Study of the thermal decomposition of melt-quenched Ni-rich metastable bcc and amorphous Ni-Zr alloys

Á Cziráki, I. Geröcs, B. Fogarassy, G. Van Tendeloo, F. Sommer, I. Bakonyi

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Abstract

The phase transformation sequences during thermal decomposition are investigated for Ni-rich melt-quenched body-centred cubic (bcc) and amorphous Ni-Zr alloys. Transmission electron microscopy (TEM) and X-ray diffraction (XRD) are used to determine the structure of crystallization products occurring after heating the melt-spun ribbon samples to various degrees of the phase transformation process monitored by differential scanning calorimetry (DSC). A single DSC peak is observed for both the bcc and amorphous Ni91Zr9 alloys and a two-step process is indicated by DSC for the amorphous Ni90Zr10 alloy. In the bcc-Ni91Zr9 alloy which is actually a Ni(Zr) solid solution phase, the phase transformation starts with the precipitation of Ni5Zr crystallites followed, after a sufficient depletion of the matrix in Zr, by the subsequent transformation of the bcc-Ni(Zr) lattice to face-centred cubic (fcc) Ni. In the amorphous alloy of the same composition, the final products are fcc-Ni and Ni5Zr but at intermediate stages of the phase transformation, bcc-Ni(Zr) crystallites also appear. In the a-Ni90Zr10 alloy, the first DSC peak corresponds to the formation of the bcc-Ni(Zr) phase which then decomposes (second DSC peak) to the equilibrium phases fcc-Ni and Ni5Zr. Thus, in addition to the previous observation of the formation of the metastable bcc-Ni(Zr) phase by rapid quenching from the melt here we present evidence that this phase can form also after partial crystallization of metallic glasses of appropriate chemical compositions.

Original languageEnglish
Pages (from-to)265-282
Number of pages18
JournalInternational Journal of Non-Equiulibrium Processing
Volume10
Issue number3-4
Publication statusPublished - Dec 1 1997

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Keywords

  • Amorphous alloy
  • Calorimetry
  • Crystallization
  • Ni-Zr
  • bcc-Ni(Zr)

ASJC Scopus subject areas

  • Materials Science(all)
  • Metals and Alloys

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