Effect Of La₂O₃ On Compound Modified Layers Of Laser Cladding Metal Ceramic-ion Sulfurizing

Sea water hydraulic pump is the key component in the hydraulic driving system of sea water.However,due to its harsh working environment,seawater hydraulic pumps are prone to wear and corrosion failures,which seriously affect the service life of seawater hydraulic pumps.The composite layer prepared by laser cladding and low temperature ion sulfurizing technology has the properties of antifriction,abrasion resistance and corrosion resistance,which can effectively alleviate the above problems.However,the sensitivity of Ni based cermet coating is very large,and the internal quality of the coating is very poor.Moreover,the Fe content of Ni based cermet coating is relatively small.The thickness of sulphide coating prepared on the surface is relatively thin and homogeneous,which is not conducive to the full self-lubricating performance.La₂O₃ has been widely applied in the field of metal ceramic coating surface modification and chemical heat treatment and infiltration.However,too little La₂O₃ or too much is not conducive to the quality of coating,so it is necessary to conduct systematic research on it.First of all,La₂O₃ for the influence of the structure and properties of Ni based organization of metal ceramic coating were studied by using Ni based WC powder by laser cladding on the surface of A3steel,the macro morphology and microstructure observation of cladding layer,phase composition analysis,performance test,study the different content of La₂O₃ for the rule and mechanism of cladding the layer organization and performance influence,and ultimately determine the optimum adding amount of La₂O₃.The experimental results show that too much or too little La₂O₃ is not conducive to the quality of cladding coating.Adding proper amount of La₂O₃ can obviously reduce the crack sensitivity of the cladding layer,reduce the inclusions,cracks and holes in the coating,and increase the density.It can also refine the grain of cladding layer,weaken the directivity of dendritic growth,make it tightly arranged,make WC distribute evenly,accelerate the dissolution of WC particles,but have little effect on the phase of cladding layer,but only form La₂Ni₇ phase.With the addition of La₂O₃,the hardness of the cladding layer is improved,the tribological property is obviously improved,and the corrosion resistance has been improved to a certain extent.In determining the best value in the laser cladding layer La₂O₃ was added on the basis of 260degrees in the insulation condition of 2hour ion sulphurizing on the surface of the cladding layer,the use of La₂O₃ in the laser cladding layer on ion sulphurizing process of catalysis,by observing the infiltration influence on infiltration of sulfide layer and structure and mechanism of La₂O₃ the performance test of sulfur layer in the cladding layer,in order to improve the layer thickness and uniformity.The experimental results show that the sulfide particles in the sulphide layer on the surface of the cladding layer are white and small and mainly grow on the Ni base.In the cladding layer of La₂O₃ segregation on grain boundaries,and grain refinement of the cladding layer,purified tissue,activation of the surface of the cladding layer in the atmosphere,ion sulphurizing process of adsorption of more S2-is attached to the surface of the cladding layer,the ion sulphurizing has catalytic effect,the layer color is more deep and more uniform,the sulfide particles increased,the grain size becomes larger,the content of S is higher,after energizing sulphurized layer thickness doubled.More content of FeS,WS₂ and FeS₂ phase was detected in the sulphurized layer after La₂O₃,but the variety of the phase did not change obviously.At the same time,the sulfur permeable layer shows good antifriction performance under the condition of dry friction and artificial sea water.Under dry friction condition,the friction coefficient is 8%and more stable than that of the unpermeable seepage layer,and the wear scar is narrower and shallower.The width and depth are 370 and 0.948 m,respectively.Under the condition of artificial seawater lubrication,the percolation layer shows a better antifriction performance than that under the dry friction condition,reducing by about 50%.After La₂O₃ infiltration,the friction coefficient of the seepage layer under artificial seawater condition is the lowest and the most stable,which is about 0.25.The weightlessness of wear has also been reduced obviously,and the wear scar is narrower and shallower.