Accession Number:

ADA056247

Title:

Structural Imperfections in Amorphous Metals.

Descriptive Note:

Technical rept.,

Corporate Author:

HARVARD UNIV CAMBRIDGE MA DIV OF APPLIED SCIENCES

Personal Author(s):

• Spaepen,Frans

Report Date:

1978-05-01

Pagination or Media Count:

32.0

Abstract:

The experimental evidence of the existence and nature of imperfections in amorphous metals is reviewed. It derives from observations of microscopic homogeneity, density measurements, positron annihilation studies, inhomogeneous flow and measurements of the various atomic transport coefficients shear viscosity, diffusivity, structural relaxation rate and crystal growth rate. In contrast with crystal imperfections, which tend to be discrete and localized due to the constraints imposed by the long range periodicity, imperfections in amorphous metals tend to be more extended and diffuse. This is illustrated by the collapse and annihilation of a vacancy in a two-dimensional amorphous dynamic hard sphere model, and the observations are generalized for other defects in three dimensions. It is concluded that the most fruitful way of describing defects in amorphous metals is as sites with small local perturbations of the ideal short range order, which allows local configurational rearrangements. It is suggested that different types of rearrangement nearest neighbor changes, shear, volume annihilation are possible at different sites, and that the concentration and lifetime of each type of site determines the time constant of the corresponding atomic transport process. Author

Descriptors:

• *METALS
• *AMORPHOUS MATERIALS
• *DEFECTS(MATERIALS)
• SHEAR PROPERTIES
• DENSITY
• MICROSTRUCTURE
• TRANSPORT PROPERTIES
• STRUCTURAL RESPONSE
• RELAXATION
• DIFFUSIVITY
• VISCOSITY
• ATOMIC PROPERTIES
• CRYSTAL GROWTH
• HOMOGENEITY
• POSITRONS
• ANNIHILATION REACTIONS

Subject Categories:

• Properties of Metals and Alloys

Distribution Statement:

APPROVED FOR PUBLIC RELEASE