Ti frames: 6AL/4V vs. 3AL/2.5V
bob_hunt
difference in the ride between 6AL/4V vs. 3AL/2.5V Ti road frames. I'm
in the market and have noticed that the 6/4 frames are now pretty
standard stock from companies like Lighspeed and Dean. thx, bob.
Gary Helfrich
: Can anyone give me a technical or subjective impression of the
: difference in the ride between 6AL/4V vs. 3AL/2.5V Ti road frames. I'm
: in the market and have noticed that the 6/4 frames are now pretty
: standard stock from companies like Lighspeed and Dean. thx, bob.
If the tubes are the same dimensions, there is no difference between a
Ti-6Al-4V bike and one constructed of Ti-3Al-2.5V. Ti-6Al-4V is
*slightly* stronger than Ti-3Al-2.5V. 6/4 must be close to a full anneal
in order to produce tubing, so the textbook difference in strength does
not apply here. 6/4 is not as ductile as 3/2.5 either. The Dean and
Litespeed are using seamed tubing from Valley Metals. While the sheet
will have slightly higher strength levels than the seamless product,
there is no crystallographic alignment of the material in the seamed
tube. This will result in slightly lower fatigue life for the same UTS
in the material.
I don't think that there is any real gain in performance except profit
margin realized by using 6/4 as bike tubing.
Gary Helfrich
Arctos Machine
Ryun G. Pavlicek
between the two, how is it there is such a weight difference
between the ultimate and the vortex which are otherwise so
similar?
--
Ryun Pavlicek
Dept of Sociology
University of Virginia
Mike Locke
I recollect seeing a substantial difference between full hard 3/2.5 Ti
yield and full anneal 6/4 Ti yield strengths. It is not at all clear to
me that a 3/2.5 Ti frame can be made from full hard materials. I beleive
the modulus of elasticities are different also.
On such an expensive frame, it seems likely to me that the 6/4 would be
heat treated to achieve full hard after it is shaped/welded.
--
--
S'later, Mike Locke
Gary Helfrich
: For the metallurgically impaired,if there is no real difference
: between the two, how is it there is such a weight difference
: between the ultimate and the vortex which are otherwise so
: similar?
The tubing is thinner in the 6/4 bike.
Gary Helfrich
Arctos Machine
Gary Helfrich
: I recollect seeing a substantial difference between full hard 3/2.5 Ti
: yield and full anneal 6/4 Ti yield strengths. It is not at all clear to
: me that a 3/2.5 Ti frame can be made from full hard materials. I beleive
: the modulus of elasticities are different also.
Here are real numbers on real tubing, not something plucked from a textbook:
Material Yeild (MPa) Elongation in 2" at failure
Ti-6Al-4V 930 8%
Ti-3Al-2.5V full hard 865 10%
Ti-3Al-2.5V CWSR105 810 18%
Ti-3Al-2.5V annealed 550 40%
The modulus can be affected by cold work and heat treatment to a slight
degree in alpha/beta titaniums. The differences are not significant to a
bike designer, nor is the very slight difference between different
alpha/beta alloys of any significance.
Full hard 3/2.5 is never used in bike frames because of the low
elongation. My own feeling is that materials with elongation much below
15% do not belong in a bike frame. I like materials that will bend
significantly before they fail. Of course, if you use composites, the
strength is so high that failure will never occur, so there it is ok to
use materials with the ductility of fine china and hold it together with
glue.
Ti 6Al-4V which is used to produce seamless tubing has
extremely low interstitial levels. Low interstitials will result in
improved ductility at the expense of strength. Titanium is far more
sensitive than most other metals to crystallographic orientation.
This orientation is expressed as the contractile strain ratio, or CSR.
Tube that is formed from sheet material and used as is has a very poor
CSR value compared to seamless tube. There is not commercially available
Ti-6Al-4V sheet that has low enough interstitials to be reworked after
forming. Even if you were to have the special sheet made, the weld will
behave in a entirely different way from the parent material (from a
crystallographic standpoint only) and give you a product that has
inconsistent properties.
: On such an expensive frame, it seems likely to me that the 6/4 would be
: heat treated to achieve full hard after it is shaped/welded.
Heat treatment destroy any beneficial cold work. People are far too
obsessed with yield strength. Heat treating Ti-6Al-4V is not that
effective when there are low interstitials. To grossly oversimplify, you
need dirty material in order to get good results from heat treatment.
