Liquid separation in Cu–Zr–Ag ternary alloys

Abstract

While cooling beyond a certain temperature limit (T SEP ) the Cu-Zr-Ag ternary melt of the separated field in the ternary diagram decomposes into an Ag-rich liquid (L 1 ) and another liquid rich in Cu and Zr (L 2 ) both under equilibrium and non-equilibrium conditions. The master alloy samples were melted and cast in a wedge-shaped copper mould, in order to obtain a gradient of cooling rate. The shape of separated melt, its size and distribution were investigated. The boundaries of the liquid ternary miscibility gap have been enlarged owing to high cooling rate. The results confirm that the volume fraction of the separated phases has increased due to higher cooling rate. Three microstructure types can be distinguished during the liquid separation process as a function of L 1 .

Solidification processes in Cu–Zr–Ag amorphisable alloy system

“…2c) was very different from the slowly cooled structure. In the matrix needle-like phases appeared: one had an elevated Ag-content with low Zr-content (Cu 25 (Fig. 2f), which composition was the same as that of the abovementioned Cu-Zr rich phase (Cu 43 Zr 31 Ag 26 ).…”

“…The minimum thickness of the wedge was about 20 µm, the maximum thickness was 3 mm. According to our previous research [25], the cooling rate was above 20000 K/s near the tip of the wedge sample. At its base the cooling rate was about 2000 K/sec.…”

Phase Separation in Rapid Solidified Ag-rich Ag-Cu-Zr Alloys

“…Several factors may influence the microstructural evolution of phase-separated glass; a critical temperature, compositional range in the miscibility gap, symmetry of the spinodal curve, glass-forming ability of the liquid, and cooling rate 6,7 . In addition, the microstructural evolution is influenced by viscosity and diffusivity of the melt 8 .…”

“…Size of the phase-separated structure also depends on time interval between an onset of the phase separation and completion of the solidification 9 . The boundaries of the liquid ternary miscibility gap can also be enlarged by applying high cooling rates 7 . Basically, two types of structures are observed in liquid-liquid phase separation owing to different separation mechanisms: interconnected-type structure due to spinodal decomposition, and droplet-type structure due to the nucleation and growth mechanism 6 .…”

“…The bright and dark phases corresponded with the Ag-rich phase and Cu-Zr-rich phase (or Ag-poor phase), respectively, according to the backscattered microscopy and EDX measurements. Dispersion of droplets of the Ag-rich liquid in the Cu-Zr-rich liquid indicated that volume fraction of the Ag-rich phase in the ribbon was less than 50 vol.% [7] . Different sizes and morphologies of the melt-spun Ag 60 Cu 20 Zr 20 ribbon changed across thickness of the ribbon.…”