Viscous flow behaviour of NixZr100?x metallic glasses from Ni30Zr70 to Ni64Zr36

Abstract

The compositional dependence of viscous flow in the NixZr100−x amorphous system was investigated under non-isothermal conditions at a heating rate of 10 K min−1in the compositional range fromx=30 tox=64 at % with the aid of a Hereaus TMA 500 dilatometer. The crystallization behaviour of the same glassy alloys under the same non-isothermal conditions was studied with a Perkin-Elmer DSC 7 differential scanning calorimeter. The characteristic crystallization and viscous flow parameters (the onset temperature,Tx, of crystallization; the temperature,Tm, of maximum heat evolution of the first crystallization step; the enthalpy, ΔHx, of crystallization; the activation energy,Qx, of crystallization; the glass transition temperature,Tg; the viscosity values η (Tg) and ηmin; and the activation energy for viscous flowQη (T>Tg), were shown to be dependent on composition. This dependence was examined on the basis of the equilibrium phase diagram of the Ni-Zr-system, and it is shown that glassy alloys possessing eutectic compositions manifest the greatest thermal stability because of the long-range atomic diffusion needed for crystallization to occur. Glassy alloys with nearly peritectoid compositions show low thermal stability, as no long-range diffusion is needed for the formation of the stable crystallization end-products NiZr2 and NiZr. In all cases, the crystallization process is governed by viscosity flow of these glassy alloys.