Friction behavior of quenched and tempered steel in partial and gross slip conditions in fretting point contact

Tangential traction caused by friction in contacting surfaces is a major factor in fretting fatigue that increases stress levels and leads to a reduction in fatigue life. Friction in fretting contact was studied in partial, mixed and gross slip conditions on quenched and tempered steel. Measurements were made with sphere-on-plane contact geometry for polished and ground surfaces. Friction was evaluated from on-line energy ratio and, after the tests, from wear marks. A maximum friction coefficient of over 1.0 was measured at mixed slip zone with polished surfaces, whereas ground surfaces promote lower values in similar operating conditions. The friction coefficient dependence on load cycles and loading frequency is also presented and briefly discussed. The friction data and understanding thus gained is to be used for evaluation of crack initiation with the numerical fretting fatigue model.     

Finite element simulation and experimental validation of fretting wear

A finite element-based method is presented for simulating both the fretting wear and the evolution of fretting variables with number of wear cycles in a cylinder-on-flat fretting configuration for application to aeroengine transmission components. The method is based on a modified version of Archard’s equation and is implemented within a commercial finite element code. Fretting tests are employed to determine the coefficient of friction (COF) and the wear coefficient applicable to the contact configuration and loading conditions. The wear simulation technique is incremental in nature and the total simulation time has been minimised via mesh and increment size optimisation. The predicted wear profiles have been compared with profilometer measurements of fretting test scars.     

Oil-Lubricated Fretting Behaviors of 304 Stainless Steels under Different Fretting Strokes and Normal Loads

The influence of oil lubrication on the fretting wear behaviors of 304 stainless steel flat specimens under different fretting strokes and normal loads has been investigated. The results proved that fretting regimes and fretting wear behaviors of 304 stainless steels were closely related to the fretting conditions. In general, the increase in normal load could increase wear damage during sliding wear. However, according to the results, a significant reduction in wear volume and increase in friction coefficient was observed when the normal load was increased to critical values of 40 and 50 N at a fretting stroke of 50 μm due to the transformation of the fretting regime from a gross slip regime to partial slip regime. Only when the fretting stroke further increased to a higher value of 70 μm at 50 N, fretting could enter the gross slip regime. There was low wear volume and a high friction coefficient when fretting was in the partial slip regime, because oil penetration was poor. The wear mechanisms were fatigue damage and plastic deformation. There was high wear volume and low friction coefficient when fretting was in the gross slip regime, because the oil could penetrate into the contact surfaces. Unlike the wear mechanisms in the partial slip regime, fretting damage of 304 stainless steels was mainly caused by abrasive wear in the gross slip regime.     

不同水介质下GCr15/45#钢微动腐蚀行为研究

在洁净水、酸性水和海水3种不同水介质条件下，对GCr15／45^#钢进行了不同位移幅值的微动磨损试验。结果表明：洁净水和酸性水改变了微动区域，降低了摩擦系数和磨损量，具有润滑效果，磨损受水润滑和介质腐蚀双重作用影响,且润滑作用随位移幅值的增加而减弱；对海水，摩擦系数与干态相近,电化学腐蚀作用强烈，磨痕中可观察到大量点蚀坑。     

On the behaviour of an oil lubricated fretting contact

Although many engineering situations involving fretting damage are lubricated, comparatively little has been reported on this aspect of fretting wear. The viscosity of the lubricating oil and its boundary layer performance are expected to influence fretting behaviour, in addition to the normal fretting parameters, such as stroke and contact force.

This paper examines the effect of lubrication regime, oil viscosity and stroke on the behaviour of a ball-against-flat specimen arrangement. Ball and flat specimens were both manufactured from a bearing steel (SUJ2). Polybutane oils, without additives, covering a range of viscosities from 1 to 10 000 cSt, and fretting strokes up to 35 μm were investigated. The lubricating oil was added to the fretting interface after 0, 3 and 2000 fretting cycles had been completed. Lubrication regime, oil viscosity and stroke were all found to affect fretting behaviour in terms of both coefficient of friction (or traction coefficient) and wear. For strokes less than 9 μm, i.e. for conditions approaching almost complete ‘stick’, coefficient of friction values under oil lubrication were well in excess of double those observed without it. These high values suggest that the oil was unable to penetrate into the fretting contact region, but did maintain a shield around it, so that metal-on-metal contact was maintained under oxygen deprived conditions. The lowest values of steady state coefficient of friction (≈ 0.2) were observed when oil lubrication was applied after 2000 cycles had been completed, indicating that surface roughening and the presence of oxide films and oxidised debris assisted penetration of the lubricant into the fretting contact zone.     

