Wear Of Graphite Research Articles

Evaluation of wear and friction properties of graphite modified Lubri polylactic acid with various infill fabricated by additive manufacturing techniques

AbstractThree‐dimension (3D) printing technology, also known as additive manufacturing, is a manufacturing technology that creates three‐dimensional objects by depositing material layer by layer, as opposed to subtractive manufacturing methods. However, the newness of the technology brings with it many unknowns. In particular, the raw materials used are constantly increasing. For this reason, testing each raw material used in many aspects and to determine the optimum production conditions is important for the wide use of 3D printing technology. These optimal conditions may be the parameters used to produce a material, and sometimes they can appear as a new material. In addition, the production of new materials with varying production parameters is fundamental research topic that requires comprehensive study. For all these purposes, in this study, a new material type known as Lubri PLA (LPLA) was selected and produced in different filling types and subjected to a series of friction and wear tests. Thus, it is aimed to determine the tribological properties of the material. Additionally, samples were produced in ten different infill types (grid, lines, triangels, hexagon, cubic, octal, zigzag, diagonal, diagonal 3D and gyroid) to show the effect of filler type on friction and wear behavior. These filler types were used for both PLA and Lubri PLA materials and a total of twenty samples were produced. Thereby, it is aimed to conduct a comprehensive study showing the effect of both material difference and filling type on friction‐wear behavior. Diameter deviations, hardness deviations, friction coefficient, temperature, specific wear rates (SWr), and vibration were selected as output parameters. According to the analysis of the test results, the best result in terms of material structure was given by Lubri PLA, while the best result in terms of filling type was obtained with Diagonal 3D filling type. In addition, the lowest vibration level was obtained in the LP‐Diagonal 3D sample with 0.041 mm/s2, while the highest vibration level was obtained in the P‐Grid sample with 1.756 mm/s2.Highlights LPLA closed to nominal value in diameter and hardness deviations Addition of graphite nanoparticle increased the dimensional accuracy Diagonal 3D infill type Lubri PLA composites showed the superior performance Graphite modified Lubri PLA composites demonstrated superior performance

Friction and Wear of Polyimide and Graphite Filled Polyimide Composites under Hydrogen Environment

Friction and Wear of Polyimide and Graphite Filled Polyimide Composites under Hydrogen Environment

Study on the Tribological Behavior and the Interaction between Friction and Oxidation of Graphite Reinforced by Impregnated Phosphate at High Temperatures.

The stability of the graphite seal device is a key factor for the normal operation of aero engines. However, conventional graphite exhibits poor comprehensive performance due to its porous structure, which limits its application at high temperatures. Therefore, in this paper, phosphate was used to impregnated graphite pores, and the interaction between the friction, wear, and oxidation of phosphate-impregnated graphite against superalloy at high temperatures was studied through pin-on-disk friction tests. The results revealed that the coefficient of friction (COF) of matrix graphite fluctuated greatly, from 0.07 to 0.17, in the range of 100 °C to 500 °C, while the COF of impregnated graphite was stable, at around 0.13, from 100 °C to 500 °C. The wear rates of the two types of graphite were close from 20 °C to 300 °C, while the wear rate of the impregnated graphite was significantly lower than that of the matrix graphite at higher temperatures, from 400 °C and 500 °C. The reason was that the impregnated phosphate reacted with graphite at a high temperature, forming the inert site which helped to inhibit the oxidation and maintain the mechanical properties of the impregnated graphite at high temperatures. In addition, the impregnated graphite could maintain better integrity of the contact surface and reduce the inclusion of large hard metal oxides, thus effectively reducing the abrasive wear of the disk. Therefore, the wear depth of the superalloy disk samples with impregnated graphite was significantly lower than that of the matrix graphite. The results promote the application of phosphate-impregnated graphite under the high temperature conditions of aero engines.

