
Rolls-Royce’s single-crystal turbine blade casting foundry - pcl
https://www.theengineer.co.uk/issues/june-2015-online/jewel-in-the-crown-rolls-royces-single-crystal-turbine-blade-casting-foundry/
======
fitzwatermellow
Fantastic read! Now why can't all technical and scientific journalism hold
itself to this standard? Instead of making the prevailing assumption that your
average reader has the I.Q. of a parsnip and the scientific literacy of a
kindergartener ;)

Have always felt single-crystal foundaries could be a great driver for
building low Earth orbit microgravity factories. There has been extensive
research in the labs on ISS dedicated to making highly spherical ball
bearings, long macromolecular protein crystals and extreme density refractory
metal composites. But is anyone contemplating large scale commercial
production? With the cost of delivery dropping, it seems like it might be a
idea worth re-considering!

~~~
cheeseprocedure
"The Engineer" is a trade publication, so its writers have a very different
target to hit than, say, those of a daily paper.

------
byebyetech
This is the best documentary on how RR makes the jet engine and the blades. 1
hour long but once you click it, it would be hard to stop!

[https://youtu.be/VfomloUg2Gw](https://youtu.be/VfomloUg2Gw)

~~~
akamaka
If you liked that documentary, you might love this older one, which features
Stanley Hooker. It's amazing to get the perspective of the legendary engineer
himself, and it goes much more in depth into the technical problems and
business challenges.

[https://www.youtube.com/watch?v=by4lH2whhjk](https://www.youtube.com/watch?v=by4lH2whhjk)

~~~
teh_klev
Haven't seen that before, hugely enjoyable and entertaining.

------
rayiner
For context:
[https://upload.wikimedia.org/wikipedia/commons/thumb/7/75/Tu...](https://upload.wikimedia.org/wikipedia/commons/thumb/7/75/Turbofan_operation.svg/2000px-
Turbofan_operation.svg.png).

The blade in the first picture would sit in the high-pressure turbine, just
behind the combustion chamber. Note that the flow path of a jet engine
corresponds directly to the pressure-temperature transitions of the Brayton
cycle, which governs the operation of gas turbines:
[https://www.grc.nasa.gov/www/k-12/airplane/Images/braytonts....](https://www.grc.nasa.gov/www/k-12/airplane/Images/braytonts.gif).

If you're wondering _why_ Rolls Royce goes to so much trouble to build turbine
blades that can handle high temperatures, see:
[http://web.mit.edu/16.unified/www/SPRING/propulsion/notes/no...](http://web.mit.edu/16.unified/www/SPRING/propulsion/notes/node27.html).

Also note that difference in size between the XWB's fan in the second picture
(of the article) and the turbine blade in the first picture. The XWB is a
high-bypass-ratio turbofan, which means almost all the air taken in by the
3-meter-diameter fan bypasses the core of the engine, generating thrust at low
exit velocity. Only about 1/10th the air goes through the core of the engine.
There, it is compressed, so by the time you get to the HPT, the flow path is
quite narrow. As the turbine section removes energy from the hot air, it cools
and expands, and the flow path gets wider.

------
vlehto
I'd like to note few things: single crystal is the best way to fight creep,
but that's it. This is very specific problem with very specific solution. For
most engineering problems you would prefer high fatigue strength or high
ductility. Single crystal is poor for both.

Another thing is that single crystal metal is very distinct from amorphous
metal. Neither has grain boundaries, but single crystal is very strictly
ordered structure while amorphic is completely disorganized. As a result,
single crystal tolerates high temperatures extremely well, while amorphic is
worse than regular metals.

Both are distinct from powder metallurgy. Which in turn has very high amount
of grain boundaries.

Interesting thing here is that in regular steel, the grains are single
crystals while the boundaries are often amorphic. So in a way you have
"composite" material. (It's not technically composite, because both substances
have same elements in same proportions.)

