The effect of neutron irradiation damage on niobium oxygen alloys

Abstract

An investigation was undertaken to determine the effect of neutron irradiation damage on the low temperature deformation characteristics of niobium oxygen alloys. Alloys containing from 57 to 10,590 at. ppm oxygen interstitial content were tested in compres-sion by strain rate cycling at a base strain rate of 8.33 × 10^-5 s^-1. Tests were conducted between 25 and 500 K on both nonirradiated crystals and crystals irradiated at a fluence of ∼2.0 × 10¹⁹ neutron/cm² (E > 1 MeV). A parametric analysis of dislocation mecha-nisms was performed using the theory of thermally activated dislocation motion.

From the results of this investigation the following conclusions were made: The in-trinsic lattice is the rate-controlling barrier at low oxygen concentrations. The oxygen interstitials appear to be part of the rate-controlling barrier at higher oxygen concentra-tions. The irradiation damage has very little effect on the magnitude of effective stress of the irradiated samples irrespective of the oxygen concentration. The differences in effective stress between irradiated and nonirradiated samples are due to the effect of oxygen on the effective stress of the nonirradiated samples and a scavenging mechanism. The transmission electron microscopy results indicate that the oxygen atoms act as nu-cleation sites for the observable defects. There is qualitative agreement between the increase in the internal stress and the observable defect density. However, there is ab-solutely no agreement between the observable defect density and the changes in the dif-ferences in the effective stress between the irradiated and nonirradiated samples, or the almost zero change in the effective stress of the irradiated samples.