Structure and thermal stability of a melt-quenched single-phase nanocrystalline Hf61Fe39 alloy

The formation of a single-phase nanocrystalline Hf61Fe39 alloy with the fcc-Hf2Fe structure was achieved in a single step by melt-quenching, similarly to the previously reported nanocrystalline HfNi5 phase in a melt-quenched Hf11Ni89 alloy. Structural studies by X-ray diffraction and transmission electron microscopy have been performed for the nanocrystalline Hf61Fe39 alloy in both the as-quenched state and after various heat treatments. It was found that the asquenched state exhibits an average grain size of about 50 nm and a lattice parameter remarkably lower than the value known for the stoichiometric fcc-Hf2Fe phase. Differential scanning calorimetry has been used to reveal phase transformations and to establish the heat evolution and activation energy of transformation. The nanocrystalline Hf61Fe39 alloy shows high thermal stability with an activation energy of 1.29 eV corresponding to a grain growth above 800 K. (orig.)