Tribological Properties of Adaptive Ni-Based Composites with Addition of Lubricious Ag2MoO4 at Elevated Temperatures

The Ni-based self-lubricating composites with addition of 10 and 20?wt% Ag₂MoO₄ were fabricated by powder metallurgy technique, and the effect of Ag₂MoO₄ on tribological properties was investigated from room temperature to 700?°C. The tribo-chemical reaction films formed on rubbing surface and their effects on the tribological properties of composites at different temperatures were addressed according to the surface characterization by SEM and Micro-Raman. The results show that the Ag₂MoO₄ decomposed into Ag and Mo during the high-temperature fabrication process. The friction coefficient and wear rate of the composites decrease with the increasing of temperature and Ag₂MoO₄ contents and the composites with addition of 20?wt% Ag₂MoO₄ exhibits the lowest friction coefficient (0.26) and wear rate (1.02?×?10^?5?mm³?N^?1?m^?1) at 700?°C. The composition of the tribo-layers on the worn surfaces of the composites is varied at different temperatures. It is proposed that the improving of tribological properties of the composites at high temperatures are attributed to the synergistic lubricating effect of silver molybdate (reproduced in the rubbing process at high temperatures) and Fe oxide (transfer from disk material to the pin) formed on the worn surface.     

Friction and Wear Behaviors of Ag/MoS2/G Composite in Different Atmospheres and at Different Temperatures

Silver-based composite with 15?vol% MoS₂ and with 5?vol% graphite was prepared by powder metallurgy method. The impacts of the counterface materials, atmosphere, and temperature on the tribological behavior of the composite were investigated. It was found that when sliding against brass less effective lubricating film formed, causing a higher friction and wear comparing with ASTM-1045 steel. With the increasing proportion of oxygen in the O₂/N₂ atmosphere, the wear rate and friction coefficient ascended slightly. At 200?°C, the combination lubrication of graphite, MoS₂, and Ag contributed to a low friction coefficient (0.07) and wear rate (6.56?×?10^?6?mm³/Nm). At 400?°C, graphite lost its lubricating role, while silver became excessively soft. Large amount of MoS₂ was oxidized into MoO_3, and the residual MoS₂ formed some island-like lubricating films. Severe adhesive wear occurred on the contact surface, which led to a high friction coefficient (0.25) and a great increase of the wear rate (23.2?×?10^?6?mm³/Nm). At 600?°C, a relatively low friction coefficient (0.1) was obtained because of the formation of high-temperature solid lubricants, (Ag₂Mo₄O₁₃ and Ag₂Mo₂O₇) and liquid Ag₂Mo₂O₇. However, the wear rate at 600?°C was the highest (32.6?×?10^?6?mm³/Nm) due to the thick transfer layer.     

Quantitative atom probe analysis of carbides

Compared to atom probe analysis of metallic materials, the analysis of carbide phases results in an enhanced formation of molecular ions and multiple events. In addition, many multiple events appear to consist of two or more ions originating from adjacent sites in the material. Due to limitations of the ion detectors measurements generally underestimate the carbon concentration. Analyses using laser-pulsed atom probe tomography have been performed on SiC, WC, Ti(C,N) and Ti₂AlC grains in different materials as well as on large M₂₃C₆ precipitates in steel. Using standard evaluation methods, the obtained carbon concentration was 6-24% lower than expected from the known stoichiometry. The results improved remarkably by using only the ¹³C isotope, and calculating the concentration of ¹²C from the natural isotope abundance. This confirms that the main reason for obtaining a too low carbon concentration is the dead time of the detector, mainly affecting carbon since it is more frequently evaporated as multiple ions. In the case of Ti(C,N) and Ti₂AlC an additional difficulty arises from the overlap between C₂⁺, C₄²⁺ and Ti²⁺ at the mass-to-charge 24 Da.     

