Tribological performance of in-situ transformed Cf/Al2O3 self-lubricating composite

Friction and wear behaviors of in-situ Cf/Al2O3, Cf/Al2O3, and Al2O3 were examined under dry sliding, water, PAO oil and PAO+carbon nanotube (CNT) grease at applied load of 6.86 N by ball-on-disk sliding tribotester. Both in-situ Cf/Al2O3 and Cf/Al2O3 were fabricated by hot-press sintering in vacuum. In-situ Cf/Al2O3 used cheap and flexible pre-oxidized polyacrylonitrile fibers to in-situ transform into Cf during sintering and that Cf/Al2O3 used commercial Cf directly. The experimental results indicate that in-situ Cf/Al2O3 has comparable friction-reduction ability with Cf/Al2O3 under dry and water lubrication. Specifically, friction coefficient μ of in-situ Cf/Al2O3 reduces from 0.45 to 0.39 with time and fluctuates around 0.17 under dry and water lubrication respectively, while μ of Al2O3 is about 0.52 and varies around 0.35. Meanwhile, in-situ Cf/Al2O3 shows best wear-resistance among the three specimens with slightest spalling under dry and water lubrication because in-situ Cf has good interfacial bonding with matrix. However, lubrication property of carbon fibers are hidden by good lubricants (PAO and PAO+CNT grease), the worn surfaces of all of three specimens look like polished. All these results indicate that in-situ Cf/Al2O3 should be a better and cost-effective self-lubricated composite.