I am brazing stainless steel at 1100 deg C using pure copper as brazing filler metal. I want to stop the migration of Fe to the molten braze filler and intergranular penetration of copper into SS. Palladium may act a diffusion barrier to suppress both of the diffusion processes. I also want to avoid a nickel strike on the substrate.
The use of palladium is to avoid the intergranular penetration of Cu into SS. As you want to avoid penetration of Fe into brazement, you may have to optimize the time for brazing (use lesser time). Even the thickness of palladium, braze gap and temperature will matter.
I am considering pure copper as brazing filler metal to join Nb and SS. The problem is that Fe migrates to Nb interface and makes brittle Fe-Nb intermetallic. If Fe migration can be stopped then the joint can be ductile. Diffusion barriers are generally not effective at brazing temperature of pure copper (~1100oC). We thought Pd plating may work but perhaps this may not be the case. Even with extreme control of time, Fe-Nb and associated brittle failure is a certainty. High Pd BFM may also be good but our aim is to bake the joint at 800oC; therefore Pd-Ag-Cu family is also ruled out. Increasing Pd thickness may work? Can you suggest the thickness? Ni also makes intermetallics with Nb so we wanted to avoid Ni strike before Pd plating.
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