A Kinetic Study of the Non-isothermal Crystallization of a Zr-Based Bulk Metallic Glass

The kinetics of the non-isothermal crystallization of Zr₅₅Cu₃₀Al₁₀Ni₅ bulk metallic glass was studied by differential scanning calorimetry in the mode of continuos heating. It is found that both glass transition and crystallization of the amorphous alloy behave in a marked kinetic nature. The activation energy E and frequency factor k₀ for crystallization were determined by the Kissinger method, which yields E = 230kJ/mol, and k₀ = 4.2 x 10¹²/s. The value of k₀ is much smaller than that for conventional amorphous alloys, demonstrating that the atomic mobility in bulk metallic glasses is quite sluggish. The crystallization mechanism in the non-isothermal process was analysed in terms of the kinetic transformation equation for the solid-state phase transformation. This reveals that the crystallization kinetic function f(x) for Zr₅₅Cu₃₀Al₁₀Ni₅ can be described by the Johnson-Mehl-Avrami equation, i.e. f(x) = (1-x) -\ln (1-x)^(n-1)/n, with n = 1.75. This indicates that the non-isothermal crystallization of Zr₅₅Cu₃₀Al₁₀Ni₅ bulk metallic glass is governed by diffusion-controlled one-dimensional growth. Finally, the different crystallization mechanisms in the isothermal and non-isothermal processes are discussed.