Investigation of antiwear coatings deposited by the pvd process

The tribological properties of various PVD‐deposited coatings (vacuum arc method) have been tested, both single‐layer coatings (TiN, CrN, Ti(C,N), and Cr(C,N)) and multilayer coatings (Cr(C,N)/CrN/Cr and CR(C,N)/(CrN+Cr₂N)/CrN/Cr). An unlubricated ball‐on‐disc tribosystem was used in which an Al₂O₃ ball is pressed against a coated steel disc rotating in the horizontal plane. A novelty of the method is the removal of wear debris from the contact zone using a draught of dry argon. This improves the repeatability of the test results and the stability of the tribological characteristics. It is shown that CrN coatings exhibit the best antiwear properties and Ti(C,N) the worst. Multilayer coatings have better antiwear properties than single‐layer ones. The friction coefficients for CrN and Cr(C,N) coatings are much smaller than for the commonly used TiN. A correlation has also been found between the physical properties of the coatings tested (adhesion of the coating to the substrate assessed in scratch tests, and coating hardness) and their antiwear properties. An improvement in coating‐substrate adhesion results in wear reduction, while greater hardness (causing a coating embrittlement increase and a change in the wear mechanism) brings about greater wear. There is no correlation between the physical properties and the friction coefficients of the coatings tested.     

Tribological and electrochemical performances of Cr/CrN and Cr/CrN/CrAlN multilayer coatings deposited by RF magnetron sputtering

CrN/CrAlN and Cr/CrN/CrAlN multilayers were grown with dual RF magnetron sputtering. The application of these multilayers will be wood machining of green wood. That is why ball-on-disc and electrochemical tests in NaCl aqueous solution were realized to elucidate the tribological and corrosion behavior of these coatings as they will be exposed to wear and corrosion during wood machining process. The samples/alumina and samples/WC coupling showed different wear mechanisms. The 300 nm thick Cr/CrN/CrAlN multilayer demonstrated the best tribological behavior and corrosion resistance. The influence of growth defects on corrosion resistance has been shown.     

活塞环表面离子镀硬质膜的摩擦学性能研究

为了改善发动机活塞环的摩擦学性能和提高其使用寿命,采用离子镀技术在活塞环表面制备了CrN硬质膜,并利用SRV摩擦磨损试验机考察了硬质膜的摩擦学特性,研究结果表明离子镀硬质膜的摩擦系数基本与镀铬层一致,但磨损量远低于镀铬层的磨损量,与两种涂层活塞环配副的缸套试样的磨损量基本相当。     

Architecture of Multilayer Cr/CrN Coatings for Wear Protection in Seawater: Cr/CrN Ratio and Total Thickness

Cr/CrN multilayer coatings with various Cr/CrN thickness ratios and total thicknesses were deposited on 316L stainless steel by multi-arc ion plating. The coatings were systematically characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), and nanoindentation. Tribological behaviors were investigated using a ball-on-disk tribometer in artificial seawater. The results showed that the multilayer coating phases changed from Cr₂N + CrN to Cr + Cr₂N + CrN phases with an increase in Cr/CrN thickness ratio. The adhesion showed a slight difference for the coatings with different thickness ratios but significantly increased with total thickness. The hardness was also slightly improved by thickening the coatings. The friction coefficient and wear rate were lowest at a thickness ratio of about 0.3. However, there was no large difference in the friction coefficient between coatings with different thicknesses. The wear rate was lower for the thicker coatings under various loads. The load-bearing capacity was also improved by thickening the coatings.     

