Jet Engine: Turbine Blades and Temperature

[_Mayday_]

Hey!

I am trying to find some figures on the environmental conditions a turbine blade in a Jet Engine would have to withstand, and the materials that are necessary to prevent the blade from failing.

I have taken the example of the 'Trent Engine' or so I think it is called. I have read that temperatures in the combustion chamber can reach temperatures of up to 2000 degrees. Would this be the temperature that the blades are exposed to, or would there be a large variance in temperature. I say this because you would need an accurate measurement of the temperature, from which you would decide on which materials to use. I would have thought that the temperature would have been relatively similar to that as the blades aren't made of a single metal, but of ceramics or alloys. I'm sure you can see this isn't really a field that I know alot about but what other environmental factors would this material have to cope with? I can think of changes in pressure and the huge speeds the blades would move at as other problems.

Regarding the properties the material would have to possess I have considered Stiffness (Young's Modulus), Yield Stress, Plasticity (or the lack of it), elastic strain and the breaking stress of the material. I think Once I have a few material to work with I can research them.

I have google searched around but have found it difficult to actually find a site that answers my question directly while also allowing me to do a bit of reading around it. If anyone could provide me with a link or two I would be most grateful.

_Mayday_

[Astronuc]

Off the top of my head, Inconel 718 and 738 (738LC) are candidates, but I think there are more advanced alloys which are now used.

This might be of interest - http://criepi.denken.or.jp/en/e_publication/a1998/98seika11.pdf

CMSX4 is a more modern alloy.
http://www.patentstorm.us/patents/6299986/description.html
Table 1. Composition of Ni based superalloy CMSX4

Element Ni Co Cr Al Ti Ta Mo W Re Hf
wt% 61.7 9.0 6.5 5.6 1.0 6.5 0.6 6.0 3.0 0.1
at% 63.7 9.3 7.6 12.6 1.3 2.2 0.4 2.0 1.0 0.03
from - http://etd.library.pitt.edu/ETD/available/etd-07192004-165714/unrestricted/slaney_ms_etd2004.pdf (8.3 MB) use <save target as> to download

Historically - High-Purity Chromium Metal: Supply Issues for Gas-Turbine Superalloys (1995)
http://books.nap.edu/openbook.php?record_id=9248&page=22

Those should be good to get one started.

[FredGarvin]

Inco and Hastelloy are the two big older ones that come to mind. CMSX-4 is widely used because of the Rhenium content. However, along with material is the manufacturing process used. Most hot section blades are going to be single crystal formulations.

The 2000°F number is a good general number to go with as far as TIT numbers go.

http://www.c-mgroup.com/spec_sheets/CMSX_4.htm

[_Mayday_]

Thank you very much for all of your help. Astronuc, thanks for that link to the table, there were other parts of the paper that answered a few questions thanks.

When considering which materials to use, what environmental factors would you need to include. I guess the high temperatures would be one, but what else would the material have to survive?

[xArcherx]

I'm currently in the middle of my AVN (Aviation) course at CFB Borden. We just finished engines.

You're right about the temperature as a good average. The chamber doesn't melt because of a boundary layer of air that is intraduced through vent holes in the chamber liner. The temperature does decrease much between the chamber and the turbine blades. This is because you want the air to have this high energy. As the exhaust turns the turbines, they extract the energy from the air, causing it to cool down. Not really slow down. The whole idea of the plane moving forward is based upon the speed at which the exhaust is expelled out the back. Low volume of air expelled at high velocity as apposed to props which expel (displace) large volumes of air at low velocity. Newton's third law if I remember correctly.

The two types of materials commonly used is ceramic (already mentioned) and Nickel alloys (nickel alloys being the most common used for the fan blades while ceramic is used for the chamber). On top of the material is the design. Often the blades have vents. Cooler air is taken from the compressor section, diverted through these vent tubes and then expelled out the vent holes over the body of the blades. So the passing of cooler air helps keep the blades from getting too hot. The biggest enemy to turbine blades is the formation of stress cracks from the repeated heating and cooling.

An important thing to keep in mind is balance. As long as the entire turbine is well balanced, you won't have to worry about speeds in the subsonic range. The material will be well capable of holding the the turbine together under the centrifugal force (crack free, of course). Other than balance the another important thing is keeping the speed of the blades subsonic. When the blades pick up speed, the outer tips travel faster than the base of each blade. This means that the tips will reach super sonic speeds while the base is still subsonic. Besides the development of dangerous and damaging shock waves, there is also an unbalance of force between the supersonic and subsonic areas. The shock waves will also slow down the exhaust gases resulting in a drop of thrust. Unless the design compensates for such. Then you're talking new engines (like the scram jet). The formation of shock waves is also accompanied by an increase in temperature which can lead to uneven expansion and cracks.

