Microstructural analysis of deformation in neutron-irradiated fcc materials

Plastically deformed microstructures in neutron-irradiated face centered cubic (fcc) materials, copper, nickel, and 316 stainless steel (316SS), were investigated by transmission electron microscopy (TEM). Neutron irradiation in the range of 65-100 °C up to 1 displacement per atom (dpa) induced a high number density of black spots, stacking fault tetrahedra (SFT) and Frank loops, which resulted in irradiation-induced hardening. Deformation of irradiated fcc materials induced various microstructures, such as dislocation channels, stacking faults, and twins. In the 316SS irradiated to 0.1-0.8 dpa, the deformation microstructure consisted of a mixture of dislocation bands, tangles, twins, dislocation channels, and also martensite phase. Deformation-induced martensite transformation tends to occur with dislocation channeling, suggesting that localized deformation could lead to transformation of austenite to martensite at a high stress level. At higher irradiation doses (0.1-1 dpa), dislocation channeling became the dominant deformation mode in fcc materials, and is coincident with prompt plastic instability at yield. The channel width seems to be wider when the angle between tensile direction and dislocation slip direction is close to 45°. Furthermore, the correlation between channel width and resolved shear stress appears to be material dependent, with copper having the greatest slope and 316SS the smallest.