|Hardcoat anodizing (also called hard coat anodizing, or hard anodizing) is a process that forms a very hard, dense, and relatively thick coating of aluminum oxide. This coating is particularly useful in applications requiring high wear resistance, in many cases outperforming hard chrome or electroless nickel. The coating material formed in this process occurs in nature as corundum, and is the second-hardest naturally occurring substance, second only to diamond. Hardcoat is often described as being "file hard", since it is difficult to scratch, even with a mill file.
Some common applications of this coating are for pulleys, guides for fibers, and parts for conveyor systems. Any part that suffers sliding friction without heavy impact is a good candidate for this coating.
Hardcoat is also exceptionally corrosion resistant, being very effective against salt water and road-salt laden environments. It has proven to be very long-lived in an exposed application on long haul trucks.
Typical coating thickness is 0.002", but this can vary to some extent.