Metal: How It Works How It Works

This is the vibrant heart of a 21st century city.

There's something strange but wonderful about Piccadilly Circus.

Strange because, as far as the eye can see,

there's nothing natural.

There's not a tree, not a flower, not a blade of grass.

But wonderful because we made it.

We've transformed matter to create the world that we live in.

My name is Mark Miodownik, and as a materials scientist

I've spent my life trying to understand

what's hidden deep beneath the surface

of everything that makes up our modern world.

For me, the story of how materials have driven human civilisation

from the Stone Age to the Silicon Age

is the most exciting story in science.

Without our mastery of the stuff that we found around us,

we would have no buildings, no cars,

no roads, no art.

Nothing.

This series is the story of how we created our 21st century world,

how we unlocked the secrets of the raw materials of our planet

and created our future.

Gleaming, lustrous, volatile metals.

Everything around us is shaped by metal.

Metal has driven human civilisation - power, war, industry -

and yet it's mysterious stuff.

It's only in the last 60 years that we've begun to unravel

the secrets hidden deep within the metal at the atomic scale,

how it is that it can be strong enough to build empires

and yet soft enough that I can crumple it in my hand,

why it is that it seems inert and unchanging

and yet sometimes can behave almost as if it's alive.

Take a look at this. It looks like a normal paperclip,

but if I scrunch it up so it's unrecognisable

and then put a blowtorch on it...

HE LAUGHS

Isn't that amazing? Isn't that marvellous?

I mean, that is indistinguishable from magic.

This... This metal remembers its shape.

Normal metals don't do this.

We've engineered this metal to have a memory.

How we got from the Stone Age to being able to manipulate matter

and make metals like this is the story of this programme.

Let me take you back to when it all began -

the dawn of civilisation.

This is where our ancestors first settled.

It's where East meets West, where Africa meets Asia.

Underneath my feet, the Earth's crust is shifting.

And the geology here gave our ancestors

access to something that would change their world.

This is one of the first places on Earth

that man stepped out of the Stone Age

and transformed rock into metal.

And it all started with copper.

It's these green streaks that may have been the first clue

there was something a bit special about this rock.

Somehow, we worked out that when you've got this type of rock,

you can do something amazing with it.

We don't really know when our ancestors first discovered

what this marvellous green rock can do.

They might have just ground it up

to use it as a powder to decorate their pottery,

or maybe it happened to be just lying by the fire.

But either way, they discovered something really rather marvellous

about what this stuff can do if you add it to a fire.

Now, the thing about the fire is, you need it to be very, very hot

and for that you need a lot of air,

and that's why they built their fires on hillsides.

These hillsides are extremely windy,

so the air is being funnelled into the fire.

It's actually a genius idea.

And then, when they'd got a very hot fire,

they added the green rock.

And then they kept the temperature high for hours, and they waited.

So when the fire died down,

they would have found bits of a hard stone, black stone,

but amongst that black stone,

look, there's tiny little shiny bits of metal.

They'd transformed rock into metal, it's absolutely extraordinary!

Here we have rock... I mean, there's rock everywhere,

but they'd found the power of transformation.

Look! Look how bright that is! A bright piece of copper.

We know they did it on this hillside because we've found the remnants

from early smelting of our ancestors.

So they did that here,

and this was the beginning of human civilisation,

the age of metals.

Our ancestors realised that with copper,

they could make strong tools,

better than anything they'd had before.

This copper chisel represents the leap out of the Stone Age.

Everything we have in our civilisation today

is due to metal tools like this.

If they get blunt, we can sharpen them.

If they get bent, we can re-straighten them.

If they get damaged, we can repair them.

It's simply the perfect material for tools.

Nothing else our ancestors had in their world

could have done this - not stone, not bone, not wood.

So what's so special about metal?

It's all down to its inner structure.

Metals are made of crystals, and that's a very surprising fact,

because they don't seem to behave

anything like the crystals we are more familiar with.

I'll show you what I mean. I've got a quartz crystal here.

That's what you mean when you say "crystal".

And this is what a quartz crystal says when you hit it with a hammer.

You see? That's what we think of

when we think of crystals being hit with a hammer.

But if I say to you that this piece of metal is made of crystals,

you know already that it's not going to do that.

It's going to be quite malleable, I can do this.

In fact, that's how you work metal, you change its shape.

And that's...that's really strange, because that means

that the crystals in this metal are changing shape instead of exploding.

