Micromechanisms Responsible in Deformation of Nickel-Base Superalloy Single Crystals under Multiaxial Loading at High Temperatures

• Applicant: Dr.-Ing. Leonardo Agudo Jácome
• Subject Area: Mechanical Properties of Metallic Materials and their Microstructural Origins
• Term: from 2014 to 2020
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 257874562

The role played by Ni-based single crystal superalloys in hot sections of gas turbines remains essential after decades of implementation. Further progress in the area of high temperature resistance of this materials class can only be achieved through the interaction between (1) close-to-reality experimental setups, (2) characterization methods that provide reliable experimental data and (3) life and deformation prediction models that use this data as input.In the proposed project the applicant wishes to contribute to the advancement, the understanding, and thus the improvement of creep performance of superalloy single crystals. To this end, controlled high temperature creep tests will be performed and characterized on standard specimens and on specimens with a circular notch, which generates technically relevant multiaxial stress conditions. Specifically, experimental dislocation-based techniques shall be conducted by applying a newly developed methodology for dislocation analysis in the scanning transmission electron microscopy mode (STEM) to describe the micromechanisms responsible for high temperature creep behavior of the Ni-based superalloy single crystal LEK 94. Creep tests will be conducted at temperatures above 1000°C on the notched specimens. Focus will be set on the following points: (1) the dependence of micromechanisms involved in deformation on the multiaxiality of the stress state, (2) the effect of the presence of a circular notch on high temperature creep behavior and (3) the validation of simulation tools with experimental data obtained. Experimental data from a set of creep tests in the high temperature regime under multiaxial stress state will be generated and compiled. The data evaluated will comprise dislocation types and densities within the individual phases and microstructural evolution induced by multiaxiality will be determined and correlated with the dislocation activity. This data is essential for proper validation of constitutive equations intended to model creep behavior of monocrystalline superalloys, which will be implemented as a last step.

• DFG Programme: Research Grants