Wetting and reaction between β′-sialon, stainless steel and Cu–Ag brazing alloys containing Ti

Abstract

Joining of sialon to austenitic stainless steel has been carried out using active brazing alloys. Copper–silver eutectic alloys do not react with sialon at 900°C and no wetting or chemical bonding occurs, however, it was shown that copper–silver with addition of Ti to form active braze alloys, reacted chemically to cause wetting and chemical bonding. The surface active effect of indium in Cu–Ag based braze alloys results in different effects at the ceramic–braze and the steel/braze interfaces. The effect of indium in increasing the activity of titanium in Cu–Ag alloys results in enhanced reaction at the ceramic–braze interface, while at the steel–braze interface the solubility and diffusion of metallic elements from the steel into the braze alloy is limited and so the extent of reaction is smaller when indium is present. The samples which were brazed at 950°C gave good bending strength, and fracture occurred in the sialon indicating that the brazing process had produced an excellent interfacial bond.