Mechanical properties and development of supersolvus heat treated new nickel base superalloy AD730^TM

¹ Aubert & Duval, BP. 1, 63770 Les Ancizes Cedex, France
² Siemens Industrial Turbomachinery AB, 61283 Finspong, Sweden
³ Aubert & Duval, 75 boulevard de la Libération, BP. 173, 09102 Pamiers Cedex, France

^a Corresponding author: alexandre.devaux@eramet-aubertduval.com

Abstract

The enhancement of efficiency in power generation gas turbine requires the development of new superalloys capable of withstanding higher temperatures. The development of AD730^TM superalloy was achieved to provide to this new cast & wrought (C&W) superalloy a higher combination between mechanical properties, microstructural stability and cost than that of other C&W superalloys with a temperature capability up to 750 ^∘C. Supersolvus heat-treatment of AD730^TM was studied to improve the creep properties of fine grain AD730^TM superalloy which were not high enough to reach the foreseen conditions of future power generation gas turbine disks. Firstly, the grain growth was studied to select the supersolvus temperature 1120 ^∘C and to obtain a homogeneous coarse grain microstructure. Then, various supersolvus heat-treatments with different cycles were tested and applied on a forged pancake with a section representative of power generation gas turbine disk. The average grain size was evaluated to be close to 200 μm for all heat-treatments. Tensile, creep, fatigue and fatigue crack growth tests were performed to compare the various heat-treatments. FEG-SEM examinations were also realized to discuss the relationships between heat-treatment, intragranular gamma prime precipitation and mechanical properties. Finally, a comparison made with other supersolvus heat treated C&W superalloys shows that AD730^TM properties obtained with coarse grain microstructure are at the expected level and enable applications for power generation gas turbine discs.