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Ann R. Thryft
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Re: Titanium turbine blades
Ann R. Thryft   1/3/2013 11:49:03 AM
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Warren, I'm not getting your drift. Can you tell us what you mean about South Africa as a (presumably undesirable) source of titanium?

warren@fourward.com
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Platinum
Re: Titanium turbine blades
warren@fourward.com   12/28/2012 3:44:03 PM
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South Africa?  You make my point.  Be careful of your suppliers.

 

Ann R. Thryft
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Re: Titanium turbine blades
Ann R. Thryft   12/28/2012 12:25:47 PM
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Russia isn't the only country supplying titanium: it also comes from South Africa, currently the second largest supplier, and elsewhere:
http://www.designnews.com/author.asp?section_id=1392&doc_id=251754



warren@fourward.com
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Platinum
Re: Titanium turbine blades
warren@fourward.com   12/18/2012 9:36:30 AM
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One problem I have with this whole thing is that Russia controls titanium. We could gear up for a new titanium world and Russia could cut us off. Look at the threats to the E.U. over natural gas? I would hate to be beholdin' to a belligerent government for my supplies. Remember tantalum just a few years ago?

Ann R. Thryft
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Re: Gravity
Ann R. Thryft   12/14/2012 12:50:17 PM
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Dave, thanks for weighing in on the discussion with your expertise in metals and casting processes. That's interesting to hear that the acceleration levels used in the ESA hypergravity research aren't actually as high as what's already being done in typical centrifugal casting.

Dave Palmer
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Re: Gravity
Dave Palmer   12/13/2012 4:44:49 PM
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@TJ McDermott: Casting in microgravity eliminates convective flows that normally occur due to density gradients in the solidifying metal.  This could eliminate macrosegregation.  On the other hand, I wouldn't expect macrosegregation to be a serious problem in ordered intermetallics like titanium aluminide.

Most of the microgravity casting research I've heard about is focused more on understanding the solidification process, rather than improving the microstructure per se.  By eliminating convection currents, it's easier to observe the effects of other variables, such as magnetic fields, on solidification.

20-g acceleration is actually a lot less than is typically used in centrifugal casting.  A typical centrifugal casting machine might produce something on the order of 75-g acceleration.  On the other hand, ESA's Large Diameter Centrifuge is very different from a typical centrifugal casting machine.

For the forseeable future, I would expect titanium aluminide parts to be made by either investment casting, forging, or powder metallurgy.

Ann R. Thryft
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Blogger
Re: Gravity
Ann R. Thryft   12/13/2012 1:22:32 PM
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TJ, I'm not sure I understand your question. Previous research on casting metals in space was apparently done only with microgravity, and definitely aimed at improving the microstructure. But this research, with a similar aim, uses hypergravity and results in a much lighter alloy. Given this context, can you clarify your question?

TJ McDermott
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Gravity
TJ McDermott   12/11/2012 12:28:41 AM
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The hypergravity casting process sounds like spin casting writ large.  But wouldn't one expect the molten alloy to begin separating by density?  I thought that was one reason for doing metallurgy in space, that eliminating gravity from the equation made for a better microstructure?

Ann R. Thryft
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Blogger
Re: Titanium turbine blades
Ann R. Thryft   12/7/2012 1:15:13 PM
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I agree, Dave, about the relative costs. I also agree with you and Lou: the big hurdle here is figuring out how an economical manufacturing method can be devised using that big centrifuge, or somehow duplicating its effect.

Dave Palmer
User Rank
Platinum
Re: Titanium turbine blades
Dave Palmer   12/7/2012 12:56:20 PM
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@Ann: The cost of raw titanium and raw aluminum are probably only a small part of the cost of making a turbine blade out of titanium aluminide.  As your article points out, titanium aluminide is difficult to process, and these processing difficulties are a big cost driver.

Centrifugal casting is a common way of casting hollow cylinders (such as pipes), but it sounds like ESA's Large Diameter Centrifuge is very different.  It would be interesting to know whether an economically feasible manufacturing method could be developed based on this work.

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