| The vacuum brazing of alumina(99.9% α-Al₂O₃) to Ni-Cr steel, Cu with Ag-Cu-Zr active braze alloy has been performed to investigate the interfacial reaction of Ag-Cu-Zr brazing alloy on Al₂O₃. The effect of additional element in the brazing alloy was also examined for the interfacial reaction and joint strength. EDS results showed that reaction product was composed of Zr, O and a little amount of Ag. XRD analysis indicated that the reaction product was one substance of monoclinic ZrO₂(a=5.1463, b=5.2135, c=5.3110Å) and the element of bonded metal did not participate in the formation of reaction product, in spite of the presence of silver in the reaction product. So the reaction product doesn`t contain any of dilute ceramic phase and intermetallics which are commonly seen in other active metal brazing system. Detected Ag should be from the trapped Ag grains or cluster in the reaction product during the interfacial reaction. The 3rd additional elements(Sn, Al) in the brazing alloy changed the thickness of the reaction product layer and the morphology of the brazement. But fracture strength was strongly influenced by the morphology- of the brazement which was closed to ductility of brazement. Maximum shear strength of 140.5MPa was obtained for the Al₂O₃/steel joint brazed with Sn added brazing alloy due to the improvement of brazement ductility. Al₂O₃/Cu joint had relatively low strength due to the decreased brazement gap and distinct brazed region was not observable because the excessive inter-diffusion and the reaction between Cu, Zr of brazing alloy and bonded copper. |
|
