METALLURGICAL REACTIONS CONTROLLING THE BRAZING OF AL2O3 WITH AG-CU-TI FILLER ALLOYS

Metallurgical reactions controlling the Ti activation in brazing of Al 2O3 have been studied by means of microstructural and thermodynamic an alysis. The reactions of titanium with oxygen and copper are shown to be decisive in active brazing. The miscibility gap in the Ag-Cu-Ti sys tem divides the liquid braze into Ag-rich (L1) and TiCu-rich (L2) liqu ids. The liquid L2 reacts with alumina forming the mixed oxide (Ti, Al )(4)Cu2O. Besides with alumina, Ti reacts with oxygen that the filler alloys usually contain and forms a brittle ribbon composed of TixO and Ti-Cu-O phases in the braze, The formation of Ti oxides next to the a lumina is possible only in the filler alloys of highest Ag content.