[_Mayday_]

Thanks Archer!

Your help is much appreciated. Would anyone have like a time line of information on the 'evolution' of the turbine blade, with young's modulus and other material properties?

[_Mayday_]

How have the materials of the turbine blade changed over time in terms of their properties. For example I would think that the melting point of the material would have to have increased...

[xArcherx]

Both material and design has....

Improved in handling higher temperatures.
Improved in strength.
Improved in efficiency.
Decreased in cost.

Those sort of things.

[FredGarvin]

How have the materials of the turbine blade changed over time in terms of their properties. For example I would think that the melting point of the material would have to have increased...
Like I said in my post above, probably the biggest advancement has been in single crystal alloys. The properties most effected by material changes are strength (obviously) but also fatigue and creep resistance.

[_Mayday_]

I'm struggling to find any statistics showing what you have said, it seems to be hard to find information on this, as alot of the hits direct me to Wind Turbines. From the links provided I have gained some idea of what is in the blades these days, but finding evolution like statistics that show a general trend are somewhat more difficult.

[Astronuc]

Mayday, there may be a survey paper - somewhere - but it's probably buried out there.

Anyway, TMS (The Metallurgical Society) has a period conference on Superalloys, which covers materials for gas (combustion) turbines.

Meanwhile, try this -
http://www.eprictcenter.com/infocenter/ct_o_and_m/pdf/creep7_paper02_msw.pdf

[_Mayday_]

That's great Astro, really nice that. Figures like that are exactly what I am after, thank you very much :smile:.

[_Mayday_]

If you do find that survey let me know, otherwise thank you for all your help!

[Astronuc]

Here is a GE paper on their Advanced Gas Turbine Materials and Coatings
http://www.gepower.com/prod_serv/products/tech_docs/en/downloads/ger3569g.pdf


Cartech produces several superalloys
http://www.cartech.com/news/wr_age_harden_superalloys.html


Special Metals, High-Performance Alloys for aircraft, land-based & marine gas turbines
http://www.specialmetals.com/documents/gas%20turbines.pdf

Special Metals Corp, PRODUCT HANDBOOK OF HIGH-PERFORMANCE ALLOYS
http://www.specialmetals.com/documents/Product%20Handbook%20Part%201.pdf


NASA Report
NASA Contractor Report 174639
Literature Survey on Oxidations and Fatigue Lives at Elevated Temperatures
http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19840012606_1984012606.pdf

[_Mayday_]

Astronuc, those links are amazing thank you so much!

[_Mayday_]

Hey Again.

Does anyone have any data that would tell me which materials where used in the turbine blades over time? Almost like an evolution of materials? I've found this incredibly difficult, and also with these materials I would like to be able compare things like tensile strength, melting points etc. Any help would be great. Thanks!

[Astronuc]

Hey Mayday, see this related thread - "Chromium use in Gas Turbine Engines"
http://www.physicsforums.com/showthread.php?t=253554

The NIST article by Reed et al gives some trends. The actual history is hard to find and the current materials would be proprietary, i.e. not available to the public. Materials, processes and component geometry/design can give a particular vendor a commerical advantage if they can operate more efficiently and reliably, so that information is often considered proprietary or 'trade secret'.

Here's a site thnat maybe of interest -
http://www.ul.ie/elements/Issue6/Gas%20Turbine%20Blades.htm - perhaps one can contact them.

Welding material, gas turbine blade or nozzle and a method of repairing a gas turbine blade or nozzle
http://www.freshpatents.com/Welding-material-gas-turbine-blade-or-nozzle-and-a-method-of-repairing-a-gas-turbine-blade-or-nozzle-dt20070308ptan20070054147.php

(one can go to USPTO) and download the patents free - the patents may contain details of base metal (alloy) composition.


You might try to contact Rolls Royce or one of their suppliers, Doncasters, about materials.

