Friction Coefficient Of Composites Research Articles

Microstructure and Properties of Mo-Based Composites Reinforced by Al<sub>2</sub>O<sub>3</sub>

Mo-based composites with Al2O3 particles were developed in order to enhance the wear resistance of molybdenum alloys. Using Al2O3 power and pure Mo power as raw materials, the Molybdenum powders mixed with Al2O3 particles were prepared using planetary ball mill. And then the Mo-based composites with 3-10vol.% Alumina were prepared by compaction and sintering at 1840°C. The morphology of the Molybdenum powder and microstructure of the composites were analyzed by SEM and XRD. The micro-hardness, density and wear property of composites were researched. The results show that the microstructure of composites is composed of α-Al2O3 particles and Molybdenum matrix. With the increase of Alumina content, the microhardness of Molybdenum matrix increases, and the density first increases and then decreases. The friction coefficient of composite is scarcely affected by the alumina content. While the wear resistance of the composites rises with the increase of Alumina content. The wear failure is caused by abrasive wear characterized by obvious plow furrow and abrasive dust on the worn surface.

Dry sliding wear and friction studies on AlSi10Mg–fly ash–graphite hybrid metal matrix composites using Taguchi method

The aim of the investigation is to study the influence of parameters such as sliding distance, sliding speed, load and fly ash content on dry sliding wear loss and coefficient of friction (COF) of AlSi10Mg–Fly ash–graphite hybrid composites using Taguchi method. A pin-on-disc wear testing equipment was used to conduct the dry sliding wear tests on the hybrid composite produced through the liquid metallurgy route. Signal to noise ratio response analysis and analysis of variance were used to investigate the influence of parameters, and correlation between the parameters was established by multiple linear regression models. It was determined that sliding distance was the most dominant factor influencing the wear and COF of hybrid composites. There was a decrease in wear with increases in sliding speed and fly ash content. However, the COF of composites increased with increasing load, but decreased with increases in sliding distance, sliding speed and fly ash content. At higher sliding speeds, a mechanically mixed layer (MML), containing fractured fly ash particles and oxides of aluminium and iron form between the pin and the counterface. This MML helps to reduce the chance of direct metallic contact, thereby lowering the wear loss and COF. Multiple linear regression models were developed which could be effectively used to predict the wear loss and COF of the hybrid composites. Abrasive wear was the dominant wear mechanism at low loads and when the load was increased to 26·98 N, the wear mechanism changed to mixed abrasion–delamination wear with a drastic increase in the wear loss of the hybrid composite. Mild oxidative wear was predominant at high sliding speeds (3 m s−1) and lower loads.

Low Friction Coefficient Property of Super Fiber-Reinforced Composites

This paper focuses on using the high strength and low friction coefficient properties of 'super fibers', such as ultra-high molecular weight polyethylene, to develop high performance fiber-reinforced composites with low friction coefficient properties. Dyneema SK60 (an ultra-high molecular weight polyethylene fiber) and three other representative high performance fibers (super fibers), are optimized in combination with an epoxy resin polymer matrix and compression molding to produce new low friction composites. As a result, for the developed four super fiber-reinforced composites, an obvious difference of friction coefficient properties was observed. The friction coefficients of composites across the fiber lay-up were generally lower than those of specimens cut along the direction of the fiber lay-up with a significant fiber direction dependence. The Dyneema fiber-reinforced composite exhibited the lowest and most stable friction coefficient properties. This low friction coefficient may be attributed to a phenomenon of 'reticular residue effect' as the most likely cause. The fiber mass fraction of the composites contributed a significant amount to the antifriction properties of the materials: samples with a higher fiber mass fraction had a lower friction coefficient. These results indicated that the developed composites described here, with high strength and low friction coefficients, are expected to find wide application in the field of anti-friction parts and energy saving.

Tribological Properties of Cu Based Friction Composites with In Situ Synthesized TiC Filler

The Cu based friction composites using graphite as solid lubricant with different weight rations of Ti, i.e. 8 wt.%, 12 wt.%, 16 wt.%, 20 wt.%, were sintered by powder metallurgy (P/M) method. The structure of the composites was characterized by X-ray diffraction (XRD) and the tribological properties was studied on block-on-ring tester. XRD results verified presence of TiC phase which was in-situ synthesized through reaction of Ti and graphite in the composites, and the content of TiC was increased with the increased Ti content. The in-situ synthesized TiC phase which was fine and distributed uniformly improved tribological properties of Cu based friction composites significantly. The hardness, wear rates and friction coefficient of composites were increased with increasing amount of in-situ synthesized TiC.

