Microstructure of rapidly solidified Co–Cu–Si–B immiscible alloys with an amorphous phase

•The microstructure of Co–Cu–Si–B alloys was investigated with wide Co/Cu ratios.•A macroscopically phase-separated dual-layer and entangled structure was observed.•A nano-emulsion-like structure was observed within the phase-separated Co-rich layer.

The microstructure of Co–Cu-based (Co0.75Si0.10B0.15)100−xCux alloys was investigated for a wide range of Co/Cu ratios, with a focus on liquid phase separation and amorphous phase formation. The simultaneous occurrence of liquid phase separation and amorphous phase formation was confirmed in rapidly solidified (Co0.75Si0.10B0.15)100−xCux (x = 10–50) alloys. Nano-scale emulsion-like structures were found in the macroscopically phase-separated Co-rich region in the (Co0.75Si0.10B0.15)100−xCux (x = 30, 50) alloys. The microstructure in the Co–Cu–Si–B alloys strongly depended on the solidification process and the Co/Cu ratio.

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