Cobolt base Powder
Cobalt base alloys typically contain tungsten and carbon for strengthening.
Carbon has low solid solubility in cobalt and therefore, most of it partitions
in WC, W2C and M6C or other carbides. These hard phases have a strengthening
effect, making such alloys maintain high hardness and strength at temperatures
under 800 C. The cobalt-chromium-tungsten-carbon alloys generally have excellent
properties to resist high temperature wear, oxidation and thermal fatigue.
Cobalt has a hexagonal-close-packed (hcp) crystal structure at temperatures below
417 C. Intrinsically, it has low coefficient of friction resulting in excellent wear resistance.
At temperatures above 417 C, cobalt transforms from hcp to fcc (face-centered-cubic)
crystal structure, thereby, generating thermal stresses. Therefore, it is recommended that
in weld overlaying and spraying, the parts being coated are pre-heated to 500-600 C
to avoid cracking in the coating or overlay.