Abstract
In this study, the difference between in-phase (IP) and out-of-phase (OP) thermomechanical fatigue (TMF) cycling at 100–850 °C of a single-crystal superalloy is investigated both from a mechanical response and resulting microstructure perspective. Results indicate that there is no significant difference in fatigue lives between IP and OP TMF when similar strain ranges and crystal orientations are considered. The deformation mechanisms occurring during IP and OP TMF are similar where the main deformation mechanism for this alloy is localized deformation bands and crack initiation is preferred to these bands. Other TMF mechanisms, such as recrystallization and oxidation, are also discussed.
Highlights
The role of gas turbines in the energy market has changed over the last decade with the introduction of more renewable energy sources
During start-up and shut down of the engine, the turbine blade will be subjected to thermomechanical fatigue (TMF) cycling which means that temperature and load are cycled at the same time
From the perspective of TMF life at the same mechanical strain range, the present study shows that there is no clear difference in fatigue life between IP and OP TMF cycling for the tested alloy and test condi tions
Summary
The role of gas turbines in the energy market has changed over the last decade with the introduction of more renewable energy sources. Today gas turbines are more frequently used as a complementary energy source to for example wind and solar power rather than the sole energy source This means that the gas turbine industry is facing new challenges since today’s engines need to be designed for an increased number of starts and stops. An increased number of starts and stops of the turbine engine, will lead to new types of loading conditions for critical components compared to earlier when the turbine instead was run over longer period of times. First stage turbine blades in land-based gas turbines are subjected to extreme conditions, for example temperatures up to 1000 ◦C To handle these harsh environments, Ni-based superalloys are used since they show excellent mechanical properties and oxidation resistance at high temperatures [1]. The fatigue properties might be improved by having a single-crystal material since it is possible to obtain a lower Young’s modulus compared to a poly-crystal material and a low Young’s modulus leads to lower stress state in the material during straincontrolled fatigue
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