Mo-MoSi_2 gradient coating on Mo substrate was prepared by siliconizing process,using the polysilicon as silicon atoms.The gradient layer was analyzed by the experimental results,theoretical analysis,and thermodynamic calculation.The silicon,molybdenum content of gradient coating shows a gradual change regulation.The reaction between silicon and molybdenum is most likely to generate Mo_5Si_3,then MoSi_2,finally Mo_3Si,but when the silicon content is excessive,the Mo_5Si_3 and Mo_3Si will react with silicon and generate MoSi_2.The gradient layer is mainly constituted by Si and MoSi_2,only about 1/10 gradient layer is constituted by Mo_5Si_3 and Mo_3Si,and the stable existences of Mo_5Si_3 and Mo_3Si are mainly determined by the silicon content.Along the Mo substrate to the surface of the coating,the phase composition of gradient coating changes as follows:Mo → transition layer,Mo(main phase) + Mo_3Si + Mo_5Si_3 →intermediate layer,and MoSi_2(main phase) + Mo_5Si_3 +Si→surface layer MoSi_2(main phase) + Si,and the experimental temperature has no effect on phase composition of gradient coating.
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