Microstructure And Properties Of Rare Earth Modified Ni-based Composite Cladding Layer

Both metallic and ceramic materials have their own unique properties and significant weaknesses of performance.The combination of the excellent properties of metallic and ceramic materials has been investigated in the field of materials science for many years.Metal-ceramic composite coatings incorporate the high hardness and wear resistance of ceramic particles as well as the excellent plastic toughness of metal alloy materials,which has become an important component of research on modern surface technology.In this paper,Ni Cr BSi,a nickel-based alloy with outstanding wear resistance,corrosion resistance and high temperature oxidation resistance,was selected as the bonding phase.In addition,WC,one hard particle with high hardness and wear resistance,was integrated into the composition.Simultaneously,the rare earth oxide CeO₂was incorporated into the metal-ceramic composite coating as a special modified material.WC/Ni-based composite coatings with rare earth oxide CeO₂modification were formed on the surface of 45#steel by vacuum cladding technology.On this account,metal-ceramic composite coating with superb wear resistance and superior corrosion resistance was obtained.Considering the phase composition,organization and morphological characteristic,tribological property and corrosion resistance,the modification effect and influence mechanism of the CeO₂addition with different content on the composite coatings were characterized and analyzed.The results have demonstrated that:The phase composition,microstructure morphological characteristics,types and contents of constituent elements in microregion were examined by X-ray diffraction,scanning electron microscopy,and energy dispersive spectroscopy.The transition area between the cladding coating and the substrate was divided into diffusion layer,diffusion fusion layer and metallurgical fusion layer,in which to better formation of interface bonding.The reticular structure with special morphology has been exhibited in the various phases of the composite coating,which is divided into"mesh"areas and"mesh line"areas.Among them,the mesh area has been mainly occupied by theγ-（Ni,Fe）matrix phase,while a large amount of chromium-carbon compounds,Ni B phase and Fe Ni₃eutectic structure were formed by adsorption on theγ-（Ni,Fe）grain boundaries.The"mesh"area has formed the"skeleton"through the distribution of reinforcement particles,which mainly consist of WC,W₂C,Ni₃Si and（W,Cr,Fe）C multiphase compounds.Basically,there is no more considerable change in the composition of the coating phase after the addition of CeO₂.Nevertheless,it is obvious that the composite coating structure has significantly occurred grain refinement,resulting in the densification and uniformity.The corrosion potential and the corrosion current density of each coating were analyzed by electrochemical tests.Consequently,the corrosion resistance of the CeO₂-modified coatings have also been improved to some extent.With the increase of CeO₂content,the corrosion potential value of the CeO₂-WC/Ni-based composite coating became increased and then decreased.On the contrary,the corrosion current density became decreased and then increased.The coating with CeO₂content of 1.5 wt.%has showed the more positive corrosion potential value and the lowest corrosion current density,which displays the optimum corrosion resistance.The corrosion potential has been increased by 25.1%compared to the unmodified coating,and the corrosion current density has been decreased by62.2%compared to the unmodified coating.The microhardness and tribological behavior of each coating were investigated by microhardness tester and tribological wear test respectively.The relationship between the hardness value and the wear rate of the coating surface was analyzed based on the experimental data.The CeO₂-WC/Ni-based composite coating with 1.5 wt.%CeO₂addition has showed the highest hardness value of surface and the lowest coefficient of friction,as well as the lowest wear rate.The wear rate is 32.3%lower than that of the unmodified coating.According to correlation analysis,which indicated that the tribological mechanism of CeO₂modification could be attribute to the reinforcing action from microstructure refinement,which in turn leads to more advanced wear resistance.