22.08.2015   Comprehensive nuclear materials

Radiation-Induced Precipitation

As previously outlined in Sections 1.03.3.9 and

1. 03.4, phase changes associated with irradiation can be manifested in a variety of geometries, including randomly distributed matrix or grain boundary preci­pitates, continuous grain boundary films, precipitate — free zones near grain boundaries or other point defect sinks, spatially ordered arrays of precipitates, large-scale (>100nm) phase transformations, and

Подпись: Figure 37 Radiation-induced precipitates on {001} habit planes observed next to a grain boundary in V-4Cr-4Ti following neutron irradiation to 0.1 dpa at 505 °C. The fringe contrast in the precipitate interior is due to the a/3{001) displacement vector of the precipitates relative to the vanadium alloy matrix. The beam direction was {111} and the diffraction vector was g = 011. Reproduced from Rice, P. M.; Zinkle, S. J. J. Nucl. Mater. 1998, 258-263, 1414-1419. Подпись: Figure 38 Voids and small helium-filled bubbles in a copper-boron alloy following fission neutron irradiation to 1.2 dpa at 350°C. Reproduced from Zinkle, S. J.; Farrell, K.; Kanazawa, H. J. Nucl. Mater. 1991, 179-181, 994-997.

dissolution or growth of thermally stable precipitates. Preferential coupling of solute atoms to point defect fluxes can lead to modifications in the chemistry of precipitates as well as nucleation ofphases that would not be stable under thermal equilibrium conditions. Figure 37 shows an example of radiation-induced platelet precipitates observed in the grain interiors of V—4Cr—4Ti following neutron irradiation to 0.1 dpa at 505 °C.224 A precipitate-free zone is observed adjacent to the grain boundary in this figure.