Inside the metal crystal,

the basic building blocks of everything in the universe, atoms,

are arranged in a regular lattice structure.

But they're not static.

When they're hit, metals can shuffle atoms from one side to the other,

like a Mexican wave.

They can move, rearrange themselves,

and this is why the crystal can change shape.

Metals alone behave like this.

As well as not shattering when you hit them,

they actually get stronger.

The impact creates waves of shuffling atoms

which collide with each other and create blockages.

These make it harder for the atoms to shuffle around,

making the metal stronger.

So the more hammering you do,

the more blockages you form in the crystal,

and so the stronger the metal gets.

It was the strength of metal over stone and wood

that became its main attraction.

With metal tools,

our ancestors could conceive of grandiose projects.

It's believed the limestone blocks that built the pyramids of Egypt

were carved using copper chisels.

But soon copper wasn't enough.

Our love affair with metals consumed us.

Here on the shores of what's now Israel,

metals from distant lands were traded.

And it was one of these, tin, that moved on the story of metals,

as our ancestors began to mix metals together.

So they took some copper...some tin,

and they melted them together to make a mixture,

which we call an alloy.

And they created a new metal, bronze.

Bronze was the creation of man the metal-smith,

rather than a gift of nature,

and it gave its name to a new era, the Bronze Age.

Now, this is a nail made out of pure copper,

and as metals go, copper's pretty weak.

Have a look at this.

After a while, it just can't get any further,

and so the metal itself buckles.

If I do the same with tin nail... let's see what happens.

Tin is actually softer than copper, even.

That's a real joke for a nail, isn't it?

But here's the odd thing.

The mixture, a bronze nail...

well, this is much stronger.

Ha-ha-ha-ha!

It's so strong it's knocking the wood out of this vice.

So that's odd, isn't it? You add two soft metals together,

and you get something much harder and much stronger.

How do you explain that?

In bronze, the tin atoms replace some of the copper atoms,

which are smaller.

This interferes with the lattice structure,

making it more difficult for the atoms to shuffle across the crystal.

This makes the new alloy much stronger.

The strength of bronze

gave us the means not only to build, but to destroy.

As well as tools,

we made the swords and shields of conquest and dominion.

Bronze propelled the evolution

of a new, complex, more technological society.

It also created new occupations,

such as mining, manufacturing and trading metals.

Bronze dominated the world for 2,000 years.

But it wasn't the metal to take us into the industrial age.

About 1200 BC, another metal rose to prominence.

Iron.

Iron is one of the most plentiful elements in the Earth's crust,

but it's fiendishly difficult to work with.

Owen Bush has spent nearly 20 years learning how to tame iron.

It doesn't look very promising

as a way to start a civilisation, does it?

-It's the basics, the beginning of it.

-So what happens next?

-You take this stuff...

-Heat it up.

-OK.

-And hit it.

Pure iron can't be easily extracted from its native rock.

There are several stages before it can be hammered into submission.

So this whole process of bashing it

and putting it back in the furnace is to get purer and purer iron.

-Yes, it is.

-You're trying to purify

this very strange substance that's come out of the furnace.

Yeah, I'm literally beating the crap out of it.

As Owen continues to hammer the iron,

more and more impurities are exposed to the air and burn off as sparks.

By bashing it, you're left with a purer metal.

This is wrought iron,

wrought at the blacksmith's anvil.

If you'd like to have a bash, by all means.

I would love to do that, I've never done that before.

Mastery of iron by our ancestors would not have been easy.

To show me just how difficult it is to work with, Owen challenges me

to make the simplest and most common of iron products.

Well, we're going to try and squash it flat and forge a nail out of it.

I know in theory what this stuff should do,

but I've never hit it with a hammer, I've never done what you do.

-That's good to go.

-OK.

Right.

-That's it.

-Oh, yeah, so there's bits flying off, I can really feel...

You can feel something happening in the metal.

There's a kind of response to you.

-There's something addictive to this.

-Yeah, it's primal, isn't it?

-Yeah!

-Now, yeah, back in.

-Back in, yeah.

You can see, when it came out, it was bubbling,

and as it cools down the...

Yeah, then I can see it becoming a bit brittle.

It sort of freezes in your hands and you're not making any headway.

Yeah, well, you're getting feedback from it,

and because every bit's different, you have to use that feedback

so you don't end up with a flattened, destroyed blob, fundamentally.

