Anwendungsgrenzen von modernen Nickelbasis-Superlegierungen in effusionsgekuehlten Bauteilen zukuenftiger Gasturbinen

The deformation and damage behaviour of two nickel-base superalloys, CMSX-4 and SX CM186LC, have been investigated. Hot-tensile, tensile creep and low-cycle-fatigue tests have been performed on single crystal and directionally solidified variants at temperatures up to 1000 C to compare their tensile-, creep- and fatigue behaviour. The strength and fatigue properties of both materials were significantly influenced by their different microstructures. Comparing the single crystals materials, CMSX-4 exhibited in strain rate controlled tensile tests (1000 C) higher strength properties than SX CM186LC. The heterogeneity of the microstructure development of SX CM186LC favoured crack initiation and explains the worse fatigue behaviour. Crack growth followed mainly in the interdendritic regions. In the temperature range of 750 to 1000 C, the creep resistance of SX CM186LC was lower than that of CMSX-4. In isothermal fatigue tests the advantage of the single crystal variants compared to the directionally solidified variants was demonstrated. Bond coating of MCrAlY on single crystal specimens seemed to have a positive effect on life time compared to directionally solidified variants. The difference in the materials behaviour could be clearly demonstrated by a comparison between the homogeneous microstructure of CMSX-4 and the heterogeneous microstructure of SX CM186LC. Based on some oxidation test results mentioned in the open literature together with isothermal oxidation tests carried out in a temperature range of 550 to 1000 C, CMSX-4 exhibited good oxidation resistance, which meant that the cooling channels (drillings) did not close up due to oxide scale formation. Principally this work concentrated on the set-up and testing method for in-situ investigations in the scanning electron microscope (SEM). In-situ investigations in the SEM were carried out to obtain a description of micro-crack (smaller than 100 mm) initiation and growth, starting from laser drilled cooling channels. The development of the SEM investigation showed that crack initiation started mainly at the base of the drilling, crack propagation appeared to be perpendicular to the main load stress direction and crack growth ran along the cooling channels located perpendicular to the main load. In-situ testing in the SEM represents a new testing method. The results which described the material behaviour could be used in the evaluation of the operational limits of effusion cooled components in modern industrial gas turbines. (orig.)Available from TIB Hannover: RA 831(4067) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman