During β-processing of α/β and β titanium alloys, variant selection (VS) of grain boundary α (GBα) is one of the key factors in determining the final transformation texture and mechanical properties. ...It has been observed frequently that GBα prefers its 〈0001〉α pole to be parallel to a common 〈110〉β pole of the two adjacent β grains and results in a micro-textured region across the grain boundary (GB) and, as a consequence, slip transmission may take place more easily across that GB. In order to investigate how such a special prior β GB contributes to VS of GBα, we develop a crystallographic model based on the Burgers orientation relationship (BOR) between GBα and one of the two β grains. The model predicts all possible special β grain boundaries at which GBα is able to maintain BOR with both β grains. A new measure for VS of GBα, (βΔJβBOR), i.e., a measure of the deviation of the actual OR between the GBα and the non-Burgers grain from the BOR, is proposed. For the particular alloy chosen for experimental observations, Ti-5553, it is found that when the misorientation angle θm of (βΔJβBOR) (instead of the closeness between two closet {110}β poles between two β grains widely used in literature) is less than 15°, misorientation between the two β grains dominates the VS of GBα and, in particular, the variant with minimum θm is always selected for GBα. A possible effect due to grain boundary plane inclination on VS is also discussed.
In additively manufactured (AM) metallic materials, the fundamental interrelationships that exist between composition, processing, and microstructure govern these materials' properties and potential ...improvements or reductions in performance. For example, by using AM, it is possible to achieve highly desirable microstructural features (e.g., highly refined precipitates) that could not otherwise be achieved by using conventional approaches. Simultaneously, opportunities exist to manage macro-level microstructural characteristics such as residual stress, porosity, and texture, the last of which might be desirable. To predictably realize optimal microstructures, it is necessary to establish a framework that integrates processing variables, alloy composition, and the resulting microstructure. Although such a framework is largely lacking for AM metallic materials, the basic scientific components of the framework exist in literature. This review considers these key components and presents them in a manner that highlights key interdependencies that would form an integrated framework to engineer microstructures using AM.
This paper discusses the structural and compositional changes at the nanometer scale associated with the nucleation and growth of α precipitates in the β titanium alloy Ti-5553 (Ti–5Al–5Mo–5
...V–3Cr–0.5Fe
) with ω precipitates acting as heterogeneous nucleation sites. The microstructural evolution in this alloy, during β-solutionizing, quenching and aging type heat-treatments, has been investigated by combining results from scanning electron microscopy, orientation imaging microscopy, transmission electron microscopy, high-resolution TEM and three-dimensional atom probe (3DAP) tomography. Athermal ω precipitates form in this alloy on quenching from above the β transus temperature. On isothermal annealing at low temperatures, these ω precipitates coarsen to form chemically ordered ω precipitates, accompanied by the nucleation of the stable α phase. Annealing at higher temperatures leads to dissolution of ω and further growth of α precipitates accompanied by clustering of different α variants in self-accommodating morphologies. 3DAP results indicate that annealing at lower temperatures (∼350
°C) leads to initial nucleation of α precipitates with a non-equilibrium composition, nearly identical to that of the β matrix. Subsequent aging at higher temperatures (∼600
°C) leads to more pronounced partitioning of alloying elements between the two phases. These results indicate that the structural body-centered cubic to hexagonal close-packed transformation and the compositional partitioning of alloying elements occur in sequential steps, resulting in a mixed-mode displacive-diffusional transformation, similar to the bainite transformation in steels.
For multi-phase soft matter systems, optical microscopy is frequently employed to distinguish the different phases. Unfortunately, optical microscopy does not succeed in all cases. Consequently, ...researchers sometimes require more advanced imaging techniques with superior resolution or sample penetration capabilities. One such complex system is a mixed aqueous-and-oil foam stabilised by colloidal particles, which is composed of two immiscible foams organised as the dispersed and continuous phases of an emulsion. While its morphology has been extensively studied using fluorescence confocal microscopy, not all questions have been answered. While the aqueous phase bubble interfaces are stabilised by silica particles and the oil phase bubble interfaces are stabilised by fluorinated particles, it remains to be seen how the aqueous-oil interfaces are stabilised. Hence, to gain insights into the role of the different particles at the interfaces, we employ cryogenic scanning electron microscopy (Cryo-SEM) and energy-dispersive X-ray spectroscopy (EDS). We find that the hydrophobic silica particles reside at both the aqueous-air and aqueous-oil interfaces. In contrast, the fluorinated particles, which exhibit hydrophobic and oleophobic properties simultaneously, are exclusively found at the oil-air interfaces.
Cryo-SEM combined with EDS can provide new insight into the structure of complex composite materials.
Abstract
Stimuli-responsive emulsions offer a dual advantage, combining long-term storage with controlled release triggered by external cues such as pH or temperature changes. This study establishes ...that thermo-responsive emulsion behaviour is primarily determined by interactions between, rather than within, interfaces. Consequently, the stability of these emulsions is intricately tied to the nature of the stabilizing microgel particles - whether they are more polymeric or colloidal, and the morphology they assume at the liquid interface. The colloidal properties of the microgels provide the foundation for the long-term stability of Pickering emulsions. However, limited deformability can lead to non-responsive emulsions. Conversely, the polymeric properties of the microgels enable them to spread and flatten at the liquid interface, enabling stimuli-responsive behaviour. Furthermore, microgels shared between two emulsion droplets in flocculated emulsions facilitate stimuli-responsiveness, regardless of their internal architecture. This underscores the pivotal role of microgel morphology and the forces they exert on liquid interfaces in the control and design of stimuli-responsive emulsions and interfaces.
Several remote sensing studies have documented widespread thermokarst lake expansion in continuous permafrost regions of North America over the past few decades. Other studies have found no long-term ...trends in water body extents, but large intra- and inter-annual changes driven by precipitation. These differences could be due to geographic variability in physical conditions (geology, climate, permafrost and hydrology) or in the data and methods used to extract water bodies. This study tested water extraction methods over the Tuktoyaktuk Coastal Plain, Northwest Territories (NWT), Canada, based on the Landsat 5 shortwave infrared (SWIR) channel and validated them using water extents obtained from 0.5m resolution orthophoto imagery. Methods included applying thresholds to generate binary land/water classifications, as well as deriving 30m water fractions from both linear unmixing and a new histogram breakpoint method. Results indicated that the histogram breakpoint method outperformed other methods, underestimating overall water fraction by 0.26% and overestimating the number of pure 30m water pixels by 0.66% compared to water fractions calculated from orthophotos. The breakpoint method was then applied to a stack of 17 near peak-of-season Landsat 5 and Landsat 7 images acquired between July 4 and August 18 from 1985 to 2011 to create a water fraction time-series for examining both trends and inter-annual variation in water extent. Results showed an overall expansion of lake area along margins by 55km2 with isolated lakes experiencing rapid drainage totalling 15km2, leading to a net water area increase of 40km2 over the 26-year period.
•A new Landsat water extraction technique outperforms traditional methods.•Trends in Landsat water are computed from 1985 to 2011 over the Tuktoyaktuk Plain.•Results show expansion for most lakes, while few lakes exhibited rapid drainage.•The net result of expansion and drainage is an overall increase in lake area.•Results are consistent with previous studies, but not with a study of the same region.
