Effect of Co doping on hot corrosion behavior of aluminide coating on Mo-rich single-crystal superalloy exposed to Na2SO4+NaVO3 at 750 °C and 900 °C

Abstract

This study presents a comparative investigation on the hot corrosion behavior of Mo-rich single-crystal superalloys with simple aluminide coatings and Co-modified aluminide coatings under molten salt corrosion by 75 wt. % Na 2 SO 4 + 25 wt. % NaVO 3 mixture at 750°C and 900°C. The results reveal that Co doping significantly enhances the resistance of aluminide coatings to combined sulfur-vanadium hot corrosion at both low and high temperatures. During hot corrosion, the Co-modified coating develops a multilayered oxide structure consisting of CoO/CoAl 2 O 4 /Al 2 O 3 . This unique microstructure formation can be attributed to the synergistic effects of Co-induced suppression of outward Al diffusion in the coating and the dissolution of the outer Al 2 O 3 scale by VO 3 - ions. Furthermore, the presence of CoO effectively reduces the inward penetration tendency of VO 3 - . At the elevated temperature of 900°C, Co addition demonstrates additional benefits by inhibiting the outward diffusion of Mo from the substrate, promoting its solid solution stabilization in the interdiffusion zone. This mechanism effectively suppresses MoO 3 dissolution into the molten salt, thereby preventing acidification-induced acceleration of hot corrosion propagation.