Primary transformation kinetics in Zr-Al-Ni-Cu-Pd bulk metallic glass correlated with relaxation state

The primary transformation kinetics of nanoicosahedral quasicrystalline (QC) phase formation were investigated in Zr₆₅Al_7.5Ni ₁₀Cu_12.5Pd₅ bulk metallic glass (BMG) in various relaxation states. A less relaxed (unrelaxed) BMG exhibited higher activation energy for atomic diffusion in the glassy structure than that of a relaxed one, which represents a change in the nucleation and grain growth kinetics of the primary phase with the relaxation state. Actually, the grain growth rate of a QC particle near the crystallization temperature was approximately 1 × 10^-9 m/s in the less relaxed BMGs, which was less than half of that in the relaxed BMGs. In contrast, the calculated homogeneous nucleation rate significantly increased in the less relaxed samples. It increased with the volume fraction transformed in the early stage. It is concluded that the relaxation state of glassy alloys markedly affects the primary transformation kinetics. The current study also indicates a necessity of development of the relaxation state for structure controlling in industrial applications of BMGs.