Relation of normal load with test temperature at mild−severe wear transition state for Mg−Gd−Y−Zr alloy

The wear behavior and mild−severe(M−S)wear transition of Mg−10Gd−1.5Y−0.4Zr alloy were investigated within a temperature range of 20−200℃.The morphologies and compositions of worn surfaces were examined to identify the wear mechanisms using scanning electron microscope and energy dispersive X-ray spectrometer.The microstructure and hardness in the subsurfaces were analyzed to reveal the M−S wear transition mechanism.Under a constant loads of 20,35 and 40 N,each wear rate−test temperature curve presented a turning point which corresponded to the M−S wear transition.In mild wear,the surface material was plastically deformed and hence was strainhardened,whereas in severe wear,the surface material was dynamically recrystallized and consequently was softened.It has been found that the critical temperature for M−S wear transition decreases with increasing the normal load,and the normal load exhibits an almost linear relationship with critical temperature for M−S wear transition.This work reveals that the M−S wear transition of the studied alloy conforms to the surface DRX temperature criterion.

Correlation between test temperature, applied load and wear transition of Mg97Zn1Y2 alloy

Dry sliding wear tests were performed on Mg97 Zn1 Y2 alloy at various temperatures of 20,50,100,150 and 200°C using a pin-on-disc wear testing machine in order to reveal mild-severe(M-S)wear transition mechanism during elevated-temperature wear testing.It was shown that at each test temperature,the wear rate increased with increasing load,and all wear rate-load curves demonstrated two distinct stages i.e.mild and severe wear stages.The predominant wear mechanisms operating in mild and severe wear stages were analyzed,and they were indicated in the mild and severe wear regimes of a wear mechanism transition map,respectively.M-S wear transition mechanism was analyzed by comparison of microstructure transformation and hardness change in subsurfaces of samples tested in mild and severe wear stages,from which M-S wear transition mechanism was confirmed as softening of surface material arising from dynamic recrystallization(DRX)microstructure transformation.The M-S wear transition load was found to have a linear relationship with test temperature,and decreased with rising test temperature.M-S wear transition obeyed a critical surface DRX temperature(SDT)criterion under given conditions,and the transition loads were estimated at various test temperatures by using the criterion.

Transitions in Wear and Friction of Carbon Fiber Reinforced Copper Matrix Composite Sliding Against AISI-1045 Steel

The friction and wear properties of carbon fiber reinforced copper matrix composite in dry sliding against AISI-1045 steel was evaluated by a block-on-ring test machine. It was shown that the low frictional factor and wear rate of the composite block could be maintained when pressure or velocity was below a certain value. But when the pressure or velocity exceeded the critical value, the friction factor and wear rate tended to increase rapidly with pressure and sliding velocity. The morphologies, elemental compositions, and surface profile of worn composite surfaces at different wear stages were analyzed by means of scanning electron microscopy, energy dispersive spectrometry, and profile-meter. It was found that low values of friction and wear were due to a thin solid film forming on the surface of the composite block which includes carbon and copper at a mild wear stage. The film could impede adhesion and provide some degree of self-lubrication. When the film included more metal elements and were damaged, severe wear happened, and the wear rate increased sharply. As a result, a transition diagram in friction and wear was constructed, which provided pressure and velocity conditions of change from mild wear and low friction to severe wear and high friction for the wear-resisting design.

WEAR TRANSITIONS OF C/Cu COMPOSITE MATERIALS

An unlubricated sliding friction test on C/Cu composite materials is described. The result of the test proves that adhesive wear is the domination. At a certain speed, when the load upon the test block is light, the wear rate remains low level and the friction pair has a good antifriction performance. But when the load increases to a certain value, the wear transitions happen, the wear becomes severe.

Modifying element diffusion pathway by transition layer structure in high-entropy alloy particle reinforced Cu matrix composites

The Al0.3CoCrFeNi high-entropy alloy(HEA)particles reinforced Cu matrix composites(CMCs)were fabricated by mechanical alloying and sintering.Transition layer structure was obtained by multi-step ball milling to investigate the related influence on element diffusion behavior and wear properties of CMCs.The results indicate that a new Cu transition layer is generated,and the thickness is about 5μm.Cr element diffuses into the interface via the transition layer,which forms the complex oxide.Because of the structure of Cu transition layer,the diffusion rates of Ni,Co and Fe increase,especially the Ni element.The wear resistance of CMCs is improved by 30%,which is due to the improvement of interface bonding strength,compared with the CMCs without transition layer.This method is applicable to the development of advanced HEA reinforced metallic matrix composites.

