Hot corrosion of nanostructured CoNiCrAlYSi coatings deposited by high velocity oxy fuel process

This paper focuses on the structure and cyclic hot corrosion behavior of nanostructured MCrAlY coatings used in thermal barrier coatings of gas turbines as the bond coat. Cryomilling in a liquid nitrogen environment was used to prepare nanostructured CoNiCrAlYSi powders, as characterized by scanning electron microscopy and X-ray diffraction. Also, the long-term hot corrosion resistance of the coating deposited by high velocity oxy fuel thermal spraying of the cryomilled powders was studied in a molten salt medium of Na2SO4-Na2VO3 at 880 °C up to 640 h. According to the results, the cryomilling process improved the corrosion resistance of the nanostructured coating, as compared with coarse-grained CoNiCrAlYSi coatings. This improvement was attributed to some α-Al2O3 particles dispersed in the structure, created by cryomilling, and high-diffusivity paths, created by nanocrystallization, which favors the formation of a continuous α-Al2O3 barrier layer on the top of the coating.