Fretting wear of carburized titanium alloy against ZrO2 under serum lubrication

Fretting wear of carburized titanium alloys was investigated on the universal multifunctional tester (UMT) with the ball-on-flat fretting style under bovine serum lubrication. The tangential load and friction coefficient during the fretting process were analyzed, and the evolution of fretting log during the fretting process was investigated to understand the wear mechanism of the titanium alloy and carburized titanium alloy. Furthermore, the wear scar was examined using a SEM and three-dimension surface profiler. It was found that the friction coefficient of the titanium alloy increased faster than that of carburized titanium alloy in the first stage under serum lubrication, and then remained steady with a similar value in the second stage. The Ft-D curve indicated that there was wear mechanism transition from gross slip to mixed stick and slip. Finally, it was observed that there was a slight damage of the titanium alloy and carburized titanium alloy showed excellent performance during the fretting wear process under serum lubrication. All of the results suggested that carburized titanium alloy was a potential candidate for the stem material in artificial joints.     

粘结MoS2固体润滑涂层的转动微动磨损特性

采用粘结法在LZ50钢表面制备MoS2固体润滑涂层,研究MoS2涂层及LZ50钢基体在干态不同角位移幅值下的转动微动磨损行为。在分析转动微动动力学特性的同时,结合光学显微镜、扫描电子显微镜、电子能谱仪以及轮廓仪对磨痕形貌进行微观分析。结果表明:涂层和基体的转动微动运行区域仅呈现部分滑移区(Partial slip regime,PSR)和滑移区(Slip regime,SR),未观察到混合区。涂层改变基体的微动运行区域,使得PSR缩小,SR运行区域向小角位移幅值方向移动。由于MoS2涂层的固体润滑作用,涂层的摩擦因数在整个试验过程都明显低于基体。在PSR,涂层损伤轻微;在SR,涂层的转动微动磨损机制主要表现为剥层和摩擦氧化。研究表明粘结MoS2固体润滑涂层具有明显的防护作用,显著降低LZ50钢的转动微动磨损。     

人股骨皮质骨轴面微动摩擦磨损特性研究

采用高精密微动试验台外加体液恒温循环装置,在一定法向载荷和不同位移幅值条件下,研究了天然活性人股骨皮质骨对纯钛的微动摩擦磨损行为。试验结果显示：随位移幅值的增加,股骨皮质骨的微动运行状态从部分滑移向完全滑移状态转变,详细讨论了不同位移幅值下摩擦因数随循环次数的演变规律。微观观察表明：接触表面处于部分滑移状态时损伤轻微,而在完全滑移状态下磨损较严重。人股骨皮质骨的磨损机理主要表现为磨粒磨损和微骨折导致的剥层剥落。微动磨痕的深度随位移幅值的增加而增加,而且磨痕深度与摩擦因数有很好的对应关系。研究认为控制植入体/骨界面的微动幅度有利于提高皮质骨抗微动损伤的能力。     

An investigation of fretting behaviour of several metallic materials under grease lubrication

Fretting wear tests under grease lubrication have been carried out on an aluminium alloy, 52100 steel and low-alloy steel. The sphere–flat contact configuration is used. The influence of the displacement amplitude and normal load is investigated. Comparison between dry and lubricated contact of aluminium alloy, between 52100/52100 steel and 52100/low-alloy steel contact with grease lubrication has been carried out. Results show that grease lubrication strongly affects fretting behaviour. Base oil that separated from the grease during friction may result in accelerated contact wear by fretting.     

