Friction and Wear Performance of Boron Doped, Undoped Microcrystalline and Fine Grained Composite Diamond Films

Chemical vapor deposition （CVD） diamond films have attracted more attentions due to their excellent mechanical properties. Whereas as-fabricated traditional diamond films in the previous studies don＇t have enough adhesion or surface smoothness, which seriously impact their friction and wear performance, and thus limit their applications under extremely harsh conditions. A boron doped, undoped microcrystalline and fine grained composite diamond （BD-UM-FGCD） film is fabricated by a three-step method adopting hot filament CVD （HFCVD） method in the present study, presenting outstanding comprehensive performance, including the good adhesion between the substrate and the underlying boron doped diamond （BDD） layer, the extremely high hardness of the middle undoped microcrystalline diamond （UMCD） layer, as well as the low surface roughness and favorable polished convenience of the surface fine grained diamond （FGD） layer. The friction and wear behavior of this composite film sliding against low-carbon steel and silicon nitride balls are studied on a ball-on-plate rotational friction tester. Besides, its wear rate is further evaluated under a severer condition using an inner-hole polishing apparatus, with low-carbon steel wire as the counterpart. The test results show that the BD-UM-FGCD film performs very small friction coefficient and great friction behavior owing to its high surface smoothness, and meanwhile it also has excellent wear resistance because of the relatively high hardness of the surface FGD film and the extremely high hardness of the middle UMCD film. Moreover, under the industrial conditions for producing low-carbon steel wires, this composite film can sufficiently prolong the working lifetime of the drawing dies and improve their application effects. This research develops a novel composite diamond films owning great comprehensive properties, which have great potentials as protecting coatings on working surfaces of the wear-resistant and anti-frictional components.

Friction Behaviors of the Hot Filament Chemical Vapor Deposition Diamond Film under Ambient Air and Water Lubricating Conditions

The friction behavior of the hot filament chemical vapor deposition（HFCVD） diamond film plays a critical role on its applications in mechanical fields and largely depends on the environment. Studies on the tribological properties of HFCVD diamond films coated on Co-cemented tungsten carbide （WC-Co） substrates are rarely reported in available literatures, especially in the water lubricating conditions. In this paper, conventional microcrystalline diamond（MCD） and fine-grained diamond（FGD） films are deposited on WC-Co substrates and their friction properties are evaluated on a reciprocating ball-on-plate tribometer, where they are brought to slide against ball-bearing steel and copper balls in dry and water lubricating conditions. Scanning electron microscopy（SEM）, atomic force microscopy（AFM）, surface profilometer and Raman spectroscopy are adopted to characterize as-deposited diamond films; SEM and energy dispersive X-ray（EDX） are used to investigate the worn region on the surfaces of both counterface balls and diamond films. The research results show that the friction coefficient of HFCVD diamond films always starts with a high initial value, and then gradually transits to a relative stable state. For a given counterface and a sliding condition, the FGD film presents lower stable friction coefficients by 0.02-0.03 than MCD film. The transferred materials adhered on sliding interface are supposed to have predominate effect on the friction behaviors of HFCVD diamond films. Furthermore, the effect of water lubricating on reducing friction coefficient is significant. For a given counterpart, the stable friction coefficients of MCD or FGD films reduce by about 0.07-0.08 while sliding in the water lubricating condition, relative to in dry sliding condition. This study is beneficial for widespread applications of HFCVD diamond coated mechanical components and adopting water lubricating system, replacing ofoil lubricating, in a variety of mechanical processing fields to implement the green production process.

