Kind: captions
Language: en
This is one of the most powerful jet
engines in the world. And it actually
runs at temperatures 250° C hotter than
the melting point of the materials that
make it up.
>> That's 12,200°.
>> So the question is, why doesn't a jet
engine just melt into a puddle? We are
right at the boundaries of the laws of
physics.
>> That is wild. It's at the same
temperature now as it would be inside
the jet engine. But here, they're
liquid. Every time I get on a plane, I'm
thinking, "This is never going to work."
>> And yet, it does work. Right now, there
are over 10,000 planes in the sky
powered by engines just like these.
Maybe you are on one right now. So, how
do they work?
This is a jet engine, specifically a
turboan engine. At the front is this
giant fan. During takeoff, these
rotating blades push 1.3 tons of air
backwards every second, and around 10%
of that air gets compressed. The
compressors force the air into
increasingly narrow chambers. They
compress the air to about 50 times
atmospheric pressure. And just by doing
that, the air heats up to around 600° C.
This compressed air is then forced into
the combustion chamber where fuel is
sprayed in through a ring of nozzles and
ignited. That chemical reaction gives
off a lot of heat. So the temperature
jumps to around 1,500° C. So now you've
got this high pressure gas from the
combuster that just wants to expand. And
now it's got an incredible amount of
thermal energy. But between the
combustion chamber and the outside air
is this
rows of turbine blades. So in order for
the gas to expand and get out, it needs
to push these turbine blades out of the
way. And in pushing the blades, that is
how it transfers its energy to the
engine. This is where all the power
really comes from. In modern jets, on
takeoff, each high-pressure turbine
blade is generating as much power as a
Formula 1 car. And there are 68 of them.
As the gas rushes through the turbine
and nozzle, its pressure drops from
around 50 atmospheres down to one, and
it expands by almost 20 times. And that
spins these turbine blades up to 12,500
revolutions per minute. The fan that is
pushing all that air backward and all
those compressors that squeeze the air
down, all of that is powered by the
turbines back here. It's a kind of
funny, really counterintuitive way to
think about an engine. It's what's
happening in the back that's actually
driving everything up front. As the hot
exhaust gas is shot out the back of the
engine, it pushes the engine forward.
That generates thrust. But did you know
that in a modern passenger jet, this
accounts for less than 20% the thrust of
the engine? The vast majority of the
thrust, over 80% of it, just comes from
that big fan at the front of the jet.
Remember how only 10% of the incoming
air gets compressed? The other 90%
bypasses all that. It's simply propelled
backwards by the fan. and it goes right
around the guts of the engine and comes
straight out the back. The fan pushes
that air backwards. So, the air pushes
the fan forwards. That's how you get 80%
of the thrust. It's basically a huge
ducted propeller. So, why do it this
way? I mean, why not compress all the
incoming air and put it all through the
combustion chamber and turbines?
Well, some fighter jets do exactly this,
and it makes for very powerful engines,
but they're also horribly inefficient.
To see why, remember that the [music]
impulse pushing the plane forward is
equal to the change in the momentum of
the air backwards. So, you've got
options. For example, you could push
twice as much air back half as fast, or
you could push half as much air back
twice as fast. Both will generate the
exact same impulse, but the kinetic
energy of the air is proportional to V
squared. [music] So it takes four times
as much energy to speed up the air in
the second case. And a lot of that
energy is just wasted in [music] the
exhaust. So ideally, you want to push as
much air backwards as possible with only
a [music] small change in velocity.
That's why jets have gotten bigger and
bigger over the years. and the
increasing fraction of bypass air has
the added benefit that it surrounds the
hot exhaust gases and that reduces noise
coming away from the jet. But there is
another major factor when it comes to
engine efficiency and that is
temperature. At cruising altitudes
around 35,000 ft the outside air is
around55°
C while inside the engine it's over
1,500°.
