A Study on the Mechanical and Tribological Properties of Carbon Fabric/PTFE Composites

Carbon fabric reinforced polytetrafluoroethylene (PTFE) composites with different PTFE content, viz. 30, 40, 50, 60, and 70 vol%, were fabricated by a dispersion impregnation technique followed by a hot-press process. The composites were evaluated for their mechanical and tribological properties. The tribological tests were conducted on a friction and wear tester with a ring-on-block arrangement. The mechanical properties were also tested and their relationship with tribological properties was analyzed. The worn surface and wear debris were analyzed by a scanning electron microscope (SEM) to study the wear mechanism. It was found that the resin content had a great influence on both the mechanical properties and the tribological properties, and the tribological properties were correlated with the mechanical properties. The composite with 50 vol% PTFE showed promising tribological behaviors under the selected test conditions.     

Microstructures and tribological properties of plasma sprayed WC-Co-Cu-BaF2/CaF2 self-lubricating wear resistant coatings

A promising WC-Co-Cu-BaF₂/CaF₂ self-lubricating wear resistant coating was deposited via atmospheric plasma spraying (APS) process by using homemade feedstock powders composed of WC-Co, Cu and BaF₂/CaF₂ eutectic. The as-prepared cermet coatings had better frictional behavior comparing with the WC-Co coating. Moreover, the often-occurred decarburization of WC in APS process was noticeably improved due to the binding of copper and BaF₂/CaF₂ phase, which not only offered effective solid lubrication, but also acted as bind phases to mend the microstructure and protected WC from decomposition. The optimized specimen contained 10 wt.% Cu and 10 wt.% BaF₂/CaF₂ in a WC-Co matrix, which had excellent frictional and wear performance. The wear mechanism of the self-lubricating wear resistant coating was discussed with the microstructures, compositions and mechanical properties of the composite materials in detail.     

Tribological characterization of chromium nitride coating deposited by filtered cathodic vacuum arc

CrN coatings were prepared by filtered cathodic vacuum arc (FCVA) technique. The influence of the deposition parameters (nitrogen partial pressure PN₂, substrate bias voltage V_s and preheating of the substrate) on the structural, mechanical and tribological properties of the FCVA CrN coatings was investigated. Further, the FCVA CrN coating was compared in dry reciprocating sliding with commercial multi-arc ion plating (MAIP) CrN coating as to friction and wear properties. Profilometer, scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDX) were used to evaluate the wear scars and the wear mechanisms were discussed. The results showed that the structural, mechanical and tribological properties of the FCVA CrN coatings were significantly dependent on the deposition parameters. The FCVA CrN coating deposited with PN₂ of 0.1 Pa, V_s of −100 V and without preheating exhibited the optimal mechanical and tribological properties. The FCVA CrN coating exhibited much better anti-abrasive and anti-spalling properties than the MAIP CrN coating, which was resulted from significant reduction of macroparticles and pitting defects by the FCVA technique. The MAIP CrN coating suffered severe concentrated wear by a combination wear mechanisms of delamination, abrasive and oxidative wear when high normal load was applied, while for the FCVA CrN coating the wear mechanisms were ultra-mild abrasive and oxidative wear.     

The effect of carbon nanotubes on the corrosion and tribological behavior of electroless Ni-P-CNT composite coating

In this study, Ni-P-CNT composite coating was successfully deposited on the surface of copper by electroless plating. X-ray diffraction (XRD) analysis and scanning electron microscopy (SEM) were used to characterize the coatings. The wear behavior of the coatings was investigated using a pin-on-disk test rig and subsequently friction coefficient data were reported. The corrosion behavior of the Ni-P and Ni-P-CNT coated specimen were evaluated through polarization curves and electrochemical impedance spectroscopy (EIS) in 3.5 wt.% NaCl aqueous solution at the room temperature. The results indicated that the incorporation of carbon nanotubes (CNTs) in the coating improved both tribological behavior and corrosion resistance. These improvements have been attributed to superior mechanical properties, unique topological structure and high chemical stability of nanotubes.     

Composite ceramic-Ni60 coating fabricated via supersonic plasma spraying

Using the supersonic plasma spraying (SPS) technique, a composite ceramic-Ni60 coating was prepared on a 45# steel substrate. The particle morphology, coating morphology, and phase structure of the coating were analyzed via scanning electron microscopy and X-ray diffraction. Moreover, the tribological properties of the coating were determined via friction and wear experiments. The results revealed that: the crystal structure of the SPS-produced coating is composed of six phase-structure types, and the coating structure was dense with low porosity. During the wear test (rotation speed of ball: 300 rpm, load: 50 N), the friction coefficient decreased by 32.75%, and the coating underwent abrasive wear (wear mechanism).     

