Thermo-Mechanical and Low Cycle Fatigue Failure Behavior Relevant to Temperature Regime in a TBCed Superalloy Specimen

Steady state and non-steady state thermo-mechanical fatigue failure is great concern in this work. At first steady state thermo-mechanical fatigue failure behavior was investigated using the round-bar TBC specimens, after getting basic data of mechanical properties of the bond/top coats and the substrate alloy. The failure behavior was compared with that during isothermal low cycle fatigue (LCF). Next non-steady state TMF tests were carried out in which non-steady state thermal stress was significant in the TBC specimen, compared with the properties under the steady state TMF. The experimental work clearly demonstrated that the TMF failure lives were significantly changed depending on the temperature regime during TMF and LCF. Of particular importance was found in the non-steady state TMF tests. The non-steady state TMF cycling promoted the delamination of ceramic top coat, resulting in a significant reduction in fatigue life.