Metallic glasses are commonly brittle, as they generally fail catastrophically under uniaxial tension. Here we show pronounced macroscopic tensile plasticity achieved in a La-based metallic glass which possesses strong β relaxations and nanoscale heterogeneous structures. We demonstrate that the β relaxation is closely correlated with the activation of the structural units of plastic deformations and global plasticity, and the transition from brittle to ductile in tension and the activation of the β relaxations follow a similar time-temperature scaling relationship. The results have implications for understanding the mechanisms of plastic deformation and structural origin of β relaxations as well as for solving the brittleness in metallic glasses.

The mechanisms of plastic deformation of glassy solids and structural origin of ␤ relaxation are two fundamental issues. We provide compelling experimental evidence that the activation of shear transformation zones ͑STZs͒ and ␤ relaxations in metallic glasses are directly related, and the activation energy of the ␤ relaxation and the potential-energy barriers of STZs are nearly equivalent. Our results suggest an intrinsic correlation among potential STZs, ␤ relaxation, and the inhomogeneous atomic structure of metallic glasses, which has implications for understanding the deformation mechanism and structural origin of ␤ relaxation in glasses.Plastic deformation of metallic glasses ͑MGs͒ far below glass transition temperature T g is a long-standing issue. [1][2][3][4] Microscopically, MGs are proposed to deform by plastic rearrangements of atomic regions involving tens of atoms termed shear transformation zones ͑STZs͒, 3,4 and a consequence of formations and self-organizations of STZs that induce macroscopical shear banding of MGs. As recognized by Johari et al., 5 the relaxation of supercooled liquids and glasses are governed by two main processes: a fast process, that is the ␤ relaxation which is a locally initiated and reversible process, and a slow process, termed the ␣ process, which is a large-scale irreversible rearrangement of the material. The ␤ relaxation, which is an Arrhenius process, 5-7 persists from supercooled liquid regime to glassy states, and is separated from the non-Arrhenius ␣ relaxation at a crossover temperature. 5-7 It has been proved to be an intrinsic and universal feature of glasses but poorly understood. 5,6 Usually, it is related to localized motions with cooperative nature, a reminiscent of STZs in MGs. From the theory of potential-energy landscape ͑PEL͒, 7,8 the ␤ relaxations were identified as hopping events across subbasins within an inherent megabasin ͑inherent structure͒ while ␣ relaxations entail escape from one megabasin and eventually jump into another ͑e.g., see Fig. 1 in Ref. 8͒. Experimentally, the activation energy of the ␤ relaxations, E ␤ , can be determined by dielectric spectroscopy, 6 differential scanning calorimeter, 9 and by dynamic mechanical spectroscopy ͑DMS͒. 10 Since MGs are good conductors, dielectric method that commonly used in nonmetallic glasses is not feasible. The DMS, which is widely used in field of polymer glasses, 6 has been employed for studying the ␤ relaxation in MGs. 10 Based on the PEL theory and the Frenkel's analysis of shear strengths in dislocation free solids, Johnson et al. 11 proposed a cooperative shear model ͑CSM͒ to understand the deformation mechanisms and rheological properties of MGs. 11,12 The CSM gives rise to functional relations between viscosity and shear modulus ͑e.g., see Ref. 12 for a review͒. According to the CSM, activation of isolated STZs confined within elastic matrix could be associated with the ␤ relaxation. 13 However, the validity of this correlation, which is the fundamental conceptual standpoint of CSM, 11,13 re...

Articles you may be interested inEffect of physical aging on Johari-Goldstein relaxation in La-based bulk metallic glass Evidence for viscous flow nature in Zr60Al15Ni25 metallic glass subjected to cold rolling Dynamic mechanical analysis in La-based bulk metallic glasses: Secondary (β) and main (α) relaxations J. Appl. Phys. 112, 083528 (2012); 10.1063/1.4759284 Heating and structural disordering effects of the nonlinear viscous flow in a Zr 55 Al 10 Ni 5 Cu 30 bulk metallic glass Appl.

Vitrification from physical vapor deposition is known to be an efficient way for tuning the kinetic and thermodynamic stability of glasses and significantly improve their properties. There is a general consensus that preparing stable glasses requires the use of high substrate temperatures close to the glass transition one, Tg. Here, we challenge this empirical rule by showing the formation of Zr-based ultrastable metallic glasses (MGs) at room temperature, i.e., with a substrate temperature of only 0.43Tg. By carefully controlling the deposition rate, we can improve the stability of the obtained glasses to higher values. In contrast to conventional quenched glasses, the ultrastable MGs exhibit a large increase of Tg of ∼60 K, stronger resistance against crystallization, and more homogeneous structure with less order at longer distances. Our study circumvents the limitation of substrate temperature for developing ultrastable glasses, and provides deeper insight into glasses stability and their surface dynamics.

The surface viscosity and self-diffusion of a Pd-based metallic glass were measured using annealing-induced decay of its surface submicron gratings. Strong surface dynamics and surface diffusion with the value of more than 105 times faster than bulk diffusion are found at temperatures below glass transition. The high surface dynamic induces a fast crystallization below glass transition temperature at the free surface which is more than 100 times faster than that in bulk.

The origin of dramatic slowing down of dynamics in metallic glass-forming liquids toward their glass transition temperatures is a fundamental but unresolved issue. Through extensive molecular dynamics simulations, here we show that, contrary to the previous beliefs, it is not local geometrical orderings extracted from instantaneous configurations but the intrinsic correlation between configurations that captures the structural origin governing slow dynamics. More significantly, it is demonstrated by scaling analyses that it is the correlation length extracted from configuration correlation rather than dynamic correlation lengths that is the key to determine the drastic slowdown of supercooled metallic liquids. The key role of the configuration correlation established here sheds important light on the structural origin of the mysterious glass transition and provides an essential piece of the puzzle for the development of a universal theoretical understanding of glass transition in glasses.

Articles you may be interested inUnderstanding the correlations between Poisson's ratio and plasticity based on microscopic flow units in metallic glasses Low beryllium content Zr-based bulk metallic glass composite with plasticity and work hardenability J. Appl. Phys. 115, 043519 (2014); 10.1063/1.4863454 Symmetry breaking and other nonlinear elastic responses of metallic glasses subject to uniaxial loading

Direct atomic-scale observations and measurements on dynamics of amorphous metallic nanoparticles (a-NPs) are challenging owing to the insufficient consciousness to their striking characterizations and the difficulties in technological approaches. In this study, we observe coalescence process of the a-NPs at atomic scale. We measure the viscosity of the a-NPs through the particles coalescence by in situ method. We find that the a-NPs have fast dynamics, and the viscosity of the a-NPs exhibits a power law relationship with size of the a-NPs. The a-NPs with sizes smaller than 3 nm are in a supercooled liquid state and exhibit liquid-like behaviours with a decreased viscosity by four orders of magnitude lower than that of bulk glasses. These results reveal the intrinsic flow characteristics of glasses in low demension, and pave a way to understand the liquid-like behaviours of low dimension glass, and are also of key interest to develop size-controlled nanodevices.