Microstructure and bond strength of Ni-Cr steel/Al2O3 joints brazed with Ag-Cu-Zr alloys containing Sn or Al

Sintered Al2O3 was joined to Ni-Cr steel by the actise metal brazing route with Ag-Cu-Zr brazing alloys containing Sn or Al. A single ZrO2 layer with a monoclinic structure was formed at the Al2O3/brazement interface by the m igration of Zr in the molten brazing alloy to the Al2O3 surface, followed b y a redox reaction between the Al2O3 and Zr. The remainder of the brazement formed a Cu-Ag eutectic alloy. Precipitates CuZr2 and Cu-Zr-Al were formed in the brazements of the Ni-Cr steel/Al2O3 joints brazed with Ag-Cu-Zr all oys and Al containing Ag-Cu-Zr alloys, respectively. On the other hand, no precipitates were formed in the brazement of the Ni-Cr steel/Al2O3 joints b razed with Sn containing Ag-Cu-Zr alloys. The Ni-Cr steel/Al2O3 joints braz ed with Sn containing Ag-Cu-Zr alloys showed much higher fracture shear str engths than those blazed with Ag-Cu-Zr alloys or Al containing Ag-Cu-Zr all oys. MST/4329.