Nanographite platelets (NGPs) are used as multi-functional fillers to develop cementitious composites because the unique carbon-carbon hexagonal plane structure makes NGPs have excellent mechanical, electrical, dielectric and thermal properties. In this paper, cementitious composites filled with NGPs are fabricated to investigate the effect of NGPs on mechanical, thermal and electromagnetic properties of cementitious composites. Experiment results show that the addition of NGPs can effectively modify the above-mentioned properties of cementitious composites. When the content of NGPs reaches 5%, the hardness of the composites increases 1.5-fold, the abrasive loss per unit area of the composites reduces by 71%, the abrasion depth of the composites reduces by 73%, the thermal conductivity of the composites increases by 77%, the specific heat of the composites decreases by 17.7%, the damping ratio of the composites increases by 20%, and the electromagnetic wave reflectivity of the composites decreases by 38% compared with pure cementitious composites.

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Mechanical, thermal and electromagnetic properties of nanographite platelets modified cementitious composites

Influence of nano-potassium titanate particles on the performance of NAO brake-pads

The brush materials modified with organosilicon were prepared by the powder metallurgy method, and their current-carrying friction and wear properties were compared with those of brush materials modified with SiO2. The materials were characterized by SEM, XRD, XPS, deep etching, and roughness. The results showed that, compared with the SiO2, organosilicon can significantly reduce the wear rate of brush materials by 67–88%, because the SiOC fiber produced by pyrolysis of organosilicon could control the graphite content on the friction surface by reducing abrasive wear. In the aspect of wear mechanism, organosilicon could greatly reduce the abrasive wear of the materials and the mated materials, but aggravated the adhesive wear of the materials.

Study on current-carrying friction and wear properties of copper-graphite brush material reinforced by organosilicon

Sintered Cu-based frictional materials were developed by using powder metallurgy (PM) method. The materials are aimed for application in a passenger car as a dry friction clutch. Effects of sintering temperature and composition on mechanical and tribological properties were determined. It was found that improper frictional material formulations caused inferior properties, particularly when the sintering temperatures were increased. Admixing of high Sn content (8 wt. %) resulted in decreases of sintered density and hardness with increasing sintering temperature. High Sn contents caused swelling of the sintered materials. Tribological properties (friction coefficient and wear rate) of the sintered specimens of the investigated materials were insensitive to sintering temperatures in the range of 800-950 °C but they were strongly influenced by chemical compositions. Addition of 3 wt. % graphite lowered the friction coefficient, which subsequently lowered the wear rate of the sintered material. To increase friction coefficient, one of the crucial properties of the dry friction clutch, of the sintered Cu-based frictional materials, two approaches were employed. In the first approach, substitution of graphite by SiO2 powders could improve the material friction coefficient. In the second approach, decreases of graphite content from 3 to 1 wt. % and of Sn content from 8 to 2 wt. % were conducted. The latter approach not only improved friction coefficient but also improved sintered density and hardness of the Cu-based frictional materials.

Tribological Properties of PM Cu-Based Dry Friction Clutch

To investigate the relationship between dandification mechanism of SiO2 particles and materials performance under different friction speeds,Cu-graphite-SiO2 sintered materials were prepared through powder metallurgy.The tests were conducted on a pin-on-disk tester in speed range of 7.8-47.1 m/s.The results demonstrate that the effects of SiO2 on the friction and wear performance of the materials are closely related to the friction speed.At low friction speed,the friction coefficient increases with increasing content of SiO2 particles,this is attributed to the effect of SiO2 scratch,which can improve the friction force remarkably under static load.However,the wear rate is not sensitive to the content of SiO2 particles.At high friction speed,the SiO2 particles are broken by impact action and embedded in the matrix softened at high temperature,which results in reduction of scratch influence,and makes the friction coefficient insensitive to SiO2 content.The increase of surface hardness causes the wear rate to fall with increasing content of SiO2 particles.

Effects of content of SiO_2 particles on tribological behavior of Cu-matrix friction materials

Cu-based nanometer composites with ω（n-SiO2）=1.0 % nano-SiO2 were prepared through ball milling and powder metallurgy technology. The friction and wear performance of the composites was investigated by ball-disk friction and wear tester. The microstructure and wear morphology were studied by drainage and field scanning electronic microscope (FSEM), respectively. The results indicate that ball milling can improve the spatial distribution of nano-SiO2 in the copper matrix. With the ball milling time increasing, the dynamic friction coefficient and wear rate of the composites decrease firstly and then increase. The composite milled 10 h has the lower friction coefficient and wear rate, and its main mechanism is abrasive wear.

Research on Tribological Properties of Nano-SiO2/Cu Composites

The Cu-based friction materials with nano-graphite were prepared through powder metallurgy technology. The microstructure and friction performance were studied through scan electronic microscope (SEM) and friction tester, respectively. The results indicate that coefficient of the Cu-based friction materials with 2 wt% nano-graphite is high and stable. Comparing with the friction materials without n-C, the wear resistance and heat resistance of the friction materials with nano-graphite has been improved by 11 % and 25 %, respectively. The nano-graphite particles will reduce the abrasive wear and enhance the wear resistance of the Cu-based friction materials.

Yuan Yuan Li

Papers

Research on Tribological Properties of Nano-SiO2/Cu Composites

Effect of Nano-Graphite on Friction Performance of Cu-Based Friction Material