1
00:00:06,791 --> 00:00:08,525
Steel and plastic.

2
00:00:08,525 --> 00:00:13,423
These two materials are essential to so
much of our infrastructure and technology,

3
00:00:13,423 --> 00:00:17,129
and they have a complementary set
of strengths and weaknesses.

4
00:00:17,129 --> 00:00:18,900
Steel is strong and hard,

5
00:00:18,900 --> 00:00:21,249
but difficult to shape intricately.

6
00:00:21,249 --> 00:00:23,885
While plastic can take on 
just about any form,

7
00:00:23,885 --> 00:00:26,072
it's weak and soft.

8
00:00:26,072 --> 00:00:28,424
So wouldn't it be nice if there
were one material

9
00:00:28,424 --> 00:00:30,616
as strong as the strongest steel

10
00:00:30,616 --> 00:00:33,507
and as shapeable as plastic?

11
00:00:33,507 --> 00:00:36,092
Well, a lot of scientists 
and technologists

12
00:00:36,092 --> 00:00:41,039
are getting excited about a relatively
recent invention called metallic glass

13
00:00:41,039 --> 00:00:44,290
with both of those properties, and more.

14
00:00:44,290 --> 00:00:47,509
Metallic glasses look shiny and opaque,
like metals,

15
00:00:47,509 --> 00:00:51,120
and also like metals,
they conduct heat and electricity.

16
00:00:51,120 --> 00:00:53,500
But they're way stronger than most metals,

17
00:00:53,500 --> 00:00:56,101
which means they can withstand
a lot of force

18
00:00:56,101 --> 00:00:58,449
without getting bent or dented,

19
00:00:58,449 --> 00:01:00,193
making ultrasharp scalpels,

20
00:01:00,193 --> 00:01:02,253
and ultrastrong electronics cases,

21
00:01:02,253 --> 00:01:03,089
hinges,

22
00:01:03,089 --> 00:01:04,132
screws;

23
00:01:04,132 --> 00:01:05,632
the list goes on.

24
00:01:05,632 --> 00:01:08,019
Metallic glasses also 
have an incredible ability

25
00:01:08,019 --> 00:01:10,755
to store and release elastic energy,

26
00:01:10,755 --> 00:01:13,133
which makes them perfect 
for sports equipment,

27
00:01:13,133 --> 00:01:14,258
like tennis racquets,

28
00:01:14,258 --> 00:01:15,320
golf clubs,

29
00:01:15,320 --> 00:01:16,700
and skis.

30
00:01:16,700 --> 00:01:18,219
They're resistant to corrosion,

31
00:01:18,219 --> 00:01:22,375
and can be cast into complex shapes
with mirror-like surfaces

32
00:01:22,375 --> 00:01:24,499
in a single molding step.

33
00:01:24,499 --> 00:01:26,812
Despite their strength 
at room temperature,

34
00:01:26,812 --> 00:01:29,202
if you go up a few hundred 
degrees Celsius,

35
00:01:29,202 --> 00:01:31,062
they soften significantly,

36
00:01:31,062 --> 00:01:34,474
and can be deformed into
any shape you like.

37
00:01:34,474 --> 00:01:35,832
Cool them back down,

38
00:01:35,832 --> 00:01:38,278
and they regain the strength.

39
00:01:38,278 --> 00:01:41,206
So where do all of these wondrous
attributes come from?

40
00:01:41,206 --> 00:01:45,519
In essence, they have to do with
metallic glass' unique atomic structure.

41
00:01:45,519 --> 00:01:48,154
Most metals are crystalline as solids.

42
00:01:48,154 --> 00:01:52,278
That means that if you zoomed in
close enough to see the individual atoms,

43
00:01:52,278 --> 00:01:56,304
they'd be neatly lined up
in an orderly, repeating pattern

44
00:01:56,304 --> 00:01:58,587
that extends throughout 
the whole material.

45
00:01:58,587 --> 00:01:59,871
Ice is crystalline,

46
00:01:59,871 --> 00:02:01,124
and so are diamonds,

47
00:02:01,124 --> 00:02:02,219
and salt.