碳纳米管增强镍磷基复合镀层研究

对CVD方法制备的碳纳米管进行表面改性处理，然后在液相中分散，利用化学共沉积方法形成碳纳米管镍磷基复合镀层，研究了碳纳米管表面改性后的红外谱、碳纳米管复合镀层的表面形貌、硬度及摩擦学行为.结果表明：碳纳米管的加入明显地提高镍磷复合镀层的硬度和改善了镍磷复合镀层的摩擦性能.硬度达到946HV，20N载荷时摩擦系数为0.7，增至80N时降为0.6；相同条件下与传统耐磨材料SiC增强的镍磷基复合镀层相比，具有更低的摩擦系数和磨损量. 关键词： 碳纳米管 表面改性 复合镀层 摩擦行为     

脉冲磁控溅射MoS2-Ti涂层常温及高温真空摩擦磨损性能

利用脉冲磁控溅射法，以铝青铜合金(C63200)和硅片为基底，制作不同Ti含量的MoS₂-Ti复合涂层。通过XRD、SEM、EDS、光学显微镜、多环境摩擦试验机等表征了涂层的结构成分和摩擦性能。结果表明：随Ti含量的增加，涂层致密度提升，S、Mo原子比上升。Ti的掺入使涂层由高度结晶态向非晶态转变。Ti含量增加，涂层摩擦磨损性能先上升再下降，常温真空下含3%Ti的涂层拥有稳定和低至0.015的摩擦系数，23%Ti的涂层失去润滑性。温度升高到400℃，涂层摩擦系数由0.015~0.04上升至0.07~0.1，含13%Ti的涂层高温真空下在800s后润滑失效。磨痕形貌显示，含3%Ti的涂层磨痕最窄，温度升高宽度增加不大，含13%Ti的涂层磨损严重，400℃真空环境下很快磨穿，纯MoS₂和13%Ti涂层摩擦时发现大量磨粒和破碎磨屑。     

Investigation on the Tribological Properties of POM Modified by Nano-PTFE

The tribological properties of polyoxymethylene (POM) modified by nano-polytetrafluorethylene (nano-PTFE) were investigated by a block-on-ring wear tester. For comparison, modified POM with micro-polytetrafluoroethylene (micro-PTFE) was also studied. The modified POM with a much lower concentration of nano-PTFE showed the similar tribological properties compared with POM modified by micro-PTFE. The friction coefficient decreased with the increase of nano-PTFE, while the wear rate showed the lowest value when the concentration of nano-PTFE was 2%. Scanning electron microscope (SEM) micrographs revealed that transfer films played an important role in the friction process. The transfer films decreased and stabilized the friction coefficient. Comparing to POM/2%nano-PTFE, when the concentration of nano-PTFE reached 4%, the mechanical properties decreased significantly, possibly due to poor dispersion of nano-PTFE.     

Formation of titanium carbide layer by laser alloying with a light-transmitting resin

The weight reduction of mechanical components is becoming increasingly important, especially in the transportation industry, as fuel efficiency continues to improve. Titanium and titanium alloys are recognized for their outstanding potential as lightweight materials with high specific strength. Yet they also have poor tribological properties that preclude their use for sliding parts. Improved tribological properties of titanium would expand the application of titanium into different fields.Laser alloying is an effective process for improving surface properties such as wear resistance. The process has numerous advantages over conventional surface modification techniques. Many researchers have reported the usefulness of laser alloying as a technique to improve the wear resistance of titanium. The process has an important flaw, however, as defects such as cracks or voids tend to appear in the laser-alloyed zone.Our group performed a novel laser-alloying process using a light-transmitting resin as a source for the carbon element. We laser alloyed a surface layer of pure titanium pre-coated with polymethyl methacrylate (PMMA) and investigated the microstructure and wear properties. A laser-alloyed zone was formed by a reaction between the molten titanium and thermal decomposition products of PMMA at the interface between the substrate and PMMA. The cracks could be eliminated from the laser-alloyed zone by optimizing the laser alloying conditions. The surface of the laser-alloyed zone was covered with a titanium carbide layer and exhibited a superior sliding property and wear resistance against WC-Co.     

