Characteristics of thin surface layers of cobalt-based alloys deposited by laser cladding

Thin surface layers of cobalt-based alloys (Stellite 6 and Tribaloy T-900) and 410 stainless steel (SS) were deposited on mild steel substrates by a coaxial laser cladding process. This process could produce a thin surface layer of less than 0.5 mm with low energy input. Laser-clad Stellite 6 and Tribaloy T-900 specimens exhibited refined dendritic microstructure. The interdendritic eutectics consisted of either small carbides or intermetallic compounds randomly distributed in a cobalt-rich solid solution, unlike the lamellar structure as observed in conventional weld overlays. The hardness values of the laser-clad layers were generally higher than those of conventional welding deposits owing to the refined effect. The wear and corrosion resistance of S-6 and T-900 specimens were considerably better compared to those of laser-clad 410 SS specimens. In addition, the T-900 specimen had substantially lower corrosion rates than the S-6 specimen in hydrochloric acid solution. Experimental results indicated that wear and corrosion characteristics of the T-900 specimen were excellent; however, preheating was required to avoid cracking in the laser cladding process.