Nano structure of rapidly quenched Cu-(Zr or Hf)-Ti alloys and their devitrification process

The structure and primary devitrification process of the melt-spun Cu ₆₀(Zr or Hf)₃₀Ti₁₀ alloys were investigated. It was confirmed that the compositional segregation in the diameter range of 5-10 nm exists in the as-quenched state. The nanocrystalline particles with cubic structure are observed in the glassy matrix in the high-resolution transmission electron microscopy images, of which size is corresponding to the scale of compositional segregation. Small-angle X-ray scattering measurement also indicates the development of nanoscale inhomogeneity with the same size as that of nanocrystalline particles. The nanocrystalline region has high Cu content. In contrast, Zr or Hf and Ti elements are enriched in the glassy region. These results are recognized as the formation of novel structure consisting of the glassy and nanocrystalline phases. It is suggested that the precipitation of bcc CuZr phase as a primary crystallization phase proceeds in the glassy phase remaining the nanocrystalline phase in the Cu-Zr-Ti alloy. Meanwhile, the glassy and nanocrystalline phases are transformed to an orthorhombic Cu₈Hf₃ phase at the initial crystallization stage in the Cu-Hf-Ti alloy. These differences of crystallization process are consistent with the results of thermodynamic and kinetic analyses of the transformation mode.