Amorphous carbon coatings mainly composed of sp3 and sp2 bonds have a great potential to be widely used in modern industry for their attractive properties, such as high hardness, high wear resistance and low friction coefficient. However, the high internal stress and poor adhesion of amorphous carbon coatings limit the range of industrial applications. In order to reduce the internal stress and improve the tribological performance, a series of carbon-based coatings with different atomic fraction of Cr were prepared by magnetron sputtering. The microstructure of coatings was characterized by XRD, SEM, TEM, XPS and Raman spectra. The mechanical and tribological properties of coatings were analyzed. The results showed that with the increase of atomic fraction of Cr, the carbon-based coatings changed from amorphous structure to nano-crystalline/amorphous composite structure, the ratio of sp2 bond increased and the ratio of sp3 bond decreased gradually. Also, the hardness and the internal stress showed a decreasing trend with the increase of atomic fraction of Cr. In addition, a small amount of Cr doping could effectively reduce the friction coefficient and specific wear rates of coatings. Excessive Cr doping is beneficial to the increase of the ratio of sp2 bond, however, the dispersion distribution of the metal phase leads to the increase of the friction coefficient and specific wear rates, so that the tribological properties were deteriorated.
随着现代化工业的日益发展,越来越多的机械部件开始朝着高精度、高速度、高质量的水平发展,作为机械部件的主要基础件——轴承的摩擦失效问题越来越突出。精密机械传动系统中,由于其相对运动部件之间几乎是零间隙装配,传统的通过在摩擦副之间形成连续油膜来隔离部件以减少磨损的“引入润滑介质实现减磨延寿”的制造理念已很难实现。例如在谐波减速器中的柔性轴承因难以形成连续油膜而处于钢与钢之间的直接接触摩擦,其摩擦系数(一般大于0.5)远大于形成连续油膜的摩擦副之间10-2 [2~4]数量级的摩擦系数,从而导致摩擦副过早失效,严重缩短工件的使用寿命。而为解决此类有相对运动精密机械基础件的“减磨延寿”问题,在其表面制备1 μm左右厚度的高导热、低摩擦系数并有纳米金属微晶起增韧作用的碳基离子镀层的表面处理成为有效途径。
实验采用MSIP019型闭合场非平衡磁控溅射离子镀设备沉积不同Cr含量的碳基离子镀层。设备真空腔直径450 mm、高400 mm,平面阴极靶材为高纯C靶(约99.99%)及Cr靶(约99.99%)各一块,对称布置于圆柱形炉腔两侧,靶材直径100 mm,通过调整阴极磁铁排布及磁场强度将靶材表面放电面积缩小至45 cm2左右。实验基体选取P型(100)单晶Si片和M2高速钢片,其中,单晶Si片主要用于检测镀层的微观结构、内应力以及力学性能;高速钢片主要用于检测镀层的摩擦学性能。基体材料在使用前分别采用CH3COCH3 (丙酮)和CH3CH2OH (乙醇)溶液各超声波清洗20 min,清洗完成后用N2吹干放置于真空腔内120 mm处。实验在高纯Ar气氛中进行,真空度抽至3.0×10-3 Pa以上,气压保持在1.1×10-2~1.2×10-2 Pa范围内。碳基离子镀层的制备过程主要包括等离子体清洗、沉积纯Cr打底层、沉积过渡层和沉积工作层4个步骤。沉积工作层时,C靶电流为1.5 A,基体偏压为-60 V,沉积时间为2 h,通过改变Cr靶电流调节工作层Cr含量,具体实验参数如
利用JSM-6700F场发射扫描电子显微镜(SEM)和Dimension Icon型原子力显微镜(AFM)观察镀层表面与截面的微观形貌;利用Renishaw inVia Relfex型Raman光谱仪对镀层进行结构分析;利用AXIS ULTRA型X射线光电子能谱(XPS)分析镀层的元素组成及化学状态;利用XRD-7000S型X射线衍射仪(XRD)分析镀层的相结构,Cu靶(波长为0.15406 nm),电压40 kV,电流30 mA,步长0.02°,扫描速率8°/min,扫描范围(2
(2) 碳基离子镀层均以sp2杂化键为主,随着Cr含量的增加,镀层中的sp3杂化键含量减小,sp2杂化键含量增大,一定范围内提高了sp2杂化键的有序度,促使其发生石墨化转变。并且随着Cr含量的增加,镀层中C—Cr化合键含量增加,当Cr含量为25.5%时,出现大量2~10 nm的纳米晶团簇,其微观结构由典型的非晶结构转变为纳米晶/非晶复合结构。
The authors have declared that no competing interests exist.
