Slip statistics for a bulk metallic glass composite reflect its ductility

Abstract

Serrations in the stress-time curve for a bulk metallic glass composite with microscale crystalline precipitates were measured with exceptionally high temporal resolution and low noise. Similar measurements were made for a more brittle metallic glass that did not contain crystallites but that was also tested in uniaxial compression. Despite significant differences in the structure and stress-strain behavior, the statistics of the serrations for both materials follow a simple mean-field model that describes plastic deformation as arising from avalanches of slipping weak spots. The presence of the crystalline precipitates reduces the number of large slips relative to the number of small slips as recorded in the stress-time data, consistent with the model predictions. The results agree with mean-field predictions for a smaller weakening parameter for the composite than for the monolithic metallic glass; the weakening parameter accounts for the underlying microstructural differences between the two.

Why the Crackling Deformations of Single Crystals, Metallic Glasses, Rock, Granular Materials, and the Earth's Crust Are So Surprisingly Similar

“…The model does not require fitting parameters or operation in the steady state, and it allows for the formation of shear bands. This model has also shown agreement with experimental results for a number of materials [e.g., [4][5][6][7][8][9][10].…”

Beyond Serrated Flow in Bulk Metallic Glasses: What Comes Next?

“…There is thus a structural component in monolithic BMGs that contributes to the scaling as shown in Figure 2(a) that so far remains fully undefined. This is much different to the case of metallic-glass matrix composites, where the statistics of stress-strain instabilities changes towards smaller event sizes [43,44] -a result that naturally emerges due to the introduction of internal micro-structural length scales where crystallites lead to shear-band deflection and arrest. [45] In fact, some first evidence has been provided that even the scaling exponent a directly scales with the volume fraction and average size of the crystalline phase.…”

Experimental evidence that shear bands in metallic glasses nucleate like cracks

“…It has been previously observed that the introduction of crystalline dendrites into the BMG may mitigate the formation of large avalanches 34 and increase ductility 35 . Interestingly, in 34 the observed foot occurrence rate differs greatly between the monolithic metallic glass, 89%, and the composite, 19%.…”