Wear of micro diamond tool in ultra-precision turning under dry and minimum quantity lubrication conditions

Minimum quantity lubrication (MQL) is an effective way to reduce the cutting temperature and tool wear. To reveal the effect of MQL on the wear of micro diamond tool, a calculation model for the cutting temperature of micro diamond tool under dry friction condition is established firstly by using the Fourier’s law of heat conduction. Regarding the boundary film as a layer of heat-conduction medium, a revised calculation model for the temperature distribution on tool rake face under MQL condition with different cutting fluids is further established. The predicted results indicate that low viscosity is beneficial to the wetting of cutting fluid on tool-chip contact interface, which can relieve the friction. The reduction of friction finally decreases the cutting temperature. Secondly, the cutting temperature–dependent wear volume of micro diamond tool is predicted by using the Usui wear rate model in response to different cutting fluids and different cutting distances. In dry cutting, the graphite wear of micro diamond tool prevails. However, the application of MQL can slow down the graphitization of diamond, so the wear of micro diamond tool visibly decreases. Finally, cutting experiments with different cutting fluids are performed to verify the established models. The experimental observations agree well with the theoretical prediction results. Such satisfactory consistency confirms that the cutting fluid with low viscosity can reduce the cutting temperature and inhibit tool wear effectively.

Effects of sliding speed, periodic pauses, and atmospheric moisture content on the wear of graphite against cast iron

The effects of sliding speed, periodic pauses in sliding, and atmospheric humidity on the sliding wear of graphite against cast iron were investigated. Each variable was changed while maintaining the others constant. The geometry of the wear test involved two rings in tangential contact, in which there was oscillatory rotation of the axes of the rings to produce reciprocating contact. This “twin-ring tribometer” was operated in an atmosphere-controlled chamber. As relative humidity increased, the wear rate of the graphite decreased due to an acceleration of the severe-to-mild wear transition. Non-friction time exceeding 10 s in duration owing to the pause after each sliding movement led to early onset of mild wear, which resulted in a reduction of the total wear. As the sliding speed decreased, the wear of graphite decreased with a corresponding change in the wear mode from severe to mild. This behavior is explained in terms of the friction that occurs during instances of relative motion within the real area of contact. When the contact period was long, as was associated with low sliding speed, small wear particles were generated leading to an acceleration of the severe–mild wear transition.

Experimental study to estimate the surface wear of nuclear graphite in HTR-PM

The aim of this study was to simulate the surface wear of graphite components in a pebble-bed nuclear reactor caused by the moving fuel balls and, thus, to help evaluate the integrity of the whole graphite structures over their service life. To this end, wear tests were conducted on the chewing machine with a specially designed load jig. The test specimens included graphite plates and graphite spheres, to represent the graphite bricks and fuel spheres, respectively. The main parameters, including volume loss of graphite plates and spheres, micro-morphology of the wear surface and weight and particle size of graphite dust generated, were studied in this work.

Nuclear graphite wear properties and estimation of graphite dust production in HTR-10

The issue of the graphite dust has been a research focus for the safety of High Temperature Gas-cooled Reactors (HTGRs), especially for the pebble bed reactors. Most of the graphite dust is produced from the wear of fuel elements during cycling of fuel elements. However, due to the complexity of the motion of the fuel elements in the pebble bed, there is no systematic method developed to predict the amount the graphite dust in a pebble bed reactor. In this paper, the study of the flow of the fuel elements in the pebble bed was carried out. Both theoretical calculation and numerical analysis by Discrete Element Method (DEM) software PFC3D were conducted to obtain the normal forces and sliding distances of the fuel elements in pebble bed. The wearing theory was then integrated with PFC3D to estimate the amount of the graphite dust in a pebble bed reactor, 10MW High Temperature gas-cooled test Reactor (HTR-10).

Wear behavior of WC-Ni sliding against graphite under water lubrication

Wear of hard materials in contact with softer materials is a neglected area of research. However, we observed considerable wear phenomenon at a hard WC-Ni surface sliding over soft graphite under water lubrication. The influences of applied load and the application history on the wear of surface were addressed in our experimental design. Wear of both graphite and WC-Ni surfaces increased with a greater applied load and repeated sliding. The topographies of the worn surfaces showed clear micro-scratches on the hard WC-Ni surface. Scanning electron microscopy and X-ray photoelectron spectroscopy analyses revealed that the abrasive wear of the WC-Ni surface could be attributed to hard WC particles embedded in the graphite surface. These hard particles were formed by shearing of sharp WC-Ni asperities under certain conditions and intrinsic defects of the WC-Ni surface could accelerate this wear process.

