Characterization of alumina–alumina/graphite/monel superalloy brazed joints

Active metal brazing of alumina with alumina, graphite and monel 404 superalloy was performed at 910 °C for 5 min using TICUSIL (68.8Ag–26.7Cu–4.5Ti in wt.%) as the braze alloy in vacuum of 5 × 10−6 mbar. The brazed joints were characterized by X-ray diffraction, scanning electron microscopy, energy dispersive X-ray analysis, nanohardness and Young's modulus measurements by depth sensitive indentation technique. X-ray diffractrometry showed that the Ti-based compounds were formed at the substrate–filler alloy interfaces of the brazed joints as reaction products. The cross sectional microstructures of the brazed joints were observed by scanning electron microscopy. The energy dispersive X-ray analysis determined the elemental compositions at the selective points of the joint cross section, which supported the X-ray diffraction results. The nanohardness and Young's modulus of the substrate–filler alloy interface showed no abrupt change, which suggests reliable joint performance in service.