To investigate their effect on the fretting wear (FW) and fretting fatigue (FF) resistance of a Ti6Al4V alloy, the diamond-like carbon (DLC) and graphite-like carbon (GLC) films were deposited on a Ti6Al4V alloy substrate using closed field unbalanced magnetron sputtering. The basic film properties, such as surface morphology, micro-structure, micro-hardness, bonding strength, and toughness were investigated by atomic force microscopy, X-ray photoelecton spectroscopy, nano-hardness testing, scratch testing and by a home-made repeated press-press test system, respectively. The FW and FF resistance was studied using home-made devices. The results show that DLC and GLC films can reduce the friction factor while the FW and FF resistance of the titanium alloy were improved significantly. However, the FW and FF resistance of the DLC film on the titanium alloy was better than that of the GLC film. This was attributed to the excellent properties of bonding strength and toughness of the DLC film. Moreover, the effect of bonding strength and toughness is more important than that of friction factor in improving the FW and FF resistance.
61Influence of the ultrafine additives on the rheological properties of the lubricants.61Application of variational method in hydrodynamic lubrication theory.61Friction and vibration in the fluid-film bearings when lubricated with the oils with ultrafine additives.
Abstract The tribological properties of Fe-Cr-B alloys were studied sliding against SiC ball in liquid paraffin oil. The boron played an important role in improving tribological properties of alloys. The friction coefficients of alloys decreased with the increase of normal load and sliding speed. The Fe-Cr-B alloys showed better wear resistance than that of Fe-Cr alloy. Fe-21 wt.% Cr-7 wt.% B alloy had the best tribological properties. The wear mechanism of Fe-Cr alloy was abrasive wear and plastic deformation. The wear mechanism of Fe-Cr-B alloys was microploughing and fatigue flaking pits.
New in this work is that optimised DLC coatings were applied to ball bearings for space applications. The torque and life tests of coated pairs of angular contact bearings in air revealed that relatively high bearing torques are generated which increase with time, but the amount of coating wear generated during in-air operation appears relatively light. In vacuum, low torques are generated after a prolonged running-in period. Low-torque life exceeds that observed for MoS 2 MoS 2 mathContainer Loading Mathjax by a factor of about two. It is concluded that, in contrast to MoS 2 MoS 2 mathContainer Loading Mathjax coated bearings, DLC-coated bearings for space applications might therefore be capable of undergoing in-air ground testing without too much disruption of the subsequent in-space performance.
The present work is a contribution towards the development of new and novel low friction coatings for automotive engine cam and cam follower components. A series of hardened and tempered 100Cr6 steel (a 1.0% C, 1.5% Cr bearing steel) rollers, coated with three different coating materials: (i) Cr 2N; (ii) CrN + nC (where nC refers to nano-/micrometer-sized carbon particles embedded in the CrN matrix) and (iii) Cr + W–C:H were compared to uncoated 100Cr6 steel using a specially adapted thrust bearing test. The counterface materials, in all tests, comprised two uncoated 100Cr6 steel washers. Tests were conducted in two oils: FVA-3 and SAE10W40. The latter contained various additives whilst the former was additive free. In both lubricants, the uncoated test rollers failed through pitting caused by rolling contact fatigue and a very similar roller life was obtained. Six modes of failure mechanism were observed for the coated rollers. Only two of these resulted in the premature pitting of the substrate via rolling contact fatigue. The rates of degradation of all the coatings was strongly influenced by the type of lubricant used. In the FVA-3 oil, the durability of the Cr 2N > Cr + W–C:H > CrN + nC coatings, whereas in the SAE10W40 oil, the durability of the Cr + W–C:H > Cr 2N > CrN + nC coatings. The CrN + nC coatings were the least durable of all the coatings and failed through exfoliation (adhesive failure) along or near the coating-substrate interface. The Cr + W–C:H gave the best overall coating durability and were degraded via a combination of polishing wear with micro-/nano-delamination and micro-pitting.
