Titanium 0.9mm Tig any ideas?

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Hi GuysGot a set of headers off a super motard husaberg to repair. They have some fatigue cracks in them. Made from 0.9mm 20gauage titanium whats the story with welding it?Obviously i need some filler, is it worth purging? some one told me to preheat? It can't be that hard the welds are very tidy so can't be to much like hard work, looks similar to stainless?Any thoughts much appreciated...
Reply:Though I have never welded Titanium pipe myselves, it's on the list for some headers for my TL1000.Titanium is very 'flammable' or sparky (like in sparky kneesliders). So backing gas would be a good idea. Next i guess like stainless you should make the welding spot clean, that means removing deposits from the inside of the pipe and thus cutting it before welding it again. This will prevent forming carbides which will cause rapid cracking after putting some stress in the pipes again.The 0.9mm shouldn't be a problem with low current DC, maybe some pulse is handy. I'm quite sure you shouldn't attempt to work without filler.That's my knowledge status right now. Made me remember to get some thin-walled Ti pipes and bends and have a go.
Reply:Thanks, these are super light it's a real cool bike. Meant to be ex world series my friend imported it. We done some back country roads with it a few weeks back.
Reply:I just had a friend of mine who had his first experience with welding Titanium except it's on a C5 Z06 vette. It had some fatigue cracks and he was welding a bypass tube in the muffle. He didn't clean the inside but he did back purge it. When he fixed the fatigue cracks he noted the filler was very "sticky" but it did weld much like stainless he said. When he welded the bypass tube on he cleaned the area VERY well on the outside and said it went much smoother. I don't know what his setting were, but overall didn't sound too terribly difficult and the weld came out very nice.If I was baller enough I'd buy some Ti to practice on but that stuff is ludicrously expensive.Miller Syncrowave 180SDMillermatic 175
Reply:Clean the weld joint thoroughly with a new stainless steel wire brush, and then wipe down with alcohol or acetone.  You must back-purge the weld, or you'll get titanium nitridesin the HAZ, as the titanium reacts with nitrogen in the air.  Contaminated welds will be very brittle.  Proper purging will yield a weld bead that is mirror bright.  If all the conditions are right, titanium is nice to weld on.  The puddle flows easily, and it doesn't build up heat like stainless can.  You'll need a gas lens for your TIG torch and maybe even some trailing purge on the front side of the weld; depending on how thick the material is and how long it stays hot.  A little color(straw or pale yellow) on weld and HAZ is tolerable, but any dark color is a sign of inadequate shielding gas coverage.  Rainbow colors on the weld are pretty but a sign of severe contamination.  You can purge with argon,helium, or a mixture of both.  Helium will produce a hotter arc than argon, and will tend to rise.  Argon, being denser than air, will tend to fall, and fill low spots in the part.  Depending on the complexity of the part shape, you can use these tendencies to make shielding the weld easier; of course it also depends on you comfort with welding vertically and/or overhead.Benson's Mobile Welding - Dayton, OH metro area - AWS Certified Welding Inspector
Reply:Thanks guys! Got some filler wire on the way... very expensive i might take some pics befor after might help someone else out one day...,As for discoloration i always thought that the rainbow effect was just the different levels of heat the material went through? I weld alot of brand new 0.9mm stainless. If settings are correct (pulse) i get a awesome colour coming out of the HAZ does that have something to do with the copper backing bar i'm using to draw heat from the weld?
