Effect Of CeO₂ On Microstructure And Properties Of Fe-based Composite Coatings On Die By Laser Cladding

Aiming at the wear,fracture and other failure forms of H13 hot-working die steel,the surface modification of H13 by laser cladding technology was carried out with iron-based composite powder with Ce O₂.The optimum process parameters are obtained by means of a combination of numerical simulation of the temperature field and theoretical calculations,and the cladding sample was prepared on the H13 substrate.To investigate the effect of Ce O₂content on the microstructure,phase composition,crack morphology and residual stress of the coatings.According to the working conditions of the hot work mold,the effect of Ce O₂on the hardness,high temperature wear resistance,high temperature oxidation resistance and impact toughness of the coatings was investigated.The research is important for improving the performance of hot work moulds based on H13 steel at low cost,extending the service life of moulds and expanding the application of laser cladding technology in the field of moulds.H13 hot work die steel and Fe901 iron-based powder is taken as the research objects,with the help of ANSYS Workbench finite element simulation software,the Gauss heat source model is used to numerically simulate the temperature field of the laser cladding process to explore the influence of process parameters on the temperature of the molten pool.The accuracy of the numerical simulation and the determination method is verified by introducing theoretical calculations.Taking into account the maximum temperature,the melting point of the substrate and the cladding material,and the size of the melt pool,a suitable range of process parameters was determined.The optimum process parameters were determined through experimental verification,which laid the foundation for subsequent chapters of experimental research.Based on the process parameters determined by numerical simulation,WC-reinforced Fe-based composite coatings with different Ce O₂contents were prepared on H13 substrates by laser cladding with process parameters obtained from numerical simulations.The methods of microstructure observation and property testing of cladding layers and their characterization were discussed.The analysis and determination of cladding materials and processes,the preparation of microstructure and property testing specimens were prepared.The equipment and methods of observing the microstructure,phase composition and crack morphology of cladding layers based on scanning electron microscope(SEM)and ray diffractometer are determined.The microstructure in the clad layer was observed by SEM,and the influence of Ce O₂was investigated and the mechanism of action was analysed.The physical phase analysis was carried out by X-ray diffractometer to obtain the composition of the clad layer.The influence of Ce O₂on the hardness distribution along the depth direction was studied by microhardness tester.The influence of Ce O₂on the crack shape and residual stress distribution of the clad layer was analysed with colour imaging technique and X-ray residual stress tester.The results showed that the addition of Ce O₂did not have a significant effect on the phase composition of the coatings.The microhardness of the coatings with Ce O₂was 4-5 times that of the H13substrate,and the hardness fluctuation was significantly reduced.With the addition of Ce O₂,the number of cracks decreased significantly,and the types of cracks changed from reticulocytes to transversal.The distribution of residual compressive stress on the surface of the coatings was basically consistent with the distribution of cracks.Combined with the working conditions of hot work die steel,high temperature wear tests and high temperature oxidation tests were conducted on the substrate and the coatings,while the morphology and hardness after oxidation were observed and analyzed to study the influence of Ce O₂on the high temperature oxidation resistance and red hardness of the coatings.On the basis of the hardness and wear resistance of the coatings meeting the performance requirements of the hot work die steel,the substrate and clad layer with the best wear resistance were selected for impact toughness testing.It is demonstrated that the friction coefficient,section profile of wear track and wear weight loss of the coatings were significantly reduced compared to the substrate,owe to the addition of Ce O₂refining the coatings structure,promoting the refinement and uniform distribution of WC particles,thus reducing the micro-cutting effect on the grinding balls on the coatings.Although the hardness of the coatings were reduced after oxidation,they were still 3-4 times the hardness of the H13substrate.Due to the fine grain strengthening effect of Ce O₂,while the hardness and wear resistance of the cladding layer were improved,the impact toughness was also maintained at a higher level.