フェノール樹脂複合材の摩耗特性に対する雰囲気効果（大気中水分効果の検証と摩擦分解ガス効果の提唱）

For the purpose of clarifying the water vapor effect on brake pad wear, two experiments were performed. In the first set of experiments, wear tests were conducted using four pads under three relative humidity conditions (0.8%RH, 35%RH and 65%RH). The tested pads were simplified formulation of commercial brake pad, each of which contains either CeO2, CuO, graphite as additive or no additives. Wear test results showed that wear amount of the three pads containing CeO2, CuO and non-additive at 0.8%RH was larger than those of pads at 35%RH and 65%RH. Analyses of wear debris and of the worn surfaces of both pad and disk showed that adhesion between pad and disk was relatively high at 0.8%RH. In the second set of experiments, adsorption tests of pad specimens left under 35%RH and 65%RH conditions were conducted. Test results indicated that water vapor in the environment physically adsorbed the pad materials. From the two sets of experiments, it is concluded that water vapor in ambient air adsorbed on the worn surfaces of pad and disk contributed to reduce the adhesion between them. On the other hand, adding graphite to the pad material decreased pad wear even at 0.8%RH. In order to elucidate this mechanism, the specimen of pure graphite was rubbed against disk material at 0.8%RH, 2.5%RH, 3.5%RH, and 65%RH. Wear of graphite at 0.8%RH and 2.5%RH was by some orders of magnitude higher than that at the other humidity conditions. On the disk specimen, graphite was clearly transferred at 0.8%RH. These results mean that the adhesion of graphite is very high at 0.8%RH. Therefore, the wear reduction mechanism of the pad with the addition of graphite at 0.8%RH was concluded as follows. Degraded gases from phenolic resin adsorbed the graphite surface at frictional interface, which caused to reduce its high adhesion to the disk material under very low humidity condition.

Wear of hybrid radial bearings (PEEK ring-PTFE retainer and alumina balls) under dry rolling contact

Wear of poly ether-ether-ketone (PEEK) radial ball bearing (composed of PEEK ring, PTFE composite retainer and alumina balls) was investigated. The PEEK radial bearings were produced by lathe machining, and their rolling contact wear tests were carried out at high rotational speed in dry condition. The PEEK adhesion film including PTFE and graphite wear particles was observed on the raceway of the bearing׳s inner ring during the test. Due to the PEEK–PTFE adhesion film accumulation, the wear rate decreased to one tenth of all-PEEK bearing. Moreover alumina balls were not stuck, and the operation temperature was less than glass transition temperature of PEEK. It was found that the PEEK–PTFE adhesion film improved dramatically wear and rotational performance of the bearing.

Statistical multi-objective optimization of electrical discharge machining parameters in machining titanium grade 5 alloy using graphite electrode

In industrial applications, particularly in aero, marine and medical industries, titanium has received great attention as a useful material and electrical discharge machining as its machining process. Selection of optimal machining parameters in a multi-objective environment is essential for specific workpiece and tool material combination, which is the concern of industries to improve the overall productivity at less cost. In this article, optimization of critical electrical discharge machining parameters such as pulse current, on time of pulse, off time of pulse and tool geometry depending on the responses such as titanium machining rate, graphite wear rate, surface roughness and deviation between entry and exit while machining titanium grade 5 alloy with graphite tool electrode at negative polarity is presented. Taguchi’s L27 orthogonal array was used to design the experiment with interaction between factors. The weighing method was used to integrate different objectives into one performance. The optimal combination of process parameters was found statistically using signal-to-noise ratios. Significance was checked by analysis of variance. Optimum parameters were found to be pulse current 15 A, on time of pulse 50 µs, off time of pulse 200 µs and cylindrical tool geometry. Resultant percentage improvements in different responses were presented.

