On the Metallurgy of Active Brazing

Abstract

Advanced ceramics like silicon nitride are increasingly used as structural components in demanding high temperature applications as well as in electronics industry. Complex, multicomponent structures for engineering applications generally. The interfacial microstructures formed when Si3N4 is brazed with Ag-Cu-Ti braze alloys have been discussed in several recent studies. In order to resolve which chemical reactions are possible under various joining conditions and thereby to be able to control the brazing of Si3N4 the reactions in brazing has to be studied using both microstructural and thermodynamics. In this work the earlier determined ternary Ti-Ag-Cu and Ti-Is-N systems have been applied to the brazing of silicon nitride with AgCuTi alloys. Using direct brazing experiments at various temperatures and thermodynamic analyses performed by combining the most recent available thermodynamic data and experimental information the chemical reactions controlling the brazing process are determined and a description of the am is presented. It is shown that the miscibility gap found in the ternary Ti-Ag-Cu system exists during brazing and divides the liquid braze into Ag-rich (Ll) and Ti- and Cu-rich (L2) liquid. The liquid L2 segregates at the ceramic interface and reacts with the silicoa quaternary Ti-Si-Cu-N compound