Tribological behavior of select MAX phases against Al2O3 at elevated temperatures

The layered M_n+1AC_n ternary carbides – MAX phases – Ta₂AlC, Ti₂AlC, Cr₂AlC and Ti₃SiC₂ were tested under dry sliding conditions against alumina at 550 °C and 3 N load (for a stress of ≈0.08 MPa) using a pin-on-disk tribometer. Ta₂AlC and Ti₂AlC exhibited low specific wear rates, SWRs, (≤1 × 10⁻⁶ mm³/N m), while the coefficients of friction, μ, were 0.9 and 0.6, respectively. At 0.4, μ of Ti₃SiC₂ was the lowest measured, but the SWR, at ≈2 × 10⁻⁴ mm³/N m, was high. With a μ of 0.44 and a SWR of 6 × 10⁻⁵ mm³/N m the Cr₂AlC sample was in between. No visible wear of Al₂O₃ counterparts was observed in all the tribocouples. Tribofilms, which were mainly comprised of X-ray amorphous oxides of the M and A elements and, in some cases, unoxidized grains of the corresponding MAX phases, were formed on the contact surfaces. The correlations between observed tribological properties and tribofilm characteristics are discussed.     

Friction coefficient and wear rate of sputter-deposited thin films and plasma-sprayed thick coatings at high temperatures in room air

Silver, calcium fluoride (CaF_x with x = 1.85) and chromium-carbon (Cr₃C₂) thin films were deposited onto various tribological test specimens by sputtering. The friction properties of sputter-deposited Ag and CaF_x single layers as well as Ag/CaF_x multilayer films were determined by ball-on-disk tribological tests conducted in room air under various experimental conditions. The tribological properties (friction coefficient and wear rate) of sputter-deposited CaF_x films were also determined at 500°C by pin-on-disk tribological tests performed with pin specimens made of cobalt-based alloy (alacrite). Chromium-carbon films sputter-deposited onto alacrite disk and counterfaces were found to be of interest for reducing the formation of alacrite wear debris in the wear tracks; thus reduced friction coefficient and wear rate values were obtained. The friction behavior of sputter-deposited CaF_x/Cr₃C₂ thin bilayer structures and plasma-sprayed (PS) chromium carbide/Ag/BaF₂-CaF₂ eutectic composite coatings (PS-212 type coatings) was investigated by plane-on-plane tribological tests conducted in room air at 500°C and 700°C. The friction performance of solid lubricant thin bilayer films was compared with that of thick PS-212 type coatings similar to coatings developed by NASA.     

Friction and wear properties of Ni–Cr–W–Al–Ti–MoS2 at elevated temperatures and self-consumption phenomena

The composites of Ni–Cr–W–Al–Ti–MoS₂ with different adding amount of molybdenum disulfide (6–20 wt.%) were prepared by powder metallurgy (P/M) method. Their mechanical properties and tribological properties from room temperature to 600 °C were tested by a pin-on-disk tribometer. The effects of amounts of molybdenum disulfide, temperature, load, and speed on the friction and wear properties of composite were discussed. Besides, the tribological properties against different counterface materials, such as alumina, silicon nitride and nickel-iron-sulfide alloys were also investigated. Results indicated that the molybdenum disulfide was decomposed during the hot-press process and the eutectic sulfides of chromium were formed. The hardness and anti-bending strength can be improved by adding 6 wt.% molybdenum disulfide due to reinforcement of molybdenum. The friction coefficients and wear rates of composites decrease with the increase of adding amount of molybdenum disulfide until a critical value of 12 wt.%. The composite with 12% MoS₂ shows the optimum friction and wear properties over the temperature range of RT 600 °C. The friction coefficients of composite with 12% MoS₂ decrease with the increase of temperature, load, and sliding speed, while the wear rates increase with the increasing temperature and are insensitive to the sliding speed and load. The friction coefficients of less than 0.20 at 600 °C and mean wear rates of 10⁻⁵ mm³/N m are obtained when rubbing against alumina due to the lubrication of sulfide films and glaze layer formed on the friction surface at high temperature, while a relatively low wear rate of around 10⁻⁶ mm³/N m presents when rubbing against nickel-iron-sulfide alloys. At high temperature, wear rates of composite containing sulfide are inversely proportional to friction coefficients approximately.     

