Microstructure and wear resistance of nickel–carbon nanotube composite coating from brush plating technique

This paper investigates the microstructure and wear resistance of nickel–carbon nanotube (CNT) composite coating deposited by brush plating technique. The Ni/CNT coating deposited with a pulse current source has less porosity, higher hardness and higher wear resistance than that with a DC source. CNTs greatly improve the coating performance. The wear mechanism is mainly the smearing of the Ni/CNTs coatings, instead of the fracture for the Ni coatings.     

Chemical effects in sliding wear of aluminum

The mechanism of the sliding wear of metals in corrosive media was investigated. In particular, the role of chemical heterogeneities on chemical interactions between the sliding surface and its environment was studied using 2024 aluminum alloy and sodium chloride solutions of varying pH and NaCl concentration. Sliding wear tests with a cylinder-on-cylinder geometry were performed at a sliding speed of 1 m min^?1 and a normal load of 9.8 N (1 kgf). The results show that at pH = 0 and pH = 14, the wear rate is dominated by the dissolution of aluminum into the NaCl solution. In the intermediate pH range, the wear rate is shown to be controlled by the conjoint actions of corrosion and delamination wear. Microscope examination of the worn specimens by means of a scanning electron microscope further confirms that the mode of corrosion is of a localized nature.     

Tribological systems and wear factors

Compilation and analysis of practical data concerning numerous different cases of wear lead to a useful conception of wear evaluation. The present investigation is limited to tribosystems where abrasive and adhesive wear occurs. Data from the literature and from actual measurements which specify all the relevant circumstances and conditions for separate cases of wear are listed. The “wear factor” for each item listed is calculated from the worn volume, the load and the sliding distance. All the wear factors are grouped in a restricted number of main tribo-groups and worked into a preliminary diagram. This demonstrates the trend of wear factor levels for different systems and the scatter per group. The applicability of the diagram for further evaluation is illustrated.     

Chemical aspects of wear of alumina ceramics

In our investigation, the effects of the tribochemically-induced dissolution of alumina ceramics and modulation of near-surface forces (surface charge) within the tribocontact were studied. The wear and friction behaviors of alumina were investigated using a reciprocating sliding test in different chemical environments. The samples for the tests were hemispherical pins and plates of polished alumina, both prepared by a near-net-shaping method.

The sliding tests were conducted in water-based liquids with different pH values or with the addition of a polyelectrolyte to control the surface charge at solid surfaces. The coefficient of friction was continuously recorded during the tests and the wear-loss was subsequently determined for all samples. The results show a significant effect of the chemical agents on the coefficient of friction as well as on the material-removal rate in different aqueous media. The results are discussed in terms of the chemical and electrochemical properties of the materials in the tribocontact.     

Device for the control and measurement of brush forces to an accuracy of a few grams-force while monitoring brush resistance and brush wear at currents up to 500 A or more

A brush holder is described which permits the electrical performance of a brush to be tested under currents of up to at least 500 A and speeds of up to at least 70 m s^?1 and under brush forces that can be applied and maintained within close limits. Simultaneously, the brush wear can be monitored continuously.     

Friction and wear of diamondlike carbon on fine-graindiamond

Friction and wear behavior of ion-beam-deposited diamondlikecarbon (DLC) films coated on chemical-vapor-deposited (CVD),fine-grain diamond coatings were examined in ultrahigh vacuum,dry nitrogen, and humid air environments. The DLC films wereproduced by the direct impact of an ion beam (composed of a 3 :17 mixture of Ar and CH₄) at ion energies of 1500 and700 eV. Sliding friction experiments were conducted withhemispherical CVD diamond pins sliding on four differentcarbon-base coating systems: DLC films on CVD diamond; DLC filmson silicon; as-deposited, fine-grain CVD diamond; andcarbon-ion-implanted, fine-grain CVD diamond on silicon. Resultsindicate that in ultrahigh vacuum theion-beam-deposited DLC films on fine-grain CVD diamond (similarto the ion-implanted CVD diamond) greatly decrease both thefriction and wear of fine-grain CVD diamond films and providesolid lubrication. In dry nitrogen and in humid air,ion-beam-deposited DLC films on fine-grain CVD diamond films alsohad a lowsteady-state coefficient of friction and a low wear rate. Thesetribological performance benefits, coupled with a wider range ofcoating thicknesses, led to longer endurance life and improvedwear resistance for the DLC deposited on fine-grain CVD diamondin comparison to the ion-implanted diamond films. Thus, DLCdeposited on fine-grain CVD diamond films can be an effectivewear-resistant, lubricating coating regardless of environment.     