The hot high-pressure gas inside the
engine wants to expand into the much
colder, lower pressure air outside. It's
that difference that lets the engine
turn heat into useful work. But there's
a fundamental limit to how much work any
heat engine can get from that. It's
called the carno efficiency. It's equal
to 1 minus the temperature of the cold
outside air divided by the temperature
of the hot gas inside the combustion
chamber. So looking at this, you can
improve the efficiency of the engine in
two ways. Either fly where the air is
colder or raise the temperature in
[music] the combustion chamber. One
problem with that though is that it
turned the inside of a jet engine into
one of the harshest environments we have
ever built in which machinery has to
survive. To keep a turbine blade whole
and unaffected within an engine is like
putting an ice cube inside your oven,
turning up to max, leaving for work,
coming back after an eight hour shift,
and finding it still completely frozen
in the oven. That's what we've got to
try and do within that engine.
>> It sounds absurd.
>> Not only do the turbine blades sit in a
stream of gas that's over,500° C,
they're also spinning at 12,500 RPM with
the tip of each blade slicing through
the air at nearly 1,900 kmh.
Now, every blade wants to fly straight,
but it's forced to [music] spin in a
circle, which means something has to be
constantly pulling it inwards. That's
the centrial force. If you take a
representative 300 g high-pressure
turbine blade and run it at that speed
and radius, it has to be pulled inwards
with a force equal to the weight of 20
metric tons. That's roughly the weight
of two London double-decker buses
tugging on each blade as it spins, all
while they're glowing hot.
To make matters worse, at these
temperatures, oxygen wants to react with
the metal of the blades itself. And on
top of all that, the air rushing through
the engine often carries dust, sand, and
pollutants that can damage and erode the
surfaces inside. And somehow these
blades have to survive this punishment
for tens of thousands of flight hours
without deforming, cracking, or failing.
They really determine how efficient you
can make the engine because you can't
make the engine so hot that the blades
can't withstand that temperature. So
they determine the maximum temperature
of the combustion chamber and therefore
the maximum efficiency you can realize
with a jet engine. So what kind of metal
could possibly survive these conditions?
Well, we sent Veritassium producer
Amelia to the department of material
science and metal energy at Cambridge
University to put some different metals
to the test.
>> So this is the steel. This is the steel
sample. Yes.
>> Okay.
>> So, we got about 200 megapascals to
start with, which is sort of comparable
to some of the stress that's seen by
these components in real applications.
And we're going to put that stress on
and then slowly increase the
temperature. This is a mild steel. It's
relatively strong and easy to form into
complex shapes. It seems like a pretty
good bet for a turbine blade. And at
first, under this load and at these low
temperatures, it holds up pretty well.
We're essentially tugging on all the
atoms within the metal. We're not
breaking or forming any bonds. We're
just making them flex a little and that
slightly changes the spacing between the
atoms. And as a result, the metal gets
slightly longer. This resulting change
in size, specifically the per unit
change in length, is what we call
strain. Critically, at this stage, the
material is behaving elastically. If we
remove the load right now, the material
just snaps back to its original size. In
an engine, some elastic deformation like
this will occur. It can't be too big or
it'll cause problems. But what we really
don't want is plastic deformation if the
shape changes permanently. And that's
exactly what starts to happen as we keep
increasing the temperature.
>> It's getting hot now. That's a little
bit of oxide.
>> There you go. See this starting to
deform.
>> Now bonds are breaking and reforming as
the metal atus deforms permanently.
But this doesn't happen all at once. So
I got the mechanical engineer on our
team, Henry, to build this demo.
Okay, so you can see we're getting a
bunch of tiny little bubbles. And just
naturally, they're packing into this
hexagonal arrangement. And there
actually a lot of materials that have
atomic structures just like this. But
you can see it's not perfect. Like right
here, you can see there's an extra half
plane of atoms. Well, in this case,
bubbles. This is called an edge
dislocation.
And it becomes really interesting when I
try to pull this raft apart. You can see
these little dark lines that zip back
and forth. Those are dislocations and
they move through the lattice. As the
dislocation moves, it'll cause one plane
of bubbles to shear past the other one,
which shifts the structure by exactly
one spacing. But there isn't just one
dislocation. There are plenty of them.
And altogether their movement produces
dramatic changes in the overall shape.
That's exactly what's happening here.
