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The incipient plasticity of an amorphous solid represents the onset of shear deformation, which is a stochastic progress closely related to microstructure evolution. It is well known that the cooling rate plays a crucial role in the microstructure evolution of a glass. Nevertheless, how the cooling rate affects the incipient plasticity is still unclear. In this work, the incipient plastic deformation of the amorphous phase in Cu 47.5 Zr 48 Al 4 Nb 0.5 bulk metallic glass composites (BMGCs) cast with different cooling rates is systematically studied. The incipient plasticity of the glassy matrix of the BMGCs is found to occur via a first displacement burst, the occurrence of which is more stochastic as the cooling rate decreases. According to the auto-correlation functions and cooperative shear model, the stochastic behavior is attributed to the effects of the cooling rate on the initial free volume and subsequent activated shear transformation zones (STZs). A higher content of free volume is present in the glassy matrix of the studied samples cooled at a faster rate, which facilitates the operation of STZs. Moreover, the larger incipient burst size is correlated with the higher content of free volume and larger STZs in the glassy matrix. The larger STZs result in more preferable propagation of multiple shear bands, leading to less stochastic deformation and more obvious plastic deformation. This study provides further understanding on the incipient plasticity of glassy matrix in BMGCs. Image 1 • Hardness and elastic modulus of amorphous phase are higher at a lower cooling rate. • The deformation of amorphous phase is more stochastic as cooling rate decreases. • Larger shear transformation zones facilitate the formation of multiple shear bands. • Initial free volume is the dominant role in mechanical behavior of amorphous phase. [ABSTRACT FROM AUTHOR]

The plastic deformation of metallic glasses (MG) is well-known to occur via shear transformation zones (STZs) on the scale of atomic clusters, yet fracture of MG takes place via shear bands of the micron scale. So far, understanding on how the operation of STZs leads to shear localization and fracture remains limited. In this work, tensile tests on Cu/Zr-based MG micro-wires show that both the first-yield and fracture stress exhibit the Weibull distribution, and fractography reveals that shear localization in the form of intense shear bands leads to shear fracture. Molecular dynamics (MD) simulations show that shear bands form via the correlated emergence and operation of discrete STZs close to one another. To describe how the stochastic yet correlated occurrence of the discrete STZs leads to shear localization, a model is constructed to relate the probability of the successive operation of discrete STZs, to their nucleation density. The model predicts that, if nucleation density of the STZs grows along the strain path, as prior shear events triggers the emergence of new STZs, then successive occurrence of discrete shear events speeds up rapidly to an asymptotic state which is exactly the condition of shear localization and shear banding. Furthermore, the MD results suggest an exponential growth law for the occurrence of the STZs along the strain path, which also gives predictions in good agreement with the experimental Weibull distributions of the first-yield stress of Cu/Zr-based MGs. • Tensile tests show that both first-yield and fracture stress of Cu/Zr-based MG micro-wires exhibit Weibull distributions. • MD simulations show that shear bands form via the correlated formation of successive shear zones of atomic sizes. • A statistical model is proposed to describe the survival probability against successive occurrence of discrete shear events. • The model predicts that shear localization is a consequence of acceleration of shear event occurrence, as in MD simulation. • An exponential growth law for the shear event occurrence agrees with both the MD and experimental results. [ABSTRACT FROM AUTHOR]

The plastic stability of bimetals composed of a Ti-based metallic glass composite (MGC) and a pure titanium (PT) under tension has been investigated. The results reveal that the plastic stability of the MGC/PT bimetal is strongly dependent on the thickness fraction of the MGC: when the thickness fraction of the MGC decreases to a critical value, a homogeneous plastic deformation occurs in the MGC/PT bimetals, i.e. the strain localization and necking of the MGC is effectively suppressed. This unique phenomenon is explained using the normalized strain-hardening rate, and the quantitative relationship between the normalized strain-hardening rate of the MGC/PT bimetals and the thickness fraction of the MGC is thereby established. [ABSTRACT FROM AUTHOR]

Fe-based metallic glasses are known to have excellent soft magnetic properties, but restricted to the disastrous annealing embrittlement. A novel class of Fe 84- x B 14+ x Zr 2 (x = 0, 3, 6) metallic glasses with extraordinary annealing bending ductility and excellent soft magnetic properties were developed. The metallic glasses exhibit a high B S of 1.54–1.64 T and a low H C of 4.1–5.8 A/m. It is noteworthy that the Fe 84 B 14 Zr 2 metallic glass exhibits the highest ductile to brittle transition temperature among all Fe-based metallic glasses reported to date and the ductile to brittle transition temperature decreases with the decrease of Fe content. Moreover, the well-distributed shear bands can still be formed during bending for Fe 84 B 14 Zr 2 metallic glass after 680 K annealing. Pronounced β-relaxation peak has been observed for Fe 84 B 14 Zr 2 metallic glass in its relaxation spectra. We demonstrate that the bending deformation ability is closely correlated to the β-relaxation. The underlying mechanism for the extraordinary bending deformation ability of Fe 84 B 14 Zr 2 metallic glass after annealing can be attributed to the heterogeneous structure with plenty of loosely packed zones as revealed by the pronounced β-relaxation and high resolution transmission electron microscopy. • Fe 84 B 14 Zr 2 MG with good soft magnetic properties exhibits extraordinarily high DBT temperature. • Fe 84 B 14 Zr 2 MG shows pronounced β-relaxation, relating to plenty of loosely packed zones. • The β-relaxation is regarded as an indication for the bending ability of metallic glasses after annealing. [ABSTRACT FROM AUTHOR]

