Titanium frames and aging
 

I've found a titanuim framed trike for my wife (who can't balance a two wheeler) and in asking around I got this response:

"But titanium ages (becomes brittle) and it might be hard to find someone who can weld titanium."

First I've heard of this- I know about hydrogen embrittlement in welding Ti, but never heard that the tubing gets brittle.
Anyone notice older Ti frames cracking?

Did you hear that from someone who sells carbon fiber bikes?

LOL. I know about CF failure modes too.

Considering that most folks consider Ti a lifetime frame - count me as skeptical of this claim.

From whom did you hear this and do you have good reason to trust his/her opinion?

I used to work for a company that had its own brand ouf Ti bikes manufactured, and the failure rate of the frames was much much lower than the aluminum bikes we sold. I have never before heard this statement about Ti becoming brittle. I got myself a Ti frame while I worked there and it is the only MTB frame I have ever had that has lasted longer than 2 years without breaking.

I have no reason to especially trust that person's opinion aside from he is in the bike business. There's a lot of "gas" going around-I've seen some here with folks saying that Ti frames have cracked on them. So I thought to ask the question directly.

FWIW I've seen nothing in the literature on this but I'm not a metalurgical engineer. having a bad weld is one thing- that's pretty common with bad technique.

It can fatigue and crack as will aluminum and less often steel. If it was welded properly (shield gas in and outside the tube until the temp dropped below 800F) it should be ok.

Steel fatigues and cracks, too, if subjected to stress above a certain point - which is likely for lightweight steel frames.

I would think a recumbent trike would generally be overbuilt enough to keep stresses in the frame low, but it varies from bike to bike.

From what I've read, most of this issues with titanium bikes cracking is directly attributable to poor welding technique. More specifically, proper technique calls for purging the inside of the tubing, along with the exterior puddle, with argon gas.

Nice little write-up over on Firefly's site:
http://fireflybicycles.com/1112

IIRC, doesn't ti, in general, have a much higher fatigue threshold than steel or aluminium? I seem to recall some 1st gen rear suspension bike where the rear swing arm was just bending ti (sans a point fulcrum of sorts).... Oh if only I could find that article...

Seems that if Ti got brittle with age, we would have a whole bunch of airplanes falling out of the sky...

There's all sorts of nonsense said about all frame materials. Ti is used in some extremely harsh environments, and holds up very well there, surpassing even the best steel alloys.

However there is some truth in the issue of welding being more difficult than either steel or aluminum, so that might be a factor if you're planning lots of modifications.

I think he got it cofused sith Magnesium that does degrade with age.
Most classic race/sport car owners who own cars with magnesium wheels know this very well and are forced to retire wheelsets on their cars after they get a certain number of years old so they can still drive/race their cars safely. My uncle had to change out the Halibrand magnesium wheels on his 1965 427 Cobra a couple of years ago because of this.

Chombi

Yes.

Ibis. 5" of travel from frame flex.

A Ti frame that is made and welded of a proper alloy using proper welding techniques(emphasis on proper in both cases) can easily be an heirloom. I have a '96 vintage Litespeed Catalyst with about 75,000 miles on it and it is still in perfect shape and i know of other litespeeds with well over 100,000 miles so mine isn't a rarity. So a good frame by a good maker will last nearly indefinitely. Litespeed, Titus, Moots, Seven and others make very durable Ti frames.

That said, a poor choice of alloy (CP grade instead of 3Al/2.5V or 6Al/4V) and/or welding without adequate attention to inert gas shielding can and has produced brittle, crack-prone frames. One of the first commercial Ti frame, the Teledyne Titan from the early 70's was made of "standard diameter" CP grade titanium and developed a well-deserved reputation for early failure. Also, some '90's Russian frames made of CP Ti and without adequate welding care were also very failure prone.

The title led me to believe that this thread would be about older guys lusting after titanium bikes.

Been thinking that the ti version of my V-Rex would be nice to ride...................

http://bikeforums.net/attachment.php...hmentid=260640

Just an observation: Not much discussion of broken/breaking ti frames seen on BF. Of course, not a ton of ti frames.

Back-Handed Defense of Ti Frames
 

I love my Ti frame. But it is in the process of failing. I am still riding it, but the top bit of the seattube, between the tops of the seat-stays, the stress of me riding and landing heavily on the super extended seatpost is bending back quite noticeably. I am a big guy.

I have seen a couple other ti frames that had failed, due to crashing and manufacturing defects. But is very very seldom.

I am curious - who is the maker of this trike?

Airplanes are made with aluminum and are inspected regularly because the material has a finite fatigue life.

Yes, ..... and no.

Aluminum, and other metals do have a fatigue life, but that's based on stress cycles, not on time. If you parked a plane on the tarmac for 5 years, there'd be no fatigue of the aluminum.

Well, kinda. Airplanes are made up of many materials. A 787 is 50% composites, 20% aluminum and 15% titanium. You can bet that Boeing would not be using titanium metal on that airplane is there were any concerns about the metal becoming brittle with age. Read for yourself here:

http://www.boeing.com/commercial/aer...icle_04_2.html

Titanium has been widely used in military and commercial aircraft for many years for it's strength, light weight and resistance to corrosion and fatigue.

SR-71 Blackbird 80% Ti, I'd imagine a bit more extreme stress than a bike frame undergoes?

True, but since it hot so hot during every flight it "anealed" itself each time. But, you are correct, Ti was chosen for it's construction to withstand both the heat and stresses that Al was unsuiteable for.

Whoever said this was thinking simplistically and may not know their metallurgy. First, you need to determine the exact titanium alloy used:

CP - commercially pure, weakest, but still roughly the same fatigue-life as steel, much more than aluminium

3/2.5 - 3% aluminium and 2.5 vanadium, most commonly used in bike-frames, about 5-10x the fatigue-life of chromoly steel

6/4 - 6% aluminium, 4% vanadium. strongest used in bike-frames, has 20-30x the fatigue-life of chromoly steel

Basically, if you would consider buying an aluminium or steel frame, pretty much any titanium frame will outlast them. Problems with titanium frames have never come from the material. Rather from design and manufacturing issues. Such as insufficient back-flushing of the tubing or not using a welding chamber. This causes hydrogen embrittlement of the joints that can result in cracks later. Aluminum and steel frames also face these issues as well.


BTW - the 167bhp NCR Leggera supermoto is based upon a Ducati and weighs in at 300-lbs, or 150-lbs less than the factory bike. It has a 10-lb titanium frame and a titanium swingarm made by welding custom-formed sheets together (weighs 1/2 the original aluminium unit). Every single nut and bolt on that bike has been replaced with titanium versions, many hollowed-out for even more weight-savings. I won't mention anything about the plentiful use of carbon-fibre in the latest Ducatis or GP bikes...

Not to mention the titanium is used in the highest stress area of the planes, the jet-engine turbine-fan blades!!!