Wear And Corrosion Properities Of Ni-based Alloy Coating With Spherical Chromium Carbides

In this paper,the composite coating of Ni-base alloy with different contents of chromium carbides was produced on AISI4145 steel by plasma transfer arc welding?PTAW?process.The microstructure of composite coatings was examined by XRD,SEM and EDS.The wear and corrosion properities of coatings were studied.The corrosion properities were exaimed in three different environments.The results show as followings:The Ni-based chromium carbides coatings had a good bonding with AISI 4145H substrate.The main consistance of Ni-based alloy composite coatings with spherical chromium carbides was?-Ni,?-?Ni,Fe?,Cr₃C_2,Cr₇C₃ and a small amount of M₂₃?C,B?₆,?M=Fe,Cr,Ni?.The chromium carbides can easily decarburize to formed the Cr₇C₃ and M₂₃?C,B?₆ during the welding process.When content of chromium carbide reaches to 50 wt.%,more carbides are formed in the structure,and the microstructure is greatly refined compared with 40 wt.%.The hardness of coatings was significantly improved,with the increase of the content of chromium carbide.While stable friction coefficient gradually decreases.When the content of chromium carbides reached to 50 wt.%,the friction coefficient is smallest.From worn scars of3D non-contact maps and the depth map of the cross-section,the amount of wear loss obviously decreased with the increased chromium carbides.The wear mechanism of surfacing layer changes significantly with increased chromium carbides.Adhesive wear occured in the Ni surfacing layer.While adhesive wear and abrasive wear occurred in the Ni-10Cr₃C₂,Ni-20Cr₃C₂ coating and the adhesive wear act as the main wear mechanism.When reach to Ni-50Cr₃C₂,the main wear mechanism changed into abrasive wear.The shedding phases participated in the process of friction and severed as a three-body in the coating surface.The Ni-50Cr₃C₂ coating showed the best wear resistance among all coatings.The self-corrosion current density of Ni-based chromium carbide coating in 3.5%NaCl solution gradually decreased with increased content of chromium carbides.A typical passivation phenomenon appeared in polarization curves.The arc radius of capacitive reactance gradually increased,and corrosion resistance of the coating was improved.Passivation formed in 0.5 mol/L H₂SO₄ solution,and an approximately linear region appeared in the low-frequency capacitive arc.With the increased content of chromium carbide,the self-corrosion current density decreased.The coatings suffered seriously dissolved in 0.5 mol/L HCl,and the micro-cell caused some pits.The larger crack,even forming channels,causing more serious damage to inner coating.The coating was suffered severely dissolution in 0.5 mol/L HCl.Some oxides in corrosion products can protect the inner metal be corred.Among all Ni-based coatings with chromium carbieds,Ni-50Cr₃C₂ coating had lower self-corrosion current density in the three solutions,which showed Ni-50Cr₃C₂ coating had the best corrosion resistance.