Question: We have a customer asking for a component made from SS 316Ti. We currently vacuum braze most of our stainless steel 316L parts using nickel BNi-9 BFM. The titanium in the 316Ti metal raises questions, and I believe it could cause some weak bonding or wetting issues since titanium will easily oxide. So, can we still use the same brazing process and filler metals for both our 316L and 316Ti components, or do we have to prepare the parts differently?
Answer: Be very careful when using 316Ti stainless steel in a brazing application. The titanium content in this alloy is allowed to go as high as about 0.70%, with typical contents around 0.5%. When the titanium content of any metal is about 0.4% and higher, I always recommend that the brazing surfaces be electrolytically nickel plated so that oxygen present in any brazing atmosphere (including vacuum) will not react with the titanium on the surface to form titanium oxides.
When the level of titanium in the base metals is at levels of 0.4% or higher, there may be sufficient titanium oxides formed on the surfaces of the parts to significantly inhibit brazing, resulting in a lot of rejected, nonbrazed parts! By placing a layer of electrolytic nickel onto the brazing surfaces, approximately 0.0005-0.0008 inch (0.015-0.020 mm) thick, you should find that you will have sufficient protection to allow for normal brazing of those 316Ti parts.
Once the parts have been electrolytically nickel plated, verify the effectiveness of the plating via a blister test on a 316Ti coupon that you should submit to your plater along with the regular parts you want plated. The test coupon should have the identical surface contours as the parts you intend to braze. The coupon should be heated in a furnace to above 600°F (about 300°C) or more. Check to see if the plating blisters or not. If blisters are seen, send the parts back to the plater to be stripped, properly cleaned and re-plated. If it passes the blister test, then go ahead and braze the parts just like you are now doing with the BNi-9.