Tensile and bending thermo-mechanical fatigue testing on cylindrical and flat specimens of CMSX-4 for design of turbine blades

This paper briefly describes thermo-mechanical fatigue tests performed on cylindrical and flat specimens of the single crystal material CMSX-4 in 〈0 0 1〉, 〈0 1 1〉 and 〈1 1 1〉-orientation. The test matrix was defined based on the thermo-mechanical loading identified at different positions of actual turbine rotor blades. It included tensile strain-controlled TMF-test conditions on the cylindrical plain specimens and tensile load-controlled TMF-test conditions on the flat specimens with a variable number of straight and angled holes. Flat specimens without holes were tested under load-controlled bending TMF conditions. Different cycle types of in-phase, out-of-phase and phase-shift were applied. A summary is given about the test results including S-N-curves, fracture sections and hysteresis loops and about empirical modeling for prediction of fatigue life of the material. The developed algorithms that predicted the lives in good agreement with the experimental ones cover a large range of thermo-mechanical loading conditions and are applicable to the design of future turbine blades.