Cavitation Erosion Resistance of High Speed Water-lubricated Sliding Bearing Material and Its Surface Modified Layers

Author:Ding Hong Qin

Supervisor:jiang shu yun

Database:Doctor

Degree Year:2019

Download:108

Pages:141

Size:15606K

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Water lubricated sliding bearing is characterized by low friction power,high rotary accuracy,environmental friendliness and low cost,and will be widely applied in high-speed machine tool spindle and other fields.The water-lubricated sliding bearing facing the spindle of high speed machine tool must have high rotary accuracy,long working life and durable accuracy.However,traditional water-lubricated sliding bearing materials can no longer meet the requirements of high-speed and precise water-lubricated sliding bearing.In particular,under high-speed working conditions,the water-lubricated sliding bearing is prone to cavitation erosion.Therefore,the key problem to be solved urgently is what kind of material is used to manufacture high-speed and precise water-lubricated sliding bearings and how to improve the anti-cavitation ability of water-lubricated sliding bearings.This paper has carried out a systematic research on this key problem.(1)Cavitation erosion resistance of high speed water-lubricated sliding bearing journal material and its surface modified layersThe cavitation erosion resistance for two types of stainless steels containing the 304stainless steel and the 17-4PH stainless steel are studied by an ultrasonic vibration system.The mass loss,SEM morphology and electrochemical test are adopted to assess the surface damage for two types of stainless steels.The surface modification of stainless steels are carried out,and the cavitation erosion resistance and erosion mechanism of the surface modification layers are studied.Two types of Cr3Si nano-coating and ZrC nano-ceramic coating are prepared on the stainless steel for improving the cavitation erosion resistance by the double glow discharge sputter technique,respectively.Three types of diffusion layers are prepared on the stainless steel using gas nitriding,gas carburizing and carbonitriding process.Cavitation erosion resistance of the surface modified layers are studied by an ultrasonic vibration system integrated with an electrochemical workstation.The mass loss,SEM morphology and electrochemical test are adopted to assess the surface damage of the surface modified layers on the high speed water-lubricated sliding bearing.The results show that the mass loss and erosion damage of the 17-4PH stainless steel are decreased as compared to the 304 stainless steel.The cavitation erosion originates from the stress accumulation and plastic deformation on the stainless steel surface.With increasing the test time,fatigue cracks are generated on the surface of the material and extended inward,leading to fatigue fracture.The mass loss and erosion damage of the Cr3Si nano-coating and ZrC nano-ceramic coating are significantly decreased as compared to the stainless steel.In the surface modified layers,the Cr3Si nano-coating and ZrC nano-ceramic coating have the finer grain size and higher hardness value comparing with the stainless steel,and the cavitation erosion resistance of the stainless steels are significantly improved.But the gas nitrided diffusion layer has no significant improvement for stainless steel.The erosion mechanism are attributed to the insufficient adhesive strength and defects of the surface modified layers on the high speed water-lubricated sliding bearing.The capability order for the surface modified layers is the ZrC nano-ceramic coating,Cr3Si nano-coating,gas nitrided diffusion layer,carbonized diffusion layer,carbonitrided layer.In conclusion,the ZrC nano-ceramic coating possesses excellent mechanical property and cavitation erosion resistance.(2)Cavitation erosion resistance and tribological properties of high speed water-lubricated sliding bearing bush materialThe special graphite material has good self-lubricating property and is expected to be used for high-speed water-lubricated sliding bearing bush.Silicified graphite,isostatic graphite,carbon graphite and furan resin graphite are prepared in this study.Cavitation experiments are studied by an ultrasonic vibration system for evaluating the cavitation erosion resistance.Tribological tests are conducted by a tribometer for assess the friction and weat property.The results show that the capability order for the special graphite is silicified graphite,isostatic graphite with 8%porosity,isostatic graphite with 14%porosity,furan resin graphite,carbon graphite.Due to the high hardness,silicified graphite exhibits an excellent cavitation erosion resistance compared with carbon graphite,furan resin graphite and isostatic graphite.Under dry sliding condition,the friction coefficient of the isostatic graphite is obviously higher than that of the carbon graphite,and the wear rate is obviously lower than that of the carbon graphite.The friction coefficient and wear rate of the carbon graphite and isostatic graphite decrease under water lubrication.The wear form of the carbon graphite is mainly exfoliation wear,while the wear form of the isostatic graphite is mainly abrasive wear.The Isostatic graphite exhibits excellent tribological properties due to small particle size,uniform structure and isotropy.