Metals 金屬
Engineering materials are normally split into 4 categories - metals, polymers, ceramics and composites.
工程材料通常分為 4 類——金屬、聚合物、陶瓷和複合材料。
Understanding the different types of materials, their properties and how to use them effectively is a crucial part of
engineering.
了解不同類型的材料、它們的特性以及如何有效地使用它們是工程的關鍵部分。
Around two thirds of the elements in the periodic table are metals, although for engineering purposes we’re
particularly interested in just a handful of them.
元素週期表中大約三分之二的元素是金屬，儘管出於工程目的，我們只對其中的一小部分特別感興
趣。
Iron is probably the most important of them all, because it’s used to create steel, a high strength material with a
wide range of engineering applications.
鐵可能是其中最重要的一種，因為它用於製造鋼鐵，一種具有廣泛工程應用的高強度材料。
Aluminum is commonly used because its alloys have high strength-to-weight ratios.
鋁是常用的，因為它的合金具有高強度重量比。
It has a relatively low melting temperature, which makes it easier to process and use for casting, and it’s relatively
inexpensive.
它的熔化溫度相對較低，因此更容易加工和用於鑄造，而且價格相對便宜。
Like Aluminum, Titanium has excellent strength-to-weight properties, although it is even stronger, making it a
popular choice for aerospace applications.
與鋁一樣，鈦具有出色的強度重量比，儘管它更堅固，使其成為航空航天應用的熱門選擇。
Its high melting point makes it suitable for applications at high temperatures, but makes processing more difficult.其
高熔點使其適用於高溫應用，但使加工更加困難。
It’s also much more expensive than Aluminum.它也比鋁貴得多。
Other important metals include Magnesium, Copper, and Nickel.其他重要金屬包括鎂、銅和鎳。
The key to using these metals effectively lies in understanding how they’re structured at the atomic level.
有效使用這些金屬的關鍵在於了解它們在原子水平上的結構。
The atoms of a pure metal are packed together closely, and are arranged in a very regular grid.
純金屬的原子緊密堆積在一起，排列成非常規則的網格。
Because of this regular structure, metal is what we call a crystalline material, and the grid the atoms are arranged in is
called the crystal lattice.
由於這種規則的結構，金屬就是我們所說的晶體材料，而原子排列的網格被稱為晶格。
Not all materials have a regular structure like this.並非所有材料都具有這樣的規則結構。
In glass for example the atoms are arranged randomly, so it’s an amorphous material, not a crystalline one.
例如，在玻璃中，原子是隨機排列的，因此它是一種無定形材料，而不是結晶材料。
We can think of the crystal lattice as a repeating number of identical units, that we call the unit cell.
我們可以將晶格視為重複數量的相同單元，我們稱之為單位晶格。
There are several different ways the atoms of a metal can pack together, which means that there are several different
types of unit cell.
金屬的原子可以通過幾種不同的方式聚集在一起，這意味著有幾種不同類型的單位晶格。
At room temperature, copper atoms for example pack together as shown here, where there is an atom at the corner of
each unit cell and one at the centre of each face.
例如，在室溫下，銅原子會堆積在一起，如圖所示，其中每個單位晶格的角落有一個原子，每個面的
中心有一個原子。
We can see this better if we shrink the size of the atoms and display the bonds between them.
如果我們縮小原子的大小並顯示它們之間的鍵，我們可以更好地看到這一點。
This is called the face-centred cubic structure, or FCC.這稱為面心立方結構，或 FCC。
But iron atoms prefer to pack together in a structure where the atoms at the centre of each face are replaced by a
single atom in the middle of the unit cell.
但是鐵原子更喜歡堆積在一個結構中，其中每個面中心的原子被單位晶格中間的單個原子取代。
This is the body-centred cubic structure, or BCC.這是體心立方結構，或 BCC。
And titanium atoms prefer to pack together in what’s called the hexagonal close-packed structure.
鈦原子更喜歡以所謂的六方密堆積結構（ＨＣＰ）堆積在一起。
These are the three most common crystal structures in metals.這是金屬中最常見的三種晶體結構。
Both the FCC and the HCP structures have a packing factor of 74%, meaning that the atoms occupy 74% of the total
volume of the unit cell.
FCC 和 HCP 結構的填充因子均為 74%，這意味著原子佔據了單位晶格總體積的 74%。
The BCC structure is slightly less closely packed, with a packing factor of 68%.
BCC 結構的緊密堆積程度略低，堆積係數為 68%。
The close packing of the atoms is one of the reasons metals have much higher densities than most other materials.原
子的緊密堆積是金屬比大多數其他材料具有更高密度的原因之一。