Tribological properties of Fe7Mo6-based-alloy lubricated with poly-alpha-olefin containing PN additive

Tribological properties of Fe–Mo type disk specimens were investigated against ASTM 52100 steel balls under the lubrication of poly-alpha-olefin (PAO) and PAO containing 1.5 mass% alkyl-phosphonic acid-triazole-methanamine (PN additive). Both the Fe₇Mo₆-based alloy and Mo disk specimens exhibited lower friction and lower wear rates than the Fe and gray cast iron disk specimens under the lubrication of PAO. The friction coefficients of the Fe₇Mo₆-based alloy disk specimens were reduced to 0.07 by adding 1.5 mass% PN additive to PAO. No wear volume loss was observed on the Fe₇Mo₆-based alloy disk specimens when they were lubricated with PAO containing 1.5 mass% PN additive.     

Friction and wear behaviors of C/C-SiC composites containing Ti3SiC2

In the present paper, friction and wear behaviors of a carbon fiber reinforced carbon–silicon carbide–titanium silicon carbide (C-SiC–Ti₃SiC₂) hybrid matrix composites fabricated by slurry infiltration and liquid silicon infiltration were studied for potential application as brake materials. The properties were compared with those of C/C-SiC composites. The composites containing Ti₃SiC₂ had not only higher friction stability coefficient but also much higher wear resistance than C/C-SiC composites. At an initial braking speed of 28 m/s under 0.8 MPa pressure, the weight wear rate of the composites containing 5 vol% Ti₃SiC₂ was 5.55 mg/cycle, which was only one-third of C/C-SiC composites. Self-lubricious film-like debris was formed on the composites containing Ti₃SiC₂, leading to the improvement of friction and wear properties. The effect of braking speed and braking pressure on the tribological properties of modified composites were investigated. The average friction coefficient was significantly affected by braking speed and braking pressure, but the wear rate was less affected by braking pressure.     

Advanced Friction–Wear Behavior of Organic Brake Pads Using a Newly Developed System

The objective of this study was to investigate the influence of an advanced performance system on the tribological behavior of brake pad material using a specially designed brake pad tester system following standard SAE J-661. The tribological behavior and friction and wear characteristics of the organic brake pad samples were evaluated. During braking tests, the samples, in contact with a cast iron disk, were studied at different disc speeds, temperatures, and braking cycles under a constant pressure. In order to understand the friction and wear behavior, the unworn surfaces, worn surfaces, and wear debris were characterized by means of scanning electron microscopy (SEM) and energy-dispersive X-ray (EDX). Furthermore, the surface characteristics and differences in the wear modes of the brake pad samples were examined. Wear debris was permitted to deform the brake pad surfaces, leading to friction layers and enabling the estimation of the friction behavior of the brake pads. The results showed that the best friction–wear behavior was obtained with lower braking cycles at low speeds and temperature. Thus, the newly developed brake pad tester system proved very effective in evaluating the performance of the brake pad samples.     

Friction and wear properties of αFeSi2–Si alloy,ReSi1.8 and MoSi2 in ethyl alcohol

In this study, Fe–X at% Si alloy (X=70.5, 80.0 and 96.0), Re–64.3 at% Si and Mo–66.7 at% Si disk specimens were prepared by spark plasma sintering, and their friction and wear properties were investigated when they were slid against Si₃N₄ ball specimens in ethyl alcohol. The friction and wear properties of Si ingots were also examined. Fe–70.5 at% Si, Fe–80.0 at% Si, Fe–96.0 at% Si and Re–64.3 at% Si disk specimens exhibited friction coefficients as low as 0.15. It is considered that the low friction of the Fe–70.5 at% Si, Fe–80.5 at% Si and Fe–96.0 at% Si disk specimens was due to the formation of low friction silicon alkoxide and polyoxysilane on the worn surfaces of the disk specimens and the paired ball specimens. Re–64.3 at% Si disk specimens exhibited the highest microvickers hardness of all the disk specimens prepared in this study. In addition, the microvickers hardness of the Fe–X at% Si (X=70.5, 80.0, 96.0 and 100) disk specimen increased with increasing the Si content. Moreover, it was difficult to obtain dense Fe–90.0 at% Si disk specimens by sintering the annealed and crushed Fe–90.0 at% Si powder. However, dense Fe–96.0 at% Si disk specimens could be obtained by sintering the Fe–90.0 at% Si powder at 1403 K.     

