Emerging technologies are focusing on deposition methods of coating the steel surface with a hard metal (or combinations of metals) that is harder than that of the steel. These coatings are known as ultra-hard coatings or surface-deposition techniques. There are many different methods of the application of coatings that can be put down onto a metal substrate to improve its wear and corrosion characteristics.

Generally, the coatings can be subdivided into many different categories. For example, the simple groupings include: decorative coatings, hard coatings and ultra-hard coatings.

These coatings can be further categorized into the following temperature ranges, which will be determined by the selected coating type:

•    Low-temperature coatings – up to a process temperature of 500°C (932°F)
•    Medium-temperature coatings – up to a process temperature of 1000°C (1832°F)
•    High-temperature coatings – up to a process temperature of 1700°C (3092°F)

This will be followed by the method of application of the coating to the substrate material. These include chemical vapor deposition, plasma-assisted vapor deposition and physical vapor deposition. A further subdivision can be made as to the nature of the method of application to the deposited coating, which is pack cementation and reactive gases.

With the advent, developments and growth of plasma technology, one is now able to process under vacuum conditions and accomplish both controllable and repeatable results.

We will finish our discussion on this topic next time in part 5.