Titanium Alloys?

Have some 0.030" 6Al4V sheet I was trying to heat-treat and it was warping so I'm giving up on it. A buddy had some Ti alloy that was much "stiffer"
than what I had, looking at Matweb there are all kinds of different alloys, some with Mo, Zr, Sn, some already heat-treated etc.
When looking at specs., what's important for "stiffness"? Is it tensile strength? Are there certain Ti alloys that when treated are stiffer than others?
TIA
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Once again (I think we discussed this before?), the "stiffness" of a material is the measure of its Modulus of Elasticity, or Young's Modulus. There is no necessary relationship of stiffness to strength.
All titanium alloys fall into a narrow range of elastic modulus, roughly 105 - 116 GPa. That's about half the stiffness of steel, of almost any grade (except stainless grades).
Now, excuse me if you know this, but "stiffness" by this measure is the "springiness" of a material. In other words, this is the value of resistance if you bend the material and it can still spring back. If it doesn't spring back, but bends permanently, you're looking at *strength* values, not *stiffness* values, and that's another kettle of fish.
You'll find the Modulus of Elasticity values for metals on Matweb. You'll notice that they hardly change from one alloy of titanium to another. In other words, the sheet your buddy had was no stiffer than the 6A14V that you had. It may have been slightly thicker, and only a small difference in thickness leads to a much larger difference in stiffness.
-- Ed Huntress
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Thanks for the reply Ed, you have helped with this in the past, much appreciated.
We're using it for turn fins on our model boats, we both have material that's 0.030" thick, both Ti alloys but neither of us are sure what.
Mine bends fairly easily and holds it's shape, his is hard to bend and springs back to it's original position easily. When he puts a bend in it he says he has to "over-bend" it quite a bit, I don't.
The main difference I see in these materials is tensile strength, although Young's Modulus isn't given for them all, but you say they fall into a narrow range anyway. Hardness is also similar around Rc 38, so is it the tensile strength I should be looking at?
Here's matweb specs for annealed 6-4, and heat-treated 6-2-4-2 and 6-2-4-6:
http://www.matweb.com/search/DataSheet.aspx?MatID 239
http://www.matweb.com/search/DataSheet.aspx?MatID 799&ckck=1
http://www.matweb.com/search/DataSheet.aspx?MatID 800
I'm looking for what he's got :)

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OK, that's a yield-strength issue then, not "stiffness."

Yes. Bending strength, the resistance to taking a permanent bend, is a combination of tensile and compression *yield* strength, but for metals, their ratio is fairly constant. Tensile strength is not quite in proportion to yield strength for some alloys, but, if you can't find yield strength, tensile strength will get you close enough. Matweb does provide you with tensile yield strength so that's the best figure to use for comparison among titanium grades.

The last one should be noticeably more resistant to permanent bending than the first.
BTW, is there a reason you're using titanium for this job? If weight isn't an issue, then consider the fact that 410 stainless steel, for example, has about the same resistance to permanent bending (around 800 - 900 MPa) but roughly twice the resistance to springing (around 200 GPa versus 110 for titanium). In other words, it's no stronger, but it should have twice the resistance to flutter and so on. It's also close to twice as heavy as titanium, but that can't be a big deal with a 0.030" thick fin.
-- Ed Huntress
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Thanks again Ed, so high tensile strength is what I'm after.
Actually weight is a huge factor, these are for record attempt boats and any weight on the right sponson has to be minimized to help counter prop-walk. I'm running in a class that has a 120+ mph record and my buddy I mentioned just broke the record in his class running 103+, here's pix if you're interested:
http://gallery.intlwaters.com/thumbnails.php?album 02
Here's the fin I'm talking about on my hull:
http://gallery.intlwaters.com/albums/userpics/10068/normal_ScanImage011.jpg
Wonder if one of the magnesium alloys might be better?

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Oh, those are cool, Terry, and they look like a lot of fun. We were discussing here recently that my uncle raced model hydros like that in the 1930s, in a 35cc IC class and in a steam class (he used gasoline-fired flash steam). I sure wish I had the photos of those.

It looks to me like you have four engineering factors here: weight, hydrodynamic drag, stiffness, and strength. Magnesium has roughly the same ratio of strength/weight and stiffness/weight of most metals (titanium is somewhat out of line, having high strength/weight but low stiffness for its strength). So magnesium would result in a thicker, if somewhat ligher, fin.
I couldn't begin to evaluate the engineering options, but as a materials freak, the first thing I would look at is unidirectional boron-fiber aluminum composite. The second thing I'd look into would be a boron-fiber epoxy composite. I'm not making life easy for you with that one. d8-)
-- Ed Huntress
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Ed Huntress wrote:

Is this really a materials issue?
Or Temper?
--
(remove the X to email)

Now just why the HELL do I have to press 1 for English?
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If the object is to have the highest possible stiffness and strength for a given density, it's really a materials issue -- and metal-matrix composites look to me like the winner. Since the volume of material is low and the objective is very high, it may be worth the effort and hassle.
And it is a hassle. Just cutting the stuff can be a nightmare. BTW, most of the aluminum composites available today are not boron-fiber reinforced, but other ceramics, like aluminum oxide and boron nitride.
-- Ed Huntress
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Having the fin as thin as possible is the most important, then weight and strength. Looks like a heat-treated Ti alloy is in fact the best choice, other than some "unobtainium", LOL!
Thanks again for all your help, my goal is to travel our 330' course in 1.8 sec!