Tribological characterisation of siliconcarbonitride ceramics derived from preceramic polymers

Amorphous SiCN ceramics were prepared in a laboratory scale as disk shaped specimens with 10 mm diameter and 0.3 mm thickness. The friction and wear behaviour was characterised in gross slip fretting tests under unlubricated conditions at room temperature against steel (100Cr6) and ceramic (Al₂O₃). Tests with a ball-on-disk contact were performed in laboratory air with different content of water vapour. The results show clearly that the relative humidity has a significant effect on friction and wear behaviour. All tests in dry air lead to higher friction and higher wear rate than in normal air. Improved friction and wear behaviour was observed with increasing pyrolysis temperature up to 1100 °C of the SiCN specimens. This is attributed to increasingly better mechanical properties and higher stiffness of the amorphous network due to the evaporation of gaseous organic species and the formation of free graphite like carbon.     

The effect of Al2O3 on the friction performance of automotive brake friction materials

This study consists of two stages. In the first stage, bronze-based break linings were produced and friction-wear properties of them were investigated. In the second stage, 0.5%, 1%, 2% and 4% alumina (Al₂O₃) powders were added to the bronze-based powders and Al₂O₃ reinforced bronze-based break linings were produced. Friction–wear properties of the Al₂O₃ reinforced samples were aslo investigated and compared to those of plain bronze-based ones. For this purpose, friction coefficient and wear behaviour of the samples were tested on the grey cast iron disc. The hardness and density of the samples were also determined. Microstructures of the samples before and after the sintering and the worn surfaces of the wear specimens were examined using a scanning electron microscope (SEM). The sample compacted at 350 MPa and sintered at 820 °C exhibited the optimum friction–wear behaviour. With increase in friction surface temperature, a reduction in the friction coefficient of the samples was observed. The lowest reduction in the friction coefficient with increasing temperature was for the 2% and 4% Al₂O₃ reinforced samples. The SEM images of the sample indicated that increase in Al₂O₃ content resulted in adhesive wear. With increase in Al₂O₃ content, a reduction in mass loss of the samples was also observed. Overall, the samples reinforced with 2% and 4% Al₂O₃ exhibited the best results.     

Size,Shape, and Elemental Composition of Airborne Wear Particles from Disc Brake Materials

During braking, both the rotor and pads experience wear, generating particles that may become airborne. In field tests, it is difficult to distinguish these particles from others in the surrounding environment, so it is preferable to use laboratory test stands to study the amount of airborne wear particles generated. The purpose of this work is to investigate the possibility of separate, capture, and analyze airborne wear particles generated by a disc brake in a disc brake assembly test stand. This test stand used allows the cleanliness of the air surrounding the test specimens to be controlled and thus the airborne portion of the wear particles to be studied separately. One pair each of low-metallic (LM) and non-asbestos organic (NAO) brake pads was tested against grey cast iron rotors. Before testing, the elemental contents of the brake materials were analyzed using glow discharge optical emission spectroscopy (GDOES). The concentration and size of airborne wear particles were measured online during testing. In addition, airborne wear particles were collected on filters during the tests and afterward analyzed using scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX). The analyzed wear particles contained elements such as iron, titanium, zinc, barium, manganese, and copper. Both the low-metallic and non-asbestos organic type of brake pads tested display a bimodal size distribution with peaks at 280 and 350 nm. Most of the airborne particles generated have a diameter smaller than 2.5 μm.     

