Structural features of a high-temperature creep of single-crystal molybdenum in a wide range of the applied stresses. 2. Substructure-hardened state

The salient features of dislocation-structure formation are studied in substructure-strengthened single-crystalline molybdenum under the creep deformation at 1633 K (0.57 T-m) and applied stresses 10-30 MPa by X-ray diffraction, light microscopy, and transmission electron microscopy methods. Strengthening is obtained with preliminary 5% creep strain at 1073 K (0.37 T-m) and applied stresses 40 MPa. The structure sources of hardening (up to 17 MPa) and softening (above 17 MPa) are revealed. They are related with stability of subgrain boundaries created during preliminary deformation, The main difference between states is as follows: within the strengthening-stresses' range, the creep rate is controlled by the Weertman mechanism of edge-dislocations' climb out of subgrain boundaries; within the weakening-stresses' range, the creep rate is controlled by diffusion recovery inside the subgrain boundaries, and the rotation deformation mode appears.