抄録
This paper studies crack growth behaviors in thermal fatigue tests for René80 conventional cast and YH61 single crystal nickel base superalloys. A cylindrical specimen with 19.5mm outer diameter and 2mm thickness was used in the thermal fatigue tests. A rapid temperature gradient in cylinder thickness was realized by induction heating of the outer surface and water cooling of the inner surface. Thermal fatigue tests were conducted by changing the outer surface temperature from 303 to 1173K and temperature holdings of 10 and 60minits were inserted at 1173K. Temperature gradient in thickness was 650K. Crack growth behaviors were inspected with interrupting tests. Crack initiation sites coincided with the ‹100› direction on the outer surface whereas ‹110› direction on the inner surface. It was confirmed that crack initiation sites coincide with stress distribution obtained from a structural analysis considering the anisotropy of the single crystal. Cracks were arrested at the depth of approximately 1.0mm due to stress gradients in the specimen.
