Irradiation hardening in columbium

Abstract

The influence of neutron irradiation on strength and ductility of columbium has been studied as a function of grain size and irradiation temperature (77°–330°C). Irradiation-induced hardening has been analyzed in terms of σ i , the frictional stress opposing the motion of dislocation, and the constant k y as determined from both a Petch-type equation ( σ ly = σ i + k yd − 1 2 ) and the extrapolation of stress-strain curves. The increase in lower yield strength on irradiation was found to be a function of irradiation dose and irradiation temperature, and was mainly due to an increase in σ i . Both methods of analysis gave different and unexpected values for k y . The irradiation hardening was accompanied by severe reductions in metal ductility and, in some cases, complete embrittlement. The loss of ductility at the relatively low total neutron doses examined (7.5 × 10 19nvt) was a function of irradiation dose, irradiation temperature, and grain size. Since the range of grain sizes studied included those levels characteristic of commercial wrought and recrystallized columbium, the severe effect of irradiation on ductility is of direct technological interest. The observed embrittlement of columbium after a relatively small amount of irradiation hardening is discussed.