timz
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Hi-bypass Fan Blades: What Metal?

Fri Jul 25, 2008 7:25 pm

An older high-bypass engine-- in the 1970s, say-- the fan blades are titanium alloy, or what? (A guy seems to think they aren't alloy, just pure titanium.) Were the blades on low-bypass engines (JT3D, JT8D) titanium or some other alloy?

Roughly what percentage of, say, a PW4098's fan blade weight is titanium?
 
KELPkid
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RE: Hi-bypass Fan Blades: What Metal?

Fri Jul 25, 2008 7:53 pm

The fan blades didn't have to take any exceptional heat like the compressor section or the exhaust disks do, so I'd imagine that in the fan section, it is probably the lightest alloy that will do the job (although in the fan, strength matters, as the fan has to be able to withstand bird strikes, stones, etc.). IIRC, Rolls-Royce used titanium for the RB.211 fan blades after the Holofil blade fiasco...
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Soku39
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RE: Hi-bypass Fan Blades: What Metal?

Fri Jul 25, 2008 11:09 pm

Having toured the factory that makes compressor blades for the engines on the A380, 737, ERJ 135/45/170, F-16 etc etc I can say that the vast majority of the blades were made of titanium. I do not however know what kind of metal is used for the turbine section.
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LY744
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RE: Hi-bypass Fan Blades: What Metal?

Fri Jul 25, 2008 11:19 pm



Quoting Soku39 (Reply 2):
I do not however know what kind of metal is used for the turbine section.

Nickel alloys AFAIR. Although I may be corrected by the real experts, I'm going to say that it's unlikely that pure titanium, or any other pure (element) metal, would be used in the engine. The fan blades are probably made from a Ti alloy.


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Soku39
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RE: Hi-bypass Fan Blades: What Metal?

Sat Jul 26, 2008 1:25 am



Quoting LY744 (Reply 3):
The fan blades are probably made from a Ti alloy.

Well of course, but it's not like they told a bunch of pilots their secret concoction, but the base metal that is alloyed with other things is far and away majority titanium.
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LY744
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RE: Hi-bypass Fan Blades: What Metal?

Sat Jul 26, 2008 1:32 am



Quoting Soku39 (Reply 4):
Quoting LY744 (Reply 3):
The fan blades are probably made from a Ti alloy.

Well of course,

I'm referring to part of the original question:

Quoting Timz (Thread starter):
the fan blades are titanium alloy, or what? (A guy seems to think they aren't alloy, just pure titanium.)

LY744.
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Soku39
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RE: Hi-bypass Fan Blades: What Metal?

Sat Jul 26, 2008 1:59 am

roger that, sorry about the misunderstanding.
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tdscanuck
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RE: Hi-bypass Fan Blades: What Metal?

Sat Jul 26, 2008 4:29 am



Quoting Timz (Thread starter):
A guy seems to think they aren't alloy, just pure titanium.

Early on, they could have been. Commercially pure Ti is a decent material in its own right, although the alloys are better. It's not nearly as bad as, say, pure Al vs. Al alloy.

Quoting Timz (Thread starter):
Roughly what percentage of, say, a PW4098's fan blade weight is titanium?

Probably about 90%. The most common Ti alloy in overall aircraft use is Ti-6-4 (6% aluminum, 4% vanadium)...although the fans may use something exotic, I suspect the alloying fraction is probably similar.

Quoting Soku39 (Reply 2):
I do not however know what kind of metal is used for the turbine section.

Tends to be very exotic nickel alloys with a variety of coatings, fancy casting processes, and basically every other known metallurgical trick.

Quoting LY744 (Reply 3):
I'm going to say that it's unlikely that pure titanium, or any other pure (element) metal, would be used in the engine.

Agreed, although pure Ti is a lot more useful that most other pure metals.

Quoting Soku39 (Reply 4):
Well of course, but it's not like they told a bunch of pilots their secret concoction

If fan blade repairs are allowed, it will be in the Engine Shop Manual. You can get the base material for any repairable part because the OEM has to supply the repair instructions (true for airframe structure as well).

Tom.
 
ex52tech
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RE: Hi-bypass Fan Blades: What Metal?

Sat Jul 26, 2008 4:40 pm



Quoting Tdscanuck (Reply 7):
If fan blade repairs are allowed, it will be in the Engine Shop Manual. You can get the base material for any repairable part because the OEM has to supply the repair instructions (true for airframe structure as well).

I remember looking it up back when I was overhauling CF-6's in TUL, but I can not remember the whole concoction. As I recall mostly titanium, and some other metals.

I know that the JT3D's were not pure titanium, but a blend. There was a version of the J57, that did have Titanium compressor blades, I believe it was the J57-P-29.
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jetmech
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RE: Hi-bypass Fan Blades: What Metal?

