Although the atomic structure of amorphous alloys, which lacks long-range translational symmetry, may appear homogeneous at the macroscopic scale, their local dynamic and/or static properties however ...vary significantly according to the recent experimental and simulation results. In the literature of amorphous alloys, the nature of such local heterogeneities is currently an issue under debate. More importantly, since amorphous alloys are in a thermodynamically nonequilibrium state, their local structures constantly evolve during structural relaxation, physical aging and mechanical deformation. As such, local structural heterogeneities, which vary with the thermal and mechanical history of amorphous alloys, could provide a key to understand the structural origin of their mechanical behavior, such as anelasticity, viscoelasticity, plasticity and fracture. In this review article, we first review mechanical spectroscopy or dynamic mechanical analyses as an important tool to study the relaxation dynamics in amorphous alloys, with a focus on the possible correlation between the secondary (also called β) relaxation and the local structural heterogeneities of amorphous alloys. After that, we discuss the recent advances on the understanding of structural heterogeneities in metallic supercooled liquids and the influence of the structural heterogeneities on the overall mechanical properties of the corresponding amorphous alloys. Finally, we briefly discuss the further development of research on this subject.
•Corbicula fluminea worldwide distribution was modeled using different environmental datasets.•The climatic environmental variables led to more accurate modeling.•South African and Australian ...environments are particularly prone to invasion.•Results may support the introduction of measures to delay/prevent invasions.•Ensemble models can help understanding the threat posed by invasive species.
Niche-based models (NBMs) are increasingly being used to predict the biological distribution of species, as well as the importance of different environmental variables on their habitat adequability. Here, we investigate the reliability of these models in predicting habitat suitability for Corbicula fluminea, an important freshwater bivalve invasive species. In order to determine the influence of topographic vs. climatic variables, three datasets were used: (1) CorbiculaTOPO with topographic variables (altitude, slope and a compound topographical index); (2) CorbiculaMIX, combining climatic (annual mean temperature, mean temperature of warmest quarter, mean temperature of coldest quarter and annual precipitation) and topographic variables and (3) CorbiculaCLIM with only the climatic variables. Nine different types of models, implemented in BIOMOD2, were used and an ensemble of NBMs was built. We aimed to know how climatic suitability for these invaders changes when using different datasets of environmental variables; if the predictive reliability is similar between datasets; and which environmental variables better explain habitat adequability. Model performance was very similar between CorbiculaMIX and CorbiculaCLIM. CorbiculaTOPO was the dataset with the least accurate predictions. Mean temperature of the coldest quarter and altitude were the variables that influenced C. fluminea distribution the most. The use of an ensemble of predictions allowed us to clearly identify areas with potential to be invaded by the bivalve, in which records are not yet detected. This information can be used in management, to implement measures to delay or prevent invasions, as well as for the identification of the environmental variables that favor that invasive potential.
Lacking the structural information of crystalline solids, the origin of the relaxation dynamics of metallic glasses is unclear. Here, we report the evolution of stress relaxation of high-entropy ...metallic glasses with distinct β relaxation behavior. The fraction of liquidlike zones, determined at each temperature by the intensity of stress decay, is shown to be directly related to both the aging process and the spectrum of relaxation modes obtained by mechanical spectroscopy. The results shed light on the intrinsic correlation between the static and dynamic mechanical response in high-entropy and conventional metallic glasses, pointing toward a sluggish diffusion high-entropy effect in the liquid dynamics.
The short-range ordered but long-range disordered structure of metallic glasses yields strong structural and dynamic heterogeneities. Stress relaxation is a technique to trace the evolution of stress ...in response to a fixed strain, which reflects the dynamic features phenomenologically described by the Kohlrausch-Williams-Watts (KWW) equation. The KWW equation describes a broad distribution of relaxation times with a small number of empirical parameters, but it does not arise from a particular physically motivated mechanistic picture. Here we report an anomalous two-stage stress relaxation behavior in a Cu sub(46) Zr sub(46) Al sub(8) metallic glass over a wide temperature range and generalize the findings in other compositions. Thermodynamic analysis identifies two categories of processes: a fast stress-driven event with large activation volume and a slow thermally activated event with small activation volume, which synthetically dominates the stress relaxation dynamics. Discrete analyses rationalize the transition mechanism induced by stress and explain the anomalous variation of the KWW characteristic time with temperature. Atomistic simulations reveal that the stress-driven event involves virtually instantaneous short-range atomic rearrangement, while the thermally activated event is the percolation of the fast event accommodated by the long-range atomic diffusion. The insights may clarify the underlying physical mechanisms behind the phenomenological description and shed light on correlating the hierarchical dynamics and structural heterogeneity of amorphous solids.
