Tensile properties and microstructure of Zr-1.8Nb alloy subjected to 140-MeV C4+ ion irradiation

Tensile properties and microstructure of a Zr-1.8Nb alloy subjected to 140-MeV C4+ ion irradiation at 573 K up to 5.3 dpa have been investigated by using 0.18 mm-thick tensile specimens. Irradiation damage was introduced into the tensile specimens homogeneously over entire thickness using a variable energy degrader. Irradiation-induced strengthening and embrittlement (loss of ductility) were successfully evaluated. The yield strength of irradiated specimens (3.1- and 5.3-dpa) was 137% and 145% of unirradiated specimen, whereas the total elongation of those irradiated specimens was less than a half of unirradiated specimen. It appears that the rate of embrittlement is fairly faster than the rate of strengthening. Transmission electron microscopy (TEM) observation on the 3.1-dpa specimen revealed that the bcc-Nb/Zr precipitates originally contained in the alloy were stable in terms of crystal structure and size. The size and number density of dislocation loops were 7.2 nm and 1.2 × 1021/m3 for the -loops, 15.4 nm and 6.5 × 1020/m3 for the -type loops, respectively. The increase of yield strength expected from these dislocation loops was ∼64% of the actual irradiation-induced strengthening, indicating that the dislocation loops are the main contributors for the irradiation-induced strengthening.