Studies on the Role of Cold Spray Ni-20Cr and Ni-50Cr Coatings to Reduce Wear of T-22 and SA-516 Steels

Cold gas dynamic sprayed (CGDS)  nickel chromium coatings have great potential for industrial applications; however, they are not yet widely used due to inadequate experimental and scientific database for specific industrial applications. Two such Ni-Cr coating powders namely Ni-20Cr and Ni-50Cr were deposited on T-22 and SA-516 steels by CGDS spray technique, in order to enhance the wear resistance of the steels. T-22 and SA-516 steels find many applications in the manufacture of components of thermal power plants, where they suffer from different types of wear. The as-sprayed coatings were characterized by XRD and SEM analyses. Subsequently the sliding wear behaviors of the uncoated, Ni-20Cr and Ni-50Cr coated T-22 and SA-516 steels were investigated according to ASTM standard (G99-03) on a pin-on-disc wear test rig. Cumulative wear rate and coefficient of friction (µ) were calculated for the coated, as well as, the uncoated specimens for 30 N normal load at a constant sliding velocity of 1 m/sec. Some of the worn-out surfaces were characterized by SEM analysis. Both the as-sprayed coatings exhibited typical irregular sized globule morphology. The XRD analysis for both the coatings indicated the formation of Ni as the most prominent phase for both the steels. Very low intensity peaks were also identify and categorized to the Cr phase. It has been observed that the cold spray Ni-20Cr and Ni-50Cr coatings can be useful to reduce the wear problem of T-22 and SA-516 steels. The coatings were found to be successful in retaining their surface contact with the substrate during the wear testing. The Ni-50Cr coating could be recommended as a slightly better choice to reduce the wear of the T-22 and SA-516 steels, in comparison to the Ni-20Cr coatings.