Micro-pillar compression of proton-irradiated chromium examined using cross-sectional site selection, electron microscopy, and molecular dynamics simulation

M Pena and YC Li and ZH Hu and K Cooper and L Hawkins and D Chen and FA Garner and L Shao, JOURNAL OF NUCLEAR MATERIALS, 600, 155299 (2024).

DOI: 10.1016/j.jnucmat.2024.155299

Deformation of proton-irradiated chromium was investigated using micro- pillar compression and electron microscopy. After 2 MeV proton irradiation at 350 degrees C, four micro-pillars were prepared from a single grain on the polished specimen cross section. Depending on the distance away from the irradiated surface, hardness as a function of local damage level was studied. All pillars developed a narrow deformation band on one set of near-adjacent 110 planes, arising from closely-positioned parallel gliding. The critical resolved shear stress for gliding along < 111 >/110 was measured to be 59.6 MPa in unirradiated material beyond the proton range. The critical stress increased by 20 % after 0.5 dpa, and by 58 % after 1 dpa, with saturation of hardening occurring by 0.7 dpa. Post-compression characterization using transmission electron microscopy showed extensive formation of nanometer size voids in a matrix dominated by tangled dislocations. No twinning was observed. The experimental observations are in good agreement with molecular dynamics simulation of pillar compression of chromium, showing dislocation gliding along < 111 >/110 and < 111 >/112. The continued stability of chromium for LWR application requires extension of the exposure level from 1 dpa to similar to 15 dpa expected for typical fuel pin exposure.

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