In the world of materials and finishes, Diamond-Like Carbon (DLC), also called amorphous carbon (a-C), is not one coating but an entire category of coating materials. DLC has properties that change depending on the bonding of the carbon atoms and presence or lack of other materials in the coatings. These materials include hydrogen, silicon, or metals. Generally, DLC is known for:
- high hardness
- low friction
- wear resistance
- a striking dark gray color
- chemical inertness
- corrosion resistance
We can adjust these properties for different applications, customizing them to specific needs for improving the appearance, performance, and durability of components in wide array of different industries (if you are interested in using DLC on firearms, also visit our DLC for gun coating page). Let’s back up and talk about what makes the carbon in DLC so unique.
Graphite vs diamond: what is diamond-like carbon?
Carbon (atomic symbol C) is an element that has some interesting and useful properties. In one form, it makes up graphite, a very soft, black, conductive material made of layers that slide easily relative to one another. Pencil ‘leads’ are made of graphite because it glides easily and is soft enough to leave behind residue on paper.
On the other hand, diamond is also made of carbon. Diamond is clear, electrically insulating and extremely hard: the hardest naturally occurring material on earth. We use small diamonds for cutting other hard materials and large ones are considered precious gems. In fact, diamond has properties that are nothing like graphite. Both materials are made of the same element, and the only difference between graphite and diamond is the bonding and structure of the carbon atoms in each.
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Atomic bonding and structure
Carbon is tetravalent, which means that it has four electrons available for molecular bonds with other atoms. In graphite, only three of these electrons form bonds with other carbon atoms, forming a two-dimensional plane of hexagonal shapes via sp2 bonding. These individual layers are called graphene. The bonds within these layers are very strong, but when additional layers are added, the bonding between the layers is weak, so the sheets can easily slide past one another. That is what makes graphite soft and gives it some of its other properties.
Diamond, on the other hand, has all four electrons forming molecular bonds with other carbon atoms. These carbon atoms form a three-dimensional tetrahedral shape via sp3 bonding. The carbon atoms pack together very tightly inside the diamond crystal and the bonds are quite strong. The result is the hard, clear crystal we are familiar with that is formed deep within the earth or in a laboratory under extremely high pressures.
Like graphite and diamond, DLC is made of carbon, but it has a combination of sp2 and sp3 bonds. As a result, a DLC coating has a combination of the properties of both diamond and graphite. For example, it can be very hard but also have very low friction. In the coating process, we tune the properties by changing process conditions and energy to change the bonding. As sp3 bonding increases, the coating becomes harder and more like diamond, or “diamond-like.” Pure carbon with mostly sp3 bonding is called tetragonal amorphous carbon (t-aC).
Doping: adding more than carbon
Additionally, we can further adjust the properties by adding other elements such as to name a few. Adding other elements to the Diamond-Like Carbon is called doping. Just like impurities in diamond can change properties such as color, adding other materials can adjust the properties of these coatings, making it possible to tune the color, conductivity, hardness, wear resistance, friction, and many other properties.
Alphabet Soup: Sorting out the acronyms
There are lots of different acronyms and abbreviations for different types of DLC coatings, and there are often several different ways to refer to the exact same type of coating. This is where DLC coatings can start to get really confusing, so I’ve broken it down in an easy-to-understand chart.
The chart shows just a few examples of naming conventions. For DLCs, the metal is often specified using its atomic abbreviation in the place of the ‘Me’ (e.g. W-DLC or a-C:Ti). The types can be combined as well, for example: metal-doped hydrogenated DLC (Me-C:H). Often, a DLC name includes a number that represents the atomic percentage of hydrogen or metal doping. The variations go on and on, but it really doesn’t need to be that complicated. Now, the next time someone mentions DLC, you will know the answer to “what is diamond-like carbon?”
If you think one of these Diamond-Like Carbon coatings might be right for you and your product, contact Vapor Technologies, Inc. We can help you cut through the mystique of all the variations and develop a coating solution that is specific to your product needs. You can also access more information about VT-Diamond coatings on our DLC coatings page and in this downloadable DLC fact sheet.