Nickel-base superalloy materials technology for advanced IGT applications

The firing temperatures of all gas turbines, both industrial power generation and aircraft engines, have increased over the past -30 years. More recently, the rate of temperature increase has slowed for aircraft engines but not for industrial gas turbines (IGT). As a result, the materials temperature capability requirements for these two classes of gas turbines are converging. For many years, the high performance requirements of military and commercial aircraft engines fueled the development of advanced materials and processes. Many of these high temperature materials are now being used in industrial gas turbines as output, efficiency, and reliability requirements continue to grow. Directionally solidified and single-crystal nickelbase superalloys have been developed for investment casting of hot gas path components and have been scaled up to the part sizes required for IGT components but not without significant challenges in producibility, defect allowances, and repair. Wrought nickel-base superalloys such as Alloy 706 and Alloy 718 are being used in IGT rotor structures after significant advances in ingot melting/casting, forging, and inspection. This paper will discuss the application of nickel-base superalloys in industrial gas turbines with particular emphasis on the technology development required to produce hot gas path and rotor components in large IGT sizes. Processing scale-up from aircraft engine-sized parts to large IGT-sized parts has presented unique materials development and processing challenges. (AU)