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.