| The Si₃N₄/STS304 joints vacuum-brazed with four types of Cu-Ag-Ti brazing alloy was shearing-tested. For the joints showing interfacial fracture the position, morphology and microchemistry of reaction products on the fracture surface of Si₃N₄- side was investigated by scanning electron microscope (SEM) equipped with energy-dispersive spectrometer (EDS). Types and fratures of interfacial reaction products observed on the fracture surface are following : first, titanium silicide that is a layer structure and contains the network-shaped microcrack ; second, iron titanium silicide that is a granular (grain size is about several hundred nanometer in dia.) and layer structure ; third, Fe-Ti compounds can be classified into Fe-Ti-Si-Cr and Fe-Ti-Cr systems, the former is the angular-type grains (of several micrometer in size) and the latter is a compound showing the brittle cleavage fracture ; fourth, Cu-Ti-Fe compound that is a granular (grain size is about several hundred nanometer in dia.) and layer structure. All the compound consisted of a granular structure showed a intergranular fracture. Interfacial fracture of Si₃N₄/STS 304 joints is classified into three types as following ; first, seperation (fracture) at the interface between Si₃N₄and titanium silicide ; second, complex fracture varying the path through each interface between reaction products ; third, a part of fracture occur in the second form, but a large part of fracture occur through the inner of reaction products. The shear strength of Si₃N₄/STS304 joints showing three types of interfacial fracture is below 42 ㎫, average 180 and 202 ㎫ respectively. Therefore, the more the strength of joints is high, the more fracture occur through the inner of reaction products than at the interface between reaction products. |
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