Influence of Testing Temperature on Low-Cycle Fatigue Strength of Thermal Barrier-Coated Ni-Base Superalloy

Thermal barrier coating process has been established in gas turbine and was used for some parts operating at elevated temperature. Thermal barrier coating was constructed with ceramics layer and bond layer as MCrAlY alloy (where M is Ni, Co or Fe). The mechanical properties such as ductility of CoNiCrAlY alloy change drastically with temperature. Then it is important to clarify the influence of temperature on low-cycle fatigue property of thermal barrier coated material. Low-cycle fatigue tests of thermal-barrier coated Ni-base superalloy were performed at room temperature, 773 K, 973 K and 1 088 K. From the experimental results, decrease in fatigue life of the thermal-barrier coated Ni-base superalloy was observed at room temperature as compared with that of the uncoated one. On the other hand, fatigue life of the coated one was increased as compared with that of the uncoated one at 1 088K. Difference in fatigue life between coated and uncoated material was explained by a crack initiation behavior, which was obtained by A. C. potential method and observation by optical microscope. The number of cycles to crack initiation of coated specimen is smaller than that of uncoated one at room temperature. On the other hand, crack initiation life of coated specimen is larger than that of uncoated one. If was discussed from the experimental results that crack initiation and fatigue life were affected by the ductility of the bond layer