Observations of the irradiation hardening behavior in neutron irradiated HT-9 steels through in situ TEM nano-mechanical tests

Nano-compression and nano-tensile tests were used to investigate the behavior of HT-9 steel neutron irradiated to 4.29 dpa at 469 °C. The deformation of both as-received and neutron irradiated HT-9 was monitored in situ with a transmission electron microscope, which allowed linking microstructure of the material with the evolution of mechanical properties and identifying the mechanisms governing irradiation-induced hardening of these steels. In nano-compression tests, dislocation-mediated deformation is the deformation mechanism in HT-9 steels irradiated at elevated temperatures. In nano-tensile tests, while dislocations contribute to hardening, grain boundaries determine the deformation mechanisms and eventual fracture of HT-9. The paper further examines the size effect for nano-mechanical tests by varying sample dimensions and comparing obtained results to the micro- and bulk-scale mechanical test data.