Effect of Liquid-phase Siliconizing Process on Silicon Diffusion Behavior in Mo Matrix

Abstract

MoSi 2 functionally graded coating on Mo substrate is prepared by liquid-phase siliconizing technology. The SEM, GDS and XRD analysis shows that the silicon content in gradient layer appears in three changing regularities. 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 3 Si + Mo 5 Si 3 → intermediate layer MoSi 2 → surface layer MoSi 2 (main phase) + Si. According to the Si-Mo diffusion couple and Arrhenius equation, the activation energy (Q) was obtained as 430 kJ·mol -1 , and the Arrhenius dependence of D on temperature can be described as D = 4.9 × 10 -3 exp(-430000/RT) m 2 /s. The diffusion temperature has an important influence on silicon diffusion coefficient. As the diffusion temperature increases, silicon diffusion coefficient is also gradually increasing.

Mo–Si–B alloys for ultra-high-temperature space and ground applications: liquid-assisted fabrication under various temperature and time conditions

“…The RMI method itself has been already page 4 of 22 commercialized, and the most spectacular example of its application is the large-scale fabrication of near-net shaped SiC/C ceramic matrix composites for aviation and space applications [7]. Here, the concept of liquid-assisted siliconizing process proposed by Zhang et al [8][9][10][11][12][13][14][15][16] for the fabrication of Si-MoSi2 functionally graded coatings or bulk materials by a hot-dipping of Mo substrate in a Si bath, is adopted. This method offers many advantages over other ones, such as a simple experimental setup, pressure-less and clean conditions (no toxic chemical activators), limited temperature ranges, fast diffusion rate of Si, good product quality, reproducibility, etc.…”