Ni基耐熱合金の高温クリープ疲労損傷に及ぼすひずみ速度の影響の基礎検討

抄録

Ni-based auperalloys are used in harsh high-temperature creep-fatigue environments. It has been reported that the lifetime is drastically decreased under creep-fatigue loads. However, the details of the mechanism of significant strength degradation in these environments have not yet been clarified. In this study, the authors focused on the strain rate during the creep-fatigue loads as a new dominant factor in the damage acceleration mechanism of Ni-based superalloys. Electron backscatter diffraction (EBSD) was used for continuous observation of the change in Image Quality (IQ) value of grains and grain boundaries under the different strain rate, 10 N/s and 100 N/s. As a result, it was found that the IQ value decreased significantly at grain boundaries perpendicular to the load when the strain rate was high. In the creep-fatigue test, the initial intergranular cracking started to appear at the grain boundaries perpendicular to the load when their IQ value degraded to 80 % of that of the received material. In addition, intergranular cracking occurred at grain boundaries which consisted of the difference in Schmid factor larger than 0.03.