不同基体CrN/CrCN多层涂层海水环境摩擦学性能研究*

为研究不同基体材料对CrN/CrCN多层涂层在海水环境下摩擦学性能的影响,采用多弧离子镀技术在H65铜合金、TC4钛合金和316L不锈钢基体上沉积CrN和CrN/CrCN多层复合涂层,通过XRD、SEM等技术对涂层的结构进行表征,通过结合力、硬度测试和摩擦磨损试验分析涂层在大气环境和海水环境下的力学性能和摩擦学性能。结果表明:CrN/CrCN多层涂层的内应力相对于CrN明显减小,且硬度相对CrN涂层较高;TC4钛合金为基体的涂层结合力较好且涂层硬度较高;在海水环境下涂层的摩擦因数相对于大气环境都有较大幅度下降,其中,以TC4钛合金和316L不锈钢为基体的涂层摩擦因数较小;以H65铜合金为基体的2种涂层在海水中的磨损率高于大气中,而以TC4合金、316L不锈钢为基体的CrN/CrCN多层涂层在海水环境下的磨损率低于大气环境;TC4钛合金为基体的CrN/CrCN多层涂层在海水环境下具有最低的磨损率,表明TC4钛合金更适合作为海水环境下CrN/CrCN多层涂层耐磨的基体材料。     

A method for the tribological testing of thin,hard coatings

A new method has been developed for tribological testing of thin, hard antiwear coatings, using a ball‐on‐disc tribosystem, under conditions of dry sliding. In this, an Al₂O₃ ball is pressed against a coated steel disc. Wear debris is removed from the contact zone by a stream of dry argon in this novel method. This improves the stability of the tribological properties and the repeatability of the test results. All test conditions are precisely defined, in particular: the type of motion, air relative humidity, ambient temperature, sliding speed, load, tribosystem spatial configuration, substrate material, substrate hardness and roughness, and coating thickness. The method developed has been used to test various physical vapour deposition coatings (deposited by the vacuum arc method), i. e., single‐layer TiN, Ti(C,N), CrN, and Cr(C,N), and multilayer Cr(C,N)/CrN/Cr and Cr(C,N)/(CrN+Cr₂N)/CrN/Cr. It is shown that CrN coatings exhibit the best antiwear properties, and Ti(C,N) the worst. Friction coefficients for CrN and Cr(C,N) coatings are much lower than for the more commonly used TiN. Multilayer coatings have better antiwear properties than single‐layer ones.     

Low Friction CrNMPP/TiNDCMS Multilayer Coatings

Transition metal nitrides like CrN and TiN are widely used in automotive applications due to their high hardness and wear resistance. Recently, we showed that a multilayer architecture of CrN and TiN, deposited using the hybrid—high power impulse magnetron sputtering (HIPIMS) and direct current magnetron sputtering (DCMS)—HIPIMS/DCMS deposition technique, results in coatings which indicate not only increased mechanical and tribological properties but also friction coefficients in the range of diamond-like-carbon coatings when tested at RT and ambient air conditions. The modulated pulsed power (MPP) deposition technique was used to replace the HIPIMS powered cathode within this study to allow for a higher deposition rate, which is based on the complex MPP pulse configuration. Our results on MPP/DCMS deposited CrN/TiN multilayer coatings indicate excellent mechanical and tribological properties, comparable to those obtained for HIPIMS/DCMS. Hardness values are around 25 GPa with wear rates in the range of 2 × 10⁻¹⁶ Nm/m³ and a coefficient of friction around 0.05 when preparing a superlattice structure. The low friction values can directly be correlated to the relative humidity in the ambient air during dry sliding testing. A minimum relative humidity of 13% is necessary to guarantee such low friction values, as confirmed by repeated tests, which are even obtained after vacuum annealing to 700 °C. Our results demonstrate that the co-sputtering of high metal ion sputtering techniques and conventional DC sputtering opens a new field of applications for CrN/TiN coatings as high wear resistance and low friction coatings.     

Interlayer thickness influence on the tribological response of bi-layer coatings

The present work deals with the influence of coating thickness on the tribological response of bi-layer model coatings consisting of CrN with Cr interlayer with varying Cr/CrN thickness ratios on high-speed steel. Ball-on-disc experiments were carried out in ambient air at room temperature and alumina balls as counterbodies. The mechanical stresses in both layers generated during the tests were calculated with the software package Elastica. Wear tracks on the samples were characterised using both scanning electron microscopy and optical profilometry. The results show that the interlayer thickness plays a determinant role in the tribological response of the coatings provided that the CrN layer thickness exceeds a critical value to withstand mechanical wear.     

