A TEM study of α-phase stability in Zr-2.5 Nb pressure tubes following neutron irradiation (A TEM study of α-phase stability)

The α-phase in Zr-2.5 Nb pressure tubes has been analysed after irradiation with neutrons for temperatures between 523 and 573 K. The α-phase contains Nb in supersaturated solid solution (about 0.5−1 wt% Nb) in the as-fabricated condition. Irradiation results in the formation of small discrete precipitates having diameters of about 5 nm. Energy Dispersive X-ray (EDX) analysis using a scanning transmission electron microscope (STEM) was complicated by the presence of a self-generated X-rays in the irradiated material and by the fact that the precipitates were small relative to the foil thickness (typically 100–200 nm). Techniques developed to measure segregation of impurities at interfaces were employed to show that the precipitates were Nb-rich, their formation being consistent with a decrease in Nb concentration in the matrix.