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Ann R. Thryft
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Blogger
Re: Titanium turbine blades
Ann R. Thryft   12/7/2012 12:13:37 PM
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The cost of titanium isn't as astronomical as it used to be, based on information I've heard from several manufacturers that make fasteners, engine parts, and other components for the aerospace industry. Prices have been declining for a decade or so, as new sources have become available. Combining it with aluminum, as in this alloy, has helped to bring that cost down even more.

Dave Palmer
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Platinum
Titanium aluminide
Dave Palmer   12/7/2012 11:47:00 AM
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@Ann: Thanks for posting this.  Metals and metalcasting are two of my favorite topics.

Nickel aluminide has been around for decades, but it is difficult to cast, so it is only in the past few years that it has started to be taken seriously as an alternative to superalloys in turbine applications.  General Electric uses investment-cast nickel aluminide for the low-pressure turbine blades in its GEnx engines, and also uses a nickel-aluminide coating on the high-pressure turbine blades.  NASA did a lot of work to support this.

It will be interesting to see whether casting in this type of centrifuge is a practical manufacturing method.

tjoneill
User Rank
Iron
Titanium turbine blades
tjoneill   12/7/2012 10:52:19 AM
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Interesting article but there are some practical realities to overcome.

There are three types of blades in a modern gas turbine engine--fan, compressor, and turbine.  The fan blades form the large fan at the front of the engine that essentially acts like a propeller (or bird shredder) and operates at low temperatures.  FAA engine certification rules designate the fan blade a critical part as failure can result in conditions hazardous to continued flight.

Compressor and turbine blades are not considered critical in this respect as the thinking is even if a failure occurs and the engine is shut down as a result, the fragments exit the tailpipe with no hazard to continued safe flight of the aircraft.  One may argue that an engine shutdown is unsafe although the aircraft is certified to fly on one engine.  Blades are extremely high integrity parts.

Maybe this is a leap in metallurgical technology however we are a long way from replacing reliable and durable single crystal nickel superalloys with any titanium alloy in the hot section of gas turbine engines.  Current designs are running turbine inlet gas temperatures above the melting point of the nickel blade and vane materials--cooling is key here and this design requirement demands internally cooled blade and vane castings that are difficult to produce.  

The cold (compressor) section may be more suitable for the material although again current designs are pushing temperatures at the compressor exit above 1200F.   For fan blades applications, integrity will have to be demonstrated rigorously.  Composites are currently used in this application with great success to reduce weight. 

Also any practical use must consider the fabrication cost of the material which appears astronomical.

naperlou
User Rank
Blogger
carbon fiber composites
naperlou   12/7/2012 10:19:47 AM
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This is an interesting approach.  It will be interesting to see how they come up with a practical way to get the effect of casting in a centrifuge. 

GE is taking a different path.  They are using carbon fiber composites and ceramics.  This is another way to make these complex shapes. 

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