What I began to learn with Owen

is just how much of this process is trial and error,

how different iron ores could behave very differently.

All the variables of heat, of ore, of fuel

meant that the quality of your iron

depended absolutely on the quality of your blacksmith.

You're just hammering down to give it a bit of a head.

Lovely.

That's quite satisfying.

You got some good hits in there.

There we have our little nail.

What a beauty! My first nail.

And it was the iron nail

that was to underpin the next great civilisation.

The Romans were expert at manipulating iron.

Their blacksmiths travelled everywhere with them,

forging the weapons and shields of Empire.

But the Romans never built big with iron.

They were limited by what the blacksmith could do at his anvil.

And so, we would be constrained for another 1,500 years

until the next great step in our mastery of metals

a new technology that would unleash the Industrial Revolution.

Ironbridge Gorge in Shropshire was at the heart of this new revolution.

A man called Abraham Darby started making iron pots

and, almost overnight,

he turned this sleepy valley into the iron capital of England.

The key was the fuel.

Darby realised that, with fires made from coke,

partially burned coal, he could reach much higher temperatures.

And that would do something that would transform iron.

When it got hot enough, something happened

that opened up vast new possibilities for iron.

It melted and became liquid.

This was the birth of a new type of iron cast iron.

18th century engineers must barely have been able

to contain their excitement.

Now, instead of working iron at an anvil,

they could pour it into a mould.

And the mould could be any shape or size they wanted.

Darby's furnaces worked around the clock.

They turned the night sky red.

And the roar could be heard for miles around.

There seemed no limit to what this exuberant new industry could do.

And this was proof of it. It was built by Abraham Darby's grandson.

And it was the first iron bridge in the world.

This was a golden age of engineering,

when it seemed only our imaginations could limit us.

We crossed whole countries with iron railways.

We crossed rivers with iron bridges.

TRAIN WHISTLE SOUNDS

The engineers of the industrial world

were seduced into thinking that their every ambition was achievable.

But, the dreams were about to come crashing down.

On 1st June, 1878, the great and the good of Victorian Britain

were assembled by the banks of the River Tay here in Dundee

to applaud the opening of the longest bridge in the world.

It had been designed by Thomas Bouch,

an ambitious railway engineer, who may have considered

the Tay Bridge a stepping stone to a knighthood.

But, one dark winter's night in 1879 would change all that.

A train left Edinburgh, north, on the Aberdeen line.

Storms were raging across the country.

And when the train got to the Tay,

gale force winds were ripping through here.

As the train crossed the bridge, something terrible happened.

The iron girders cracked, and the bridge collapsed.

The train plunged into the icy waters.

There were no survivors.

It was a terrible human tragedy.

But what made it worse was that it was a man-made tragedy.

The pinnacle of our engineering achievement,

the iron bridge, had failed.

Nobody had any idea why.

It was a Victorian mystery.

I asked Rhona Rogers, from Dundee Museum, how events unfolded that night.

A couple of hours after the train had plunged into the water,

crowds began to gather on the north side of the bridge.

People looking for loved ones that were expected home

waited for news with none coming.

Tell me about Thomas Bouch, how did he react?

He was on the boat the next day that went out

to look for survivors or any signs of the wreckage,

and he was described as being in a very sorry state.

And he rapidly became very ill and then died a couple of months later.

He died from water on the lung, that's the official cause of death,

but a lot of people say it was shame and stress,

the shame and stress of what had happened, about his loss of career

and not becoming the success in life he had wanted.

How did the rest of the country react?

Was it just a local tragedy?

No, it was the longest bridge of its type at this time in the world,

so reactions were global.

It affected engineering on a world scale.

And it was a very personal thing for people in Dundee.

Quite significant, isn't it, that you can still see the remnants of the bridge now?

They're like tombstones, aren't they?

Yes, a permanent memorial to the dead, yes,

the 75 who lost their lives, of which only 45 were washed ashore.

The cornerstone of the Industrial Revolution - cast iron -

had failed catastrophically.

Now the burning question was, why?

In the immediate aftermath of the disaster,

there were many theories as to what had gone wrong.

I've come to Sheffield University to test my own theory.

Postgraduate students Ben Thomas and Lucy Johnson have designed

and built a scale model of one of the bridge's iron pillars,

and we're going to put it to the test.

So, just like in the real structure, you had these cast irons and this cross brace stuff

-is exactly how the piers of this railway bridge were constructed?

-Yeah.

