In situ SEM-EBSD analysis of plastic deformation mechanisms in neutron-irradiated austenitic steel

Abstract

In situ tensile tests, accompanied by scanning electron microscopy coupled with electron backscatter diffraction (EBSD) analyses were performed on neutron-irradiated 304L steel specimens (5.9 dpa, irradiation in boiling water reactor at 288 °C). Selected regions of interest were analyzed following tensile deformation of the specimens to increasing levels of strain, allowing for tracking and investigating strain-induced misorientation evolution, lattice rotation, twinning, and phase instability. Deformation-induced changes in EBSD misorientation parameters, such as kernel average misorientation (KAM) and grain reference orientation deviation (GROD), were analyzed as a function of the strain level (ε). The mapping of GROD values revealed the formation of specific “hot spots” (areas with high local misorientation) in the early stages of tensile deformation (ε ∼0–0.02) with values increasing much more quickly for irradiated specimens than for nonirradiated specimens. In contrast, average KAM values showed very little change in the small strain range (ε < 0.02) and fast growth at larger strain values.