Friction and wear of carbon nanohorn-containing polyimide composites

Polyimide (PI)-based composites containing single-wall carbon nanohorn aggregate (NH) were fabricated using the spark plasma sintering (SPS) process. For comparison, composites with carbon nanotube (NT) and traditional graphite (Gr) were also fabricated. The NH was produced using CO₂ laser vaporization and a graphite target and the NT was produced by a chemical synthesis method. We evaluated the friction and wear properties of the PI-based composites with a reciprocating friction tester in air using an AISI 304 mating ball. NH drastically decreased the wear of PI-based composites; the specific wear rate of composite with NH of only 5 wt% was of the order of 10⁻⁸ mm³/Nm, which was two orders of magnitude less than that of PI alone. The wear reduction ability of NT seemed to be slightly inferior to that of NH, although it was considerably better than that of Gr. NH and NT lowered the friction of composites. The friction coefficient of composite with 10 wt% NH was less than 0.25, although it was slightly higher than that of composite with 10 wt% Gr. There was no clear difference in the friction reduction effect of NH and NT. The further addition of Gr to composites with NH or NT rather deteriorated the antiwear property of composites, although the friction coefficient was slightly reduced. The transferred materials existed on the friction surface of the mating ball, sliding against composites with three types of carbon filler. These transferred materials seemed to correlate with the low friction and wear properties of composites.     

Transition of the lubricated wear of carbon steel

To study the transition of the lubricated wear of 0.53% C steel in the steady state, wear tests were carried out by rubbing the annular surfaces of two cylindrical test pieces in machine oil with no additives. The ratio of mating areas was varied to approach actual contact conditions. Three regions of variation in the coefficient of friction with contact load were determined. Fatigue wear, characterized by a friction coefficient μ ≈ 0.05 and a specific wear rate ω_s ≈ 0.005 × 10^?6 mm³ N^?1 m^?1, occurs in the first region.A transition from fatigue wear to adhesive wear, with μ ≈ 0.05?0.12 and ω_s ≈ (0.005?0.05) × 10^?6 mm³ N^?1 m^?1, takes place gradually within a specific load range. Finally, adhesive wear predominates above the load level that marks the end of the transition. The same behaviour was analysed through stepwise loading tests. The onset of transition and seizure occurs at constant mean surface temperatures. However, the end of transition is also affected by factors other than temperature. The results are compared with the transitions reported by the International Research Group on Wear of Engineering Materials of the Organization for Economic Cooperation and Development.     

Medium carbon steel alloy design for wear applications

The fracture characteristics of steels are strongly influenced by martensite substructure, retained austenite stability, and morphology. Attractive strength-toughness properties have been attained with Fe-Cr-C-Mn alloys. These alloys, when tested under sliding wear conditions, also exhibit good wear resistance which compares favorably with that of commercial wear-resistant alloys. The most significant finding is an apparently strong correlation between sliding wear resistance and retained austenite, which in turn appears to correlate with Charpy impact properties. Little correlation was observed between hardness and wear resistance for the experimental steels.     

Genesis of superlow friction and wear in diamondlike carbon films

Diamondlike carbon (DLC) films offer enormous possibilities for applications that require low friction and high wear resistance. The range of physical, chemical, mechanical, electrical, and optical properties offered by these films is also exceptional and can meet the increasingly multifunctional application needs of machine elements, microelectronics, and biological systems. Since the early 1990s, carbon has been used as a precursor in our laboratory for the design and synthesis of superhard and low-friction carbon films. As a result of systematic studies over the years, in 1997, we developed a new class of DLC films that provide friction and wear coefficients of 0.001–0.005 and 10⁻¹⁰–10⁻⁹ mm³/N m, respectively, in inert-gas or vacuum test environments. This paper will mainly concentrate on the tribology of these superlow-friction carbon films and provide an update on our understanding of the fundamental tribological mechanisms of such films. It will also expand on the effects of hydrogen within the films and gaseous species within the test environments on friction and wear.     

