On the Characteristics of Grain Boundary Migration in Pure Metals under the Fatigue at Elevated Temperatures

The results observed at the early stage of the high-temperature fatigue are summarized as follows: (1) The grain boundaries move in parallel with the maximum shear stress direction of the specimen axis. (2) Accordingly, the grain boundaries of polycrystals are gradually migrated orthogonally in the maximum shear stress direction under reversed stress. (3) The characteristics peculiar to the above grain boundary migration are observed not only on the specimen surface but also in its interior. The reasons for the above phenomena are discussed in connection with the release of the stored energy resulting from the repeated boundary sliding, the occurrence of slips in the matrix almost in parallel with the maximum shear stress direction, and a smaller amount of the vacancy flow than that of creep. (Received October 2, 1965)