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The Strength and Fracture of Passive Oxide Films on Metals

Published online by Cambridge University Press:  10 February 2011

M. Pang ,
D. E. Wilson  and
D. F. Bahr
M. Pang
Affiliation:
Mechanical and Materials Engineering, Washington State University, Pullman, WA 99164-2920
D. E. Wilson
Affiliation:
Mechanical and Materials Engineering, Washington State University, Pullman, WA 99164-2920
D. F. Bahr
Affiliation:
Mechanical and Materials Engineering, Washington State University, Pullman, WA 99164-2920
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Abstract

Passive films have been grown electrochemically on a polycrystalline titanium alloy. By varying the applied voltages, the film thickness is varied. A testing apparatus has been constructed to allow measurements of nanomechanical properties during electrochemical testing using a Ag/AgCl reference electrode in a traditional three-electrode potentiostatic scan. The stress at which oxide film fracture occurs is correlated to the applied potential. Observations of in situ film fracture measurements on single grains during immersion show the strength of the film remains constant in environments in which the film is inert, but decreases by approximately 20% in solutions which lead to corrosion. The fracture mode of the oxide has been observed using atomic force microscopy, and is shown to qualitatively match the largest tensile stresses which develop using elastic contact mechanics. A simplified model for determining the maximum tensile stress around an indentation is presented, and is used to show the stress required for fracture increases approximately linearly with increasing applied anodic polarization, from 850 MiPa to approximately 3 GPa for applied potentials between 1 and 9 V.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 594: Symposium V – Thin Films - Stresses & Mechanical Properties VIII , 1999 , 501
Copyright
Copyright © Materials Research Society 2000

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References

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