Abstract
The large plasticity observed in newly developed monolithic bulk metallic glasses under quasi-static compression raises a question about the contribution of atomic scale effects. Here, nanocrystals on the order of 1–1.5 nm in size are observed within an Fe-based bulk metallic glass using aberration-corrected high-resolution transmission electron microscopy (HRTEM). The accumulation of nanocrystals is linked to the presence of hard and soft zones, which is connected to the micro-scale hardness and elastic modulus confirmed by nanoindentation. Furthermore, we performed systematic simulations of HRTEM images at varying sample thicknesses, and established a theoretical model for the estimation of the shear transformation zone size. The findings suggest that the main mechanism behind the formation of softer regions are the homogenously dispersed nanocrystals, which are responsible for the start and stop mechanism of shear transformation zones and hence, play a key role in the enhancement of mechanical properties.
Highlights
Despite ultra-high strength and elastic energy absorption capacity, the negligible plasticity in most metallic glasses has been an important barrier obstructing property optimization and their widespread use[1,2]
The new generation microscopes with spherical aberration correction (Cs-corrector) and monochromator have marked a new era in the field of electron microscopy with sub-eV energy resolution and sub-Angstrom spatial resolution[19,20]
Using modern aberration-corrected high-resolution transmission electron microscopy (HRTEM) imaging, the medium-range-order/ nanocrystalline clusters embedded in the amorphous phases were captured in real space[21,22,23]
Summary
Despite ultra-high strength and elastic energy absorption capacity, the negligible plasticity in most metallic glasses has been an important barrier obstructing property optimization and their widespread use[1,2]. The extent of deformation in these specific alloys has been linked to the homogenous and concurrent nucleation and evolution of a high-density of shear bands (SBs) throughout the volume and their intersection with each other Compared to their counterparts with detectable second phase crystallinity and/or devitrification in their pre-deformed state[7,8,9,10,11], as well as generated upon deformation (in which plastic shear is absorbed or deflected by the homogeneously dispersed second phases or voids)[12,13,14,15,16,17], the underlying intrinsic mechanism for achieving large plasticity for these monolithic BMGs is still unclear.
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