Sliding wear of silicon carbide modified by etching with chlorine at various temperatures

The effect of reaction temperature on the formation of a carbon layer on the surface of SiC has been investigated. Subsequently, the tribological properties of the formed carbon layers were studied. The experimental procedure involved exposing reaction-bonded SiC balls to a flowing gas mixture of 5% Cl₂, 2.5% H₂, and Ar at a high temperature of 800, 1000, or 1200 °C. A ball-on disk tribometer was used to investigate the friction and wear behavior of the treated specimens. While partially unreacted SiC phases were observed in the layer modified at 800 °C, rhombohedral graphite crystals were formed in the layer modified at 1200 °C. Compared to untreated SiC, the treated SiC materials were found to have relatively low friction coefficients and better wear resistance. Increasing the treatment temperature was found to improve the tribological performance of the resulting surface-modified SiC balls. A possible reason for this tribological improvement has been discussed based on the observed carbon phases.     

Friction and Wear Properties of Silicon Carbide in Water from Different Sources

Low friction and low wear of SiC sliding against itself in water at room temperature have been well reported in the past 20 years, and some practical applications have been developed. However, the properties of friction and wear in pure, deionized or distilled water have been mainly observed and not in water from sources in nature. In this article, the fundamental properties of friction and wear between SiC ball and disk are observed in water from ground, river, and sea, and the results are compared with those in deionized water in the viewpoints of modes of lubrication and wear and the resultant values of friction coefficient and wear rate. The smallest friction coefficient (μ_ℓ = 0.005) in steady state is observed in deionized water and the largest (μ_ℓ = 0.013) in sea water. The smallest wear rate (w _s = 2.2 × 10⁻⁷ mm³/Nm) is observed in sea water and the largest (w _s = 3.1 × 10⁻⁷ mm³/Nm) in deionized water. The intermediate values of μ_ℓ and w _s between the smallest and the largest ones are observed in ground and river water. The modes of lubrication and wear, which generated observed values of μ_ℓ and w _s, are considered as mixed lubrication and tribochemical wear. The chemical elements of Na, Cl, Mg, and K in sea water observed on wear particles and pits are thought effective to generate the largest value of μ_ℓ and the smallest value of w _s.     

Tribological characteristics of magnetron sputtered MoS2 films in various atmospheric conditions

The friction and wear behaviors of magnetron sputtered MoS₂ films were investigated through the use of a pin and disk type tester. The experiments were performed for two kinds of specimens (ground (Ra 0.5μm) and polished (Ra 0.01 μm) substrates) under the following operating condifions: linear sliding velocities in the range of 22 -66 mm/s(3 types), normal loads varying from 9.8-29.4 N(3 types) and atmospheric conditions of air, medium and high vacuum(3 types). Silicon nitride pin was used as the lower specimen and magnetron sputtered MoS₂ on bearing steel disk was used as the upper specimen. The results showed that low friction property of the MoS₂ films could be identified in high vacuum and the specific wear rate in air was much higher than that in medium and high vacuum due to severe oxidation. It was found that the main wear mechanism in air was oxidation whereas in high vacuum accumulation of plastic flow and adhesion, were the main causes of wear.     

Mechanical and experimental investigation on nuclear fuel fretting

A mechanical approach to the nuclear fuel fretting problem is studied in this paper to find a possible and efficient way of a wear restraint. Two different contours of the spacer grid spring and dimple were developed to increase the contact area. Fretting wear experiments were carried out for the developed springs and tube specimens. Contact forces of 10 and 30 N, and slip displacements of 50–100 μm were applied under the environment of air as well as water at room temperature. Wear scars on the rods were examined to observe the effect of the mechanical approach on the wear. Especially, the influence of a contour deviation which occurred during fabrication and the wear particle accumulation in the clearance region were investigated in detail. It was found that the contact shape influenced the feature and the behavior of the length, width and volumetric shape of the wear. For the model of fuel fretting wear, equivalent depth (D_e) is suggested as a new parameter that can represent the wear severity.     

