Dose dependence of strength after low-temperature irradiation in metallic materials

This study intends to review and characterize the low-temperature (<473 K [200 C]) irradiation-hardening behaviors in metallic materials and to propose new interpretations on the dose dependence of strength, particularly in the prehardening and saturation regimes. The analysis of results of yield stress-dose curves indicate that four dose-dependence regimes exist: the prehardening, main hardening, saturation, and embrittlement regimes. The semilog plots of yield stress vs dose data revealed that the prehardening regime displaying zero hardening or softening was common at least for the alloys with low-dose data available. It was observed that the dose range of the prehardening regime increased with the strength of material, which indicates that slower initiation in irradiation hardening is expected when strength is higher. For the majority of the metallic materials analyzed, it was reconfirmed that the exponent of the power-law hardening function was evaluated to be about 0.5 in the main hardening regime and about 0.1 in the saturation regime. In these positive hardening regimes, the low strength pure metals such as Fe, Ta, Cu, and Zr displayed lower hardening exponents. The minimum dose to the saturation of irradiation hardening was in the range of 0.003 to 0.08 dpa, depending on the category of materials. It was also reaffirmed that there exists a strong relationship between the saturation in irradiation hardening and the occurrence of plastic instability at yield.