Reply:Heat tint colours are just due to a thickened oxide layer refracting light differently- individual colours denote the temperature when gas shielding was lost. For stainless (and most alloys) it's not usually that big of a deal although some specs won't allow any discolouration beyond straw/gold on stainless and 'bluing' duplex stainless can affect it's propertiesTitanium (and some others like tantalum) are different beasts. Ti is actually a very common element, the reason it's so expensive is because it's so awkward (read expensive) to refine- given the chance (above 500ish C) it'll react with many other elements to form brittle compounds. It's also susceptible to hydrogen porosity It's all been covered by 'A DAB will do' really but cleanliness is king- no abrasives/files/brushes (stainless only) that have used on anything else, no dirty gloves, fingerprints are often a no no too. Purging is a must! An oversize gas lense and 1"+ ceramic a good idea. Trailing cups (an extra gas shield attached to the ceramic to protect the weld as it cools) are often used for longer welds- probably not needed here. Up the preflow to a couple of seconds min and add some extra postflow. Snip the end of the filler after stops if it's got any colour and obviously keep it within the gas shield. Other than that approach it as you would stainlessNo preheat necessary but warmish to the touch to avoid moisture (hydrogen source) is a good idea. As said, the filler can have a tendancy to 'stick' to the puddle, especially at the edgesThis is awaiting my attention when i can get my mits on a suitable offcut to replace the butchered section (and some). It was apparently a small crack before someone 'had a go'While this isn't as easily purged as a tube, providing plenty of argon coverage to the weld cap will be easier for me- got to fold up a 'purge box' to protect the back so making it deep enough to flood the whole weld area with argon is easy to doNo one has actually been able to quantify Ti embrittlement to me ('they' say the blow from a hammer can shatter the weld if the embrittlement is severe enough) but a little blueing is acceptable for some applications according to TWI.
Reply:To clarify the titanium embrittlement issue.The reason that all codes only allow a light straw/brown color is that is the color that refracts from the titanium vapor floating down back on the part, and is indicative of adequate shielding.  Darker colors indicate reaction of the titanium with atmospheric oxygen.Overheating of titanium in an oxygen environment results in an oxygen stabilized layer on the surface of the material known as an "alpha case".  This layer is extremely thin, but is very brittle, and cracks which will readily form in the alpha case will propogate right through the material.  Yes, a blow from a hammer will make the material shatter like glass.  I've had 30 degree reverse bend specimens snap like a dried twig from a welder that didn't purge adequately.Purge the inside of the header, tape up your purge inlet side, and tape the exit with a small hole so that you build up a small (1/2 to 1 psi) positive pressure on the id.  Use a gas lens to ensure good coverage and no turbulence in the shield gas, and the use of a trailing cup is strongly suggested.  Use argon only, do no use helium as it will compromise the shielding.  Use as low an amperage as practical, and make multiple welds tied into each other to prevent the buildup of heat in the adjacent metal.  The alpha case can form on the base metal that has been overheated away from the weld, and you can have a situation wherin the weld itself is integral, but cracks can form outside the HAZ, and you'll just end up chasing them away from the weld.I r 2 a perfessional
Reply:Cheers for that Kbnit but if i can rack your brains a little more...First thoughts from your explanation, removing the alpha case layer (akin to brushing or passivating stainless) would deal with the embrittlement. This is obviously not (reliably at least) the case or no one would go to the trouble of making special trailing cups, dams or welding in an inert chamber. Again 'they' say that the colour is an indication that embrittlement likely occured and given Ti's extreme affinity for O2, N etc means that embrittlement can occur beyond the discoloured area. Or could it be simple as the alpha case is likely to crack during final cooling, propogating (at least) micro cracks into the unaffected base?Reason i'm curious is that you see bike exhausts with extensive bluing occuring from service temperatures alone. Granted it's not exactly a super critical application with regards to strength but vibration and brittleness don't exactly mix...I was going to post a couple of pics of bike frames/swingarms made from grade 5 that'd have you shaking your head (lots of 'pretty' colours) as an example of what some people appear to be getting away with but their website no longer exists (may be a big clue ). I did post it last time Ti came up in discussion but unfortunatly linked to it rather than directly posting a pic. Oh well
Reply:Hotrodder,"removing the alpha case layer (akin to brushing or passivating stainless) would deal with the embrittlement." - Yes, in the aerospace industry, materials indicating alpha case are "chemically milled", meaning that they are put into a solution of hydroflouric acid and nitric acid, which will evenly remove anticipated amounts of material for the calculated time required to remove the case.  You could mechanically remove it for less critical applications, it runs .0002 to .0006 inches deep."Or could it be simple as the alpha case is likely to crack during final cooling, propogating (at least) micro cracks into the unaffected base?" - Generally not, failure of the unit is usually seen during an applied bending or torsional stress."Reason i'm curious is that you see bike exhausts with extensive bluing occuring from service temperatures alone. Granted it's not exactly a super critical application with regards to strength but vibration and brittleness don't exactly mix..." - In general, if the performance application is generating temperatures in titanium that cause the surface of the metal to turn blue, there is going to be some formation of alpha case.  Which is probably why Krum is welding his buddy's header.  "Fatigue cracks" are not common in titanium in a mounted application like a header, IMHO.  More likely the formation of an alpha case and an applied stress.Okay, now my brain is fully racked.  I r 2 a perfessional
Reply:Originally Posted by kbnitTo clarify the titanium embrittlement issue....Use argon only, do no use helium as it will compromise the shielding.  ...
