WEBVTT

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Steel and plastic.

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These two materials are essential to so
much of our infrastructure and technology,

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and they have a complementary set
of strengths and weaknesses.

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Steel is strong and hard,

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but difficult to shape intricately.

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While plastic can take on 
just about any form,

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it's weak and soft.

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So wouldn't it be nice if there
were one material

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as strong as the strongest steel

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and as shapeable as plastic?

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Well, a lot of scientists 
and technologists

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are getting excited about a relatively
recent invention called metallic glass

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with both of those properties, and more.

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Metallic glasses look shiny and opaque,
like metals,

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and also like metals,
they conduct heat and electricity.

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But they're way stronger than most metals,

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which means they can withstand
a lot of force

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without getting bent or dented,

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making ultrasharp scalpels,

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and ultrastrong electronics cases,

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hinges,

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screws;

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the list goes on.

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Metallic glasses also 
have an incredible ability

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to store and release elastic energy,

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which makes them perfect 
for sports equipment,

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like tennis racquets,

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golf clubs,

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and skis.

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They're resistant to corrosion,

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and can be cast into complex shapes
with mirror-like surfaces

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in a single molding step.

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Despite their strength 
at room temperature,

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if you go up a few hundred 
degrees Celsius,

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they soften significantly,

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and can be deformed into
any shape you like.

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Cool them back down,

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and they regain the strength.

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So where do all of these wondrous
attributes come from?

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In essence, they have to do with
metallic glass' unique atomic structure.

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Most metals are crystalline as solids.

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That means that if you zoomed in
close enough to see the individual atoms,

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they'd be neatly lined up
in an orderly, repeating pattern

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that extends throughout 
the whole material.

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Ice is crystalline,

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and so are diamonds,

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and salt.

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If you heat these materials up enough
and melt them,

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the atoms can jiggle freely
and move randomly,

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but when you cool them back down,

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the atoms reorganize themselves,

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reestablishing the crystal.

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But what if you could cool 
a molten metal so fast

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that the atoms couldn't 
find their places again,

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so that the material was solid,

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but with the chaotic, amorphous internal
structure of a liquid?

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That's metallic glass.

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This structure has the added benefit
of lacking the grain boundaries

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that most metals have.

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Those are weak spots where the material
is more susceptible to scratches

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or corrosion.

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The first metallic glass was made
in 1960 from gold and silicon.

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It wasn't easy to make.

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Because metal atoms 
crystallize so rapidly,

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scientists had to cool the alloy down
incredibly fast,

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a million degrees Kelvin per second,

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by shooting tiny droplets
at cold copper plates,

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or spinning ultrathin ribbons.

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At that time, metallic glasses could
only be tens or hundreds of microns thick,

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which was too thin 
for most practical applications.

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But since then, 
scientists have figured out

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that if you blend several metals
that mix with each other freely,

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but can't easily crystallize together,

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usually because they have very different
atomic sizes,

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the mixture crystallizes much more slowly.

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That means you don't have to cool
it down as fast,

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so the material can be thicker,

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centimeters instead of micrometers.

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These materials are called bulk
metallic glasses, or BMGs.

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Now there are hundreds of different BMGs,

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so why aren't all of our bridges
and cars made out of them?

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Many of the BMGs currently available
are made from expensive metals,

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like palladium and zirconium,

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and they have to be really pure

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because any impurities 
can cause crystallization.

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So a BMG skyscraper or space shuttle
would be astronomically expensive.

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And despite their strength,

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they're not yet tough enough
for load-bearing applications.

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When the stresses get high,
they can fracture without warning,

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which isn't ideal for, say, a bridge.

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But when engineers figure out
how to make BMGs from cheaper metals,

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and how to make them even tougher,

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for these super materials,

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the sky's the limit.