PHASE-SEPARATION IN MULTICOMPONENT AMORPHOUS-ALLOYS

Metallic glasses have been obtained in the form of small ingots with t he composition Zr40Ti14Cu11Ni10Be25, by means of water quenching. All glasses transform on annealing to a mixed state comprising a nanocryst alline phase embedded in an amorphous matrix. The transformation of th e glasses occurs via a phase separation in the amorphous alloy, follow ed by the formation of the nanocrystalline phase. The process is analy zed by means of isothermal and non-isothermal differential scanning ca lorimetry (DSC) and X-ray diffraction. The isothermal heat of transfor mation has two steps as a function of temperature which are due to the transformation sequence. Similarly, non-isothermal traces have multip le signals, the intensities of which depend on the heating rate. A Ni3 6Fe32Ta7Si8B17 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 mu m. On annealing, an austenitic nanocrystalline phase is obtained through a n ucleation and growth mechanism. In practice, the growth is limited and rarely proceeds beyond a particle size of 10 nm, as revealed by trans mission electron microscopy. The present results allow a comparison of the DSC behaviour for alloys undergoing devitrification with differen t mechanisms. (C) 1998 Elsevier Science B.V. All rights reserved.