Severe Hot Corrosion of the Superalloy IN718 in Mixed Salts of Na2SO4 and V2O5 at 700 °C

This study presents hot corrosion behavior of the superalloy IN718 in 100 wt.% NaCl (salt S) and in salt mixtures of 60 wt.% Na 2 SO 4 + 40 wt.% V 2 O 5 (SM1) and 75 wt.% Na 2 SO 4 + 15 wt.% NaCl + 10 wt.% V 2 O 5 (SM2), deposited separately by spray gun technique, at elevated temperature of 700 °C. The weight gain per unit area at 700 °C was increased by 49% for salt S, 153% for the dual salt mixture SM1, and only 8% for the triple salt mixture SM2, in comparison with that observed earlier at 600 °C. The marked increase in the severity of corrosion at 700 °C is attributed to formation of the highly damaging compound NaVO 3 that significantly enhances the oxygen activity, in the SM1 coated samples. The effect of surface roughness and dislocation density on corrosion behavior at 700 °C, however, is found to be similar to that at 600 °C. Ultrasonic shot peening, a novel technique of surface modification, is found to enhance the hot corrosion resistance in the salt mixture SM1 at 700 °C appreciably due to extensive grain refinement to nanoscale and formation of highly protective Cr 2 O 3 layer in the surface region.