微动疲劳参数对钢丝微动疲劳磨损演化的影响*

微动疲劳易引起钢丝表面磨损和横截面积损失,进而造成钢丝断裂失效并缩短钢丝绳使用寿命。不同微动疲劳参数（接触载荷、疲劳载荷、钢丝直径和交叉角度）引起差异的钢丝微动疲劳磨损特性,故研究微动疲劳参数对钢丝微动疲劳磨损演化规律影响至关重要。基于摩擦学理论和Marc仿真软件构建钢丝微动疲劳磨损模型,探究接触载荷、疲劳载荷、交叉角度和钢丝直径对钢丝微动疲劳磨损演化的影响规律。结果表明：钢丝微动疲劳磨损体积主要与接触载荷和疲劳载荷有关;疲劳钢丝的磨损深度、磨损率及磨损体积随着接触载荷的增加而增大,且不同接触载荷下疲劳钢丝磨损体积均随着循环次数的增加而呈线性增加;随疲劳载荷幅值的增加,疲劳钢丝的磨损深度、磨损率及磨损体积均呈增加趋势;在不同疲劳载荷范围下疲劳钢丝的磨损体积均随着循环次数的增加而呈线性增加;当接触载荷、疲劳载荷及钢丝间摩擦因数相同时,不同交叉角度和不同加载钢丝直径下疲劳钢丝的磨损体积相同。     

TiAlZr合金微动磨损性能研究

采用高精度液压式微动磨损试验机研究了TiA lZr合金在不同微动运行区域的微动磨损行为,建立了其运行工况微动图。试验结果表明:滑移区、混合区和部分滑移区的摩擦因数随循环次数变化呈现不同的规律,其中部分滑移区摩擦因数较低,磨损体积随着位移幅值的增大而增大;滑移区、混合区磨损体积随着法向载荷的增加而增大,而部分滑移区磨损体积随着法向载荷的增加而减小;滑移区磨屑堆积于中心区域,磨损以磨粒磨损和剥层机制为主;混合区磨损机制主要表现为粘着磨损与磨粒磨损并存;部分滑移区磨损轻微。     

AZ91D镁合金微动磨损特性研究

采用液压高精度材料试验机考察了平面一球面接触的AZ91D镁合金摩擦副的微动磨损行为，分析了位移幅值、法向载荷和频率等参数对摩擦因数和磨损体积的影响，考察了不同实验条件下的磨斑形貌，并探讨了其磨损机理。结果表明：AZ91D镁合金的微动区域可分为部分滑移区、混合区和滑移区3个区域，粘着磨损、疲劳磨损和磨粒磨损分别是3个区域的主要磨损机制；磨损体积随着位移幅值和法向载荷的增加而增大，但却随着频率的增大而减小。在微动部分滑移区和混合区，摩擦因数随着位移增大迅速增加；在微动滑移区，摩擦因数随法向载荷的增大而减小，而位移幅值和频率对摩擦因数的影响较小。     

Fretting wear behavior of nanocrystalline surface layer of copper under dry condition

Unlubricated fretting tests were performed with a nanocrystalline surface layer of a 99.99 wt.% copper fabricated by means of surface mechanical attrition treatment (SMAT), in comparison with a coarse-grained (CG) copper. The measured friction and wear data show that the fretting wear resistance is markedly enhanced with the nanocrystalline surface layer relative to the CG counterpart. The friction coefficient and wear volume of the SMAT Cu are lower than that of the CG Cu. For both samples, the friction coefficients and wear volumes increase with an increasing applied load and fretting frequency. A rapid increase of the friction coefficient and wear volume under an applied load above a critical value (30 N for the SMAT Cu and 20 N for the CG Cu) is noticed, corresponding to the formation of a continuous oxide layer between two contact surfaces. Also two sharp increases of the friction coefficient and wear volume at fretting frequencies of 50 Hz and 175 Hz were observed for the SMAT and the CG Cu. The former is correlated with the formation of a continuous oxide layer, while the latter corresponds to wearing away of the oxide layer.     

Evaluation of fretting wear based on the frictional work and cyclic saturation concepts

It is time consuming or even impossible to simulate the whole process of fretting wear, since it always involves millions of cyclic loadings. This paper focuses on the modeling and evaluation method of fretting wear for the typical bridge type fretting test with a flat pad. The frictional work on the contact interface is chosen as the parameter to evaluate the fretting wear. To verify the fretting wear model, the predicted wear profile is compared with that obtained by the experimental results. Fretting wear always includes plastic deformations due to the edge stress singularity. The effect of cumulative plastic deformation is also taken into account in the wear model. The role of the coefficient of friction at the contact interface on the fretting wear has also been discussed.     

