This paper reviews the literature relating to the hardening and embrittlement of body-centered-cubic transition metals by neutron irradiation near room temperature, and introduces some new results on the dependence of irradiation hardening in molybdenum on neutron dose and strain rate. A critical assessment is made both of the results to be found in the literature and of these new results, and it is concluded that, although we now have a moderately good phenomenological picture of irradiation hardening and embrittlement in these metals, the underlying mechanisms are still obscure. Evidence presently available suggests, however, that for doses up to about 1018 nvt (>1 Mev) these effects are due principally to the pinning of dislocations by point defects, while at higher doses the interaction of moving dislocation with defect clusters and dislocation loops also becomes important.

A summary is given of some recent work carried out by the authors on yielding and flow in several unirradiated body-centered cubic transition metals, especially columbium. The results, which have revealed some new features in the deformation behavior of these metals, should be used in planning future studies of irradiation hardening and embrittlement.