Kinetics of phase transformations in Ni87P13 alloy upon heating

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Abstract

Ni87P13 amorphous electroless alloy was prepared. For the alloy the structural disorder parameter was calculated and the alloy was investigated by means of the temperature dependence of the resistivity. Kinetic parameters of spherulitic growth process were evaluated. The spherulitic structure was characterized by use of transmission electron microscope.

Introduction

For compositions that have a good glass forming ability there are important empirical rules [1], [2] to be fulfilled. The alloys at or near deep eutectic point show a good glass forming ability (GFA) and the factors limiting eutectic growth can promote the amorphization of metallic alloys [1], [3], [4], [5]. When the polymorphic melting curves (T0 curves) for the system drop steeply with composition, in the alloys for which the primary composition is in the region between T and T lines (for a two-component system) partitionless solidification is thermodynamically impossible and metastable undercooled liquid turns into a glassy state when the temperature falls below Tg. One of the most important features of amorphous metallic alloys is thermal stability. The potential applications of bulk metallic glasses such as the possibility of plastic deformation or soldering with use of viscous flow [6] or the conscious controlling of the crystallization process in order to achieve the appropriate properties depend largely on the knowledge of the processes and microstructures that are created during heating of the material. It is also very crucial to study the processes occurring during heat treatment because of the new potential characteristics and applications of the materials. Therefore, the aim of the present work is to define the structures formed during crystallization and the kinetics of crystallization in Ni87P13 amorphous alloy.

Section snippets

Experimental

The studies were performed on Ni87P13 electroless alloy [7]. The X-ray study of the as-deposited alloy was performed using a TURM 62 device equipped with a HGZ3 goniometer. Cu (λ = 1.54718 Å) radiation and a quartz monochromator were applied. During intensity measurement in the range of angle Θ (5–62°) scanning by 0.1° was used. On the basis of the measurements the radial distribution function H(r) was calculated. Assuming that the atomic radii for nickel and phosphorus are 1.3 and 1.28 Å,

Results and discussion

The X-ray spectra of the investigated alloys suggested that the alloy is amorphous or is at least nano-crystalline (Fig. 1) and the diffraction results allowed the calculation of the values of η°AB (short range order parameter) and ξ (atomic disorder parameter). The value of normalized coefficient of short-range order η°AB is negative (−0.38603). This indicates that there is a general tendency for clustering of the same kind of atoms. This may indicate that the Ni–Ni and P–P neighbourhoods are

Conclusions

  • 1.

    The structural disorder parameter ξ in the case of the studied alloys is below 5.75. Such low ξ values suggest that the alloy is amorphous in as-deposited state.

  • 2.

    The value of the normalized short–range order coefficient η°AB is negative. This is due to the tendency for separation of the constituents within the amorphous matrix.

  • 3.

    During the heating of the studied alloy three temperature regions can be observed: (1) below 563 K, (2) between 563 and 633 K, (3) above 633 K. The second region may be

Acknowledgement

The financial support by the KBN research project No. 4 T08D 00524 is gratefully acknowledged.

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