Investigation of crystallization kinetics and deformation behavior in supercooled liquid region of CuZr-based bulk metallic glass

Abstract

In this paper, a systematic study of crystallization kinetics and deformation behavior is presented for (Cu ₅₀Zr ₅₀) ₉₄Al ₆ bulk metallic glass in the supercooled liquid region. Crystallization results showed that the activation energy for (Cu ₅₀Zr ₅₀) ₉₄Al ₆ was calculated using the Arrhenius equation in isothermal mode and the Kissinger–Akahira–Sunose method in non-isothermal mode. The activation energy was quite high compared with other bulk metallic glasses. Based on isothermal transformation kinetics described by the Johson–Mehl–Avrami model, the average Avrami exponent of about 3.05 implies a mainly diffusion controlled three-dimensional growth with an increasing nucleation rate during the crystallization. For warm deformation, the results showed that deformation behavior, composed of homogeneous and inhomogeneous deformation, is strongly dependent on strain rate and temperature. The homogeneous deformation transformed from non-Newtonian flow to Newtonian flow with a decrease in strain rate and an increase in temperature. It was found that the crystallization during high temperature deformation is induced by heating. The appropriate working temperature/strain rate combination for the alloy forming, without in-situ crystallization, was deduced by constructing an empirical deformation map. The optimum process condition for (Cu ₅₀Zr ₅₀) ₉₄Al ₆ can be expressed as T∼733 K and $\stackrel{.}{\text{ε}}$ ∼ 10 ⁻³ s ⁻¹.