Titanium question for all the highly skilled veterans out there.

[Hillbillysmith]

I don't mean to sound cross on this one but I'm not looking for guesses only FACTS....

Somebody i know wants titanium welded to stainless for exhaust purposes. Can this be done in a shop setting?? I say shop setting because i know just combining the two materials can be done but it's through explosion welding, electron beam welding, and high pressure diffusion processing.... I told them it can't be done directly but could be tig brazed with an uncoated silicon bronze filler wire. But i also got to thinking, is there a transition material the the two materials will readily weld to individually???? Maybe cobalt in between or use cobalt filler AS the transition material?? Nickel based material like inconel, Monel, incalloy, hastalloy??? Any wisdom on the subject is appreciated..... *potentially experimentation with this subject* but it'll be an expensive experiment so little by little. B)

With this, keep in mind, I'm trying to figure out a way to inhibit (as much as possible) the diffusion of the iron (Fe) chromium (Cr) and nickel (Ni) into the titanium side (primarily the Fe) and visa versa. To keep intermetallics from forming at any phase.... This is where i believe tig brazing is the only solution but the heat of the application is where my concern derives from the way of the braze.

-Hillbilly

[doc]

Hillbilly

  Why don't you PM SAMCRO here on the site? I think he'd be the most qualified to answer your question or send you to where you could find it.

[Hillbillysmith]

This question is actually kind of indirectly directed toward him but i also know that there are MANY talented and intelligent welders out there who could potentially help so i don't want to possibly narrow my chances by only asking one person.

-Hillbilly

[pkrankow]

Apparently it can be brazed with a silver bearing filler. No personal experience, but exhausts should be below 500F so solder should hold up fine.

Phil

 

Mod note: Must have missed the part about guessing
 

[Robert Yates]

Titanium welded to stainless:

 

When titanium is welded with steel the intermetallic phases TiFe and TiFe2 form, which are very hard and brittle and prevent the production of technically useable welds. One way to achieve ductile welds of steel and titanium is to use intermediate layers of materials capable of being welded with both titanium and steel, without brittle phases occurring. One such material is vanadium. Titanium/vanadium/steel joints have been produced successfully by resistance spot, electron beam and diffusion welding.

 

Titanium Properties are as follows;

Titanium’s higher melting point, lower density, lower ductility,  & sensitivity toward contamination during welding. You MUST Have Ultimate Cleanliness! This is to Say…. titanium should be free of air drafts, moisture, dust, grease and other contaminants, which might find their way into or onto the metal. Molten titanium weld metal must be totally protected from contamination by air. Also, hot heat-affected zones and root side of titanium welds must be shielded until temperatures drop below 800°F (427°C). titanium can be welded to zirconium, tantalum and niobium.

 

Welding Processes

Titanium and its alloys are most often welded with the gas tungsten-arc (GTA or TIG) and gas metal-arc (GMA or MIG) welding processes. Titanium welding wire is covered by AWS A5.16-70 Specification (“Titanium and Titanium-Alloy Bare Welding Rods and Electrodes”). It is generally good practice to select a filler metal matching the properties and composition of the titanium base metal grade. However, for both commercially pure grades and alloys, selecting a weld wire one strength level below the base metal is also done.

 

Brazing is Brass ! all other forms are “Welding types” Torch brazing is not applicable to titanium. As to say any brazing techniques will Contaminate the Titanium surface. Most “All” titanium should be done with argon or helium gas shielding. Alloys for brazing titanium to itself or other metals are titanium-base (70Ti-15Cu-15Ni), silver-base (various), or aluminium-base (various). The titanium base alloy requires temperatures in the vicinity of 1700°F (927°C), whereas the silver and aluminum-base alloys require 1650°F (899°C) and 1100°-1250°F (593°-677°C) respectively.

 

 

So your answer to titanium welded to stainless or to do so in a shop environment  is NO !

 

It will contaminate to weld and it will crack just as if it were cast iron. you can not weld stainless steel to it either.  To weld titanium you can set you material on stainless steel covered tables, but any tools you use such as files or brushes( always use stainless brushes) must be new and used only on the titanium.  You should also use what is called a bird nest when tiging it. A bird nest is an extra purge line that you fit next to your cup as you are welding. So, as you move your tig rig while you are welding it, the birdnest will help to cool the weld as well as give it more gas shielding. I hope this helps you. If you need more info, please feel free to let me Know .

