SiC陶瓷真空钎焊接头的组织及性能分析

采用BNi-5钎料对SiC陶瓷进行真空钎焊, 获得了力学性能良好的SiC钎焊接头, 并对焊缝的微观结构和形成过程进行了分析。研究结果表明, Ni基钎料与SiC母材发生反应生成层状界面反应层结构, 所形成的SiC钎焊接头钎缝微观形貌可以表述为:SiC母材/石墨+Ni₂Si/Ni₂Si/石墨+Ni₂Si/Cr₃Ni₂SiC/Ni+Cr₃Ni₅Si₂/Cr₃Ni₂SiC/石墨+Ni₂Si/Ni₂Si/石墨+Ni₂Si/SiC母材。所得SiC钎焊接头常温力学性能较好, 平均钎焊接头剪切强度可达到124 MPa。Ni基钎料钎焊SiC陶瓷接头的断裂位置位于钎料与陶瓷基体间的界面反应层, 主要原因是界面反应层中Ni₂Si和Cr₃Ni₂SiC等脆性化合物在钎焊接头拉伸变形过程中会产生应力集中, 在残余钎焊应力的共同作用下钎焊接头发生断裂。

Microstructures and Mechanical Properties of Vacuum Brazed SiC Ceramics Joint

Two pieces of SiC (10 mm×10 mm×5 mm) were brazed at 1180℃ for 10 min in vacuum with BNi-5 brazing paste.The microstructures, phases and mechanical properties of the brazed joint were characterized with scanning electron microscopy, energy dispersive spectroscopy and shear strength measurement.The brazed seam,~10 mm×8 mm×80 μm, formed between two 25 μm thick interfacial reaction layers.The interfacial layer comprised dominant Ni₂Si, a small amount of Ni-Cr solid solution and a little graphite; the brazed seam consisted of Cr₃Ni₂Si, Ni and Cr₃Ni₅Si₂.The average shear strength, measured at room temperature, reached 124 MPa.The fracture test results show that all fractures occurred parallel to and in either of the boundary regions between the seam's central-plane and interfacial layers, possibly because a combination of huge residual stress and the strong, highly localized stress, generated in tensile deformation of brittle Ni₂Si and Cr₃Ni₂SiC phases in the interfacial layer.