| Water hydraulics which uses seawater or fresh water as the working medium is a typical green production technology.It has the advantages of non-polluting,environmental friendliness,safety and energy conservation.However,the water medium has the characteristics of low viscosity,poor lubricity and high vaporization pressure,which seriously affects the performance and life of the friction pairs in the water hydraulic components.Furthermore,it causes many difficulties for the research and application of the water hydraulics.Therefore,the most critical bottleneck restricting the development of water hydraulics is the friction and wear characteristics of the friction pair in the water hydraulics components.One of the most commonly used materials in water hydraulics components is the corrosion resistant alloy.Generally,the corrosion resistant alloy is prepared by the traditional process of forging or casting production.However,the forging corrosion resistant alloy often has the poor friction characteristics.Also,the casting corrosion resistant alloy has the disadvantages of poor machinability,poor dimensional accuracy,roughness surface,porosity and sand hole.In contrast,the corrosion resistant metal made by powder metallurgy technology has good metal properties and friction characteristics.Meanwhile,with the rapid development of micro-nano technology in tribology,the nanoparticles antifriction technology with nanoparticles in lubricating oil nanoparticles has been widely studied.The technology can significantly improve the friction reduction and anti-wear ability of lubricating oil.In this paper,combined with the powder metallurgy technology and the nanoparticles antifriction technology,a powder metallurgy composite infiltrated by suspension with diamond nanoparticles has been proposed,which has excellent self-lubricating characteristics.The preparation and the seepage mechanism of the composite,the suspension releasing mechanism,the nanoparticles antifriction mechanism and the friction characteristics of the composite in the water medium environment were also investigated.The specific research contents of this paper are shown as follows:Firstly,a mathematical model of the seepage mechanism of composite was built based on the suspension flow characterisics,filtration characteristics and material attribute.A test rig of the preparing the composite was also set up to verify the mathematical model of the seepage mechanism and reveal the flow law of suspension through the powder metallurgy.According to this model,the relationship among suspension concentration,porosity,inlet pressure,concentration distribution of suspension and seepage time was investigated.Moreover,the optimization design method of diamond nanoparticles and seepage time was put forward,which can determine the process of suspension seeping into powder metallurgy.Then a series of composites of 316 L powder metallurgy were prepared with different porosity and concentration,which can lays the foundation for the study of the composite.Secondly,the suspension releasing mechanism was studied in the process of friction experiment,including the thermal expansion effect and the pumping effect.Based on the heat conduction equation and the finite element analysis,the temperature field of composite was obtained.In order to calculate the total volume of suspension expansion,the temperature field was discretized.In addition,the pumping effect model was built and the outlet pressure boundary acquired using the Bernoulli equation was adopted in the computational fluid dynamics simulation.The water distribution in the composite can be acquired by the computational fluid dynamics simulation.Based on the analysis of thermal expansion effect and pumping effect,the relationship between the volume of suspension releasing and the parameters such as porosity,heat flux density,pressure and rotating speed was also studied.Subsequently,the model of diamond nanoparticles antifriction mechanism was built with the molecular dynamics simulation based on the suspension releasing mechanism and the selection the appropriate size and length of time scale.The steady model was acquired by using multiple down pressure method.In addition,the relationship among the external load,diameter of diamond nanoparticles,indentation depth,friction force,friction coefficient and contact area was also investigated.Then the mechanism how the external load and diameter of diamond nanoparticles affect the friction characteristic of rolling tribology was revealed.Finally,the friction and wear experiment of the composite matched the CFRPEEK was conducted under the water medium environment.The friction characteristics of the composited,316 L stainless steel,316 L powder metallurgy and 316 L powder metallurgy oiled materials were also compared.With analyzing the friction coefficient,wear rate and surface morphology,the friction and wear properties of the composite under water medium environment were revealed.Moreover,the effect of the concentration,porosity,external load and rotation speed on the friction characteristics of the composite/CFRPEEK friction pair was also studied.Accordingly,the sensitivity of friction characteristics varying with internal factors of composite and external conditions was further proposed,which can establish foundation to apply the composite in the water hydraulic components.The composite combining the powder metallurgy technology with nanoparticles antifriction technology has better friction characteristics.In the future,the composite can be applied to the low requirements of water medium purity occasions,because a small amount of suspension can seep into the water.In addition,the composite can significantly improve work performance and service life of the friction pair in the water hydraulic components.Therefore,the research will promote the development of water hydraulics and it has important significance and broad application prospect. |
PDF Full Text Request