Characterization of interface of Al2O3–304 stainless steel braze joint

Sintered Al2O3 is brazed with 304 stainless steel (SS) using 97(Ag28Cu)3Ti active filler alloy at 900 and 1000 °C. The interfaces developed during brazing have been systematically characterized and the results show that the thickness of the interfaces is 15–20 μm and 10–15 μm on SS side and Al2O3 side respectively. The presence of TiO, Cu3Ti3O and FeTi phases at the Al2O3 interface and FeTi, and Fe35Cr13Ni3Ti7 phases at the SS interface have been confirmed through XRD and TEM studies. Microhardness analysis across the brazed interfaces suggest that the SS interface (300–600 Hv) is harder than that of the SS substrate (200–250 Hv) whereas alumina interface (550–900 Hv) is softer than that of the alumina substrate (∼ 1900 Hv). It is concluded that the various new phases that are formed during brazing are responsible for the variation in the hardness values.