I recently have been trying to qualify a process for .080 Titanium. the spec requires FPI,xray,tensile test then face bend and root bend all in that order. Twice now the samples pass all of the tests until it gets to bend testing. The first attempt failed face bend and the second attempt failed on the root bend. Does anyone have any ideas on why this happens?????
Embrittlement due to contamination of one form or another would be my first track to follow on a situation like yours.
However; Bend several unwelded specimines first as a control.
What specific alloy and filler have you chosen?
What are your surface and edge prep techniques prior to welding?
Technique (especially torch angle) is critical in GTAW of Ti, gas coverage (shielding and trail) become more and more important as thicknesses above rise 0.050.
Ti can become embrittled to the point that it will fail guided bends with less oxygen or nitrogen contamination than it takes to change the color at the crown of the weld.
The search function on this board with the time set to 999 will yeild lots of good information also.
The material is 6al 4v and the rod is the same.
Not experienced with titanium bends but a couple of questions that come to mind may be technique. Is the bend being made over the correct radius? Are you using a plunger or wrap around type bender? Wrap around is a more "gentle" bender and gives a more consistent bend.
This probably won’t be of help.... not sure though...FYI:
I had 12 of my best welders fail a 2G-bend test, on ½” A36, twice. After the second test, I discovered the intended weld joint was cut across the grain of the sheet. Therefore, we were bending the samples along the grain vs. across the grain.
We rotated the part 90 deg. on the plate, so the intended weld joint was running along the grain and everyone passed.
Are you grinding/ profiling the edges of the sample? Check your code to see what the allowable standards are for sample prep.
Cain
ADELUCA:
(A.) If you are passing all of the other tests, then it's sounds like a metallurgical issue, I would go with Lawrences observation of shielding (or lack thereof). I have run Ti welds in the past that looked like a machine performed them - nice and shiny silvery or straw/gold - then only to watch them bust out in a bend test.
1.) Are the welds being purged (at the joint root) and placed in a fixture?
(purging includes trailing cups on the face of the weld)
(B) Or, it could be the test procedure:
1.) What specification is the weld being tested to?
(acceptance crteria applicable to the weldment)
2.) What is the bend radius used for your 0.080" thick material?
(observe the the bend radii vs. specimen thickness)
3.) What is the 6Al-4V ASTM specification?
(6Al-4V has a number of specifications. This info would help to determine fixture requirments including the above noted radius and gap/opening of die for a plunger-type fixture.
4.) The rate of loading can also be an issue. I've seen test labs run a plunger-type fixture in a compression machine that can load relatively quickly resulting in premature failure of even simple steel specimens. Almost all of these machines have an adjustment for the rate of loading.
(see ASTM E190)
Let the forum know your resolution for the problem por favor.
As of right now we are trying the grain direction as a fix first. All of our titanium welds are done in a chamber and basically no chance of contamination. As far as the bend testing goes we have that done outside. We will be asking that vender for a description of tecnique.
Chamber welds can also fail if there are those pesky little holes in the gloves from finger probing with hot tungsten or parts, bad seals, an incorrect pump down and purge, etc.
Forum