Tribochemical reaction of Si-DLC coating in water was investigated by stable isotopic tracer. Heavy water (deuterium oxide, D 2 O) was used to carry out the friction test of the coating against a 440C ball. The worn surfaces were analyzed by ToF-SIMS. The results showed that tribochemical reaction of Si-DLC occurred with D 2 O, and CD, OD groups were formed on the contact surfaces. The formation of SiOD and CO 2 D groups was also confirmed on the worn ball surface. The tribochemical products containing hydrophilic hydroxyl and carboxyl groups are considered to be responsible for low friction and wear of Si-DLC coating and the counter part in a water environment. On the other hand, the Si amount of the coating decreased due to the rubbing. The decrease in the Si amount was not only caused by the removal of the surface layer in which Si concentrated, but also by the tribochemical reaction. The presence of Si may accelerate the tribochemical reaction resulting in the lower friction and the wear of the counter ball, although the wear of the coating increases due to chemical wear, compared with Si-free DLC coating.
Diamond-like carbon (DLC) thin films were grown on Si-(100) substrates by a magnetically-assisted pulsed laser deposition (PLD) technique. The role of magnetic field on the structural, morphological, mechanical properties and deposition rate of DLC thin films has been studied. The obtained films were characterized by Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), field emission scanning electron microscopy (FE-SEM) and nanoindentation techniques. It was found that the diamond-like character, thickness and deposition rate of the DLC films increase in the presence of magnetic field. The films deposited under magnetic field exhibit a denser microstructure and smoother surface with lower surface roughness. Meanwhile, the mechanical properties of the magnetically processed DLC thin films experience an improvement, relative to the conventionally processed ones. It seems that the DLC films deposited under magnetic field can be better candidate for hard and wear resistance coating applications.
Free-standing amorphous carbon (a-C) cantilever structures were successfully fabricated by a single photolithography step. The relatively thick (651 μm), smooth (650.75 nm), low stress ( mm/Nm) were deposited by filtered cathodic vacuum arc (FCVA) deposition system, in conjunction with high substrate pulse biasing (5 kV, 600 Hz and 25 μs). The undercutting of the cantilever was carried out, both by isotropic (in a solution mixture of 40% HF (1 part) and 70% HNO (3 parts)) as well as anisotropic (in 40 wt.% KOH) Si wet etching methods. The study reveals that it is not viable to fabricate perfect free-standing a-C cantilever structure by isotropic wet etching. However, by controlling the etching duration/rate, it is possible to fabricate the as-designed free-standing cantilever structures by anisotropic wet etching method. The SEM images of the free-standing a-C cantilever structures do not show any bulging, and which clearly shows that the intrinsic stress in the film is low enough to be used for the fabrication of micro-electro-mechanical system (MEMS) devices, such as micro-motors and gears.
Tetrahedral amorphous carbon (ta-C) films were prepared by pulsed laser deposition using a 248-nm excimer laser wavelength and up to 45 J/cm 2 laser pulse energy fluence. Fluences above 6 J/cm 2 and mean kinetic energies of the ablated species above 30 eV, respectively, as well as substrate temperatures below 100 °C were found to be necessary for the formation of ta-C films with high sp 3 percentage. Such films are completely amorphous and have up to 85% sp 3 bonds. As-deposited films show high compressive stresses in the range of 8–10 GPa. The possibilities to reduce those stresses by means of thermal and pulsed laser annealing were investigated. We found that both methods allow the preparation of nearly stress-free diamond-like carbon films with several micrometers of thickness and good adherence to Si and WC hard metal substrates. The Vickers microhardness of those films was measured to be 55–65 GPa and the Young's modulus was measured to be 800–900 GPa by using a dynamic indentation method.
Tetrahedral amorphous carbon (ta-C) films have been deposited by filtered cathodic vacuum arc technique with substrate pulse bias ranging from 61100 to 613000 V. The surface morphology, structure, stress, hardness and Young's modulus of the films were characterized using atomic force microscopy, Raman spectroscopy, surface profilometry and nanoindentation. The results show that the highest stress existed at the pulse bias voltage between 61100 and 61200 V. The mechanical properties of the films were determined directly from an Oliver–Pharr analysis of nanoindention experimental data. The highest hardness and reduced Young's modulus, which were achieved at 61200 V, were 85 and 390 GPa, respectively. By using the relationship between hardness and stress, 1-μm-thick ta-C films were successfully deposited using 612000 V with a moderate hardness of about 36 GPa and a low stress of less than 1 GPa.