Sat Jul 26, 2008 11:25 pm



Quoting Soku39 (Reply 2):
I do not however know what kind of metal is used for the turbine section.



Quoting LY744 (Reply 3):
Nickel alloys AFAIR



Quoting Tdscanuck (Reply 7):
Tends to be very exotic nickel alloys

According to the following book;

Ashby, M. F. & Jones, D.R.H., (1996), "Engineering Materials 1, An Introduction to Their Properties & Applications" pp199, 2nd ed., Butterworth Heinemann

A typical Nickel based turbine blade alloy would consist of by percentage weight; Ni 59, Co 10, W 10, Cr 9, Al 5.5, Ta 2.5, Ti 1.5, Hf 1.5, Fe 0.25, Mo 0.25, C 0.15, Si 0.1, Mn 0.1, Cu 0.05, Zr 0.05, B 0.015, S <0.008, Pb <0.0005.

Quoting Ex52tech (Reply 8):
I remember looking it up back when I was overhauling CF-6's in TUL, but I can not remember the whole concoction.

I remember seeing the general concoction used by RR for their fan blades. I will try to get a hold of it and post here ASAP.

Regards, JetMech
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WPIAeroGuy
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RE: Hi-bypass Fan Blades: What Metal?

Sun Jul 27, 2008 12:36 am



Quoting Tdscanuck (Reply 7):
Tends to be very exotic nickel alloys with a variety of coatings, fancy casting processes, and basically every other known metallurgical trick.

I actually did a project on Superalloys, and lot of it focused on gas turbine blades. The blades are made of nickel and chromium alloys, one of the most common ones goes by the name Inconel, and there are many different versions of it. Superalloys have extremely high yield strengths, but most importantly they are very strong right up to their melting point. The gas temperature in jet exhaust is actually higher than the melting point of the blades, so cooling vanes are drilled to allow cool air to pass through the blades so they can operate in extremely volitile conditions. Another interesting fact is that all the blades are one single crystal
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tdscanuck
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RE: Hi-bypass Fan Blades: What Metal?

Sun Jul 27, 2008 2:16 am



Quoting WPIAeroGuy (Reply 10):
Another interesting fact is that all the blades are one single crystal

This is true of most current designs, but certainly not all. Single crystal blades are extremely expensive and only warranted in certain sections of the engine. They also didn't exist at the time that many of the engines currently flying around today were designed.

Tom.
 
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jetmech
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RE: Hi-bypass Fan Blades: What Metal?

Sun Jul 27, 2008 5:13 am



Quoting Tdscanuck (Reply 11):
They also didn't exist at the time that many of the engines currently flying around today were designed.

I would hazard the guess that most of the turbine blades of these engines would be directionally solidified.

Regards, JetMech
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WPIAeroGuy
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RE: Hi-bypass Fan Blades: What Metal?

Sun Jul 27, 2008 2:30 pm



Quoting Tdscanuck (Reply 11):
This is true of most current designs, but certainly not all. Single crystal blades are extremely expensive and only warranted in certain sections of the engine. They also didn't exist at the time that many of the engines currently flying around today were designed.

I did a case study on the Garrett ALF turbofans on the BAe-146, which had single-crystal Inconel turbine blades. Just a guess, but I'd assume any engine designed during or after the 70's would have single crystal turbine blades.

I konw early jet engines were extremely life limited, but once they became mainstream (Comet, DC8, 707) what was the average lifespan? Were those engines using steel alloys blades or nickel based?
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tdscanuck
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RE: Hi-bypass Fan Blades: What Metal?

Sun Jul 27, 2008 4:52 pm



Quoting JetMech (Reply 12):
I would hazard the guess that most of the turbine blades of these engines would be directionally solidified.

Agreed...directional solidification is quite a bit easier than single-crystal...they're actually basically the same technique, but one takes a lot more precise control than the other.

Tom.
 
baroque
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RE: Hi-bypass Fan Blades: What Metal?

Sun Jul 27, 2008 6:01 pm



Quoting JetMech (Reply 9):
A typical Nickel based turbine blade alloy would consist of by percentage weight; Ni 59, Co 10, W 10, Cr 9, Al 5.5, Ta 2.5, Ti 1.5, Hf 1.5, Fe 0.25, Mo 0.25, C 0.15, Si 0.1, Mn 0.1, Cu 0.05, Zr 0.05, B 0.015, S <0.008, Pb <0.0005.

Fascinating mix. I wonder if the Si and C are in there on purpose or just it is a lower threshold for them as must be the S and Pb numbers? Wonder what Hf does.
 
greasespot
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RE: Hi-bypass Fan Blades: What Metal?

Mon Jul 28, 2008 12:39 am

Anytime P&W used one of their patented alloys they called it Metal X.....Usually meant it was a trade secret and you are not authorized ti know what it is alloyed with.