Comparative wear in titanium diboride coatings on steel using high energy density processes

A comparison between the tribological properties of titanium diboride (TiB₂) deposited using high energy density processes such as Pulse Electrode Surfacing (PES) and Laser Surface Engineering (LSE) has been made. The wear resistance of TiB₂ coated surface is higher than AISI 1010 steel. The wear resistance of the LSE coated TiB₂ coating is even better than that of the PES deposited TiB₂ coating. Coefficient of friction values for LSE coated TiB₂ coating (μ=0.6) are lower than PES deposited TiB₂ coating (μ=0.7). Wear occurs in PES deposited TiB₂ coating by brittle fracture and attrition type mechanisms whereas mixed adhesive–abrasive wear in LSE deposited TiB₂ coating occurs by localized plastic deformation of the soft matrix phase Fe from a “composite” layer on the surface.     

Measurements of tribological properties of poly(pyrrole) thin film bearings

We report the results of a recent study on the tribological properties of electropolymerised thin films at light loads and low speeds. Poly(pyrrole) films incorporating different counter-ions have been electrochemically deposited onto gold electrodes on the plano-convex glass substrates and studied extensively. The measuring apparatus has been greatly improved from that reported earlier and now provides simultaneous monitoring of frictional force and wear. High precision capacitive gauging is employed to provide high resolutions of frictional force of better than 100 μN and height variation (wear) of 2 nm. A large number of specimens of poly(pyrrole) grown from five different counter-ions were prepared and their performances evaluated. The film morphology of each type of film was examined by atomic force microscopy (AFM) for control of the variability of film formation. Results are presented for the friction coefficients and wear rates observed for the films typically at a load of 2 N and a sliding speed of 5 mm s⁻¹. The effects of normal loading force and sliding speed on the friction coefficient are also discussed with a load range of 0.2–5 N and a sliding speed up to 30 mm s⁻¹.     

MoSx/MoSx-Mo纳米多层膜的制备及其环境摩擦学特性

用直流磁控溅射在钢基体上交替溅射制备了MoSx/MoSx-Mo纳米多层膜。采用划痕仪测试薄膜与基体的结合力;采用SEM和XRD分析了纳米多层膜的形貌和显微结构;在球-盘式微摩擦试验机上测试了纳米多层膜在真空和潮湿空气中的摩擦学性能。结果表明,纳米多层膜的结合力优于纯MoS2膜。随着溅射沉积气压的升高,MoSx(002)面择优取向减弱,纳米多层膜的结合力下降。溅射气压0.24 Pa沉积的纳米多层膜在真空和潮湿空气中都呈现出最低的摩擦因数和磨损率,具有优异的环境摩擦磨损特性。     

薄膜涂层摩擦学性能的灰色分析与预测

运用灰色系统理论，采用GM(1，1)直接建模预测法，对离子镀(Ti，Cr)N、TiN、CrN膜层的摩擦学性能进行了分析和预测。结果表明，对膜层摩擦学性能采用灰色理论进行分析与预测，可预测不同影响因素下膜层的摩擦系数和磨损率，其误差较小；能为膜层设计和工程实际使用提供指导依据。     

Studies of the tribological and mechanical properties of laminated CrC–SiC coatings produced by r.f. and d.c. sputtering

Multilayer CrC–SiC coatings were produced by both direct current and radio frequency sputtering of Cr and Si targets in an Ar–C₂H₂ atmosphere. Coatings of constant thickness of about 4 μm, but with the number of layers varying between two and 200, were prepared and studied. Investigations of coating morphology were performed by scanning elecron microscopy (SEM), and coating composition was investigated using Glow Discharge Optical Spectroscopy (GDOS) and Auger Electron Spectroscopy (AES). Microhardness measurements, scratch adhesion, pin on disc, ASTM rubber wheel and impact wear tests were performed and the results were related to the individual layer thicknesses. It is shown that the improvement observed in hardness tests does not necessarily result in the improvement of other mechanical properties, e.g. adhesion and toughness. When two comparatively hard materials are combined in a multilayer coating, the result can be an increase in brittleness due to an absence of plastic release mechanisms for dislocation accumulation at layer boundaries. Thus, it is necessary to seek a compromise in the hardness of multilayer films in order to achieve optimal behaviour across a range of different surface contact conditions.     