The origin of paramagnetic centers in graphite-like amorphous carbon is investigated. The films were deposited by the ion beam assisted deposition (IBAD) and have a concentration of sp2 sites of about 90% and zero energy band gap. The density of the film and the electrical resistivity are close to these of crystalline graphite. However, the hardness and stress of the films are similar to those of diamond-like carbon. Electron spin resonance (ESR) performed at the X-band (9.4GHz) revealed an unexpected low density of paramagnetic centers, ascribed to conduction electrons with a g-value of about 2.003.
Two hard, carbon-based solid lubricant coatings, Graphit-iC 64 and Dymon-iC 64, have been developed which offer considerable benefits over traditional diamond-like carbon (DLC) coatings. Both have extremely high wear resistance and load-bearing capability, in contrast to many commercial DLCs which tend to be brittle, and very low friction characteristics. The development of the coatings is described, and details of their tribological properties in air and water are given. The structure of the coatings has been studied and related to the tribological properties, and the mechanism for the low friction and wear rates is discussed. The coatings are proving successful in increasing the lifetime and efficiency of many mechanical parts, including automotive fuel injection components, gears, bearings, tappets, gudgeon pins, etc. They offer benefits for tooling, used for forming or machining of soft materials, and are used on dies and moulds. Other application areas include surgical tools and implants.
Graphite-like amorphous carbon (GLC) films were fabricated by unbalanced magnetron sputtering on silicon and stainless steel substrates. The effects of deposition bias voltage on the microstructure, mechanical and tribological properties of the resultant films were investigated by means of X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, atomic force microscopy (AFM), high resolution transmission electron microscopy (HRTEM), nano-indentation and tribological experiments, respectively. The results show that the present films are dominated by sp 2 sites, and the microstructure and properties of the resultant films strongly depend upon the deposition bias voltage. Namely, the sp 3 content, hardness, elastic modulus and critical load monotonically increase with increasing deposition bias voltage from 50 to 150 V, and then they decrease with further increasing the bias voltage to 185 V, while internal stress decreases at first and then increases with further increasing of deposition bias voltage. The films deposited at different bias voltages have high surface roughness. Tribological properties of the films are closely related with the deposition bias voltage, 150 V is the optimum value for obtaining good wear resistance.
61Microstructure and property of GLC film are dependent on deposition target power.61Decreased elastic modulus leads to the increase of friction in ambient air.61Water lubrication results in the similar low friction if the GLC film can survive.61Decrease of mechanical properties causes the increase of wear rate in ambient air.61Decrease of film compactness generates the increase of wear rate in water.
The Closed Field Un-Balanced Magnetron Sputter Ion Plating (CFUBMSIP) process is now routinely used in a production environment and is characterised by a high degree of flexibility in terms of the substrates and coating materials which can be used. Compared to classical magnetron sputtering the closed field system produces higher ion current density which gives high quality coatings and excellent adhesion. The ability to vary the deposition parameters over a wide range, permits the modification of not only the composition and the structure but also the morphology (density and growth mode) of the films. This paper describes, that in particular, a range of carbon coatings from transparent, electrically insulating to black, conductive coatings, can be produced. Tribological tests concerning adherence, hardness and wear properties in atmospheric and lubricated conditions are presented. The effects of the nature of the substrates with different hardness properties (M42, stainless steel and Al) are investigated.
Two new coatings based on graphite and MoS 2 have been developed. They combine low friction with high hardness, high load capacity and exceptionally low wear. Both coatings act as solid lubricants, providing protection for both the coated surface and any opposing uncoated surface. The coatings are finding application in improving the general performance of cutting and forming tools and also make possible high-speed machining. The graphite-based coatings have exceptional wear properties under water or oil and results from wear tests under a wide range of conditions are given. A number of practical applications are given, including the protection of artificial hip joints. The advantages offered by the use of such coatings for many mechanical components are demonstrated.