刚性接触网弓网磨耗机理及应对策略

[目的]刚性接触网具有净空要求低、设备零件少等优点,但也存在着弓网磨耗速度较快、跟随性较差等缺点。在上海轨道交通线网中,架空刚性接触网线路占比逐年提升,受电弓碳滑板及接触线异常磨损情况也有上升趋势。因此需分析刚性接触网弓网磨耗机理,并采取相应的应对策略。[方法]以上海轨道交通刚性接触网线路为例,分析了刚性接触网弓网磨耗机理,并提出了应对策略。[结果及结论]通过改良刚性接触网拉出值布置形式能够改善碳棒局部异常磨损。拉出值范围内的滑动摩擦距离占比平均,可有效改善受电弓碳板局部磨损严重情况。在实际工程中,汇流排跨距应根据线路条件不同进行设置,最大不建议超过10 m。当跨中挠度过大时,应适当增加定位点,以缩短跨距。可通过适当降低列车牵引电流来控制部分锚段接触线磨耗速度过快的情况。

基于实测数据的车辆轮对磨耗模型研究

[目的]基于上海轨道交通17号线列车轮对实测数据,研究轮对磨耗规律,建立轮对轮缘厚度和轮径磨耗模型,以提高城市轨道交通车辆的安全性和维护效率。[方法]对轮对实测数据进行预处理,消除数据误差;采用曲线拟合和误差分析方法建立轮缘厚度和轮径的磨耗模型,并以磨耗速率拟合标准差,以及真实值与误差拟合曲线之间误差值的拟合标准差作为该模型的评价指标,评估轮缘厚度及轮径磨耗模型的准确性;分别针对1701次和1721次列车进行轮对磨耗模型验证。[结果及结论]1701次和1721次列车轮对轮缘厚度磨耗速率4次拟合曲线的拟合标准差,以及真实值与误差拟合曲线之间误差值的6次拟合曲线的拟合标准差均接近于零,验证了该车辆轮对磨耗模型的准确性,能够精确预测上海轨道交通17号线同一车型不同列车及同一列车不同位置的轮对磨耗情况。

氮空位调控晶格畸变度强化(NbMoTaW)N_(x)薄膜的力学性质和耐磨损性

高熵过渡金属氮化物(HENs)具有热稳定性,抗腐蚀、抗氧化性以及优异的力学性质,可用作结构部件及运动部件的表面防护薄膜。然而,受HENs组元多样性的影响,宽泛可调的金属组分与HENs力学性质之间的映射关系相当复杂。本工作以(NbMoTaW)N_(x)薄膜为研究对象,基于磁控溅射方法调节薄膜生长过程中氮气流量,制备了不同氮含量的(NbMoTaW)N_(x)(x=0,0.59,0.80,0.95)薄膜,研究了(NbMoTaW)N_(x)薄膜的成分、结构、形貌与性能,并对薄膜力学性质的主要影响机制进行了系统探究。结果表明,通过调节氮空位,实现了对氮原子及金属原子亚晶格畸变度的协同调控,得益于氮原子和金属原子亚晶格的高畸变度,(NbMoTaW)N_(0.80)样品具有最高的硬度与最好的耐磨损性能。排除电子结构、残余应力、晶粒尺寸等力学性质影响因素后,进一步确认了HENs薄膜晶格畸变度与力学性质之间的直接关系。本研究寻找到一条简洁的晶格畸变度调控策略,为调节、优化氮化物薄膜性能,进而更好地解决复杂服役环境下防护薄膜的机械损伤问题提供了新的思路。

不同结构溶聚丁苯橡胶/顺丁橡胶并用胶的相容性及性能

将不同乙烯基含量和苯乙烯基含量的溶聚丁苯橡胶(SSBR)与顺丁橡胶(BR)共混并用,研究了SSBR的微观组成对共混胶料相容性、硫化特性、静态力学性能、动态力学性能和磨耗性能的影响。结果表明,中高苯乙烯基含量的SSBR与BR并用后,硫化速率增加,门尼黏度和玻璃化转变温度降低,加工性能和耐低温性能得到改善,但payne效应、压缩温升增大,抗湿滑性能降低;随着SSBR与BR之间的溶解度参数差值减小,玻璃化转变温度向低温方向移动的幅度增大,并用胶的相容性增加,促进了磨耗性能的提升。

