Irradiation hardening behavior of polycrystalline metals after low temperature irradiation

Irradiation hardening behaviours of body-centered cubic (bcc), face-centered cubic (fee), and hexagonal close-packed (hcp) alloys and pure metals were characterized after neutron, or proton and neutron irradiations at low temperatures ( less than or equal to 200 degreesC). In the regression analysis, the radiation-induced increase in yield stress, Deltasigma(YS), was expressed in the form of a power law: Deltasigma(YS) = h(dpa)(n), where h and n are the regression coefficients and dpa is displacements per atom. The log log plots of A,Deltasigma(YS) vs. dpa data showed two distinctive regimes: a low-dose regime where a rapid hardening occurs and a high-dose regime where the log-log plot shows a considerably reduced slope. Mean values for n obtained from the 19 metals were about 0.5 for the low-dose regime and about 0.12 for the high-dose regime. Some ductile metals like Fe, Cu and Zr displayed lower It and n values. Doses to reach the regime of reduced irradiation hardening.. D-S.. were in the range 0.003-0.07 dpa. Comparisons between radiation effect parameters led to a conclusion that the transition from the low-dose to the high-dose regime in irradiation hardening occurs either when the tensile specimen undergoes prompt plastic instability at yield or when saturation of defect cluster density occurs. (C) 2004 Elsevier B.V. All rights reserved.