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Enhanced Mechanical Hardness in Compositionally Modulated Fe/Pt and Fe/Cr Epitaxial Thin Films

  • B. J. Daniels (a1), W. D. Nix (a1) and B. M. Clemens (a1)

Abstract

The hardnesses and elastic moduli of sputter-deposited Fe/Pt and Fe/Cr multilayers grown on MgO(001) are evaluated as a function of composition wavelength, Λ. Structural determination by x-ray diffraction showed these films to be oriented in the plane as well as out of the plane. The mechanical behavior of these films was evaluated by nanoindentation. The combination of nanoindentation and x-ray diffraction is an attempt to determine the structural underpinnings of the mechanical behavior of these metal multilayer systems. For both systems there is no observed enhancement in the elastic modulus (the so-called supermodulus effect) across a wide range of bilayer spacings. Nanoindentation results show that for Fe/Pt multilayers, the hardness is enhanced over that expected from a simple rule of mixtures by a factor of approximately 2.5, with a maximum enhancement of 2.8 times this value at a wavelength of 25 Å. This enhancement in hardness occurs for bilayer spacings from 20 Å to 100 Å and is not a strong function of Λ over this range. Results for Fe/Cr multilayers show a hardness enhancement over a similar wavelength range of approximately two times the rule of mixtures value, with a maximum enhancement of 2.2 times this value at a wavelength of 40 Å. The larger hardness enhancement in the Fe/Pt system may be due to the structural barrier (FCC/BCC) to dislocation motion between the two materials. The dominant mechanism responsible for the hardness enhancement in Fe/Pt and Fe/Cr multilayers is not yet known, however three models for dislocation interactions which could account for the hardness enhancement in these multilayers are discussed.

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Enhanced Mechanical Hardness in Compositionally Modulated Fe/Pt and Fe/Cr Epitaxial Thin Films

  • B. J. Daniels (a1), W. D. Nix (a1) and B. M. Clemens (a1)

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