Long-Term Lubrication at 500 °C Using Continuously Replenishable Solid Lubricating Film Polymerized In Situ by Gasified Monomers PA and PPD

Abstract

Through the introduction of gas-phase monomers phthalic anhydride (PA) and p-phenylenediamine (PPD), replenishment of lubricants during high-temperature friction processes could be realized. According to Fourier transform infrared spectroscopy (FTIR) and gas chromatography–mass spectrometry (GC-MS) analyses, in a 10-min ball–disc friction test at 500 °C, the introduced monomers contacted and polymerized in the gas phase to form solid products with the structure of imides or long carbon chains, which provided superior thermal stability. Solid lubricating films were generated on the disc surface by the physical deposition of these polymerized products and then fall off and attach to the contact position of the ball to form a transfer film. Compared to nonlubricated friction, the coefficient of friction (COF) was reduced from 0.54 to 0.24, and the wear rates of the balls and disc were reduced from 8.32 × 10−6 to 0.65 × 10−6 mm3·N−1·m−1 and from 2.62 × 10−4 to 7.48 × 10−6 mm3·N−1·m−1, respectively. With continued friction but no further introduction of monomers, the solid lubricating film generated in the initial 10 min could provide even more remarkable lubrication for at least the next 15 min, with a minimum COF of 0.01. This could be related to the reinforcing and synergistic lubricating effect of carbonized product powders that gradually formed a continuous phase on the polymerized products’ matrix. After the COF increased, low friction could be re-attained by reintroduction monomers, but lubrication would be limited by the previous wear. This novel lubricating film shows potential in high-temperature lubrication, because it has both the effectiveness and stability of solid lubrication and the replenishability of gas lubrication.