Tribological characteristics of hardened-and-tempered structural steels turned by inserts covered with multicomponent PVD coatings

The effect of coatings deposited on cutting tools using the PVD method on the tribological characteristics of the surface layer after the finish turning of 41Cr4 and 30CrMnSi steels is considered. The tribological characteristics of the turned surfaces change substantially. The best results are achieved when using the (AlTi)N coating, which ensures substantial decreases in the coefficient of friction (by 35–40%) and the temperature in the friction zone (by up to 30%). The dependences of the wear on the friction path are linear; the wear rate of the surfaces turned by the coated tools is significantly lower than that for the surfaces turned by the uncoated tools. Compared to the uncoated R25 hard alloy, the difference in the wear rates reaches 60% in favor of (AlTi)N and (TiAl)N coatings. A decrease in the thickness of the coating from 4 to 2 μm leads to a growth in the coefficient of friction and the temperature. An X-ray structural analysis of the surface layers of the turned specimens has revealed the presence of Fe-Al solid phases, which improve the wear resistance of the surface and the efficiency of coatings like (AlTi)N.     

Tribological behaviour and wear mechanism of MoS2–Cr coatings sliding against various counterbody

MoS₂–Cr coatings with different Cr contents have been deposited on high speed steel substrates by closed field unbalanced magnetron (CFUBM) sputtering. The tribological properties of the coatings have been tested against different counterbodies under dry conditions using an oscillating friction and wear tester. The coating microstructures, mechanical properties and wear resistance vary according to the Cr metal-content. MoS₂ tribological properties are improved with a Cr metal dopant in the MoS₂ matrix. The optimum Cr content varies with different counterbodies. Showing especially good tribological properties were MoS₂–Cr8% coating sliding against either AISI 1045 steel or AA 6061 aluminum alloy, and MoS₂–Cr5% coating sliding against bronze. Enhanced tribological behavior included low wear depth on coating, low wear width on counterbody, low friction coefficients and long durability.     

Friction and wear properties of duplex MAO/CrN coatings sliding against Si3N4 ceramic balls in air, water and oil

It is evident that the micro-arc oxidation (MAO) ceramic coatings often exhibit relatively high friction coefficients as sliding against many mating materials. To reduce the friction coefficient for the MAO coatings, the duplex MAO/CrN coatings were deposited on 2024Al alloy using combined micro-arc oxidation and reactive radio frequency magnetron sputtering. The microstructure and phase of the duplex coatings were observed and determined using scanning electron microscope (SEM) and X-ray diffraction (XRD), respectively. The friction and wear behaviors of the duplex coatings sliding against Si₃N₄ balls in air, water and oil were investigated using a ball-on-disk tribometer. The wear rate of the duplex coating was determined by non-contact optical profilometer and the wear tracks on the duplex coatings were observed by SEM. The results showed the CrN coatings mainly consisted of Cr, CrN and Cr₂N phases. The duplex coatings/Si₃N₄ tribopair exhibited the highest friction coefficient in air, while displayed the lowest friction coefficient in oil. When the normal load and the sliding speed increased, the friction coefficient in air increased from 0.65 to 0.72, whereas decreased from 0.58 to 0.36 in water and 0.20 to 0.08 in oil. The specific wear rates for the duplex coatings in air were higher than those in oil. In comparison to the MAO coatings, the duplex MAO/CrN coatings displayed excellent tribological properties under the same conditions.     

纳米表面工程与摩擦学

利用表面工程技术解决摩擦磨损问题具有高效、实用等特点。随着科学技术的迅速发展，纳米材料和纳米技术在表面工程中得到了广泛应用，由此出现了“纳米表面工程”。利用纳米表面工程技术制备的涂层和镀层有着非常优异的摩擦学性能。本文叙述了作者近年来的有关工作，包括热喷涂纳米陶瓷涂层、热喷涂纳米自润滑涂层、纳米陶瓷／聚合物复合涂层、纳米复合电镀层以及纳米电泳沉积层的摩擦磨损特性和机制。     