Influence of Polyalkylmethacrylate VII on Boundary Film Formation,Friction,Wear and Efficiency of Lubricants

Polyalkylmethacrylates(PAMAs) are well-known as viscosity index improvers and dispersant boosters.This paper shows that PAMAs are able to adsorb from oil solution on to metal surfaces,to produce thick,viscous boundary films.These films enhance lubricant film formation in slow speed and high temperature conditions and thus produce a significant reduction of friction.A systematic study of this phenomenon has made use of the highly flexible nature of PAMA chemistry.A range of dispersant and non-dispersant polymethacrylates has been synthesized.The influence of different functionalities,molecular weights and architectures on both boundary film formation and friction has been explored using optical interferometry and friction-speed charting.From the results, guidelines have been developed for designing PAMAs having optimal boundary lubricating properties.Through their ability to form boundary films PAMAs can significantly contribute to reduce wear in engine,gear and hydraulic lubrication.As a consequence of their viscometric and tribological performance PAMAs can furthermore improve fuel and energy efficiency in different,namely engine and hydraulic applications.Extensive work is currently conducted in the lubricant industry to develop engine oils with lower sulfur,phosphorus and metal content(low SAPS) and to optimize their frictional properties through the use of friction modifiers or synthetic base stocks.We have investigated the contribution of PAMA viscosity index improvers and boosters to improve fuel economy and to reduce wear levels.This paper reports our efforts to develop a new range of PAMAs that have been optimized in terms of composition,architecture,molecular weight and functionality and which can be used in low viscosity,low SAPS formulations to help meet the stringent requirements of modern engine oils.

Effects of fragments on W-DLC films properties under boundary lubrication condition in the friction system

Abstract Effects of film fragments in the friction system on friction and wear properties of tungsten doped diamond-like carbon films （W-DLC） were studied in the condition of boundary lubrication. It could be observed that the average friction coefficient was increased after introducing film fragments into the friction system, where these film fragments can accelerate the breaking of the extreme thin oil film which could separate two friction surfaces when the system is under boundary lubrication conditions. The increasing friction load can accelerate the friction ehenfieal reaction on the friction interface and lead to the crushing effect on film fragments, which decreased the friction coefficient of friction system. It was also found that the wear width, depth, and volume of the film increased by introducing film fragments and applying great load.

SYNTHESIS OF PERFLUORO-1-OCTANESULFONATED FULLERENE AND THE FRICTION PROPERTIES OF ITS THIN FILM

A star-shaped compound of perfluoro-1-octanesulfonated fullerene was synthesized. The measurement of the friction for its spin-coating film by friction force microscopy (FFM) reveals that the films possess lower friction force compared to that of the star-shaped C-60-polystyrene films.

FRICTION PROPERTIES OF OIL-INFILTRATED POROUS AAO FILM ON AN ALUMINUM SUBSTRATE

The porous anodic aluminum oxide (AAO) film on a pure aluminum substrate was pre pared by a two-step anodization in a 0.3M oxalic acid solution and pore-enlargem ent treatment in the phosphoric acid aqueous solution at 50℃. The diameter of h ighly ordered pore on the AAO film was about 90nm, and the thickness of the AAO film was 3μm. The mineral oil was infiltrated in the ordered nanometer sized po res of AAO film on an aluminum substrate due to the capillarity effect. The fric tion coefficient was measured using a ball-on-disk tribotester. The tests were c onducted at loads range from 490 to 2450mN and at sliding velocities between 0.1 and 0.5m·s-1. Oil infiltration in porous AAO film modified friction and consid erably improved the wear resistance. As compared to the porous AAO film, the oil -infiltrated specimen had low friction coefficient. With increasing the applied load and sliding velocity, the friction coefficient of the oil-infiltrated film decreased. It indicates that the oil-infiltrated AAO film produced a new way to modify the friction and wear of aluminum alloy.

Tribological Characteristic of Diamond-like Carbon Films Investigated by Lateral Force Microscope

Tribological characteristic of different thick diamond-like carbon (DLC) films was studied. A geometrical method was applied to calibrate the cantilever spring constant and to calculate the normal and lateral forces, respectively. Experimental results show that the lateral force under different applied loads is proportional to the normal force for the DLC films with the thickness of 153.4nm and 64.9nm. However, for the thickness of 4.48nm and 2.78nm DLC films, lateral force is nonlinear to normal force, which is opposed to the Amonton's law.The single asperity regime and the DMT model were put forward to predict the possible nanotribological mechanism between the probe and DLC film.

