Friction and Wear Properties of Micro Textured DLC Coated Surfaces in Boundary Lubricated Sliding

In the present study, the friction and wear properties of boundary lubricated textured surfaces were investigated. The capability to feed lubricant into the interface of a sliding contact and to isolate wear particles was related to the shape, size and orientation of the texture patterns. Well-defined surface textures of square depressions or parallel grooves of different widths and distributions were produced by lithography and anisotropic etching of silicon wafers. Subsequently the wafers were PVD coated with thin, wear resistant DLC coatings, retaining the substrate texture. The surfaces were evaluated in reciprocating sliding against a ball-bearing-steel ball under starved or amply lubricated boundary lubrication conditions.     

微造型表面纹理的制备及摩擦机理研究

通过降低接触面积来减小表面纹理磨损,又通过对润滑油的存储实现动压润滑以及二次润滑来达到减摩抗磨的作用。在滑动接触过程中,接触条件不断变化,表面微造型加工质量的优劣以及是否依据其摩擦机理进行了纹理设计都会对摩擦特性的评估产生重要影响。本文对微造型纹理表面滑动接触中的摩擦机理进行了综述,介绍了表面微造型制备技术和表面微造型的应用,并探讨了表面微造型技术可能的发展方向。     

常用钢磨削纹理方向与其表面摩擦因数的关系

采用平面磨削加工方法在20钢、45钢、40Cr钢表面加工出不同方向纹理(0°,30°,45°),研究了磨削加工纹理方向与其表面粗糙度和摩擦因数的关系.结果表明:相同磨削加工条件下,不同表面纹理方向的材料表面粗糙度由大到小依次为0°,30°,45°;当摩擦方向与表面纹理成一定角度时的摩擦因数要比其与表面纹理垂直时的要小;40Cr钢摩擦因数受表面纹理方向的影响要比45钢、20钢的要小.     

Nanostructure-Textured Surfaces with Low Friction and High Deformation Resistance

Nanotextured surfaces can effectively reduce friction and adhesion, especially in applications with micro- and nanoscale contact interactions. However, for these surfaces, a common weakness is a lack of structural integrity of the individual nanotextures when subjected to contact loading, resulting in permanent deformation at even the moderate contact forces encountered in microscale systems. Nanostructure-textured surfaces (NSTSs), composed of arrays of novel Al/a-Si core–shell nanostructures (CSNs), have been developed with a desirable combination of low friction and high deformation resistance. When subjected to nanoscratch testing, these surfaces are shown to have extremely low coefficients of friction (as low as ～0.015), as well as no detectable nanostructure deformation at contact forces up to 8,000 μN (estimated contact pressure greater than 1 GPa). In addition, the NSTSs have low adhesion (pull-off) forces on the order of less than 1 μN. The unique properties of these NSTSs provide avenues for designing low-friction, deformation-resistant surfaces that could benefit a variety of fields, including micro/nanoelectromechanical systems (MEMS/NEMS), microelectronics, magnetic recording, or any other application where the mechanical integrity of nanostructures is important.     

Effect of Molecularly Thin Lubricant on Roughness and Adhesion of Magnetic Disks Intended for Extremely High-Density Recording

For extremely high-density recording using conventional technologies, the fly-height needs to decrease to less than ten nanometers. To allow such operation, disk and slider surfaces must become extremely smooth, down to root-mean-square (RMS) roughness values of a few angstroms. For super-smooth disks, molecularly thin lubricants are applied to improve tribological performance of head/disk interfaces. The focus of this study is to quantify the effect of lubricant thickness in terms of detailed roughness parameters and to evaluate the effect of roughness and molecularly thin lubricant on adhesion of magnetic disks intended for extremely high-density recording. Three identical ultra-low-flying disks have been fabricated from the same batch for this particular experiment. To investigate the effect of molecularly thin lubricants on disk roughness, super-smooth magnetic disks with increasing lubricant thickness have been measured and studied, using a primary roughness parameter set. It describes amplitude, spatial, hybrid, and functional aspects of surface roughness and is used to quantify the extremely smooth disk roughness as a function of lubricant thickness. It is found that in addition to simple amplitude parameters, hybrid and functional parameters also capture small features on the disk roughness and show distinct trends with increasing lubricant thickness. Subsequently, a continuum-based adhesion model that uses three parameters from the primary roughness parameter set, is used to predict how the varying thickness of molecularly thin lubricant and the resulting disk roughness affect intermolecular forces at ultra-low-flying head-disk interfaces. It is found that a thicker lubricant layer of 2nm causes higher adhesion forces for ultra-low-flying-heights in the range of 1–3 nm     