~~~
castratikron
Thanks for this. I'd think a metal would fracture very easily if there existed
a well defined boundary inside, which is what a crystal is. Seems like a
property you wouldn't want inside of a jet engine, but what do I know.

~~~
vlehto
When we talk crystals in material science it just means that the atoms are
organized. There are relatively few common structures.

[https://media1.britannica.com/eb-
media/37/1537-004-7657F6AC....](https://media1.britannica.com/eb-
media/37/1537-004-7657F6AC.jpg)

"Grain" refers to crystal that internally has that crystal structure, but
externally has whatever shape it just happens to have. Grain and crystal are
almost synonyms. Regular steel has grains inside, which then have atoms inside
organized in crystalline way. In between the grains are "grain boundaries"
which are not organized in any way. Different grains have different
directions.

If a crack starts to grow through steel, it first needs to penetrate a
crystal. It can go "easy" by following some plane that doesn't have any atoms
laying on it. Then it needs to go through amorphic (=disordered) boundary
region, but now the crack can't go easy. The next grain extremely is unlikely
to have nice plane continuing right after the first one. In practice the crack
will have to follow winding path and this long path will consume more energy
than short one.

Here is image of steel grain structure. The white are grains, the black are
amorphic boundary regions.

[http://www.scielo.br/img/revistas/jbsmse/v33n2/a13fig01.jpg](http://www.scielo.br/img/revistas/jbsmse/v33n2/a13fig01.jpg)

Practically making grain size smaller is one of the best ways to resist crack
growth (=fatigue strength). Other possibilities is to have different sized
atoms in the crystals, so there are no perfectly straight planes for the crack
to grow. And it's also possible to several different crystal structures in
different crystals. But also different structures inside single crystal.

Here is "pearlite" microscopic image. The black stripes are one crystalline
structure and the white ones are another. But they are well aligned and
therefore don't require any disorganized boundary when they are side by side.

[http://www.eng.utah.edu/~lzang/images/pearlite.jpg](http://www.eng.utah.edu/~lzang/images/pearlite.jpg)

Sometimes you get bullshit like excessive boundary precipitation. Like in some
stainless steels in certain heat treatments, the chromium relocates to the
grain boundaries. This leaves the base metal chromium free and makes it soft.
And also the grain boundary becomes lot more distinct entity. Now the crack
can easily travel along the boundary layer, as the pure chromium boundary is
not that well attached to the steel grains.

Also normal cast iron suffers from carbon flakes that are easy crack
propagating mediums. Metals attach to metals nicely, but carbon is not
metallic, so it's automatic weak spot. Broken cast iron can have almost black
cracking surfaces. For this reason guys invented "nodular cast iron". The
carbon makes little balls inside the iron, so it offers very little ways for
cracks. It has almost as good mechanical properties as steel, but is lot
easier to cast.

TL;DR Grain boundary is usually not distinct surface inside the material. It's
just where one way to organize atoms shifts into another way to organize
atoms. But it's still continuous solid.

~~~
castratikron
Okay, it's all coming back to me now. I remember in one physics class we
talked about magnetic grains. So this is the same thing.

When someone says "single-crystal", I think of a structure with zero boundary
regions, a structure made up of one big grain. This is what was in the title
of the article. Does that describe this turbine blade?

~~~
vlehto
Yes. Exactly.

------
orf
I had the chance recently to see the Mayor of the City of London's (the
strange city-within-a-city bit of London) two Rolls Royce's they keep for
formal occasions up close. They are super rare (only ~400 ever made), worth a
whole lot of money and looked _amazing_.

I'm not a car person but you can't help but feel a shiver when you see a car
like that. The engines where the same as the ones they used in the Spitfire
fighter planes during WW2 (6.5 liter v8!), full white leather interior, a
retractable partition between the passengers and the chauffeur.

I know this isn't strictly about the article but I thought I would share
anyway. Rolls is one of the things that makes me proud to be British.

Here's a picture: [http://c8.alamy.com/comp/C1ETKT/city-of-london-lord-
mayors-o...](http://c8.alamy.com/comp/C1ETKT/city-of-london-lord-mayors-
official-car-1984-6750-cc-rolls-royce-by-C1ETKT.jpg)

Edit: It's a Phantom VI - [https://en.wikipedia.org/wiki/Rolls-
Royce_Phantom_VI](https://en.wikipedia.org/wiki/Rolls-Royce_Phantom_VI), and
the first article on Google is unfortunately this:
[http://www.dailymail.co.uk/news/article-1165522/Lord-
Mayor-L...](http://www.dailymail.co.uk/news/article-1165522/Lord-Mayor-
London-8217-s-chauffeur-accused-drink-driving---boss-8217-s-200-000-Rolls-
Royce.html)

~~~
daemoncoder
Spitfires used v12's, not V8's.

~~~
orf
Ahh, shame, you're right. They where 27 litre as well! That would be a bit
extreme. Seems someone was silly enough to put it in a car though:
[https://www.youtube.com/watch?v=u43pWEwI6xY](https://www.youtube.com/watch?v=u43pWEwI6xY)