Friction and wear properties of Fe7Mo6-based alloy in ethyl alcohol

In this study, the friction and wear properties of Fe₇Mo₆-based alloy, Fe and Mo disk specimens sliding against ASTM 52100 steel and Cu and SiC ball (or pin) specimens in ethyl alcohol were evaluated using an Optimol SRV oscillating friction and wear tester. The Fe₇Mo₆-based alloy disk specimens exhibited more stable friction coefficients than the Fe and Mo disk specimens when slid against the ASTM 52100 steel ball specimen. On the other hand, the Fe/SiC tribo-pairs exhibited the lowest average friction coefficients (0.14-0.17).     

Wear behavior of Cu–La2O3 composite with or without electrical current

A new type Cu–La₂O₃ composite was fabricated by internal oxidation method using powder metallurgy. Sliding wear behavior of the Cu–La₂O₃ composites was studied by using a pin-on-disk wear tester under dry sliding conditions with or without electrical current, rubbing against GCr15 type bearing steel disk at a constant sliding speed of 20 m/s. The influence of varying applied load and electrical current was investigated. The worn surfaces were examined using scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) to determine the wear mechanisms. The results showed the Cu–La₂O₃ composites had an electrical conductivity of 81.9% IACS (International Annealed Copper Standard, 100% IACS = 58 MS/m) and a hardness of HV105. The wear rate of the Cu–La₂O₃ composite pins increased with the increase in the electrical current at high sliding speed. The main wear mechanisms of the Cu–La₂O₃ composites were found to be adhesive wear, abrasive wear and arc erosion.     

Fretting wear behaviors of nanometer Al2O3 and SiO2 reinforced PEEK composites

The influence of diameter and content of Al₂O₃ particles on the tribological behaviors under fretting wear mode was investigated. The surface of PEEK composite and steel ball were examined by SEM and EDS, to identify the topography of wear scar and analyze the distribution of chemical elements in the friction counterparts, respectively. It can be found that the filling of Al₂O₃ powder improves the fretting wear resistance of PEEK composite. With the increase of Al₂O₃ diameter, the area of wear scar on specimen increases first and decreases afterward. However, the wear of composites increases monotonically with increasing Al₂O₃ content. Although the filling of 10 wt.% and 200 nm PTFE powder in PEEK makes the lowest wear of all specimens, no synergistic effect was found when Al₂O₃ and PTFE were filled into PEEK composite together. For the friction pair of PEEK composite and steel ball, abrasive wear and adhesive wear dominate the fretting wear mechanism during fretting. Thermal effect plays a very important role during fretting; thus the property of temperature resistance for polymer material would affect the wear degree on the surface of wear scar.     

Tribological properties of solid lubricants (graphite,Sb2S3, MoS2) for automotive brake friction materials

The effect of three different solid lubricants (graphite, Sb₂S₃, and MoS₂) in the brake friction material on various aspects of friction characteristics was investigated. Three friction material specimens were produced based on an experimental formulation, and they contained 10 vol.% graphite, 7 vol.% graphite + 3 vol.% Sb₂S₃, and 7 vol.% graphite + 3 vol.% MoS₂, respectively, fixing the composition of other ingredients. Tribological properties of the friction materials were obtained using a brake dynamometer. Results showed that the friction materials containing Sb₂S₃ and graphite improved friction stability and fade resistance. The friction materials with Sb₂S₃ and MoS₂, on the other hand, exhibited disadvantages in terms of wear resistance, anti-fading, and DTV (disk thickness variation) generation.     

