A NEWLY DESIGNED NICKEL-BASED SUPERALLOY GH750 FOR 700°C ADVANCED ULTRA-SUPERCRITICAL POWER PLANTS

A new nickel-based superalloy, designated as GH750, was developed to meet the requirements of high temperature creep strength and corrosion resistance for superheater/reheater tube application of A-USC power plants at temperatures above 750 degrees C. This paper introduces the design of chemical composition, the process performance of tube fabrication, microstructure and the properties of alloy GH750, including thermodynamic calculation, room temperature and high temperature tensile properties, stress rupture strength and thermal stability. The manufacturing performance of alloy GH750 is excellent and it is easy to forge, hot extrusion and cold rolling. The results of the property evaluation show that alloy GH750 exhibits high tensile strength and tensile ductility at room and high temperatures. The 760 degrees C/100,000h creep rupture strength of this alloy is larger than 100MPa clearly. Microstructure observation indicates that the precipitates of GH750 consist of the precipitation strengthening phase gamma', carbides MC and M23C6 and no harmful and brittle TCP phases were found in the specimens of GH750 after long term exposure at 700 similar to 850 degrees C. It can be expected for this new nickel-based superalloy GH750 to be used as the candidate boiler tube materials of A-USC power plants in the future.