'The corners of each pier of the bridge were made of cast iron,

'and that's what we're testing today.

'The first test is to see how good the pillar is at carrying loads under compression.'

'Could the cast iron have collapsed just under the weight of the train?'

Cast iron's supposed to be quite strong in compression,

so we've got a very simple compression test straight through the middle here.

'We started to apply pressure to the model.

'But before the pillar gave way, this happened...'

LOUD METALLIC CLANG

Oh dear, what was that? What happened there?

There's no obvious breaks, which is good news.

It may be that it started to crack up here on the test rig.

Really?

-So we might have broken the test rig...

-No, don't say that!

Lucy, give me hope.

-We can't see that anything's obviously broken with the bridge itself.

-OK.

So, the good news is that the bridge is stronger than our test rig?

It looks that way, yeah.

'Cast iron is known to be strong under compression,

'and the bridge had taken the weight of the train many times before.

'But there were other forces at play on the bridge that night,

'not least the strong winds.'

So, because of the wind, the gale force winds, there were forces

on these cast iron struts that would be making them bend that way.

They were all trying to bend over like a tree in the wind,

and the question is, can that material take that kind of force?

'In that situation, one side of the bridge will be compressed,

'but the other side will stretch.

'So I took a single bar from the model

'and this time I put it in a machine that tests the metal under tension.

'I'm going to see what happens when you stretch it.'

BANG

'With very little force, it snaps.'

'At the point where the bar broke is evidence of what makes cast-iron weak.'

Look at where it's fractured. There's this enormous hole there.

That is an impurity in the material which has very little strength,

and when you use a microscope to look at this material

you see not only big flaws in it, like these strange holes,

but deep inside the metal there are loads of little black blobs,

black-grey blobs, and they are a material called graphite.

They're embedded in the material, and there's no way to remove them,

you can make them smaller but they are always going to be in cast iron.

It's the very process of making cast iron that causes its weakness.

The casting process traps in many of the impurities

that a blacksmith would have hammered out.

The most important one is graphite - carbon.

It forms lumps that sit within the microstructure of the metal.

And it's these lumps that make the metal weak.

This is what graphite looks like.

You know it, because it's the stuff of your pencil.

It's a very weak material,

so if you have loads of this stuff embedded in your iron,

it's not surprising that that iron is going to be weak.

But back in the 19th century, this interior world of metals

was still hidden from us.

What it comes down to is this - we were building bridges out of iron

without fully understanding the material.

We needed to change our relationship with metal

from one of mastery to one of understanding.

All we really knew was that cast iron had failed us.

We desperately needed a stronger metal.

But the answer wouldn't lie in making the purist iron possible.

It would turn out to be far more complex.

The Victorian engineers looked to history for the strongest iron they could find.

The metal smiths of old used it to make swords of legendary strength.

They called it 'good iron'.

We call it steel.

Back in the forge, Owen is going to reveal the secret of good iron -

making the iron pure, but not too pure.

Following the techniques of ancient swordsmiths,

he hammers the iron and then folds, and heats and folds again,

exposing more and more of the iron to the air, so the impurities burn away.

So I'm just going to cut it in half...

Then bend it back on itself.

Back in the fire.

We had four layers, now we've got eight, next fold 16.

If this was to be the edge material of the blade I'd probably

take it up to somewhere between 700 and couple of thousand layers.

A thousand layers?

-So what's coming off the edge there?

-That's iron oxide.

-So that's its skin, really?

-Yeah.

'Through a combination of skill and experience the swordsmiths knew

'when their metal was pure enough to hammer into a blade.

'Then they added at touch of magic - it's called quenching.

'They thrust the red hot blade into a cooling liquid.

'When they drew it out again the edge had hardened.'

When you read the accounts written down about this process,

you find all sorts of weird materials,

like, people would get the urine of a redheaded boy,

or they'd get a goat which had only fed on the fern for three days

and they would quench into that - what do you think about this?

If it worked, if your master smith taught you to quench in the urine of a redheaded boy,

then if it worked for him there's no reason why you'd stop.

And, also it adds mystique, doesn't it?

'Technique and temperature worked a mysterious alchemy,

'creating a metal that kept its sharp edge.

'A metal with almost magical properties.'

The master swordsmiths had manipulated iron so skilfully

they had unwittingly created a totally new metal.

Steel.

The strong, reliable metal the Victorian engineers needed

to fulfil their growing ambitions.

