Preparation And Properties Of Wc Reinforced Nickel-based Coatings By Plasma Transferred Arc Welding/Melt Injection

In mineral processing,petroleum exploration and other industries,machinery that have been in abrasion environments for a long time will reduce the service life and production efficiency of the equipment.Generally,a metal-based protective layer with high wear resistance is deposited on the surface of the component to improve the wear resistance.Nickel-based Tungsten carbide（WC）composite coating has many advantages such as high hardness,good abrasion resistance,good corrosion resistance,etc.,and is suitable for surface strengthening modification of a variety of wear components.plasma transfer arc welding（PTA）is often used to prepare such composite coatings,but during the welding process,the WC particles have some problems such as burnout and transitional thermal decomposition,and high-brittleness secondary carbides are formed in the coating.This phase is prone to rupture during the wear process,reducing the wear resistance of the coating.In addition,during the cladding process,WC is prone to settling in the molten pool,which weakens the strengthening of WC on the top of the coating,but during the wear process,it is precisely the top of the coating that exerts wear resistance.Therefore,starting from the technology and materials,controlling the thermal decomposition and distribution of WC in the coating is of great significance to improve the overall performance of the nickel-based WC composite coating.In this study,based on the PTA,the plasma melt injection was lead to prevent WC from sinking to the bottom and achieve continuous distribution in the coating.In addition,the WC was clad with nickel to further reduce the thermal decomposition of WC in the molten pool,aims to prepare WC reinforced nickel-based composite coatings with excellent properties.In this paper,the original WC was nickel-coated by electroplating.Through comparison and analysis of experimental results,economical and efficient plating solution formulas and technology parameters were obtained.The plating rate reached5.91%,the solution stability was good,and single solution could maintain high efficiency for 4 h.The experiment used Ni-coated WC（Ni/WC）powders after plating for 2 hours.The nickel layer was dense and uniform with a thickness of 10μm.During the plating process,nickel atoms crystallized and grew depending on the“growth points”,and a dispersed nickel crystal grain was formed on the surface of the WC particles.The continuous nickel atoms crystallized and adhered to the previous nickel grains.Many grains grew and diffused together to form a compact nickel layer and completely clad the core WC.In this study,Nickel-based coatings were prepared by Plasma Transferred Arc Welding/Melt Injection,WC and Ni/WC were used for the reinforcement phase.By optimizing the technology parameters,there are more WC in the upper part of the coatings and the distribution of WC is continuous and dispersive.Both coatings have relatively uniform microstructures,mainly composed ofγ-Ni,Cr₂₃C₆,Cr B,WC,W₂C,and M₇C₃ compounds.A large number of dispersive and uniformly hard phases in the coatings hindered the growth of nickel crystal grains,which plays a significant role in strengthening integral coatings.The pre-plated nickel layer can prevent WC from oxidation and thermal decomposition during the welding process,and can also enhance the wettability with nickel-based alloys.The hardness of WC reinforced nickel-based coating was 1006.27±40.25 HV₁,the fracture toughness was 1.61,and the coefficient friction was 0.21;the hardness of Ni/WC reinforced nickel-based coating was 905.77±36.23 HV₁,the fracture toughness was 3.13,and the coefficient friction was 0.26.The wear mechanism of both was slight adhesive wear,but the latter showed better wear resistance due to the finer brittle secondary carbides in the coating.The pre-plated nickel layer improved the toughness and wear resistance of the WC reinforced nickel-based coating,and the wear mass was only 1/30 of the Q235 steel.