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Continuous Microindentation of Passivated Surfaces in Surface Active Media

Published online by Cambridge University Press:  15 February 2011

Shankar K. Venkataraman ,
He Huang ,
David L. Kohlstedt  and
William .W. Gerberich
Shankar K. Venkataraman
Affiliation:
Department of Chemical Engineering and Materials Science, University of Minnesota, Minneapolis, MN 55455.
He Huang
Affiliation:
Department of Chemical Engineering and Materials Science, University of Minnesota, Minneapolis, MN 55455.
David L. Kohlstedt
Affiliation:
Department of Geology and Geophysics, University of Minnesota, Minneapolis, MN 55455.
William .W. Gerberich
Affiliation:
Department of Chemical Engineering and Materials Science, University of Minnesota, Minneapolis, MN 55455.
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Abstract

Continuous microindentation tests on electropolished, single crystal Fe(3wt%Si) and Ni surfaces with thin passivation layers exhibit sharp discontinuities in the load-displacement behavior. At the discontinuity, which occurs at a load of 1.8 mN for Fe(3wt%Si) and 0.1 mN for Ni, stresses below the indenter were close to the theoretical strength of the corresponding metal. Microindentation tests performed to loads less than the discontinuity point showed an elastic load-unload behavior. On removing the passive film with a NaCl or HC1 solution, strengths are one to two orders of magnitude smaller in the presence of the chloride ions. On evaporation of the liquid, the load at the discontinuity returned to its initial value due to repassivation, indicative of a passivation oxide layer with varying thickness. This conclusion was verified by ellipsometry. Even though the elastic load-unload behavior on the passivated surface suggests elastic behavior, both elastic finite element and non-linear, elastic perfectly plastic finite element solutions strongly suggest that this might not be the case. Several suggestions as to the reasons for the deviation from continuum theory are presented.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 308: Symposium M1 – Thin Films: Stresses and Mechanical Properties IV , 1993 , 543
Copyright
Copyright © Materials Research Society 1993

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References

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