| The Si₃N₄/STS304, Si₃N₄/Cu and Si₃N₄/Si₃N₄, joints was vacuum-brazed with three types of Cu-Ag-Ti braze alloy at 1163 K for 1.6 ks. The microstrusture and microchemistry of reaction products formed at the Si₃N₄/braze alloy interface have been investigated by scanning electron microscope(SEM) equipped with energy-dispersive spectrometer(EDS). The reaction prodsct of Si₃N₄/STS304 joint was a layered structure consisted of nonstoichiometric titanium silicide and iron titanium silicide which was formed by soild-state reaction between titanium silicide and Fe dissolved from the stainless steel. For the joint brazed with Cu-Ag-Ti-Al rather than Cu-Ag-Ti alloy, Cu-Ag-Ti-Sn alloy, thickness of iron titanium silicide layer was decreased and shear strength was increased. The reaction product of Si₃N₄/Cu and Si₃N₄/Si₃N₄joints were a single layer consisted of nonstoichiometric titanium silicide without the formation of the second reaction layer. The former consists of Ti, Si and a small amount of Cu, the latter consists of Ti and Si only. The thickness of those reaction product layer was considerably decreased in comparision with that of the Si₃N₄/STS304 joint(the reaction layer thickness of Si₃N₄/STS304, Si₃N₄/Cu and Si₃N₄/Si₃N₄joint brazed with Cu-Ag-Ti alloy were about 3.50, 0.45 and 0.55㎛ respectively). Also the shear strength of those joints was considerably increased in comparision with that of the Si₃N₄/STS304 joint(the shear strength of Si₃N₄/STS304, Si₃N₄/Cu and Si₃N₄/Si₃N₄joint brazed with Cu-Ag-Ci alloy were average 30, 232, and 256 MPa respectively). Conclusively, whether the second reaction product layer is formed or not depends on the type of adhered metal, and the variation of those thickness depends on the chemical composition of brazing alloy. When the reaction layer is a single layer consisted of nonstoichiometric titanium silicide and the formation of second reaction layer is minimized, high shear strength joints can be obtained. |
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