溶聚丁苯橡胶/天然橡胶并用胶的性能研究

研究不同苯乙烯基和乙烯基含量的溶聚丁苯橡胶(SSBR)/天然橡胶(NR)并用胶的相容性、物理性能、动态性能和干地摩擦性能等。结果表明:中高苯乙烯基含量的SSBR与NR并用后,胶料的门尼粘度减小,硫化速率增大,加工性能提高,硫化胶的压缩生热降低,耐低温性能提高,但抗湿滑性能降低;随着SSBR与NR的溶解度参数差值的增大,SSBR与NR的相容性降低,SSBR/NR硫化胶的玻璃化转变温度变化率呈减小趋势;随着SSBR与NR的相容性提高,分散相NR对SSBR/NR硫化胶性能的影响程度增大,有利于降低硫化胶的压缩生热,提高耐磨性能,但硫化胶的干地摩擦因数明显减小。

地铁车轮踏面中部滚动接触疲劳机制研究

滚动接触疲劳是地铁车轮常见的一种损伤形式,对车轮的服役安全及其维护具有重要影响。文章针对国内某条地铁线路上地铁车辆车轮出现的滚动接触疲劳问题,通过开展现场调查测试和仿真分析,研究了车轮磨耗形式对车轮踏面滚动接触疲劳的影响。结果表明,在该线路上运行的车轮约42%在踏面中部出现滚动接触疲劳,斜裂纹与水平线的夹角基本在40°~50°,并且出现滚动接触疲劳的车轮普遍存在W型磨耗。在车轮出现W型磨耗后,当车辆通过半径小于600 m的曲线时低轨侧车轮接触位置更加集中,蠕滑力合力方向基本与车轮踏面疲劳裂纹垂直,接触应力显著增大,接触区车轮材料更容易处于棘轮效应区,而且车轮的损伤值是LM型踏面的3倍左右。车轮出现W型磨耗是导致该线路车轮踏面中部出现滚动接触疲劳的根本原因。

适用于不同导高区域的接触线快速定位磨耗检测方案

[目的]接触线磨耗会影响弓网间正常受流,是影响列车运行安全的重要因素,因此快速、精确地检测接触线磨耗非常重要,提出了适用于不同导高区域的接触线快速定位磨耗检测方案。[方法]设计了多台高速线阵摄像机配合线激光的接触线磨耗检测方案,介绍了该检测方案的检测系统组成、快速定位接触线方法和具体的检测步骤。针对户外段和隧道段两种应用场景进行了接触线磨耗检测试验。[结果及结论]检测试验结果表明,该检测方案可对不同导高区域的接触线的磨耗进行检测,检测方法可行,检测精度较高。

类金刚石膜层制备及摩擦磨损性能

为解决某型扭力臂轴及配合衬套的磨损问题,使用磁控溅射和等离子增强化学气相沉积技术,在30CrMnSi-Ni2A表面制备了渐变过渡结构的类金刚石膜层(DLC)。使用球磨法、纳米压痕法、划痕法测量DLC膜层性能,膜厚为4.3μm,硬度≥1900 HV,膜基结合力≥30 N。经过滑动磨损测试,膜层摩擦系数≤0.2,摩擦磨损率≤2×10^(-6) mm^(3)·r^(-1)。经过20000转次耐磨测试,与硬铬镀层的扭力臂轴对比,DLC膜层配合衬套的磨损量远低于硬铬镀层配合衬套,可满足扭力臂轴耐磨润滑需求。

通过调整刚性接触网正弦波拉出值改善运营线路中弓网异常磨耗的应用实践

[目的]我国早期设计的城市轨道交通线路的刚性接触网以正弦波布置方式为主,运营中普遍存在弓网异常磨耗情况。已运营线路受正线轨行区施工条件限制,无法进行大范围施工改造,致使此问题长期得不到解决,需要研究其优化调整措施。[方法]通过计算正弦波拉出值布置方式下受电弓表面各计算段工作时与接触网的滑动摩擦距离,并对各计算段的滑动摩擦距离占比进行了统计分析,找出致使受电弓异常磨耗的3个原因。结合运营线路定位点的布置情况,调整拉出值数据,依次对这3个原因提出了优化措施。对比了优化前后的正弦波拉出值,并对优化调整措施的效果进行分析。[结果及结论]与原有正弦波布置方式的拉出值相比,优化后布置方式的拉出值中,受电弓磨耗最大倍数由6.23倍下降至1.47倍,受电弓磨耗平均值倍数由3.52倍下降至1.08倍。在西安地铁2号线部分区段实施了该优化措施后,2年内弓网无明显异常磨耗,受流质量良好。