Corrosive wear of carbon and austenitic stainless steels in NaCl solution

The wear rates of an AISI 52100 carbon steel and a type 316 austenitic stainless steel and the corrosion current I from the rubbing steels were measured in NaCl solution to study the interrelationship between the corrosion and wear of the steels. An on-off cyclic loading test was also conducted to examine the effect of static corrosion during an unloading period on the corrosive wear of the steels.

It was found that the wear rates of the carbon steel and the type 316 stainless steel reach a maximum at NaCl concentrations of about 3% and 0.1% respectively. The on-off cyclic test has shown that corrosive wear of the steels is influenced by static corrosion during an unloading period. The increment †I of the corrosion current due to sliding was associated with the corrosive wear rate of the steels.     

Tribo-electrification mechanisms for self-mated carbon steels in dry severe wear process

The tribo-electrification mechanisms and wear behavior are investigated for self-mated metal pairs of iron and carbon steels (0.2% C, 0.45% C, 0.7% C) under the dry severe wear condition in the reciprocating friction tester. Results show that with increasing the carbon percentage of the steels, the formation mechanism of the wear particle varies from the macro-asperity removal of the slip-tongue to the micro-asperity removal of the wedge. Meanwhile, the variation of tribo-electrification with the sliding time appears to be more serious. The polarity of tribo-electrification is significantly influenced by the difference between the wear losses of the plate and pin specimens. This means the tribo-electrification is mainly caused by the effect of the material transfer for self-mated carbon steels. Under the higher surface hardness, the mean amplitude of the friction coefficient is decreased and the mean amplitude of tribo-electrification is increased. Results also show that the mean amplitude of tribo-electrification for self-mated carbon steels is linearly proportional to the electric resistivity and the relative wear rate, but inversely to the dynamic real contact area.     

Sliding wear behavior of mesocarbon microbeads based carbon materials

The sliding wear behavior of mesocarbon microbeads (MCMBs) based carbon materials was investigated. Samples were sintered at 1300 °C from pure MCMBs without ball-milling (C0) and ball-milled MCMBs doped with 3, 5, 10 wt.% nano-SiC (C3, C5 and C10). The results indicated that C0 sample had poor sliding wear property; ball-milling and doping nano-SiC contributed to the improvement of sliding wear property. The mean friction coefficient values of the C0–C10 samples against H62 brass alloy were 0.38, 0.24, 0.21, and 0.30, respectively. Mass loss increased with increasing sliding time, and C0 and C3 had the highest and lowest mass loss, respectively. The worn surface images showed C0 sample had broad wear tracks and was free from debris layer, while the worn surfaces of C3 and C5 were rather smooth because of the formation of adherent contact films without any significant fracture. These good sliding wear properties were related to small grains, uniform high hardness and large amount of aromatic layers along contact surface.     

Chemical analysis of wear tracks on magnetic disks by TOF-SIMS

Surface reactions on magnetic recording disks have been studied during sliding with ceramic sliders in the main chamber of TOF-SIMS. Chemical change of lubricant oil in the wear track was observed by the chemical image of TOF-SIMS. The magnetic disk surface was covered with perfluoroalkyl polyether lubricant (Fomblin Zdol). The Si tip slider surface was covered with Al₂O₃, DLC, TiN or c-BN coating. Experimental conditions were as follows: 0.8 mN of load and a sliding speed of 0.01 m/s. Lubricant oils were decomposed with Al₂O₃ and TiN slider surfaces. Metal (Al, Ti) fluorides were detected by TOF-SIMS in the sliding track. Material transfer occurred by chemical wear of slider material. From TOF-SIMS observation, the decomposition of lubricant molecules was initiated at the end group of molecules (-CF₂CH₂OH). On the other hand, DLC and c-BN sliders suppressed the decomposition reaction of PFPE oils. In conclusion, hard and chemical inert materials such as DLC and c-BN are suitable for a long-life HDI.     

