Showing papers on "Quenching published in 2019"

In Situ Solid Electrolyte Interphase from Spray Quenching on Molten Li: A New Way to Construct High-Performance Lithium-Metal Anodes.

Abstract: Uncontrollable growth of Li dendrites and low utilization of active Li severely hinder its practical application. Construction of an artificial solid electrolyte interphase (SEI) on Li is demonstrated as one of the most effective ways to circumvent the above problems. Herein, a novel spray quenching method is developed in situ to fabricate an organic-inorganic composite SEI on Li metal. By spray quenching molten Li in a modified ether-based solution, a homogeneous and dense SEI consisting of organic matrix embedded with inorganic LiF and Li3 N nanocrystallines (denoted as OIFN) is constructed on Li metal. Arising from high ionic conductivity and strong mechanical stability, the OIFN can not only effectively minimize the corrosion reaction of Li, but also greatly suppresses the dendrite growth. Accordingly, the OIFN-Li anode presents prominent electrochemical performance with an enhanced Coulombic efficiency of 98.15% for 200 cycles and a small hysteresis of <450 mV even at ultrahigh current density up to 10 mA cm-2 . More importantly, during the full cell test with limited Li source, a high utilization of Li up to 40.5% is achieved for the OIFN-Li anode. The work provides a brand-new route to fabricate advanced SEI on alkali metal for high-performance alkali-metal batteries.

Study of heat treatment parameters for additively manufactured AlSi10Mg in comparison with corresponding cast alloy

Abstract: A solution, quenching and ageing heat treatment is often performed on additive manufactured AlSi10Mg parts to dissolve the anisotropy due to the layer-by-layer building. This study investigates the influence of temperature and duration of solution and ageing treatment on microstructure, hardness and density of AlSi10Mg alloy produced by direct metal laser sintering. A parallel investigation is carried out on AlSi10Mg samples produced by gravity casting to analyse the different response to the same heat treatment conditions. The highest hardness, combined with an acceptable increase of porosity, is reached after selected heat treatment parameters. It was also found that, compared to the as-produced condition, this treatment leads to a decrease of ultimate tensile strength, without affecting the yield strength of additive manufactured samples, and reduces the difference in properties along the two building directions. The high properties of the as-produced samples are related to the finer microstructure and, as proved by the differential scanning calorimetric measurements, to the self-quenching phenomenon.

Microstructure and Properties of Novel Heat Resistant Al–Ce–Cu Alloy for Additive Manufacturing

Abstract: The microstructure and properties of the novel heat resistant Al–3Ce–7Cu alloy produced by selective laser melting were investigated. Fine Al11Ce3 and Al6.5CeCu6.5 eutectic phases were found in the microstructure. Annealing at temperatures in the 250–400 °C range leads to a decrease in the hardness. Hardness has larger values after annealing at 350 and 400 °C than at 250 °C due to the precipitation of nanosized particles. The low hardness after quenching and aging at 190 °C is caused by quench stress relief and the absence of aging hardening because of poor solid solution. The as-printed yield strength, ultimate tensile strength and elongation are 274 MPa, 456 MPa and 4.4%, respectively. High mechanical properties of the Al–3Ce–7Cu alloy were demonstrated by high temperature tension and compression tests.

(INVITED) Review of luminescent properties of Ce3+-doped garnet phosphors: New insight into the effect of crystal and electronic structure

Abstract: The absorption and luminescence properties (centroid shift and crystal field splitting of 5 d orbitals) of Ce 3+ -doped garnets are summarized from the viewpoints of chemical composition (electron negativity and optical basicity) and the local crystal structure of the Ce 3+ ion (bond length and distortion). Clear trends exist between (1) the centroid shift of 5 d energy ( e c ) and the optical basicity of the host garnets and between (2) the crystal field splitting of the lowest 5 d 1 -5 d 2 levels ( Δ 12 ) and a new distortion parameter obtained from the crystal structure data. The data of quantum yield and quenching temperatures of Ce 3+ -doped garnets are also considered, indicating the thermal ionization process as the main mechanisms for the quenching process. Based on our recent experimental results, to prove the thermal ionization process, the principle and the most important features of the photocurrent excitation (PCE) and thermoluminescence excitation (TLE) spectra measurements are summarized. Finally, a general trend for the quenching temperature of Ce 3+ luminescence in the garnets is discussed in terms of the energy gap between the lowest 5 d 1 level and the conduction band bottom obtained from the vacuum referred binding energy (VRBE) diagram.

