Titanium and SS316

By TimGary (****)

Date 07-09-2009 20:58

While I'm not expierienced in this application, I'm wondering about your atmospheric shielding.
I assume you've taken steps to ensure that no oxygen may reach the HAZ?

By sazid98 (*)

Date 07-09-2009 22:34

Yes i used argon to shield the weld zone during and after welding.

By ssbn727 (*****)

Date 07-11-2009 00:06 Edited 07-11-2009 00:27

Okay, Now when you mention the "Weld zone" are you including the backside of the joint as well?
What type of joint is it? Are the members of the same thickness?
What grade of argon shielding gas are you using?
Are you performing the weld in an enclosure, and checking how many ppm's of Oxygen is within the enclosed atmosphere?
Are you trying to fuse the 2 base metals together without filler metal? If not, then is the joint configuration conducive to achieving minimal residual stresses within the joint?

Most important of all beside having taken all of the necessary precautions required when welding Ti, how clean are both of the two base metals? I ask this because if the stainless is not as clean as it should be when attempting to join it to Ti which must be given the "White Glove" treatment always, then contamination may be migrating from the stainless member into the weld. Welding may not be the way to join these two metals, so have you considered Diffusion bonding along with a Hot Isostatic Pressure densification process?

All of these considerations MUST be taken into account before one can even attempt to achieve any margin of success.
We look forward to your response.

Respectfully,
Henry

By aevald

Date 07-09-2009 23:22

Hello sazid98, there are a few folks who frequent the forum that could probably shed some light on the question you are asking, Lawrence, 803056, and probably ssbn727. They all have experiences in that area. In lieu of them answering at this time I would suggest googling Timet or Teledyne Wah Chang and searching some of their information. My memory of this sort of thing tells me that you are looking at some issues with joining these two materials by welding. You might have to resort to a brazing process or soldering instead if that is a viable alternative. Looking forward to other responses. Best regards, Allan

By Steve.E (**)

Date 07-10-2009 11:00

Well Ill throw my hat into the ring . The only interlayer I have ever heard of for titanium is pure silver . The company I work for has extensive titanium welding experience however I have never tried this welding this welding process and can only remember it as a repair solution for explosion bonding by Dupont.

By 803056

Date 07-10-2009 18:50

You might have some luck with a solid state welding process, but I doubt you'll have much success with a fusion welding process due to the intermetallic compounds and due to the limited solubility of titanium in austenitic stainless steel.

I did have a client that tried to line their 700 foot tall boiler stack with titanium. The contractor welded stainless steel lugs to the carbon steel liner and then the titanium sheets to the stainless lugs. Within days they had 4 by 8 foot sheets of titanium raining down on the plant and surrounding country side. Fortunately no one was killed.

Then again, nothing ventured, nothing gained. I've seen situations were the proposed solution was scoffed at by the "experts" only to have it work very nicely when it was executed.

Best regards - Al

By Lawrence (*****)

Date 07-10-2009 19:13

Al may be on to it with Solid State processes

Friction stirr has been known to join Titanium to Aluminum... Don't know about Stainless

But the University of Wisconsin has done some research on arc preheat prior to FSW with some results.. Maybe contact the alum associated with the link below.

http://www.ibridgenetwork.org/warf/arc-enhanced-friction-stir-welding

By sazid98 (*)

Date 07-13-2009 01:17

thank you all for your very informative responses.
In response to SSbn, i meant the weld zone both top and bottom side and the thicknesses were same. the grade of the argon gas was grade 5.0 high purity. I know shielding is a big issue in welding of Ti and people douse vacuum chamber but we are not still implementing that for some constraints. we are doing it without any filler metal. thank you for your suggestions regarding the cleaning. right now i am polishing the meting surfaces with sand paper and cleaning it with acetone afterwards and before welding.

Steve, yes i have found literature where people used silver based alloys and even one case i have found people using polymer. but we want to do it without any interlayer first. But looks like its not so easy.

Lawrence, you are right there are many works done on ti and SS friction stirred welding. i have also seen some works done on this two pair for fusion welding but in lap joint. now i wonder what was the speciality. the paper was written in japanese so i could only figure out some paramaters from there.

I have found a new idea from one of the journals in order to face this challenge of cracking. i will let you know once i do it.

However one more question for you folkes. i have welded two pieces Ti grade 2 and found that some kind of white powder formed on top of the weld zone. is it Ti oxide?

take care guys.

best

Sazid

By ssbn727 (*****)

Date 07-13-2009 06:13 Edited 07-13-2009 06:16

Thanks for your reply but, you said you're using sandpaper? could you please elaborate because, sandpaper is a BIG TIME NO - NO!!! Especially with Ti...

Another potential problem may just be the type of acetone you are using... Can you tell us what is the exact type of acetone you are using?

You do not need to use a vacuum chamber with a laser (Electron Beam would usually require a vacuum), you just need to make sure that the atmosphere is as oxygen free as possible (less than 10 ppm or less would be suitable), and with a totally inert atmosphere - Argon. What type of laser system are you using? I hope it's not a Carbon Dioxide system. ;)

To answer your next to last question... Yes it is! The source(s) of oxygen being introduced into the weld that's causing the oxidation is what you should be eliminating because, there are a number of possibilities for contaminating the metal surfaces... One must backtrace step by step such as controlling the amount of oxygen within the atmosphere by checking the ppm's of oxygen prior to welding, to using the correct type of acetone when cleaning the surfaces, to making sure one does NOT USE SANDPAPER to remove any surface oxides that may or may not be present on ALL of the surfaces that make up the joint.

