REACTION LAYER CHARACTERIZATION OF THE BRAZE JOINT OF SILICON-NITRIDETO STAINLESS-STEEL

This investigation studies the role of titanium in the development of the reaction layer in braze joining silicon nitride to stainless steel using titanium-active copper-silver filler metals. This reaction laye r formed as a result of titanium diffusing to the filler metal/silicon nitride interface and reacting with the silicon nitride to form the i ntermetallics, titanium nitride (TiN) and titanium silicide (Ti5Si3). This reaction layer, as recognized in the literature, allows wetting o f the ceramic substrate by the molten filler metal. The reaction layer thickness increases with temperature and time. Its growth rate obeys the parabolic relationship. Activation energies of 220.1 and 210.9 kJ/ mol were calculated for growth of the reaction layer for the two filte r metals used. These values are close to the activation energy of nitr ogen in TIN (217.6 kJ/mol). Two filler metals were used in this study, Ticusil(68.8 wt% Ag, 26.7 wt% Cu, 4.5 wt% Ti) and CB4 (70.5 wt% Ag, 2 6.5 wt% Cu, 3.0 wt% Ti). The joints were processed in vacuum at temper atures of 840 to 900 degrees C at various times. Bonding strength is a ffected by reaction layer thickness in the absence of Ti-Cu intermetal lics in the filler metal matrix.