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Well, good luck. Let us know how you do with it.
-- Ed Huntress
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Sure will thanks!

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Guessing here, but maybe you are looking for Titanium-Nickel alloy (TiNi)?
If I remember correctly that is what the bows are made of on my glasses. You can bend them almost 90 deg and they will spring back to their original shape. Here is some info from a research project I found:
=="Tensile Properties and Transformation Temperatures of Ti-Ni Alloy Dental Castings Added Cu
Hisashi Doi, Equo Kobayashi, Takayuki Yoneyama and Hitoshi Hamanaka
Department of Metallurgy, Division of Biomaterials, Institute of Biomaterials and Bioengineering, Tokyo Medical and Dental University (2-3-10, Kanda-Surugadai, Chiyoda-ku, Tokyo 101-0062) Original Paper: J J Dent Mate Vol. 20 No. 1 48-53 (2001) Keyword: Titanium-nickel alloy, Superelasticity, Mechanical properties
The application of the Ti-Ni base alloy to dentistry is expected to utilize its shape memory effect and super-elasticity properties. The transformation temperature changes when part of the nickel in a Ti-Ni alloy is replaced with copper. In this study, the super-elastic property of Ti-Ni alloy in which part of the nickel was replaced with 10mol% of copper was investigated, and the application of this alloy to dental casting was also examined. The results of this study showed that the super-elasticity of dental casted Ti-Ni-Cu alloy with 10mol% of replacement copper was good and that this maybe a useful method of reducing the quantity of nickel in Ti-Ni based alloy." == From Mat-world:
Titanium Nickel Alloy TiNi Alloy Ti-Ni (50:50 wt%) Ingots, Wires, Sputtering Target, Sheet, Plate, Disk
http://www.mat-world.com/En_elements/ti.html
Maybe this is the stuff you are looking for or could use...
--
Leon Fisk
Grand Rapids MI/Zone 5b
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Thanks for the reply, but no, I need to put a slight bend in it, just need it to be stronger than the annealed stuff I have.
Found out the "other" alloys (662, 6242, 6246) harden better than good 'ol 6-4, so I'm looking for something like this:
http://www.matweb.com/search/DataSheet.aspx?MatID 246&ckck=1
Tensile way up there and quite a bit harder too. Turns out that finding heat-treated Ti isn't that easy, most of the robot places and surplus on e-bay only have annealed.
Anyone have any idea where to fin a small amount of 0.025-0.030" hardened sheet?
TIA

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On Fri, 9 May 2008 08:48:28 -0400, "Terry Keeley" <tkee(no

No idea, but I would try being honest with some of the big suppliers and see if they might help. Just send out some email explaining what you what to try and the application for it and see what happens. Sometimes these places will help the little guy out.
I found this place that seems to have something like what you want:
http://www.harveytitanium.com/productline/6Al2Sn4Zr2Mo.aspx
I think this place is related to the previous:
http://www.rolledalloys.com/trc/6Al2Sn4Zr2Mo.aspx
and a ThomasNet search:
http://www.thomasnet.com/products/forgings-aircraft-aerospace-30870257-1.html
Good luck...
--
Leon Fisk
Grand Rapids MI/Zone 5b
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Thanks much, I did look at Harvey Titanium and may just make some calls...
wrote:

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On Wed, 7 May 2008 19:34:20 -0400, "Ed Huntress"

can you work harden titanium by hammering it to shape?
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Titanium alloys in general don't work-harden very much. Some, hardly at all. The stronger titanium alloys are hardened by precipitation hardening, much like aluminum and the precipitation-hardening stainless steels (17-7PH, A-386, etc.).
-- Ed Huntress
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I thought titanium alloys did work harden and that made them difficult to machine. In that you needed to get the tool under the work-hardened layer.
Dan
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wrote:

Not that I know of, Dan. Titanium has a reputation for not work-hardening very much. It's worth checking out, in the machining context, but I'm pretty sure that's the situation in general.
Titanium can be miserable to machine -- I remember doing some machining of it back in the mid-'70s -- but my recollection is that it was more tough and gummy than hard. But that's pretty far back in memory for me.
-- Ed Huntress
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Hmmm. I did a little looking on the internet and found sites that said Titanium work hardens about like 1020 steel, that is not a lot. But they followed this with warnings not to do anything that would work harden it. Possibly more because it will gall and also because it does not conduct heat well. So it sounds as if you can't harden titanium much by work hardening, you need to machine it as if it does work harden.
Dan
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