SiCf/SiC复合材料耐高温氟熔盐腐蚀性能研究

实验研究了熔渗(MI)工艺、浸渍-裂解(PIP)工艺和化学气相渗透(CVI)工艺制备SiC_f/SiC复合材料在800℃的氟熔盐(46.5mol% LiF-11.5mol% NaF-42.0mol% KF)中的腐蚀行为, 通过X射线衍射仪、扫描电镜以及能谱仪等表征手段, 对腐蚀前后样品的物相组成和微观结构进行了分析。实验结果表明, 不同工艺获得的SiC基体与高温氟熔盐的相容性与基体组成有关; MI-SiC中的游离Si相以及PIP-SiC和CVI-SiC中的富氧相是SiC基体中的两种腐蚀弱区, 易被熔盐选择性腐蚀; MI-SiC_f/SiC复合材料以纤维束间游离Si基体腐蚀为主, PIP-SiC_f/SiC复合材料基体腐蚀损伤集中在网络状富氧带, CVI-SiC_f/SiC复合材料的腐蚀损伤主要是沉积层间的含氧边界以及由此造成的基体层状剥离。与MI和PIP样品相比, CVI基体纯度高, 结晶度好, 表观腐蚀速率仅为0.0445 μg/(mm²·h), 具有更好的耐氟熔盐腐蚀性能。

Corrosion Behavior of SiCf/SiC Composites in High Temperature Fluoride Salt Environment

Corrosion behavior of SiC_f/SiC composites, which were prepared via molten infiltration(MI), polymer impregnation and pyrolysis(PIP), and chemical vapor infiltration process(CVI), respectively, was studied by immersion in 46.5mol% LiF-11.5mol% NaF- 42.0mol% KF eutectic salt at 800℃. The evolution of phase composition and microstructure was characterized by X-ray diffraction and scanning electron microscope with energy dispersive spectrometer. The SiC matrix of SiC_f/SiC composites, derived from different preparation process, has different compositions and microstructures, leading to various compatibility with fluoride salt at high temperature. Residual free Si in MI-SiC matrix and O-contained phase in PIP-SiC matrix are the weak area with worse corrosion resistance in liquid fluoride salt and will be corroded preferentially in terms of thermodynamic. Due to the higher purity and better crystallinity over the MI-SiC matrix and PIP-SiC matrix, CVI-SiC matrix shows more excellent compatibility with fluoride salt at high temperature and has the smallest corrosion rate of 0.0445 μg/(mm²·h). Least weak area confined to the O-rich boundaries between deposited layers may account for the good corrosion resistance of CVI SiC matrix.