Abstract
In this work, the deformation behavior of as-prepared (AP) and structurally relaxed (SR) Cu–Zr–based nanoglasses (NGs) are investigated using nano- and micro-indentation. The NGs are subjected to structural relaxation by annealing them close to the glass transition temperature without altering their amorphous nature. The indentation load, p, vs. displacement, h, curves of SR samples are characterized by discrete displacement bursts, while the AP samples do not show any of them, suggesting that annealing has caused a local change in the amorphous structure. In both the samples, hardness (at nano- and micro-indentation) decreases with increasing p, demonstrating the indentation size effect. The micro-indentation imprints of SR NGs show evidence of shear bands at the periphery, indicating a heterogeneous plastic flow, while AP NG does not display any shear bands. Interestingly, the shear band density decreases with p, highlighting the fact that plastic strain is accommodated entirely by the shear bands in the subsurface deformation zone. The results are explained by the differences in the amorphous structure of the two NGs.
Highlights
At room temperature, conventional amorphous alloys such as bulk metallic glasses and melt-spun ribbons (MSR) exhibit limited plasticity as deformation gets localized into one dominant shear band, leading to catastrophic failure (Schuh et al, 2007)
We have considered the following facts while developing this model: 1) Structural relaxation leads to a decrease in free volume and STZ density, which is manifested in a reduction in the interface width and an increase in local atomic density inside the GGs and 2) the subsurface deformation volume increases with increasing indentation load implying that a larger volume of the material beneath the indenter undergoes plastic deformation
The free volume has a marked influence on the deformation behavior of Cu–Zr NGs, with structurally relaxed (SR) NGs exhibiting a higher H than the as-prepared (AP) NGs
Summary
Conventional amorphous alloys such as bulk metallic glasses and melt-spun ribbons (MSR) exhibit limited plasticity as deformation gets localized into one dominant shear band, leading to catastrophic failure (Schuh et al, 2007). STZs, unlike dislocations, are nearly impossible to observe directly using experiments, but the molecular dynamic studies show that they occur in the vicinity of regions containing high free volume. It seems that one of the ways to increase the plasticity of amorphous alloys is to produce a structure containing areas of high free volume.
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