Erosion of elevated-temperature corrosion scales on metals

Combined erosion-corrosion poses a considerable problem to the design of long-lifetime metallic components in energy conversion systems. To gain some insight into this problem, scales were formed on stainless steel at elevated temperature and were subsequently eroded at room temperature to determine the nature of the erosion rates and the mechanism of scale removal. Thin corrosion scales were formed on stainless steel 310 and on an experimental Fe-18Cr-5Al-1Hf alloy at high temperatures (900 and 980°C) in gas mixtures with various levels of oxygen and combined O₂-S₂. The corroded specimens were eroded at room temperature in an air-solid particle stream using SiC particles 50 μm in size at a velocity of 60 m s^?1. The conditions of the corrosive exposures, the rates of erosion of these scales and the microscopic appearance of the eroded surface were correlated to determine the mechanism of thin scale erosion.     

Friction and wear properties of rice husk ceramics under dry condition

The friction and wear behaviors of rice husk (RH) ceramics, prepared by carbonizing the mixture of rice husk and phenol resin at 900 °C in N₂ gas environment, sliding against high carbon chromium steel (JIS SUJ2), austenitic stainless steel (JIS SUS304), and Al₂O₃ under dry condition were investigated using a ball-on-disk tribometer. The test results show that the friction coefficient of RH ceramics takes very low values 0.05–0.08 and 0.06–0.11 sliding against SUJ2 and SUS304, respectively, and much higher values around 0.14–0.23 against Al₂O₃. It was also shown that SUJ2 provides the lowest specific wear rate values below 10⁻⁹ mm²/N, while, those of SUS304 and Al₂O₃ mostly stayed between 10⁻⁹ to 10⁻⁸ mm²/N range. The worn surfaces of counterparts were observed with optical microscopy and analyzed using cross-sectional transmission electron microscopy with energy dispersive X-ray spectroscopy and electron diffraction. It was suggested that the tribological behaviors of RH ceramics are closely related with the formation of a transferred film, consisted of amorphous silica and carbon particles, on a counterpart surface. The transferred film was formed readily on SUJ2 balls, whereas for SUS304 the presence of the film was subject of the sliding conditions. Moreover, formation of the transferred film could not be detected on Al₂O₃ counterparts.     

Tribological properties of molybdenum disulphide nanoparticles in soybean oil

Abstract

The tribological properties of soybean oil (SO) with different molybdenum disulfide (MoS₂) additives (hollow nanosphere, nanoplatelet and microplatelet) were investigated. MoS₂ hollow nanospheres remarkably improved the tribological properties of SO. SO with MoS₂ hollow nanospheres decreased abrasive plowing and changed the main wear pattern on the steel friction surfaces into chemical corrosion. The MoS₂ hollow nanospheres easily entered the contact region than the other MoS₂ particles to lubricate the friction pair because of its good dispersibility in SO. The tribochemical reactions among MoS₂ hollow nanospheres, SO and friction material produced a lubricating film composed of MoO₃, Fe₂O₃, carbon containing compounds. Thus, the MoS₂ hollow nanospheres have potential lubricating applications with SO. By contrast, MoS₂ nanoplatelet and microplatelets had lesser effects on the lubricating effect of SO. The MoS₂ nanoplatelets, even with its smaller size and more active chemical properties, had more difficulty in entering into the contact region because of its low dispersibility in the base oil.     

Corrosion inhibition of mild steel using Novel Bis Schiff’s Bases as corrosion inhibitors: Electrochemical and Surface measurement