But the problem is, as we've just seen,

it takes a huge amount of time, effort, expertise,

to just make this one, small blade.

So, if the Victorians were going to use steel,

they were going to have to learn how to mass-produce it.

And in order to do that they would have to find out what was going on inside this metal.

A clue would come from another feature of the swordsmith's art.

The pattern of the sword was the must-have mark of quality.

Dipping the swords in acid made the intricate swirling patterns,

created by the folding, twisting and hammering, become more pronounced.

This process was called etching.

And etching would be the key to revealing the secret of steel,

exactly what it was made of.

Here in Sheffield, in 1863, the single-minded dedication

of one man provided the flash of insight that changed everything.

Henry Clifton Sorby was perhaps the last great scientific amateur

in an age when science was becoming the concern of professionals.

Sorby pretty much invented the idea of looking at metals through microscopes.

He was ridiculed by his colleagues.

But he persevered, and it's lucky for as he did.

Here, I'm proud to say, I have in front of me

the original samples he first made.

Sorby prepared his steel samples in exactly the same way

as the ancient sword Smiths - he etched them.

And when he looked at the intricate patterns under the microscope,

Sorby discovered the secret of steel's strength.

This is a 150-year-old sample that he prepared.

Let me show you what he saw and no-one else had ever seen.

The microscope revealed that steel was a very pure form of iron, much purer than cast-iron.

But there's still a small amount of impurity there.

The dark bits that look like rivers are crystals that contain carbon.

It turned out the whole premise of the iron industry had been false.

Everyone had thought that what you had to do was beat out the impurities -

the purer the iron you could get the better it would be -

And they were wrong.

Instead, what was needed was precisely the right amount of impurity.

An alloy of iron and carbon in exactly the right proportions.

This is the crystal lattice of pure iron.

And this is steel.

Carbon atoms sit in the gaps between the iron atoms,

making steel much stronger.

But you have to have just the right amount of carbon.

In cast iron, there's too much carbon

and the spare carbon atoms form larger blobs within the crystal

and make the metal weaker.

Now we knew what made steel so strong.

But we were still in the dark about how to produce it cheaply

and on the industrial scale that the 19th-century demanded.

One day, a Sheffield-based engineer called Henry Bessemer

stood up at a British science meeting and shocked his audience

by announcing he could mass-produce steel.

It required no hammering, no beating, no folding.

He could make tonnes of the stuff in this, his Bessemer converter.

This huge bucket that Bessemer designed would have contained

an enormous amount of molten iron,

and that, of course, was full of carbon.

So what Bessemer suggested was that you made this pipe that goes down the bottom here,

and they pumped air through the liquid iron,

and that air contained oxygen, and the oxygen reacted

with the carbon to create carbon dioxide.

And Bessemer's idea was to just do that long enough to get

the carbon content of the iron down to about 1%.

And he designed these enormous cranks on the side here,

so when the carbon content of the steel is exactly right

you just crank the whole bucket over and out pours masses

and masses of this beautiful, liquid steel.

'I'm going to make steel in a way that's based on Bessemer's principle.

'Molten iron, which is full of impurities like carbon, is poured into a bucket.

'I blow oxygen through it,

'just as air was blown through Bessemer's converter.

'The oxygen reacts with a carbon to form carbon dioxide,

'removing most of the carbon.

'So you should be left with just the right amount of carbon to make steel.'

Well, the process may be simple, but it's insane.

I mean you are pumping oxygen or air through a liquid metal,

and it gets white hot and it's bubbling and you think,

this is fine, making a small cauldron of it,

but imagine making a bucket load of the stuff the size of this room!

That's what Bessemer was doing, and having a go at it

I realise quite how avant-garde he was.

What he was proposing was really extraordinary.

But the process had a major disadvantage - it just didn't work.

It was too difficult to hit precisely

the right amount of carbon - just under 1%.

Bessemer and his converter faced financial ruin.

But not for long.

British metallurgist Robert Forester Mushet came to his rescue.

He suggested they should remove all the carbon

and then add 1% back in.

It worked.

For the first time we could mass-produce high-quality steel.

We now had a metal that was strong enough

and tough enough to fulfil our ambitions.

The breakthrough made Bessemer's name,

but he had to be forced to acknowledge the part Mushet had played.

In the end, Bessemer had to agree to pay him

£300 a year for the rest of his life.

With mass-produced steel we'd cracked the problem of strength.

90% of the metal we make today is steel.

