Cobalt Alloys
Cobalt Alloys
alloys based on cobalt; used primarily in the manufacture of components operating at high temperatures, such as blades for turbojet engines.
“Casting” cobalt alloys are alloys of the Co-Cr-C-X system, where × is tungsten, molybdenum, niobium, or nickel, that exhibit good casting properties. Since hardening of these alloys is effected mainly by the carbide phases, they contain 0.2–1.0 percent carbon. The addition of boron improves the casting properties of the alloys but it may decrease their weldability.
Cobalt alloys are highly resistant to thermal fatigue. The average thermal expansion coefficient is low [(15.9–16.5) × 10-6 1/ °C] within the temperature range of 20°–870°C. The most heat-resistant cobalt alloys maintain their durability at temperatures up to 1100°C. Long-term ultimate strength 
meganewtons per sq m, or 7 kilograms-force per sq mm. Cobalt alloys of the Co-Cr-Ni-Mn system, which contain up to 50 percent Co (deformable cobalt alloys), exhibit high resistance to thermal fatigue and can be worked under pressure. Cobalt alloys called stellites (30 percent Cr, as well as W, Si, and C) are used for hard-facing of machine tools and parts (without subsequent heat treatment) to increase their wear resistance. As a basic or alloying element, cobalt is one of the magnetic materials.