 

Best Regards

 

Sam

[Hillbillysmith]

That was my exact thought on the topic. I did not know about zirconium, tantalum, niobium, or vanadium so i thank you for that information.... So, Sam, would i have been correct to tell him to tig graze the joints with silicon bronze rod?? I believe I'll conduct an experiment on this subject. Weld, test, and record my data.

-Hillbilly

[HWHII]

Hate to be a spoiler here but I can give you a case where titanium is welded to stainless steel in a shop enviroment. When I worked for CAID Industries one of their products they manufactored are cathodes for solvent extraction method of minning copper. One of there designs envolved a copper bar 1" x 11/4" x 54" long wrapped in 16ga 316L stainless then TIG welded all they way around on the ends and fused the seem to make a water tight seal. Then there was a 1/8" slot horizontal milled 1/2" into the bar to except a sheet of 10ga titanium 48" x 50" then the titanium sheet was welded to the stainless wrapped copper bar with trailing gas. If memory serves me correct the filler metal was titanium a filler. I have personally welded thousands of these cathodes. More common we welded stainless sheets to copper bars with a 2% deoxidized copper filler in a water bath about 3/4" deep circulated by a swamp cooler pump from a lower water tank. I believe they have photos of this on their web site at caid.com if you are interested. If you go to their web site and click on Minning Technology and go to the photo gallery there are some pictures of some titanium cathodes at the bottom of the page. These have a titanium head and a stainless steel bottom. So in this case 10ga titanium sheets and 10ga stainlees steel sheets were welded directly together. If you need to now the titanium filler I could make a call and see if I can get it.

[Robert Yates]

Hill Billy,

 

is it a O2 sensor to a Ti exhaust  ?

 

No! silicon bronze rod is not compatible with Ti & SS. However to give you a Fighting chance to do your experiment try DC Negative and it will flow much better.

 

Here are acceptable rods for Ti welding/TIG work . **** Note!the Rods are Very expensive start out around $275.00 price pre LB ****

 

Name Temperature  C/F Composition  Solidus  Liquidus

Ag-5Al  --  780/1436 -- 810/1490

Ti-20Zr-20Cu-20Ni --  842/1548 -- 848/1558

Ti-15Ni-15Cu --  830/1526 -- 850/1562

Ag-26.7Cu-4.5Ti  -- 830/1526 -- 850/1562

Ag-9Pd-9Ga  --  845/1553 -- 880/1616

Ti-15Cu-15Ni   --  902/1656 -- 932/1710

Ag-21.3Cu-24.7Pd  -- 900/1652 -- 950/1742

 

 

 

Titanium is what I call a “heat monster” meaning it will take twice as much heat input as the same thickness of stainless. If your weld is to have 100% penetration your tack welds must have to have 100% penetration it is very difficult to be welding a 100% penetration bead and run over a tack weld that’s not 100% through and hold your 100% penetration throughout your bead. Titanium is very unforgiving in relation to this; for example, if you fail to penetrate on your first pass you cannot correct this by welding back over it like you can with steel or stainless the weld will have to be removed and redone.

 

Use Thoriated tungsten, you can use Lanthanated but if you have a lot of titanium to weld you’ll wish you had Thoriated tungsten. These are your only two choices, you may have read in one of my posts that we had problems with Tri-mix; well titanium is the metal where we had the most problems.

Always connect the ground lead to the WORK with a positive clamp (“C” type clamp) never ever use a spring clamp. This can lead to an internal burn where the ground clamp was connected and it cannot be seen visually when you’re done but yet when you put it in service that’s where the part fails not at your weld. When we do larger heat exchangers we actually weld two to four taps on the exchanger and bolt the ground lead to the part, so even if you have a burn you cut the tab off at the end of the job.

Be careful when you start your weld, titanium during its transition from room temperature to its melting point of 3000deg becomes very magnetic. At room temperature it’s not, and at 3000deg it’s not, just during the transition, so keep your filler rod out of the zone until you have the puddle established. The filler rod during welding becomes very sticky because you must keep it under the shield at all times and this makes the filler rod very hot, so if you touch anything it will stick to it, and I mean stuck good. This is a big reason why you need the large cup, 1” or larger. This allows you to keep the filler rod cooler but still under the shield.

 

Sam

[HWHII]

I was talking with my friend who is a quality control manager and a Level III AWS CWI and he informed me that they stop the practice of welding titanium to stainless sometime ago because of weld deterioration and failure of the weld in long term service. He also informed me that can be done but it is not a recommended practice. So sorry for putting out some bad info.