It's allowed as to travel across the globe by rail...

..by road...

..and by sea.

Strong, reliable steel enabled us to build great cities.

The construction industry would be nowhere without steel,

and the destruction industry benefited just as much.

But steel was not the answer to all our ambitions.

Aluminium would be the metal of the next century.

The century when the secret inner world of metals would finally be revealed.

The thing about metals is they all look roughly the same.

But they're not the same. This is steel and this is aluminium.

Aluminium is three times lighter than steel.

Here was the perfect metal to take us into the next age

the age of flight.

Except for one thing aluminium is just not strong enough.

Scientists around the world began to look for ways to make aluminium stronger.

Among them was the German metallurgist, Alfred Wilm.

Wilm knew that our ancestors had strengthened copper by mixing it with tin,

and what made steel strong was having the right combination of iron and carbon.

So, he set about mixing aluminium with other metals.

He finally ended up with an alloy of aluminium, copper,

manganese and magnesium.

He named it duralumin.

And then he thought, when you want to make really hard steel,

what you do is you quench it, so he took those alloys

and he put them in a furnace and he quenched them.

Here it is...

..and I'm going to quench it.

Now, once he'd quenched the alloys the moment of truth came.

Would it be as strong as steel?

No.

And this happened time and time and time and time again.

Until he could take the disappointment no more.

He stormed out of his lab and...

..went boating for a few days.

But while he was messing about on the river,

something remarkable happened.

Something that Wilm had neither planned nor even imagined possible.

This is the same alloy.

The only differences is it's a week later now, and watch this.

It's much, much stronger.

'And this is what Wilm found when he returned from his boating trip.

'Without Wilm lifting a finger, his alloy had transformed itself

'from a weak, bendy substance into a strong, rigid one.

'It was almost as though the lump of inert metal

'he had left behind was a living thing that had changed over time.

'It had grown harder as it aged.'

What Wilm had discovered was something called age hardening.

Let me show you how it works.

So, if this is a crystal of aluminium,

we know that's really soft.

What we need is something that's going to make it stronger.

Actually, he'd found an alloy which, when you leave it over time,

tiny little crystals grow inside the aluminium crystals.

They emerge out of a kind of atomistic mist, and it's those

that harden the crystal, they make it stronger, they reinforce it.

As new crystals grow, they interfere with the lattice,

and the aluminium alloy's ability to shuffle atoms and change shape.

This makes it harder and stronger.

Wilm had solved the problem of how to make aluminium stronger.

And he had also revealed metals to be mutable, almost living materials.

So many of the great discoveries of science come by happy accident.

From Alfred Wilm's despair came a new understanding of metals,

an understanding that would finally allow us to conquer the skies.

His alloy, duralumin, was used to make the fuselage of the Spitfire -

the only Allied aircraft to remain a front line fighter throughout the Second World War.

War forced the pace, with new and better alloys.

Peacetime brought the desire for passenger flight.

We were about to push metals harder than ever before.

In great secrecy, the De Havilland company here in Hertfordshire

embarked on an ambitious plan to build the world's first commercial jet aircraft,

to tame and harness changeable, mutable metal

and build a plane strong and reliable enough

to soar twice as high as man had gone before.

The plane was the ultimate in modern technology.

It went higher and faster, and boasted a pressurised cabin

for the comfort of the jet age passengers and crew.

It was also the most tested aircraft of its time.

Mike Ramsden was one of the test engineers on this,

'the De Havilland Comet.'

Can you remember the moment when you stood on an airfield

looking at this Comet taking off, the comet you'd tested?

It was...

It was like watching something from outer space, it was so...

..new, and it sounds corny, doesn't it?

But there was nothing else like it in the world.

When the crew were up at double the height

and double the speed of propeller airliners,

they just couldn't believe it,

being able to see both sides of the Channel at the same time.

And flying high, you had pressurised the cabin.

Yes, this was a very big engineering challenge.

To pressurise the fuselage

so that human beings could survive at that height.

It was the way to go, it was the way to fly.

It was the way to arrive.

It seemed that a golden age of air travel had dawned.

But it was about to turn to disaster.

A year to the day after the first passenger flight,

a Comet disintegrated in midair, killing everybody on board.

Within months, two more Comets had crashed into the Mediterranean.

The entire fleet was grounded.

There was something going on at the heart of metal we didn't understand.

Did the whole staff, you and all your workmates,

did you all feel responsible?

Did we feel guilty, you mean, of killing 100 people?