点/线/面接触条件下喹唑啉酮胺润滑油添加剂的摩擦学性能

目前杂环化合物作为润滑油添加剂在机械润滑领域受到重视,但对无硫磷含氮杂环化合物在多种接触方式下的摩擦学性能的研究还不多。合成一种新型无硫磷喹唑啉酮胺润滑油添加剂并利用四球试验机、环块试验机和万能摩擦磨损试验机分别考察了点/线/面接触条件下其在液体石蜡中的摩擦学性能,再用光学显微镜、扫描电子显微镜和X射线光电子能谱仪对其摩擦表面进行分析。试验结果表明:油溶性喹唑啉酮胺在液体石蜡中能显著改善基础油的摩擦磨损状况,明显提高基础油的承载能力,表现出良好的摩擦学性能,其作用机理是其在摩擦过程中与金属表面发生了摩擦化学反应,生成了含氧化亚铁、有机氮化物和含氮金属配合物等的复合膜,有效地提高了液体石蜡的减摩抗磨性能。     

Nano-mechanical and tribological characteristics of ultra-thin amorphous carbon film investigated by afm

The mechanical as well as tribological characteristics of coating films as thin as a few nm become more crucial as applications in micro-systems grow. Especially, the amorphous carbon film has a potential to be used as a protective layer for micro-systems. In this work, quantitative evaluation of nano-indentation, scratching, and wear tests were performed on the 7nm thick amorphous carbon film using an Atomic Force Microscope (AFM). It was shown that AFM-based nano-indentation using a diamond coated tip can be feasibly utilized for mechanical characterization of ultra-thin films. Also, it was found that the critical load where the failure of the carbon film occurred was about 18μN by the ramp load scratch test. Finally, the wear experimental results showed that the quantitative wear rate of the carbon film ranged 10^-9~10^-8 mm³/N cycle. These experimental methods can be effectively utilized for a better understanding the mechanical and tribological characteristics at the nano-scale.     

Tribological behaviour of sintered 316L stainless steel impregnated with MoS2 plain bearing

The mechanical and tribological properties of sintered 316L stainless steel impregnated with molybdenum disulfide (MoS₂) were investigated. Tests were carried out at room temperature for two specific ranges of PV value (1.1 and 1.8 MPa m/s). The results prove that the friction coefficient and the wear are strongly influenced by the addition level of MoS₂.

In this paper, MoS₂ powder was mixed with 316L powder before being processed via compacting and sintering steps. The microstructure, hardness, tensile strength and elongation at breaking point of the sintered specimens were evaluated. The friction and wear properties of the materials were examined by a partial plain bearing wear test rig under dry conditions at room temperature and in air. Although some of mechanical properties of the composite decreased with increasing MoS₂ amount, the MoS₂ was very effective in reducing the friction and wear of the composites. Particularly, the sintered 316L–15% MoS₂ materials at 1.1 PV value showed a reduction of friction coefficient by approximately 20–25% when compared to the sintered 316L specimen without addition of MoS₂. In addition, wear of specimen with addition of MoS₂ was also reduced to some extent (5–10% weight loss reduction) at this specific PV value.     

Si3N4-hBN陶瓷复合材料与Fe-B合金配副的摩擦学特性研究

利用MMU-5G销-盘式端面磨损试验机考察Si3N4-hBN陶瓷复合材料与Fe-B合金配副分别在干摩擦和水润滑条件下的摩擦磨损性能,分别采用扫描电子显微镜( SEM)、激光扫描显微镜(LSM)、X光电子能谱(XPS)、X射线能谱(EDS)和X射线衍射(XRD)分析摩擦面及磨屑的形貌与物质组成.结果表明,hBN的加入未能有效地改善Si3N4-hBN/Fe-B合金摩擦副的摩擦学性能,干摩擦条件下,Si3N4-hBN摩擦表面微凸体与Fe-B合金中的硬质相Fe2B发生碰撞而导致脆性断裂和剥落,发生磨粒磨损,摩擦因数均高于0.9,磨损率均高于10-5 mm3/ (N·m)数量级;水润滑条件下,由于水流带走了磨屑,避免磨粒磨损的发生,为Si3N4-hBN摩擦表面发生化学抛光提供条件,化学抛光使销、盘试样的摩擦表面变得光滑,从而获得较为优异的摩擦学性能.     

