Welding brazing Titanium Grade 5 ????

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Hello everybody,I want to weld/braze a Titanium Grade 5 flange onto a cast iron cylinder head exhaust port. What would be better to use or is it impossible to weld/braze these materials together??Pic:Thank you...
Reply:I would assume no, If for no other reason than their respective thermal expansion rates are quite a bit off.
Reply:When you find out how, let us know. New methods pop up every day.Weld like a "WELDOR", not a wel-"DERR" MillerDynasty700DX,Dynasty350DX4ea,Dynasty200DX,Li  ncolnSW200-2ea.,MillerMatic350P,MillerMatic200w/spoolgun,MKCobraMig260,Lincoln SP-170T,PlasmaCam/Hypertherm1250,HFProTig2ea,MigMax1ea.
Reply:You are going to want to take that question to the experts.http://www.aws.org/cgi-bin/mwf/board_show.pl?bid=8Have we all gone mad?
Reply:Someone asked me to do something similar once a few years back. I looked into it and it is possible to attach the titanium to the cast iron through like 5 different buttered layers of weld. I can't remember what the materials were now but basically you ended up stacking around 5 different materials before getting to the titanium. Expensive and the weakest link would be the weakest filler which wasn't much if I recall. Can you make the part out of stainless? Cast iron really likes mechanical means of fastening. Can you bolt a titanium plate on and then weld this to it? Looks like there isn't much room so you would probably have to bury the bolts in the weldment (don't weld over them unless they are titanium bolts). You would possibly have problems with sealing though.Millermatic 252Lincoln 175 plusTA 185tswTA 161stlhypertherm pmax 45Victor torchHenrob torchAn S10 for each day of the week
Reply:This is where it needs to be welded...There is a weight issue. I want to make the exhaust system as light as possible. The set up is for a twin turbo. The flange will be put on the existing exhaust port. Is it possible to braze it onto the cast cylinder head??
Reply:Basically no, you will not be able to do this. If you do find the correct buildup of layers it definately would be sketchy at best and will most likely fail. What is the application? I would never trust anything welded or brazed onto a cylinder head in a turbo application. Too much heat, extra weight of turbo, and vibration, even if it is supported with bracing. If you want to save that piece then I would suggest making it into a v band setup with a flange bolted to head and the other welded to your piece. This just seems like a very poor setup. Maybe its not but need a better idea of what is going on.Millermatic 252Lincoln 175 plusTA 185tswTA 161stlhypertherm pmax 45Victor torchHenrob torchAn S10 for each day of the week
Reply:Joinability aside (Ti forms brittle intermetallics with most disimilar joints) the maximum service temp for grade 5 is typically listed as 400*C and closer to 300C when creep resistance is important (say when bits of turbo or pipework are hung off it and subjected to vibration and expansion/contraction from the heat cycling). Compare that to say 304L with a max intermittant servce temp of 800 odd Celsius and max continuous a little over 900C. 321 stainless has similar temp limitations but higher strength and creep properties at elevated tempsThis is why for world class motorsport/money no object applications inconel is the material of choice, weight saving achieved by using a thinner wall than possible with stainless alloys
Reply:Hotrodder beat me to it. I was going to add this this morning. Titanium exhaust works great on natural aspirated things but turbo systems get hot! Often time after running them hard you can see everything glowing read. Titanium needs to be in an inert atmosphere above the temps hotrodder listed. Also if weight is an issue then how come the cast iron head? Aluminum head offers more advantages then just weight, you can generally run either more boost or advanced timing because of cooler cylinder head temps.Millermatic 252Lincoln 175 plusTA 185tswTA 161stlhypertherm pmax 45Victor torchHenrob torchAn S10 for each day of the week
Reply:Why not fab a titanium manifold to weld your titanium flange to?
Reply:The cylinder head is from an ironhead V2 motorcycle engine. Ironheads are know to have exhaust port leaks. You need a positive exhaust gas sealing or you will never get good turbo spool up.This is how the cylinder head looks..This is the inside of the flange...The new exhaust port is placed over the existing cast exhaust port...What material whould be the best? (chrom moly/ stainless) Welding or bracing ? ...?
Reply:3/32 8018 should be fine.  Just make sure to peen it with a bag of nickles (or similar medium) later to relieve any stresses.Have we all gone mad?
Reply:If you want this to last and not fail then definately only use a mechanical connection between the head and exhaust. Any welded or brazed part to the head there with the heat changes and vibration will fail. I know people have welded stainless v band connections to turbine housings with some success but it isn't something I would ever rely on. If you are going through the trouble of  putting a turbo/turbos on then do it right. Are you boring out the port to match the larger flange you have in picture? If you bore the port it will leave less material to bolt to. I would tap at least 3 holes in the flat of the round port and bolt a stainless machined flange that you can v band clamp to with rest of header. 304 stainless will probably work fine in most applications. If you are racing and running this hard  then you may want to look into 321 or even iconel materials as they will hold up to the heat better. Also you mentioned twin turbo. One cylinder per turbo can be very ineffecient and usually doesn't work well cause of the time gaps between exhaust pulses. One turbo would likely work much better cause you would get a more "fluid" flow of exhaust gases.Millermatic 252Lincoln 175 plusTA 185tswTA 161stlhypertherm pmax 45Victor torchHenrob torchAn S10 for each day of the week