Reply:I am also curious. Helium used to be the gas used for TIG(hence the name Heli-arc).It is a noble gas like argon, therefore it does not combine with or change the properties of the metal.I have never heard of problems, I'd like to know for future reference.
Reply:The rainbow colors are determined by a combination of factors temperature, gas composition, residual surface contamination.I found my test piece from school and snapped some photos for reference.  The weld is 0.052" (1.3mm) thick titanium.  It's a 4" long square groove weld.  The weld passed visual inspection and X-ray evaluation.  I've attached photos of the front, back and the X-ray for those interested.The bead width isn't real uniform, mostly because I was free-handing the weld and traveling very fast.  It's tough to keep the weld from falling out at the end of the joint if too much heat builds up in the material.Note the color is bright, with no rainbow.  The weld was made with a gas lens and a back purge block.  Incidentally, if you gin up a metal back purge fixture, make sure to clean it just as thoroughly as the base metal.  Contaminants picked up by the back purge argon contaminated several of mine and my classmate's first trial welds.Dave Originally Posted by KrumThanks guys! Got some filler wire on the way... very expensive i might take some pics befor after might help someone else out one day...,As for discoloration i always thought that the rainbow effect was just the different levels of heat the material went through? I weld alot of brand new 0.9mm stainless. If settings are correct (pulse) i get a awesome colour coming out of the HAZ does that have something to do with the copper backing bar i'm using to draw heat from the weld?
Reply:Dave,You're correct about there being no interactions with the helium, and given the nature of welding titanium, the added cost would be justified if it provided superior shielding, but, yes, as you noted, it tends to rise, so the metal welded behind the torch doesn't have shield gas on it as long as it would if you used argon, which, being heavier, stays on the workpiece longer.  So I guess it would be a physical effect, in that it doesn't provide the same coverage as argon, but not a metallurgical effect, unless that lack of adequate coverage led to the formation of the alpha case.  Did that make sense?And, yes, revhard, helium was originally the gas of choice, as noted by the name "Heli-Arc".  And I still use it today in mixture with argon when I'm welding aluminum.  For most applications involved in TIG, argon is just as good a shield gas and cheaper.I r 2 a perfessional
Reply:Originally Posted by kbnitDave,You're correct about there being no interactions with the helium, and given the nature of welding titanium, the added cost would be justified if it provided superior shielding, but, yes, as you noted, it tends to rise, so the metal welded behind the torch doesn't have shield gas on it as long as it would if you used argon, which, being heavier, stays on the workpiece longer.
Reply:well this is getting in depthHaHa, as for alpha layers it may be interesting to note there is slight pitting around the area that gets the main blast from the exhaust port...As for Helium as a sheilding gas, we use it for blowing up kids balloons in New Zealand argon is kingstill waiting on wire will print this out and take it down to the shop.One question is it worth pulsing to control heat and may help the filler stick issue?Thanks for all the info guys you are salt of the earth
Reply:Its easier to control the filler sticking issue without a pulser.  On material that thin, if the filler sticks, the normal pulsed amperage doesn't always have enough heat input to dislodge the filler.  When welding Ti that thin, I feed the filler as flat against the joint as possible, and this helps minimize the issue.  I think I still have some samples with no backpurge floating around the apartment, I'll check later tonight and post pics if I can remember to.  Gives a pretty good idea of just how brittle the severe oxidation can make the piece.