Viscoplastic Behavior of the Grain Size Transition Zone in a Dual Microstructure Turbine Superalloy Disk

This study focuses on the challenging characterization of the microstructuresMicrostructure and the viscoplastic behavior (creepCreep, relaxation) within the transition region of dual microstructureMicrostructure disksDisk made of γ/γʹ Ni-based superalloysNi- based superalloy. This transition microstructureTransition microstructure, consisting in spatial variations of grain sizesGrain size and/or γʹ precipitationPrecipitation, poses difficulties in providing insights into effective modeling strategies in aero-engines. To characterize viscoplastic behavior at intermediate temperatures, stress relaxationStress relaxation tests were employed using AD730™ superalloyAD730 superalloy. A single-crystalline version of AD730™ was used to isolate the effects of different precipitationPrecipitation states (ranging from 15 to 300 nm in size), at 700 °C and 800 °C. The results reveal a significant impact at 700 °C, while no substantial impact was observed at 800 °C. Additionally, precise specimen machining was conducted in different radial zones of a dual diskDual disks to explore the influence of various grain sizeGrain size gradients, on viscoplastic behavior at both 700 °C and 800 °C. The findings indicate a progressive viscoplastic behavior along the gradient of grain sizeGrain size for both testing temperatures. Finally, the viscoplastic behavior of transition specimens was analyzed within the framework of a grain-sensitive phenomenological model. The study provides valuable insights into understanding and modeling the complex behavior of dual microstructureMicrostructure disksDisk in aero-engine applications.