Excellent tribological performance of oil-impregnated porous polyimide rubbing against Cr-rich steel balls

The tribological failures of poly-α-olefin (PAO) oil-impregnated porous polyimide (PPI) undermine the long-term reliability of aerospace bearing cages, often resulting in black product formation. Thus, addressing blackening is crucial. This study uncovers distinct tribological behaviors of PAO oil-impregnated PPI surfaces when sliding against 440 C and GCr15 steel bearing balls. Compared to GCr15/PPI, the 440 C/PPI interface exhibits fewer black products, lower friction, and reduced wear. Analysis attributes this to the higher Cr content in 440 C steel balls, facilitating a robust and dense Cr oxide film on their surfaces, which mitigates PAO oil degradation from tribo-chemical reactions with iron. Lastly, a universal approach involving Cr ion injection onto steel ball surfaces significantly enhances the tribological performance and blackening resistance of PAO oil-impregnated PPI.