Characterization and tribological investigation of self-assembled trimethoxysilyl-functionalized poly(phthalazinone ether ketone)thin films on glass substrates

Trimethoxysilyl-functionalized PPEK（PKGS） films had been designed to serve as wear resistant coatings for silicon surfaces. These surface films were formed by a dip-coating technique applied to self-assembled monolayers（SAMs）.The formation and wetting behavior of PKGS films were characterized by means of contact angle measurement.The friction coefficient of the film prepared is very low（about 0.1）,and the anti-wear behavior is good,with a lack of failure after sliding over 1800 s.

An improved wall shear stress measurement technique using sandwiched hot-film sensors

In this letter we present a novel wall shear stress measurement technique for a turbulent boundary layer using sandwiched hot-film sensors. Under certain conditions, satisfactory results can be obtained using only the heat generated by one of the hot-film and a calibration of the sensors is not required. Two thin Nickel films with the same size were used in this study, separated by an electrical insulating layer. The upper film served as a sensor and the bottom one served as a guard heater. The two Nickel films were operated at a same temperature, so that the Joule heat flux generated by the sensor film transferred to the air with a minimum loss or gain depending on the uncertainties in the film temperature measurements. Analytical solution of the shear stress based on the aforementioned heat flux was obtained. The preliminary results were promising and the estimated wall shear stresses agreed reasonablywell with the directly measured values （with errors less than 20%） in a fully developed turbulent pipe flow. The proposed technique can be improved to further increase precisions.

Frictional and Optical Properties of Diamond-Like-Carbon Coatings on Polycarbonate

In this work, diamond-like-carbon （DLC） films were deposited onto polycarbonate （PC） substrates by radio-frequency plasma-enhanced cheraical vapor deposition （RF PECVD）, and silicon films were prepared between DLC and PC substrates by magnetron sputtering deposition so as to improve the adhesion of the DLC films. The deposited films were investigated by means of field-emission scanning electron microscopy （FE-SEM）, X-ray photoelectron spectroscopy （XPS） and Raman spectroscopy. Subsequently, the following frictional and optical properties of the films were measured： the friction coefficient by using a ball-on-disk tribometer, the scratch hardness by using a nano-indenter, the optical transmittance by using a UV/visible spectrometer. The effects of incident power upon the frictional and optical properties of the films were investigated. Films deposited at low incident powers showed large optical gaps, which decreased with increasing incident power. The optical properties of DLC films correlated to the sp^2 content of the coatings. High anti-scratch properties were obtained at higher values of incident power. The anti-scratch properties of DLC films correlated to the sp^3 content of the coatings.

Microstructure and Mechanical Properties of Heat-treated GeSb_2Te_4 Thin Films

The effect of annealing on microstructure, adhesive and frictional properties of GeSb2Te4 films were experimentally studied. The GeSb2Te4 films were prepared by radio frequency （RF） magnetron sputtering, and annealed at 200℃ and 340℃ under vacuum circumstance, respectively. The adhesion and friction experiments were mainly conducted with a lateral force microscope （LFM） for the GeSb2Te4 thin films before and after annealing. Their morphology and phase structure were analyzed by using atomic force microscopy （AFM） and X-ray Diffraction （XRD） techniques, and the nanoindention was employed to evaluate their hardness values. Moreover, an electric force microscope （EFM） was used to measure the surface potential. It is found that the deposited GeSb2Te4 thin film undergoes an amorphous-to-fcc and fcc-to-hex structure transition; the adhesion has a weaker dependence on the surface roughness, but a certain correlation with the surface potential of GeSb2Te4 thin films. And the friction behavior of GeSb2Te4 thin films follows their adhesion behavior under a lower applied load. However, such a relation is replaced by the mechanical behavior when the load is relatively higher. Moreover, the GeSb2Te4 thin film annealed at 340℃ presents a lubricative property.

