Tensile Deformation and Fatigue Crack Growth in Bulk Nanocrystalline A1-7.5Mg
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.
Document Details
- Document Type
- Technical Report
- Publication Date
- Jan 01, 2003
- Accession Number
- ADP014238
Entities
People
- C. R. Feng
- H. N. Jones
- P. S. Pao
- S. J. Gill
Organizations
- United States Naval Research Laboratory