Thermal enhancement and quenching of upconversion emission in nanocrystals

Abstract: Photoluminescence is a powerful tool in temperature sensing. Recently, the application of upconversion (UC) nanocrystals (NCs) has shown great potential for nanothermometry due to high spatial resolution, superior accuracy, and its non-invasive nature. In addition to spectral changes upon heating, anomalous thermal enhancement of UC emission has been reported for UC NCs, but the underlying mechanism remains unclear. Here, we report on NaY(WO4)2 doped with the Er3+-Yb3+ UC couple in NCs and the bulk material, and investigate the temperature-dependent luminescence in both air and dry nitrogen. For UC NCs in air, strong thermal enhancement of UC emission is observed with good reversibility and accompanied by a lengthening of the decay time for the Er3+ UC emission and Yb3+ IR emission. In contrast, the measurements carried out on NCs in dry nitrogen demonstrate a transition from thermal enhancement in the first cycle to thermal quenching in the subsequent cycles. The thermal quenching is similar to that in bulk materials. Thermogravimetric analysis (TGA) and Fourier transform infrared (FT-IR) measurements reveal the presence of water coupled on the NC surface that evaporates upon heating up to ∼470 K but is readsorbed upon cooling. Based on these observations, we explain the anomalous thermal enhancement of UC NCs in air by quenching of the Yb3+ and Er3+ emissions via surface adsorbed water molecules. The present study highlights the importance of careful characterization of surface adsorbed molecules which is crucial for understanding the luminescence properties of NCs, and enables the exploration of UC NCs with higher quantum efficiencies.

Aluminum(III) triggered aggregation-induced emission of glutathione-capped copper nanoclusters as a fluorescent probe for creatinine.

Abstract: Glutathione-capped copper nanoclusters (CuNCs) are presented that display aggregation-induced emission (AIE). This feature was exploited for selective and sensitive quantification of creatinine (CRN) which is an important diagnostic parameter. In the presence of Al3+ ions, such CuNCs rapidly aggregate, and this induces enhanced a red emission. The AIE nature of CuNCs was proven via TEM and fluorimetry. On addition of CRN, the coordination between CRN and Al3+ ions led to the quenching of fluorescence due to weakening the AIE. The best fluorescence intensity was measured at excitation/emission peaks of 360/585 nm. Quenched fluorescence intensity showed a linear dependence on the concentrations of CRN in the range of 2.5–34 μgL−1 with a detection limit of 0.63 μgL−1. The sensing mechanism of probe for CRN detection is discussed. The probe was applied to the determination of CRN in spiked human serum samples and gave satisfactory results.

New insights from crystallography into the effect of refining prior austenite grain size on transformation phenomenon and consequent mechanical properties of ultra-high strength low alloy steel

Abstract: Based on new insights from crystallography, this study aims to establish the relationship between prior austenite grain size and mechanical properties and enhance our understanding of Hall-Petch relationship. The refinement of prior austenite grains was achieved by decreasing the austenitizing temperature (from 920 ℃ to 880 ℃) and quenching. In addition, samples subjected to 880 ℃ heat treatment and quenching produced a significantly higher percentage of martensite. Electron backscattered diffraction (EBSD) used to characterize the crystallographic characteristics indicated that the steel subjected to 920 ℃ heat treatment and quenched had larger prior austenite grains, belonging to the transformation of Bain group. After 880 ℃ heat treatment and quenching, the prior austenite grains were smaller and more uniform, which belonged to the transformation dominated by CP (close-packed plane) group. The transformation from Bain group to CP group was related to transformation driving force, and resulted in increase in the density of high angle grain boundaries (DHAGBs). Using thermal expansion approach to measure the initial martensite transformation temperature (Ms temperature), the samples heat treated and quenched at 920 ℃ and 880 ℃ showed Ms temperature of 400 ℃ and 427 ℃, respectively, implying that the phase transformation driving force was increased by refining the prior austenite grain. Charpy impact energy test at −40 ℃ suggested that after 880 ℃ heat treatment and quenching, the Charpy energy increased from 46 J to 92 J, consistent with the results of EBSD.