Microstructure, Photoluminescent Properties and Application of ZnO Films Grown on Al Foils

To obtain safety working before long-term early warning, we proposed a process for the preparation of luminescent films on metal substrate to detect the wear life. ZnO films were prepared on aluminum（Al） foils by the magnetron sputtering technique. The microstructure, tribological properties and photoluminescence（PL） spectra of ZnO films before and after the friction test were investigated. The microstructure of ZnO films grown on Al foils exhibited a closely packed hexagonal cone shape. ZnO films were grown along the orientation perpendicular to the substrate. The tribometric tests revealed that the average friction coefficient of ZnO films was lower and more stable than that of the substrate. The results of PL spectra indicated that the effect of Al element on ZnO films led to shifts of the defect related visible band. The luminescent center of ZnO films shifted from the emission peak at 510 nm before the friction to 647 nm after the friction, indicating that the green light shifted into the red light as the friction occurred. The visible light was helpful to understanding the failure characteristics during the friction and wear, and provide an early indicator of the impending failure.

FABRICATION AND AFM/FFM STUDIES OF C_(60)-CONTAINING POLYELECTROLYTE SELF-ASSEMBLED FILMS

An initial investigation on the roughness and frictional properties of the self-assembled thin films from polyelectrolytes is presented. Star-shaped C-60-Poly(styrene-maleic anhydride) was successful prepared. The multilayer thin films have been fabricated on mica with diazoresin as the cationic polyelectrolyte and hydrolyzed star-shaped C-60-poly(styrene-maleic anhydride) as the anionic polyelectrolyte via self-assembly technique. The crosslinking structure of the films is formed from the conversion of ionic bond to covalent bond after UV irradiation. AFM/FFM investigations provide insights into the roughness and frictional properties on a microscale. The roughness depends strongly on the number of film layers in the case of C-60-containing films. The frictional forces of the films exhibited a well behaved non-linear relationship in response to the change of applied load. It supports the prediction of enhanced load-bearing property Of C60-containing thin films.

Deposition of carbon nitride films for space application

Carbon nitride thin films were prepared by electron-beam evaporation assisted with nitrogen ion bombardment and TiN/CNx composite films were by unbalanced dc magnetron sputtering, respectively. It was found that the sputtered films were better than the evaporated films in hardness and adhesion. The experiments of atomic oxygen action, cold welding, friction and wearing were emphasized, and the results proved that the sputtered TiN/CNx composite films were suitable for space application.

Study on Property of Desensitized Explosive Film

The mechanical sensitivity, the critical thickness of detonation wave propagation and detonation velocity of desensitized PETN film were studied by experiments. The relationship between the mass of desensitizer paraffin wax and the friction sensitivity of desensitized PETN film was tested. According to the microstructure of film, the function of desensitizer was explained. It was proved that the explosive film could make explosive element micromation and kept its inherence properties by the result of testing the propagating critical dimension of the desensitized PETN film detonation wave. The explosive velocity of confined desensitized PETN film was tested by the multiplex optical fibre..

浸渍石墨材料在不同法向载荷下的磨损性能研究

研究不同摩擦体系下法向载荷对浸渍石墨的摩擦磨损特性的影响,采用扫描电子显微镜和激光共聚焦显微镜分别表征摩擦表面磨痕形貌、磨痕轮廓,对浸渍石墨与对偶球(GCr15钢球和Si_(3)N_(4)陶瓷球)的摩擦磨损情况与机制进行评估分析。结果表明:磨损痕迹随着施加载荷的增加而加深加宽,磨损率与法向载荷呈负相关,而摩擦因数、磨损体积则与法向载荷呈正相关;小载荷作用下石墨的磨损机制为黏着磨损和磨粒磨损,大载荷下则主要表现为黏着磨损、氧化磨损以及疲劳磨损;GCr15/石墨摩擦副相比于Si_(3)N_(4)/石墨摩擦副磨损率较低,在摩擦过程中形成完整、连续性更好的“第三体”转移膜减轻了磨损,对石墨基体起到保护作用。

