Microstructure Feature of Bulk Glassy Cu₆₀Zr₃₀Ti₁₀ Alloy in As-cast and Annealed States

Abstract

The microstructures of a bulk glassy Cu₆₀Zr₃₀Ti₁₀ alloy in as-cast state and annealed at glass transition temperature (T_g), i.e., 440°C, have been studied using an electron transmission microscope (TEM) and a high-resolution transmission electron microscope (HRTEM). Nanocrystals with a size of 4 nm were observed in the cast rod with a diameter of 4 mm. The nanocrystal was determined to be CuZr, which is primitive cubic structure with a lattice parameter of a=0.3262 nm by analyzing its nano-beam electron diffraction pattern, suggesting that such nanocrystals have a positive effect on mechanical properties. Obviously distinguished interval dark and bright regions were observed in the glassy Cu₆₀Zr₃₀Ti₁₀ alloy annealed for 10 min at T_g. Nanocrystalline phase with a size of ∼10 nm was recognized after the annealing treatment. The concentration distribution of Cu, Zr and Ti in the alloy annealed for 10 min at T_g was examined with a three-dimensional atom probe field ion microscopy (3DAP-FIM). It was found that the Cu and Zr elements fluctuated along depth direction while the Ti element remained almost unchanged. It is therefore interpreted that the annealing-induced nanocrystalline phase results from nucleation and growth at the sites of the Cu-rich and/or Zr-rich regions as well as from growth of the cast-in nanocrystals.