Phase separation in multicomponent amorphous alloys

Abstract

Metallic glasses have been obtained in the form of small ingots with the composition Zr 40Ti 14Cu 11Ni 10Be 25, by means of water quenching. All glasses transform on annealing to a mixed state comprising a nanocrystalline phase embedded in an amorphous matrix. The transformation of the glasses occurs via a phase separation in the amorphous alloy, followed by the formation of the nanocrystalline phase. The process is analyzed by means of isothermal and non-isothermal differential scanning calorimetry (DSC) and X-ray diffraction. The isothermal heat of transformation has two steps as a function of temperature which are due to the transformation sequence. Similarly, non-isothermal traces have multiple signals, the intensities of which depend on the heating rate. A Ni 36Fe 32Ta 7Si 8B 17 alloy has been shown to display glass forming tendency, as indicated by the reduced crystallization onset temperature of 0.6. Amorphous ribbons of this material reach a thickness of 100 μm. On annealing, an austenitic nanocrystalline phase is obtained through a nucleation and growth mechanism. In practice, the growth is limited and rarely proceeds beyond a particle size of 10 nm, as revealed by transmission electron microscopy. The present results allow a comparison of the DSC behaviour for alloys undergoing devitrification with different mechanisms.