Cermet Versus Ceramic Coatings – How Do You Choose?

Ceramic coating does not include binders, like cobalt, nickel, chromium, titanium or tungsten. More complex than typical oxides, the cermet coating is usually carbide-based, bonded with a metallic. It is the addition of metal that gives the “cermet” (ceramic-metallic) unique properties.

Maybe it is improvement in mechanical toughness you need. Or better heat transfer, thermal resistance or protection from corrosion that is required. Metal binders of the cermet coating can add “synergism”, performance properties not found in the ceramic coating or individual metals, alone. Here, we will take a look at the need for mechanical toughness, heat transfer or thermal resistance, and corrosion protection, using both ceramic coating and cermet coating, to see which type is best.

Let us start with toughness versus hardness. Ceramics are hard. Of course they are well known for their resistance to severe abrasion. They maintain great structural rigidity. But what about frictional applications involving higher mechanical stress? When the contacting surface is metal, not graphite, plastic or elastic polymer-based, and loads are much higher? Cermets are the obvious choice. They rub well against themselves, as well as against harder surfaces or virgin metal. Fracture toughness can be outstanding.

Today, with carbon-based “diamond like” coatings (DLC) and tungsten carbide coatings (WC/C), significant dry lubrication can be added to further resist adhesive (sliding contact) wear. That is a big advantage when you consider contacting surfaces that must resist seizure or galling.

Thermal spray and electrolytic plating are common means of applying the ceramic coating and cermet coating. But, for applications more dynamic in nature, and where surface conformance and dimensional stability is critical, physical or chemical vapor deposition processes can be best.

For heat transfer or higher thermal resistance, cermet coatings are better suited. It is their greater flexibility at the substrate interface during large, sudden fluctuations in temperature that make them the more favorable. Phase transformations using stabilizing additives, like yttrium or magnesium, can reduce the possibility of micro cracking under thermal stress.

Yet, ceramics are the clear winner for resistance to corrosion. In particular, it is the chromium-based oxides most inert, chemically.