ABSTRACT
Hot corrosion is a major problem commonly encountered in most gas turbines. Conventional diffusion aluminide coatings on nickel superalloys are generally used to prevent degradation due to oxidation and hot corrosion. However, there is a continuing interest to modify the aluminide coating system with a view to obtaining enhanced performance. This paper discusses the influence of precious metal additions on the stage I hot corrosion performance of modified aluminide coatings on directionally solidified MAR M002 nickel-base superalloy at 900°C in sodium sulphate and sodium chloride containing environments. The scale morphologies and the hot corrosion products formed on the coatings have been characterised using optical and scanning electron microscopy (SEM) and energy dispersive analysis by X-ray (EDX) techniques.
Precious metal additions have been observed to improve hot corrosion resistance by increasing the stability of aluminide phases through the formation of a protective oxide layer. The role of the precious element additions has been discussed in relation to their effects upon the various aspects of hot corrosion.
