Effect of temperature and reactivity of molten 55Al–Zn alloy on Co based alloy coatings

Abstract

The short service life of bearings in galvanising industry is a result of a complex set of deterioration mechanisms. This work addressed the effect of temperature and molten bath reactivity on the material of the bearings respectively. Three commercial alloys, the Co–Cr–W Stellite 6 and Co–Cr–Mo–Si Tribaloy (T400 and T800) alloy systems, were deposited by plasma transferred arc on AISI 316L plates. Coatings were evaluated for the effect of temperature exposure on hardness, microstructure and sliding abrasive wear. The reactivity with the molten 55Al–Zn alloy was assessed by immersion tests in an industrial bath. Results showed that exposure at 600°C for 168 h resulted in an increase in hardness, microstructure changes and loss of wear resistance for the Stellite 6 coatings. A superior performance to temperature was shown by Tribaloy T800 with a stable abrasive wear resistance. The three alloys exhibited a strong reactivity with the 55Al–Zn molten bath. An intermetallic layer formed on the coatings as the Al from the bath reacted with elements from the Co based alloys. This reactivity consumed the coatings, causing a reduction on thickness particularly on those processed with the T800 alloy.