We are brazing both Inconel 718 and Haynes 214 in our vacuum furnace using a nickel-based brazing filler metal. Are there any concerns about the base-metal chemistries that we should be aware of in preparing the parts for brazing?
Yes, in high-temperature brazing, you need to be concerned with the presence of any titanium and/or aluminum in the base metals in quantities greater than about 0.5%. Whenever these two easily oxidizable metal elements are present in quantities over 0.5%, there is real danger that their oxides can effectively prevent good brazing of those base-metal surfaces!
To combat this possibility, I recommend that you always electrolytically nickel plate both the Inconel 718 and the Haynes 214 since each of these two metals contain significant quantities of these minor elements: Inconel 718 contains about 0.6% aluminum and about 0.9% titanium (about 1.5% combined), and the Haynes 214 contains about 4.5% aluminum (no titanium).
In my experience (and in my opinion), this nickel plating needs to be done. The only exception (again, in my experience) has been when both of those metals have been thoroughly pre-cleaned by a fluoride-ion cleaning (FIC) process, which effectively depletes the surface of aluminum, titanium and chromium. You can then directly braze those metals without the need for further nickel plating.
Therefore, if the parts have not been FIC cleaned, I urge you to have those parts plated prior to braze. Then do a blister test on the Ni plating when it comes back from the plating company (and prior to allowing the parts to go to the brazing operation). It is very important that you test the integrity of the nickel plating prior to submitting the parts for brazing.