Everywhere that stress is high enough,
billions of dislocations are moving and
interacting. The steel starts to deform
continuously [music] under this constant
load in a process called creep. It takes
energy to break the atomic bonds as a
dislocation travels through the lattice.
So as we ramp up the temperature and all
the atoms get more thermal energy, it no
longer requires as much stress to break
these bonds. becomes much easier for the
dislocations to move. The metal
effectively gets softer. Now the steel's
strength drops so much that the slow
time dependent creep gives way to rapid
deformation. As it stretches, it rapidly
decreases in cross-section and
eventually the remaining metal can no
longer bear the load.
Now you could try doing similar tests
for other metals like this titanium
alloy. Titanium is about half as dense
as steel. Should feel that's quite a bit
lighter.
>> Yeah, it's like loads lighter.
>> So, if we were to make turbine blades
out of titanium, each blade would be
much lighter and that would reduce the
enormous centrial forces it would
experience. So, it seems like a great
choice. And at first, it performs really
well.
>> That's 100°. It's hanging in there.
>> But as we push the temperature higher,
>> oh, I can see some glowing.
Oh, look at it. Oh, it's gone already.
>> [laughter]
>> Just like the steel, its strength drops
rapidly as temperature increases. And
that's true for most metals.
Yet, the first jet engine dating back
all the way to 1941 actually did use
steel turbine blades. It was designed by
British pilot and engineer Frank
Whittle. His engine powered the first
flight of a British jet aircraft, the
Gloucester E2839 prototype. When a
colleague excitedly told Whittle,
"Frank, it flies." He dryly quipped.
That was bloody well what it was
designed to do, wasn't it? But Whittle's
prototype had two major flaws. The first
was that the gas inside the engine only
reached temperatures of around 780° C,
which was one of the reasons it was
inefficient. And the second was that it
was only allowed to fly for up to 10
hours. Any longer and it was too likely
parts inside the engine would fail. And
both of these drawbacks were largely due
to the steel turbine blades. Something
that occurred to me is why aren't they
made out of tungsten? I mean, because
tungsten doesn't melt until 3,400° C,
which is more than twice the temperature
inside a modern jet engine. But tungsten
is also incredibly dense. It's about 2
and 1/2 times denser than steel. And
it's also brittle, which makes it hard
to manufacture. And using a material
that heavy wouldn't just make the blade
a problem. The components that hold the
blade in the engine would also have to
carry much higher loads well beyond what
current materials can handle. So you can
optimize for one thing like the melting
point or a different thing like strength
or weight, but the turbine pushes every
variable to its limit. So what are these
blades actually made of?
Well, to find out, we went to
Rolls-Royce's precision casting facility
in Derby. And it turns out the world's
most advanced metal parts begin life as
well something surprising.
>> What is with the like the pink and the
green there? Well, I'll come and show
you. I'll come and show you.
>> I'm just seeing so many cool things
around here. Like what is that? Why does
it look like that?
>> You just enter this room and I smell the
wax.
>> Smells like a candle factory in here.
>> Absolutely. So investment casting is a
really really ancient technology. So,
our ancestors have been doing investment
casting to make jewelry, to make weapons
for millennia. We've just perfected it
here to make turbine blades. It's so
wacky. This is just not how I'd expect
it to happen at all.
>> Turbine blades strike me as one of the
most high-tech things in the world.
>> Yep.
>> And yet, this facility is using wax as a
starting point.
>> What [music] you will see through our
tour today is that actually it's a
really highly technological process.
This is our wax pattern die. This is how
a turbine blade starts its life. So this
is what's going to go inside the wax
pattern, a ceramic core. This is going
to create the hollow inside the turbine
blade. So what's happening now is we're
injecting into the dye. So that's the
the very start of the life of a turbine
blade.
>> That is really neat.
>> What we'll actually see is that a lot of
these features such as the aeraf foil
and the amul surfaces are not touched
further. So we will cast that and that
will remain as cast as it goes into the
engine.
>> Every surface here has to be perfect
because this wax is what will become the
blade.
>> So Kim is our wax pattern assembler. So
she's responsible for taking the product
straight from that dye. Making sure that
things like die lines have been removed.
