Relationships between the fretting wear behavior and mechanical properties of thin carbon films

Mechanical load can drastically affect the properties of orthopedic implant materials. Damage of these materials usually occurs in contact surfaces, caused by abrasion, adhesion, fretting, delamination, pitting and fatigue depending on friction, lubrication, contact area, surface finish and level of loads (stresses).Carbon-based films are biocompatible with good bearing capacity, wear resistance, corrosion resistance and have a low coefficient of friction. However, great intrinsic stress prevents their wider application, mainly as implant coatings. To reduce this undesirable effect special deposition procedures are under development and/or the films are doped with suitable elements. It must be emphasized that DLC is not a material but a group of materials with a variety of properties. The relationships between the fretting wear behavior and mechanical properties of films based on carbon deposited by DC using the pulsed arc discharge PVD nitrogen doped (a-C) and the filtered pulsed arc discharge deposition system (ta-C) were tested.The composition of carbon films (sp³, sp²) was determined by Raman spectroscopy. Mechanical properties of elastic modulus and hardness were determined by a NanoTest apparatus with diamond Berkovich tip using the Oliver-Pharr procedure and adhesion was measured by nanoscratch tests. Tribological behavior was analyzed by fretting tests with a corundum ball under dry sliding lubricated conditions.The good performance of the hard carbon coatings is often discussed. Results from this study of fretting and the associated lubrication (bovine serum) show that ta-C coatings, despite their high hardness, have very low friction coefficients and low volume losses.     

影响微电子机械系统成品率和可靠性和粘合力和磨擦力

章评述了影响微电子机械系统（MEMS）成品率和可靠性的粘合力和摩擦力问题。在用氢氟酸（HF）腐蚀牺牲层、释放多晶Si微结构、干燥时,由于Si片表面薄层水的表面张力使两片亲水、间隙在微米量级的Si片粘合起来,称为“释放有关粘合”。粘合也发生在封装后器件中,当输入信号过冲时,由于Si片表面的化学状态将Si片粘合起来,称为“使用中粘合”。解决粘合的最好办法是：在MEMS微结构的表面涂以抗粘合薄膜,将成品器件在干燥气氛下封装。介绍了抗粘合薄膜的制备工艺和目前存在的问题。相比之下,具有高速运动的MEMS,其摩擦力问题更为复杂。应和抗粘合薄膜,解决了粘合,也降低了摩擦力,但摩擦依然存在。摩擦带来磨损,降低器件可靠性和寿命。寻找既抗粘合、又耐磨的薄膜,是解决高速运动MEMS可靠性和寿命的一个关键。     

Effect of deposition pressure on the adhesion and tribological properties of a-CN<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>H films prepared by DC-RF-PECVD

Hydrogenated carbon nitride (a-CN _x H films) was deposited on n-type single-crystal Si (100) by direct current radio frequency plasma-enhanced chemical vapor deposition (DC-RF-PECVD), under the working pressure of 5.0–17.0 Pa, using the CH₄ and N₂ as feedstock. The composition and surface morphology of the a-CN _x H films were characterized by means of Raman spectroscopy and atomic force microscopy, while the Young’s modulus, elastic recovery, adhesion strength, and tribological properties were evaluated using nano-indentation, scratch test and friction test system. It was found that the surface roughness and Raman spectra peak intensity ratio I _D/I _G of the films increased with the increase of working pressure, while the Young’s modulus, elastic recovery and adhesion strength of the films significantly decreased. Moreover, the tribological properties of the films also varied with the working pressure. The wear life sharply increased with the increase of working pressure from 5.0 Pa to 7.5 Pa, further, an increase in the deposition pressure led to a gradual decrease in the wear life, consequently, the a-CN _x H film deposited at 7.5 Pa exhibited the longest wear life. The deposition pressure seemed to have slight effect on the average friction coefficients, whereas the surface roughness and adhesion strength have deteriorated with increasing deposition pressure.     

