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The amorphous/amorphous nanolaminates (A/ANLs) have aroused great attentions owing to their tunable structure and enhanced mechanical properties. However, the plastic deformation mechanism of A/ANLs have yet been clarified. Here, we systematically examined the mechanical properties and deformation behavior of series of NiNb/ZrCuNiAl A/ANLs via nanoindentaion test. It was found that both the amount and morphology of amorphous/amorphous interface (A/AIs) played crucial roles in the plastic deformation of A/ANLs. Less and straighter A/AIs facilitated multiple shear banding deformation, of which the hardness increased with decreasing layer thickness, as the A/AIs hindered the propagation of shear bands (SBs). Whilst, more and wavier A/AIs promoted homogeneous deformation, of which the hardness stayed at a much lower value and was relatively irrelevant with the layer thickness, for the promoted activation of shear transformation zones by A/AIs. Our results provide guidance for modifying the mechanical properties of amorphous alloys with interface engineering design.

Pulse electrodeposition is utilized to prepare Co–Fe–P metallic nano-glasses (NGs) containing glassy grains with an average size D

The variations in local yield strength and plasticity of a Zr-based bulk metallic glass at different fictive temperatures (Tf) are studied. To probe the size and distribution of microscopic carriers of plasticity, spherical-tip nanoindentation and microindentation are employed. With nanoindentation, events signifying the departure from Hertzian elastic contact, which manifest as pop-ins in the load-displacement response and correspond to incipient plasticity, are recorded and analyzed. Results indicate that with increasing Tf, the incipient plastic event and the number of subsequent pop-ins increases. Using statistical analysis of the scatter in strength, the activation parameters for shear transformation zones (STZs) in all specimens are determined. By considering the linear accumulation of STZs to form a shear band, the increase in shear yield strength along with plasticity, with increasing Tf, is explained.

Work-hardening behavior could be rarely observed in amorphous alloys during plastic deformation because the dilation and softening effect often occur in shear bands. Here, we proposed a novel mechanism to realize an excellent work-hardening rate ( R = dσ de ) in ZrCu/NiNb amorphous/amorphous nanolaminates (A/ANLs), which is investigated by in-situ uniaxial micro-pillar compression tests. The work-hardening rate value (25.24 GPa) obtained in ZrCu/NiNb A/ANLs with single layer thickness (h) 5 nm and volume ration 1:1, is relatively high, when comparing with the values in other results that considered the effect of crystalline phases and structural heterogeneity on work-hardening rate in composites. Such a high work-hardening effect is attributed to serious suppression of shear transformation zones (STZs) percolation by amorphous/amorphous interfaces. This work-hardening effect increased sharply as h decreases to 5 nm.

In this study, the orthogonal micromachining of a Zr-based bulk metallic glass (BMG) was carried out at different cutting speeds and undeformed chip thicknesses. The work softening behavior of the micromachined sub-surface was characterized via nanoindentation. It was observed that the serrated flow in the load-displacement curves during nanoindentation depends on the previous machining conditions. The softening in the machined subsurface was studied up to a depth of 300 µm and the minimum and the maximum reductions in nanohardness with respect to unmachined region were 13% and 37%, respectively. Furthermore, the shear transformation zone volume of the machined surface was determined and its correlation with the cutting force coefficients Kc and Kt was observed. Differential scanning calorimetry (DSC) reveals an increase in the free volume due to micromachining of BMG. This work presents a nanoindentation-based framework and insight into the changes occurring in the sub-surface due to severe plastic deformation in BMG.

In this paper, the evolution of high pressure phase (HPP) in an imperfect single crystal due to the existence of nanovoids is investigated. The nanovoid misfit strain and its stress are properly linked to its radius. The Ginzburg-Landau coupled with elasticity equations are solved for the HPP evolution. The energy barrier between the HPP and the low pressure phase, entropy jump, transformation strain function and the relation between critical and equilibrium temperatures are determined based on the phase transformation (PT) equilibrium and instability pressures and the HPP transformation strain. The obtained PT pressure which shows an exponential reduction vs. the radius and a linear increase vs. temperature, is found mostly smaller than the theoretical solution. The HPP grows from the nanovoid surface and along the line of zero shear transformation strain. Above some critical radius, the HPP growth is promoted and continues along the boundaries. The transformation work distribution reveals a faster initial growth for larger radii. The HPP growth is evaluated based on the thermodynamic equilibrium and instability criteria. The growth rate and velocity of the HPP tip nonlinearly decrease with temperature. Interestingly, the average shear stress varies very similar to the HPP concentration. The HPP growth is also investigated for different applied pressures so that above some pressure, the HPP growth proceeds along the boundaries and the growth rate increases as the pressure increases. The current study can be used to better understand the PT nano mechanisms of various HPPs.

This study investigates the effect of deep cryogenic cycle treatment (DCT) on the microstructure and mechanical behaviors of Ti33Zr30Cu9Ni5.5Be22.5 bulk metallic glass (BMG). The results revealed that after the DCT, the relaxation enthalpy increased, whereas the Ti33Zr30Cu9Ni5.5Be22.5 BMG still maintained a complete amorphous nature. As the cycle numbers increased, the room-temperature plasticity of the Ti33Zr30Cu9Ni5.5Be22.5 BMG represented a tendency to increase first and then decrease. When the cycle numbers increased to 30, the Ti33Zr30Cu9Ni5.5Be22.5 BMG obtained the maximum compressive plasticity of 7.8%, which is 5.6 times that of the as-cast specimen, accompanied by a higher strength. Moreover, the nanoindentation results demonstrated that the Ti33Zr30Cu9Ni5.5Be22.5 BMG that underwent the DCT possessed a larger pop-in size, a lower initial pop-in force and a lower hardness. The shear transformation zone (STZ) theory was employed to elucidate the plasticising mechanism induced by the DCT for the Ti33Zr30Cu9Ni5.5Be22.5 BMG. The larger STZ volumes and the lower shear band formation energy induced through the DCT promoted the densification of multiple shear bands, which is the principal reason for the excellent plasticity after the DCT.

Although chemical structural heterogeneities were induced into metallic glasses (MGs) to improve their ductility, the nature of the influence of the heterogeneous structure on their deformation behavior is still unclear. Here, by using microalloying elements to tailor the microstructure in Cu-Fe-Zr MGs, the formation of heterogeneous structure and the correlation between the heterogeneous structure and the deformation behavior are discussed. The results show that a honeycomb-like heterogeneous structure is formed in the (Cu0.5Fe0.5)40Zr59X1 (X Nb and Ta) alloys. From a viewpoint of dynamic, the nature of the microalloying effect on the microstructure has been analysed. The deformation behavior of (Cu0.5Fe0.5)40Zr59X1 MGs with a high population of nanoscale glassy particles (NGPs) is investigated by nanoindentation and bending test. These glassy particles play an interesting role in the internal record of the local structure evolution. It was found that NGPs contiguous to shear bands (SBs) coarsen by Ostwald ripening. However, NGPs within SB would dissolve due to direct mechanical shearing and mixing. It indicates that the volume of shear transformation zone decreases obviously in the heterogeneous MGs due to the high fraction of interfaces. This work is of significance in understanding the relationship between structure and property of MGs.