Structure and crystallization of rapidly quenched Cu-(Zr or Hf)-Ti alloys containing nanocrystalline particles

The structure and primary crystallization process of the melt-spun Cu₆₀ (Zr or Hf)₃₀Ti₁₀ alloys were investigated. Compositional segregation in the diameter range of 5-10 nm was observed in the as-quenched state, in the high-resolution transmission electron microscopy images, nanocrystalline particles are observed in the glassy matrix, the size of which corresponds to the scale of compositional segregation. The glassy region has comparatively high Zr or Hf and Ti contents. In contrast, the Cu element is enriched in the nanocrystalline phases. The nanocrystalline phases are identified as the cubic structure with a lattice constant of approximately 0.5 nm. These results are recognized as the formation of novel structure consisting of the glassy and nanocrystalline phases. It is suggested that the precipitation of body-centred-cubic CuZr phase as a primary crystallization phase proceeds in the glassy phase, the nanocrystalline phase remaining in the Cu-Zr-Ti alloy. Meanwhile, the glassy and nanocrystalline phases are transformed to an orthorhombic Cu₈Hf₃ phase in the initial crystallization stage in the Cu-Hf-Ti alloy.