Purpose: The aim of the present investigation is to evaluate the corrosion inhibiting properties of four novel synthesize compounds namely N¹,N^1′-(1,4-phenylene)bis(N⁴-(4-nitrobenzylidene)benzene-1,4-diamine) SB-I, N¹,N^1′-(1,4-phenylene)bis(N⁴-benzylidenebenzene-1,4-diamine) SB-II, N¹,N^1′-(1,4-phenylene)bis(N⁴-(4-methylbenzylidene)benzene-1,4-diamine) SB-III, N¹,N^1′-(1,4-phenylene)bis(N⁴-(4-methoxybenzylidene)benzene-1,4-diamine) SB-IV for mild steel in 1 M HCl. Corrosion inhibitors find wide application in industries during pickling of steel, descaling and oil well acidization. Inhibitors have attracted great attention due to cost effectiveness and simplicity of the methods. Method: Different experimental techniques such as weight loss, open circuit potential (OCP), electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization were used to evaluate the corrosion inhibition performance of SBs for mild steel in acid solution. After the corrosion experiments, the surface morphology of metal surface in the absence and presence of SBs were studied by scanning electron microscopy (SEM) and Atomic force microscopy (AFM). Findings: The corrosion inhibition efficiency of SBs for mild steel are 71.42% (SB-I), 89.52 (SB-II), 92.85 (SB-III), 96.19 (SB-IV). Tafel polarization revealed that all the SBs behaved as mixed-type inhibitor but predominantly of cathodic type. The inhibition actions of these Schiff base molecules blocked the electrode surface by means of adsorption of the inhibitor molecule on metal surface, obeying the Langmuir adsorption isotherm. SEM/AFM studies of the metal surfaces confirm the protection of metal surface in presence of inhibitor as compared to the damaged surface in blank acid solution.     

Low energy ion scattering study of MoO3BiPO4 biphase catalysts

The scattering of 1.5 keV He⁺ ions (ISS) was applied to analyse the surface composition of biphase MoO₃BiPO₄ catalysts. The combination of ISS analysis and sputter etching by the ion beam allowed the cleaning process of the surface to be followed in detail. Depending on the catalyst preparation procedure, a contamination of the BiPO₄ phase by Mo was either observed or not. The peak ratios were determined for the stationary spectra and were compared to the computed differential scattering cross section.     

Sliding wear characteristics of gas boronized steel

The wear characteristics and the mechanism of sliding wear of boronized steel under unlubricated conditions were studied. Characteristic wear curves of FeB and Fe₂B boride layers formed on SAE 1045 steel were similar in form. The maximum wear rates were obtained under a sliding velocity of 0.30 m s^?1 for FeB specimens and 0.50 m s^?1 for Fe₂B specimens. Under such conditions both mechanical wear caused by scratching and oxidative wear occurred. Under conditions of mild wear the wear loss was caused mainly by oxidative wear. Under conditions of heavy wear destruction of the sliding surface was caused by thermal stress. The wear debris was composed principally of iron oxides (α Fe₂O₃, Fe₃O₄) formed by oxidative wear, α iron and borides (FeB, Fe₂B) produced by mechanical wear and B₂O₃ produced by the preferential oxidation of boron in the boride layer.     

Tribological Properties of Films Formed by the Reaction of Carbon Tetrachloride with Iron

The tribological properties of halide films grown on iron by reaction with carbon tetrachloride vapor at a temperature of 617 K and a pressure of 1.7 Torr are compared, in ultrahigh vacuum, with FeCl₂ films evaporated onto the surface. It is found that the reactively formed film has a slightly lower limiting friction coefficient than the evaporated layer (~0.06 compared to ~0.08), which may be due either to the diffusion of some carbon into the substrate or the formation of a more oriented layer when this is formed reactively. The major difference between the reactively grown and evaporated film is that the evaporated layer attains the minimum friction when ~40 ? of FeCl₂ has been evaporated, while the reactively formed layer has a minimum friction coefficient when a film of 6±2 ? has been deposited. In the case of the evaporated FeCl₂ film, the growth of second and subsequent layers proceeds before the first layer is complete. It has been shown that the friction coefficient reaches its minimum value after completion of the first monolayer, a process that is complete after the evaporation of ~40 ? of FeCl₂. In the case of the film formed by reaction with CCl₄, the halide film grows directly on the surface implying that the FeCl₂ monolayer thickness is ~6 ?. This value is in good agreement with the layer thickness in bulk ferrous chloride.     