Btw, what grade of stainless steel are you using?
Also, is the stainless steel being prepared in the same manner as the Ti? If it is, then you need to adjust your metal preparation whereby both "MEMBERS" of the joint are given the same upgraded treatment in order to insure that oxygen is not being introduced into the weld from either metal, from the shielding as well as the backing or trailing gas, from the use of "SANDPAPER?", or from the use of an incorrect type of cleaning agent. Nine out of ten times the reason why Ti welds are contaminated is because of not adapting to demanding that it is of the utmost priority to clean, clean, clean in the proper manner, and to control the amount of oxygen down to less than 10 ppm, or less.

This link may be of some use for you:
http://eagar.mit.edu/3.37/H-337-39.pdf

These two may also be helpful:
http://eagar.mit.edu/3.37/H-3371-18.pdf

http://eagar.mit.edu/3.37/H-3371-19.pdf

So, get rid of the sandpaper, and use something ("scotchbrite" pads from 3M) that will not leave any residual loose sand grains, or inadvertently impregnate the surfaces with whatever is in the sandpaper...
If you are using acetone, make darn sure you use a reagent grade of acetone ,and not the stuff that comes out of 55 gallon drums because if you do use a non-reagent grade of acetone... You end up degreasing the members with grease!!! pardon the pun but, the non-reagent grade has oil in it, and hydrocarbons even from one's fingernail left on the surface of Ti is enough to cause porosity, oxidation, and yes brittleness in the weld.

Respectfully,
Henry

By js55

Date 07-13-2009 13:33

Let me preface by saying I shore (mispelling intended)ain't no expert on titanium but given the Fe and C content (not to mention beta stabilizers like Cr and Ni) of stainless steel, and barring an education, I would say I don't see how you can avoid embrittlement with a mixed weld deposit from fusion welding, even if you do avoid initial cracking. It will still be embrittled. Solid state as Al and Lawrence said is the way to go. Even if you cook it to relieve the beta phase hardness you will still have th intermetallics to deal with.
Am I off base here?

By ssbn727 (*****)

Date 07-13-2009 15:36

I agree with you Jeff, Al, and Lawrence, and that's why I suggested an alternative to laser welding the joint but, since we do not even know what type of application this is being attempted for, we're really taking shots at a target through a "black hole" so to speak. ;)

One important consideration is controlling the amount of interstitial elements when welding Ti... Oxygen, Carbon, Nitrogen, and the plethora of alloying elements found in all grades of stainless will have certainly high enough levels of interstitial elements within their composition alone to cause a mini "landfill of garbage" within, and along the grain boundaries after solidification that embrittlement is virtually guaranteed with just about any fusion welding process... The only exception would be in using a solid state process whereby the metal is agitated to it's plastic state (plenty of simplification here, so bear with me please) in order to fuse the two members in question without having to have the metals go through such extreme transformation phase changes that would occur if one used a fusion process where melting both members could not be avoided. ;)

It is also precisely the reason why I posted the links in my last post... To inform the originator of this thread to consider the fact that embrittlement will occur regardless of the welding process used... It's only a matter of how much is acceptable within the design considerations involved.

Laser welding sounds like an ideal process when one is uninformed of it's limitations... For example ,the laser does a lousy job of attempting to weld Aluminum because of the fact that Aluminum reflects light so well...

However, the most important factor of consideration is understanding the metallurgy between these two metals, and the limitations imposed when attempting to fuse the 2 very different metals together, especially without any added filler or bonding with an interlayer. Still, much more information needs to be given in order to suggest an appropriate joining process for the specific application and currently, we only have bits and pieces. ;)

Hopefully, more will be revealed. ;)

Respectfully,
Henry

By sazid98 (*)

Date 07-14-2009 21:14

Thank you all again for your advices. I have been revisiting the literature part to answer few more questions before doing the welding again.

Yes so far deciding the intermetallics are a biggest challange specially for this case of finite cooling. I dont know may be friction stirred welding would be better than laser welding but i am trying to find out it with doing laser welding.

I am useing ASTM 316 stainless steel and grade 2 CP Ti.

I have already ordered the policsining cloth from 3M and my acetone is reagent grade. lets see what happens with the new idea although its not an easy one to implement regarding the setup i have.

thank you again.

enjoy the summer

best

Sazid

By sazid98 (*)

Date 08-01-2009 18:03

Hi guys i have successfully joined the pair together. i have not perform any testing yet. so yet early to comment about the weld quality.

thank you to all of you for your advices

By 803056

Date 08-02-2009 18:56

I suspect the bends will be glass like, i.e., snap!

The tensile tests likewise should snap with brittle fracture and relatively low loads.

I taught a welding class at a local aerospace engine manufacturer a few years ago in conjunction with the business outreach program offered by a local college. One of the welders accidently tried to weld stainless steel with titanium filler metal or vice versa, I forget which, but the bang that it made before he even reached the end of the coupon could be heard across the welding lab.

Best regards -Al