THERMAL-STABILITY AND GRAIN-GROWTH OF A MELT-SPUN HFNI5 NANOPHASE ALLOY

A single phase HfNi5 nanocrystalline (NC) sample was prepared by quenching a Hf11Ni89 alloy with the melt-spinning technique. A randomly oriented HfNi5 nanophase material with an average grain size of about 10 nm was formed in the as-quenched state. Differential scanning calorimetry (DSC), transmission electron microscopy (TEM), and X-ray diffraction (XRD) analysis were used for the investigation of the thermal stability and grain growth of the NC HfNi5 sample. On heating the NC sample at a constant heating rate, two exothermal peaks appear in the DSC curve, corresponding to a grain-growth process of the HfNi5 nanophase prior to a precipitation process of Ni solid solution. It was found the grain-growth temperature of the NC HfNi5 phase is approximately equal to the crystallization temperature of the same compositional amorphous alloy. The average grain boundary energy in the NC sample calculated by means of the calorimetric results, is about 0.36J/m(2). Activation energies for the grain growth and Ni precipitation are calculated by using the Kissinger equation. It was obtained that the value of the activation energy for the HfNi5 nanophase grain growth is close to that for the volume self-diffusion in Hf. The grain growth mechanism and the thermal stability of the NC material are also discussed.