So where the die blocks come together
and leave a small amount of flash. The
operative word in in all of wax assembly
is smooth. Every tiny imperfection in
the wax would become a flaw in the
metal. So this takes an incredible
amount of skill. Then it's a case of
getting that wax pattern attached to the
unit runner to create the assembly.
>> I mean the thought that occurs to me,
right? Shouldn't you be doing this with
a robot? Can't you know?
>> Yeah. Yeah. So, Rolls-Royce has
facilities that do this by robot, but
our facility in particular is very much
focused on bringing in those new
products, and it's far far easier for us
to [music] work with human beings to
develop that method of manufacturer
that's going to bring the next
generation of product through.
>> I'll bet I can see the skill here. Like,
it's phenomenal. I'll just make a mess
of it.
>> Absolutely. So would I.
>> Would you like to go?
>> No. [laughter]
>> Once the wax assembly is perfect, it's
ready for the next stage. Everything
that is wax is going to become air.
[music] It's going to become negative
space, right? It's going to become our
cavity. And then we're going to fill
that air with [music] metal. So, we take
that wax assembly and we've got to build
a shell.
Shell is made of many different layers.
It's a zirkon based uh shell system.
We're going to dip into a primary
slurry. It's really quite thin, like a
light syrup or a thin honey.
>> Oh, yeah.
>> And what that's designed to do is map
all of those really complex geometric
features. Beautiful. It's like making
icing.
>> So, that's actually the analogy we use.
So, it's a bit like if you put icing on
top of a bun or a cake, you need to
sprinkle it with some sugar afterwards.
Otherwise, it's all going to slop off
the top. So, we've got the slurry on
there. We're going to get a nice even
coat, drain it, make sure that it's an
even thin layer, and then we're going to
sand. And that's then going to set that
layer in place. So cool. Wow.
We're then going to dry it. So, it's air
dried for many, many hours. And then we
can create our backup layers. So our
backup layers, it's a much thicker
slurry, more like a treele. And the sand
is much coarser, more like a granulated
sugar. And we're going to maybe put
four, five, maybe even six layers to
back up because what we need is we need
a mold that can withstand the casting
parameters that we're putting it under.
You know, it's it's it's got a lot of
work to do. The wax is then melted out
and the mold is fired.
>> Oh yeah,
that is wild.
cleaned and tested to make sure there
aren't any cracks. When it's done, the
shell is ready to hold molten metal.
>> This is a billet of alloy that's going
to fill the whole of that mold. So, just
that amount of metal is going to fill
that whole mold there.
>> It doesn't look like enough.
>> This is a nickel alloy. The first nickel
alloys used in jet engines were
developed in the 1940s. By adding
chromium and cobalt, engineers created
alloys that could handle 800 to 900° C,
around 100° hotter than the steel used
before. And these alloys could keep
their strength for thousands of hours, a
10-fold improvement in life. But the
real [music] breakthrough came when they
added a touch of aluminum. So, we wanted
to see how it held up under the same lab
conditions as the steel and titanium.
>> What temperature are we at now?
>> That's uh 700°.
>> 700. And steel's long gone.
>> Steel's long gone.
>> That's 800°.
>> 800? Yes.
>> In fact, [music] around this
temperature, it's actually getting
stronger. So, why would heating a metal
make it stronger?
Well, when these nickel alloys were
first used in jet engines, no one
actually knew. But about 10 years later,
electron microscopes had improved enough
for engineers to finally see what was
happening inside.