Nanotribology and nanomechanics in nano/biotechnology

Owing to larger surface area in micro/nanoelectromechanical systems (MEMS/NEMS), surface forces such as adhesion, friction, and meniscus and viscous drag forces become large when compared with inertial and electromagnetic forces. There is a need to develop lubricants and identify lubrication methods that are suitable for MEMS/NEMS. For BioMEMS/BioNEMS, adhesion between biological molecular layers and the substrate, and friction and wear of biological layers may be important, and methods to enhance adhesion between biomolecules and the device surface need to be developed. There is a need for development of a fundamental understanding of adhesion, friction/stiction, wear, the role of surface contamination and environment, and lubrication. MEMS/NEMS materials need to exhibit good mechanical and tribological properties on the micro/nanoscale. Most mechanical properties are known to be scale dependent. Therefore, the properties of nanoscale structures need to be measured. Component-level studies are required to provide a better understanding of the tribological phenomena occurring in MEMS/NEMS. The emergence of micro/nanotribology and atomic force microscopy-based techniques has provided researchers with a viable approach to address these problems. This paper presents an overview of micro/nanoscale adhesion, friction, and wear studies of materials and lubrication studies for MEMS/NEMS and BioMEMS/BioNEMS. It also presents a review of scale-dependent mechanical properties, and stress and deformation analysis of nanostructures.     

Tribological properties of Ta‐C‐N and Ta‐N thin films

The amorphous Ta‐C‐N and Ta‐N thin films were deposited using magnetron sputtering on silicon wafer under the similar condition. The as‐prepared thin films were characterized using scanning electron microscope (SEM), optical profiling system, nano‐indentation and friction test instruments. The results show that, compared with the Ta‐N thin film, the Ta‐C‐N thin film has higher nano‐hardness (9.45 GPa) and elastic modulus (225.71 GPa). Furthermore, the lower friction coefficient and wear rate of the Ta‐C‐N thin film are 0.238 and 5.94×10^–6 mm^–3· N^–1·m^–1, respectively. The wear surface of Ta‐C‐N thin film is smoother than that of the Ta‐N thin film. Therefore, it shows better anti‐wear properties.     

Tribological characteristics of self-assembled nanometer film deposited on phosphorylated 3-aminopropyltriethoxysilane

Thin films deposited on the phosphonate 3-aminopropyltriethoxysilane (APTES) self-assembled monolayer (SAM) were prepared on the hydroxylated silicon substrate by a self-assembling process from specially formulated solution. Chemical compositions of the films and chemical state of the elements were detected by X-ray photoelectron spectrometry (XPS). The thickness of the films was determined with an ellipsometer, while the morphologies and nanotribological properties of the samples were analyzed by means of atomic force microscopy (AFM). As the results, the target film was obtained and reaction might have taken place between the thin films and the silicon substrate. It was also found that the thin films showed the lowest friction and adhesion followed by APTES-SAM and phosphorylated APTES-SAM, whereas silicon substrate showed high friction and adhesion. Microscale scratch/wear studies clearly showed that thin films were much more scratch/wear-resistant than the other samples. The superior friction reduction and scratch/wear resistance of thin films may be attributed to low work of adhesion of nonpolar terminal groups and the strong bonding strength between the films and the substrate.     

Preparation, Properties and Application of C/C-SiC Composites Fabricated by Warm Compacted-in situ Reaction

Carbon fibre reinforced carbon and SiC dual matrices composites (C/C-SiC) show superior tribological properties, high thermal shock resistance and good abrasive resistance, and they are promising candidates for advanced brake and clutch systems. The microstructure, mechanical properties, friction and wear properties, and application of the C/C-SiC composites fabricated by warm compacted-in situ reaction were introduced. The results indicated that the composites were composed of 50-60 wt pct carbon, 2-10 wt pct residual silicon and 30-40 wt pct silicon carbide. The C/C-SiC brake composites exhibited good mechanical properties. The value of flexural strength and compressive strength could reach 160 and 112 MPa, respectively. The impact strength was about 2.5 kJ·m^-2. The C/C-SiC brake composites showed excellent tribological performance, including high coefficient of friction (0.38), good abrasive resistance (1.10 μm/cycle) and brake steadily on dry condition. The tribological properties on wet condition could be mostly maintained. The silicon carbide matrix in C/C-SiC brake composites improved the wear resistance, and the graphite played the lubrication function, and right volume content of graphite was helpful to forming friction film to reduce the wear rate. These results showed that C/C-SiC composites fabricated by warm compacted-in situ reaction had excellent properties for use as brake materials.     

