Deformation-induced nanocrystallization in Al-rich metallic glasses

Nancy Boucharat 2Rainer Hebert 2Harald Roesner 2Ruslan Z. Valiev 1Gerhard Wilde 2

1. Institute of Physics of Advanced Materials, Ufa State Aviation Technical University, K.Marks St.12, Ufa 450000, Russian Federation
2. Forschungszentrum Karlsruhe, Institute of Nanotechnology, P.O.B. 3640, Karlsruhe D-76021, Germany

Abstract

Al-rich metallic glasses have attracted extensive attention due to occurrence of a primary crystallization reaction that yields microstructures composed of nanocrystal dispersions at extremely high number densities (up to 1023 m-3) within an amorphous matrix. This specific microstructure with the resulting solute redistribution results in a remarkably high tensile strength. While thermal treatment is often applied for examining crystallization reactions, nanocrystal formation has recently been observed in metallic glasses during different deformation processes. We report here structural analyses of Al88Y7Fe5 glass that has been subjected to high-pressure torsion straining (HPT) at room temperature. HPT straining is used as consolidation process that allows producing bulk materials from amorphous ribbons obtained by rapid quenching. It is shown that an extremely high number density of small Al nanocrystals develops already at room temperature when the sample is subjected to a large shear strain. Moreover, nanocrystals appear to be distributed homogeneously throughout the sample without any evidence of strong coarsening. Although the exact mechanism of deformation-induced nanocrystallization generates still controversial discussions, these results demonstrate that applying very large shear strains to marginally glass-forming vitrification products is a promising method for synthesizing homogeneous nanostructures of adjustable grain size. To analyze the mechanisms of deformation-induced crystallization in metallic glasses in detail, plastic deformations at lower strain such as cold-rolling or in-situ straining in the TEM have been performed at room temperature. Based upon these results, likely mechanisms that account for the formation of homogeneous ultrafine nanostructures using severe plastic deformation are discussed.

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Presentation: invited oral at E-MRS Fall Meeting 2005, Symposium I, by Nancy Boucharat
See On-line Journal of E-MRS Fall Meeting 2005

Submitted: 2005-04-12 08:56
Revised:   2009-06-07 00:44
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