双粗糙面滑动过程摩擦因数的变化分析

采用W-M函数建立具有分形特征的三维双粗糙面接触模型,考虑了接触界面间的黏着效应,在滑动速度、法向载荷及界面剪切强度等参数变化下,运用有限元方法探讨了粗糙体在滑动过程中摩擦因数的变化情况。结果显示,滑动速度、法向载荷及界面剪切强度等参数对摩擦因数的变化有一定的影响,边界润滑工况下平均摩擦因数为0.28,无润滑工况下平均摩擦因数为0.713,最大界面剪切强度时的平均摩擦因数为0.73;随着界面剪切强度的减小、法向载荷的增大、滑动速度的增加,滑动摩擦因数有所减小。与相关文献结论或实验结果进行比较,证明了上述结果的正确性。分析结果可为摩擦学设计和摩擦材料的制备提供理论参考。     

The significance of surface topography in engineering

All machining processes leave characteristic topographic features on the surfaces of components. This paper reviews a wide range of examples in which the surface topography of a component has been found to bear a significant effect on its function. Problems in manufacture which are related to surface roughness requirements are also disccused.     

摩擦副表面气膜屏蔽微细电解加工微织构及摩擦性能分析

采用气膜屏蔽微细电解加工方法在金属平面副、圆柱副表面加工不同阵列形貌微织构。通过试验将该方法与微细电解加工的微织构尺寸精度、表面质量、摩擦性能进行对比,研究结果表明,气膜屏蔽微细电解加工的微织构相比微细电解加工方法加工的微织构平面副及圆柱副凹槽深径比分别提高了约45.6%和25.8%,改善了加工的定域性,提高了加工精度。进一步的摩擦磨损试验结果表明,相较于微细电解加工方法,气膜屏蔽微细电解加工出的平面副及圆柱副微凹槽的表面摩擦因数分别减小了13.6%与16.2%,表面摩擦性能得到了提高。     

Effect of Ultraviolet Irradiation on the Interactions between Perfluoropolyether Lubricant and Magnetic Disk Surfaces

To tailor the characteristics of molecularly thin lubricant films, magnetic disk surfaces coated with nanometer-thick perfluoropolyether AM3001 lubricant films were irradiated with 184.9 and 253.7 nm ultraviolet (UV) rays. We elucidated the effect of UV irradiation on the interactions between the lubricant and the magnetic disk surface via surface energy, bonded lubricant thickness and lubricant spreading measurements for films with and without UV irradiation. We found that UV irradiation decreased the dispersive and polar surface energies of the lubricant films by 20 and 80%, respectively; increased bonded lubricant thickness; and decelerated lubricant spreading. These results indicated that dispersion and polar interactions between lubricant molecules and the magnetic disk surface were strengthened by UV irradiation.     

超光滑表面的加工、表征和功能

超精密加工的目标是通过表面质量控制获得预定的表面功能。一定的加工过程产生相应的表面特征 ,而表面特征在很大程度上又决定着表面的实际功能。为了通过预先设计及加工控制获得要求的功能表面 ,必须对超光滑表面的加工、表征、功能及其相互关系进行全面而深入的研究     

Experimental and theoretical evaluation of friction at contacting magnetic storage slider–disk interfaces

To understand better the friction force and wear processes at contacting slider–disk interfaces, we have developed an experimental method for measuring and a theoretical method for calculating the friction force. For this study, a slider with a 1500 μm² contact pad located at the recording head is burnished against a relatively rough disk (～12 Å rms), which ensures smooth sliding. In the experimental method, the friction force is measured as the disk is spun-down to bring the slider–disk interface into an increasing degree of contact. A modified air bearing code is used to determine the experimental normal contact force for each friction measurement. In the theoretical method, the friction force and other relevant interfacial forces are calculated using an improved sub-boundary lubrication (ISBL) rough surface model. The friction force calculation in this model is based on the force needed to induce yielding of the individual disk asperities contacting the flat surface of the contact pad without any assumption of the coefficient of friction. Good agreement is found between the measured and theoretical friction vs. normal contact force curves, indicating that the model is capturing the essential origins of friction at this interface. The model also provides valuable insights into how wear particles may be generated at this contacting slider–disk interface.     

Theoretical and Experimental Study of a Thermal Contact Conductance Model for Elastic,Elastoplastic and Plastic Deformation of Rough Surfaces

This study developed a thermal contact conductance model that takes into account surface asperities with elastic, elastoplastic and plastic deformation. The surface asperity model considers the continuity and smoothness of variables across different modes of deformation. Experiments were also conducted to measure thermal contact conductance for samples with different surface roughness when the contact pressure was increased or decreased. The trend of the test data supports the theoretical results.     