Preparation and Properties of Al<sub>2</sub>O<sub>3</sub> Ceramic Reinforced Mo-Based Composites by Al(NO<sub>3</sub>)<sub>3</sub> Precursor

To enhance the wear resistance of molybdenum alloys, Mo-based composites reinforced by Al2O3 ceramic particles were developed. Using Al(NO3)3 aqueous solution and MoO3 as raw materials, the Molybdenum powders mixed with Al2O3 particles were prepared by liquid-solid incorporation, drying, pyrolysis of Al(NO3)3 and deoxidation of MoO3 by H2. And then the Mo-based composites with 3-10vol.% Alumina were prepared by compaction and sintering at 1840°C. The morphology of the Molybdenum powder and microstructure of the composites were analyzed by SEM and XRD. The micro-hardness, density and wear property of composites were researched. The results showed that α-Al2O3 ceramic particles and Molybdenum matrix compose the composites. With the increase of Alumina content, the molybdenum powders become fine and rule, the grains of composites become fine, the microhardness of Molybdenum matrix increases, and the density first increases and then decreases. The friction coefficient of composite is scarcely affected by the alumina content. While the wear weight of the composite decrease with the increase of Alumina content. There are obvious plow furrow and abrasive dust on the worn surface, showing the abrasive wear characterization.

Wear resistance of hot-pressed Si3N4/SiC micro/nanocomposites sintered with rare-earth oxide additives

The wear resistance of hot-pressed silicon nitride/silicon carbide micro/nanocomposites as well as monolithic silicon nitrides sintered with the same rare-earth oxide sintering additives (La2O3 ,N d 2O3 ,Y 2O3, Yb2O3 and Lu2O3) has been investigated under dry sliding conditions. The friction coefficient decreased with a decreasing ionic radius of rare-earth elements in both the monoliths and the composites. The friction coefficient of composites was always lower in comparison with that of Si3N4 monoliths. Similarly, the specific wear rate significantly decreased with a decreasing ionic radius of rare-earths either in monolithic or composite materials. The composites always exhibited lower specific wear rate compared to the monoliths. Mechanical wear (micro-fracture) and tribochemical reaction were found as the main wear mechanisms in all investigated materials. The higher bonding strength in the case of materials sintered with additives of a smaller ionic radius restricts dropping of the individual silicon nitride grains during wear experiments. This high bonding strength and the high fracture toughness are the reasons why the ceramics doped by Lu exhibited the best wear resistance. The Evans and Marshall lateral-crack chipping model based on the fracture toughness and hardness values well describes the wear rate of the investigated micro/nanocomposites.

Effect of Aramid Fiber and ZnO Nanoparticles on Friction and Wear of PTFE Composites in Dry and LN2 Conditions

The tribological performance of PTFE and PTFE-based composites filled with aramid fiber and ZnO nanoparticles in dry sliding and liquid nitrogen (LN 2 ) conditions was studied comparitively. The wear scars on the test specimen were observed by scanning electron microscopy (SEM). The transfer films of the composite material formed on the sliding interfaces were studied by X-ray photoelectron spectroscopy (XPS). The tribological test results of the tribo-pairs with two ANSI 440C steel pins sliding on a composite disk showed that, compared with the pure PTFE, the friction coefficient of the PTFE-based composites filled with both aramid fiber and ZnO nanoparticles is reduced in dry sliding in room temperature (RT) air, whereas its friction coefficient is increased in LN 2 . The friction coefficient of the composite filled with 5 wt% ZnO nanoparticles alone increases compared to unfilled PTFE in both RT air or in LN 2 conditions. While in LN 2 , the friction coefficient of the same 5% ZnO material is lower, and the wear resistance is higher than those under dry sliding, the C–F bond cleavage in PTFE was found in transfer films formed in dry sliding or LN 2 conditions, and the F atoms were combined with Fe atoms from the sliding steel pins.