Fine control of perovskite crystallization and reducing luminescence quenching using self-doped polyaniline hole injection layer for efficient perovskite light-emitting diodes

Abstract: Organic–inorganic hybrid perovskites (OHPs) are promising emitters for light-emitting diodes (LEDs) due to the high color purity, low cost, and simple synthesis. However, the electroluminescent efficiency of polycrystalline OHP LEDs (PeLEDs) is often limited by poor surface morphology, small exciton binding energy, and long exciton diffusion length of large-grain OHP films caused by uncontrolled crystallization. Here, crystallization of methylammonium lead bromide (MAPbBr3) is finely controlled by using a polar solvent-soluble self-doped conducting polymer, poly(styrenesulfonate)-grafted polyaniline (PSS-g-PANI), as a hole injection layer (HIL) to induce granular structure, which makes charge carriers spatially confined more effectively than columnar structure induced by the conventional poly(3,4-ethylenedio ythiphene):polystyrenesulfonate (PEDOT:PSS). Moreover, lower acidity of PSS-g-PANI than PEDOT:PSS reduces indium tin oxide (ITO) etching, which releases metallic In species that cause exciton quenching. Finally, doubled device efficiency of 14.3 cd A-1 is achieved for PSS-g-PANI-based polycrystalline MAPbBr3 PeLEDs compared to that for PEDOT:PSS-based PeLEDs (7.07 cd A-1). Furthermore, PSS-g-PANI demonstrates high efficiency of 37.6 cd A-1 in formamidinium lead bromide nanoparticle LEDs. The results provide an avenue to both control the crystallization kinetics and reduce the migration of In released from ITO by forming OIP films favorable for more radiative luminescence using the polar solvent-soluble and low-acidity polymeric HIL.

Size-dependent diffusion controls natural aging in aluminium alloys

Abstract: A key question in materials science is how fast properties evolve, which relates to the kinetics of phase transformations. In metals, kinetics is primarily connected to diffusion, which for substitutional elements is enabled via mobile atomic-lattice vacancies. In fact, non-equilibrium vacancies are often required for structural changes. Rapid quenching of various important alloys, such as Al- or Mg-alloys, results for example in natural aging, i.e. slight movements of solute atoms in the material, which significantly alter the material properties. In this study we demonstrate a size effect of natural aging in an AlMgSi alloy via atom probe tomography with near-atomic image resolution. We show that non-equilibrium vacancy diffusional processes are generally stopped when the sample size reaches the nanometer scale. This precludes clustering and natural aging in samples below a certain size and has implications towards the study of non-equilibrium diffusion and microstructural changes via microscopy techniques.

Exploring the relationship between the microstructure and strength of fresh and tempered martensite in a maraging stainless steel Fe–15Cr–5Ni

Abstract: Hierarchical microstructure engineering is an efficient design path for ultra-high strength steels. An excellent example of this is maraging stainless steel, which achieves its high-performance by combining the hierarchic martensitic microstructure and nano-sized precipitates. Relating this complex microstructure with mechanical properties, e.g. strength, is not trivial. In the present work, we therefore explore the relationship between the hierarchic microstructure, evolving with the tempering of a Cu-containing maraging stainless steel 15–5 PH, and its strength. Comprehensive microstructure characterization, including the quantification of dislocation density, effective grain size, precipitates and retained austenite fraction is performed after quenching and tempering at 500 °C. The microstructure data is subsequently used as input for assessing the evolution of individual strength contributions and thus the increase in strength of tempered martensite contributed by Cu precipitation strengthening is evaluated. It is found that the Cu precipitation and dislocation annihilation are two major factors controlling the evolution of the yield strength of the tempered martensite. The Cu precipitation strengthening is also modelled using our previous Langer-Schwartz-Kampmann-Wagner model based predictions of the Cu precipitation, and modelled precipitation strengthening is compared with the evaluated Cu precipitation strengthening from the experiments. The work exemplifies the promising approach of combining physically based precipitation modelling and precipitation-strengthening modelling for alloy design and optimization. However, more work is needed to develop a generic predictive framework.