润滑接触摩擦力的往复式实验研究

在往复式试验机上研究实际加工表面球-盘式接触混合润滑摩擦特性,比较采用不同黏度润滑油光滑接触摩擦力的大小。针对表面粗糙度幅值和纹理对摩擦行为的影响进行研究,结果表明,混合润滑时较高黏度润滑油的摩擦力较小;表面粗糙度幅值在混合润滑时对摩擦力影响较大,且随速度增加而增强,边界润滑时影响很小。与纵向纹理相比,横向纹理表面的摩擦力较小且稳定,低速时这种差别更加明显。     

不同刹车压力下C/C复合材料的摩擦性能与摩擦面研究

采用MM-1000型摩擦磨损试验机对以光滑层、粗糙层为基体炭的2种C/C复合材料在不同刹车压力下的摩擦磨损性能进行了测试。借助微区拉曼光谱和扫描电镜对其摩擦表面的石墨化度与形貌进行了分析。结果表明：以粗糙层为基体炭的C/C复合材料比以光滑层为基体炭的C/C复合材料有更优异的摩擦压力或温度特性。微区拉曼光谱检测证实在摩擦面上粗糙层基体炭相对光滑层基体炭更易变形,所以以粗糙层为基体炭的C/C复合材料的摩擦面在刹车压力达到0.59 MPa时便能形成较厚的摩擦膜,故其摩擦因数能在较高刹车压力下（1.05-1.82 MPa）保持较高的稳定值（0.31）,且磨损适当;而光滑层基体炭C/C复合材料需在刹车压力超过0.82 MPa时摩擦面才能形成较薄的摩擦膜,并且由于其导热系数低,高压刹车时摩擦表面氧化严重,所以高压刹车时其摩擦因数衰减大,线性磨损率大,尤其是质量损失急剧升高。     

壁虎在垂直的不同材料表面的运动与附着行为研究

用动物全空间运动行为-反力测试系统测试记录了大壁虎(gekko gecko)在垂直的玻璃、有机玻璃、铝和不锈钢表面的运动行为和运动反力。分析了壁虎在垂直的不同材料表面的运动附着能力与材料表面特性之间的关系。大壁虎在玻璃、有机玻璃、铝表面上采用对角步态向上爬行,运动与附着能力依次降低,在不锈钢表面不能爬行与附着。在玻璃表面的爬行速度是铝表面爬行速度的两倍。壁虎主要通过提高步频来提高速度。在运动与附着能力较弱的表面,壁虎对壁面的运动反力较小,通过降低爬行速度、提高占空比、增加腿的附着时间来保证运动的稳定与安全,并通过轴向力克服身体重力向上爬行,通过侧向力和法向力使身体稳定地附着在壁面上。壁虎在垂直表面的运动与附着能力随着接触面材料表面能的增加而提高。     

水压摩擦副中的压力与流量特性

水的低粘度使得水压润滑间隙中的惯性力与粘性力几乎处于同一数量级,因此研究摩擦副的润滑特性时,不能忽略惯性力的影响。惯性力的作用可能改变间隙流场的局部甚至全局流态,从层流变为紊流,因此应用经典润滑理论所得的计算结果将产生太大的误差。采用CFD方法从N-S方程出发对水压摩擦副中压力与流量特性的惯性影响和表面粗糙度效应进行了研究,并与经典润滑理论结果进行了对比,发现表面粗糙度和惯性力对润滑间隙中的压力和流量特性均有一定的影响。其中,惯性力对端面摩擦副中的压力分布具有一定的影响,对端面副和径向副的泄漏流量均有影响,并且惯性力使得表面粗糙度对流场流态的影响得以体现,因此以N-S方程而不是雷诺方程为模型所得的计算结果更加准确。     

[学科发展]极端工况下机械表面界面损伤与防护研究进展

中国科学院宁波材料技术与工程研究所海洋新材料与应用技术重点实验室,宁波,315201 分析了重大工程实施中极端环境的典型特点,简要介绍了机械表面界面科学的国内外研究现状与发展趋势,指出了相关研究的共性科学问题;针对国家重大战略需求和国际研究前沿,提出了极端工况下机械表面界面科学领域的研究发展方向;以重点方向——功能防护涂层研究为例,探讨了涂层材料与技术的发展趋势并评述了相关研究进展。     

表面粗糙度对碳/铜载流摩擦副摩擦磨损性能的影响

通过环-块式摩擦磨损试验研究了表面粗糙度对碳/铜载流摩擦副摩擦磨损性能的影响,并分析了磨损形貌及机制。结果表明:其摩擦因数与电弧行为密切相关,无电弧时摩擦因数曲线平滑;对磨环的表面粗糙度越大越容易产生电弧,电弧的烧蚀导致块试样的磨损加剧;不同表面粗糙度下均存在临界起弧法向压力,且随着表面粗糙度的增大而增大;载流摩擦副的磨损机制主要为磨粒磨损、粘着磨损、电弧烧蚀及材料转移。     

碳化硅增强颗粒含量和尺寸对铝基复合材料超精密车削表面的影响

用聚晶金刚石刀具(PCD)研究了增强颗粒的含量、尺寸等对SiC颗粒增强铝基复合材料超精密车削表面的影响.结果表明:SiC增强颗粒的去除方式主要有拔出、破碎和切断等,SiC颗粒的含量和平均尺寸越大,其拔出和破碎现象就越多,复合材料获得的加工表面粗糙度值也越大;当SiC颗粒主要以切断方式被去除时,可望获得含有较少坑洞和裂纹等加工缺陷的超精密切削表面.