The Performance Of Coatings Compared To Pt-Based Superalloys Intended For High Temperature Applications Subjected To Hot Corrosion: A Review

The gas turbine industry is faced with a challenge to improve the performance of engines, while simultaneously adhering to stringent environmental legislation. One way of addressing the problem is by further increasing the recipient working temperatures. Unfortunately, the use of nickel based superalloys (NBSAs) in the gas turbine industry has reached its limitations. Although coatings can be used for small increases, and air cooling is also incorporated by design, attention is towards developing stronger metallurgical materials having higher melting points, with acceptable creep and corrosion resistance. A series of ternary and quaternary Platinum-based superalloys were developed. Platinum was selected because of its higher melting points compared to nickel, similar fcc structure and better corrosion properties. Mechanical characterisation studies of Platinum-based superalloys alloys, which included oxidation, creep and hardness, demonstrated reasonable results, outperforming an oxide dispersed strengthening (ODS) Fe-based superalloy (PM2000) and a nickel based superalloy (MAR-M200). During any materials development where high temperatures are concerned, high strength is the primary property of interest. However, during the development of gas turbines, component life and reliability, which are influenced by temperature, need to be taken into consideration, and therefore creep as well as corrosion (both temperature dependant properties), are important. These properties become significant with increasing temperatures. With increasing demand for higher temperatures, it is becoming increasingly important to include hot corrosion properties of the alloy during the material selection process. A short description on hot corrosion and its degradation mechanisms are given in this paper. Coatings are currently dominating as the best practical solution to address temperature increases. This paper looks at benefits and shortcomings of coatings over Pt-based superalloys as candidates for applications under extreme conditions. Key words: Hot corrosion, Pt-based superalloys, Ni-based superalloys, Coatings