Influences of carbon fabric/epoxy composites fabrication process on its friction and wear properties

In this paper, several composites of epoxy reinforced with carbon fabric were fabricated with different processes. Tribological properties of the composites which paired with 45 carbon steel under unlubricated ring-on-ring face contact sliding condition were carried out on a friction and wear tester which was typed by MPX-2000. A scanning electron microscope (SEM) equipped with an energy-dispersive X-ray analyzer (EDS) attachment was used to analyze the worn surfaces of carbon fabric/epoxy (CF/EP) composites and counterparts after experiments. The results showed that composite fabricated with semidry process tended to exhibit a uniform μ– t behavior among specimens in the same group as well as on different layers of each specimen as compared with those fabricated with wet process. The μ– t behavior of the composite characterized by two steady stages when the cohesive content was less than 40 vol.%. The first steady-state μ decreased with the lubricant filler contents increasing and the second steady-state μ tended to be close (0.35–0.4). However, μ– t behavior remained smoothly when the cohesive content was more than 40 vol.%. Lower steady-state μ could be achieved by the composite fabricated by epoxy resin with lower softening point and modified by MoS 2 and graphite. But the wear rate increased correspondingly. SEM and EDS results indicated that lubricant component in the wear debris evenly distributed on the worn surface which underwent fatigue wear played an important part in reducing the CF/EP composite friction coefficient.

Effect of matrix on the dry friction coefficient of unidirectional fiber-reinforced composite

The coefficients of dry rest (μ0) and sliding (μs) friction on a polished disk made of quenched steel have been measured for various polymer matrices and fibers and for a composite unidirectionally reinforced with poly(amidobenzimidazole) (PABI) fibers. It is established that μ0 > μs for matrices and fibers with glass transition temperatures Tg below room temperature TR, otherwise μ0 ≈ μs. This effect is explained by a sharp growth in the plasticity of polymers at Tg, which leads to an increase in the polymer-steel contact area. For a composite with Tg > TR, the dry friction coefficients obey the relation μ0 ≈ μs≈ μe/C, where μe is the coefficients of sliding friction of PABI fibers and C is their concentration. For Tg < TR (plastic matrix), the friction coefficients of the composite and matrix are close because the latter cannot hold the fiber ends during friction. As a result, they are bent and aligned along the matrix surface or embedded in the surface layer.

Mechanical and tribological properties of PA66/PPS blend. II. Filled with PTFE

AbstractThe mechanical and tribological properties of 70 vol % PA66/30 vol % PPS blend filled with different content of polytetrafluoroethylene (PTFE) were studied in this paper. It was found that the addition of PTFE impairs the mechanical properties of PA66/PPS blend, but greatly increases the wear resistance and decreases the friction coefficient. When PTFE content exceeds 20 vol %, the friction coefficient of composite is minimum (0.15) and lower than that of pure PTFE under the same conditions (0.22). The lowest wear volume (0.44 mm3) is obtained with PA66/PPS/30 vol % PTFE composite, which decreased by 91% compared with unfilled PA66/PPS blend (4.99 mm3). The topography of transfer film and the elemental distribution were investigated by Scanning Electron Microscopy (SEM) and Energy Dispersive Spectrometer (EDS), respectively. Because of the characteristic crystalline structure, PTFE preferentially transferred to the steel ring surface and formed a thin, uniform and firmly adhered transfer layer, which reduced the ability of PA66/PPS blend to transfer and prevent the adhesion between the sample and the couterface. In addition, the superior lubrication of PTFE inhibited the frictional heat melting during sliding. All these aspects are close related to the friction and wear behavior of PA66/PPS/PTFE composite. Upon the addition of PTFE, thermal control of friction regime is not applicable to the PA66/PPS blend. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 969–977, 2006

Effect of the electric current on the friction and wear properties of the CNT–Ag–G composites

In this paper, CNT–Ag–G composite brushes were fabricated by means of powder metallurgy method. The friction coefficient, wear volume loss and contact voltage drop of composites with and without current were investigated and worn surface were observed using SEM. The results showed that the wear volume loss of composites with current was greater than that without current. The primary cause of the unfavourable influence of an electric current on brush was the increase in the roughness and intensification of the abrasive properties of the metal counterbody surface. Because of oxidation reaction and weakening of the bond between the grains in the materials of the brush surface layer, the wear volume loss of positive brush was larger than that of negative brush. Due to the forming of continuous lubrication film between brush and ring under mechanical wear, the friction coefficient of composites without current was smaller than that with current. The contact voltage drop of composites was low in the initial state of wear and then rises to a certain level and remained constant.