高转速条件下轴向柱塞泵配流副摩擦磨损特性

结合轴向柱塞泵配流副实际受力与运动形式，使用盘-环试验机在L-HM 46抗磨液压油润滑条件下，研究轴向柱塞泵配流副(38CrMoAl-CuPb15Sn5)在高转速(1800 r/min)的摩擦磨损特性并分析磨损机理。实验结果表明：与中低转速相比，高转速测试条件下的配流副更易发生粘着磨损；38CrMoAl经调质、渗氮处理后与CuPb15Sn5组成的配流副在高转速工况下摩擦磨损性能良好，其磨损率比38CrMoAl未经热处理和只渗氮处理配流副分别降低69%和57%；调质热处理可改善38CrMoAl的表面特性，减少摩擦过程中CuPb15Sn5在其表面的附着继而改善配对副摩擦特性，将有助于提高配流副的工作寿命。     

Structural and tribological characterization of tungsten nitride coatings at elevated temperature

Transition metal nitrides exhibit excellent mechanical properties (hardness and Young's modulus), high melting point, good chemical stability and high electrical conductivity. However, tungsten nitrides still stand aside of the main attention. In our previous study, tungsten nitride coatings with different nitrogen content showed excellent wear resistance at room temperature. Nevertheless, many engineering applications require good tribological properties at elevated temperature. Thus, the present study is focused on the tribological behaviour (friction coefficient and wear rate) of tungsten nitride coatings at temperature up to 600 °C.

The structure, hardness, friction and wear of tungsten nitride coatings with nitrogen content in the range 30–58 at.% prepared by dc reactive magnetron sputtering were investigated. The tribological tests were performed on a pin-on-disc tribometer in terrestrial atmosphere with Al₂O₃ balls as sliding partner. The coating wear rate was negligible up to 200 °C exhibiting a decreasing tendency; however, the wear dramatically increased at higher temperatures. The coating peeled off after the test at 600 °C, which is connected with the oxidation of the coating.     

Fabrication and Tribological Study of Graphene Oxide/Multiply-Alkylated Cyclopentanes Multilayer Lubrication Films on Si Substrates

Multilayer films based on graphene oxide (GO) and multiply-alkylated cyclopentanes (MACs) have been fabricated successfully on silicon substrate via both self-assembled and dip-coating technologies. Given the excellent mechanical properties and frictional properties of GO, the resulting multilayer films composed of GO and MACs with excellent lubricating property are expected to possess improved comprehensive tribological performances. In the current paper, the surface morphology and chemical composition of the films were analyzed using water contact angle meter, X-ray photoelectron spectroscope, and atomic force microscope. A ball-on-plate tribometer was used to evaluate the tribological performances of the films. The results showed that the new multilayer films exhibited excellent load-carrying capacity and durability. Therefore, they are hoped to find promising applications in the lubrication of microelectromechanical systems.     

A study of the friction and wear performance of MoSx thin films produced by ion beam enhanced deposition and magnetron sputtering

MoS_x thin films were deposited by ion beam enhanced deposition (IBED) and magnetron sputtering (MS) onto the surface of IBEN Si₃N₄ and TiN thin films. The friction and wear performances of thin films and 52100 steel were compared using an SRV model reciprocating testing machine. The results showed that all MoS_x films exhibit good tribological behavior. The MS MoS_x thin film has better wear resistance and the IBED MoS_x film has a longer wear life. The wear resistance of IBED Si₃N₄ and TiN thin film plus MoS_x film is 3–4 times and 8–20 times that of single IBED Si₃N₄ and TiN thin films and 52100 steel respectively. The analyses indicate that the difference in friction and wear performance between the two kinds of MoS_x thin film is determined by the x value of MoS_x, its microstructure and the atom mixing effect at the interface.     

