Cavitation-Induced Fracture Causes Nanocorrugations in Brittle Metallic Glasses

Abstract

Brittle metallic glasses exhibit a unique and intriguing fracture morphology of periodic nanocorrugations whose spacing and amplitude are of the order of tens of nanometers. We show through continuum simulations that they fail by spontaneous and simultaneous cavitation within multiple weak zones arising due to intrinsic atomic density fluctuations ahead of a notch tip. Dynamic crack growth would then occur along curved but narrowly confined shear bands that link the growing cavities. This mechanism involves little dissipation and also explains the formation of nanocorrugations.

Observation of cavitation governing fracture in glasses

“…As can be seen, discrete cavities nucleate ahead of the crack front, grow with curved sharp tips, and coalesce along an organized path; i.e., an extending tadpole-like curved tip grows from one edge of a cavity and links the other side of the growing cavity ahead of it (see also fig. S3), similar to the inference from simulation (36). It is intriguing to note that there exist nanoscale droplet-like pile-ups surrounding each cavity, corresponding to the white regions in Fig.…”

“…S1B). The above observations explain the longstanding puzzle of how the nanocorrugated fracture morphologies are formed in MGs and clarify that the periodic nanocorrugation patterns are not governed by the fluid meniscus instability or the wavy or oscillatory crack propagation but induced by the ordered cavitation process (24,(32)(33)(34)(35)(36)(37). MGs is also governed by the cavitation mechanism, resulting in the periodic wave-like nanocorrugated morphologies (Fig.…”

“…However, there is still no well-established theory that is able to explain the intriguing fracture morphological features. Specifically, how the unique nanoscale periodic corrugation structures are formed in the "mirror" zones of the brittle fracture surfaces is a pressing problem (24,(32)(33)(34)(35)(36)(37). Recently, numerous calculations and simulations have recognized that cavitation is involved in the fracture of MGs and is believed to play an essential role in the failure of MGs, as well as other glassy materials (3,(36)(37)(38)(39)(40)(41)(42)(43)(44)(45)(46)(47).…”

Elastic Fluctuations and Structural Heterogeneities in Metallic Glasses

“…Such voids are directly seen in TEM specimen without applying a Fourier analysis and are of a much larger length scale. It was therefore concluded that the formation of a microcrack proceeds via excess free volume coalescence to nanovoids, subsequently growing and thereby leading to microcracks inside the shear band . The formed microcracks were then believed to cause a shear‐band‐to‐crack transition, providing a mechanistic view on how a developed shear band can initiate fracture in an MG.…”

Unraveling the Anomalous Grain Size Dependence of Cavitation

“…Cavitation instabilities may be induced in most forms of matter, e.g. fluids [1,2], polymers [3,4], amorphous solids [5][6][7], deuterated solvents [8], liquid helium [9], biological tissue [10], engineering materials [11], through the rapid deposition of high-intensity energy, e.g. by impact [11], laser irradiation [12], ultrasound [2], hydrodynamic machinery [3], the snapping claw of the Alpheus heterochaelis [13].…”