Effects of neutron irradiation on the microstructure and microhardness of niobium-base alloys

The microstructure and microhardness of several niobium-base binary and ternary allows were investigated following fast neutron irradiation to a fluence of 18 dpa (4.8 x 10/sup 22/ n/cm/sup 2/, >0.1 MeV) at 6500C. Transmission electron microscope (TEM) procedures were employed to observe the microstructure of the alloy specimens following neutron irradiation and in the unirradiated condition. Micorhardness measurements were made on irradiated and unirradiated specimens to obtain information on the effects of irradiation on mechanical properties. Neutron irradiation of the Nb-1Mo and Nb-5Mo-1Zr alloys produced voids and a high density of dislocation loops. No voids were observed in the irradiated Nb-1Zr alloy. Microhardness measurements of the irradiated alloys indicated that the effect of the fast neutron irradiation was to increase the microhardness of all the niobium-base alloys. The magnitude of the microhardness increase was found to be a function of the alloy composition, with the smallest increase observed in the Nb-5Mo-1Zr alloy. The observations in this study are in agreement with the previous work, which has shown that molybdenum and zirconium additions were effective in suppressing void formation in niobium-alloys for irradiation temperatures up to -- 11000C