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- Gamma titanium aluminide (3)
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Eingeladener Vortrag
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The aim of this research was to investigate the influence of nominal temperature errors on test results and to develop the nominal temperature tolerance for TMF-tests. This concept was confirmed with series of specially developed TMF-tests with defined temperature errors, performed on one test material (NIMONIC 90) in a temperature range of 400850 °C. These tests should show the influence of temperature errors on test results with an emphasis on lifetime in comparison with reference tests. It is shown that with a limited number of specimens and only one test material, it is possible to propose a reasonable general temperature tolerance for TMF-tests, valid for a wide range of materials and test conditions.
The uniaxial, torsional and axial-torsional thermomechanical fatigue (TMF) behavior of the near-γ TiAl-alloy TNB-V5 was investigated. TMF tests were performed at 400-800 °C with mechanical strain amplitudes ranging from 0.15% to 0.7%. The tests were conducted thermomechanically in-phase (IP) and out-of-phase (OP).
For the same lifetimes, uniaxial IP tests required the highest strain amplitudes, while OP test conditions were most damaging and needed the lowest strain amplitudes. The Mises equivalent mechanical strain amplitudes of pure torsional tests were found in between uniaxial in-phase and out-of-phase tests for the same lifetimes. The non-proportional multiaxial out-of-phase test showed a lower lifetime at the same equivalent mechanical strain amplitude compared to the other types of tests.
The microstructure has been characterized applying electron microscopy and microstructural parameters such as fraction of twinned grains, grain size, lamellar distance and dislocation density have been quantified.