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Stability and formation kinetics of TiN and silicides in Ti/Si3N4 and Tii/Si diffusion joints have been investigated. Reactions in the diffusion couples were studied experimentally in the temperature range between 950 and 1100 "C. Isothermal sections and activity diagrams of the Ti-Si-N system were calculated using the recent thermodynamic data. Both the thermodynamic calculations and experimental results indicate that TiN and Si react with each other and form TiSi, and even S&N4 if the activity of nitrogen is high enough. Similarly, results from the TiiSi,N4 couple were in good accordance with calculated phase equilibria. The experiments carried out in vacuum ampoules and in a vacuum furnace showed that the gas phase has a strong effect on the reactions. 0 1995 American Institute of Physics.

This article reviews the progress that has been made in developing and applying joining techniques for Si3N4 and discusses our understanding of the influence of process selection on the materials science of the formation and properties of joints. High-performance Si 3 N 4 joints can be produced, but it is clear that much work remains to be done before the use of such joints in hot-stressed applications can be disregarded as a problem.

Metallurgical reactions controlling the Ti activation in brazing of Al2O3 have been studied by means of microstructural and thermodynamic analysis. The reactions of titanium with oxygen and copper are shown to be decisive in active brazing. Themiscibility gap in the Ag–Cu–Ti system divides the liquid braze into Ag-rich (L1) and TiCu-rich (L2) liquids. The liquid L2 reacts with alumina forming the mixed oxide (Ti, Al)4Cu2O. 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 alumina is possible only in the filler alloys of highest Ag content.

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