Strains in Fe/Cr Trilayers and Multilayers Epitaxied on Mgo and Sto\Mgo

Abstract

High Cr ferritic martensitic steels are good candidates as structural or cladding materials for the next generation of nuclear power plants (generation IV and fusion reactors). The addition of Cr prevents corrosion and the FeCr ferritic form is only weakly sensitive to the swelling phenomenon and minimizes atomic segregation under high-energy neutron irradiation. Diffusion processes and magnetic properties need to be fully understood to optimize these structural materials for high temperature and high flux use. Here, Fe/Cr trilayers and multilayers are prepared as model systems designed to furnish simple data comparable with calculation results of diffusion or magnetic properties. Their structure (epitaxy, residual strains and dislocations) is characterized in detail. Superlattices with high crystalline quality are prepared, with Fe and Cr in coherent epitaxy. In-plane residual strain in Fe is +0.40(5)% on MgO substrates and varies from 1.70(9)% to 0.47(2)% depending on the total thickness of the trilayers on STO\MgO substrates. Thanks to these strains, the contrast between Fe and Cr is enhanced, which opens the way to future kinetics studies using XRD in this system, which is far more efficient (non-destructive and rapid) than HRSTEM-EELS or APT for obtaining data at different times and annealing temperatures.

Keywords: superlattices, FeCr, residual strains, epitaxy dislocations, x-ray diffraction, scanning transmission electron microscopy, electron energy loss spectroscopy, atom probe tomography