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.
Highlights
A degree of universality1 has been observed recently in the noise that occurs during plastic deformation in a diverse set of materials such as small volumes of crystalline metals,2,3 granular media,4–6 metallic glasses,7–9 and high entropy alloys,10 among others.11–13 A simple model1 provides predictions for the detail-independent aspects of the statistics of the noise and intuition for the underlying micromechanical processes
The fundamental premise of the model is the weak spots in the material slip, and since the weak spots are elastically coupled to one another, they can cause other weak spots to slip in a cascade of slips known as a slip avalanche
We have previously demonstrated7 that the statistics and dynamics of the slip avalanches in a monolithic metallic glass follow twelve different statistical properties predicted by the mean-field model
Summary
A degree of universality has been observed recently in the noise that occurs during plastic deformation in a diverse set of materials such as small volumes of crystalline metals, granular media, metallic glasses, and high entropy alloys, among others. A simple model provides predictions for the detail-independent aspects of the statistics of the noise and intuition for the underlying micromechanical processes. The statistics of the slips (e.g., the size distribution, duration distribution, duration as a function of size, etc.) have been demonstrated to show tuned critical behavior, meaning that the statistics produce predicted power-law exponents over a scaling regime that is limited in extent by a cutoff that is a function of tunable parameters such as the specimen size, applied stress level, strain rate, extent of weakening in the material, and stiffness of the mechanical test system. We have previously demonstrated that the statistics and dynamics of the slip avalanches in a monolithic metallic glass follow twelve different statistical properties predicted by the mean-field model.. Where τa,r is a “sticking” stress at which a failing cell resticks after it has slipped Often, this sticking stress is assumed to be zero because the universal predictions of the model do not depend on its value
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