What's the Difference Between Stellite® and Colmonoy® Hardfacing?

Hardfacing is a broad term used to describe any metalworking process that applies a harder material to a substrate to provide protection of some kind. Most commonly for wear and abrasion, hardfacing can also offer protection from corrosion or impact damage. There are many hardfacing methods such as thermal spray, laser cladding, and welding. For aggressive wear scenarios, people typically look towards a hardface weld coating due to its metallurgical bond. The two most common material families applied this way are Stellites and Colmonoys. To take a better look at these two material families, we’ll talk about the most common types, the differences between them, and the best applications for each.

Stellite® materials are cobalt-based materials while Colmonoy® materials are nickel-based. Nickel-based and cobalt-based coatings are named as such for the material that makes up most of their composition. They are both families of alloys that contain differing amounts of other elements such as carbon, chromium, boron, silicon, iron, molybdenum, and some containing tungsten carbide as well.  Most alloys in each family can be applied via thermal spray, welding, or spray and fuse. Examples of nickel-based coatings are Colmonoy® 88 and Colmonoy 6. Some popular alloys of cobalt-based coatings are Stellite® 1, Stellite® 6, Stellite® 12, and Wallex® 50. These variations in alloy composition are the reasons behind the differences between these two material families.

The foundational difference between the cobalt- and nickel-based coating families is hardness. As is typical with most hardfacing solutions, increasing hardness means decreasing ductility. But just because a coating is harder doesn’t mean it’s the right one for every wear situation. Nickel-based coatings tend to be harder which handles abrasive wear better but may crack in impact wear situations. Cobalt-based on the other hand are more ductile and handle impact wear a little better, especially when welded. With cobalt-based you do have to be careful at higher temperatures because their hardness will decrease as the operating temperature increases. Due to their more ductile nature, cobalt-based coatings do handle metal-to-metal wear better and tend to have a lower coefficient of friction. The cobalt-based coatings may also handle corrosion better in certain situations. Neither material family is superior to the other but can be best matched to certain operating environments.

Due to its ductile wear properties and metal-to-metal performance, cobalt-based coatings do well as valve steam coatings, bushing coatings, piston rod coatings, and many more. Some will still prefer nickel-based coatings for these situations instead due to their superior performance at high temperatures. In hard abrasive environments like material handling screw conveyors, nickel-based coatings will offer the most protection. Other applications for nickel-based hardface coatings include valve seats, ball valves, and other valve components. Both material families have countless other applications in various industries.

As with most coating solutions, each material has its best use case. Nickel-based and cobalt-based coatings are no different. Welded and spray & fused nickel-based and cobalt-based coatings offer high wear protection in harsh, abrasive environments. Their variations are slight so working with a professional coating manufacturer is advised. They will be able to assess your operating environment and recommend which of these materials will be best.

Learn more about hardface welding at HTS Coatings