Tuning Correlative Heterogeneity and Related Properties in Ni-Nb-Tm (Tm=Zr, Y, Gd) Metallic Glasses

Abstract

Herein, we systematically investigated how to tailor correlative heterogeneity and related properties in Ni-Nb-(Zr, Y, Gd) metallic glasses (MGs). The Ni₆₀Nb_40-xZr_x MGs (x=0-20 at.%) with Nb-Zr atomic pair (〖∆H〗^mix=+4 kJ/mol) exhibited correlative atomic scale chemical and topological heterogeneities upon Zr addition, which can be evaluated by EXAFS analysis. Interestingly, a statistical analysis of strain burst sizes along with in situ bending test showed that the easier nucleation of chaotic shear bands is promoted with the aid of stress localization induced by the heterogeneities. The bulk specimens (d=1 mm) for 8 and 10 at.% of Zr with increased glass-forming ability (GFA) exhibited enhanced plasticity without the reduction of fracture strength, implying cooling rate effect on heterogeneity-induced plasticity. Contrastively, the Ni₆₀Nb_40-y(Y, Gd)_y MGs with Nb-Y or Nb-Gd atomic pair (〖∆H〗^mix=+30 kJ/mol) showed hierarchically correlative nanoscale phase separated microstructures, which can be carefully interpreted by construction of metastable miscibility gap. The microstructures rely on four different variables (the composition, the symmetry of a miscibility gap, the critical temperature and the GFA of each phase) and provide a weak interface resulting in extreme brittleness as well as drastically decreased GFA. We believe that the results of this study would provide an effective guideline for tuning correlative heterogeneity and related properties in MGs via manipulation of enthalpy relationship and cooling rate.