Tribological Behavior Of Composites Research Articles

Tribological properties of nickel-based self-lubricating composite at elevated temperature and counterface material selection

Solid lubricating materials are necessary for development of new generation gas turbine engines. Nickel-based self-lubricating composites with graphite and molybdenum disulfide as lubricant were prepared by powder metallurgy (P/M) method. Their tribological properties were tested by a MG-2000 high-temperature tribometer from room temperature to 600 °C. The structure of the composite was analyzed by XRD and worn surface morphologies were observed by optical microscope. The effects of counterface materials on tribological behavior of composites were investigated. It was found that chromium sulfide and tungsten carbide were formed in the composite by adding molybdenum disulfide and graphite, which were responsible for low-friction and high wear-resistance at elevated temperatures, respectively. The average friction coefficients (0.14–0.27) and wear rates (1.0–3.5 × 10 −6 mm 3/(N m)) were obtained for Ni–Cr–W–Fe–C–MoS 2 composite when rubbed against silicon nitride from room temperature to 600 °C due to a synergetic lubricating action of graphite and molybdenum disulfide. The optimum combination of Ni–Cr–W–Fe–C–MoS 2/Ni–Cr–W–Al–Ti–C showed lower friction than other counter pairs. The graphite played the main role of lubrication at room temperature, while sulfides were responsible for low friction at high temperature.

Friction and wear properties of copper matrix composites reinforced with short carbon fibers

The friction and wear properties of the copper matrix composites reinforced with short carbon fibers (CFs) were studied. The influence of short CFs contents, load and rotating speed on tribological behavior of composites was discussed. The results indicate that the wear resistance improve with the increasing of fiber volume fraction. Both friction coefficient and wear mass loss increase with the increase in load and rotating speed, respectively. The wear mechanism is transferred from adhesive wear for pure Cu to delamination wear for Cu/short CFs composites. A graphite film forms on the worn surface of the composite and acts as a solid lubricant.

Comparative investigation on the wear and transfer behaviors of carbon fiber reinforced polymer composites under dry sliding and water lubrication

The wear and transfer characteristics of four carbon fiber reinforced polymer composites under distilled-water-lubricated and dry-sliding against stainless steel were comparatively investigated. Scanning electron microscopy (SEM) was utilized to examine composite microstructures and modes of failure. The typical element chemical states of the transfer film on the stainless steel were examined with X-ray photoelectron spectroscopy (XPS). It is found that all the composites hold the lowered friction coefficient and showed much better wear resistance under water lubricated sliding against stainless steel than that under dry sliding. The worn of composites were characterized by plastic deformation, scuffing, micro-cracking, and spalling under both dry- and water lubricated conditions. Such plastic deformation, scuffing, micro-cracking, and spalling, however, are significantly abated under water-lubricated condition. XPS analysis conformed to that the transfer of composites onto the counterpart ring surface is significantly hindered under water lubrication. The transfer film had smaller effect on the tribological behavior of composites under water lubricated condition than that under dry sliding, because under water-lubricated condition the cooling and boundary lubricating effects of the water medium dominated the tribological behavior.

Effects of various kinds of fillers on the tribological behavior of polytetrafluoroethylene composites under dry and oil‐lubricated conditions

AbstractPolytetrafluoroethylene (PTFE)‐based composites filled with various inorganic fillers in a volume fraction of 30% were prepared. The tribological behavior of the PTFE composites sliding against AISI52100 steel under dry and liquid paraffin‐lubricated conditions was investigated on an MHK‐500 model ring‐on‐block test rig. The morphologies of worn surfaces and wear debris were observed with a scanning electron microscope (SEM) and an optical microscope. As the results, different fillers show different effects on the tribological behavior of the PTFE composites, while the composite shows much different tribological behavior under lubricated conditions as compared with dry sliding. The tribological behavior of the PTFE composites under dry sliding is greatly related to the uniformity and thickness of the transfer films. Only the PTFE composites with a transfer film of good uniformity and proper thickness may have excellent tribological behavior. The PTFE composites show much better tribological behavior under lubrication of liquid paraffin than under dry sliding, namely, the friction coefficients are decreased by 1 order of magnitude and the wear rate by 1–3 orders of magnitude. Observation of the worn composite surfaces with SEM indicates that fatigue cracks were generated under lubrication of liquid paraffin, owing to the absorption and osmosis of liquid paraffin into the microdefects of the PTFE composites. The creation and development of the fatigue cracks led to fatigue wear of the PTFE composites. This would reduce the mechanical strength and load‐supporting capacity of the PTFE composites. Therefore, the tribological behavior of the PTFE composites under lubrication of liquid paraffin is greatly dependent on the compatibility between the PTFE matrix and the inorganic fillers. In other words, the better is the compatibility between PTFE and fillers the better is the tribological behavior of the composites. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 1891–1897, 2001

The tribological behaviors of copper-coated graphite filled PTFE composites

Polytetrafluoroethylene (PTFE) composites filled with different fillers and various filler proportions were made by compression molding. The powders of graphite, copper, copper-coated graphite (CCG), and copper-mixed graphite (CMG) were selected as the fillers. The tribological behaviors of composites in sliding against a stainless steel ring were evaluated on an MM-200 friction and wear tester. The morphologies and element chemical states of the worn composite surfaces were examined with scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS), respectively. It was found that the CCG particles prepared by chemical replacement method were characterized by loose and uniform covering of graphite particles by many tiny copper particles. The preferential transfer of graphite onto the surfaces of PTFE powders during the mixing process could be prevented by copper coating method, which was beneficial to further improving the wear resistance of composites. XPS analysis showed that no tribological reaction occurred during the friction process of PTFE sliding against stainless steel ring, but there was radical -CF 3 on the worn surfaces of PTFE composites, its generation mechanism and effect on the tribological behaviors of PTFE composites still need further study.