Erosive wear properties of unidirectional carbon fiber reinforced PEEK composites

The erosive wear properties of unidirectional carbon fiber (CF) reinforced polyetheretherketone (PEEK) composites were studied. A semi-ductile erosive wear manner was found regardless of the CF orientation. Wear mechanism analysis revealed that both cutting and deformation mechanisms existed in the erosion of the composites, although different damaging forms were involved depending on the impingement angles and CF orientation. To give further support on the erosion mechanisms, a special procedure was designed to observe the cross-sectional surface of the eroded composites, and the surface temperature variation was registered. It increased with increasing impingement angle, indicating higher energy dissipation by deformation, which is consistent with the revealed shift of the main erosive wear mechanism from cutting to deformation and “wholesale” fiber fracture.     

Behavior of medium carbon steel under combined fatigue and wear

The combined fatigue-wear life of medium carbon steel (AISI 1045) was investigated under various combinations of loads and sliding wear conditions using a rotating beam test. The direction of the maximum tensile stress due to bending was perpendicular to that due to wear [1]. Tests were also performed with specimens plated with a thin layer of cadmium or nickel-gold. All of the tests were conducted in the high cycle regime. The results show that the fatigue life of all the specimens at a stress level higher than the endurance limit of the specimen was within the experimental scatter of a typical fatigue test. The effect of sliding wear on fatigue life is manifested primarily by the stress field imposed by the slider on the specimen. In the case of plated specimens, the fatigue life was not significantly affected, although the wear rate was decreased by an order of magnitude.     

Studying wear resistance of carbon steels strengthened by plasma hardening

The wear resistance of carbon steels strengthened by plasma hardening in an UDGZ-200 setup is studied using a friction machine. It has been found that the wear resistance of hardened low-carbon steel 15 is equal to ～70% of normalized steel 45, as well as the wear resistances of the hardened medium-carbon steel 45 and the hardened high-carbon U8A steel exceed the wear resistance of the normalized steel 45 by ～60 and ～90 times, respectively.     

Effects of ultrasonic vibration on the wear characteristics of a carbon steel: Analysis of the wear mechanism

To explain the fact that the wear rate of a carbon steel subjected to ultrasonic vibration decreases with an increase in the amplitude of vibration, a simple equation for the wear rate was derived using the theories of adhesive wear and analytical results of vibration. Analytical predictions were in good agreement with experimental results. One of the main factors affecting the wear behaviour under vibration is the contact time between specimens during 1 cycle of vibration. The amount of oxygen adsorbed on rubbing surfaces with repeated dynamic contact loading also affects the wear rate. The activation energy of oxygen adsorption with vibration is considered to be lower than that found in the process of ordinary wear without vibration. The variation in hardness of worn surfaces due to repeated friction passes has little effect on the wear rate with vibration.     

The effect of brush spring pressure on the wear behaviour of copper–graphite brushes with electrical current

Electrical brushes are used to conduct current between stationary part and moving part of a motor or a generator. To ensure proper current transfer and continuous contact, brushes must be loaded against the sliding contact surface with a sufficient force. High loads increase frictional losses and wear of the brushes and/or sliding surface. While relatively low contact pressure causes arcing and higher voltage drop.In this study, a novel pin-on-slip ring-type friction and wear test machine was designed and manufactured for the purpose of brush testing. Copper–graphite-based electrical brush containing 90 wt% copper and 10 wt% graphite was manufactured by powder metallurgy and the tribological behaviour and voltage drop were investigated at different brush spring pressures at 10–200 kPa with current.It was found that the specific wear curve showed three distinct wear rate regimes, such as low, mild, and severe. Severe wear was observed below 30 kPa and above 120 kPa brush spring pressures (BSP) (3 and 12 N loads, respectively). Arc erosion was the main wear mechanism below 30 kPa brush spring pressure while abrasion was dominant above 120 kPa BSP. Low and mild regimes were observed between 30–50 and 50–120 kPa BSP, respectively. SEM observations showed that a continuous surface layer was formed at the sliding surfaces of the wear samples in low and mild wear regimes. The wear debris was examined by SEM and X-ray diffractometer.