Comparative study of grain growth behavior from a supercooled liquid region of Zr₆₅Cu_27.5Al_7.5 and Zr₆₅Cu₃₅ metallic glasses

The grain growth behavior of a Zr₂Cu crystalline phase from a supercooled liquid region of Zr₆₅Cu_27.5Al_7.5 and Zr₆₅Cu₃₅ metallic glasses was examined as a function of annealing time, t_a at various temperatures. Since no distinct change of constitution and strain in Zr₂Cu phase is seen, the grain size calculated from a line-broadening of X-ray diffraction peak by Scherrer's formula can be used. The calculated grain size is in agreement with that obtained by transmission electron microscopy observation. The curve of grain size with t_a is parabolic. The grain growth in Zr₆₅Cu₃₅ takes place at lower temperature and its rate is extremely larger as compared with those of Zr₆₅Cu_27.5Al_7.5. These differences are originated from the suppression of growth of Zr₂Cy by Al atom, which retards the diffusion of Cu owing to the primary precipitation of ZrAl in Zr₆₅Cu_27.5Al_7.5. The formation of ZrAl may be attributed to the strong chemical affinity between Al and Zr. The activation energies for grain growth of 115 kJ mol^-1 for Zr₆₅Cu_27.5Al_7.5 and 363 kJ mol^-1 for Zr₆₅Cu₃₅ are obtained by the Arrhenius plot of grain growth rate against a reciprocal of temperature. These activation energies reflect the kind and/or magnitude of diffusion atoms during the grain growth.