Does 6Al-4V Titanium stress relief require a vacuum/inert gas oven?
Does 6Al-4V Titanium stress relief require a vacuum/inert gas oven?
(OP)
MIL-H-81200 for the stress relief of Titanium indicates 900° to 1200° F for 60 to 240 minutes. It also talks about various furnace atmospheres including vacuum, inert gas and others. It does not give specific requirements for the stress relief atmosphere. I've seen references to scaling occurring above 1000°F. Can I do a 900°F stress relief in an air atmosphere, or does this need a protective atmosphere? This is a welded structure from .080 thick sheet metal for a low pressure duct on a commercial aircraft.
Thanks,
-Kirby
Thanks,
-Kirby
Kirby Wilkerson
Remember, first define the problem, then solve it.





RE: Does 6Al-4V Titanium stress relief require a vacuum/inert gas oven?
An old welder friend of mine had similar problems with many 'one-off' Ti BAD parts were repairing.
He cleverly got around this by building a 321-A CRES box [thin sheet] large enough to accommodate the part. He welded shut the sides and one-end; then made a cover with tight flanges but open corners, which he screwed into position [CRES screws/nutplates]. He then welded a fitting to the opposite end of the box [fitting welded in-place over a hole!].
He then attached an inert gas-tube [or convoluted CRES HOSE] to the weld-fitting and passed the hose/tube thru the oven wall... which had a port in it that he had made specifically for this purpose.
He then flowed inert gas [IG, argon] into the box at a significant rate as the oven heated-up... which effectively purged the air from the box, replacing the local atmosphere with argon. As the oven went past ~700F to +800F he then reduced the inert gas flow to a low-steady rate for the entire SR bake process. Obviously the argon flowed from the weld-fitting on one-end of the box to/thru the 'leaky' cover on the opposite of the box. Since this process was essentially 'atmospheric pressure' there was no strain on the box from the gas or the heat. we used this for years!
NOTE. A friend's daughter did a science project on Ti-6Al-4V: she discretely heated coupons to various temperatures 'in-air' for a minimum of 15-minutes [oven stabilized at temperatures before insertion]. They went thru all of the classic color changes from straw to purple to chocolate brown indicating changes with alloy/grain/oxidation changes [alpha, alpha-beta, beta, case etc]. She Did very well at the science fair; and Her dad and I got coupon sets for mishap investigations involving over-heat/fire on Ti 6Al-4V structures. The coupons were hand-cleaned to represent real-world of mishaps only... not pristinely cleaned as in a lab.. which fully suited our purposes and hers!
http://files.engineering.com/getfile.aspx?folder=f...
Regards, Wil Taylor
o Trust - But Verify!
o We believe to be true what we prefer to be true. [Unknown]
o For those who believe, no proof is required; for those who cannot believe, no proof is possible. [variation,Stuart Chase]
o Unfortunately, in science what You 'believe' is irrelevant. ["Orion", Homebuiltairplanes.com forum]
RE: Does 6Al-4V Titanium stress relief require a vacuum/inert gas oven?
I think we're going to send this out this time, but building a box like that might be a good solution if we're running into this a lot. I've seen titanium weld repairs that have a color check to verify weld acceptability. I can't remember for sure which side blue was on, but the white at 1100° was unacceptable. I'll keep a copy of that for future reference.
-Kirby
Kirby Wilkerson
Remember, first define the problem, then solve it.
RE: Does 6Al-4V Titanium stress relief require a vacuum/inert gas oven?
Thin stuff should be done in vac or Ar.
= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, Plymouth Tube
RE: Does 6Al-4V Titanium stress relief require a vacuum/inert gas oven?
-Kirby
Kirby Wilkerson
Remember, first define the problem, then solve it.
RE: Does 6Al-4V Titanium stress relief require a vacuum/inert gas oven?
TTFN (ta ta for now)
I can do absolutely anything. I'm an expert! https://www.youtube.com/watch?v=BKorP55Aqvg
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RE: Does 6Al-4V Titanium stress relief require a vacuum/inert gas oven?
RE: Does 6Al-4V Titanium stress relief require a vacuum/inert gas oven?
RE: Does 6Al-4V Titanium stress relief require a vacuum/inert gas oven?
My 'welder friend' always welded with inert gas completely surrounding the weld zones.
For most 'routines weld-jobs' this would include carefully placed gas-nozzles flowing toward the weld from every necessary angle/side for total gas immersion [before, during, after welding].
However... he 'loved' to weld in the inert atmosphere under a 'blown' acrylic bubble that was fully purged of air and filled with slow-flowing inert gas. My fuzzy memory sorta remembers that he had [2] bubbles: (a) a~24 x 24 x ~12-high and (b) a 36 X 36 X ~18-high and a special table. There were at least 2-pairs of integral pressure-tight gloves that we worked with and port(s) in the supporting table for the TIG cables and grounds... and sometimes a turntable he used to rotate the work-piece... plus multiple inert-gas ports. I think he also made 'sheet-CRES boxes' that allowed him to boost the height of each bubble for added working space/clearance. I believe he also had other 'homemade improvements' in the set-up that facilitated the work he did on aircraft engine parts.
NOTE.
My friend was one of the most talented, disciplined, skilled and knowledgeable welders that I've ever met. Unfortunately he had a 'few personality quirks'... the most egregious of which was the knack for disappearing ~an hour or two in the middle of the workday whenever he had nothing 'pressing-to-do' [to run errands, take a late lunch, etc], which just drove his rather narrow-minded manager nuts. The day they 'fired him', I gave him a two-thumbs-up verbal recommendation to another company who hired him on the spot with a raise and better benefits. DANG.
Regards, Wil Taylor
o Trust - But Verify!
o We believe to be true what we prefer to be true. [Unknown]
o For those who believe, no proof is required; for those who cannot believe, no proof is possible. [variation,Stuart Chase]
o Unfortunately, in science what You 'believe' is irrelevant. ["Orion", Homebuiltairplanes.com forum]
RE: Does 6Al-4V Titanium stress relief require a vacuum/inert gas oven?
The finished weld fixtures were beautiful. But like most things on the F-35 project, I'm sure they cost a fortune.