As we zoom in on the alloy, a pattern
emerges. The micro structure isn't
uniform. Instead, it kind of looks like
a city grid made up of blocks with roads
in between them. Only each block is so
small over 300 would line up across the
width of a human hair. Now,
surprisingly, both the roads and the
blocks are made up of the exact same
atoms, mostly nickel with a little
aluminum. They even have the same
crystal structure, a grid of tiny cubes
with atoms sitting at the corners and at
the center of each face. The only
difference is that the atoms are
arranged slightly differently. In the
road structure, the aluminum and nickel
can take any spot. There is no repeating
sequence from cube to cube. And this is
known as the gamma phase. But in the
blocks, aluminum always takes the corner
spots and nickel the faces. And you get
a perfect repeating pattern cube after
cube. This is the gamma prime phase. And
it's this difference that is crucial
when a dislocation tries to glide
through the lattice. In the roads, this
motion is easy. Each layer of atoms can
shear smoothly past the next, [music]
leaving the structure looking unchanged
behind it. But if you try to do the same
thing in the blocks, well, now you're
actually changing the order of the
atoms. Nickel and aluminum end up
sitting in the wrong places. [music]
That takes energy, so the lattice
resists it. So when a dislocation moving
through the roads hits a block, it gets
stuck. And that's what makes this alloy
so strong. But if you keep pushing and
the stress gets high enough, dislocation
can finally force its way in. The catch
is that this dislocation leaves the
lattice in such a high energy mess that
the only way that it can keep moving is
if there's a second one right behind it
that puts things back in order. So in
the gamma prime phase, dislocations have
to travel in pairs called super
dislocations.
>> I need that creation of those super
dislocations and I need that very high
stress to be able to shear. So that's
why the strength is very high relative
to other alloys. What happens is
ultimately because you're shearing
through that gamma prime with two
dislocations. As the temperature
continuously increases, you're adding
more and more thermal energy in the
material. What happens is the atoms are
going to vibrate more and more and more.
So there's a likelihood as I'm doing
this and oscillating in three dimensions
that the thermal energy is going to
drive me to actually slip down rather
than just slip in one plane. So now if
one cross lips, they're no longer on the
same plane. Think of it as if we're
standing in in line and the only way
that you can move is if I push you,
right? And then I keep on pushing you
and then suddenly you drop. So if I now
try to push you, I I I cannot find you,
right? You're not in front of me
anymore. Your your your shoulders are
now below me.
>> Why are you touching? [laughter]
>> I should have used the other example,
you pushing me, but anyway, [laughter]
but it's exactly that. It's the it's the
exact same analogy. There's nothing to
push me anymore. there's like I am not
able to do it.
>> So now you've got these two dislocations
that are on different planes. So they
can't travel together anymore and as a
result they're both now locked into
place. And you can see that effect on
this graph. While steel and titanium
strength drops off in the nickel super
alloy you actually get a peak. That's
because the extra thermal energy lets
more dislocations cross slip and get
separated. [music] And it's that that
shuts down the motion of dislocations.
But if gamma prime is so strong, why
don't we just make the entire turbine
blade out of it? Well, that strength
comes at a cost. Gamma prime stops the
dislocation so effectively that it
becomes brittle. All it takes is one
crack or a sudden impact and it could
lead to a sudden failure. So, the real
trick is in striking the right balance
between enough gamma prime to trap the
dislocations and to prevent this creep,
but also enough gamma to keep the alloy
ductile so that it can bend without
breaking. And in our test, you can see
exactly how that plays out.
>> 1,000° and still nothing.
>> Still nothing.
>> There we go.
>> Oh my gosh.
>> That is That's,00°
C.
>> It's stretching.
>> I mean, it's still holding up like
>> it's doing a good job. That's 1200° C.
>> 1,200. That's a temperature program that
stocks and it's still surviving.
>> Still going.
>> But if you push the temperature too far,
even this alloy reaches its limits.
Cross lit becomes easier. The paired
dislocations can now hop between the
planes together. And the ordered cubes
of gamma prime start to dissolve. So the
dislocations break free and it finally
gives out.
>> Oh, it may have just uh Did it break?
>> Oh, yeah. Yeah, it did. It broke.
>> But strength alone isn't what makes
these alloys special. When you heat up
the alloy, aluminum at the surface
reacts with oxygen to form a thin
continuous layer of aluminum oxide.
Unlike the brittle oxides that form on
other materials like steel or titanium,
this layer stays intact at high
temperatures, protecting the metal
below. And by adding other elements, we
can tune these super alloys. Each one
brings a specific property that we want.