Diamondlike carbon (DLC) films, known for exhibiting attractive combination of properties, have been extensively studied in the recent past. The inherent, internal compressive stresses affecting their adhesion and their relatively low thermal stability above 400 C are two major drawbacks preventing wide usage of these films. Carbide formers incorporated into the carbon network have the potential to stabilize the film structure, relax internal stresses and improve their performance. The present work focuses on the synthesis, structure and mechanical and tribological property characterization of Cr-containing nanocomposite DLC films. The films were synthesized using a plasma-enhanced hybrid chemical vapor and physical vapor deposition process in a discharge composed of a mixture of CH 4 and Ar gases. The Cr content in the films varied up to 18 at.%. The film morphology and composition were characterized by scanning and transmission electron microscopy, X-ray photoelectron spectroscopy and nuclear reaction analysis. The mechanical and tribological behavior of the films was studied as a function of Cr concentration by conducting nanoindentation and pin-on-disc experiments, respectively. The results showed that the films can be either amorphous with dispersed metallic-like Cr (at low Cr content) or nanocomposite consisting of face-centered cubic metastable CrC nanoparticles dispersed in the DLC matrix. Films with low Cr content (< 5 at.%) were found to possess similar tribological characteristics with those of pure DLC films. Incorporation of more Cr (> 12 at.%) results in larger chromium carbide particles that have an adverse effect on wear resistance. The films with the low Cr content offer the opportunity to combine the excellent tribological behavior with other desirable properties deriving from the presence of the second phase.
C/Cr nano-scale multilayer coatings have been produced by the combined steered cathodic arc/unbalanced magnetron sputtering technique. The coating was deposited by non-reactive unbalanced magnetron sputtering from three graphite targets and one chromium target at deposition temperatures of 250, 350 and 450 °C. In scratch adhesion tests C/Cr coatings deposited on M2 HSS showed values exceeding critical load of 70 N. The XRD and TEM analysis revealed the amorphous nature of the coatings. Higher deposition temperatures led to an increase in crystallinity. Raman spectroscopy also showed that the amount of the carbon disorder depends on the deposition temperature, increasing from 68 to 86% for deposition temperatures of 250 and 450 °C, respectively. In pin-on-disc tests, C/Cr coatings exhibit a low coefficient of friction of between 0.1 and 0.2, when sliding against 100Cr6 steel ball. These low values were retained for tests in air, de-ionised water and engine oil. Remarkably low sliding wear coefficients of 2×10 6117 m 3/Nm for the coating and 1×10 6119 m 3/Nm for the counterpart were measured after 22.6 km sliding distance. However, the increased crystallinity of the coatings produced at higher deposition temperature leads to an increase in the friction coefficient. The C/Cr coatings, used as an overcoat on TiAlCrYN coated cemented carbide end mills, led to reduction of the rake and the flank wear rates by factor of 7 when machining extremely abrasive Ni based alloys.
用离子束辅助非平衡中频磁控溅射技术,在Si,高速钢或不锈钢基体上分别沉积得到了具有多组分过渡金属层缓冲的W梯度掺杂类金刚石碳(DLC)膜,研究了W靶电流对DLC膜组成、结构和性能的影响。实验表明,随着W靶电流增大,薄膜中W掺杂量增加,W的碳化物含量增加,sp~3结构含量减少;薄膜的纳米硬度和弹性模量逐渐增大,且材料抗塑性参数H/E随之增大;随W靶电流增大,材料与基体结合力增强,划痕实验临界载荷在80—100 N之间,材料摩擦系数增大;但磨损率因W掺杂而明显减小,且随W靶电流增大而减小。样品表面元素分布均匀,粗糙度(R_a)较小,R_a值在7.56—15.8 nm之间。
采用非平衡磁控溅射沉积技术在SCM415渗碳淬火钢基片上沉积 了无氢Ti掺杂类金刚石(Ti-DLC)薄膜和无氢高纯类金刚石(DLC)薄膜,通过调节Ti靶的溅射功率使获得的Ti-DLC薄膜Ti含量(原子分数) 为1.9%-34%.利用Raman分光光谱仪、XPS,XRD、显微硬度计及纳米划痕仪分析研究了Ti-DLC的组织结构、显微硬度及薄膜附着力.结果 表明,利用非平衡磁控溅射得到的Ti-DLC薄膜,在Ti含量小于25%时,Ti-DLC薄膜仍具有类金刚石薄膜的sp2,sp3结构,但Ti的掺杂促进 了sp3键向sp2键的转变.掺杂的Ti以TiC纳米晶的形式存在于非晶态的DLC中.掺杂Ti后薄膜的硬度明显降低,而薄膜附着力明显改善;但是当Ti 含量超过3%后,薄膜附着力无明显变化,硬度逐渐回升.
