Study On The Technology And Properties Of Nickel Base Tungsten Carbide Composite Coating By Plasma Cladding

Under complex operating conditions,soil-engaging component such as skim coulter are subject to frequent friction and impact from sand,gravel and straw in the soil,which can easily cause serious wear and failure.In order to enhance the wear resistance of skim coulter and prolong its service life,this paper prepares coating with tungsten carbide reinforced nickel-based composite powder as the melt coating material in 65 Mn spring steel commonly used as the substrate of skim coulter,and analyzes and studies its organization and abrasive wear performance,mainly as follows.Plasma melting technology was used to melt Ni60WC35 coating on 65 Mn spring steel,and single-factor test was used to optimize the process parameters of melting current and heat treatment method in coating preparation,and it was determined that melting current of160A and 400°C preheating+400°C holding time for 2h after melting were the best conditions.The melting current test showed that with the increase of melting current,the average hardness of the coating tended to increase first and then decrease,and the average hardness reached the peak at 160A.The heat treatment test showed that the melting and decomposition of WC particles were more intense and the coating was thicker as the preheating temperature increased.The influence of the melting speed,longitudinal displacement and powder feeding amount on the plasma coating performance was investigated by using the orthogonal test system with the wear amount and average hardness as the evaluation indexes.The microstructure,composition and phase structure of the coating were analyzed by SEM,XRD diffractometer and EDS spectrometer,and the microhardness and wear of the coating were tested and analyzed by Vickers hardness tester and wet sand rubber wheel abrasive wear tester.The results show that the Ni60WC35 coating is well bonded with the substrate interface,the WC particles are basically distributed in the lower layer of the coating and the particle size is mainly concentrated in 60-120μm,mainly composed of WC and W₂C particles,Cr₂₃C₆,Cr₇C₃,Fe₃W₃C dendrites andγ-（Fe,Ni）solid solution;the average Vickers hardness of Ni60WC35 coating is 845.4HV_0.5is significantly higher than that of 65Mn spring steel 304.5HV_0.5;compared with 65Mn spring steel 2.1069g total wear,the wear of Ni60WC35 coating is 0.7946g,a reduction of about 62.2%;the wear of tungsten carbide reinforced nickel-based composite coating is mainly divided into three stages:the first stage is dominated by adhesive wear,the second stage is dominated by two-body abrasive wear,and The main wear mechanism in the third stage is three-body abrasive wear.The Ni60WC50 and Ni60WC60 coatings were prepared using the optimized process parameters,and the influence of WC content on the coating properties was analyzed.The spatial distribution and mass fraction of each phase in tungsten carbide reinforced nickel-based composite coating with different tungsten carbide contents appear very different.Compared with Ni60WC35,the WC in Ni60WC50 and Ni60WC60 coatings are almost distributed throughout the coating,and the area of hard phase peaks such as W₂C and Fe₃W₃C increases and the area ofγ-（Fe,Ni）matrix phase peaks decreases;the microhardness test results show that Ni60WC50(941.2HV_0.5)>Ni60WC60(922.8HV_0.5)>Ni60WC35(845.4HV_0.5).The results of the abrasive wear test showed that the wear performance was optimal when the tungsten carbide content was 50%,and the wear amount of Ni60WC50coating was 0.6355g,which was smaller than that of Ni60WC60（0.7216g）and Ni60WC35（0.7946g）.The hardness and wear properties of the coating were enhanced,and the hardness and wear properties reached the peak when the tungsten carbide content was 50%,but when the tungsten carbide content was too large,the hardness and wear resistance of the coating decreased.In order to further improve the coating performance,Ni60WC50 coating was selected as the research object,and the average hardness and abrasive wear of the coating were used as evaluation indexes,and the optimal combination of parameters for the Ni60WC50 coating melting process was determined by orthogonal experiments as follows:melting current 170A,melting speed 65 mm/s,and longitudinal displacement 1.00 mm.The optimized plasma melting process parameters were used to prepare wear-resistant coatings on the wear-prone parts of the skim coulter.Through microhardness and abrasive wear tests on the coating,the average cross-sectional hardness of the skim coulter coating was 892.5HV_0.5and the wear amount was 0.3056g,which was much stronger than that of the original 65Mn spring steel skim coulter of 299.6HV_0.5and 1.9998g.The feasibility of melt coating tungsten carbide reinforced nickel-based composite coating on skim coulter was verified.