Process Research And Numerical Simulation Of Niobium Alloy EB Cladding With Silicide Coating

The silicide coating was prepared by fused slurry method on Nb-based alloyNb-10W. This sintered silicide coating have disadvantages such as pores, cracks anduneven top surface. The defects of coatings had bad influence on the hightemperature oxidation resistance of silicide coatings. It is considered that theelectron beam cladding process is one of the most convenient processes to reducethe disadvantages of sintered coating and improve its oxidation resistance. Theeffect of high frequency electron beam irradiation on surface remelting andmicrostructural modification in silicide coatings wer investigated in this study. Themicrostructure, phase modification and high temperature oxidation resistance wereexamined. Scanning Electron Microscopy and X-Ray Diffraction were performed tocharacterize the phase modification and morphology of sintered coating, claddingcoating and oxidating coating. The formation of sintered coating and the oxidationresistance performance of cladding coating were studied.The results showed that the sintered coating was formed by diffusion reaction.The sintered coating was multistructure including NbSi₂body layer and Nb₅Si₃diffusion layer. After EB surface treatment, EB cladding silicide coating was formed.A modified layer called remelted layer was observed at the cladding coating surfaceand diffusion layer thickness increase. The remelted layer was comprised of columnNbSi₂phase. Compared with sintered coating, cladding coating had refined surfacegrains, reduced average surface roughness was reduced and less coating defect.Therefore, high-temperature oxidation resistance of cladding silicide coatingimproved. The EB cladding coating can offer protection for about10h underisothermal oxidation at1800℃in air.Temperature field induced by EB cladding had influence on the histologyformation of cladding coating. In this paper, based on comprehensive considerationof the interaction between electron beam and coating, the characteristic of the EBscanning figure and shape of heat source, a ring shaped heat source model withGaussian distribution was established. Taking ANSYS finite element analysissoftware as a tool, the temperature field of EB cladding silicide coating process wasinvestigated.The calculated results showed the characteristic of tempeterature field. EBcladding process had an ultrahigh heating/cooling rate in the order of103-104℃/sand an even temperature distribution at the melted region. Calculated results of numerical simulation were consistent with the experiment results, which verified theestablished temperature field model. The effects of processing parameters includingbeam current, scanning speed and beam diameter on cladding heat input andtemperature field were forecasted by means of simulation. The relationship modelbetween cladding heat input and coating penetration depth was established byapplying temperature field simulation method, which could control and forecastcoating penetration depth effectively. In addition, calculated results of numericalsimulation could reveal the formation process of the remelted layer and nanometerpores band.