TY - THES

T1 - Microstructural influences on bending resonance fatigue in nickel-based superalloy Rene'88DT

AU - Taurer, Gregor

N1 - no embargo

PY - 2024

Y1 - 2024

N2 - This master's thesis delves into the meso- and microscale fatigue phenomena of nickel-based superalloy Rene'88DT by utilization of bending resonance fatigue testing of flat mesoscale specimens, scanning electron microscopy, and data analysis. The alloy was developed for the high-pressure turbine section of large gas turbine engines in pursuance of higher lifetime and safety, while simultaneously increasing the efficiency and sustainability of the engine. This work aspires to reduce the hiatus between experimental results of fatigue damage in high-pressure turbine disks and the computational simulation and design process by identifying microstructural influences on fatigue crack initiation. Moreover, using high-resolution digital image correlation allows to measure the sub-grain strain that developed near fatigue crack initiation sites. The preparation, testing, and evaluation were done with state-of-the-art methods and software, aiming for high reproducibility and possible application to other complex materials. Preceding studies served as a guide and some of the existing theories for microstructural influences were tested for their validity. The results are consistent with the literature of fatigue damage occurring during fully reversed axial fatigue testing. Fatigue crack initiation was predominantly discovered near twin boundaries and a suitable model for energy-based slip band cracking due to dislocation motion and pile-up was examined with the generated results from this thesis.

AB - This master's thesis delves into the meso- and microscale fatigue phenomena of nickel-based superalloy Rene'88DT by utilization of bending resonance fatigue testing of flat mesoscale specimens, scanning electron microscopy, and data analysis. The alloy was developed for the high-pressure turbine section of large gas turbine engines in pursuance of higher lifetime and safety, while simultaneously increasing the efficiency and sustainability of the engine. This work aspires to reduce the hiatus between experimental results of fatigue damage in high-pressure turbine disks and the computational simulation and design process by identifying microstructural influences on fatigue crack initiation. Moreover, using high-resolution digital image correlation allows to measure the sub-grain strain that developed near fatigue crack initiation sites. The preparation, testing, and evaluation were done with state-of-the-art methods and software, aiming for high reproducibility and possible application to other complex materials. Preceding studies served as a guide and some of the existing theories for microstructural influences were tested for their validity. The results are consistent with the literature of fatigue damage occurring during fully reversed axial fatigue testing. Fatigue crack initiation was predominantly discovered near twin boundaries and a suitable model for energy-based slip band cracking due to dislocation motion and pile-up was examined with the generated results from this thesis.

KW - Nickel-basierte Superlegierung

KW - Ermüdungsversuche

KW - Biegeresonanz

KW - MTEX

KW - high-resolution DIC

KW - Python

KW - nickel-based superalloy

KW - fatigue

KW - bending resonance fatigue

KW - MTEX

KW - high-resolution DIC

KW - Python

M3 - Master's Thesis

ER -