Grain-growth in nanocrystalline zirconium-based alloys

Abstract

Crystallization and subsequent grain growth in nanocrystalline Fe₃₃Zr₆₇ and (Fe, Co)₃₃Zr₆₇ alloys were studied by TEM, differential scanning calorimetry and X-ray diffraction. The grain-growth data for both alloys obtained over a wide temperature range (about 200 °C) were fitted to different kinetic equations (with different grain-growth exponent, n). The model with n=3 (Equations 4 and 5) was found to predict in the best way the isothermal experimental data. This result gives strong evidence that crystallization (in our case by a polymorphic reaction) is indeed observed of a glass into a nanocrystalline material prior to the coarsening, rather than grain growth in an extremely fine-grained material which was never glassy at all. The activation energies for grain-growth, — 260±25 kJ mol⁻¹, were found to be practically the same for both systems. Additional information about the crystal growth kinetics of the nanocrystals in the amorphous matrix was obtained for (Fe, Co)₃₃Zr₆₇ glass.