The grade of Ti-6Al-4V that will give you a high quality product with
good CSR values and high elongation will also not respond well to
solution heat treatment.
I have had a hard time understanding why anyone would use Ti-6Al-4V as
bike frame tubing. Beta titaniums have far better properties, and the
entire frame could be heat treated after welding with equipment similar
to that used to heat treat 6061 aluminium. Beta titaniums are one of the
few materials that the modulus can be manulipulated over a large range by
cold working and heat treating. This sounds like it might be a good
winter project to keep me out of trouble.
Gary Helfrich
Arctos Machine
RR Hunt
>I have had a hard time understanding why anyone would use Ti-6Al-4V as
>bike frame tubing. Beta titaniums have far better properties, and the
>entire frame could be heat treated after welding with equipment similar
>to that used to heat treat 6061 aluminium. Beta titaniums are one of the
>few materials that the modulus can be manulipulated over a large range by
>cold working and heat treating. This sounds like it might be a good
>winter project to keep me out of trouble.
>Gary Helfrich
>Arctos Machine
Gary,
Are you saying that the lighter weight 6Al/4V tubing is more likely to
fail than conventional Ti tubes? Has anyone tried to make a mtb out
of the stuff? will they?
I know you're a framebuilder as well as a metalurgist, so what about
the ride? Anything like the butted Ti frames from Merlin, Ibis, and
Fat Chance?
Gary Helfrich
: Are you saying that the lighter weight 6Al/4V tubing is more likely to
: fail than conventional Ti tubes? Has anyone tried to make a mtb out
: of the stuff? will they?
Not really. Stiffness is more often than not the deciding issue in
designing a titanium frame. Most of the better Ti-3Al-2.5V bike have a
large margin of safety. I was just trying to make the point that 6/4 is
not that much of an improvement over the alloy already in use, and if you
are going to the trouble and expense of using a different Ti alloy than
3/2.5, there are far better choices than 6/4.
6/4 is not more likely to fail than 3/2.5, but I am not comfortable with
the mode of failure. Too brittle for my taste. Litespeed does make
bikes using welded 6/4 tubing, and I'm sure that they are fine. My own
feeling is that butting the tube is a better way to reduce the weight of
the frame.
: I know you're a framebuilder as well as a metalurgist, so what about
: the ride? Anything like the butted Ti frames from Merlin, Ibis, and
: Fat Chance?
The ride is far more dependent on the designer than the design. A 6/4
Ibis, would no doubt feel alot like a 3/2.5 Ibis. The difference in
mechanical properties between Ti-6Al-4V, and Ti-3Al-2.5V are very small,
and would not have much influence on the feel of the bike. Alloys like
15-3-3-3, where the modulus can be manipulated, will feel significantly
different.
BTW, I am a framebuilder, but I am not a metallurgist or an engineer.
I've got alot to learn before either of those titles could apply.
Gary Helfrich
Arctos Machine
Coonan1
Please explain the difference between swaged tubes and butted tubes as
they pertain to Ti bicycles. Is there a true butted tubeset available?
Thanks,
Brian
Gary Helfrich
: Gary,
: Please explain the difference between swaged tubes and butted tubes as
: they pertain to Ti bicycles. Is there a true butted tubeset available?
It depends on the definition of butting. If you mean internally butted
tubing, yes, it is available from Ancotech. Externally butted tubing is
simple to produce in house (just grind or machine the wall down in the
middle of the tube), so there is no source for externally butted tubing.
Gary Helfrich
Arctos Machine
Mike Locke
I thought such ground down butting was highly undesireable because of the
affect that it has on the crystal structure of the metal (ie, the structure
is disrupted = lower fatigue life).
Gary Helfrich
: I thought such ground down butting was highly undesireable because of the
: affect that it has on the crystal structure of the metal (ie, the structure
: is disrupted = lower fatigue life).
Another victim of the Merlin Marketing Machine. There is an optimum CSR
value for good fatigue life in titanium tubing, but it is very misleading
that this one property is the sole indicator of fatigue life in titanium
tubing. So far as the structure being disrupted, remember that every
step in making the tube will disrupt or alter the crystallographic
structure of the material. All that matters is what you end up with, not
how you got there.
Gary Helfrich
Arctos Machine