Chair for Materials Science and Engineering

High temperature plasticity of single crystal Ni-base superalloys with a special focus on cyclic loading conditions. In the first two funding periods of SFB/TR 103, the uniaxial creep behavior of single crystal Ni-based superalloys was studied extensively and other types of mechanical loading received less attention. In Marc Sirrenberg’s work, emphasis is placed on high temperature constant strain rate testing and on phenomena associated with cyclic loading. It is well known that dislocation mechanisms which govern creep differ from those which occur under constant strain rate conditions. These can give rise to a yield stress anomaly, where apparent yield stresses increase with increasing temperature. One objective is to find out how this yield stress anomaly depends on the microstructural parameters which characterize the γ/γ’-microstructure. In addition, the microstructural aspects related to cyclic loading conditions receive special attention. Specimens subjected to thermo-mechanical fatigue tests (performed at KIT) will be microstructurally analyzed and compared with specimens which were subjected to constant strain rate testing and to cyclic creep loading. The microstructural evolution in the different types of high temperature tests will be analyzed and compared. The objective is to contribute to a better understanding of elementary processes, which govern high temperature strength under cyclic loading conditions.