Ultrathin passive films effectively prevent the chemical attack of stainless steel grades in corrosive environments; their stability depends on the interplay between structure and chemistry of the ...constituents iron, chromium, and molybdenum (Fe-Cr-Mo). Carbon (C), and eventually boron (B), are also important constituents of steels, although in small quantities. In particular, nanoscale inhomogeneities along the surface can have an impact on material failure but are still poorly understood. Addressing a stainless-type glass-forming Fe 50 Cr 15 Mo 14 C 15 B 6 alloy and using a combination of complementary high-resolution analytical techniques, we relate near-atomistic insights into increasingly inhomogeneous nanostructures with time- and element-resolved dissolution behavior. The progressive elemental partitioning on the nanoscale determines the degree of passivation. A detrimental transition from Cr-controlled passivity to Mo-controlled breakdown is dissected atom by atom, demonstrating the importance of nanoscale knowledge for understanding corrosion.
The thermal stability and the quantification of the different transformation processes involved in the overall crystallization of the Fe50Cr15Mo14C15B6 amorphous alloy were investigated by several ...characterization techniques. Formation of various metastable and stable phases during the devitrification process in the sequence α-Fe, χ-Cr6Fe18Mo5, M23(C,B)6, M7C3, η-Fe3Mo3C and FeMo2B2 (with M = Fe, Cr, Mo), was observed by in-situ synchrotron high energy X-ray diffraction and in-situ transmission electron microscopy. By combining these techniques with differential scanning calorimetry data, the crystallization states and their temperature range of stability under continuous heating were related with the evolution of the crystallized fraction and the phase sequence as a function of temperature, revealing structural and chemical details of the different transformation mechanisms.
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The failure of a 144‐m‐high lava‐dam waterfall on the Río Coca, Ecuador, in February 2020 initiated a catastrophic watershed reset—regressive erosion upstream and a massive sediment pulse ...downstream—as the river evolves towards a new equilibrium grade. The evolution of this river corridor after a sudden base‐level fall embodies the “complex response” concepts long understood through laboratory experiments, numerical modelling and smaller‐scale field studies, but that have not been observed in the field before on this scale. This paper presents geomorphic and geotechnical data to characterize the evolution of the Río Coca since 2020. In the three years after the lava‐dam failure, the erosion front migrated almost 13 km upstream along the mainstem river and triggered secondary headcuts that began migrating up tributaries. Erosion of the mainstem and tributary valleys generated a sediment pulse estimated to be 277 million m3 and ~500 million tonnes (Mt) over three years, depositing sediment tens of meters thick over tens of kilometres downstream from the former waterfall. This sediment pulse is one of the largest in modern times, comparable to the annual sediment load of a major continent‐draining river but with orders‐of‐magnitude greater sediment yield. Geomorphic adjustment of the Río Coca represents a highly unusual natural disaster threatening life, property, water quality, the regional economy, major infrastructure and energy security. However, this event also provides a rare opportunity to learn how a large autogenic watershed disturbance and recovery evolve, with important lessons for interpreting the sedimentary record of volcanic landscapes.
The failure of a 144‐m‐high lava dam on the Río Coca, Ecuador, in 2020 initiated major regressive erosion as the river evolved towards a new equilibrium grade. Erosion generated a 277 million m3, ~500 Mt sediment pulse over three years, one of the largest in modern times. Geomorphic adjustment of the Río Coca represents a highly unusual natural hazard cascade and a rare opportunity to learn how a large autogenic watershed disturbance and recovery evolve.
Understanding phase changes, including their formation and evolution, is critical for the performance of functional as well as structural materials. We analyze in detail microstructural and chemical ...transformations of the amorphous steel Fe50Cr15Mo14C15B6 during isothermal treatments at temperatures ranging from 550 to 800°C. By combining high-resolution transmission electron microscopy and Rietveld analyses of X-ray diffraction patterns together with the local chemical data obtained by atom probe tomography, this research provides relevant information at the atomic scale about the mechanisms of crystallization and the subsequent phases evolution. During the initial stages of crystallization a stable (Fe,Cr)23(C,B)6 precipitates as well as two metastable intermediates of M3(C,B) and the intermetallic χ-phase. When full crystallization is reached, only a percolated nano-scale Cr-rich (Fe,Cr)23(C,B)6 and Mo-rich η-Fe3Mo3C structure is detected, with no evidence to suggest that other phases appear at any subsequent time. Finally, the corrosion behavior of the developed phases is discussed from considerations of the obtained atomic information.
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