Yes, is the short answer.

Finding the cause was now the priority for Mike

and his colleagues.

They knew metal was a mutable material,

that it could suffer from a damaging phenomenon called metal fatigue.

They had tested extensively for this.

But what they couldn't predict were the effects

of this extreme new environment and the pressurising

and de-pressurising of the cabin needed for high altitude flight.

The real problem was a combination of factors,

one of which was that this aircraft had to go higher

than ever before, up five miles high, which caused a compression

and decompression of the fuselage,

so you have it almost breathing in and out, in and out,

every time it takes off and lands.

The stress of constant pressurisation and de-pressurisation

eventually tolled on this aeroplane.

Metal will break if you bend it often enough.

In the Comet's fuselage, tiny fatigue cracks appeared.

What began as a very small fracture close to a window

spread in to a catastrophic crack.

The whole aircraft came apart mid-flight.

The cause was a combination of metal fatigue

and concentrations of stress within the fuselage.

It's a weird quirk of fate that these windows were square

because that's exactly the wrong shape

if you want to minimise the concentration of stress.

So at the corners the stress is all concentrated

and started forming little cracks,

it was those that were the big problem.

Today we know that you mustn't have square windows

in these kind of pressure structures.

If you look at any aircraft today, you'll never see a square window.

Comet changed everything.

New regulations would make sure that metal was replaced

before it became fatigued.

But the most important lesson we learnt was just how little we knew.

Extreme conditions were causing extreme reactions

inside the metal that we didn't understand.

We desperately needed to see what was happening

deep inside the metal crystal.

One young scientist was about to make a breakthrough

and I know him really well because a few decades later

he was one of my lecturers here at Oxford University,

Professor Sir Peter Hirsch.

Hirsch's team was one of the first to take thin foils of metal

and look at them under a brand new kind of microscope,

a transmission electron microscope,

which increased magnification by tens of thousands.

Hirsch would finally see inside the metal crystal

and what he found would send shock waves around the world of material science.

Meeting up with Professor Hirsch again,

he explained that in the 1950s there were theories

about why metals behaved as they did, but still no proof.

What was really needed was an experimental technique

which was universally applicable whereby you could see inside metals.

And that's what Hirsch discovered.

This is the film he took of his original experiments.

He saw for the first time deep inside the metal crystal,

where, incredibly, the metal looked like it was alive.

Those moving little lines and loops are the Mexican waves of atoms

shuffling across the metal crystal.

They're changing the shape of the crystal.

Suddenly everything fell into place.

The technique revealed a new micro-world, if you like,

inside a metal.

You suddenly saw the inside of a metal

and all sorts of things were revealed.

It was very, very exciting.

We were now in a position to prove

what had previously only been guessed at...

That metals were dynamic crystals,

that these ripples were caused by atoms

shuffling within the crystal, changing the metal's shape.

This explained what we'd known for centuries, but never fully understood...

Why metal would change shape

rather than crack when it was hit with a hammer.

And also why it became stronger when it was alloyed.

It showed that designing the internal architecture of metal

was the key to progress.

Microscopy finally allowed us to master the micro-world of metals.

Hirsch's breakthrough reignited our passion and belief for metals.

We could start to design our own metals,

and there was a huge flowering of metallurgy.

There seemed to be no problem we couldn't solve.

'And we were facing another.

'How to get a metal to work in the most extreme environment on earth.

'A jet engine.'

Let me show you what I mean.

Inside jet engines,

is an incredibly difficult place for metals to be.

Extremely hot temperatures.

Extremely high stress they had to put up with.

So they had to design a new alloy

that could cope with this environment.

And it was called "superalloy".

So-called because it was so super.

Here's a bit of it here.

I'm going to pit it against our old friend steel,

who, of course, we know and love.

I'm going to hang weights off these two wires.

It's the same weight, in both cases,

and they're the same thickness of wire.

So, now they're under the same stress.

Now, I'm going to make it harder for them,

because they'll have to hold that up while under huge temperatures,

which means me putting a blowtorch on them.

OK, are you guys ready? Let's go.

So, the steel wire succumbed within a few seconds.

And that's only a fraction of the heat inside a jet engine.

I could be here all day with the superalloy.

This superalloy can take this.

I know these metals all look the same, but inside this superalloy

is the most-exquisite microstructure,

that was designed for this purpose.

To control the movement inside the metal,

and make it unbelievably strong at high temperatures.