渐开线花键副微动磨损分析的能量耗散法

针对航空传动系统中的渐开线花键副,采用能量耗散法,建立了微动磨损量计算公式,并针对三种工况,研究工况因素对磨损分布规律的影响。研究结果表明:①理想工况下,各齿对的磨损量几乎相同,外花键齿廓上齿根接触末端为最大磨损发生位置;存在侧隙时,侧隙越小的齿间磨损越严重;存在轴线偏斜时,齿面在轴向位置的中部发生较大磨损,最大磨损发生位置向齿顶移动。②渐开线花键副设计安装时,为减少微动磨损带来的失效,应尽可能保证各齿间侧隙均匀并减小内外花键的轴线偏斜。     

Fretting wear behaviors of steel wires under friction-increasing grease conditions

Fretting wear tests were performed on the self-made fretting wear rig to investigate fretting wear behaviors of steel wires under friction-increasing grease conditions. The results demonstrated that the fretting regimes were dependent on displacement amplitudes and normal loads. The friction coefficient exhibited different variation trends in different fretting regimes. Friction-increasing grease changed the fretting running behavior and had a very good wear resistance for steel wires. Wear was slight in partial slip regime. Mixed regime was characterized by plastic deformation, fatigue cracks and abrasive wear. Slip regime presented main damage mechanisms of abrasive wear, fatigue wear and oxidation.     

Development of a test device for the evaluation of fretting in point contact

Fretting wear and fatigue may occur between any two contacting surfaces, wherever short‐amplitude reciprocating sliding is present for a large number of cycles. A test device has been developed for the evaluation of fretting fatigue and wear in partial and gross slip conditions. Three similar sphere‐on‐plane contacts run at the same time. Normal force, tangential force or displacement amplitude and constant bulk stress can be controlled and measured separately. Reciprocating tangential displacement is produced with rotational motion, the amplitude and frequency of which can be adjusted and controlled accurately by an electric shaker. The number of load cycles for crack initiation and growth is determined with strain‐gauge measurements near the fretting point of contact. The contact surfaces are measured with 3D optical profilometer before fretting measurements to determine actual contact geometry. The measurements were done with quenched and tempered steel. The initial results indicate that cracks are mostly formed in partial slip conditions, whereas fretting wear is more heavily involved in gross slip conditions. The initiation of a crack occurs near the edge of the contact in the slip direction, where the calculated cracking risk has its maximum value in partial slip conditions. The number of cracks increases as the displacement amplitude, i.e. friction force, increases in partial slip conditions. Copyright © 2008 John Wiley & Sons, Ltd.     

Fretting wear mechanisms of Zircaloy-4 and Inconel 600 contact in air

The fretting wear behavior of the contact between Zircaloy-4 tube and Inconel 600, which are used as the fuel rod cladding and grid, respectively, in PWR nuclear power plants was investigated in air. In this study, number of cycles, slip amplitude and normal load were selected as the main factors of fretting wear. The results indicated that wear increased with load, slip amplitude and number of cycles but was affected mainly by the slip amplitude. SEM micrographs revealed the characteristics of fretting wear features on the surface of the specimens such as stick, partial slip and gross slip which depended on the slip amplitude. It was found that fretting wear was caused by the crack generation along the stick-slip boundaries due to the accumulation of plastic flow at small slip amplitudes and by abrasive wear in the entire contact area at high slip amplitudes.     

Third body effects on friction and wear during fretting of steel contacts

Fretting wear proceeds through particle detachment from the contacting surfaces which, while trapped in the contact zone, can affect the frictional and wear response. Ball-on-flat fretting experiments were carried out between steel specimens under gross slip regime. A transition in the coefficient of friction was linked to a critical contact pressure. The microstructure and chemical composition of the third body evolve with the applied pressure. The evolution of the friction coefficient is strongly dependent on the third body properties. The wear is controlled by the applied load and thus the real contact area within the wear track.