THERMAL-SHOCK AND FATIGUE RESISTANCE EVALUATION OF FUNCTIONALLY GRADED COATING FOR GAS-TURBINE BLADES BY LASER-HEATING METHOD

This paper presents results of thermal shock and fatigue tests conduct ed on ZrO2-based thermal barrier coating systems under the temperature environments for advanced gas turbines. A CO2 laser heating method wa s employed to heat two types of cylindrical specimens with conventiona l two-layer coating and functionally graded coating. Acoustic emission (AE) signals and temperatures were monitored to detect the fracture p rocess of the coating systems. The measurements of AE signals and temp eratures were correlated with the growth of coating delamination. In o rder to investigate the effects of heating rate and cooling rate on th e coating fracture, four different heating/cooling thermal cycles were used in the thermal shock and fatigue tests. Using the AE and tempera ture results, the fracture process of the coating systems is examined, and the delamination growth rate during fatigue tests is determined. Based on the results, a suitable thermal cycle is determined for an ac celerated testing method of the ZrO2-based coating systems. Finally, u sefulness of application of functionally graded coating systems is dis cussed.