HOT . CORROSION OF HIGH TEMP. NICKEL BASE ALLOY

Abstract

The present study has been done to analyse the hot corrosion behaviour of Ni-base super alloy MA-754 with the salt coating of pure Na2SO4 and Na2SO4 with 15%, 30% and 60% vanadium penta oxide in the temperature range of 700°C to 900°C for 8 hours duration. The corroded specimens were studied by weight loss. Measurements' and corrosion products were identified by SEM and XRD. The alloy coated with pure sodium sulphate and 60% vanadium penta oxide + 40% sodium sulphate at 700°C and 800°C shows maximum corrosion resistance and is found to be least resistance to 30% vanadium penta oxide + 70% sodium sulphate at 900°C, this may be due to the formation of liquid phase, the prominent phases present in case of pure sodium sulphate are NiO, Cr203, Cr2S3, NiTiO3, NiS, Cr2S3 where as with the addition of vanadium penta oxide the phases are CrVO4, NaVO3, Ni(V03)2 and V205. The nature of scale change with the change in temperature and vanadium penta oxide addition. On the basis of this study it can be inferred that Ni-base super alloy may not be suitable for use at 900°C in 30% vanadium penta oxide + 70% sodium sulphate mixture environment but at low temperature it performs well, specially at 700°C and 800°C it is least susceptible to attach in pure sodium sulphate and 60% vanadium penta oxide + 40% sodium sulphate mixture. These results are only valid to throw some light on initial stages of hot corrosion.