多层石墨烯作为液体石蜡添加剂的摩擦学性能

以膨胀石墨为原料,采用不同溶剂,通过液相超声直接剥离法制备多层石墨烯,利用透射电子显微镜、原子力学显微镜对其形貌进行了表征,在多功能往复摩擦磨损试验仪上研究了石墨烯石蜡分散体系的摩擦学性能。通过扫描电镜、能谱仪分析了磨痕形貌及表面元素组成。结果表明:多层石墨烯作为液体石蜡添加剂表现出良好的减摩抗磨性能,主要是因为多层石墨烯在磨损表面形成的物理吸附膜与摩擦化学反应膜的共同作用。     

Tribological behavior of diamond-like carbon film with different tribo-pairs: A size effect study

A friction force microscope (FFM) with different probes and a ball-on-disk (BOD) tribo-meter were used to investigate the tribological properties of diamond-like carbon (DLC) films. DLC films were prepared by chemical vapor deposition (CVD) method by altering the deposition parameters, and their morphologies and structural information were examined with an atomic force microscope (AFM) and the Raman spectrum. The wear traces of the DLC films after frictional tests were analyzed by an optical microscope. It is found that surface roughness and adhesion play important roles in characterizing the tribological properties of DLC films using FFM. Moreover, the debris accumulation is another significant factor affecting the frictional behavior of DLC films, especially for the sharp tip. The difference in coefficients of friction (COFs) obtained by the BOD method among different DLC films under water lubrication is much smaller than the case without water lubrication. The variation trends in COF for the flat tip and the BOD test are similar in comparison with the result obtained with the sharp tip. The wear traces after frictional tests suggest that DLC films under water lubrication are prone to be damaged more readily.     

Ti6Al4V合金表面激光沉积复合涂层的组织和性能

为了增强Ti6Al4V钛合金的耐磨性,采用激光沉积制造方法在其表面上制备了以原位生成的TiC颗粒和直接添加的WC颗粒为增强相的耐磨涂层,观察了各涂层的微观组织,并测量了涂层的显微硬度和涂层在室温大气条件下的摩擦磨损性能。结果表明各涂层和基体呈现冶金结合,原位自生的TiC和部分熔化的WC颗粒均能够均匀弥散分布于基体上,由于增强相颗粒的弥散强化及激光沉积组织的细晶强化作用,基材的硬度和耐磨性均得到了提高。原位自生的TiC涂层比WC涂层硬度梯度分布平缓,但耐磨性稍差。     

Friction and Wear of Polyphenylene Sulfide (PPS), Polyethersulfone (PES) and Polysulfone (PSU) Under Different Cooling Conditions

The friction and wear properties of polyphenylene sulfide (PPS), polyethersulfone (PES) and polysulfone (PSU), which have similar molecular structure, were investigated using an end-face contact tribometer in three different cooling ways: sliding without air cooling, sliding with air cooling, and sliding in water. The worn surface and wear debris were observed using a scanning electron microscope (SEM). The effect of frictional heat on the tribological properties of the polymers was comparatively studied. When sliding in air, with increasing applied load, the wear rate of PPS decreased slightly initially then increased later while the wear rate of PES and PSU increased through out. The results suggested that the friction coefficient was mainly affected by the temperature of the worn polymer that was controlled by the balance of heat flow of the whole sliding contact system. When sliding in water, the friction coefficients of the three polymers decreased compared to that sliding in air and remained relatively steady through the whole process under different load. The wear rates of the three polymers had a close value and, remarkably, increased compared to that sliding in air. The water cooling and lubrication role decreased the tribological properties difference between the polymers.     

Tribological Properties of Hydroxyl-Terminated Liquid Nitrile Rubber-Modified Polyurethane/Epoxy Interpenetrating Polymer Network Composites

A series of castor oil-based polyurethane (PU)/epoxy resin (EP) graft interpenetrating polymer network (IPN) composites modified by two kinds of hydroxy-terminated liquid nitrile rubber (HTLN) was prepared. A systematic investigation of the tribological properties of the two kinds of HTLN-modified PU/EP IPN composites was carried out through a pin-on-disk arrangement under dry sliding conditions. Experimental results revealed that the incorporation of HTLN can improve the friction and wear properties of PU/EP IPN significantly. Both the friction coefficient and wear loss decreased with increasing content of HTLN. The worn surfaces of the samples were analyzed using scanning electron microscope and a three-dimensional (3D) noncontact surface-mapping profiler; the results showed that the worn surfaces of the PU/EP IPN composites became smooth when the HTLN was added. The mechanisms for the improvement of tribological properties are discussed.     

Electrodeposition and tribological properties of Ni-SrSO4 composite coatings

Ni-SrSO₄ composite coatings were electrodeposited on superalloy Inconel 718 from a Watts electrolyte containing a SrSO₄ suspension. Ni-SrSO₄ coatings were investigated by scanning electron microscope, microhardness tester, and friction and wear tester in sliding against a bearing steel ball under unlubricated condition. The incorporation of SrSO₄ into Ni matrix increases the microhardness of electrodeposited coatings. Ni-SrSO₄ composite coating exhibits a distinctly low friction coefficient and a small wear rate as contrasted with pure Ni coating and the substrate. The effect of SrSO₄ particles on microstructure and tribological properties of Ni-SrSO₄ composite coatings is discussed.     

