Furnace brazing offers two advantages which are a protective atmosphere and repeatability. However, it requires the entire components to be placed in the furnace regardless of the braze location. This research compared furnace brazing and electron beam brazing of a 316L stainless steel component. This component required multiple electron beam welds and one small braze. One issue that arose was one of the joint locations was close to the braze hole, which, if the weld was too wide, could plug the braze hole. Furnace brazing after welding was a concern as residual stress built up in the component could cause dimensional changes (distortion). Electron beam welding is a promising method as it locally heats up the area of interest, thus reducing the chance of distortion.
Three braze holes were drilled into 316L stainless steel 2 mm deep with a diameter of 1.64 mm. A 1.6 mm diameter tube was placed into the tube and a 0.635 mm diameter NIORO ring was fitted around the tube and placed on top of the joint. The sample was then brazed at 985°C for 5 minutes and quenched in argon. The electron beam welds, located close to the braze hole, were then created after the furnace braze. The electron beam brazed samples were created after welding. Electron beam brazes were created using a parabola pattern with a defocus of +300 mA at a frequency of 3 Hz. The beam was held for various soak times and then the sample was either cooled in vacuum or quenched in air. The braze and electron beam welds were then cross-sectioned and analyzed.
Electron beam brazing proved to be more successful than furnace brazing, due to the geometry of the component. The electron beam weld required to join the component was close to the braze hole. Furnace brazing before welding caused the electron beam weld to pick up the NIORO filler metal resulting in cracking due to saturation of gold in the weld and the tubes became plugged. Since furnace brazing was not an option after welding, electron beam brazing proved to be more successful. Electron beam brazing could be conducted after all the welds were made thus no NIORO filler metal was picked up by the weld and cracking was not observed.
Electron beam brazing is not as popular as furnace brazing, but in some applications can be a better option. The localized heating resulted in complete wetting of the NIORO filler metal with no distortion in the component. With the proper parameters, no defects were observed in the brazement and the tube remained unplugged, which was not observed in the furnace brazes.