Mechanical properties of ZnO thin films deposited on polyester substrates used in flexible device applications

ZnO is growing in importance as a functional film in flexible devices because of the wide range of electrical properties that can be achieved through appropriate doping and the relative abundance of Zn. We have deposited ZnO films with various thicknesses by sputtering on polyethylene terephthalate (PET) and polyethylene naphthalate (PEN) flexible substrates and measured their mechanical properties using compression and scratch tests coupled with in-situ optical microscopy. The cracking of ZnO, during compression, is thickness dependent and at lower thicknesses the films sputtered on PEN exhibit the highest crack onset strains, around 2%. During scratch testing, two major scratch failure mechanisms are observed, analyzed and discussed. It is also found that scratch resistance of ZnO is thickness dependent for both PET and PEN. At high scratch loads a secondary failure mechanism due to impregnation of film debris into the polymer substrates is observed.     

Bio-inspired polymeric patterns with enhanced wear durability for microsystem applications

At micro/nano-scale, friction force dominates at the interface between bodies moving in relative motion and severely affects their smooth operation. This effect limits the performance of microsystem devices such as micro-electro-mechanical systems (MEMS). In addition, friction force also leads to material removal or wear and thereby reduces the durability i.e. the useful operating life of the devices. In this work, we fabricated bio-inspired polymeric patterns for tribological applications. Inspired by the surface features on lotus leaves namely, the protuberances and wax, SU-8 polymeric films spin-coated on silicon wafers were topographically and chemically modified. For topographical modification, micro-scale patterns were fabricated using nanoimprint lithography and for chemical modification, the micro-patterns were coated with perfluoropolyether nanolubricant. Tribological investigation of the bio-inspired patterns revealed that the friction coefficients reduced significantly and the wear durability increased by several orders. In order to enhance the wear durability much further, the micro-patterns were exposed to argon/oxygen plasma and were subsequently coated with the perfluoropolyether nanolubricant. Bio-inspired patterns with enhanced wear durability, such as the ones investigated in the current work, have potential tribological applications in MEMS/Bio-MEMS actuator-based devices.     

Mechanical spectroscopy of nanocrystalline aluminum films: effects of frequency and grain size on internal friction

Energy dissipation by internal friction is a property of fundamental interest for probing the effects of scale on mechanical behavior in nanocrystalline metallic films and for guiding the use of these materials in the design of high-Q micro/nanomechanical resonators. This paper describes an experimental study to measure the effects of frequency, annealing and grain size on internal friction at room temperature in sputter-deposited nanocrystalline aluminum films with thicknesses ranging from 60 to 120 nm. Internal friction was measured using a single-crystal silicon microcantilever platform that calibrates dissipation against the fundamental limits of thermoelastic damping. Internal friction was a weak function of frequency, reducing only by a factor of two over three decades of frequency (70 Hz to 44 kHz). Annealing led to significant grain growth and the average grain size of 100 nm thick films increased from 90 to 390 nm after annealing for 1 h at 450?(°)C. This increase in grain size was accompanied by a decrease in internal friction from 0.05 to 0.02. Taken together, these results suggest that grain-boundary sliding, characterized by a spectrum of relaxation times, contributes to internal friction in these films.     

应用于MEMS的PZT铁电薄膜

薄膜制备工艺的发展使铁电薄膜很好的应用于MEMS, 使两者集成成为可能. 本文将详细论述铁电薄膜的优良性能, 及其与MEMS集成的关键工艺--图形化. 最后, 举例论述了PZT铁电薄膜在MEMS中的应用.     

In situ nanomechanical behaviour of coexisting insulating and metallic domains in VO<Subscript>2</Subscript> microbeams

Measuring the electrical and mechanical responses of coexisting phases at nanoscale provides a platform to engineer micro-/nanoscale pattern of metallic and insulating domains with control over properties to make novel devices. Here, we employ several in situ characterization techniques, namely Raman, optical imaging and electrical measurements, to identify the phase coexistence of metallic and insulating domains. Further, we performed site-specific in situ nanoindentation to address the spatial variation in nanomechanical properties in vanadium dioxide (VO₂) single-crystal microbeams in proximity to metal–insulator transition temperature. We also investigated load or contact depth dependence on elastic modulus at various temperatures to avoid the interference of indentation size effect on nanomechanical properties across the phase transition. The obtained results confirm the abrupt increase in elastic modulus (~17 GPa) and nanohardness (1 GPa) across the transition from monoclinic (insulator) to rutile (metal) phase.     