Most modern super alloys contain as many
as 10 different elements, all carefully
balanced in their relative abundances
for the desired properties. Chromium
improves resistance to oxidation and
corrosion. Cobalt, titanium, nobium,
tantelum, and venadium help stabilize
the gamma prime phase. Malibdinum and
iron strengthen the gamma matrix. And
then there's reinium. Reinium has one of
the highest melting points of any metal
at 3,180°
C. It's second only to tungsten. In the
nickel super alloy, it slows the atomic
scale rearrangements, enhancing the
alloys resistance to deformation, even
at temperatures above 1,000° C. It's one
of the rarest elements in the Earth's
crust at less than one part per billion.
And more than 80% of what we mine ends
up right here in jet engines.
But even with these advancements in
alloy chemistry, there's still one
fundamental problem, and that's that
metals are crystalline. Any metal you
see from the tip of this ballpoint pen
to the spoon in my coffee cup, they're
all actually made up of millions of
little crystals stuck together. It's
kind of like grains in this sugar cube.
If I crush it,
it's not like I've broken any individual
crystal. I've just broken them apart.
It's the boundaries between the grains
that are the weak point. And it's the
same thing in a metal.
So if we zoom out from the gamma and
gamma prime structure, it looks
something like this. One crystal is
basically a three-dimensional lattice of
atoms all lined up in the same
orientation. But the crystals themselves
are all in different orientations. So
where they meet, their lises don't line
up. And that mismatch leaves more open
spaces and broken bonds. And you also
get defects there like vacancies and
impurities. All of which make grain
boundaries the weakest point. And this
also has another consequence. It makes
it easier for atoms to move along the
boundaries. They become kind of super
highways for atomic diffusion. This
becomes even more of a problem at high
temperatures when atoms have more energy
to move around. Add stress like the
massive centrifugal loads on a turbine
blade and the grains can actually start
to slide past each other. The whole
[music] structure slowly deforms,
stretching almost like warm taffy. As
long as it has grains in it, it will
creep and fail far more easily. And
that's a really hard problem to solve
because normally as a molten alloy
cools, tiny crystals start to form all
throughout the liquid. So you have to
find some way to control them. This is
one of our furnaces. They're all
induction heated. There's no kind of gas
fire or anything like that. And they're
all under vacuum. So we only cast under
vacuum in the absence of any atmosphere,
but particularly oxygen, which is
obviously metallurgically going to cause
us all kinds of problems with oxides.
You start by pouring molten super alloy
into a ceramic mold that's mounted
vertically and heated to [music] about
the same temperature as the melt. The
mold fills from the root up toward the
tip. At the very bottom of the mold sits
a copper plate cooled by water. Its
surface is patterned with tiny grooves
that act as nucleation points for the
first crystals to start to form. It's
here that solidification begins. Then
the entire mold is slowly lowered out of
the hot zone. So the solidification
continues [music] in just one direction.
>> It's a very slow process in the
magnitude of hours. Once that's
finished, the whole machine will then
index round and it will push the
completed mold up out of the other side.
Oh
wow. So our casting temperatures are
roughly 1500° C.
>> It's kind of at the same temperature now
as it would be inside the jet engine.
It's absurd. Like you're making the
turbine blades at the same temperature
that they're going to operate, but like
here they're liquid.
>> Now, if we just did that on its own,
you'd end up with a blade that looks
like this.
Here's a directionally solidified blade.
And what you can probably see there is
the contrast between the grains. These
are all different crystals, but they're
all running on this axis of the blade,
which makes it significantly stronger
than an alloy that is cast where all of
the crystals are separate from each
other.
>> So, those are like individual crystals.
Is that
>> these are individual crystals? Yeah,
absolutely. So, we're we're looking at
at crystals on kind of a macro level
where normally we'd be talking about
crystals on a micro level.
In a rotating turbine, the blade is
being pulled along its length. With
columnar crystals all lined up along
this span, the blade can carry those
stresses far more effectively. There are
no grain boundaries that cut across the
blade, creating weak points [music] for
it to crack. But scientists have found a
way to do even better. If you introduce
a bend in the mold just above the chill
plate, something strange happens. The
number of columnar crystals that make it
through drops sharply. And if you add
another bend, even fewer survive. So
engineers added a helical passage known
as the pigtail here at the bottom of the
mold. The pigtail is doing the job to
select the single crystal. The spiral is
going to choke out every other grain bar
one. So we're only going to have one
grain that is then going to grow through
the entirety of that blade and cast that
blade as a single crystal. Or at least
that's the theory.
