| To improve the lubrication situations of fuel pump side plates,bearings and other components in an aero-engine at severe working conditions,long-life solid wear-resistant coatings have been widely studied by investigators.In this study,a research solution for polyimide solid lubricant coating was formulated,we have investigated the preparation process of coating by designed accelerated life tests in depth.Besides,intensive research also has been carried out to shorten the coating failure time and provide a basis for the reliability evaluation of the coating.Choosing polyimide(PI)as a binder,dimethylformamide(DMF)as a solvent,molybdenum disulfide(MoS2)and graphite as solid lubricants,and aluminum oxide(Al2O3)and antimony trifluoride(CeF3)as functional fillings.Firstly,we established a new-style wear-resistant coating.The optimum formulation ratio among precursors of PI:DMF:MoS2:graphite:Al2O3:CeF3 was 3.3:3.6:2.5:0.5:0.3:0.1 which was determined by orthogonal tests.After determining the optimum formulation ratio of wear-resistant coating,we investigated the influences of substrate pretreatment process systematically(including degreasing,rust removal,polishing,sandblasting,chromium plating and laser texturing),spraying process(including spraying pressure,speed,trigger control),surface drying process and curing process on the tribological property of this coating.Results show that a coating obtained by a pretreatment sand blasting process on copper alloy matrix has the longest anti-wear lifetime.The process parameters of the coating preparation were optimized.Specifically,the spraying pressure was 0.8 MPa during the spraying process.The spraying speed of the spray gun was 300?500 mm/s.The spray gun was perpendicular to the surface of the substrate,and the spraying overlap rate should be 50%-67%while the spraying distance was about 10 cm.Then,dried the coating for 1 h after spraying.Finally,solidified the coating for 30 minutes at 240?.In addition,we also determined that the coating meets the requirements of the national standards by testing their micromorphology,thickness,roughness,adhesion,hardness and other parameters.On these bases,the effects of the number of sand blasting,the matrix material and the type of solid particles on the anti-wear behavior of the coating were researched.The anti-wear mechanism of the coating was explored by means scanning electron microscopy(SEM)and energy-dispersive X-ray spectroscopy(EDS),we analyzed whether the coating failure mechanism before and after the accelerated test was consistent,and also analyze the whole process of coating failure.Under the premise of not changing the failure mechanism,the accelerated lift tests were carried out by using the MFT-5000 friction and wear tester.The influences of the speed acceleration mode,the load acceleration mode and the speed and load composite acceleration mode on the anti-wear lifetime of coating were studied,respectively.In addition,the Weibull failure probability curve is used to represent the life distribution of the coating.Based on the experimental data,the relationship between the fatigue life of the coating and work conditions is established and verified.In conclusion,we have investigated the influences of various process parameters on the wear resistance of the solid coating systematically,and analyzed their failure mechanisms.On these bases,accelerated life tests of the coating were carried out to provide a research basis for preparation and reliability studies. |
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