Amorphous carbon (a:C) films prepared on pure titanium (Ti) substrates exhibit relatively high intrinsic compressive stress. In order to obtain low stress films with varied electrical and mechanical properties, metal (Ti) ions are incorporated into the plasma. This is done with the help of metal containing carbon targets. Amorphous carbon films with varied percentage of Ti were deposited on polished pure Ti substrates using Filtered Cathodic Vacuum Arc (FCVA) technique together with substrate pulse biasing. Characterizations of the films were carried out using various equipments including Raman Spectroscopy, X-ray diffractometer, Atomic Force Microscopy (AFM), Pin-on-Disk Tribometer and Micro-Scratch Tester; and properties such as microstructure, crystallography, film stress, morphology, frictional coefficient and critical load were investigated as a function of Ti content in the target. The results suggest that the film prepared with 5 at.% Ti-containing carbon target, under 7 kV substrate pulse bias voltage, displays almost zero stress. However such films are inferior in its Tribological properties compared to that of pure a:C films.
W incorporated diamond-like carbon films were prepared on silicon(1 0 0) wafers using a hybrid deposition system composed of an end-Hall-type hydrocarbon ion gun and a tungsten DC magnetron sputter source. The W concentration in the films was controlled by changing the fraction of Ar in the Ar and C 6H 6 reaction gas. The chemical composition, atomic bond structure, and mechanical properties were investigated for W concentrations ranging from 0 to 8.6 at.%. When the W concentration was <2.8 at.%, the W atoms were dissolved in the amorphous carbon matrix without forming a WC 161 x phase. Amorphous and crystalline WC 161 x nano-particles appeared when the W concentration was >2.8 and >3.6 at.%, respectively. It was found that the hardness and elastic modulus were not sensitive to the W concentration in this concentration range. On the other hand, the residual compressive stress was strongly dependent on the chemical state of the incorporated W atoms. The change in mechanical properties is discussed in terms of the microstructural changes induced by W incorporation.
Metal incorporation into amorphous diamond-like carbon films can provide superior properties as metal nano-clusters or nanocrystalline metallic carbides can be embedded in the carbon network. In this work, a filtered metal plasma cathodic arc technique is used to generate a metal plasma and acetylene is introduced to the metal plasma plume to deposit metal-containing DLC (Me-DLC) films and form nanocrystalline carbide phases in the amorphous carbon matrix. The films exhibit high thermal stability up to annealing temperatures of 500 °C as revealed by X-ray diffraction, transmission electron microscopy, and Raman spectroscopy. At treatment temperature over 500 °C, a large amount of hydrogen is lost from the Me-DLC films as shown by elastic recoil detection. Breakdown and structural collapse of the film at high temperature can be attributed to the breaking of C–H bonds. Consequently, the C–C networks become more graphite-like to facilitate the formation of volatile C–O and metal oxides phases.
Carbon coatings containing a metallic component (zirconium, tantalum) were deposited with ion assistance on AISI M2 steel samples using a SVETLYACHOK source. The coatings were studied by Auger electron spectroscopy (AES), transmission electron microscopy (TEM), Raman spectroscopy (RS) and pin-on-disc tribological tests. The results have shown that the carbon coatings contain up to 20 at.% of the metallic component. These coatings have an amorphous structure with sp 3-type bonds. The presence of the coating on the surface of AISI M2 steel reduces the friction coefficient by a factor of five under the tribological conditions investigated. It is found that the tribological properties of the coatings deposited with the assistance of metal ions are significantly better than those coatings deposited with assistance of carbon ions. The latter coatings had carbon atoms with mixed sp 3顥竤p 2 bonds. The deposited composite carbon coatings are stable at a temperature of 100 C and allow a twofold improvement in the lifetime of fuel pump rods.
Pure carbon and carbon/chromium multilayer coatings were deposited using unbalanced magnetron sputtering technology in a deposition system with a three-fold rotation turntable. The physical properties, microstructure and tribological performance of these coatings were investigated. The pure carbon coating was found to have a hardness of up to 4000 HV whilst the C/Cr multilayer coatings were in general softer with the exact hardness depending on the amount of Cr in the coatings. Keeping the sputtering power of carbon targets constant, a sputtering current on Cr was found that produced coatings with the best combination of properties of hardness of approximately 2200 HV and critical load of scratch ( L c) up to 85 N. The microstructures of the coatings were analysed using scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray diffraction (XRD). The tribological performance of the coatings was investigated using a pin-on-disc test. The pure carbon coating was found to have very good wear properties at low load whilst the coatings with optimized Cr content were found to have excellent tribological performance at high load. No failure was detected in 1 h running in the pin-on-disc test using a 5 mm WC ball rubbing against a coated M42 steel substrate at a speed of 200 mm/s with a load of 140 N and contact pressure higher than 3.4 GPa. Drilling tests under dry and un-lubricated conditions on C/Cr multilayer coated high-speed steel drills showed very good cutting performance with a lifetime three times longer than that of commercial TiN-coated drills.
