Preparation, structure and physical properties of Fe-, Co- and Ni-rich melt-quenched ribbons containing Zr or Hf - Part IV: Thermal stability; DSC, TEM and thermomagnetic studies

In this part of a series of papers on Fe-, Co- and Ni-rich melt-quenched ribbons containing Zr of Hf, the results of a study of the thermal stability by differential scanning calorimetry, transmission electron microscopy and thermomagnetic measurements will be described for the amorphous Zr-Fe, Zr-Co and Zr-Ni as well as the bcc-Ni(Zr) alloy ribbons. For the amorphous alloys, a general tendency is that both the crystallization temperature and the enthalpy of crystallization decreases in the sequence Fe → Co → Ni. A comparison of two a-Zr 9 Fe 91 ribbons prepared with different quenching rates revealed that for the lower quenching rate the activation energy and the crystallization temperature are slightly smaller due to the larger number of quenched-in nuclei. For the a-Zr 9 Co 91 alloy, the crystallization products were found to be fcc-Co + Zr 6 Co 23 and although a single differential scanning calorimetry (DSC) peak only occurs, transmission electron microscopy (TEM) studies indicated that the precipitation of Zr6Co23 precedes the appearance of fcc-Co. For the Ni-based alloys, the phase transformation occurs at practically the same temperatures for both the amorphous and bcc states and the final phases are the same (fcc-Ni +Z rNi 5 ). The transformation temperatures determined from thermomagnetic measurements agreed well with the corresponding DSC data and the magnetization changes accompanying the phase transformation could be well interpreted on the basis of DSC and TEM results.