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The adsorption and reactivity properties of graphite wear fragments produced in a tribocontact depend on the gaseous environment surrounding the contact which conditions the type of wear (fatigue or abrasive wear) and the surface reactivity. The determination of the specific area of the wear fragments, using a nitrogen adsorption method (Brunauer, Emett and Teller method), permits to reach a description...
Friction coefficient μ of graphite-graphite at low dynamical load (P=5N, ν<0.04 m s −1 ) under argon gas at 1.4 × 10 5 Pa is very low (μ = 0.06). Above the critical value of sliding speed (v=0.04 m s −1 ) μ is around 0.7. The transition from the low friction state (μ=0.06) to high friction state (μ = 0.7) depends on the historic of friction, particularly on the revolutions...
The tribological behaviors of graphite, non-graphitic carbon, carbon-carbon composite, and unhydrogenated amorphous carbon in nitrogen and air are investigated. The friction and wear of all carbon materials can be similarly influenced by water vapor and oxygen. Carbon materials generally exhibit a high friction and wear behavior when there is a lack of lubricant vapors in the environment. Water vapor,...
The effect of ceramic particulate and graphite additions on the high temperature dry sliding wear resistance of two Al alloys was studied. The experiments were performed using a ring-on-flat sliding contact configuration against hardened SAE 52100 bearing steel counterfaces on an apparatus built for testing at controlled temperatures. Conditions were selected such that the materials in contact were...
Despite the long, rich history and widespread use of pencils and paper, the literature of tribology is remarkably devoid of published research on the subject. The present investigation was conducted to investigate the effects of writing core (i.e. @'lead@') grade on the wear response and static and kinetic friction coefficients associated with writing on three types of paper: standard 20 lb copier...
The lubrication of stellite in dry sliding by a graphite rod loaded against the wear track on the stellite surface was investigated. Stellite sliding against stellite was studied with a pin-on-disc machine which was also fitted with a spring loaded graphite pin. Tests were performed in air from ambient temperature to 400°C for varying sliding speed and load. It was found that the wear of the stellite...
Material transfer is a common phenomenon in dry friction, generally associated with a change in surface topography and in frictional interactions. In previous work, the actual influence of adhesion, cohesion and interfacial shear stresses on the extent of transfer (the transfer being assessed experimentally by image analysis) was established both on a theoretical and experimental basis, but at constant...
The effects of a d.c magnetic field or an electric current on the frictional behaviour of steel XC48/graphite were investigated. Experimental results are as follows.(1) At ambient atmosphere, both a magnetic field present in a tribocontact and an electric current through the sliding contact decrease the mean value of friction coefficient and decrease its fluctuations also. Electric current enhances...
A tribofilm was formed during wear tests of a Si 3 N 4 -gray iron pair lubricated with distilled water. In order to clarify the formation process of the film, wear tests of the Si 3 N 4 -gray iron pair with different sliding distances were carried out on a ring-block tester using distilled water as lubricant. After the tests, the worn surfaces of the gray iron specimens...
Extended duration solid lubrication of rolling/sliding contacts, typical of gear teeth, comprised of self-mated steel at high temperature (540°C) by carbon deposits continuously replenished through pyrolysis of acetylene feed gases, has been confirmed using a WAM-1 test machine. Adequate lubrication, denoted by a low traction coefficient (μ < 0.05), depends on a sufficient rate of solid lubricant...
The bearing characteristics of cast ZA-27/graphite composite materials with graphite particle content varying from 1-5 wt.% in steps of 2% have been investigated under lubricated, semidry and dry conditions. The composite materials were fabricated employing the liquid metallurgy technique. Graphite particles of size 80-120 μm were used to reinforce the ZA-27 alloy. The bearing tests were conducted...
Reciprocating ball-on-flat tests were conducted on prepared sections cut from cast iron, silicon nitride, and silicon nitride/12.5 vol% graphite composite valve guides over a range of temperatures, normal loads, speeds, and lubrication conditions. The purpose of this work was to ascertain whether the latter ceramic composite would produce a beneficial lubricating film on the opposing surface and serve...
The electrical conduction tensor of highly anisotropic graphite is not compatible with the mechanical and tribological tensors that leads to low friction and low mechanical wear rate in sliding electrical contact. This incompatibility increases the electrical resistance and increases thus the thermal effect and the electrical contact wear. The aim of this paper is to present the tribological behaviour...
This paper reports the friction tests results performed in open air of 20-30% relative humidity (RH) at room temperature of steel/graphite in sliding contact crossed by a DC electric current and submitted to a DC magnetic field. Magnetic field is applied normally to the sliding contact area. As have been elucidated by numerous friction tests in various experimental conditions, it was shown that the...
Pure graphite particles and graphite particles coated with an electroless nickel (EN) film were introduced into an aluminum alloy via powder metallurgy to form two kinds of 6061 aluminum alloys. Tribological performances exhibited in unlubricated frictional contacts and in oil lubricated contacts were compared for both alloys. Variations in seizure resistance, friction behavior, wear mechanism, wear...
Recently two new coatings based on graphite and MoS 2 have been developed. These combine very low friction with high hardness, very low wear and high load bearing capacity. Both coatings act as solid lubricants and provide protection for both the coated surface and any uncoated opposing surface. The development of the coatings is described briefly together with details of tribological properties...
The tribological behavior of polytetrafluroethylene (PTFE) and PTFE composites with filler materials such as carbon, graphite, E glass fibers, MoS 2 and poly-p-phenyleneterephthalamide (PPDT) fibers, was studied. The present filler additions found to increase hardness and wear resistance in all composites studied. The highest wear resistance was found for composites containing (i) 18% carbon+7%...
Severe degradations result from the friction of two antagonists in sea water environment. It is proposed to evaluate materials resistance to wear with a tribocorrosion experimental set-up which is mechanically and electrochemically instrumented. The method is illustrated with graphite and Ti 6 Al 4 V.The deposition of graphite on Ti 6 Al 4 V samples is observed and...
A nylon composite with graphite and oil was investigated for anti-static sliding applications. Electric conductivity, mechanical properties and frictional properties were measured where graphite, up to 8% and oil up to 4%, were incorporated into the nylon. Generally, what improved the conductivity, lowered the coefficient of friction and decreased the abrasive wear rate, tended to decrease the mechanical...
In order to account for the influence of environment on the frictional properties of graphite, a new model of tribocontact considering the confined volume under the pin as a triboreactor is proposed. The heart of the reactor is the mechanical production of debris displaying fresh prismatic surfaces. Both the rate of formation and the rate of deactivation of these latter are influenced by the environment...
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