'The cubes of material within the superalloy

'are called "gamma prime crystals".

'They sit within the alloy,

'affecting its ability to change shape.

'Which makes it incredibly strong,

'even at temperatures close to its melting point.'

That's pretty impressive,

and, as the jet age progressed,

scientists and engineers pushed the technology,

to create more and more powerful engines.

'Superalloys were some of the strongest metals

'we had ever created.

'But the 21st century jet engine

'would push them to their limit.

'In this extreme environment,

'even superalloys will change shape.'

One of the things we love about metals is their malleability.

When it's red hot, it behaves like plastic.

You can make it into whatever shape you want.

This is wonderful stuff to make an engine out of.

But the problem is, when you're making an engine

that needs to be operating at temperatures

that are themselves red hot,

deep inside the engine, you've got engine parts

that really musn't change shape.

'These turbine blades operate at 1,700 degrees centigrade,

'and 10,000 RPM.

'If working in those conditions

'made them lengthen, even a tiny bit,

' a phenomenon known as "creep",

'catastrophe would follow.'

These engines are designed with the precision of a watchmaker.

Here, at the back of the engine, you can see the turbine blades rotating

within the casing.

If there's any creep in those turbine blades,

they'll hit the casing, and the whole thing will seize up.

And that must not happen.

Unlike with a car, there's no hard shoulder in the sky.

'Creep can affect any metal.

'In extreme environments,

'the boundaries where crystals join

'can become routes that atoms travel along, elongating the crystals.'

So, what can we do about creep?

Metals are made of crystals,

and if the crystal boundaries are the problem,

we can't take all the crystals out.

Or can we?

'This is the Rolls-Royce turbine blade facility, in Derby.

'An entire factory dedicated to making blades,

'which work right at the heart of a 21st century jet engine.

'Here, they're actually producing turbine blades

'from a single metal crystal,

'like a giant diamond of metal.

'These blades are resistant to creep.

'Paul Withey is a casting specialist at Rolls-Royce.'

This is where we cast the single crystal turbine blades.

This is the wax model of the blade.

What actually do is, as part of the assembly process,

we'll fit in the spiral onto the bottom of it,

to allow us to grow a lot of crystals in at the bottom.

One crystal is selected through a spiral,

and made to grow through the whole of the rest of the blade.

'This is astonishing stuff.

'We've conquered creep,

'by growing our own metal.

'The crystal boundaries that cause creep

'are prevented by the spiral tube,

'which stops all but one metal crystal getting through,

'allowing that single crystal to grow into the whole mould.'

It's amazing that one of our earliest activities with metal

was to cast it.

It's really where we came from, as a civilisation.

Here we are, one of the most sophisticated pieces of metallurgy

you can possibly do, and it's casting again.

Yes. And it's actually using the same process that was used

over 5,000 years ago, to make art and religious artefacts,

and here today is being used to make

some of the most hi-tech engineering components that you can find.

'In this age of single crystal turbine blades,

'it seems that we've finally understood how metals work,

'and how to make them work for us.

'Paul, and the engineers at Rolls-Royce,

'are all upbeat about the future of metals.

'But not everybody agrees.

'Some of my colleagues in material science

'are beginning to think we've outgrown metals.

'We've mastered them,

'and now we should move on to other materials.

'But should we dismiss them so easily?'

Metals are in everything around us.

The electricity that made that kettle boil

came down a wire, and that wire itself is made of metal.

Here's some.

It's copper.

So, the Copper Age is embedded in our homes.

It delivers all our electricity to us.

Then, the Bronze Age is still here,

for anyone who likes sculpture.

Beautiful, aesthetic material.

The Iron Age is here,

and steel?

We spent thousands of years honing this material to be strong, tough,

and ultra-sharp.

Let's not forget the modern metals.

We fly around with aluminium,

but it's in our kitchens, too,

in this lovely, wafer-thin metal,

which is just extraordinarily versatile.

But there's something a little sad about the history of metals.

Each one starts out as a revolution.

But, after a while, they recede, and we take them for granted.

But I really don't think we should.

If it wasn't for metals, we'd still be in the Stone Age.

Everything around us is shaped by metals. Everything.

It's that step-by-step understanding of the internal structure of metals,

the secret world of the metal crystal,

that's been a huge intellectual achievement.

Metals have driven civilisation forward.

And, in doing so, they've defined who we are as humans.

And that's something we should be VERY proud of.

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