Phase Separation and Crystallization in the Bulk Amorphous Alloy Zr 41 Ti 14 Cu 12.5 Ni 10 Be 22.5
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IN THE BULK AMORPHOUS ALLOY
Zr 4 1Ti1 4 Cu 12.5Ni1 0 Be 22 .5
M.-P.MACl**,, N.WAND A * A.WIEDENK4NN*, H.WOLLENBERGER*, Q.WEI*, S.G.KLOSE , A.SAGELI AND H.J.FECHT *Hahn -Meitner-Institut Berlin, Glienickerstr. 100, D-14109 Berlin, FRG, **University Potsdam, Inst.Berufspdidagogik, D-14109-Golm, FRG, ***Technical University Berlin, Institute of Metals Research, Hardenbergstr. 36 PN 2-3, D-10623 Berlin, FRG ABSTRACT The decomposition and crystallization above the glass temperature of the bulk metallic glass Zr 41Ti 14Cu 12 .5 Ni 10Be 22.5 and the crystallization during solidification of the melt were investigated by means of different analytical methods, including Transmission Electron Microscopy (TEM), Small Angle Neutron Scattering (SANS), Field Ion Microscopy with Atom Probe (FIM/AP). Dependent on the thermal history these phase transitions lead to different phases and different microstructures of the alloy. During annealing above the glass tremperature the decomposition of the alloy into two supercooled liquid phases is observed by the formation of nanosized precipitates, which differ from the matrix by their Be and Ti contents. This decomposition retards significantly the subsequent crystallization , however it does not inhibit the formation of the phases which crystallize if the decomposition is bypassed by appropriate heat treatment. By stepwise crystallization a nanosized microstructure is formed consisting of three metastable phases and of stable Zr 2Cu. This microstructure differ significantly from the crystalline equilibrium microstructure resulting from slow cooling of the melt. Crystallization of the amorphous alloy by very fast heating causes totally different microstructures. INTRODUCTION Recently new metallic alloys with excellent glass forming ability have been developed, which permit the production of large bulky ingots of metallic glass 1-3. These bulk metallic glasses are rather resistant against crystallization, as beeing demonstrated by a wide temperature range of the supercooled liquid state between glass temperature T9 and crystallization5 temperature T,. The glass forming ability has been subject of detailed considerations4, . The extraordinary stability of the bulk metallic glasses has focussed attention to the process of crystallization. Different processing conditions may significantly affect the crystallization process and the resulting phases which will be generated. In particular the decomposition observed during annealing above the glass temperature was discussed controversially: it should either act as a precursor of crystallization 6 or stabilize the supercooled liquid against crystallization 7-9 . The present paper reports results of an investigation on the crystallization of the bulk metallic glass Zr41Ti 14Cu 12.5 Ni 10 Be 22 .5 by means of different analytical methods: Transmission Electron Microscopy (TEM), Energy Dispersive Analysis by X-ray Emission (EDAX) in the TEM and in the Scanning Electron Microscope (SEM), Small Angle Neutron Scattering (SANS), Field Ion Microscopy with
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