Effect of Fe ion implantation on tribological properties and Raman spectra characteristics of diamond-like carbon film

Fe ions in the fluence range of 2×1015 to 1×1017 cm-2 were implanted into diamond-like carbon (DLC) thin film of 100 nm thick, which were deposited on silicon substrate by plasma enhanced chemical vapor deposition. Effects of Fe ion implantation on microstructure and friction coefficient of the DLC were studied. With increasing Fe ion fluence, friction coefficient of the DLC film increased as compared with that of DLC without implantation, and then decreased. The Raman spectra characteristics also show a dependence on the Fe ion fluence. With increasing the ion fluence, the sp2 bonding increased in the DLC film, resulting in the decrease of friction coefficient of the film af- ter implantation. Substantial surface roughness was also measured.

Effects of Friction Heat on the Tribological Properties of the Woven Self-lubricating Liner

In the dry-sliding process of the woven self-lubricating liner which is used in the self-lubricating spherical plain bearing, the friction heat plays an important role in the tribological performances of the liner. It has important value to study on the relationship between tribological performances of the liner and the friction heat. Unforttmately, up to now, published work on this relationship is quite scarce. Therefore, the effect of friction heat on the tribological performances of the liner was investigated in the present work. The tribological behaviors of the liner were evaluated by using the high temperature end surface wear tester. Scanning electron microscopy （SEM） was utilized to examine the morphologies of worn surfaces of the liner and study the failure modes. Differential scanning calorimetry （DSC） measurement and X-ray diffraction （XRD） analysis were performed to study the behaviors of the wear debris. The temperature rise on the worn surface was calculated according to classical models. SEM observation shows that the dominating wear mechanism for the liner is mainly affected by friction shear force, contact pressure and friction heat. Higher fusion heat for the wear debris than that for the pure polytetrafluroethylene （PTFE） indicates that the PTFE is the main portion of the wear debris, and, the PTFE in the wear debris shows a higher crystallisation degree owing to the effects of friction shear force and the friction heat. Combining the calculated temperature rise results with the wear rate of the liner, it can be concluded that the effects of temperature rise o n the tribological performances of the liner become more obvious when the temperature rise exceeds the glass transition temperature （Tg） of the PTFE. The wear resistance of the liner deteriorates dramatically when the temperature rise approaches to the melting point （Ton） of the PTFE. The tribological performances of the liner can be improved when the temperature rise exceeds Tg but is far lower than Ton- The present study on the relationship between the temperature rise and the tribological performances of the liner may provide the basis for further understanding of the wear mechanisms of the liner as well as the relationship between the formation of the PTFE transfer film and the friction heat during the dry-sliding of the Finer.

Infrared Spectral Studies of Copper-Containing Film on the Steel Sample

Infrared spectral studies of copper-containing film from steel sample (worn in pair with brass in glycerol) friction zone are performed in the study. The protective film formed by the interaction of the friction triad having functional groups typical for macromolecular compounds is shown.

Measurement of Shear Stress Acting on Flat Plate Using Oil Film Interferometry

Measurements of frictional resistance play an important role in engineering practice. There are several types of air resistance acting on an aircraft, for example. One of them, frictional resistance, accounts for half of the air resistance. Oil film interferometry is one of methods for measuring the frictional resistance. Oil dropped on an object is thinly stretched by the frictional resistance. The bright and dark fringe pattern is generated when monochromatic light is applied to the oil film. The gradient of the oil thickness decreases with the lapse of time, and thus the spacing between neighboring the dark lines increases. The rate at which the spacing increases is proportional to the frictional resistance. In this study, the frictional resistance acting on a small area on a plate was measured and compared with the theoretical value. As a result, these results qualitatively agree well with each other.