>> That's crazy. So this is a starter
attached to a spiral that we've etched
so that we can reveal that structure. So
you can see down at the bottom we are
starting to grow directionally
solidified grains. But as we get up here
we can start to see that we're growing
directionally solidified grains. And
then as we're going up the spiral
>> the grains are starting to be choked out
by the upper surfaces of that spiral
until when we get to the top we're just
as a single crystal. And then that then
allows that to grow right the way
through the blade.
>> That's amazing.
>> And what we should end up with is a
blade like this. So this is a blade of a
single crystal. It's a really impressive
thing to look at. The shimmer is
beautiful.
>> Yeah.
>> Even after the blade solidifies, it's
still not ready for the engine. It's
heated again almost to its melting
point. And that might sound risky
because we've spent all this time making
sure it's a perfect single crystal. But
this heating step lets the atoms shuffle
around just enough to spread out evenly
and form the final desired microructure
of the gamma and gamma prime phases that
make these super alloys so [music]
strong.
>> And as if casting as a single crystal is
not enough actually the orientation of
that crystal is also of paramount
significance. So you may have cast this
as a single crystal, but if the crystal
orientation is is off by a certain
amount, you get completely different
stress responses within that blade.
Today, after decades of development,
over 95% of blades can be cast
successfully as single crystals.
Just think about how incredible that is.
We've gone from a turbine blade that
contained on the order of 50,000 crystal
grains down [music] to just one. When we
grow these things, they don't solidify
as a uniform front. On a microscopic
scale, the solidification front looks
like a forest of tiny treelike branches
called dendrites that are pushing their
way into the liquid. At first glance, it
looks messy, like millions of separate
trees jostling for space. There are up
to 10 elements in there, each with its
own density and melting point. Yet
somehow every one of those trees is
locked into the exact same crystal
lattice. So the final crystal is
comprised of more than six * [music] 10
the 24 atoms. That is more stars than
there are in the observable universe.
And all these atoms are repeating the
same pattern perfectly aligned from root
to tip. This completely transformed what
jet engines can do. Single crystal
blades can withstand stresses and
temperatures that would destroy ordinary
alloys. They last up to nine times
longer against creep and thermal fatigue
and are more than three times more
resistant to corrosion than blades made
from multiple grains. That's why modern
jet engines can now run for 25,000 hours
between major overhauls. Something that
would have been unthinkable before
single crystal blades.
And the impact has been huge. Between
1960 and 2010, jet aircraft became about
55% more fuel efficient. And a huge part
of that improvement comes down to
advances in these nickel super alloys.
Back in the 1960s, flying was a luxury
few could afford. A one-way flight from
New York to Paris would set you back
$310, which is about $3,750
adjusted for inflation. But as engines
became more efficient, able to handle
hotter cores [music] and equipped with
much larger fans, airlines could carry
more people farther [music] using less
fuel. So tickets got cheaper and air
travel exploded. Today, at any given
moment, there are roughly 10,000 to
14,000 planes in the sky. That scale of
movement is possible because of these
turbine blades.
In the furnace, the nickel super alloy
outperforms all the other samples,
surviving up to,200° C. But wait, that's
still 300° less than the temperature
inside a jet engine. So why don't the
blades melt? Well, there are two final
layers of defense. The first is built
into the shape of the blade itself. We
then have to leech the core out. So we
do that in a in a costic solution of
potassium sodium hydroxide [music]
um under under pressure and temperature
to leech the core out. That will leave
those core passages uh completely empty
and those passages are the real secret
to the turbine blade survival.
>> So as the air is flowing through it is
turbulent and as such it can remove much
more heat from the surface of the blade.
Yeah.
>> Than is it these ridges here that we're
talking about?
