The Effect Of Rare Earth Oxide CeO₂ On Microstructure And Properties Of Laser Cladded Co-based Alloy On H13 Steel

Rare earth has been widely used in metallurgy and other fields because of its ability to significantly improve metal structure and properties.The purpose of this paper is to investigate the effect of rare earth elements on the microstructure and properties of laser cladded cobalt-based alloys.In this paper,the process optimization study was first carried out,and then a cobalt-based cladding powder system with different Ce contents was designed.Finally,the powders with different Ce contents were clad on the surface of H13 steel with optimum process parameters.This paper has studied the effects of Ce content on the microstructure,element distribution,phase composition and hardness of the cladded layer,and then analyzed the crack sensitivity of the cladded layer.Finally,the effect of different content of Ce on the corrosion resistance and abrasion resistance of the laser cladded layer in practical working environment were revealed.The article identified 0-4% as a reasonable range for CeO₂.Nanohardness,open circuit potential and friction coefficient were used as the evaluation criteria.Using SPSS software to process data,the optimal technological parameters of the laser device are obtained: current 380 A,pulse width 8ms,frequency 4Hz.And then cladded layers with different Ce content were obtained with these parameters.The study found that the proper amount of Ce refined the microstructure.However,too much Ce would be dissolved into the metal compound as a compound,and the structure would become coarse again.When the Ce content was 2%,the microstructure would be the most refined.The addition of Ce affected the distribution of metallic elements Ni,Cr,Si,Co and Fe.The proper amount of Ce enhanced the fluidity of the bath,while the excessive Ce made the diffusion difficult.Phase analysis revealed that the addition of Ce did not change the phase composition of the coatings.The fine grain strengthening and solid solution strengthening of appropriate addition of Ce made the hardness of the coatings significantly improved.When the addition amount of Ce element was 2%,the hardness of the claded layers were increased by nearly 100 HV0.2,compared with the claded layers without Ce.The addition of a suitable amount of Ce element effectively reduced the cracks and improved the coatings' molding morphology.Through the analysis of the temperature field,the order of magnitudes of the maximum cooling rate in the laser cladding rapid cooling process was 103 K/s.This cooling rate was very easy to produce cracks.Thetransient stress field analysis and the residual stress values calculated by the Xu formula based on the nanoindentation technique both indicated that the stress value at the top of the coating and the fusion line were the largest.The larger the stress value was,the more likely the cracks were generated.In order to have practical value,the influence of Ce on the main performance of the cladding layer was studied by electrochemical workstation and friction and wear equipment.Open circuit voltage,impedance spectroscopy,and polarization curves compare corrosion resistance thermodynamically and kinetically.It was found that the corrosion resistance was 2%>1%>3%>0%>4% in 2N H2SO4 and 5% Na Cl solutions.The time,frequency and wavelet analysis of the electrochemical noise determined that the corrosion process of the coating in the sulfuric acid solution was divided into three stages: the first stage is uniform corrosion,the second stage is metastable pitting and the third stage is pitting corrosion.The paper proposes that the Ce element is mainly responsible for the first and second stages of corrosion.Both the friction coefficient and wear loss showed that the wear resistance of the cladding increased first and then decreased with the increase of Ce.When the Ce content was 2%,the wear resistance of the cladded layer was the best.When the Ce content was 1%,2% and 3%,the wear of the cladded layers were abrasive wear.And when the Ce content was 0% and 4%,the cladded layer were abrasive wear and oxidation wear.