Study On Microstructure And Properties Of Ni-based Surfacing Layer Enhanced By Plasma Surfacing WC And Rare Earth Y₂O₃

Nowadays,with the rapid development of manufacturing industry,more and more parts and components fail because of wear and tear.The surface strengthening treatment of workpiece is an effective way to improve the service life of workpiece and save economic cost.In this paper,WC reinforced nickel-based surfacing layer and Y₂O₃ modified nickel-based tungsten carbide surfacing layer were prepared on Q235 steel plate by plasma surfacing method using WC,Y₂O₃ and Ni60 powders.Firstly,the optimal technological parameters of nickel-based alloy surfacing layer were determined by orthogonal test method.Then,the effects of WC reinforced nickel-based alloy surfacing layer and Y₂O₃ content on the microstructure and properties of 30wt.%WC-Ni alloy surfacing layer were studied.The following conclusions are drawn:(1)The influences of welding current,welding speed and plasma flow rate on the surface formation,surface microhardness and abrasion of the surfacing layer were studied by orthogonal test.Finally,the optimal process parameters were determined as follows:welding current 110A,welding speed 100mm/min,plasma gas flow 4L/min.(2)When WC content in Ni60 alloy powder exceeds 30wt.%,cracks,pores and other defects appear in the surfacing layer.The main phases of Ni60 alloy surfacing layer are?-Ni,M₂₃C₆ interstitial compounds,Cr₇C₃,Cr B and Fe Ni₃ phases.After adding different contents of WC,the phases of the surfacing layer have little change,only new WC and W₂C phases are formed.With the increase of WC addition,the microstructure of the surfacing layer began to refine,the eutectic microstructure in the middle layer changed from lamellar to massive,and the eutectic microstructure in the upper layer changed from lamellar to rod-like.(3)The addition of WC significantly improves the average hardness of the surfacing layer.With the increase of WC,the hardness of the surfacing layer increases.When the addition of WC is 40wt.%,the maximum microhardness reaches 814.8HV_0.5,but the microhardness of the surfacing layer fluctuates greatly,which may be caused by the uneven distribution of WC.The pin-disc wear test can confirm that at room temperature,200°C,400°C,with the increase of WC content,surfacing wear resistance is improved.There is no significant difference in wear between the addition of 30wt.%WC and 40wt.%WC.However,when the addition of 40wt.%WC,the friction coefficient of the surfacing layer fluctuates greatly,indicating that the hard phase distribution is not uniform in the surfacing layer of Ni60+40wt.%WC.(4)By adding 0.4wt.%,0.8wt.%,1.2wt.%and 1.6wt.%Y₂O₃ to the surfacing layer of30wt.%WC-Ni-base alloy,the results show that the forming quality of the surfacing layer is improved with the increase of the addition amount of rare earth,but when the addition amount of Y₂O₃ is more than 1.2wt.%,The forming quality of the surfacing layer begins to decline.With the addition of Y₂O₃ with different content,the phase of the surfacing layer has little change,and the main phases are?-Ni(Fe),Fe Ni₃ solid solution,unmelted WC and W₂C produced by decomposition,as well as carbides such as M₂₃C₆,M₆C and Cr₇C₃.Rare earth Y₂O₃ has a great influence on the microstructure of the surfacing layer.When the rare earth content is 1.2wt%,the lamellar eutectic carbide microstructure in the middle of the surfacing layer begins to increase,and the microstructure becomes compact,and the microstructure of the upper surfacing layer appears obvious refinement phenomenon.(5)The addition of Y₂O₃ can significantly increase the average microhardness of the surfacing layer.When the amount of Y₂O₃ is 1.2wt.%,the average Vickers hardness of the surfacing layer reaches the maximum,970HV_0.5.At the same time,the wear resistance of the surfacing layer can be improved by adding appropriate amount of Y₂O₃ at room temperature,200°C and 400°C.When the amount of Y₂O₃ is 1.2wt.%,the surfacing layer has the best wear resistance and the minimum average friction coefficient,and the wear amount is 2.6mg,2.3mg and 2.8mg,respectively.