Tribological behavior of PTFE sliding against steel in sea water

In this paper the tribological behaviors of PTFE against GCr15 steel in air, distilled water, sea water and 3.5 wt.% NaCl solution were comparatively investigated. The influence of sea water composition on the tribological behavior of PTFE was also studied. Results show that the friction process in sea water was relatively stable, the friction coefficient and the wear rate of PTFE were slightly lower and a little larger than those in distilled water, respectively, but both were much lower than those in air and NaCl solution. In aqueous environment, medium affected the tribological behavior of PTFE mainly by corrosion to the counterface, the wear rate of PTFE depended on the corrosion extent of the counterface, and this wear model can be called indirect corrosive wear. In salt solution, green rusts were formed on the counterface and had some lubricating effect. In addition, the results show Mg²⁺ and Ca²⁺ were the key factors for the relatively low friction coefficient and wear rate of PTFE in sea water, because the corrosion of counterface was reduced and the lubricating effect of green rusts was enhanced as a result of the deposition of Mg(OH)₂ and CaCO₃ on the counterface.     

Tribochemical aspects of silicon nitride ceramic sliding against stainless steel under the lubrication of seawater

Tribological behaviors of Si₃N₄ ceramic sliding against 316 stainless steel under seawater lubrication were investigated and compared with those under dry sliding and pure water lubrication. The results showed that SiO₂ colloidal particles were formed on the rubbing surface of Si₃N₄ due to the friction-induced chemical reaction of Si₃N₄ with H₂O, which were further aggregated into the silica gel with the assistance of ions in seawater. Because of the boundary lubrication of the silica gel layer, both the lowest friction coefficient and the smallest wear rates of Si₃N₄ and 316 steel were obtained in seawater.     

The surface decomposition and extreme-pressure tribological properties of highly chlorinated methanes and ethanes on ferrous surfaces

Two distinct types of extreme pressure lubricant additive behavior using chlorinated hydrocarbons have been identified using a pin and v-block apparatus. The first, which has been observed previously (and referred to as Type I) and exhibited by 1,4-dichloro-butane, CHCl₃, and CH₂Cl₂, shows an initial increase of seizure load as a function of additive concentration, but reaches a plateau at higher concentrations. In contrast, the seizure load continues to increase with concentration when CCl₄ is used as an additive. This behavior is designated Type II. Both C₂Cl₆ and C₂HCl₅ exhibit both types of behavior, being Type I at lower concentrations, converting to Type II at higher concentrations. The rate of film growth on an iron foil measured with a microbalance is shown to be significantly faster for a Type II additive (CCl₄) and a Type I additive (CH₂Cl₂, CHCl₃). CCl₄ is also shown to grow according to an essentially linear rate law with an activation energy of about 38 kJ mol⁻¹.Two possible seizure mechanisms are postulated. First, seizure is considered to occur when film removal by abrasion exceeds the growth rate, thereby leading to complete removal of the protective film. Secondly, measurements of the temperature close to the interface indicate that seizure can occur at some critical temperature T_c. Measurements of the seizure load as a function of bath temperature corroborate this view and T_c appears to be about 950 K.X-ray photoelectron spectroscopy analysis of the films formed by CH₂Cl₂ decomposition shows substantial carbon depletion in the film at higher growth temperatures. Surface analysis of chemisorbed carbon and chlorine formed by CCl₄ decomposition shows that carbon is removed from the surface in this temperature range. FeCl₂ also thermally decomposes and melts at about 950 K and provides a possible alternative explanation for the onset of seizure at T_c.     

Tribological behavior of RH ceramics made from rice husk sliding against stainless steel,alumina, silicon carbide,and silicon nitride

The tribological behavior of rice husk (RH) ceramics, a hard, porous carbon material made from rice husk, sliding against stainless steel, alumina, silicon carbide, and silicon nitride (Si₃N₄) under dry conditions was investigated. High hardness of RH ceramics was obtained from the polymorphic crystallinity of silica. The friction coefficients for RH ceramics disks sliding against Si₃N₄ balls were extremely low (<0.1), irrespective of contact pressure or sliding velocity. Transfer films from RH ceramics formed on Si₃N₄ balls. Wear-mode maps indicated that the wear modes were powder formation under all tested conditions, resulting in low specific wear rates (<5×10⁻⁹ mm²/N).     

