Structural relaxation of Ti40Zr25Ni8Cu9Be18 bulk metallic glass
Résumé
Ti40Zr25Ni8Cu9Be18 bulk metallic glass has a unique quenched-in nuclei/amorphous matrix structure. The crystallization of quenched-in nuclei, when the experimental isothermal annealing time is within its incubation time, may not disturb the enthalpy relaxation, which makes it have the accordingly common enthalpy relaxation behavior with amorphous materials. The alloy's annealing time dependence of recovery enthalpy follows a stretched exponential function with the mean relaxation time obeying an Arrhenius law. The equilibrium recovery enthalpy ΔHTeq, mean relaxation time τ and stretching exponent β are all dependent on the annealing temperature, and generally, a higher annealing temperature comes with a lower value of ΔHTeq, τ and a higher value of β. Two parameters, βg and τg, representing the stretching exponent and the mean structural relaxation time at the calorimetric glass transition temperature, respectively, are correlated with glass forming ability and thermal stability, respectively. For Ti40Zr25Ni8Cu9Be18 BMG, the high value of βg, which is much higher than 0.84 and approaches unity, reveals its good glass forming ability, while, on the other hand, the low value of τg indicates a worse thermal stability compared with typical BMGs.
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