1993 年 42 巻 478 号 p. 868-873
This study investigates the effects of solidification direction on cyclic constitutive relation and creep-fatigue lives of Mar-M247LC Nickel-base directionally solidified (DS) superalloy. Strain controlled low cycle fatigue tests with 10 and 60min. hold-times in tension were carried out at 1173K in air for three kinds of specimens of which loading direction was 0°, 45° and 90° to the solidification direction. Step-up relaxation tests with a 10min. tension hold-time were also conducted for the three kinds of specimens to determine the material constants used in the creep constitutive equation. Creep-fatigue lives were significantly affected by loading direction when the fatigue lives were correlated with the total strain range; the 0° specimen had the maximum creep-fatigue life and the 45° specimen had the minimum life. On the other hand, the cyclic stress range gave a better correlation of creep-fatigue lives for all the specimens, which showed that stress is a better parameter for the life prediction. An elastic-plastic-creep constitutive equation was developed taking account of the anisotropy of Young's modulus, and the equation successfully predicted the experimental stress amplitude. The creep-fatigue life prediction method was developed based on the constitutive equation.