~~~
Sophistifunk
There are more of these projects than you might think. Final Objective (a 55
Chev) is the best, IMO: [http://www.australiastoughestcars.com.au/news/video-
merlin-v...](http://www.australiastoughestcars.com.au/news/video-
merlin-v12-powered-55-chevy/)

~~~
emmelaich
This guy "Lucky Keizer" made a 5l v-twin motorbike from a Merlin engine.

[http://www.abc.net.au/local/photos/2015/08/19/4296075.htm](http://www.abc.net.au/local/photos/2015/08/19/4296075.htm)

I saw it live once, unfortunately he couldn't start it. I suspect it's a
frequent problem.

------
cnvogel
Here's a recommendation if you are interested in understanding the basics of
turbine engines:

[https://www.youtube.com/user/AgentJayZ](https://www.youtube.com/user/AgentJayZ)

This guy, calling himself AgentJayZ, is a technician (not a designer) working
on mostly older industrial and military jet engines, and he's showing a lot of
the innards, and explaining a lot of the basics of operation of turbine
engines. Also: Loads, and loads of footage of running engines in test-stands,
which of course gets boring over time...

------
gertlex
This was a super fun read, and it felt nice to take the time to carefully read
it to understand the very complex processes it was describing.

That said, can someone explain how the pigtail accomplishes the following?:

> "The crystals grow in a straight line in the direction that the mould is
> being withdrawn, but because of the pigtail’s twisted shape, all but the
> fastest-growing crystals are eliminated."

~~~
hcrisp
By the principle of elimination by bottleneck. As the crystals grow into the
pigtail, the lagging crystals hit the already-formed leading ones or the mold
surface, leaving a primary, single crystal grain to exit the pigtail and grow
across the blade proper. This would be almost impossible to happen without the
pigtail because multiple crystal grains would grow in parallel across the
blade.

~~~
Animats
Here's a technical explanation.[1] But here's an example of triggering crystal
formation in a supersaturated solution.[2] Classic high school chemistry
experiment. Dropping a solid crystal into the supersaturated solution causes
the whole liquid to turn into a solid in seconds.

That's the basis of single-crystal casting. The solidification process relies
on operating very close to the melting point of the material. The idea is to
create an alloy mixture that's ready to crystallize, then starting the process
by dropping in a crystal and letting the liquid crystallize in a very
controlled way. The heated zone is moved through the liquid, as in zone
refining (or the solid is pulled from the heated zone, or gas cooling is used)
so that the crystal growth takes place in only a narrow layer.

This is decades old, and one of the reasons jet engines last a long time now.

[1]
[http://www.asminternational.org/documents/10192/6019788/amp1...](http://www.asminternational.org/documents/10192/6019788/amp17109p26.pdf/3def4e97-ace9-47e4-8661-2d7bc8f71f84)
[2]

~~~
FabHK
Where's [2]? Thanks!

~~~
Animats
Oops!

[https://www.youtube.com/watch?v=2Kud9eVbmRY](https://www.youtube.com/watch?v=2Kud9eVbmRY)

~~~
FabHK
Merci!

------
wbrocklebank
One other surprising thing about turbofans is that the majority of their
thrust is produced by the huge main fans (the blades which are visible as you
stand and look at the front of the engine) simply dragging the aircraft
through the air as with a turbo-prop (or boat prop). The ultra-high pressure
compression and burning stage (being discussed here) produces only 30-45% of
direct thrust but clearly powers the spinning of the large components.

My father-in-law started at RR as a graduate trainee and left 40+ years later
as its' longest serving member of staff, CEO and Chairman. he took me on tours
of these plants when I first met my wife which was an unbelievable treat.

------
porsupah
Animagraffs has a very good set of animated cutaways explaining how turbofan
and turbojet engines work:

[http://animagraffs.com/inside-a-jet-engine/](http://animagraffs.com/inside-a-
jet-engine/)

------
Justin_K
There is a cool How It's Made on these parts. Not sure if it's RR, but it
shows the complexity:
[https://www.youtube.com/watch?v=Qh9nvoRicKc](https://www.youtube.com/watch?v=Qh9nvoRicKc)

~~~
jtchang
It shows a box at the end with the GE logo. Crazy how precise the
manufacturing is.

------
filereaper
On this topic, I'd like to ask how 3D printed parts fair in the new engines
being built. [1]

I'd love to hear about this from a Metallurgical Engineer or a Material
Science Expert.

[1] [http://qz.com/667477/ge-fires-up-worlds-largest-
commercial-j...](http://qz.com/667477/ge-fires-up-worlds-largest-commercial-
jet-engine-using-3d-printed-metal-parts/)

~~~
phasetransition
My graduate research was on a corner of the class of ceramic materials that
are used as coatings on top of this type of turbine blades. Anything
specifically you would like to know?

