Erosion–corrosion behavior of cold-spray nanostructured Ni–20Cr coatings in actual boiler environment

Abstract

In the current investigation erosion–corrosion (E–C) behavior of cold-spray nanostructured Ni–20Cr coatings on SAE-213-T22 and SA 516-Grade 70 steels, under actual boiler environment was evaluated. A nanostructured Ni–20Cr powder was synthesized using a ball milling technique by the investigators. The specimens with and without coating were exposed to super heating zone of a power plant boiler at 750 °C under cyclic conditions for 15 cycles. Each cycle consisted of 100 h of heating followed by 1 h of cooling. The mass change and thickness loss data of the samples were used to study the kinetics of E–C. XRD, SEM/EDS, and X-ray mappings analyses were used to characterize the eroded–corroded samples. The coating was found to reduce the E–C rate of T22 and SA 516 steels by 100% in terms of thickness loss. Moreover, the investigated nanostructured Ni–20Cr coating was found to be more effective to reduce the E–C rates of the steels in comparison with its conventional micron-size counterpart. Erosion–corrosion resistance shown by the investigated coating under actual boiler conditions may be attributed to the presence of protective NiO and Cr2O3 phases in its oxide scale and its superior as-sprayed microhardness.