Mikromechanische Untersuchung der Kriecheigenschaften von Ni- und Co-Basis Superlegierungen bei erhöhten Temperaturen

Description

The aim of this work was to investigate microstructural and chemical inhomogeneities in Ni and Co-based superalloys on the micro- and nanoscale mechanically at high temperatures to determine their influence on the macroscopic mechanical behavior at elevated temperatures. For this purpose, combinatorial studies were carried out on diffusion couples using an integrated alloy development approach to determine the optimal Cr content in a Co-based superalloy that leads to an improved oxidation resistance while maintaining the mechanical properties. In addition, tensile creep tests were carried out with differently sized samples and microstructures to investigate the influence of miniaturization on creep properties. It was found that a reduction in diameter from 6 mm to 150 µm leads to the same minimum creep rate. However, this strong miniaturization leads to a decrease in elongation at break. In addition, compression tests at a constant strain rate and strain rate jump tests were carried out to determine the temperature- and strain rate-dependent solid solution hardening behavior of W, Ta, Re, Mo and Ru in Ni. From this, a semi-empirical model could be developed which allows the solid solution hardening of the investigated alloying elements in Ni to be quantitatively estimated as a function of temperature, strain rate and composition. Overall, the methods developed in this work can be used specifically to accelerate and optimize the alloy development of new superalloys.