Generally, single crystal blades are designed for their resistance to creep at
high temperatures. If your predominate creep mechanism is sliding at grain
boundaries in a polycrystalline material, you can impart creep resistance by
removing the grain boundaries. A single crystal is the limiting case of this
process.

3D printed parts, so far, are polycrystalline, and would be used in other
places in an engine's hot stage.

Happy to address specifics.

~~~
pcl
What sorts of considerations are important for the ceramic coating? I'd assume
that the coating is not under the same types of stress as the alloy core, and
so thermal properties would be more important. Is that true, or is load as
much of a factor there too?

~~~
phasetransition
I'm not deeply aware of the specifics of the mechanical loads near the surface
due to rotation. Generally the mandates are to match CTE between the substrate
and surface as much as feasible, and to insert a "bond" layer to help that
match.

The dominant concerns I am aware of are low thermal conductivity, thermal
stability, and lack of chemical attack in the environments in question.

------
sspyder
Not to take away from the engineering marvel that these parts and process
represent, but the timing of this article is interesting - seems PR related. I
recently read about problems ANA faced with Rolls Royce engines, specifically
the turbine blades failing. There have been at least 3 incidents of engine
failure, flights have been cancelled an all 787 engines have to be retrofitted
with new blades.

[http://www.reuters.com/article/us-ana-rolls-royce-hldg-
boein...](http://www.reuters.com/article/us-ana-rolls-royce-hldg-boeing-
idUSKCN1100X3?il=0)

[http://www.bloomberg.com/news/articles/2016-09-05/ana-
said-t...](http://www.bloomberg.com/news/articles/2016-09-05/ana-said-to-plan-
to-ask-rolls-royce-for-787-engine-compensation)

~~~
johansch
Also don't forget the A380 RR disaster-that-was-prevented-by-sheer-luck.

~~~
dredmorbius
???

~~~
jrockway
Guessing he's referring to this:
[https://en.wikipedia.org/wiki/Qantas_Flight_32](https://en.wikipedia.org/wiki/Qantas_Flight_32)

~~~
dredmorbius
That would fit, thanks.

------
doctorstupid
The high-pressure turbine is, in more ways than one, one of the the highly
optimised inner-loops of the modern world.

~~~
dredmorbius
Care to expand on that analogy?

------
akamaka
This technical paper has many pictures of the wax moulds and more details of
how the process works:
[http://www.journalamme.org/papers_vol32_1/32110.pdf](http://www.journalamme.org/papers_vol32_1/32110.pdf)

------
justinclift
For the curious, it's completely possible to buy used Rolls Royce turbine
blades on eBay. eg:

• [http://www.ebay.com/itm/331908581051](http://www.ebay.com/itm/331908581051)

Off topic side note - seems like someone's buying them, mounting them + spray
painting them at large markup:

• [http://www.ebay.com/itm/122000006766](http://www.ebay.com/itm/122000006766)

;)

------
cyberferret
Always clearly remember when I was studying for my commercial pilot licence
many years ago. In one class, an engineer took us for a tour of an airline
hangar. He stopped in front of an engine on a rig and explained that EACH
blade on the intake fan stage cost something like $40,000. That was about 4
times the price of the car I drove to that class!

~~~
userbinator
In aviation, everything is _extremely_ expensive due to the quality level
required.

------
M_Grey
It's really incredible to imagine blazing hot combustion products, and these
blades surviving in that environment for any length of time. Now I feel as
though I have a bit of a better understanding of how that comes to pass.

------
pif
Let me nitpick just a bit:

> the Riace Bronzes of Greek warriors found in the sea off Sicily

Well, Riace is in Calabria, not in Sicily. If you want to insert a nice quote
in your article, how difficult and time consuming can be to check on the
internet it in 2016?

~~~
samdoidge
Unnecessary nitpick. The sea is between Calabria and Sicily.

~~~
pif
Ehm, no, not really!

[https://www.google.it/maps/place/89040+Riace+Marina+RC/@38.8...](https://www.google.it/maps/place/89040+Riace+Marina+RC/@38.8103298,18.1975818,8z)

Same question for you as for the author: how long would have it taken to
check?

~~~
samdoidge
Your argument re: Off Calabria vs Sicily left an ambiguous zone. Showing Riace
Marina is much more convincing - I now agree :)

------
patcheudor
Look, I don't know what they are doing in UK facilkity's but I say leave those
kittens alone!

From the article: "Steve Pykett, Manufacuring manager, Rolls-Royce Advanced
Blade Casting Facilkity"

------
Gravityloss
And to think all this technology is used mostly for cheap holiday flights.

~~~
Samathy
And power multiple countries military aircraft fleets, as well a fair few
commercial and military vessels.

