Abstract: In view of the phenomenon that the mechanical seal impregnated graphite has a large amount of wear in N₂O₄ environment, the mechanism by combining the macroscopic test and microscopic examination is explored. The wear surface of graphite in mechanical seal is observed by electron microscope. The normal wear zone and abnormal wear zone are distinguished according to wear morphology, and the cause of abnormal wear is assumed. The resin corrosion model and pore cavitation model of graphite surface are proposed. The test process of static corrosion and dynamic wear is set up to verify the effect of resin corrosion and pore cavitation. The experiments are carried out in water and N₂O₄ environment, and the microstructure changes of graphite surface are observed by scanning electron microscope and infrared spectrum analysis. The average pore diameter after the medium test is 33 μm, which is twice that before the test. The results show that the N₂O₄ environment does not cause the corrosion of graphite impregnated phenolic resin, and the cause of larger wear of graphite is cavitation caused by gas phase N₂O₄ rupture inside the graphite surface pores. The wear of graphite after cavitation can reach the order of tens of microns. In order to reduce cavitation erosion of impregnated graphite, the improvement measures of three preparation processes are given. The research results can also provide reference for graphite wear research and material selection of mechanical seals of other high-speed rotating machinery.

Key words: cavitation, mechanical seal, rocket engine, turbopump, wear