Abrasive Wear of DLC/PVD Multilayer Coatings: AFM Studies

The tribological behaviour of multilayered coatings deposited on plain carbon steel was investigated by microscale abrasion tests (MSATs). The multilayered coatings consisted of an outer diamond‐like carbon (DLC) layer, a physical vapour deposition (PVD) nitride‐based interlayer, and an inner electroless Ni‐P layer. PVD TiN‐ and Ti(C,N)‐coated samples with and without the DLC outer layer were studied in order to evaluate the influence of each layer on the tribological behaviour of the multilayer‐coated system. The MSATs were carried out using a device based on ball‐cratering geometry: a hard steel sphere was rotated against the coated specimen in the presence of an aqueous suspension of SiC particles. The wear coefficients of the multilayers were calculated from the diameter of the wear craters. The morphology of the wear scars produced by the MSATs was studied by atomic force microscopy (AFM). The wear damage was described by measuring the r.m.s. roughness (S_q) on the sides of the wear craters. Roughness values were related to the wear coefficients (k_c) for the different multilayers on the basis of mathematical elaboration typical of the ‘design of experiment’ (DOE) statistical technique. The presence of the DLC outer layer reduced the roughness of the crater sides and significantly increased the wear resistance of the multilayer only in the case of the PVD TiN sublayer.     

Comparative tribological behaviors of TiN, CrN and MoNCu nanocomposite coatings

The purpose of this study is to investigate comparative tribological behaviors of Cu-doped TiN, CrN, and MoN coatings under a wide range of dry sliding conditions. TiN and CrN coatings have been developed and used by industry in numerous tribological applications including, machining, manufacturing and transportation. In contrast, MoN has attracted very little attention as a tribological coating in the past, despite being much harder than both TiN and CrN. In this paper, we will mainly concentrate on the Cu-doped versions of these coatings whose tribological properties have not yet been fully explored. The results of this study have confirmed that the addition of Cu into TiN, CrN and MoN coatings has indeed modified the grain size and morphology, but had a beneficial effect only on the friction and wear behavior of MoN. The tribological behavior of CrN did not change much with the addition of Cu but that of TiN became worse after Cu additions. Raman spectroscopy technique was used to elucidate the structural and chemical natures of the oxide films forming on sliding surfaces of Cu-doped TiN, CrN and MoN films. The differences in the friction and wear behavior of Cu-doped TiN, CrN, and MoN is fully considered and a mechanistic explanation has been provided using the principles of a crystal chemical model that can relate the lubricity of complex oxides to their ionic potentials.     

The slurry erosive wear of physically vapour deposited TiN and CrN coatings under controlled corrosion

The erosion-corrosion of mild steel (BS6323), in the presence and absence of physically vapour deposited (PVD) TiN and CrN coatings, was studied, in comparison with that of AISI 304 stainless steel, in an aqueous alkaline slurry solution containing alumina particles. The influence of applied potential and particle velocity on the total erosion-corrosion loss was examined, and the respective corrosion and erosion damage (both contributing to the overall weight loss) then assessed by means of microscopical investigation of the morphology of the damaged surface, and subsequently evaluated quantitatively. The superior erosion-corrosion resistance of both the coatings compared to that of the uncoated mild and stainless steels was shown to be due to their resistance to both wear and corrosion. According to the detailed corrosion mechanisms revealed and different responses to wear, schematic diagrams were proposed to outline the main features of the corrosion-erosion process and the individual roles of erosion and corrosion. Discrete differences, in terms of the respective erosion and corrosion processes, between the TiN and CrN coatings, and between the mild and stainless steels, were also investigated and discussed. This revised version was published online in August 2006 with corrections to the Cover Date.     

Friction and wear behaviour of low-friction coatings in conventional and alternative fuels

Today low-friction PVD coatings are used regularly in combustion engines to reduce wear and energy loss due to friction. Three coatings based on transition-metal dichalcogenides and three DLC coatings were tested with respect to tribological behaviour in non-conformal sliding contact, in five conventional and alternative fuels and fuel blending components. The friction and wear proved to vary substantially between the different tested systems. The DLC coatings exhibited extremely good wear properties, but also higher friction. Contrastingly the TMD coatings showed promising friction results, but in their present forms they do not offer sufficient wear resistance in the tested severe contact situation.     

