Plastic instability in polycrystalline metals after low temperature irradiation

The dose dependence of plastic instability behavior has been investigated for polycrystalline metals after neutron irradiation at low temperatures (<200 °C). The analyzed materials consist of 10 body-centered cubic (bcc), 7 face-centered cubic (fcc), and 2 hexagonal close packed (hcp) metals. It was found that the metals after irradiation showed necking at yield when the yield stress exceeded the true plastic instability stress, σ _IS, for the unirradiated material. It was also shown that σ_IS was almost independent of dose below a critical dose. The critical dose is called the dose to plastic instability at yield, D _C, because at higher doses the material shows necking at yield. The D_C values ranged from 0.002 to 0.2 dpa for bcc and hcp metals, except for a high purity iron, that had a D_C value of 6 dpa; whereas the fcc metals gave generally high values ranging from 0.1 to 40 dpa. It is attempted to explain the dose independence of the plastic instability stress by a straightforward shifting of tensile curves by the appropriate strain corresponding to the radiation-induced increase in yield stress. The dose independence of strain-hardening behavior suggests that radiation-induced defects and deformation-produced dislocations give similar net strain-hardening effects. Published by Elsevier Ltd on behalf of Acta Materialia Inc.