Microstructural and Tribological Properties of A356 Al–Si Alloy Reinforced with Al<Subscript>2</Subscript>O<Subscript>3</Subscript> Particles

In the present study, the effect of the Al₂O₃ particles (average size of 12 μm, 3 and 10 wt.%) reinforcement on the microstructure and tribological properties of Al–Si alloy (A356) was investigated. Composites were produced by applying compocasting process. Tribological properties of unreinforced alloy and composites were studied, using pin-on-disc tribometer, under dry sliding conditions at different specific loads and sliding speed of 1 m/s. Microhardness measurements, optical microscope and scanning electron microscope were used for microstructural characterization and investigation of worn surfaces and wear debris. During compocasting of A356 alloy, a transformation from a typical dendritic primary α phase to a non-dendritic rosette-like structure occurred. Composites exhibited better wear resistance compared with unreinforced alloy. Presence of 3 wt.% Al₂O₃ particles in the composite material affected the wear resistance only at specific loads up to 1 MPa. The wear rate of composite with 10 wt.% Al₂O₃ particles was nearly two order of the magnitude lower than the wear rate of the matrix alloy. Dominant wear mechanism for all materials was adhesion, with others mechanisms: oxidation, abrasion and delamination as minor ones.     

Corrosion wear behaviors of micro-arc oxidation coating of Al2O3 on 2024Al in different aqueous environments at fretting contact

The fretting wear behavior of micro-arc oxidation (MAO) coating of Al₂O₃ on an aluminum alloy 2024Al flat against a 440C stainless steel ball was investigated in artificial rainwater, artificial seawater and distilled water by using a ball-on-flat configuration with 300 μm amplitude at room temperature for 1 h. The morphology of the wear scars were observed and analyzed using scanning electron microscopy; the 3D-morphology and wear volume-loss were determined using a non-contact optical profilometer. Potentiodynamic anodic polarization was used to measure the corrosion behavior of the MAO coating before and after the corrosion wear test. The influences of the load, frequency and aqueous medium on the friction coefficient and wear volume-loss of the coatings were also analyzed. Results show that the friction coefficient decreases generally with an increase of the frequency in the three aqueous solutions; whereas it presents different variation trends as the load increased. In addition, aqueous environment does significantly influence the friction coefficient, the friction coefficient was the largest when fretting occurred in distilled water, smaller when fretting occurred in rainwater, and the smallest when fretting occurred in seawater. Particularly the remarkable antifriction effect of the seawater is of note. The wear-loss of the MAO coating in the distilled water is the largest at low frequency; however, it increases rapidly in rainwater and seawater at high frequency due to the corrosion effect of Cl^? ion as well as its accelerating effect to the wear process, and results in larger wear-loss than that in distilled water, which implies a positive synergism between corrosion and wear.     

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.     

Effect of Matrix Alloying of Fe on Friction and Wear Properties of Cu-Based Brake Pad Materials

Abstract

Argon-gas-atomized Cu–Fe prealloyed powder was used to prepare Cu-based composites, and the effect of matrix alloying of Fe on microstructure and friction and wear properties of the brake pad material was systematically investigated on an MS3000 friction and wear tester. The results indicate that matrix alloying of Fe induces the precipitation of a uniformly distributed iron-rich phase at the interior of grains, the segregation of the iron-rich phase along SiO₂–matrix interface, and the formation of pearlite in the vicinity of the graphite–matrix interface, which favors the strengthening of copper matrix, improves interfacial bonding, and protects the third body. The prealloyed sample exhibits relatively high friction coefficient and enhanced friction stability, as well as reduced wear loss when the braking speed is lower than 200?km/h. At higher braking speed (>200?km/h), the breakage of the iron-rich phase leads to an unstable friction coefficient and high wear loss.     

磁流变液制动器的设计与制动性能测试

磁流变液制动器是一种可控回转阻力的新型制动装置。本文设计并制作了一种盘式磁流变液制动器 ,对其制动力矩进行了静态测试。实验表明 ,在使用自制的磁流变液的条件下 ,最大制动力矩达到 10 N· m。文中还分析了影响磁流变液制动器制动性能的因素