Mechanical and microstructural investigations of processes governing annealing and shear creep anisotropy of the single crystal superalloy CMSX-4 at temperatures above 1000 C

In aero-engines as well as in the next generation of gas turbines single crystal blades will be extensively used. In the hottest zone of the blade at the leading edge a multiaxial stress state exists which is due to a temperature gradient towards the cooling channel. An interesting question is how the mechanical properties of the blade are influenced by the crystallographic orientation perpendicular to the growth direction of the blade in combination with this multiaxial stress state. The aim of this study is to provide biaxial creep data in the temperature region above 1000 C. The method of testing is the double shear creep test. FEM calculations were performed to prove the viability of the shear geometry in terms of (i) homogeneity of shear stress and (ii) stress redistribution during creep. Microstructural investigations of annealed samples show the influence of internal stress fields which lead to the evolution of dislocation networks around the γ'-particles and to directional coarsening of the γ'-particles. The coarsening behaviour of γ'-particles differs strongly between dendritic and interdendritic regions. (orig.)