多元CrMoSiCN系列薄膜结构及摩擦学特性研究进展

从三元含Mo的Cr-Mo-N、Mo-Si-N、Mo-C-N薄膜到四元Cr-Mo-Si-N、Mo-Si-C-N薄膜,综述多元系列薄膜的结构、力学及摩擦学性能的研究进展;分析在不同气体压力、制备方法与参数、不同元素含量下薄膜结构的变化,阐述薄膜结构与其力学性能和摩擦学特性的关联。指出:多元Cr-Mo-Si-C-N系列薄膜结构、硬度、摩擦因数强烈受到薄膜中Mo、Si、C、N元素含量的影响,其中力学特性还与薄膜微结构紧密相关;薄膜的摩擦学特性与晶粒生长细化和作为润滑剂的无定形基质有关;在摩擦过程中发生的摩擦化学反应也有效地提高了薄膜的耐磨性。对于四元Cr-Mo-C-N和多元Cr-Mo-Si-C-N薄膜,建议进一步研究在水润滑与非润滑的不同条件下,例如在海水或者空气干摩擦环境下,是否由于薄膜结构组分的不同而有效地形成含Mo的氧化物的自润滑膜,以提高薄膜在更多场合下的适应性和减摩性。     

Tribological Behaviour of N(C)-Alloyed W–S Films

In this study, sputtered W–S–N(C) films were deposited by rf magnetron sputtering with increasing N or C content. The coatings were tribologically tested in a pin-on-disk apparatus with increasing applied normal loads in two different environmental conditions, normal room atmosphere and dry nitrogen atmosphere. W–S–N(C) films without or with low N(C) addition had high wear rates, whatever the environment was, but induced low wear in the counterbody material and low friction coefficients. The coatings alloyed with high N content showed excellent wear resistance and a very low friction coefficient (<0.05) when tested in dry nitrogen but the opposite behaviour under room conditions. For their part, high C-containing coatings showed an excellent tribological behaviour in both environments, not as good as N-alloyed films in dry nitrogen but much better under room conditions. The wear and friction coefficients were lower in dry nitrogen than in humid air. Globally, the alloying with N(C) resulted in wear rates in W–S–N(C) films two orders of magnitude lower than in an unalloyed one, keeping the friction coefficient at the same level or even lower. The wear behaviour was interpreted as a function of several factors including; the mechanical strength of the coatings, the adhesion of the films to the substrate, the porosity and the structural arrangement of the film.     

Tribological properties of metal-plastic multilayer composites under oil lubricated conditions

Three kinds of metal-plastic multilayer composites, which were composed of a steel backing, a middle layer of sintered porous bronze and a surface layer of polytetrafluoroethylene (PTFE) filled by Pb or Cu₂O powders, were prepared. The friction and wear properties as well as the limiting pressure times velocity (PV) values of these metal-plastic multilayer composites sliding against 45 carbon steel under both dry and oil lubricated conditions were evaluated on a MPV-1500 friction tester with a steel axis rotating on a journal bearing. The worn surfaces of these metal-plastic multilayer composites and the transfer films formed on the surface of steel axis were examined by electron probe microscopy analysis (EPMA). Experimental results show that filling of Pb to PTFE reduces the friction coefficient and wear of the composite, while filling of Cu₂O to PTFE increases the friction coefficient but decreases the wear of the composite. The friction and wear properties as well as the limiting PV values of these metal-plastic multilayer composites can be greatly improved with the oil lubrication. EPMA investigations show that Pb and Cu₂O fillers preferentially transfer onto the surfaces of steel axis, which may enhance or deteriorate the adhesion between transfer films and steel surfaces. Meanwhile the transfer of these metal-plastic multilayer composites onto the steel surface can be greatly reduced with oil lubrication, which results in the remarkable decrease of the wear of these metal-plastic multilayer composites.     

Tribological and mechanical properties of carbon nitride thin coating prepared by ion-beam-assisted deposition

Carbon nitride thin films may become good competitors for diamond-like carbon, due to their high hardness, high wear resistance, and low friction coefficient. At present, there are only a few studies of the effect of CN _x coating hardness and internal stress on its tribological properties, such as coating life and frictional behaviour. This work deals with tribological and mechanical properties of a carbon nitride coating prepared by ion-beam-assisted deposition (IBAD). Friction coefficients in the range of 0.10–0.12 were observed for the best CN _x coatings sliding against silicon nitride under ambient conditions. A nonlinear correlation between coating life and its internal stress and hardness was found.