Deformation in metals after low-temperature irradiation: Part I – Mapping macroscopic deformation modes on true stress–dose plane Original Research Article

Macroscopic deformation modes, elastic, uniform plastic, and unstable plastic deformation modes, are mapped in tensile true stress–dose space for more than two dozen metallic materials consisting of 13 body-centered cubic (bcc), 11 face-centered cubic (fcc), and two hexagonal closed packed (hcp) metals. The boundaries between different deformation zones are set by the true stress versus dose curves: the yield stress (YS), plastic instability stress (PIS), and true fracture stress (FS) plotted as functions of dose. Values for these true stresses are obtained from uniaxial tensile tests or calculated from engineering tensile data using a linear strain-hardening model for necking deformation. The relatively low-strength annealed fcc metals display large uniform plasticity regions, while unstable deformation regions are dominant in the harder bcc and hcp metals. PIS values for all materials are independent of dose except for the precipitation-hardened IN718 alloy, where a decrease of PIS occurs due to an irradiation-induced change in second phases. In the bcc materials for high-temperature application, such as 9Cr ferritic/martensitic steels, sintered molybdenum, vanadium, and tantalum, the radiation-induced embrittlement is characterized in terms of FS decreasing with dose at relatively high doses. FS is nearly dose-independent below the critical dose for embrittlement. It is concluded that the tensile stress-based deformation mode maps effectively integrate mechanical property information and characterize differences in radiation effects between crystalline structures or material groups.