炭纤维增强C/SiC双基体复合材料的制备及性能(英文)

以针刺炭纤维整体毡为预制体,联用化学气相沉积法与熔融渗硅法制得炭纤维增强C/SiC双基体(C/C-SiC)复合材料;研究了C/C-Si材料的显微结构、力学性能和不同制动速度下的摩擦磨损性能及机理。结果表明:C/C-SiC材料具有适中的纤维/基体界面结合强度,弯曲强度和压缩强度分别达240MPa和210MPa,具有摩擦系数高(0.41～0.54),磨损小(0.02cm3/MJ),摩擦性能稳定等特点.随着制动速度提高,C/C-Si材料的摩擦磨损机制也随之变化:在低速制动条件下主要表现为磨粒磨损;中速时以黏着磨损为主;高速时以疲劳磨损和氧化磨损为主。     

Al_2O_3颗粒镀铜对铜基粉末冶金摩擦材料Al_2O_3-Fe-Sn-C/Cu摩擦磨损性能的影响

通过对陶瓷摩擦组元的表面进行化学镀铜来改善铜基粉末冶金摩擦材料中陶瓷相与基体间的结合效果,从而提高材料摩擦磨损性能。分别采用镀铜Al2O3颗粒和未镀铜Al2O3颗粒与铜粉和铁粉等经混合、压制、加压烧结制备Al2O3-Fe-Sn-C/Cu摩擦磨损试样。测试并分析了摩擦材料的微观结构、力学性能及摩擦磨损性能。结果表明:摩擦组元镀铜可使硬质颗粒与铜基体结合紧密;摩擦材料的布氏硬度增加了12%,弹性模量提高了约7%,摩擦系数提高了5%~10%,线磨损量降低了20%~50%;表面镀铜后的Al2O3颗粒不易脱落,摩擦系数稳定性提高了13%~23%。研究结果表明,摩擦组元表面镀铜可提高材料的综合性能。     

Si3N4和52100钢对磨副材料对CrN薄膜干摩擦学行为的影响

利用阴极电弧离子镀技术在316L不锈钢基体上制备了CrN薄膜。采用扫描电子显微镜(SEM)、X射线衍射仪(XRD)、纳米压痕仪对CrN薄膜的形貌、成分和力学性能进行了表征。为了研究Si_3N_4和52100钢对磨副材料对CrN薄膜和316L不锈钢干摩擦行为的影响,在2N、5N、8N三种载荷下,将CrN薄膜和316L不锈钢基体与Si_3N_4陶瓷球和52100钢球分别进行了往复式滑动干摩擦实验。采用扫描电子显微镜观察了磨痕的微观形貌,并对CrN薄膜和316L不锈钢基体的磨损机制进行了分析。结果表明:CrN薄膜表面平整,缺陷较少;CrN薄膜的纳米硬度约为28GPa,弹性模量约为350GPa;与Si_3N_4陶瓷球相比,CrN薄膜与52100钢球摩擦时摩擦因数相对较小(保持在0.7左右)且更加稳定;316L不锈钢的摩擦因数远大于CrN薄膜且波动较大;对磨球为Si_3N_4陶瓷球时,CrN薄膜的主要磨损机制为磨粒磨损,伴有少量的氧化和黏着磨损,316L不锈钢的磨损机制主要为磨粒磨损和塑性变形,伴有少量的氧化和黏着磨损;对磨球为52100钢球时,CrN薄膜的主要磨损机制为黏着磨损,伴有少量的氧化,316L不锈钢的磨损机制主要为黏着磨损,伴有少量的氧化和磨粒磨损。CrN薄膜与两种对磨球的磨损量均小于316L不锈钢基体的磨损量,说明CrN薄膜有效提高了基体的耐磨性。     

Microstructure and Tribological Behavior of Stripe Patterned TiN Film Prepared with Filtered Cathodic Vacuum Arc Deposition (FCVAD)

