| Corrosion and wear are common failures of metal materials.As one of the new technologies of surface repairing and strengthening,plasma spray welding has a wide application prospect.However,the problems such as poor binding of layer and substrate,cracking and holes are the key to promote this technology.In this paper,Ni60A powder,Ni60A+Ni Cr-Cr3C2 and Ni60A+Ti-Fe composite powder was prepared to Ni-base composite coating by PTA-400E-ST plasma spray welding equipment on the surface of 45 steel respectively.Micro-structure and structure characteristics of the different layers were investigated by OA,XRD,SEM and EDS;the mechanical properties,corrosion resistance were studied by micro-hardness analysis and abrasive wear test and electrochemical corrosion test.The results showed that:In the preparation of Ni-based spray welded layer on the surface of 45 steel,welding current and welding speed on the spray welding layer of Ni-based have a great effect on the quality,adjusting the process parameters can obtain no cracks,porosity,and with a good sex of Ni-based spraying welding layer.When NiCr-Cr3C2 is added to Ni60A powder,the powder's fluidity become poor,increasing welding current,adjusting welding speed and increasing powder delivery gas can effectively reduce the adverse effect of NiCr-Cr3C2 on molding performance.When Ti-Fe powder is added to Ni60A,the powder fluidity becomes poor and Ti easy to oxidation,on the basis of Ni-based spray welded layer parameters,increasing welding current,improving the protection of gas can obtain better formability,and strong bonding force generated in situ TiC reinforced nickel-based composite spray welding layers.The Ni-based spray welding coating is mainly composed of columnar and dendritic crystal,which have a small amount?Cr,Fe?23C6 and?Cr,Fe?7C3,which are typical ductile phase matrix and hard phase.Carbide hard phase of the spray welding layer increases after adding NiCr-Cr3C2,At the same time a few sharp and diamond Cr3C2 appeared,solid solution strengthening and grain refining.In the process of spray welding,Cr3C2 is first dissolved to form solid solution.With the increase of content,solid solution is saturated,Cr3C2 exists in the matrix as independent enhancement phase,When the content reaches 15%,the particle enhancement of Cr3C2 reaches the maximum,besides that a lot of sharp edge and corner are intertwined.These phases can further improve the toughness and hardness of matrix.Adding4%Ti-Fe alloy powder In Ni60A powder,TiC and TiB2 are generated.The reason is that the compound reaction between Ti and C?B to form TiC and TiB2 which dispersed in the matrix and precipitation during cooling.The micro-hardness results showed that the average micro-hardness of Ni-based spray welding coatingis 605HV0.2.After adding NiCr-Cr3C2,when the content from 5%to 15%,the micro-hardness of spray welding layer increase with increasing content,15%NiCr-Cr3C2micro-hardness reach a maximum value of 920HV0.2.2 and the average hardness is 857 HV0.2,which is related to Cr3C2 grain refining and particle enhancement effect significantly.TiC can be generated in situ by adding 2%-4%Ti-Fe alloy powder.In the cooling process,TiC precipitates out and the Ni-based spray welding layer is strengthened.The micro-hardness of the coating promotes with the increase of Ti-Fe alloy,and the micro-hardness of 4%spray welding coating is up to 904HV0.2,with the average micro-hardness of 865HV0.2.The wear test results show that the wear loss rate of Ni-based spray welding layer is1.24%.As the amount of NiCr-Cr3C2 added in the coating,the weight loss of the sample decreased to 5%first and then increased.The wear resistance is the best at 15%NiCr-Cr3C2added,the wear loss percentage decrease to 0.95%,which is about 23%higher than that of the Ni-based spray welding coating.For Ti C enhanced Ni-based coating,the abrasion resistance increased with the increase of Ti content,which is compared with the pure Ni-based coating.After adding 4%Ti-Fe alloy power,the furrow of the spray welding layer can hardly be seen on the surface,with only a few scratches and peeling pits,the wear weightlessness rate from1.24%to 0.95%,the wear resistance increases about 35%.In compare to the above coating,it is more effective to improve the abrasion resistance of the material by using in situ formation of TiC enhancement Ni-based coating.The electrochemical corrosion in 0.5mol/L hydrochloric acid medium results showed that,the addition of NiCr-Cr3C2 and Ti-Fe can significantly improve the corrosion resistance of the Ni-based spray welding layer,and the order of corrosion resistance is Ti-Fe>Ni Cr-Cr3C2>Ni60A.The self-corrosion potential of the Ni-based spray welding coating is-0.2506V,and the self-corrosion current is 1.133×10-6mA.After adding Ni Cr-Cr3C2,spray welding layers corrosion resistance increasing with the content of 10%-20%NiCr-Cr3C2,The 10%and 15%self-erosion currents are 1.724×10-7mA and 2.509×10-7mA respectively.Corrosion resistance is the best when 10%NiCr-Cr3C2 is added.After adding 2%-4%Ti-Fe alloy powder,the spray welding coating corrosion resistance increases with the Ti-Fe content,and the self-corrosion current of 4%Ti-Fe content is 3.044×10-7mA,the corrosion current is decreasing and the corrosion resistance is the best.Furthermore,the TiC enhanced Ni-based spray welding layer has better economical and usable than Cr3C2 reinforced Ni-based spray welding coating in the environment of acid abrasion and corrosion.In conclusion,The corrosion resistance of the materials can be significantly improved by using Cr3C2 and in-situ TiC enhancement the Ni-based alloy spray welding coating.However,with the cheap and available raw materials of titanium ferroalloy,the suitable spray welding process can be used to obtain composite coating with better performance of wear resistance and corrosion resistance.The results of this study have a great guiding effect on the development and remanufacturing of abrasion materials in petrochemical and mineral processing industries. |
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