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The intrinsic correlation between the fracture morphology evolution and the structural heterogeneity of flow units in a typical Zr 52.5 Ti 5 Cu 17.9 Ni 14.6 Al 10 (vit105) metallic glass (MG) upon annealing was investigated. By systematically tuning the annealing time at temperature below the glass transition temperature, a series of dimple-like fracture morphology were obtained, which is the unique fingerprint-like pattern for every annealing state. Based on the structural relaxation model of flow units, the evolution of the typical dimple sizes, the largest and smallest dimple size, with annealing were well fitted. Then the evolution of flow unit density was estimated from the fracture morphology evolution, which displays the same evolution trend with that measured from thermal relaxation. A stochastic dynamic model considering the interaction of activated flow units was proposed to analyze the effect of the initial flow unit density and the flow unit interaction intensity on the dynamic evolution of dimple distribution. Our work may provide a novel scheme to investigate the structural fingerprint information on flow units from fracture morphology, and enlighten the microscopic structural origin of the ductile-to-brittle transition during structural relaxation in MGs.

The dynamic evolutions of different fracture morphologies in the fracture surface of brittle Mg-based metallic glasses (MGs) were systematically and quantitatively studied by SEM and AFM. It shows that the evolution of the fracture morphology pattern is dominated by an effective dynamic parameter of critical crack tip curvature radius. Based on crack tip plastic zone and shear transformation zone (STZ) theories, a theoretical model for the evolution of the crack tip curvature radius by considering the activation of STZs during fracture was proposed. The model can simulate the crack propagation process, and predict the critical crack tip curvature radius and the fracture pattern transition between the dimples and the periodic corrugations solely occurring in brittle MGs. These results have implications for understanding the microscopic fracture mechanism and the structural origin of fracture in MGs.

Cu50Zr40Ti10 (at%) glassy ribbon was prepared by melt spinning. The effect of mechanical tension on its thermal and corrosive properties was investigated by differential scanning calorimetry and electrochemical polarization experiments, respectively. After mechanical tension, the crystallization temperature and the crystallization enthalpy almost maintain the same, while the relaxation temperature and the glass transition temperature decrease. In addition, the activation energy of the glass transition decreases from 74.8 +/- 1.7 KJ mol(-1) to 71.0 +/- 1.9 KJ mol(-1). The activation energy of the relaxation decreases from 70.0 +/- 4.4 KJ mol(-1) to 50.5 +/- 3.8 KJ mol(-1) at low heating rate, while increases from 186.1 +/- 9.4 KJ mol(-1) to 289.4 +/- 9.4 KJ mol(-1) at rapid heating rate. On the other hand, corrosion potentials polarized in all studied solutions sharply decrease, while the corrosion current densities increase. The pitting corrosion vanishes in 1 M chloride-containing solutions. The passive potential and the passive current density both decrease in 0.5 M H2SO4. The corroded surface micrographs in all studied solutions remarkably change. In addition, the difference of corrosive behavior in 0.5 M H2SO4, 1 M HCl, and 1 M NaCl is also discussed. (C) 2013 Elsevier B.V. All rights reserved.