Effect of Sheet Nanocarbon on Properties of Low Carbon Al<sub>2</sub>O<sub>3</sub>-C Refractories

Sheet nanocarbon-Al2O3 composite powders were produced by vibratory milling using expanded graphite and Al2O3 powders as raw materials. The effect of different vibratory milling time on phase compositions and microstructure of the composite powders were investigated by X-ray diffraction (XRD), field emission scanning electron microscope (FESEM). Then sheet nanocarbon-Al2O3 composite powders were used as additives to produce low carbon Al2O3-C refractories which had a carbon content of 6%. The results showed that about 50nm thickness sheet nanocarbon and Al2O3 composite powders were produced via 15h milling with expanded graphite to Al2O3 powders weight ratio of 1:2. With the increasing of milling time, the (002) diffraction peaks of graphite wear off gradually and nanosheet was desquamated from expanded graphite; It is beneficial to improve the bulk density, cold modulus of rupture (CMOR) and thermal shock resistance of Al2O3-C refractories when adding certain sheet nanocarbon-Al2O3 composite powders. The sample containing 0.5% sheet nanocarbon had a CMOR of 18.51MPa after 1000 °C heat processing in N2 atmosphere, while sample without adding any sheet nanocarbon was only 12.35MPa; The residual cold modulus of rupture (CMORTS) of sample containing 1% sheet nanocarbon was 4.22MPa after thermal shock test, while that of sample without nanocarbon was only 2.18MPa.

Theoretical Analysis on the Tribological Properties of HTGR-10 Graphite

The friction contact modals on the friction contact are summarized here. Based on Finite Element Method, the contact pressure on rough surface is calculated. The influence of the worn surface on the distribution of contact pressure is also investigated. According to our experimental result of graphite wear rate, we estimate the wear of graphite pebble used in HTGR-10. It shows that the 80% graphite will wear out in 10 years running time.

Effects of thermal and thermomechanical treatments on sliding wear of graphite crystallised white cast iron

The effects of thermal and thermomechanical treatments on sliding wear of graphite crystallised white cast iron (GWCI) were studied. Due to the inherent embrittlement of GWCI, a laminated metal in which the GWCI is cladded by low carbon steel was prepared for this study. Three cylindrical samples (GWCI-A, GWCI-B and GWCI-C) were machined from the same laminate. GWCI-A was kept in as-cast state while GWCI-B and GWCI-C underwent the thermal and thermomechanical treatments, respectively. The pin-on-disc type sliding wear tests were performed on the GWCI layers at room temperature. The microstructures and wear mechanisms were analysed by optical microscope, scanning electron microscope and the Vickers hardness test. Experimental results demonstrated that the GWCI, after laminating with ductile steel, can be deformed at high temperature with crack-free. The thermomechanical treatment produced a finer microstructure and crushed primary carbides in GWCI-C. Both GWCI-B and GWCI-C displayed plenty of secondary carbides in supercooled austenitic matrix, which was more favourable to squeeze the graphite and form the oxide layers than the matrix of martensite plus retained austenite in GWCI-A. The wear resistance of GWCI-C was superior to that of GWCI-A and GWCI-B because the oxidational wear rather than delamination dominated the sliding wear process.

Survey of dust production in pebble bed reactor cores

Graphite dust produced via mechanical wear from the pebbles in a pebble bed reactor is an area of concern for licensing. Both the German pebble bed reactors produced graphite dust that contained activated elements. These activation products constitute an additional source term of radiation and must be taken under consideration during the conduct of accident analysis of the design. This paper discusses the available literature on graphite dust production and measurements in pebble bed reactors. Limited data is available on the graphite dust produced from the AVR and THTR-300 pebble bed reactors. Experiments that have been performed on wear of graphite in pebble-bed-like conditions are reviewed. The calculation of contact forces, which are a key driving mechanism for dust in the reactor, are also included. In addition, prior graphite dust predictions are examined, and future areas of research are identified.

Fretting contact study of Ti–6Al–4 V/graphite couples in a dry shaft/bearing contact with thrust: Influence of plasma nitriding of the titanium alloy

