Polyamide 66, with excellent mechanical and self-lubrication properties, has been widely used in wear-resistant application as paired material with metal. Yet in certain special service conditions, the pure PA66 can not meet the requirement of the high wear-resistant property. It is of significant importance to improve the frictional wear properties of PA66.
PA66 matrix composites filled with nano-Si3N4, graphite and PTFE was prepared via twin-screw extrusion and injection molding in this paper. The mechanical and tribological properties of the PA66 nano-composites were systematically studied. Investigations had been made on the effect of the nano-Si3N4 loading, solid lubricant and filler dispersity on the mechanical and tribological properties of the PA66 nano-composites and the wear mechanism was also discussed.
It is revealed that the tensile and flexural strength of the Si3N4/PA66 nano-composite did not have a significant change with low nano-Si3N4 loading. Further increasing of nano-Si3N4 content would cause the agglomerating of Si3N4 nano-particles, thus the tensile and flexural strength decreased. The frictional coefficient of the composites decreased consistently with increasing nano-Si3N4 content. However the wear rate of the composite decreased first and then increased with the increasing of Si3N4 content.
Based on the investigations on the Si3N4+graphite+PTFE/PA66 nano-composite, It is indicated that the tribological properties of the composite were effectively improved with the addition of solid lubricant, though their mechanical properties become weakened. Besides, with the addition of solid lubricant, the frictional coefficient and wear rate of the composite decreased at low nano-Si3N4 loading. If the loading of the nano-particles was too high, the tribological properties deteriorated. The nano-composite possessed the optimum tribological properties with a certain nano-particle loading.
Si3N4 particles in the wear debris were inlaid back into the worn surface of the Si3N4/PA66 and Si3N4+graphite+PTFE/PA66 composites during sliding, thus enhancing the sample surface and improving the wear ability of the composites. But when the nano-Si3N4 content is high, the worn surface became rough and the transferred film was too thick and its bounding with the counterpart was weak, resulting an abrasive wear dominated mechanism of wear.
In order to make the fillers well dispersed in PA66 matrix and obtain better mechanical and tribological properties, the nanoparticles and graphite were treated by high energy ball milling, and the screw configuration was also optimized. The composite prepared via the optimization of the screw configuration had better mechanical properties and lower fictional coefficient and wear rate. As to Si3N4+graphite+PTFE/PA66 treated by high energy ball milling, the mechanical properties showed insignificant change, and the frictional coefficient of the composite decreased while the wear rate almost un-changed.
The tribological properties of the PA66 matrix composite filled with dispersed nano-particles were improved to certain degree. Through high energy ball-milling and the optimization of the screw configuration, the dispersity of nano-particles was improved, and so too the tribological properties. However, the dispersion of the nano-particles has not reached the nano-sized dispersity in the PA66 matrix. Further investigations are still needed to do with this nano-composite.
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