Ni-base superalloy single crystals are used to make turbine blades for gas turbines which operate in aero engines and power plants. They have to withstand mechanical loads and hot corrosion at temperatures above 1000°C. For their excellent chemical and mechanical high temperature properties they rely on their chemical composition, their crystallographic orientation in a given loading scenario and their microstructure. The chemical composition of Ni-base superalloys is complex, they can contain up to 10 alloy elements. Directional solidification is used to produce single crystalline microstructures and while [001] is the targeted solidification direction, deviations from this natural growth direction can occur. The microstructure of single crystal superalloys consists of small ordered cuboidal particles (L12-phase, typical average cube edge length: 300 nm, volume fraction: 75%) separated by narrow percolating γ-channels (fcc, typical average channel width: 50 nm, average volume fraction: 25%). The present contribution summarizes new results which were obtained in the collaborative research center SFB/TR 103 funded by the German research association DFG. First, the effect of decreasing the concentration of d-shell elements by as little as 1% is investigated [1]. Second, the effect of loading directions in uniaxial tensile and biaxial shear creep testing is considered, focusing on both, small deviations from specific directions (e.g. from the [001] direction in tensile testing) and on different loading geometries (e.g. comparison between [01-1](111) and [-211](111) shear creep behavior) [2,3]. And finally, microstructural effects on creep are considered, with a focus on large scale (dendritic and interdendritic regions) and small scale (fine and coarse γ/γ’-microstructures) heterogeneities. Special emphasis is placed on the evolution of dislocation substructures during creep and new aspects of the pairwise cutting of γ’-particles [4] by dislocations are considered [5].

[1] O.M. Horst et al., Exploring the fundamentals of Ni-based superalloy single crystal (SX) alloy design: Chemical composition vs. microstructure, Materials and Design, 195 (2020) 108976
[2] L. Heep et al., The effect of deviations from precise [001] tensile direction on creep of Ni-base single crystal superalloys, Scripta Mater., 207 (2022) 114274
[3] D. Bürger et al., How nanoscale dislocation reactions govern low- temperature and high-stress creep of Ni-Base single crystal superalloys, Crystals, 10 (2020) 134
[4] H. Gleiter, E. Hornbogen, Precipitation hardening by ordered particles, Materials Science and Engineering, 2 (1968) 285-302
[5] X. Wu et al., On the nucleation of planar faults during low temperature and high stress creep of single crystal Ni-base superalloys, Acta Mater., 144 (2018) 642-655