Can I use nitrogen on a nickel braze?

We had a customer enquiring for advice this week.

They had been conducting a braze cycle using AMS4777 braze filler metal when the the vacuum failed on their furnace. They had just reach above 950C when they had to abandon the cycle.

Their question was it is safe to use nitrogen in this situation in order to accelerate the cooling process and could they simply repeat the braze cycle with the same parts again.

Our primary concern is that as a rule we recommend you avoid doing any brazing with nitrogen. Purging the parts with nitrogen prior to brazing could potentially introduce nitrogen into the braze and cause issues.

AMS guidance does not list nitrogen as a recommended atmosphere for nickel brazing for a number of reasons. These include the risk of nitrogen embritterment, boron-nitride formation (AMS4777 in particular contains boron), as well titanium and other metal nitrides forming. Please read Dan Kay's excellent article below for a more detailed analysis:

https://kaybrazing.com/brazing-articles/1000918-why-is-a-nitrogen-atmosphere-disallowed-when-nickel-brazing-per-ams-2675/

Additionally, as they had got very close to the solidus of AMS4777 the alloy might have started to melt, with a failed vacuum there is clearly a risk of oxidation of the parts.

We know that no-one wants to dispose of parts for a theoretical chance of issues, and we also know that whilst brazing a part twice is not common it can be done.

If there is no obvious signs of oxidation then we would suggest conducting a test re-braze with one part and judge the outcome.

We should emphasise of course that using nitrogen in brazing is not guaranteed to cause problems but it can cause problems and that is why we don't recommend it.

Using nitrogen to quench your parts after the braze cycle is completed in full should cause no issues at all.