When nickel brazing Inconel 718 base metals in a vacuum furnace some of the difficulties experienced with the brazing include base metals that come out of the furnace dark and discolored, and the brazing filler metal doesn’t wet the surfaces well. In this article we will explain why this is happening, and what can be done about it?

This is not an uncommon problem with a variety of base metals containing small amounts of titanium and/or aluminum. Both titanium and aluminum will easily oxidize, and once those oxides are formed they cannot be easily removed in a standard vacuum-furnace atmosphere. Yes, vacuum is an “atmosphere” in normal production environments since the level of vacuum in the furnace during typical brazing is such that there is, relatively speaking, a goodly number of air molecules still in the furnace, including moisture in that air. Of course, moisture represents the presence of oxygen, which can indeed react with either titanium or aluminum to form very tenacious titanium oxides and aluminum oxides on the surface of the base metal, which will inhibit or prevent brazing filler metal (BFM) flow. By Dan Kay