Ar-ion-milling-induced structural changes of Cu50Zr45Ti5 metallic glass

Fu, Engang; Carter, Jesse; Martin, Michael; Xie, Guoqiang; Zhang, X.; Wang, Y.Q.; Littleton, R. T.; McDeavitt, Sean M.; Shao, Lin

doi:10.1016/j.nimb.2009.12.007

Cited by 20 publications

(12 citation statements)

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“…If ion irradiation induces phase segregation, entropy will drop due to the reduced number of microscopic states26, thus increasing Δ G l–s . Previous studies on different MGs have observed the agglomeration of nanocrystals of a new phase and subsequent formation of stable nuclei from the agglomeration27, but such phase separation was not observed in the present study and will not be a significant driving force for nanocrystallization. Furthermore, introducing excess free volume will decrease the specific heat capacity and thus increase Δ G l–s although the effect is small.…”

contrasting

confidence: 79%

Sink property of metallic glass free surfaces

Shao

Price

et al. 2015

Sci Rep

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When heated to a temperature close to glass transition temperature, metallic glasses (MGs) begin to crystallize. Under deformation or particle irradiation, crystallization occurs at even lower temperatures. Hence, phase instability represents an application limit for MGs. Here, we report that MG membranes of a few nanometers thickness exhibit properties different from their bulk MG counterparts. The study uses in situ transmission electron microscopy with concurrent heavy ion irradiation and annealing to observe crystallization behaviors of MGs. For relatively thick membranes, ion irradiations introduce excessive free volumes and thus induce nanocrystal formation at a temperature linearly decreasing with increasing ion fluences. For ultra-thin membranes, however, the critical temperature to initiate crystallization is about 100 K higher than the bulk glass transition temperature. Molecular dynamics simulations indicate that this effect is due to the sink property of the surfaces which can effectively remove excessive free volumes. These findings suggest that nanostructured MGs having a higher surface to volume ratio are expected to have higher crystallization resistance, which could pave new paths for materials applications in harsh environments requiring higher stabilities.

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confidence: 79%

Sink property of metallic glass free surfaces

Shao

Price

et al. 2015

Sci Rep

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“…The sample was attached over a hole window area in the chip at a 13° incline angle to the chip surface, to allow final thinning down to electron transparency with 5 kV Ga + . As discussed below, sample thinning induced partial crystallization of the TEM sample (Fu et al, 2010). Crystallization may be due to the primary ion beam, but the angle between the beam and the sample was quite low (~2°), which should have minimized damage.…”

Section: Methodsmentioning

confidence: 99%

Electron Correlation Microscopy: A New Technique for Studying Local Atom Dynamics Applied to a Supercooled Liquid

Zhang

Besser

et al. 2015

Microsc Microanal

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Electron correlation microscopy (ECM) is a new technique that utilizes time-resolved coherent electron nanodiffraction to study dynamic atomic rearrangements in materials. It is the electron scattering equivalent of photon correlation spectroscopy with the added advantage of nanometer-scale spatial resolution. We have applied ECM to a Pd40Ni40P20 metallic glass, heated inside a scanning transmission electron microscope into a supercooled liquid to measure the structural relaxation time τ between the glass transition temperature T g and the crystallization temperature, T x . τ determined from the mean diffraction intensity autocorrelation function g 2(t) decreases with temperature following an Arrhenius relationship between T g and T g +25 K, and then increases as temperature approaches T x . The distribution of τ determined from the g 2(t) of single speckles is broad and changes significantly with temperature.

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“…Substantial efforts have been made to alleviate brittle behavior by various toughening mechanisms. − One possibility is to reduce the specimen size to below some critical dimension on the order of ∼100 nm, where metallic glasses have been reported to undergo a size-induced brittle to ductile transition in compression − and in tension. , The origin of this transition is still being pursued because the experimental results are inconsistent with some literature reporting this transition to occur at 400, 200, and 100 nm , or not seeing any suppression of catastrophic failure even for sample sizes down to 150–300 nm. − Most of the existing literature on nanomechanical deformation of individual metallic glass nanostructures describes experiments on samples fabricated using a focused ion beam (FIB). This milling technique irradiates the sample surface with a relatively high-energy ion beam, which can potentially lead to a modification of the local atomic arrangements or even to surface crystallization. − Molecular dynamics (MD) simulations by Xiao et al revealed that ion bombardments suppressed shear band formation in 106.4 eV-irradiated Zr-based metallic glass nanowires (7.8 nm in diameter and 17.7 nm in length) . An alternate synthesis of individual nanosized metallic glasses suitable for mechanical testing is necessary to ascertain whether the size-induced brittle-to-ductile transition is a real physical phenomenon and to shed further light on understanding the deformation mechanisms in metallic glasses at small scales.…”

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confidence: 99%