In the interest of clarifying the mechanism of improving the oxidation resistance of the coating by MoSi2 modification, the surface microstructure of the TaB2-40wt% SiC/SiC coating and the TaB2-20wt% MoSi-20wt% SiC/SiC coating after TGA tests are displayed in Fig.1. As presented in Fig.1(a), it is evident that the Ta-oxides, the grey particles, were uniformly distributed on the coating surface at a low magnification. However, Fig.1(b), the magnification of Fig.1(a), shows the existence of the Ta-oxide aggregate structure which is incapable of greatly improving the stability of the glass layer. In contrast,a novel phenomenon that more SiO2 glass phase was generated on the coating with MoSi2 modified can be observed from Fig.1(c).Moreover, it should be noted that the traces of liquid flow and Ta-oxide dispersion can be found distinctly from Fig.1(d). Numerous tiny Ta-oxides were able to be dispersed in the glass layer on account of the excellent fluidity provided by a large quantity of SiO2 glass phase. In this case, the outermost glass layer became viscous and stable, providing a more efficient barrier against oxygen than the pure SiO2 glass layer. Thus, the addition of MoSi2 significantly elevated the oxidation protective property of the coatings. What's more, what the SEM micrographs show is coincident with the results of the TGA tests.
Fig,1(a) SEM micrograph of the TaB2-40wt% Si/SiC coating after TGA tests;(c) SEM micrograph of the TaB2-20wtaMoSi-20wt% SiC/SiC coating after TGA tests;(b,d) magnification of (a,c).
本文由桑尧热喷涂网收集整理。本站文章未经允许不得转载；如欲转载请注明出处，北京桑尧科技开发有限公司网址：http://www.sunspraying.com/
|
