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铸造记忆材料

Shape Memory Materials

[奏乐]
[MUSIC PLAYING]
你见过一种材料加热时这样做吗?
Have you ever seen a material do this when it gets heated?
这不是普通的材料。
This is not an ordinary material.
这是形状记忆材料。
This is a shape memory material.
它有记忆一种特殊形状的能力
It has the ability to remember a specific shape
当加热时变回这种形状
and change into that shape when heated.
那么这种材料是什么机理呢
So how do these materials work?
这全都基于相变。
It’s all based on phase transformations.
你也许见识过相变
You’ve probably seen phase transformations
当水结冰时。
when water freezes.
这是液态水到固态相变。
This is a transformation from liquid water to solid water.
水沸腾时也发生了相变
There is also a phase change when water boils.
此时,液态水变成了水蒸气。
Here, the liquid water becomes water vapor.
那么这种相变有什么区别呢
Well, what is the difference between the phases?
差别在于单个水分子
The difference is how the individual water molecules
被重新排列
are arranged.
在液态水中,它们松散聚集在一起
In liquid water, they’re loosely packed together
所以他们可以移动 越过彼此
so they can move past one another.
在冰中,它们紧密挤在一起
In ice, they’re tightly packed together
它们不能改变地方
and they can’t change places.
但你知道实际上
But did you know there are actually
冰有多重固相
multiple solid phases of ice?
六角冰相
There’s a hexagonal ice phase that
直到零下150华氏度下是稳定的
is stable till negative 150 degrees Fahrenheit.
立体冰相只稳定存在于低于零下150
And a cubic ice phase that is only stable below negative 150
华氏度下
degrees Fahrenheit.
所以这是如何契合形状记忆材料?
So how does this fit into shape memory materials?
这些材料也有多重固相
These materials also have multiple solid phases.
在一个低温阶段,称为马氏体
There is a low temperature phase that is called Martensite.
但是如果你升高温度
But if we increase the temperature,
原子排列会变成另一种相
the atomic alignment changes into another phase
叫做奥氏体
called Austenite.
在低温下,我们有马氏体
So at low temperatures, we have Martensite.
在高温下,我们有奥氏体
And at high temperatures, we have Austenite.
我们怎样设置这个记忆形状?
How do we set the memory shape?
为了得到我们想要的形状,我们
To set the shape that we want, we
必须控制材料在奥氏体阶段
must hold the material in the Austenite phase
于高温下
at high temperatures.
在这里,我们用螺丝将金属线固定在铁板上合适的位置
Here, we have used screws to hold the wire in place
再将它放进火炉
on a metal plate, which we then put into the furnace
加热
to heat it.
在火炉里,金属丝转变成奥氏体
Inside the furnace, the wire transforms into Austenite,
这样就设置成这个记忆形状
which sets the memory shape.
当我们冷却它时,它就会转变成马氏体
When we cool it down, it transforms into Martensite,
但是这没有改变形态
but it does so without changing the shape.
在图中,你能看到原子有马氏体
In the graphic, you can see that the atoms have the Martensite
结构但是它们排列成菱形图案
structure but they align in a zigzag pattern,
所以整体形状没有改变
so the overall shape does not change.
现在我们可以随意弯曲这根金属丝
Now we can bend the wire however we like.
这种材料不改变相
The material does not change phase,
但排列方式有些许改变所以它们
but the alignment pattern changes slightly so that they
排列成一个方向
align in one direction.
这会导致永久形变
This results in a permanent shape change.
现在如果我们加热这根金属丝,它会经历
Now if we heat up the wire, it goes through the phase change
从马氏体到奥氏体的形变,它会返回到
from Martensite to Austenite, and it returns back
初始形状
to its original shape.
我们可以重复这个几乎任何我们想要的形状。
We can repeat this for almost any shape we want.
形状记忆材料也显示出
Shape memory materials also exhibit
另一种特殊特性称为超弹性
another special property called superelasticity.
这是我们之前看到的相同形状
Here’s the same shape we saw before,
现在我们逐渐拉开它
and now we will pull it.
但不像之前,这次形状
But unlike before, this time the shape
没有改变而是恢复原状
doesn’t change but it goes right back to its original shape.
这种称为超弹性
This is called superelasticity.
这也因为相变作用
This also works because of phase transformations.
这种材料成分略有不同
This material is a slightly different composition
所以在室温下,它处于奥氏体相
so that at room temperature, it is in the Austenite phase.
如果我们加压这种材料,我们能强迫它
If we stress the material, we can force it
变成马氏体,这样会改变形状
into Martensite phase, and this will change the shape.
但是如果我们释放压力,它会回弹
But if we release the stress, it goes right back
到奥氏体相并且初始形状
to the Austenite phase and the original shape
由于在此温度下处于稳定状态
because that is where it is stable at this temperature.
你或许在眼镜上见过这个
You may have seen this before in eyeglasses
可以拉伸而不被永久弯曲
that can be stretched without being permanently bent.
我们已经向你展示了形状记忆如何
We’ve shown you how the shape memory
产生和超弹性基于相变原理工作
effect and superelasticity work based on phase transformations.
这是一个例子 材料科学家如何研究
This is an example of how material scientists study
材料
materials.
他们试图解释所观察到的特性
They try to explain observed properties in terms
依照其内部结构
of the internal structure.
那么一旦他们了解其根本原理
Then once they understand the underlying principles,
他们可以用这些制作更好的材料
they can use them to make even better materials.
[奏乐]
[MUSIC PLAYING]

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