The disastrous annealing embrittlement of Fe-based metallic glasses with excellent soft magnetic properties is a long-standing issue. In order to alleviate the annealing embrittlement without worsening the soft magnetic properties, ferromagnetic elements Co and Ni are introduced to the Fe 84 Si 2 B 13 P 1 metallic glasses. The microstructure, mechanical and magnetic properties are investigated by synchrotron diffraction, two-point bending test and magnetometry. It is found that, in contrast to Co, proper Ni substitution for Fe significantly optimizes the H c of Fe 84 Si 2 B 13 P 1 metallic glasses and keeps the B s at a high level. According to bending tests, the ductile-brittle transition temperature of the metallic glasses increases slightly with Ni substitution and decreases prominently with Co substitution. Ultimately, the ductile Fe 82 Ni 2 Si 2 B 13 P 1 metallic glasses with B s of 1.65 T and H c of 3.4 A/m have been successfully obtained. Macroscopically, the cheerful propensity to form well-distributed shear bands during bending of Ni-substituted annealed alloys contributes to their good ductility. Furthermore, the alteration of ductile-brittle transition temperature can be conducted by the structural change at the medium-range scale as revealed by the pair distribution function measurements. After annealing the compression at atomic scale ranging from 6 Å to 16 Å of Co-substituted metallic glasses may hinder the creation of well-distributed shear bands and give rise to the deterioration of bending ductility. This work provides a perspective to understand the ductile-brittle transition of metallic glasses from the atomic scale. • With proper substitution of Ni for Fe, H c of Fe 84 Si 2 B 13 P 1 alloys decreases and B s keeps at a high level. • The bending ductility of annealed ribbons improves by Ni substitution. • The Ni-substituted alloys show good propensity to form well-distributed shear bands during bending. • Medium-range structure compression of Fe 78 Co 6 Si 2 B 13 P 1 alloy results in its ductility deterioration. [ABSTRACT FROM AUTHOR]

Metallic glasses are structurally heterogeneous on the atomic and nano scales. However, few investigations have been conducted on how the structural heterogeneities in these two scales co-evolve during annealing. In this work, the atomic and nanoscale structural heterogeneity evolution accompanying the magnetic softness is systematically discussed based on the literature and our previous synchrotron X-ray diffraction and atomic force microscopy results. We revealed the co-evolution mechanism of structural heterogeneities on the atomic and nano scales during annealing via the insight of percolation theory from the point of view of the local five-fold symmetry of the clusters. The results indicate that the reduction of atomic-scale structural heterogeneity during annealing is accompanied by an increase in the degree of local five-fold symmetry of the clusters and an alteration in their connection patterns. As the local five-fold symmetry of clusters in Fe-based metallic glasses reaches the percolation threshold, the nanoscale liquid-like regions tend to transform into solid-like regions. The great degree of percolation causes the pronounced weakening of the nanoscale structural heterogeneity accompanying changes in the shape and number of the liquid-like regions. The reduction of the number of liquid-like regions causes a reduction in vertical anisotropy and magnetic softening due to a more uniform and less free volume within the sub-circular shaped liquid-like region. • The evolution of the atomic/nano scale structural heterogeneity and its relation to the magnetic softness was discussed • The co-evolution mechanism of structural heterogeneities on the atomic and nano scales during relaxation is revealed. • The shape of liquid-like regions tend to become nearly circular during relaxation contributing to magnetic softening. [ABSTRACT FROM AUTHOR]

A large tensile plastic deformation was achieved in ZrCu-based metallic glass composites with a metastable B2 phase. It was found that the B2 phase can effectively promote the density of the stress concentration sites and enhance the formation and interaction of multiple shear bands, which significantly stabilize the tensile plastic deformation of metallic glass composites. Based on the concept of the normalized strain-hardening rate, the critical volume fraction for the stable tensile plastic deformation of metallic glass composites was determined. [ABSTRACT FROM AUTHOR]

• The relaxation-induced evolution of nanoscale structural heterogeneity is analyzed by atomic force microscopy in Fe 80 Si 9 B 11 metallic glass. • The degeneration of nanoscale structural heterogeneity induces the improvement of soft magnetic properties. • The soft magnetic properties can be optimized by selectively tailoring the intrinsic structural heterogeneity of Fe-based metallic glass. Despite the mesoscopic isotropic nature of metallic glasses, there is a certain degree of structural heterogeneity down to the nanoscale. However, how structural heterogeneity affects the magnetic properties is still unclear. In this work, the relaxation-induced structural heterogeneity and magnetic properties evolution of Fe 80 Si 9 B 11 metallic glass were investigated by atomic force microscopy (AFM) and Mössbauer spectroscopy. We revealed that the correlation-length of nanoscale heterogeneity relates closely with the ferromagnetic exchange interaction together with the magnetic anisotropy, providing experimental evidence of the intrinsic link between the nanoscale structural heterogeneity and magnetic properties for Fe-based metallic glasses. The degeneration of nanoscale structural heterogeneity induces the enhancement of the ferromagnetic exchange interaction and weakening of the magnetic anisotropy. Our results have a vital significance in understanding the structure-property relationship of metallic glass. [ABSTRACT FROM AUTHOR]