SiC/SiC-哈氏合金异质连接机制及其氟熔盐腐蚀特性分析

Microstructure and Corrosion Behavior of Brazed Joints of SiC/SiC Composites and Hastelloy N Alloy Using Cu-Ni Alloy

以Cu-2.67Ni钎料,采用钎焊工艺获得了SiC/SiC复合材料-哈氏合金异质接头,并研究了其在800℃的FLiNaK熔盐中的腐蚀行为。利用不同手段表征了接头微观结构和氟熔盐腐蚀行为。结果表明, Ni、Cr、Mo等合金元素以及SiC中的Si元素发生互扩散。Cr元素替代Ni元素,在焊料–复合材料界面富集并形成不连续碳化物层。高温钎焊加速Ni扩散并侵蚀SiC,低温钎焊导致焊料熔融不充分。钎焊过程中的元素扩散改变了哈氏合金的组成,导致其耐腐蚀性能恶化。Cr与Si的选择性溶出导致钎焊接头及合金的腐蚀损伤,这与热力学计算结果一致。

SiC fibers reinforced SiC ceramic matrix composites were brazed to Hastelloy N alloy using Cu-2.67Ni(mass percentage) alloy. The obtained joints were corroded in FLiNaK molten salt at 800 ℃for 100 h. Microstructure evolution and corrosion behavior of joints were characterized. Alloy elements, e.g. Ni, Cr and Mo, diffuse from Hastelloy N alloy into Cu-Ni joint seam, while the Si element in SiC/SiC composites diffuses into joint seam even the Hastelloy N alloy. Cr element enriches near the interface between SiC composites and joint alloy to form discontinuity interlayer, which acts as the active metal instead of Ni. Higher temperature contributes to both the diffusion process and the erosion of SiC by Ni, and lower temperature would lead to the incomplete fusion of brazing fillers. The diffusion of elements during the brazing changes the composition of the joint seam and Hastelloy N alloy, which caused the deterioration of corrosion resistance of alloy. The selective corrosion of Cr and Si, supported by thermodynamic calculation, results in the corrosion of both joint seam and alloy.