Dynamic control of thermal transport in solid-state systems is a transformative capability with the promise to propel technologies including phononic logic, thermal management, and energy harvesting. ...A solid-state solution to rapidly manipulate phonons has escaped the scientific community. We demonstrate active and reversible tuning of thermal conductivity by manipulating the nanoscale ferroelastic domain structure of a Pb(Zr0.3Ti0.7)O3 film with applied electric fields. With subsecond response times, the room-temperature thermal conductivity was modulated by 11%.
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IJS, KILJ, NUK, PNG, UL, UM
Uniaxial mechanical testing conducted at room temperature (RT) and 77 K on hydrogen (H)-exposed nickel was coupled with targeted microscopy to evaluate the influence of deformation temperature, and ...therefore mobile H-deformation interactions, on intergranular cracking in nickel. Results from interrupted tensile tests conducted at cryogenic temperatures (77 K), where mobile H-deformation interactions are effectively precluded, and RT, where mobile H-deformation interactions are active, indicate that mobile H-deformation interactions are not an intrinsic requirement for H-induced intergranular fracture. Moreover, an evaluation of the true strain for intergranular microcrack initiation for testing conducted at RT and 77 K suggests that H which is segregated to grain boundaries prior to the onset of straining dominates the H-induced fracture process for the prescribed H concentration of 4000 appm. Finally, recent experiments suggesting that H-induced fracture is predominately driven by mobile H-deformation interactions, as well as the increased susceptibility of coherent twin boundaries to H-induced crack initiation, are re-examined in light of these new results.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
Twin boundaries play an important role in the thermodynamics, stability, and mechanical properties of nanocrystalline metals. Understanding their structure and chemistry at the atomic scale is key to ...guide strategies for fabricating nanocrystalline materials with improved properties. We report an unusual segregation phenomenon at gold-doped platinum twin boundaries, which is arbitrated by the presence of disconnections, a type of interfacial line defect. By using atomistic simulations, we show that disconnections containing a stacking fault can induce an unexpected transition in the interfacial-segregation structure at the atomic scale, from a bilayer, alternating-segregation structure to a trilayer, segregation-only structure. This behavior is found for faulted disconnections of varying step heights and dislocation characters. Supported by a structural analysis and the classical Langmuir–McLean segregation model, we reveal that this phenomenon is driven by a structurally induced drop of the local pressure across the faulted disconnection accompanied by an increase in the segregation volume.
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We experimentally investigate the role of size effects and boundary scattering on the thermal conductivity of silicon-germanium alloys. The thermal conductivities of a series of epitaxially grown ...Si(1-x)Ge(x) thin films with varying thicknesses and compositions were measured with time-domain thermoreflectance. The resulting conductivities are found to be 3 to 5 times less than bulk values and vary strongly with film thickness. By examining these measured thermal conductivities in the context of a previously established model, it is shown that long wavelength phonons, known to be the dominant heat carriers in alloy films, are strongly scattered by the film boundaries, thereby inducing the observed reductions in heat transport. These results are then generalized to silicon-germanium systems of various thicknesses and compositions; we find that the thermal conductivities of Si(1-x)Ge(x) superlattices are ultimately limited by finite size effects and sample size rather than periodicity or alloying. This demonstrates the strong influence of sample size in alloyed nanosystems. Therefore, if a comparison is to be made between the thermal conductivities of superlattices and alloys, the total sample thicknesses of each must be considered.
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CMK, CTK, FMFMET, IJS, NUK, PNG, UM
Recent experimentally validated alloy design theories have demonstrated nanocrystalline binary alloys that are stable against thermally induced grain growth. An open question is whether such thermal ...stability also translates to stability under irradiation. In this study, we investigate the response to heavy ion irradiation of a nanocrystalline platinum gold alloy that is known to be thermally stable from previous studies. Heavy ion irradiation was conducted at both room temperature and elevated temperatures on films of nanocrystalline platinum and platinum gold. Using scanning/transmission electron microscopy equipped with energy-dispersive spectroscopy and automated crystallographic orientation mapping, we observe substantial grain growth in the irradiated area compared to the controlled area beyond the range of heavy ions, as well as compositional redistribution under these conditions, and discuss mechanisms underpinning this instability. These findings highlight that grain boundary stability against one external stimulus, such as heat, does not always translate into grain boundary stability under other stimuli, such as displacement damage.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
The present study focuses on the low cycle fatigue (LCF) behavior of strain-hardened 316L stainless steel under plastic strain control, aiming to understand the influence of internal hydrogen on ...fatigue performance and cyclic deformation behavior for energy-related technologies. The strain-hardened 316L specimens tested at plastic strain amplitudes between 0.1% and 0.7% with and without hydrogen displayed continuous cyclic softening. Internal hydrogen increased the cyclic strength of this steel, with a greater difference in strength at low plastic strain amplitudes. A Bauschinger analysis revealed that effective stresses represented the major contribution to the flow stress for all material conditions and amplitudes. At low plastic strain amplitudes, effective stresses were responsible for differences in cyclic strength between hydrogen precharged and non-charged specimens. In contrast, back stresses became more significant at high amplitudes, and more similar deformation structures were observed. Although internal hydrogen reduced the total LCF lifetime at all amplitudes, this degradation was more significant in the low amplitude regime. This result is attributed to high effective stresses that led to the onset of multiple slip at lower cumulative plastic strains in the hydrogen precharged condition compared to the non-charged condition at low amplitudes. In addition, the evolution of the apparent elastic response of the material suggests that the primary crack(s) nucleated at a smaller percentage of the total lifetime and propagated in fewer number of cycles in the hydrogen precharged than in the non-charged condition. Fracture surface and gage section observations revealed a transgranular crack path and planar slip traces in both material conditions, with internal hydrogen promoting multiple slip at lower values of cumulative plastic strain than in the non-charged condition.
