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Tensile Deformation and Fatigue Crack Growth in Bulk Nanocrystalline Al-7.5Mg

Published online by Cambridge University Press:  11 February 2011

P.S. Pao ,
H.N. Jones ,
S.J. Gill  and
C. R. Feng
P.S. Pao
Affiliation:
Materials Science and Technology Division, Naval Research Laboratory Washington, DC 20375, U.S.A.
H.N. Jones
Affiliation:
Materials Science and Technology Division, Naval Research Laboratory Washington, DC 20375, U.S.A.
S.J. Gill
Affiliation:
Materials Science and Technology Division, Naval Research Laboratory Washington, DC 20375, U.S.A.
C. R. Feng
Affiliation:
Materials Science and Technology Division, Naval Research Laboratory Washington, DC 20375, U.S.A.
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Abstract

The fatigue crack growth kinetics and tensile deformation of bulk nanocrystalline Al-7.5Mg were investigated. Nanocrystalline particulates were first prepared by mechanically ball milling spray atomized Al-7.5Mg powders in liquid nitrogen. These particulates were then degassed, consolidated by hot isostatic pressing, and extruded into rods. Bulk nanocrystalline Al-7.5Mg has significantly higher fatigue crack growth rates and lower fatigue crack growth thresholds than those of ingot-processed 7050-T7451. The fatigue crack growth thresholds exhibit only a weak stress ratio dependency and can be identified as having a Class I behavior when using the fatigue classification proposed by Vasudevan and Sadananda. In 3.5% NaCl solution, fatigue crack growth rates of bulk nanocrystalline Al-7.5Mg are as much as three times higher than those obtained in air. Tensile fracture of bulk nanocrystalline Al-7.5Mg is preceded by the formation of a localized shear band. In contrast to the low dislocation density in the as-extruded material, the gage section and the shear band region both exhibited a high dislocation density and dislocation cell structure.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 740: Symposium I – Nanomaterials for Structural Applications , 2002 , I1.4
Copyright
Copyright © Materials Research Society 2003

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References

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