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2 Archives of Materials Science

2 2004

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Vitrification and crystallization of marginally glass-forming alloys.

Wilde G., Boucharat N., Dinda G.P., Rösner H.

Archives of Materials Science

2004

Vol. 25, nr 4

391-397

Thermally- and deformation-induced nanocrystallization has been investigated in marginally glass forming Al-rich alloys. Conventional calorimetry and microcalorimetry results coupled with detailed and quantitative microstructure analyses using dark-field and high-resolution transmission electron microscopy yielded a quantitative description of the kinetics of nanocrystallization in its earliest stages. These results form the basis for the development of advanced processing strategies to synthesize amorphous/nanocrystalline composite structures with even higher nanocrystal number densities, potentially giving rise to increased stability and improved performance of these new materials.

Crystallisation sequence during the devitrification of Al-based glassy alloys.

Boucharat N., Rösner H., Valiev R.Z., Wilde G.

Archives of Materials Science

2004

Vol. 25, nr 4

357-363

The effect of thermal treatment and severe plastic deformation such as high pressure torsion straining (HPT) on the crystalisation behaviour of rapidly quenched Al88Y7Fe2 glasses was investigated. Calorymetry and microstructural analyses clearly indicate that HPT strongly promotes the development of an extremely high density of nanocrystals. Thus, plastic deformation of marginal glass formers at ambient temperature presents an alternative and rather efficient synthesis route for the development of new bulk nanostructured materials. Additionally, it is shown that the diffusional control during crystallization involves the formation of a concentration gradient of varying magnitude at the interface of growing Al-nanocrystals, affecting the nucleation conditions for new phases. Indeed, the adjustment of the concentration gradient within a certain interval can promote the formation of the so-called "transient" phase. The results obtained indicate that the control of the concentration gradient represents a new perspective for active phase selection.