•316L stainless steel was LCF tested under plastic strain control.•Continuous softening was observed with and without internal hydrogen.•Internal hydrogen increased cyclic strength but reduced initiation and total lifetimes.•Lifetime differences at low amplitudes were consistent with high effective stresses.•Internal hydrogen promoted multiple slip at lower cumulative plastic strains.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
A significant experimental challenge in testing proposed relationships between structure and properties is the synthesis of targeted structures with atomistic control over both the structure and the ...composition. SnSe2(MoSe2)1.32 was synthesized to test the hypothesis that the low-temperature synthesis of two interleaved structures would result in complete turbostratic disorder and that the disorder would result in ultralow thermal conductivity. SnSe2(MoSe2)1.32 was prepared by depositing elements to form a precursor containing Sn|Se and Mo|Se bilayers, each containing the number of atoms required to form single dichalcogenide planes. The nanoarchitecture of alternating Sn and Mo layers is preserved as the dichalcogenide planes self-assemble at low temperatures. The resulting compound contains well-formed dichalcogenide planes that closely resemble that found in the binary compounds and extensive turbostratic disorder. As expected from proposed structure–property relationships, the thermal conductivity of SnSe2(MoSe2)1.32 is ultralow, ∼0.05 W m–1 K–1.
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We present large-scale atomistic simulations that reveal triple junction (TJ) segregation in Pt–Au nanocrystalline alloys in agreement with experimental observations. While existing studies suggest ...grain boundary solute segregation as a route to thermally stabilize nanocrystalline materials with respect to grain coarsening, here we quantitatively show that it is specifically the segregation to TJs that dominates the observed stability of these alloys. Our results reveal that doping the TJs renders them immobile, thereby locking the grain boundary network and hindering its evolution. In dilute alloys, it is shown that grain boundary and TJ segregation are not as effective in mitigating grain coarsening, as the solute content is not sufficient to dope and pin all grain boundaries and TJs. Our work highlights the need to account for TJ segregation effects in order to understand and predict the evolution of nanocrystalline alloys under extreme environments.
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Selecting specific 2D building blocks and specific layering sequences of van der Waals heterostructures should allow the formation of new materials with designed properties for specific applications. ...Unfortunately, the synthetic ability to prepare such structures at will, especially in a manner that can be manufactured, does not exist. Herein, we report the targeted synthesis of new metal–semiconductor heterostructures using the modulated elemental‐reactant technique to nucleate specific 2D building blocks, control their thickness, and avoid epitaxial structures with long‐range order. The building blocks, VSe2 and GeSe2, have different crystal structures, which inhibits cation intermixing. The precise control of this approach enabled us to synthesize heterostructures containing GeSe2 monolayers alternating with VSe2 structural units with specific sequences. The transport properties systematically change with nanoarchitecture and a charge‐density wave‐like transition is observed.
Layered cake: The modulated elemental‐reactant technique provides a unique route to the targeted synthesis of new van der Waals heterostructures. VSe2 and GeSe2 were selected as 2D building blocks to inhibit cation intermixing. The kinetic control offered by this approach enabled heterostructures with varying stacking sequences to be prepared.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
The characterization of the three-dimensional arrangement of dislocations is important for many analyses in materials science. Dislocation tomography in transmission electron microscopy is ...conventionally accomplished through intensity-based reconstruction algorithms. Although such methods work successfully, a disadvantage is that they require many images to be collected over a large tilt range. Here, we present an alternative, semi-automated object-based approach that reduces the data collection requirements by drawing on the prior knowledge that dislocations are line objects. Our approach consists of three steps: (1) initial extraction of dislocation line objects from the individual frames, (2) alignment and matching of these objects across the frames in the tilt series, and (3) tomographic reconstruction to determine the full three-dimensional configuration of the dislocations. Drawing on innovations in graph theory, we employ a node-line segment representation for the dislocation lines and a novel arc-length mapping scheme to relate the dislocations to each other across the images in the tilt series. We demonstrate the method for a dataset collected from a dislocation network imaged by diffraction-contrast scanning transmission electron microscopy. Based on these results and a detailed uncertainty analysis for the algorithm, we discuss opportunities for optimizing data collection and further automating the method.
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