>> Yeah, these ridges here. and they're
intentional to trip the trip the flow
>> trip and turbulate that air flow so that
it's removing as much heat as possible
[music] from the metal. So then we get
on to the really juicy part which is
film cooling. So we talked about the ice
cube in the oven stat keeping our blades
as cool as possible. So this is where we
start to drill in what we call film cool
holes. And what we're aiming to do is
we're aiming to get into those cooling
passages. So we saw that core earlier
on. They are the cooling passages
inside. And these holes have got to get
right into those cooling passages to
allow the air to come out. And the air
is then going to blow as a film over the
surface of the blade, a film cool hole
to create a film of air which is
preventing that metal from from melting
in those temperatures.
This cooling air isn't exactly cold. It
actually comes from the high pressure
compressor section of the engine at
around 600°.
But that is cool enough to help keep the
blades from melting. But it's still not
quite enough. And you can't just add
more cooling air because every extra bit
of air you use from the compressor you
lose from thrust and actually make the
engine less efficient. So every turbine
blade is also coated with two protective
layers. First, a thin metallic bond coat
that resists oxidation and then a
ceramic top coat. Even though it's only
about a quarter of a millimeter thick,
this ceramic coating can keep the metal
beneath it 100 to 170° cooler than it
would otherwise be. And this is the
final barrier that stops the blades from
melting. So now we've got this insane
piece of engineering that can survive
the 1500° gas, the intense [music]
load, and the oxidation problem should
be solved. Well, it would be except for
one thing.
At 36,000 ft, you wouldn't believe this,
but there's dirt and dust in the
atmosphere that our engines are
ingesting. The dirt and dust comes in,
it sticks on the blades, but it also
goes through the whole cooling circuit
and it blocks the cooling from getting
through to cool the blades and then the
blades burn up. Usually, every time I
get on a plane, I'm thinking this is
never going to work. [laughter]
No, I mean it's incredible how an engine
can work cuz there's so many moving
pieces. There's so many parts. The
environment's so terrible. And now we
have this dust and dirt which is really
bad.
>> I am at test bed 80 and they're about to
fire up this jet engine and then throw
dust into it. The same stuff that makes
up sand and volcanic ash. Exactly what
real engines encounter in flight. So
this engine is the 97K. It goes on the
A350 and is our higher thrust version of
that. So 97,000 pounds of thrust is what
this engine's producing. When we're
running a an engine like this, we try
and carefully recreate exactly what
happens in service.
>> How much dust goes in the engine?
>> Not very much. Um it was surprising when
I found out exactly how much we put in.
It's in the order of tablespoons worth
per cycle.
>> Start master on. Condition power on.
Master fuel lever on. Start request in
three, two, one. Now,
>> so what does the dust actually do inside
a jet engine?
>> So, once it gets through to the hot
section of the engine and hits kind of
turbine blades, it's going to be melted.
And so, uh, it sticks to the outside of
our turbine components and it slowly
rips layers of that, um, thermal barrier
coating off and then you lose your, uh,
temperature reduction that comes from
the barrier coating. So, your nickel
alloy underneath it gets hotter and
hotter and that's when starts to
deteriorate the turbine.
That's why engineers at Rolls-Royce are
still refining these blades, developing
new ceramic coatings designed to resist
molten dust and extend the life of the
turbine by up to 30%. That's just the
latest step in a story that's been
unfolding for decades. [music] These
blades have been refined and perfected
to the point where they operate right at
[music] the edge of what is physically
possible. You're always on a knife edge,
pushing every material, every process to
the limit to build an engine that can do
the [music] seemingly impossible, run
hotter than its own melting point. The
more I learned about the brutal
environment these blades have to
survive, the more it felt like they
shouldn't work at all. [music] And yet,
they do. Every day, these machines carry
millions of people across the world, and
we barely stop to think about them.
[music] They're a monument to human
ingenuity. What happens when we refuse
to accept limits? When we turn the
impossible into the routine.
I can't grow a single crystal turbine
blade in my kitchen, but with the help
from this video sponsor, KiwiCo, I can
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[music] Every few hours, my kids would
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had grown. They were totally fascinated,
and it sparked so many questions about
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Pretty soon, we were talking about how
metals are crystallin, too, and setting
ourselves the challenge of growing one
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And it's not just chemistry. They've got
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There is something for every age and
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>> and like hard to make, but not too hard,
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>> So, if you want to try out Kiwi Co,
click the link in the description or
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