Carbon/chromium (C/Cr) coatings were co-deposited using unbalanced magnetron sputtering deposition technique. The tribological properties including wear mechanism and microstructures of the coatings were investigated using pin-on-disc tribometer, X-ray diffraction (XRD) and transmission electron microscope (TEM). The coatings were characterised by a high hardness (652200 HV), a low coefficient of friction (<0.1) and a very low wear rate under very high loads. The pin-on-disc tests of C/Cr coated tool steel against WC ball (5 mm of diameter) revealed low friction coefficient 0.06–0.1 depending on load and low wear rate 6510 6117 m 3/Nm with little dependence on load and sliding speed for the test using load up to 80 N and siding speed up to 400 mm/s for 1 h. Critical sliding speed was found above which, the wear rate was higher. The pin-on-disc tests of C/Cr coated austenitic 316 stainless steel against WC ball under a load of 10 N at siding speed of 400 mm/s for 1 h revealed a low friction coefficient 650.1 and a very low wear beyond the limitation of the as used wear measurement technique could detect. Microstructure of the coated stainless steel was investigated. XRD profiles of the coating exhibited typical patterns for amorphous-like material, with no crystal-like peaks identified. Cross-sectional TEM analysis of the rubbed tracks of the coated stainless steel revealed some deformation in the substrate near the interface. However, no sign of interfacial spallation was observed, indicative of excellent adhesion of the coating to the substrate. The selected area electron diffraction patterns taken from the rubbed and unrubbed regions of the coating were interpreted and discussed. The tribological performance of this novel C/Cr coating is believed to be closely related to its graphite nature. The high resolution TEM (HRTEM) cross-section analysis of the coating on stainless steel substrate revealed that the outer-most surface of the rubbed track was reoriented due to the rubbing in a 1-h pin-on-disc test under a load of 10 N. Finally, the relationship between deposition parameters and tribological performance of the coating is also discussed in this paper.
The model and theoretical understanding of the Raman spectra in disordered and amorphous carbon are given. The nature of the G and D vibration modes in graphite is analyzed in terms of the resonant excitation of states and the long-range polarizability of bonding. Visible Raman data on disordered, amorphous, and diamondlike carbon are classified in a three-stage model to show the factors that control the position, intensity, and widths of the G and D peaks. It is shown that the visible Raman spectra depend formally on the configuration of the spsites in sp-bonded clusters. In cases where the spclustering is controlled by the spfraction, such as in as-deposited tetrahedral amorphous carbon (ta-C) or hydrogenated amorphous carbon (a-C:H) films, the visible Raman parameters can be used to derive the spfraction.
Carbon thin films are very important as protective coatings for a wide range of applications such as magnetic storage devices. The key parameter of interest is the sp 3 fraction, since it controls the mechanical properties of the film. Visible Raman spectroscopy is a very popular technique to determine the carbon bonding. However, the visible Raman spectra mainly depend on the configuration and clustering of the sp 2 sites. This can result in the Raman spectra of different samples looking similar albeit having a different structure. Thus, visible Raman alone cannot be used to derive the sp 3 content. Here we monitor the carbon bonding by using a combined study of Raman spectra taken at two wavelengths (514 and 244 nm). We show how the G peak dispersion is a very useful parameter to investigate the carbon samples and we endorse it as a production-line characterisation tool. The dispersion is proportional to the degree of disorder, thus making it possible to distinguish between graphitic and diamond-like carbon.
The effect of annealing on the structure of diamond-like carbon (DLC) thin film fabricated by focused-ion-beam chemical-vapor deposition (FIB–CVD) was investigated. The near-edge x-ray absorption fine-structure spectrum of the carbon K-edge over the excitation energy range of 275–32002eV was measured on the FIB–CVD DLC thin film by annealing for 102h in a temperature region from room temperature (RT) to 127302K. The sp 2/( sp 2 + sp 3) ratio maintained ≈ 0.4 in an annealing temperature region from room temperature to 52302K and steeply increased from ≈ 0.4 to ≈ 0.7 with annealing temperature from 52302K to 77302K. The I( D)/ I( G) ratio, which was obtained from the Raman spectrum, also indicated a similar dependence on annealing temperature. The graphitization of thin film fabricated by focused-ion-beam chemical-vapor deposition (FIB–CVD) by annealing was confirmed to start at ≈ 60002K.