Fretting wear or wear by small displacements is defined when two contacting surfaces (first-bodies) are subjected to small amplitude reciprocating motion of micron order. This phenomenon is observed in many mechanical assemblies and it can significantly reduce the contact mechanisms life. This paper reports on the influence of nitriding treatment of the titanium alloy on the fretting tribological behaviour of graphite/Ti–6Al–4 V couple in a dry shaft/bearing contact with thrust. Two contact geometries are investigated: cylinder-in-cylinder and flat/flat. These fretting contacts are subjected to low-amplitude oscillatory movements, with temperature reaching 270 °C. The nitriding treatment for the Ti–6Al–4 V was carried out with a gas mixture N 2/H 2 at moderate temperature (700 °C) for 12 h. In these conditions, the maximum surface hardness was improved by a factor three. In this study, the mechanism of transfer and wear of graphite against Ti–6Al–4 V nitrided or not, have been studied with a scanning electron microscope, an optical microscope and an interferential microscope. The morphological and profile analysis performed on rubbing surfaces showed various aspects of wear: prints, craters, transfer ... and allowed to explain the location, development and origin of the degradation. The friction couples have showed differences between the tests realised with the shafts with or without nitriding and especially at an elevated temperature. We discuss the experimental results and we suggest several possibilities in order to understand some specific tribological behaviour: impact of the third body, of the abrasion, etc.

Simulation of Atomic-Scale Wear of Graphite - Nanotip Induced Graphene Formation

The atomic-scale wear, the formation process of the graphene during the lateral line scan process of the nanoscale tip on the multi-layered graphene substrate is studied by using molecular relaxation method. The nanotip is scanned in line forward (along [1 2 -3 0] direction) and backward under the constant-height mode. Analysis of the effect of the tip height on the relative motion of the nanotip, the 1st graphene layer, and the 2nd graphene layer, reveals the transition from the nanotip state to the graphene tip state. During the nanotip state the mean lateral force rapidly increases as the mean loading force increases. Here the friction between the tip and the surface occurs. However, during the graphene tip state, takes nearly the constant value independent of . Here the internal friction among the 1st, the 2nd and the 3rd graphene layers occurs. The marked scan directional dependence and the increase of near the graphene edge appears. The irreversible shift of the graphene layer after all the scan processes can explain the mechanism of the elementary process of the atomic-scale wear. [DOI: 10.1380/ejssnt.2009.173]

Friction in full view

The authors report the direct observation of a single asperity tungsten tip sliding on graphite by in situ transmission electron microscopy (TEM) nanomanipulation. The in situ TEM studies have confirmed that graphitic flakes transfer to a sliding tungsten probe, validating proposed friction mechanisms explaining the unique tribological properties of graphite. Wear of graphite was observed, typically removing sheets of graphite on the order of ten basal planes in thickness. Consistency between wear flake thickness and interfacial dislocation standoff distances is discussed.

Temperature effect on IG-11 graphite wear performance

IG-11 graphite, used in the 10 MW high temperature gas-cooled test reactor (HTR-10), was tested under different temperatures on an SRV standard wear performance tester. The experiment temperatures were room temperature, 100, 200, 300 and 400 °C. According to the reactor structure, the experiments were designed to test graphite–graphite and graphite–stainless steel wear. The wear debris was collected, and the worn surfaces and debris were observed under scanning electronic microscope (SEM). It was found that there were different wear mechanisms at different temperatures. The main wear mechanism at room temperature was abrasive wear; at 200 °C, it was fatigue wear; at 400 °C, adhesive wear was observed. This difference was mainly due to the change of stress distribution at the contact area. The distribution of wear debris was also analyzed by EDX particle analysis software.

The importance of unbound hydrogen and increased aromatic structure on the friction and wear behaviour of amorphous hydrogenated carbon (a-C:H) coatings

It has been observed that amorphous hydrogenated carbon (a-C:H) coatings, which have a wear life in dry nitrogen, contain a significant fraction of unbound hydrogen and are characterized by larger aromatic clusters as seen in the enlargement of the D peak in the Raman spectra. A correlation is made between the presence of unbound hydrogen, which is associated predominantly with the surfaces of aromatic clusters, and the wear life of a-C:H coatings in dry nitrogen. It is hypothesized that high-energy edge-site/edge-site interactions of graphitic clusters is responsible for accelerated wear under dry nitrogen test conditions analogous to the dusting wear of graphite. However, where unbound hydrogen is present its release in sufficient quantities leads to passivation of these high-energy sites, reducing the coefficient of friction (COF) to values as low as 0.02. Under ambient laboratory conditions passivation of these sites occurs with the aid of water vapour. The interplay of the various factors, including material and environmental, that influence the value of the COF under ambient conditions is discussed.