found to be independent of the applied bulk stress level. Further, tangential force was directly related to relative slip and this relationship was independent of other fretting variables.     

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。     

基于用户材料二次开发的Ti6Al4V切削加工三维有限元模拟

采用Ti6Al4V在大应变、高应变率和高温条件下的流动应力模型,通过用户材料二次开发写入Deform-3D材料库中,在此基础上开展了不同参数条件下Ti6Al4V高速车削加工的热—力耦合有限元模拟试验,对切削力、切削温度和刀具磨损随切削参数的变化进行深入研究。与试验结果的比较表明,采用二次开发的用户材料模型,可以提高切削力仿真精度,实现对整个切削过程的更准确预测。对切削力影响由大到小依次是背吃刀量、进给量、切削速度。从切削力的角度来选择切削参数时,优先选取较高的切削速度,其次考虑较大的进给量。对切削温度影响最大的是切削速度,且切削速度与切削温度呈正比关系,背吃刀量影响最小。从切削温度角度选择切削参数时,应选用较大的进给量和背吃刀量,适当减小切削速度。切削速度对刀具磨损的影响最大,所以,为了延长刀具的使用,必须合理地选择切削速度。     

脂肪醇对Ti6Al4V/钢摩擦副摩擦磨损性能的影响

采用SRV型摩擦磨损试验机分别考察了Ti6Al4V/钢摩擦副在多种脂肪醇润滑下的摩擦磨损性能。结果表明,与液体石蜡相比,碳链长度小于碳8的脂肪醇作为Ti6Al4V/钢摩擦副的润滑剂表现出良好的润滑性能,其润滑机制是在Ti6Al4V磨损表面形成吸附膜。载荷和频率明显影响Ti6Al4V/钢摩擦副在脂肪醇润滑下的摩擦磨损行为和摩擦磨损机制:当载荷较小时,Ti6Al4V磨损表面主要发生轻微的擦伤;随着载荷增加,Ti6Al4V磨损表面擦伤严重并在更高载荷下发生较为严重犁沟和塑性变形。     

Increasing the tribological performances of Ti–6Al–4V alloy by forming a thin nanoporous TiO2 layer and hydroxyapatite electrodeposition under lubricated conditions

In this study, comparative investigation of (i) untreated Ti–6Al–4V alloy, (ii) nanoporous thin TiO₂ layer formed by controlled anodic oxidation and (iii) electrodeposited hydroxyapatite coatings into porous oxide layer was carried out for evaluation of sliding-wear performances in a bio-simulated environment. Wear mechanisms, wear volumes and friction coefficients of the three types of surfaces under lubricated conditions in a bio-simulated solution were recorded and analyzed. The results presented herein show that, under the investigated tribocorrosion conditions (under reciprocating sliding), both surface treatments applied have improved the wear resistance and friction coefficients as compared to the untreated Ti–6Al–4V alloy surface.