CrCN/CrN+ta-C multilayer coating for applications in wood processing

The paper presents mechanical and tribological properties of CrCN/CrN and CrCN/CrN+ta-C multilayer coatings. Tetrahedral carbon (ta-C) layer formed using the pulse cathodic arc evaporation method are characterised by high hardness –45 GPa, very low friction coefficient—below 0.1 and a low wear rate −1.3×10⁻¹⁷ m³N⁻¹ m⁻¹ providing promising application perspectives.Three sets of tools—planer knives for cutterheads were tested: uncoated (as reference), tools with a CrCN/CrN coating and tools with CrCN/CrN coating with additional friction-reducing tetrahedral carbon (ta-C) layer. The results of investigations indicate that the “tool life” depends on the type of coating and machining conditions. The blades covered with CrCN/CrN multilayer coating after machining of dry, seasoned pine timber showed a twofold increase of durability, and knives covered with CrCN/CrN+ta-C multilayer coating were characterised further by about 15% higher durability. Durability of knives tested in the course of rounding of wet pine timber, despite relatively high depth of machining was improved and for cutters with a CrCN/CrN coating increased more than twice, while the use of the additional ta-C layer on the multilayer coating improved durability by almost 5 times.     

不同石墨烯添加量下MoS2基复合涂层的摩擦磨损及耐腐蚀性能

为改善MoS2基固体润滑涂层的摩擦磨损性能和耐蚀性能,制备了不同石墨烯（GE）添加量的MoS2复合涂层,利用HSR-2M摩擦磨损试验机测试了复合涂层的摩擦磨损性能,并分析了其磨损机理,通过极化曲线、交流阻抗谱（EIS）研究了涂层在3.5%NaCl溶液中的电化学腐蚀行为。试验结果表明,0.8-GE/MoS2复合涂层的摩擦磨损和耐腐蚀性能最优,其平均摩擦因数和磨损率分别为0.232和2.379×10-13 m3/(N·m),较未添加石墨烯的MoS2涂层分别降低了49.56%和43%,腐蚀速率（1.96×10-8 A/cm2）较纯MoS2涂层（5.54×10-6 A/cm2）降低了近2个数量级。石墨烯的二维片状结构具有良好的自润滑性能,在涂层中均匀分布时能有效阻隔腐蚀介质的渗透,因此,石墨烯的添加提高了MoS2基复合涂层的摩擦学性能和耐腐蚀性能,石墨烯的最优添加量为0.8%（质量分数）。     

Influence of the carbon content on the corrosion and tribocorrosion performance of Ti-DLC coatings for biomedical alloys

Biomedical alloys are prone to suffer corrosion and wear phenomena coming from the hostile environment of the body and friction processes, respectively. Diamond-like carbon (DLC) coatings are known to be excellent candidates for using as protective coatings on biomedical alloys, not only due to their excellent tribological properties but also due to their chemical composition and stability. In this work, three Ti-DLC PVD coatings with different compositions were deposited on Ti6Al4V alloy and their corrosion and tribocorrosion responses were evaluated in simulated body fluid. Excellent tribocorrosion response has been found especially in case of coatings with high carbon content. Additionally significative reduction of friction and wear has been obtained in comparison to the substrate response.     

Effects of carbon content on the high temperature friction and wear of chromium carbonitride coatings

Chromium nitride-based coatings are often used in application at high temperature. They possess high wear and oxidation resistance; however, the friction coefficient is typically very high. Therefore, we doped CrN coatings by carbon with the aim to improve tribological properties at elevated temperature, particularly to lower the friction. CrCN coatings were prepared by cathode arc evaporation technology using constant N₂ flow and variable C₂H₂ flow. The coatings with a thickness of 3-4 μm were deposited on hardened steel substrates and high-temperature resistant alloy. The carbon content varied from 0 at.% (i.e. CrN) up to 31 at.%. The standard coating characterization included the nano-hardness, adhesion, chemical composition and structure (including hot X-ray diffraction). Wear testing was done using a high temperature tribometer (pin-on-disc); the maximum testing temperature was 700 °C. The coatings with carbon content 12-31 at.% showed almost identical tribological behaviour up to 700 °C.