Development and characterization of laser surface cladding (Ti,W)C reinforced Ni–30Cu alloy composite coating on copper

To improve the wear resistance of copper components, laser surface cladding (LSC) was applied to deposit (Ti,W)C reinforced Ni–30Cu alloy composite coating on copper using a cladding interlayer of Ni–30Cu alloy by Nd:YAG laser. The microstructure and phases of the composite coating were investigated by scanning electron microscopy (SEM), X-ray diffraction (XRD) and X-ray energy dispersive microanalysis (EDX). Microhardness tester and pin-on-disc wear tester were employed to evaluate the hardness and dry-sliding wear resistance. The results show that crack-free composite coating with metallurgical bonding to the copper substrate is obtained. Phases identified in the (Ti,W)C-reinforced Ni–30Cu alloy composite layer are composed of TiWC₂ reinforcements and (Ni,Cu) solid solution. TiWC₂ reinforcements are distributed uniformly in the (Ni,Cu) solid solution matrix with dendritic morphology in the upper region and with particles in the mid-lower region. The microhardness and wear properties of the composite coating are improved significantly in comparison to the as-received copper substrate due to the addition of 50 wt% (Ti,W)C multicarbides.     

Improvement on HVOF sprayed Diamalloy coatings by laser irradiation

We investigated the structure change, surface properties (roughness, porosity, and hardness), tribological, and electrochemical performances of HVOF sprayed Ni-20Cr-10W-9Mo-4Cu-1C-1B-1Fe (Diamalloy-4006) coatings before and after laser irradiation. The results showed that the friction and wear resistance of the coatings were improved significantly with an optimized laser irradiation process. The improvement can be attributed to the improved roughness and hardness, as well as the formation of oxides Cu _x O and Cr₂O₃ tribofilms. With the laser irradiation treatment, the local corrosion of the coating had a decrease and the selective corrosion resistance of the Diamalloy-4006 coating was improved as a result of the decreasing the size and number of the pores, especially compact interface achieved by laser irradiation.     

Research on tribological behaviors of composite Zn/ZnS coating under dry condition

A composite Zn/ZnS coating was prepared by a novel compound technology-combining high velocity arc spraying and low temperature ion sulfurizing in this paper. The surface and cross-section morphologies were observed by scanning electron microscopy (SEM). The X-ray diffraction (XRD) pattern for the Zn/ZnS coating implies that it mainly consists of Zn and ZnS. The nanohardness and elastic modulus were measured by a nano-indentation tester. The tribological behaviors were investigated on a ball-on-disk wear tester under dry condition. The results showed that the friction coefficient and worn depth of the composite Zn/ZnS coating were low and stable, indicating that it had excellent friction-reduction and anti-wear properties under dry condition.     

The structure and tribological behaviors of CrN and Cr-Ti-N coatings

The Cr-Ti-N coatings with different composition were deposited in a medium frequency magnetron sputtering system on Si (1 1 1) substrates. The structures, surface morphology and wear properties were measured. The binary CrN coatings, formed a single-phase fcc structure with nearly random (1 1 1), (2 0 0) and (2 2 0) orientation, while for the Ti was introduced, coatings show a preferred orientation of (2 0 0). Cr-Ti-N coating shows a much smoother surface than CrN coating. Cr-Ti-N coating with 31.75% Ti content shows the best wear behavior. The excellent tribological properties of this composition coating are corresponding to the solid solution nitride structures.     

A Critical Review on Physical Vapor Deposition Coatings Applied on Different Engine Components

Friction and wear in different engine components have crucial effects on the engine performance, combustion efficiency, oil consumption and lifetime of the internal combustion (IC) engine. Under certain loads, speeds, and temperatures, the metallic components of the IC engine, especially the piston and valve system suffer from a higher friction. Thin film coating is one of the novel techniques to reduce the frictional forces and improve the mechanical properties of engine components. Due to some versatile tribological properties, increasing attention has been paid to the physical vapor deposition (PVD) technology in the recent decade to deposit thin film coating on engine components. This article presents a comprehensive literature review on thin film coatings for IC engine components deposited by PVD technique. Issues related to tribological properties (wear and coefficient of friction) and mechanical properties (hardness and roughness) are also highlighted. Scientific improvements are presented in the light of literature. It is revealed that PVD coating is significantly effective on wear resistance, scuffling resistance, surface roughness, and friction of the components in IC engine. Laboratory test and data from actual service so far suggest that the plasma-activated electron beam evaporation coating is perhaps one of the best choices for smooth surface finishing with improved mechanical and tribological properties. However, there are still some problems in its practical usage. This compressive review paper presents the major shortcomings of PVD coatings on IC engine components and the possible solutions if any. Finally, a number of issues have been reported which need to be encountered for further studies.