Here are a couple of points to help you troubleshoot. I'm just quoting from memory here as I don't have the time to research all the details, but maybe it will help...
1. Some grades of Titanium require post weld heat treatment. Is yours that type?
2. When you say the welds are coming out nice and silver, If you mean the base metal and weld is showing no discoloration it's probably ok. If the base metal or the weld has a grayish silver discoloration it is contaminated. Dark blue discoloration is OK. (in this matter Titanium is different from stainless)
3. Sometimes contamination is not identifiable through discoloration. The best way to check for this is through hardness testing. The weld and HAZ should result with hardness very close to that of the unwelded base metal. As contamination's detrimental result is excessive hardness of the weld and HAZ, a discrepancy here is an indication of contamination.
4. You should be using pure, moisture free purge gas from liquid, running through thoroughly leak tested stainless steel piping. Use no rubber flex hose. If flex hose is required, use polyethylene tubing.
Good luck and please let us know your end result.
Tim
Tim,
1. We are doing a post weld stress relieve as required by our customers spec.
2. Yes I mean that the base metal and weld are very near the same color.
3. I do not belive that we are getting contamination. The x-rays are coming out fine. We also have tried hardness testing and found no problem.
Tim,
Thanks for your repley !
1. We are doing a post weld stress relieve as required by our customers spec.
2. Yes I mean that the base metal and weld are very near the same color.
3. I do not belive that we are getting contamination. The x-rays are coming out fine. We also have tried hardness testing and found no problem.
Tim has made a critical point you may be missing.
The x-ray in many cases will not indicate the contamination required to embrittle Titanium. Are you testing your purity within the purge box? If yes what are the readings? His suggestion of hardness testing is wise. You could test hardness in pre weld base metal, the weld nugget and HAZ prior to stress relief and also after stress relief to pinpoint exactly when the embrittlement occurs. Its possible that something is going foul during stress relief operations.
Edit: Also you could run a stress relief cycle on unwelded sample coupons and see how they do in a guided bend.
Is it possible (after you have eliminated all contamination/embrittlement potentials) for you to make a filler substitution to a more ductile CP Ti? Many factory aerospace specs allow for such a substitution.
Lawrence,
Thanks for the backup! My next suggestion was going to be a change of filler metal. Your suggestion to purity test the purge box is a good one.
Adeluca,
If I remember correctly, Titanium will absorb contaminates at just 400 degrees F. Is your stress relieving process considerate of this sensitivity?
Are you using a cleaning solution on the base and filler metals that may be leaving a contaminating residue?
If all these things check out, I would bet the problem is the filler metal.
Good Luck,
Tim
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