Study On Tribological Characteristics Of Laser Cladding High-entropy Alloy Coating On Friction Pair Of Gear Pump

Because of smooth-running characteristics,the gear pump is widely used to transport desalinated seawater.The gear pump can be divided into external and internal gear pumps according to the different gear meshing modes.Compared with the external gear pump,the internal gear pump has the advantages of small volume,high efficiency,smooth transmission,low noise,and long service life.Because the key parts of the involute internal gear pump will not only suffer from friction and wear,corrosion and other problems in the seawater environment,when the wear and corrosion occur at the same time,there will be a positive interaction between them,resulting in the corrosion and wear phenomenon.Corrosion wear will cause friction and electrochemical corrosion on the surface of workpiece materials,leading to rapid degradation of the surface of materials,affecting the properties of materials,and thus greatly reducing the operational stability of Marine equipment.In recent years,the properties of high entropy alloy have been greatly improved compared with those of traditional copper alloy,so people pay more attention to it.Laser cladding technology is widely used as a very mature coating preparation technology,so it is desirable to prepare high entropy alloy coating by laser cladding technology to improve the performance of mechanical parts.To improve the service life of the internal gear pump,high entropy alloy coating with wear resistance,corrosion resistance and high-temperature resistance was prepared by laser cladding technology on the surface of the key parts of the gear pump.It is significant to save production resources and costs and improve economic benefits.Two alloy systems FeCoNiCrMo_x（x=0,0.3,0.6,0.9,1.2）high-entropy alloy coating and FeCoNiCrMo_x（x=0,0.3,0.6,0.9）additive gradient high-entropy alloy coating were prepared according to the actual working conditions of gear pump parts and coating performance requirements.The microstructure,phase structure,hardness and other mechanical properties of the coating were characterized,tested and analyzed.3D modelling of the involute internal gear pump is carried out.Static simulation and structural optimization of the shell,the key parts of the gear pump to build a simple coating model and substrate material comparison simulation,transient dynamics analysis to obtain the maximum deformation and maximum stress value,the simulation results for further analysis and exploration.First,FeCoNiCrMo_x（x=0,0.3,0.6,0.9,1.2）high-entropy alloy coating was prepared on upper 40Cr steel by laser cladding technology.The effects of different Mo contents on the microstructure,phase structure,hardness,bending resistance,wear resistance and corrosion resistance of FeCoNiCrMo_x coating were investigated.In order to further study the effects of different Mo contents on the properties of FeCoNiCrMo_x gradient high-entropy alloy coatings,laser cladding technology was used to prepare FeCoNiCrMo_x（x=0,0.3,0.6,0.9）gradient high-entropy alloy coatings on upper 40Cr steel.The microstructures and properties were measured and analyzed.The results show that for FeCoNiCrMo_x（x=0,0.3,0.6,0.9,1.2）high-entropy alloy coating,the increase of Mo content will change the phase structure of the coating.The main phase of FeCoNiCrMo₀ coating is the FCC crystal structure.The phase structure of FeCoNiCrMo_x（x=0.3,0.6,0.9,1.2）coating is composed of the FCC phase andσphase.The addition of the Mo element causes lattice distortion of the coating microstructure,refines the microstructure grain,and increases the hardness of the coating.The results of the electrochemical experiment,neutral salt spray test and corrosion wear test show that the tribological properties of FeCoNiCrMo_x high-entropy alloy coating are different at different temperatures with saturated salt water as the medium.The wear resistance of FeCoNiCrMo_1.2is the best under the wet friction condition of 25℃.The wear resistance of the coating is improved with the increase of Mo content,and the wear volume decreases gradually.However,in the friction and wear experiment at 50℃,the temperature increase will cause the saturated salt water to precipitate a certain amount of salt particles between the friction pairs,aggravating the degree of wear.In addition,the corrosion of saturated salt water is positively correlated with friction and wear,and the two promote corrosion and wear each other.FeCoNiCrMo_0.9 has good high-temperature friction resistance.However,the excessive Mo content in FeCoNiCrMo_1.2 coating leads to the precipitation of Cr and Mo enrichedσphase in the dendrites,while Cr and Mo elements are poor in the dendrites.As a result,there is an obvious potential difference between the dendrites and the dendrites,resulting in galvanic corrosion of the coating,further leading to the deterioration of corrosion and wear resistance.In the additive gradient high-entropy alloy coating FeCoNiCrMo_x（x=0,0.3,0.6,0.9）under different heat treatments,the coating hardness increases gradually along the matrix to the coating direction.With the increase of Mo content in the cladding layer,the grain thinning from the bottom to the top of the coating is obvious.In addition,the segregation of the Mo element is particularly obvious in the intergranular area.According to the bending test results,the maximum bending force and bending elastic modulus of the coating without heat treatment reach the maximum.The elastic modulus and bending strength of the coating are higher than 40Cr,and the coating has good bending resistance.The Mo element on the surface of the coating can also form Mo O₃,which effectively inhibits the intrusion of Cl^-and improves its corrosion resistance.The continuous increase of Mo element content in the coating leads to solid solution strengthening,fine crystal strengthening andσphase precipitation as the hard phase in the alloy structure.The combined action of these three factors greatly increases the hardness of the untreated FeCoNiCrMo_x（x=0,0.3,0.6,0.9）additive gradient high entropy alloy coating,thus improving the wear resistance of the alloy.The wear resistance of the coating under dry friction at 25℃and the corrosion resistance under wet friction at 25℃and wet friction at 50℃are all the better than those of 40Cr material.Thus,it can be seen that FeCoNiCrMo_x（x=0,0.3,0.6,0.9）additive gradient high-entropy alloy coating has good wear resistance,corrosion resistance,high temperature and high salt resistance.