Ok, since a few people have inquired and I see these terms being used interchangeably so often, I thought I'd post an informational update on surface coatings we are considering for the upcoming "Titanium Clicky" project (clearly a working title, not exactly poetry but for the moment it'll do).
First of all, PVD stands for physical vapor deposition, not a coating but rather a method of applying a coating. DLC on the other hand is diamond like carbon, this is a specific type of coating. DLC is often applied by... wait for it... physical vapor deposition. It should be noted that DLC can also be applied by IBD (ion beam deposition) and CVD (chemical vapor deposition). PVD is often used due to it being both practical and economical in production environments.
Now back to DLC. As the name implies, diamond-like carbon has some of the valuable properties of diamond (sorry, bling-bling isn't one of them), specifically hardness and durability. It can be applied as a coating on almost any material that is compatible with the vacuum in which it is usually produced and is often coated onto metals. In fact, the harder the metal (such as steel or titanium) the better as softer materials (such as aluminum) will be prone to the “eggshell effect”. This is when the underlying material below the surface is soft while the actual outer coating, the shell, is very hard. You may not break through the surface but you will be able to deform the structure underneath it. You can see this when you get a dent on a coated part but the surface doesn’t actually get scratched. When applied in pure form, DLC is as hard as natural diamond (and possibly even harder). In pure form these diamond coatings offer extraordinary protection against abrasive wear and attack from atmospheric moisture and chemical vapors.
Although smooth when seen with the naked eye, DLC coatings are actually textured at the microscopic level. In DLC the “cobbles” are not crystalline; they are amorphous because they are made from random alternations between cubic and hexagonal lattices. The cobbles have no long-range order and so they have no fracture planes along which to break. The result is a very, very strong surface coating which is not prone to chipping or flaking and has excellent wear resistance.
The biggest downside to DLC? It's limited in color to dark gray and black and it is very, very expensive. Prepping the surface underneath will allow some variance in finishes (polished then coated will be shinny, blasted then coated will be matte) but the basic color of carbon is... well, black.
If you want pretty, you may also consider TiN or titanium nitride but that my friends is a story for another update.
Long story short, these are both optional coatings we are considering adding to the upcoming "Titanium Clicky" pen project. What does everyone think?