In this research, has studied Joining of nano/ultrafine grained 304L austenitic stainless steel to nickel-base inconel 718 superalloy. The nano/ultrafine grained steel has produced by advanced thermomechanical martensitic method. The sheet of the steel cut as the dimensions of 10×100×40 mm. after that, applied 80% cold rolling at -15 °C to the samples to reaching the thickness of 2 mm. the cold rolled sheet has cut and the heat treatment cycle at 700 °C for 300 min applied to the samples. It led to reaching the reversed austenitic microstructure. To study the microstructure of the rolled and heated samples, has used the transition electron microscope (TEM). The TEM pictures indicating fully martensitic and nano/ultrafine grained microstructure, respectively. The samples of the inconel 718 has cut by the wire-cutter. To joining the AISI 304L and inconel 718 used nickel-based interlayer BNi-2. Ultrasonic treatment applied to the samples to removing the surface oxidation and the impurity. The joining collection has fixed by the fixture and puted in aceton. The bonding has done in 1050 °C for three times of 5, 15 and 60 min. the furnace with vacuum atmosphere has used for the joining. After joining the samples, the bonded are cross sectioned and has used standard metallographic ways. Prepared joint areas has observed by the optical microscopy, scanning electron microscopy and field-emmission scanning electron microscopy. The energy dispersive spectroscopy (EDS) used to studying the chemical composition of the phases. Result showed that samples bonded in 5 and 15 minutes, have a joint zone with eutectic and intermetallic phases and solid solution phase. The jointed sample in 60 min, has solidified fully isothermally. Besides these regions, the diffusion affected zone observed in joint zone. The mechanical test showed a higher micro hardness in isothermally solidified zone against other regions. The presence of the intermetallic phases in the joint zone, led to a lower strength and the highest strength has gained from the bonded sample in 60 minutes.
