Growth Kinetics and Microstructure Evolution of Intermediate Phases in MoSi2-Si3N4-WSi2/Mo Diffusion Couples

摘要

The growth kinetics and silicon diffusion coefficients of intermediate silicide phases in MoSi2-3.5 vol. Si3N4-5.0 vol. WSi2/Mo diffusion couple prepared by spark plasma sintering were investigated in temperatures ranging from 1200 to 1500 A degrees C. The intermediate silicide phases were characterized by x-ray diffraction. The microstructures and components of the MoSi2-Si3N4-WSi2/Mo composites were investigated using scanning electron microscope with energy-dispersive spectroscopy. A special microstructure with MoSi2 core surrounded by a thin layer of (Mo,W)Si-2 ring was found in the MoSi2-Si3N4-WSi2 composites. The intermediate layers of Mo5Si3 and (Mo,W)(5)Si-3 in the MoSi2-Si3N4-WSi2/Mo diffusion couples were formed at different diffusion stages, which grew parabolically. Activation energy of the growth of intermediate layers in MoSi2-3.5 vol. Si3N4-5.0 vol. WSi2/Mo diffusion couple was calculated to be 316 +/- 23 kJ/mol. Besides, the hindering effect of WSi2 addition on the growth of intermediate layers was illustrated by comparing the silicon diffusion coefficients in MoSi2-3.5 vol. Si3N4-5.0 vol. WSi2/Mo and MoSi2-3.5 vol. Si3N4/Mo diffusion couples. MoSi2-3.5 vol. Si3N4-5.0 vol. WSi2 coating on Mo substrate exhibited a better high-temperature oxidation resistance in air than that of MoSi2-3.5 vol. Si3N4 coating.