Preparation Of Silicide Coating By Laser Irradiation And High Temperature Preformance

As a lightweight structural material with good high temperature mechanical properties,graphite materials have a wide range of applications in the fields of metallurgical industry,aerospace and other service environments.However,graphite materials are oxidized in an aerobic environment above 400°C,which greatly limits their practical application,and coating technology is an effective way to improve their oxidation resistance.The excellent high temperature oxidation resistance and ablation resistance of SiO₂ coating and SiC coating make it the choice for preventing oxidation of graphite materials.Traditional methods for preparing coatings mainly include slurry method,sol-gel method,vapor deposition method,embedding method,thermal spraying method and the like.Although these methods can prepare nano-coating materials with high specific surface area and good dispersibility,the existence of long manufacturing cycle,difficult preparation temperature control,accompanying additional product formation,pollution of the environment and other shortcomings limit their large-scale commercial production and the application.As a clean and pollution-free heat source,laser has an ultra-fast heating effect on the material and a transient unbalanced energy output mechanism,which provides good conditions for the synthesis of nano-coating materials.In this paper,a sol-gel composite laser irradiation method is adopted,using a homogeneous mixture of tetraethyl orthosilicate,oxalic acid,deionized water and absolute ethanol as a precursor,and IPG 500 with galvanometer scanning system is used under the protection of Ar gas.The fiber laser is irradiated to obtain an SiO₂coating for improving the high temperature oxidation resistance of the graphite material.The experimental results show that when the laser power is 260 W,the scanning speed is 15 mm/s,and the laser energy density is 14.4 kJ/cm²,the prepared SiO₂ coating has the strongest oxidation resistance.The nano-particles of the SiO₂coating are uniformly and densely distributed,and the oxygen molecules are not easily infiltrated to oxidize the graphite substrate.At 750°C,the high-temperature oxidation resistance of the SiO₂-coated graphite substrate was improved by 13%compared with the graphite substrate without the SiO₂ coating.In addition,coatings of different thicknesses have different effects on improving the high-temperature oxidation resistance of the graphite substrate.When the thickness of the SiO₂ coating is 0.5 mm,the weight loss rate is 5.8%;and when the thickness of the SiO₂ coating is1.0 mm,the weight loss rate is 5%,this is because the 1.0 mm thick coating provides a denser environment;when the thickness of the SiO₂ coating is 1.5 mm,the weight loss rate is increased to 7%.The reason is that when the coating is thick,the internal and external shrinkage is inconsistent,resulting in unbalanced tensile and compressive stress,and cracks are likely to occur at high temperatures,providing oxygen for the erosion of the substrate.In addition,it is found that when the laser energy density is too high,a small amount of additional product SiC is generated.In order to study the effect of SiC on the high temperature oxidation resistance of graphite materials,the micro-SiC powder was preliminarily mounted on the graphite substrate by powder coating.The nano-SiC coating was prepared by laser irradiation and optimized by experiments.The optimum process parameters for the preparation of SiC coatings.The experimental results show that the high temperature oxidation resistance of the prepared SiC coating is the strongest when the laser power is 260 W,the scanning speed is 20 mm/s,the laser energy density is 10.83 kJ/cm².This is because the SiC coating prepared at this time is evenly distributed and dense,which has contributed to the infiltration of oxygen.By comparing and analyzing the oxidation resistance of the obtained SiO₂coating and SiC coating,it can be found that when the temperature is higher than750°C,in practical applications,the SiO₂ coating can reduce the weight loss rate of the graphite substrate by about 10%.It can improve the high temperature oxidation resistance of the graphite substrate.When the temperature is lower than 750°C and higher than 675°C,the SiC coating can reduce the weight loss rate of the graphite substrate by about 6%,and improve the high temperature oxidation resistance of the graphite substrate.When the temperature is lower than 675°C,the effect of improving the oxidation resistance of the graphite substrate is basically the same.In this paper,the optimal process parameters for the preparation of anti-oxidation coatings for graphite materials are obtained by combining theory with experiments.The mechanism of laser preparation of nano-coating materials and the effects of laser energy density on the microstructure,phase and crystal structure of the samples were investigated.Compared with the traditional method of preparing coating,the method of laser preparation of nano-coating material has the advantages of short production cycle,uniform distribution of nanoparticles,high controllability of growth and green pollution in production process.