Effect of atmospheric pressure on friction and wear of 0.45% C steel in fretting

Oxidative wear is significant in fretting wear when sufficient oxygen is supplied. In vacuum, however, oxide does not form readily. In this paper friction and wear behaviours were studied at various atmospheric pressures in order to clarify the effect of ambient pressure on them.Experiments were conducted with 0.45% C steel at ambient pressures from 1.0 × 10⁵ to 1.3 × 10^?3 Pa. The load was 14 N, the peak-to-peak slip amplitudes were 35 and 110 μm and the frequency was usually 8.3 Hz.Friction behaviours are characterized into three types according to the ambient pressure: 1.0 × 10⁵ ? 10 Pa, 10 ? 10^?1 Pa and below 10^?1 Pa. The coefficient of friction increases with a decrease in ambient pressure below 1 Pa. The critical pressure in fretting is found to be 10 Pa, above which the oxidation rate is independent of the ambient pressure and α-Fe₂O₃ is formed. Wear decreases with ambient pressure below the critical pressure where Fe₃O₄ is formed. Adhesive transfer of metallic debris occurs below 10^?1 Pa.The relationship between the coefficient of friction and oxide thickness is obtained analytically, and the effect of frequency on the oxidation rate is considered.     

TiSiC,TiSiC-Zr,and TiSiC-Cr Coatings—Corrosion Resistance and Tribological Performance in Saline Solution

TiSiC coatings alloyed with Zr and Cr were deposited on Si and 316 L steel substrates by a cathodic arc method in a CH₄ reactive atmosphere. The corrosion and wear behavior of the coatings in 0.9% NaCl solution was investigated. Corrosion resistance of the coatings was evaluated by electrochemical tests. The electrochemical polarization measurements were conducted at room temperature in the potential range ?1 and 1.5 V, with a 0.167 mVs^?1 scan rate. Compared to the uncoated 316 L substrates, the coated ones showed nobler characteristics, with more electropositive corrosion potentials, lower corrosion current densities, and higher polarization resistances. TiSiC-Zr exhibited the lowest corrosion current density (0.62 μAcm^?2) and the highest protection efficiency (69.5%). The tribological performance of the coatings under corrosive conditions (0.9% NaCl solution) was investigated using a ball-on-disc tribometer (6-mm-diameter sapphire ball, 5 N load, 0.15 ms^?1 sliding speed, 400 m sliding distance). The TiSiC-Cr coating demonstrated the best wear behavior, with a wear rate of 3.2 × 10^?6 mm³N^?1m^?1, followed by TiSiC and TiSiC-Zr. The morphologies and compositions of the worn surfaces were examined by scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS) in order to identify the wear mechanism. Corrosion, debris adhesion, and oxidation were found to be the dominant wear processes.     

The tribochemistry of silicon nitride: effects of friction, temperature and sliding velocity

In order to obtain information on the mechanisms of tribochemistry in silicon nitride, we studied the effects of chemical parameters (temperature and concentration of reagent) and tribological parameters (load and sliding speed) on the kinetics of the reaction, i.e. the rate of material removal. The temperature dependence of the wear rate of silicon nitride has been studied in several solutions. In CrO₃ and in KOH, the removal rate increases with temperature; the apparent activation energy is 20 kJ/mole in CrO₃ and 22 kJ/mole in KOH. In water, material removal is temperature independent, in KMnO₄, its rate decreases with increasing temperature. These changes are accompanied by parallel variations in the coefficient of friction. The reaction rate presents a complex dependence on the concentration of CrO₃ solutions. In water and CrO₃ solutions, we observed a strong dependence of friction and material removal rate with the load. With the changes in temperature, concentration and load, it is found that the reaction rate (in mm³/(N·m)) is linear with the coefficient of friction above a threshold value μ_th≈0.2. The velocity dependence is complicated by the phenomena of mixed lubrication. In all cases, the lack of solid wear particles and the production of ammonia have verified the tribochemical nature of the material removal. The mechanism of stimulation of the chemical reaction by friction is a quasi-static stretching of the bonds at the interface and a high local vibration energy of the atoms at the sliding contact.     