Doncasters wins Rolls Royce Trent 800 contract
http://www.airframer.com/news_story.html?release=570
MELBOURNE, UK: Doncasters, the leading global manufacturer of precision components and assemblies for the aerospace industry, has won a contract worth €40m to manufacture low pressure (LP) directionally solidified (DS) investment cast blades for the Rolls-Royce Trent 800® engine. The Trent 800® is used in the long-range, wide-body and twin-engined Boeing 777 airliner.

The blades will be manufactured at Doncasters' Precision Casting facility in Bochum, Germany, a world class site dedicated to high volume cast superalloy blade and vane airfoils for high-temperature, tight tolerance applications for aerospace and industrial gas turbines.

Over $25m has been invested over recent years to make the site unique in its field in the manufacture of leading edge equiaxed, directionally solidified (DS) and single crystal (SX) castings. Bochum has its own manufacturing facilities for the production of superalloys and ceramic cores – capabilities include hot isostatic pressing (HIPing), heat treatment and world-leading liquid metal cooling technology (LMC). As all key manufacturing and supply chain processes are in-house, the site also offers complete supply chain management and the capacity to deliver large volume manufacturing to customers' tight and often changing schedules.

[Astronuc]

Here is an interesting dissertation - http://hdl.handle.net/1853/22637 - A Parametric Physics Based Creep Life Prediction Approach to Gas Turbine Blade Conceptual Design

Download the pdf. It contains a lot of good information.

See particularly page 44 (67 of 347 in the pdf) and figure 22, and the following section 1.5.2 Materials.

Also see - APPENDIX C - MATERIAL DATABASE METALLIC COMPOSITIONS

The list of references is excellent!

[_Mayday_]

Hey Astro thanks for the links, I will look at them now.

On this link in table 1 under Fe for some of the alloys it says "bal." what does that actually mean?

http://www.cartech.com/news/wr_age_harden_superalloys.html

[Astronuc]

Bal = balance, i.e. if one sums up the compositions of the alloying elements, one will obtain a number less than 1.0 or 100%, and the balance is the difference between 100% and the sum (in %) of the other elements. That table is bit unorthodox, because bal. normally refers to the main (base) element, and they are mixing steels (primarily Fe-based) with Ni and Ni-Cr superalloys.

That table (listing of Pyromets and Waspaloy) transitions from Fe-based to Ni or Ni-Cr based alloys. A-286 is a stainless steel (Fe-Ni-Cr) with 14.5 Cr and 25 Ni. Pyromet 718 (Alloy 718, Inconel 718) is a Ni-Cr-Fe alloy (52.5 Ni, 18.5 Cr, 19 Fe - Cr and Fe are about the same), and Pyromet X-750 (Inconel X750, incidentally developed for the X-15 project) is high Ni, Ni-Cr-Fe (72 Ni - 15 Cr - 9max Fe). Inconel is Inco's trademark alloy name.

Some tables don't even mention balance, so one has to know if the main (base) element is Fe, Ni, Co.

So one can refer to Fe-based, Ni-based, Co-based superalloys, where Fe, Ni, Co is the majority element and the other elements have lesser content, although the sum of other alloying elements could exceed the proportion of individual base metal.

[_Mayday_]

From that table 2 I want to pick out 5 or 6 of the alloys say 2Ni-based 2Fe-based and 2Co-Based or something like that and then link those figures to the one on temperature and stress rupture.

I thought something like

A-286
NCF-3015
Waspalloy
Pyromet 41
Pyromet 706

Is there another place where I could find the value for Cobalt? And what makes up the rest of those alloys as it doesnt add up to anything like 100%. Am I right in saying those figures are the percentage weight of the element in the alloy? Thanks

[_Mayday_]

Oh nevermind, I found another source, on the same site on like a fact sheet. They have like ranges, so I will average them I think, as I only want to gain an idea of trends etc.

[Astronuc]

Usually and by convention, such composition data are given in weight (mass) percent, because this is how alloys are made. At the manufacturer, there is a blend sheet/list for each alloy, and one takes so many kgs of the primary metal and adds the corresponding masses of each alloying element.

So one could take 1000 kgs or 10000 kgs and use the wt% to deterimine the necessary masses of alloying elements.

Speaking of trends - see - TRENDS IN HIGH TEMPERATURE ALLOYS (1998)
http://crswnew.cartech.com/wnew/techarticles/TA00006.html
Unfortunately it's dated, but that should give an idea of what's in service now.


Check this one out too - NEW REQUIREMENTS FOR FERROUS-BASE AEROSPACE ALLOYS
http://crswnew.cartech.com/wnew/techarticles/TA00003.html