Hot corrosion behaviour of thermally sprayed CoCrAlY coating irradiated by high-current pulsed electron beam

Abstract

Microstructural modifications and hot corrosion behaviour of plasma spraying CoCrAlY coatings before and after high-current pulsed electron beam (HCPEB) irradiation were investigated. The microstructural observations revealed that the coarse surface of plasma spraying CoCrAlY was remelted and changed as a wavy aspect with a compact appearance. The fast heating and melting, and self-quenching effects induced by HCPEB treatment normalized the thermal spraying defects, refined the grains, and changed the elemental distributions. Cyclic hot corrosion test of two kinds of coatings in Na2SO4/K2SO4 (75:25, wt.%/wt.%) eutectic salt was performed at 900 °C in air. After 80 h hot corrosion, the relatively loose and non-protective scale was formed with poor adherence on the initial porous surface, which made the initial coating highly susceptible to hot corrosion. Comparatively, the irradiated coating displayed a stable and slow-growing kinetic curve of very small mass change, revealing that resistance to hot corrosion was superior to that of the initial one. The irradiating effects promoted the formation and self-healing of a dense and adherent Al2O3 scale in the initial stage, which effectively suppressed the formation of internal oxides and sulfides. The results demonstrated that HCPEB technique is an effective way to prolong the service life of MCrAlY coatings.