Hello, I am working on the dual phase titanium alloy, Ti-6Al-4V. I have to carry out heat treatments above 950 °C. In order to avoid oxidation, the heat treatments must be performed under controlled atmosphere (Ar for instance). I am wondering if we can use Nitrogen as a controlled atmosphere? in this case can N atoms affect the alloy's surface or even diffuse inside it?
You can use only Ar, He, Ar + He or vacuum chamber when heating Ti or Zr above 300 C
You can use Argon instead of Nitrogen. Nitrogen is also an interstitial element whose content should be below 350 ppm for titanium alloy. When heat treated above 950 oC, Nitrogen will diffuse into the substrate.
Hi Nabil,
We always did the heat treatment of Ti-6Al-4V under vacuum.
Nitrogen gas is not used for the atmosphere of ordinary heat treatment furnace of titanium. Although it may be used for the purpose of curing the surface, the diffusion rate of nitrogen passing through the titanium nitride is too slow, so the method of direct nitridation with nitrogen gas is not optimal. CVD method which converts to plasma by using mixed gas such as CH 4 + NH 3, etc. are often used.
Hi Mr Nabil,
Absolutely the nitrogen will diffuse on the surface, and it makes Nitrides with all of Ti, Al and V. The nitrogen atmosphere is not suitable for this purpose. As Mr. Mikhail said you can use only Ar, He, Ar + He atmospheres or vacuum chamber for your work.
Be successful.
Nabil
You already got good answers. However I stress that never use nitrogen in heat treatment of titanium or its alloys, unless you want titanium nitrite. if you are using argon or helium, try to setup a trap to remove residual moisture or oxygen from it. However, best to use vacuum in combination of first mechanical pump and then diffusion pump to get high vacuum and then raise to your heat treatment temperature.
Dr. K
Protective argon is not enough. You will need a vacuum at at least 10-6 millibar. C, N and O will all at these temperatures go in solid solution i Ti alloys. MX will not form, if the diffussion is higher than X availible
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