61Diamond like carbon films were deposited by coupling DC/RF magnetron sputtering.61The films prepared have high mass density and low internal stress.61The diamond like carbon films were deposited will be used in inertial confinement fusion (ICF) experiments.
DLC (a-C:H) films were deposited by the plasma enhanced chemical vapor deposition (PECVD) on silicon substrate and then post-implanted by plasma immersion ion implantation (PIII) at different voltages and ion species (Ar, N 2 and C 2H 2). Microstructure, dielectric constant and nano-hardness of the modified DLC films were studied. It is found that implanted C 2H 2 ions can effectively increase the nano-hardness of DLC films from 13.5 to 25.3 GPa and reduce the dielectric constant to 2.5 in the bias voltage range of 6135 to 6140 kV. The improved properties are mainly associated with the increase in the ratio of sp 3 C C/sp 2 C C bonds and the reaction mechanisms in the implantation zone are discussed.
Diamond-like carbon (DLC) films were deposited by a cathodic arc plasma evaporation (CAPD) process, using a mechanical shield filter combined with a magnetic filter with enhanced arc structure at substrate-bias voltage ranging from 61 50 to 61 30002V. The film characteristics were investigated using Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM) and high-resolution transmission electron microscopy (HRTEM). The mechanical properties were investigated by using a nanoindentation tester, scratch test and ball on disc wear test. The Raman spectra of the films showed that the wavenumber ranging from 900 to 180002cm 61 1 could be deconvoluted into 114002cm 61 1, D band and G band. The bias caused a significant effect on the sp 3 content which was increased with the decreasing of I D/ I G ratio. The XPS spectra data of the films which were etched by H + plasma indicated the sp 3 content are higher than those of the as-deposited DLC films. This implied that there is a sp 2-rich layer present on the surface of the as-deposited DLC films. The nanoindentation hardness increased as the maximum load increased. A 38002nm thick and well adhered DLC film was successfully deposited on WC-Co substrate above a Ti interlayer. The adhesion critical load of the DLC films was about 3302N. The results of the wear tests demonstrated that the friction coefficient of the DLC films was between 0.12 and 0.2.
Coating a surface with a thin layer changes the surface material properties and is an important tool for controlling friction and wear. The tribological mechanisms, scale effects and parameters influencing the friction and wear of coated surfaces are discussed. The basic friction and wear mechanisms can be reduced to: friction by adhesion, ploughing and hysteresis and wear by adhesion, abrasion and fatigue combined with material fracture. The tribochemical and surface physical effects and surface fatigue taking place before material fracture are treated here as pure surface material modification mechanisms. Scale effects in a tribological contact are illustrated by explaining typical surface roughness related tribological mechanisms for diamond and DLC coated surfaces. For diamond coatings asperity interlocking effects are important for rough surfaces, graphitisation is a dominating mechanism for smooth engineering surfaces and hydrogenising of dangling bonds may be crucial for physically smooth surfaces. For DLC coated surfaces, surface graphitisation is important with rougher surfaces; building up transfer layers and graphitisation is crucial for smooth engineering surfaces and hydrogenising of dangling bonds can explain superlubricity for physically smooth surfaces. An analysis of dominating surface parameters such as elastic, plastic and fracture behaviour of the top surface, the coating, the coating/substrate interface and the substrate in addition to the coating thickness forms the basis for surface modelling. A stress intensity factor analysis of crack growth shows the importance of considering both modes I, II and III loading, crack spacing and location of crack, while crack orientation, location in crack field as well as load biaxiality have minor influences. It is shown how surface 3D FEM modelling generates stress and strain values at the nano level, within bond layers at coating/substrate interfaces and around cracks and forms the basis for better understanding the origin of wear.
78 GLC coating exhibits different tribological properties against metals. 78 The differences are highly dependent on adhesions and wear behaviors of the metals. 78 GLC coating could show low friction and wear against GCr15 and Ti in air. 78 GLC coating is more suitable to machine common metals in water.