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.
|Number of pages||18|
|Journal||International Journal of Non-Equiulibrium Processing|
|Publication status||Published - Dec 1 1997|
- Amorphous alloy
ASJC Scopus subject areas
- Materials Science(all)
- Metals and Alloys