The present paper reports on the electrochemical properties of a wide range of high entropy alloys (HEAs) in a 0.6 M NaCl solution. A consolidated treatise of the topic has to date been lacking, and ...the purpose of the work herein is to present a primitive galvanic series for numerous HEAs, along with a broad survey of results typifying their electrochemical characteristics, passivity and comparative electrochemistry. The results are coupled with microstructural characterisation. The range of potentials for HEAs is comparable to or nobler than austenitic stainless steel, with a number of HEAs displaying higher pitting potential (E
pit
) values than stainless steels, in spite of possessing heterogeneous microstructures.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
In titanium alloys, variant selection (VS) of grain boundary α (GBα) at prior β grain boundaries (GBs) during α precipitation has a significant influence on the subsequent transformation pathway and ...transformation texture development of the α phase, and thus on the final mechanical properties. In this paper, we assess systematically the applicability of all current empirical rules for VS of GBα at prior β GBs using experimental characterization of GB misorientation, boundary plane inclination, and orientation relationships between the GBα and adjacent β grains in Ti-5553. We find that all these VS rules may be violated for a given β grain boundary. Based on the experimental observations, the frequencies of each of these empirical rules being either violated or followed have been assessed, and from this assessment, we analyze theoretically whether the arguments underlying each of these rules are physically sound and why rules are violated, and then discuss when a sound prediction may be made using these empirical VS rules.
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Decades of research has been focused on improving the high-temperature properties of nickel-based superalloys, an essential class of materials used in the hot section of jet turbine engines, allowing ...increased engine efficiency and reduced CO
emissions. Here we introduce a new 'phase-transformation strengthening' mechanism that resists high-temperature creep deformation in nickel-based superalloys, where specific alloying elements inhibit the deleterious deformation mode of nanotwinning at temperatures above 700 °C. Ultra-high-resolution structure and composition analysis via scanning transmission electron microscopy, combined with density functional theory calculations, reveals that a superalloy with higher concentrations of the elements titanium, tantalum and niobium encourage a shear-induced solid-state transformation from the γ' to η phase along stacking faults in γ' precipitates, which would normally be the precursors of deformation twins. This nanoscale η phase creates a low-energy structure that inhibits thickening of stacking faults into twins, leading to significant improvement in creep properties.
Unmanned Aerial Vehicle (UAV) systems, sensors, and photogrammetric processing techniques have enabled timely and highly detailed three-dimensional surface reconstructions at a scale that bridges the ...gap between conventional remote-sensing and field-scale observations. In this work 29 rotary and fixed-wing UAV surveys were conducted during multiple field campaigns, totaling 47 flights and over 14.3 km2, to document permafrost thaw subsidence impacts on or close to road infrastructure in the Northwest Territories, Canada. This paper provides four case studies: (1) terrain models and orthomosaic time series revealed the morphology and daily to annual dynamics of thaw-driven mass wasting phenomenon (retrogressive thaw slumps; RTS). Scar zone cut volume estimates ranged between 3.2 × 103 and 5.9 × 106 m3. The annual net erosion of RTS surveyed ranged between 0.35 × 103 and 0.39 × 106 m3. The largest RTS produced a long debris tongue with an estimated volume of 1.9 × 106 m3. Downslope transport of scar zone and embankment fill materials was visualized using flow vectors, while thermal imaging revealed areas of exposed ground ice and mobile lobes of saturated, thawed materials. (2) Stratigraphic models were developed for RTS headwalls, delineating ground-ice bodies and stratigraphic unconformities. (3) In poorly drained areas along road embankments, UAV surveys detected seasonal terrain uplift and settlement of up to 0.5 m (>1700 m2 in extent) as a result of injection ice development. (4) Time series of terrain models highlighted the thaw-driven evolution of a borrow pit (6.4 × 105 m3 cut volume) constructed in permafrost terrain, whereby fluvial and thaw-driven sediment transfer (1.1 and 3.9 × 103 m3 a−1 respectively) was observed and annual slope profile reconfiguration was monitored to gain management insights concerning site stabilization. Elevation model vertical accuracies were also assessed as part of the case studies and ranged between 0.02 and 0.13 m Root Mean Square Error. Photogrammetric models processed with Post-processed Kinematic image solutions achieved similar accuracies without ground control points over much larger and complex areas than previously reported. The high resolution of UAV surveys, and the capacity to derive quantitative time series provides novel insights into permafrost processes that are otherwise challenging to study. The timely emergence of these tools bridges field-based research and applied studies with broad-scale remote-sensing approaches during a period when climate change is transforming permafrost environments.
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