Tribological Properties of Centrifugally Cast Copper Alloy-Graphite Particle Composite

摘要

Centrifugal casting technique was used to impartbetter tribological properties to the inner periphery of centrifugalcastings of a C90300 copper alloy originally containing 13 volpct graphite particles. Microstructural observation of centrifugalcast copper alloy containing graphite particles shows that agraphite-free zone and a graphite-rich zone (25 vol pct) with aunique microstructure are formed near the outer and the innerperiphery of the centrifugally cast cylinders, respectively. Weartests were conducted using a pin-on-disc apparatus runningagainst a cast-iron counterface under dry conditions at appliedloads between 44.5 and 267 N and at a sliding speed of 1 m/s.The worn surfaces of pin and counterface were analyzed usingscanning electron microscopy (SEM) and energy dispersive X-ray (EDX) analysis. The wear rate (1.89 X 10~(-13) to 7.59 X10~(-13) m~3/m) and the temperature (50deg C to 170deg C) atthe counterface for the pins from the graphite-rich zone of thecentrifugal castings were found to be lower than the frictioncoefficient (0.52 to 0.75), the wear rate (6.32 X 10~(-12) to 3.16X 10~(-11) m~3/m), and the temperature (70deg C to 200deg C)at the counterface for the pins from the graphite-free zone (ofthe same centrifugal casting under similar conditions). A greatertransfer of the copper phases from the pin to the cast-ironcounterface was observed visually from the pin of the graphite-free zone than from the pin of the graphite-rich zone, which wasalso confirmed by EDX analysis. This leads to an increase in theweight of the counterface running against the pin from thegraphite-free zone with an increase in the applied load. Despitethe presence of graphite in cast iron, the presence of graphite inthe matrix of mating copper alloys lead to improved tribologicalproperties. The effect of graphite particles on tribologicalproperties of the composites was discussed in terms of thetransfer of iron and copper phases, the interparticle distancebetween graphite in cast-iron and copper-graphite alloys, andthe deformability of the matrix containing graphite.