GS
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jetmech
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RE: Hi-bypass Fan Blades: What Metal?

Mon Jul 28, 2008 3:15 am

Quoting Baroque (Reply 15):
Fascinating mix. I wonder if the Si and C are in there on purpose or just it is a lower threshold for them as must be the S and Pb numbers? Wonder what Hf does.

I'm not a metallurgist in any way shape or form, but I'll speculate nonetheless  .

I'd guess that Si and C were there to perhaps give desirable machining and working properties as opposed to any physical characteristics they may add to the strength of the mix. Perhaps they enhance the flow characteristics of the molten metal when the blades are cast? Perhaps it helps the process of directional solidification or the formation of a single crystal?

S and Pb strike me as something different however. They way it is written, it appears that they may actually be undesirable trace impurities in the mix. I often read metallurgical reports on component failures available from the ATSB. It appears that the initiation point of many metallurgical failures is at some impurity within the body of the component. Perhaps too much S and Pb would cause a non homogeneous cluster of material to form inside a component during casting?

Apparently, hafnium (Hf), serves to "increase the adherence of protective oxide scales on nickel based alloys. It improves thereby the corrosion resistance especially under cyclic temperature conditions that tend to break oxide scales by inducing thermal stresses between the bulk material and the oxide layer".

http://en.wikipedia.org/wiki/Hafnium

Regards, JetMech

[Edited 2008-07-27 20:16:41]
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baroque
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RE: Hi-bypass Fan Blades: What Metal?

Mon Jul 28, 2008 5:24 am



Quoting JetMech (Reply 17):
S and Pb strike me as something different however. They way it is written, it appears that they may actually be undesirable trace impurities in the mix.

I am sure that will be the case. The only thing that is odd is there are no specs for P which is usually a disaster for most alloys. (There was an ill-fated plan to develop a high P steel for use in brakes on UK trains because it had less of a tendency to spark, but - well the plan was ill-fated!!).

Thank you for the inf on hafnium.
 
OldAeroGuy
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RE: Hi-bypass Fan Blades: What Metal?

Mon Jul 28, 2008 3:19 pm

On the GE90 series, the fan blades are made of carbon composite.

http://ge.ecomagination.com/assets/g...ps/pressroom/press/050506_GE90.pdf
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acNDTTech
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RE: Hi-bypass Fan Blades: What Metal?

Fri Aug 01, 2008 4:42 am

The blades that I have inspected are Ti-6, various Ni alloys including Inconel (yes, Inconel.....I was shocked when I learned that), and carbon fiber. These of course are brand new blades. One of the biggest problems associated with blades though is the grain boundries, that is why various alloys are used - to get the desired g.b. Weaknesses between these boundries is what causes them to fail. In most cases where the g.b. could be a problem, a simple high resolution ultrasonic inspection is used to actually measure these boundries. The info is given to engineering and they are the ones that decide if the g.b. is too much.

When I have done inspections on blades that have already been in service, I usually use fluorescent dye penetrants. If I find an indication, I will use another method (visual, ultrasonics, and sometimes eddy current, or x-rays) to determine if the indication is relevant or not.

Today, composite materials are being used by some manufacturers. In the future though, look for ceramics to be used. Right now, the cost is too high - but when they get a better understanding of the manufacturing processes, the price will come down.
 
tdscanuck
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RE: Hi-bypass Fan Blades: What Metal?

Sat Aug 02, 2008 12:36 am



Quoting AcNDTTech (Reply 20):
Today, composite materials are being used by some manufacturers. In the future though, look for ceramics to be used.

I can see why you'd do this for turbine blades, but why would you want a ceramic fan blade? The fracture toughness will probably never be as good as metal or CFRP, the weight would be something else, and fans don't typically have a temperature problem (which is where ceramics really shine).

Tom.
 
777wt
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RE: Hi-bypass Fan Blades: What Metal?

Sat Aug 02, 2008 2:46 pm



Quoting Greasespot (Reply 16):
Anytime P&W used one of their patented alloys they called it Metal X.....Usually meant it was a trade secret and you are not authorized ti know what it is alloyed with.

What does the MSDS say on that material if blending needs to be done?  Wink
 
acNDTTech
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RE: Hi-bypass Fan Blades: What Metal?

Tue Aug 05, 2008 7:23 am



Quoting Tdscanuck (Reply 21):
I can see why you'd do this for turbine blades, but why would you want a ceramic fan blade? The fracture toughness will probably never be as good as metal or CFRP, the weight would be something else, and fans don't typically have a temperature problem (which is where ceramics really shine

It's just some of the things that certain manufacturers have been working on. The "toughness" is definately an issue that needs to be dealt with......you know how those R&D budgets go, use it or loose it. I do believe that we will see this though - in time.

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