This paper describes an experimental investigation into the influence of the stripe interspace and applied load on the tribological behavior of stripe patterned TiN films. The stripe patterned TiN films are deposited on an H13 steel surface by masked deposition with the filtered cathodic vacuum arc discharge (FCVAD) technique. The surface micro morphology, chemical composition, crystal structure, and mechanical properties of the films is characterized using 3D white light interferometry, scanning electron microscopy (SEM), X‐ray diffractometry (XRD), and a nano‐indentation tester, respectively. The tribological performance of patterned TiN is measured using a UMT‐5 tribometer, and the friction and wear mechanisms are analyzed, compared with that of the full TiN film and H13 steel substrate. The results show that the stripe patterned TiN films has better tribological properties than the full TiN film. These results are attributed to the synergistic effect between the surface pattern and the TiN film. The stripe interspace and the applied load has a more significant effect on the wear rate of the stripe patterned TiN films than the coefficient of friction of their friction pairs. A further study, however, is needed to analyze the relationship between the applied load and the wear rates of the stripe patterned TiN films.

     

Mechanical properties and scratch resistance of filtered-arc-deposited titanium oxide thin films on glass

The mechanical properties and the scratch resistance of titanium oxide (TiO₂) thin films on a glass substrate have been investigated. Three films, with crystalline (rutile and anatase) and amorphous structures, were deposited by the filtered cathodic vacuum arc deposition technique on glass, and characterized by means of nanoindentation and scratch tests. The different damage modes (arc-like, longitudinal and channel cracks in the crystalline films; Hertzian cracks in the amorphous film) were assessed by means of optical and focused ion beam microscopy. In all cases, the deposition of the TiO₂ film improved the contact-mechanical properties of uncoated glass. Crystalline films were found to possess a better combination of mechanical properties (i.e. elastic modulus up to 221 GPa, hardness up to 21 GPa, and fracture strength up to 3.6 GPa) than the amorphous film. However, under cyclic sliding contact above the critical fracture load, the amorphous film was found to withstand a higher number of cycles. The results are expected to provide useful insight for the design of optical coatings with improved contact-damage resistance.     

Nanoscale mechanics of solid-supported multilayered lipid films by force measurement

Using atomic force microscopy and molecular force probe, we have studied the structure and nanomechanical response to nano-indentation of multilayered films of dioleoylphosphatidylcholine films prepared by solution spreading, spin-coating, and capillary methods. The influence of the film thickness on the apparent elastic (Young's) modulus is investigated. Young's moduli of samples prepared by the different methods were found to be similar for sufficiently thick films. An ostensible influence of substrate coupling on the apparent Young's modulus is observed for thinner lipid films. The results are discussed in comparison with previously reported estimates for supported lipid bilayers (membranes) and cells.     

制动用C/C-SiC复合材料摩擦学性能研究现状

C/C-SiC复合材料是高速制动材料的优良候选材料。摩擦磨损性能是衡量制动材料的主要性能指标,也是制约材料进一步应用的主要因素。主要从材料微观结构和成分以及工况条件对C/C-SiC复合材料的摩擦磨损性能的影响两方面阐述了C/C-SiC复合材料摩擦磨损性能的研究现状;分析了影响C/C-SiC复合材料摩擦磨损性能的主要材料因素和工况条件;讨论了各自影响机制;并提出了进一步提高C/C-SiC复合材料摩擦磨损性能和使役安全所需解决的问题。     

A tribological study of tetrahedral amorphous carbon films prepared by filtered cathodic vacuum arc technique

In this study, a series of tetrahedral amorphous carbon films (ta-C) were deposited on silicon, W18Cr4 V high-speed and Cr18Ni9 stainless steel substrates respectively by using pulsed filtered cathodic vacuum arc system with a MEVVA source, and ta-C film’s tribological properties, including the structure, mechanical performance, adhesion, friction and wear character, were investigated. The results show: the hardness and elastic modulus of ta-C film on a high-speed substrate were reached to 76 and 453 Gpa, respectively; and the effects of substrate and film thickness on ta-C film’s friction coefficients have been studied as well; moreover, the corresponding adhesion damage mechanism and wear damage mechanism have been investigated, respectively.