Laser Cladding Of Silicide-based Anti-oxidation Composite Coating On The Carbon Substrate

Being sensitive to oxygen constrained the development of the carbon materials in high temperature field.Silicon based coating exhibited excellent anti-oxidation protection ability at 1500?.However,there were still many shortcomings,such as long-period or weak bonding strength,in preparation technology for the anti-oxidation coating.The development of the laser cladding technology provided a new idea for the efficient preparation of silicon-based anti-oxidation coating on surface of carbon materials.In this paper,a series of Zr B₂-Si-SiC-MoSi₂ coating was fabricated by laser cladding.Based on the ANSYS simulation,the distribution of temperature and stress field associated with laser cladding process was used to guide and optimize the laser cladding parameters.The property of laser ablation resistance was evaluated by laser surface ablation.During process of the laser cladding and laser ablation,the phase transition,structure reconstitution and the variation of coating bonding strength were systematically studied by the means of weight loss,XRD,SEM and scratching failure load instrument.The mechanism of the evolution of coating morphology during laser cladding and the laser ablation resistance of the silicon based coatings were analyzed and discussed.After laser cladding,the lowest weight loss ratio of Si-MoSi₂,Si-SiC-MoSi₂,and Zr B₂-Si-SiC-MoSi₂ coating is 0.0336%,0.1480%and 0.2034%,respectively,which was influenced by the oxidable SiC and volatilizable B₂O₃ showing a gradually increasing tendency.Compared with the scratching failure load of Si-MoSi₂ coating,that of the Si-SiC-MoSi₂ coating increased by 3.6 N,2.17 N,2.2 N and 0.28 N,respectively.The coating surface flatness can be improved and the defects such as holes and cracks can be reduced with the addition of SiC phase.The internal structure was transformed from the MoSi₂-Si eutectic structure,the fine crystal zone and the interfacial Si-C reaction layer into the MoSi₂-Si eutectic,Si-SiC-MoSi₂ mixed structure and the interfacial Si-SiC diffusion reaction layer.The H12 coating was modified by adding 40wt.%Zr B₂.The internal structure of the modified coating was composed of non-oriented fine needle-like dendrites mixed with irregular particles,and the coating scratch adhesion was increased by 17.8%.Laser ablation,accompanied by oxidation and volatilization,is a process of layered oxidation and peeling.After laser ablation,the surface of Si-MoSi₂ coating formed agminated convex and a large number of pores.Meawhile,the internal eutectic structure was changed into the surface layer with large grain zone and interfacial Si-C reaction layer.The decrease of Si-MoSi₂coating scratching failure load was about 73.3%-77.7%after laser ablation.The spreading ability and thermal shock resistance of the Si-SiC-MoSi₂ coating were improved by adding SiC phase.There was no agminated convex and penetrating cracks can be observed on the surface after laser ablation.The internal eutectic structure and mixed growth morphology were transformed into Mo₅Si₃ phase with large size,and interfacial SiC-Si diffusion reaction layer.Compared with Si-MoSi₂ coating,the scratching failure load of Si-SiC-MoSi₂ coating increased by 7.57,4.15,2.43 and 0.46 times,respectively.The surface of H12?Si:SiC:MoSi₂=16.7:16.7:66.6wt.%?coating after 5times laser ablation is more flat and no severe oxidation peeling than that after laser cladding.Therefore,the scratching failure load of H12 coating increased by 57.6%compared with that after laser cladding.On the surface of coating modified with Zr B₂,Zr-Mo-Si-O melting ice structure and dense Zr O₂ protective layer can be observed.The scratching failure load of twoSi-SiC-MoSi₂coating modified with 40wt.%Zr B₂increased by 16.5%and 59.6%after laster ablation,respectively,compared with that of Si-SiC-MoSi₂ coating.