Effects of ion irradiation on structural and mechanical properties of crystalline Fe/amorphous SiOC nanolaminates

Irradiation-induced changes in the structural and mechanical properties of nanocrystalline Fe, amorphous silicon oxycarbide (SiOC), and Fe/SiOC nanolaminate films were studied using X-ray diffraction, atomic force microscopy, scanning/transmission electron microscopy, and micro/nanoindentation. The films were fabricated by magnetron sputtering and then irradiated at room temperature with 3.5 MeV Fe ions to damage levels of 10, 20, or 50 displacements per atom (dpa). Irradiation of the Fe films was found to increase the compressive residual stress and hardness. For the SiOC films, irradiation led to densification and a subsequent increase in elastic modulus and hardness. The as-deposited Fe/SiOC nanolaminate with individual layer thicknesses of 72 ± 10 nm exhibited a higher hardness compared to the Fe and SiOC films. Furthermore, cross-sectional scanning/transmission electron microscopy of the Fe/SiOC nanolaminate after indentation showed a reduction in the thickness of both the Fe and SiOC layers with no evidence of cracks, shear bands or interface delamination. The combination of increased hardness and deformability of the Fe/SiOC nanolaminate is the result of homogenous plastic co-deformation in the Fe and SiOC layers through the constraint of localized shear flow in the SiOC. Although irradiation of the Fe/SiOC nanolaminate led to recoil mixing of Fe into the SiOC layers, the nanolayered structure remained intact. Increasing the irradiation damage level from 10 to 50 dpa led to more recoil mixing and also a reduction in elastic modulus and hardness of the Fe/SiOC nanolaminate. The study suggests Fe/SiOC nanolaminates are a promising class of irradiation tolerant materials.

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