机车轮对动态检测系统过渡段设计与动态分析

机车轮对的磨损是影响机车运营稳定性的不利因素,该文设计的机车轮对动态检测线路是一种新型不驻车检测机车轮对磨损状态的专用轨道线路,显著提高轮对磨损状态的检测效率。检测线路轨道间距为1568 mm,宽于标准轨距1435 mm,此时轮对与轨道正常接触区域显著暴露,便于对轮对磨损状态进行检测。通过有限元方法模拟机车通过过渡线路的动态分析,验证该检测方法的可行性。模拟结果表明,从轨道强度、轨道变形及轮对搭载量3个方面综合评价,该机车轮对动态检测线路具有较强实用性,能够满足23 t轴重机车以36 km/h速度安全通过的要求,实现不驻车情况下对轮对磨损状态进行安全检测。

煤矿刮板输送机过渡槽修复方案研究

过渡槽作为刮板输送机的重要组成部分,其可靠性决定着整机能否正常运行。为提升过渡槽磨损修复后使用性能,通过对常规修复方案进行对比分析,针对现有修复方案的弊端,提出复合耐磨板材优化修复方案。经过井下工业性试验,验证了该方案能显著提高过渡槽耐磨性能及过煤量,可有效延长其使用寿命。

全断面硬岩地层土压/TBM双模盾构滚刀性能评价

为了提高土压(EPB)/隧道掘进机(tunnel boring machine,TBM)双模盾构掘进效率,减少滚刀磨损,以深大城际铁路机场东站—黄麻布站区间为依托,以该隧道左线里程ZDK8+583.0~ZDK8+359.8全断面硬岩掘进段为研究对象,对区间所采用的EPB/TBM双模盾构滚刀性能展开研究。首先,根据滚刀功能和类型的不同,对该区段的滚刀更换情况以及磨损状况进行统计分析,并获得最优性能的滚刀;然后,为更好地指导开仓换刀,以最优性能滚刀为例对滚刀使用寿命进行评估;最后,根据现场实际情况建立刀具信息管理系统。研究结果表明:中铁装备宽刀更适合该类地层的掘进,所搭建的刀具管理系统能很好地实现刀具信息化管理,确保现场施工更经济、高效。

轨道交通弓网装置磨损成分检测及磨损机制研究

研究轨道交通弓网装置的磨损成分及磨损机制,对列车受电弓与接触网的接触特性进行分析。通过采集列车运行中的电流、电压、速度等参数,研究弓网系统的磨损过程。观察磨屑试样的宏观与微观形貌,并利用电子探针进行元素分析,确认磨屑的主要化学成分和来源。研究结果可以为优化弓网接触装置、减少磨损提供理论依据。

基于运营磨耗数据的刚性接触网线岔参数研究

架空刚性接触网因其载流量大、结构简单、可靠性高、建设及运维费用低等特点,已成为城市轨道交通地下段牵引网首选类型。但从已运营的线路来看,较多线路存在较为严重的弓网异常磨耗,而行业内关于刚性线岔处异常磨耗的分析与处理方式记载较少。本文以运营实测数据为基础,结合理论数据分析和现场试验,总结刚性线岔异常磨耗的发生与受电弓磨损面之间的对应关系,通过优化刚性线岔参数避免线岔处的弓网冲击,从而降低异常磨耗的发展。本文可为城市轨道交通刚性线岔参数设置提供依据,同时对刚性线岔的后续设计方向给出了建议。

Effect of Silicon Additions on the Wear Properties of Grey Cast Iron

This paper investigates the wear characteristic of grey cast iron composition under dry lubrication conditions. The effects of sliding speed, applied load, time and percentage of ferrosilicon additions, on the wear rate of grey cast iron were studied. The set of experimental data were taken in a controlled and sequential manner. Scanning electron microscope was used to examine the morphology of the samples as well as the worn out surfaces. Linear regression equation and analysis of variances (ANOVA) showed that the main effect of silicon additions, load and speed variable are more pronounced on the wear behaviour of the grey cast iron. Also, the result showed that the additions of silicon improved the wear resistance of the grey cast iron as the wear parameters such as speed, load and time varied. The study showed that wear transition occurred at 3.2% silicon addition.