48
00:02:02,219 --> 00:02:04,603
If you heat these materials up enough
and melt them,

49
00:02:04,603 --> 00:02:07,985
the atoms can jiggle freely
and move randomly,

50
00:02:07,985 --> 00:02:09,590
but when you cool them back down,

51
00:02:09,590 --> 00:02:11,427
the atoms reorganize themselves,

52
00:02:11,427 --> 00:02:13,841
reestablishing the crystal.

53
00:02:13,841 --> 00:02:17,219
But what if you could cool 
a molten metal so fast

54
00:02:17,219 --> 00:02:20,055
that the atoms couldn't 
find their places again,

55
00:02:20,055 --> 00:02:21,914
so that the material was solid,

56
00:02:21,914 --> 00:02:26,356
but with the chaotic, amorphous internal
structure of a liquid?

57
00:02:26,356 --> 00:02:28,096
That's metallic glass.

58
00:02:28,096 --> 00:02:31,579
This structure has the added benefit
of lacking the grain boundaries

59
00:02:31,579 --> 00:02:33,472
that most metals have.

60
00:02:33,472 --> 00:02:36,884
Those are weak spots where the material
is more susceptible to scratches

61
00:02:36,884 --> 00:02:38,783
or corrosion.

62
00:02:38,783 --> 00:02:43,394
The first metallic glass was made
in 1960 from gold and silicon.

63
00:02:43,394 --> 00:02:44,837
It wasn't easy to make.

64
00:02:44,837 --> 00:02:47,505
Because metal atoms 
crystallize so rapidly,

65
00:02:47,505 --> 00:02:51,405
scientists had to cool the alloy down
incredibly fast,

66
00:02:51,405 --> 00:02:54,527
a million degrees Kelvin per second,

67
00:02:54,527 --> 00:02:57,456
by shooting tiny droplets
at cold copper plates,

68
00:02:57,456 --> 00:03:00,317
or spinning ultrathin ribbons.

69
00:03:00,317 --> 00:03:05,440
At that time, metallic glasses could
only be tens or hundreds of microns thick,

70
00:03:05,440 --> 00:03:08,657
which was too thin 
for most practical applications.

71
00:03:08,657 --> 00:03:10,715
But since then, 
scientists have figured out

72
00:03:10,715 --> 00:03:14,318
that if you blend several metals
that mix with each other freely,

73
00:03:14,318 --> 00:03:16,899
but can't easily crystallize together,

74
00:03:16,899 --> 00:03:19,701
usually because they have very different
atomic sizes,

75
00:03:19,701 --> 00:03:22,945
the mixture crystallizes much more slowly.

76
00:03:22,945 --> 00:03:26,034
That means you don't have to cool
it down as fast,

77
00:03:26,034 --> 00:03:27,616
so the material can be thicker,

78
00:03:27,616 --> 00:03:30,092
centimeters instead of micrometers.

79
00:03:30,092 --> 00:03:34,375
These materials are called bulk
metallic glasses, or BMGs.

80
00:03:34,375 --> 00:03:37,042
Now there are hundreds of different BMGs,

81
00:03:37,042 --> 00:03:40,109
so why aren't all of our bridges
and cars made out of them?

82
00:03:40,109 --> 00:03:44,349
Many of the BMGs currently available
are made from expensive metals,

83
00:03:44,349 --> 00:03:46,537
like palladium and zirconium,

84
00:03:46,537 --> 00:03:48,022
and they have to be really pure

85
00:03:48,022 --> 00:03:51,374
because any impurities 
can cause crystallization.

86
00:03:51,374 --> 00:03:56,386
So a BMG skyscraper or space shuttle
would be astronomically expensive.

87
00:03:56,386 --> 00:03:57,776
And despite their strength,

88
00:03:57,776 --> 00:04:02,089
they're not yet tough enough
for load-bearing applications.

89
00:04:02,089 --> 00:04:05,082
When the stresses get high,
they can fracture without warning,

90
00:04:05,082 --> 00:04:08,206
which isn't ideal for, say, a bridge.

91
00:04:08,206 --> 00:04:12,065
But when engineers figure out
how to make BMGs from cheaper metals,

92
00:04:12,065 --> 00:04:14,058
and how to make them even tougher,

93
00:04:14,058 --> 00:04:15,736
for these super materials,

94
00:04:15,736 --> 00:04:17,309
the sky's the limit.