We are currently "Vacuum furnace"brazing using SA 650 braze paste on cracks in DSR 142 Nickel alloy parts.
The parts undergo an FIC/vacuum clean prior to brazing.
In one furnace the parts are fine with a shiny silver grey surface all over.
However in another furnace the braze material only is constantly oxidised,discolored grey/black.The outer surface is porous/partially melted while the inside of the cracks show some melting and diffusion.
We have a very good vacuum level (4x10-5).
There is no obvious sign of a leak.We have carried out several burn outs.Chemical analysis shows a high concentration of Tantalum on the surface of the discolored "caked" braze material.
Any advice would be greatly appreciated...Stephen....