Microstructure and thermal behavior of two-phase amorphous Ni-Nb-Y alloy

A novel phase-separated Ni-based amorphous alloy is prepared in a glass forming system by rapid quenching of a Ni58.5Nb20.25Y21.25 melt. The microstructure consists of two amorphous Nb-enriched and Y-enriched regions with a size distribution from micrometer dimensions down to several nanometers. Decomposition takes place in the melt prior to solidification. The miscibility gap in the solid and liquid state of the binary Nb-Y system extends into the ternary Ni-Nb-Y alloy as a consequence of the positive mixing enthalpy between Nb and Y. The two-phase amorphous Ni58.5Nb20.25Y21.25 alloy crystallizes in a first step by the primary precipitation of the cubic Ni2Y phase from the Y-rich amorphous phase. At much higher temperatures the remaining Nb-rich amorphous phase crystallizes into Ni7Nb6.