A promising remedy to the failure of metallic glasses (MGs) by shear banding is the use of a dense network of glass-glass interfaces, i.e., a nanoglass (NG). Here we investigate the effect of grain size (d) on the failure of NG by performing molecular dynamics simulations of tensile-loading on Cu50Zr50 NG with d = 5 to 15 nm. Our results reveal a drastic change in deformation mode from a single shear band (d ∼ 15 to 10 nm), to cooperative shear failure (d ∼ 10 to 5 nm), to homogeneous superplastic flow (d ≤ 5 nm). Our results suggest that grain size can be an effective design parameter to tune the mechanical properties of MGs.
Ab initio study based on density functional theory is performed to study the binding energies of Mg acceptors to single oxygen in AlN and the activation energies of the resultant Mg n -O complexes ͑n =2, 3, and 4͒. It is found that such complexes are energetically favored and have activation energies at least 0.23 eV lower than that of single Mg. The lower activation energies originate from the extra states over the valence band top of AlN induced by the passive Mg-O. By comparing to the well-established case of GaN, it is possible to fabricate Mg:O codoped AlN without MgO precipitates. These results suggest the possibility of achieving higher hole concentration in AlN by Mg:O codoping.
Metallic glasses (MGs) are often perceived as quintessential structural materials due to their superior mechanical properties such as high strength and large elastic limit. In practical applications, service conditions that introduce cyclic variations in stresses and strains are inevitably involved. The fatigue of MGs is thus a topic of research and practical interest. In this review, a brief introduction on MGs, their applications and challenges, is first provided. Next, experimental studies on fatigue behaviors of both macroscopic and nanoscale MGs are summarized. The range of topics covered include the stress-life behavior, fatigue-crack growth behavior, fatigue-fracture morphology, fatigue-failure mechanisms, as well as the effects of chemical composition, cycling frequency, loading condition, and sample size on the fatigue limits. Finally, recent progresses in simulation studies on the fatigue of MGs are discussed, with an emphasis placed on the atomic-level understanding of the fatigue mechanisms.
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