Physical and Chemical Impact of Sulphuric Acid on Cylinder Lubrication for Large 2-Stroke Marine Diesel Engines

The influence of sulphuric acid, H₂SO₄, on the physical and chemical behaviour of marine Diesel engine lubricant base oils was investigated. To understand the basic interaction of H₂SO₄ with the lubricant film, the saturated hydrocarbon squalane, C₃₀H₆₂, was chosen as a simple model oil in addition to a fully formulated lubricant and its corresponding API Group I base oil HVI160B. To understand droplet formation in the lubricant, the interfacial tension between aqueous H₂SO₄ (0?C98?%w/w) and C₃₀H₆₂ measured in a previous study (Sautermeister et al., Tribology International, 38th Leeds-Lyon Symposium on Tribology, 2011) and is compared with three different API Group I base oils. Interfacial tension decreases with increasing acid concentration, but is much lower for the base oil. Both oils were emulsified with a constant volume fraction of aqueous H₂SO₄. The droplet size was smaller and more distinct for the base oil under the same shearing conditions and the emulsions with base oil were are more stable. The concentration of the dispersed phase had no significant influence on the viscosity of the emulsions compared to the viscosity of the bulk oil alone. In addition to the physical measurements, chemical reaction between H₂SO₄ and the API Group I base oil HVI160B was observed yielding bituminous matter which appears to be a complex emulsion. The critical acid concentration for the formation of bitumen was found to be 40?%w/w. Between 50 and 80?%w/w, bitumen was formed spontaneously at 85?°C and above 85?%w/w, bitumen was formed spontaneously at room temperature. The observed concentrations for bitumen formation correlate well with the first and second dissociation steps of H₂SO₄. HSO₄ ^? ions are likely to be the driving force for bitumen formation. Finally, the viscosity characteristics of two different bitumen were measured. Both were found to exhibit shear thinning and the one formed with highly concentrated H₂SO₄ created a solid deposit on the measurement equipment above 120?°C.     

Influence of BN and B4C particulates on wear and corrosion resistance of electroplated nickel matrix composite coatings

Abstract

Electrodeposition of nickel–boron nitride–boron carbide (Ni–BN–B₄C) composites was carried out from a Watt's solution containing 50 and 10?g L of dispersed boron nitride and boron carbide particles respectively. The corrosion behaviour for both Ni and Ni–BN–B₄C deposits was evaluated by polarisation curves in a 3·5% NaCl solution at room temperature. Wear resistance of the composites was also studied using pin on disc technique. Scanning electron microscopy was extensively used to understand the effect of different electroplating conditions on the concentration and distribution of particles. The results showed that BN and B₄C particle concentration in the Ni–BN–B₄C composite film was sensitively dependent on the electroplating current density and bath temperature. Meanwhile, the Ni–BN–B₄C composite films were much more resistant to corrosion and wear than pure Ni coatings.     

Tribological Properties of Pulsed Laser Deposited WSex(Ni)/DLC Coatings

The tribological performance and tribochemistry of both single-layer WSe_x(Ni) and bilayer WSe_x(Ni)/diamond-like carbon coatings formed on steel substrates by pulsed laser deposition are evaluated. The ball-on-disk tests of the coatings in air show that at a laser fluence of 100 J cm^–2 and a partial pressure of argon 2 Pa, the endurance of the top WSe_x(Ni) film in the bilayer coating is nearly four times greater than for single-layer WSe_x(Ni) film. For the top WSe₂(Ni) layer 170 nm thick, deposited onto DLC coating 200 nm, the coating friction coefficient was kept 0.03–0.09 during nearly 2 × 10⁴ cycles.