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Decoupled bulk and surface crystallization in Pd85Si15 glassy metallic alloys: Description of isothermal crystallization by a local value of the Avrami exponent

Published online by Cambridge University Press:  31 January 2011

A. Calka  and
A. P. Radliński
A. Calka
Affiliation:
The Laser Physics Center, Research School of Physical Sciences, The Australian National University, P. O. Box 4, Canberra, ACT2601, Australia
A. P. Radliński
Affiliation:
The Laser Physics Center, Research School of Physical Sciences, The Australian National University, P. O. Box 4, Canberra, ACT2601, Australia
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Abstract

Isothermal devitrification of Pd85Si15 amorphous alloys has been analyzed using differential scanning calorimetry (DSC) and x-ray diffractometry. Both as-quenched and aged amorphous ribbons were investigated. Crystallization of aged samples starts from the surface and proceeds several micrometers into the bulk. The product of this process is a layer of strongly textured palladium (111) followed by a mixture of Pd2Si, Masumoto MSI phase, and untextured palladium. Next, the crystallization occurs via a different (bulk) mechanism, resulting in a mixture of Masumoto MSII phase and untextured palladium. The bulk mechanism is the only one observed in as-quenched samples. The surface and bulk crystallization mechanisms are spatially decoupled and, therefore, the corresponding DSC data can be analyzed separately. This has been done according to the Kolmogorov–Johnson–Mehl–Avrami model and also using the recently developed concept of local value of Avrami exponent n. For both the surface and bulk crystallization the phase transition process cannot be characterized by a single value of n. Observed variation of n with the crystallized fraction x is explained by a considerable variation of the nucleation rate that takes place during devitrification.

Type
Articles
Information
Journal of Materials Research , Volume 3 , Issue 1 , February 1988 , pp. 59 - 66
Copyright
Copyright © Materials Research Society 1988

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References

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