Recovery and recrystallization in vanadium foil studied by positron annihilation and X-ray methods

The pure vanadium cold-rolled foils were sequentially annealed at elevated temperature, followed by measurements using positron annihilation and XRD techniques. It was found that in the recovery stage in the temperature range from 100 to 450 degrees C, a significant rearrangement occurs in the dislocation microstructure, which confirms the reduction of the first positron lifetime component. The recrystallization process was beginning at 650 degrees C and proceeds to 800 degrees C or more what is associated with the reduction of the intensity of the second positron lifetime associated with vacancy clusters preassembly located at the boundaries of new grains. The determined activation energy of grain migration was equal to 3.12 +/- 0.38 eV, and the recrystallization temperature was established at 700 degrees C. The significant change in the pole figures indicating recrystallization was noticed only at 1100 degrees C, however, the recrystallization process has been confirmed by the differential thermal analysis. In the temperature range from 100 to 1100 degrees C, a continuous decrease of the crystalline lattice strain was observed.