Quenching-assisted actuation mechanisms in core–shell structured BiFeO3–BaTiO3 piezoceramics

Abstract: Electromechanical actuation in piezoceramics is usually enhanced by creating chemically homogeneous materials with structurally heterogeneous morphotropic phase boundaries, leading to abrupt changes in ion displacement directions within the perovskite unit cell. In the present study, an alternative mechanism to enhance electromechanical coupling is found in both chemically and structurally heterogeneous BiFeO3–BaTiO3 lead-free piezoceramics. Such a mechanism is observed in a composition exhibiting core–shell type microstructure, associated with donor-type substitution of Ti4+ for Fe3+, and is primarily activated by thermal quenching treatment. Here, we describe the use of in situ high-energy synchrotron X-ray powder diffraction upon the application of a high electric field to directly monitor the ferroelectric and elastic interactions between these composite-like components, formed as core and shell regions within grains. Translational short or long-range ordering is observed in the BiFeO3-depleted shell regions which undergo significant structural alterations from pseudocubic Pmm relaxor-ferroelectric in slow-cooled ceramics to rhombohedral R3c or R3m with long-range ferroelectric order in the quenched state. The strain contributions from each component are calculated, leading to the conclusion that the total macroscopic strain arises predominantly from the transformed shell after quenching. Such observations are also complemented by investigations of microstructure and electrical properties, including ferroelectric behaviour and temperature-dependent dielectric properties.

Effect of quenching and tempering temperature on microstructure and tensile properties of microalloyed ultra-high strength suspension spring steel

Abstract: Effects of quenching-tempering heat treatment on microstructural evolution and fracture behavior of microalloyed high strength suspension spring 55SiCrVNb were investigated. The results showed that an optimal combination of mechanical properties was obtained at the heat-treatment of oil quenching from 900 °C and tempering at 400 °C. Specifically, the ultimate tensile strength, yield strength, elongation and area reduction reached 2021 MPa, 1826 MPa, 10.3% and 42.7%, respectively. With the increasing austenitizing temperature, the grain size increased monotonically with more carbides dissolved in the matrix, and the strength first increased significantly and then decreased slowly. Furthermore, the fracture behavior transformed from ductile fracture to brittle fracture. In addition, the strengths were weakened dramatically as the tempering temperature increased but the elongation and area reduction were enhanced. Three kind of carbides are identified at different tempering temperatures, namely the coherent M2.5C and MC carbides gradually mature into large-sized non-coherent M3C and M7C3 carbides. Moreover, the dislocation reduction, lath boundary and twin martensite decomposition and carbide coarsening were exacerbated at higher tempering temperature while the fracture behavior changed from brittle fracture to ductile fracture.

Ultrafast growth of nanocrystalline graphene films by quenching and grain-size-dependent strength and bandgap opening.

Abstract: Nanocrystallization is a well-known strategy to dramatically tune the properties of materials; however, the grain-size effect of graphene at the nanometer scale remains unknown experimentally because of the lack of nanocrystalline samples. Here we report an ultrafast growth of graphene films within a few seconds by quenching a hot metal foil in liquid carbon source. Using Pt foil and ethanol as examples, four kinds of nanocrystalline graphene films with average grain size of ~3.6, 5.8, 8.0, and 10.3 nm are synthesized. It is found that the effect of grain boundary becomes more pronounced at the nanometer scale. In comparison with pristine graphene, the 3.6 nm-grained film retains high strength (101 GPa) and Young’s modulus (576 GPa), whereas the electrical conductivity is declined by over 100 times, showing semiconducting behavior with a bandgap of ~50 meV. This liquid-phase precursor quenching method opens possibilities for ultrafast synthesis of typical graphene materials and other two-dimensional nanocrystalline materials. Nano-crystallization is essential to tune different properties of materials. Here, the authors report a synthesis strategy that involves quenching of a hot metal foil for few seconds in liquid carbon source to form graphene films of 3.6 nm grain size, showing mechanical strength of 101 GPa and semiconducting behaviour.

Slow-then-rapid quenching as traced by tentative evidence for enhanced metallicities of cluster galaxies at z ∼ 0.2 in the slow quenching phase

Abstract: Aims. As large-scale structures in the Universe develop with time, environmental effects become more and more important as a star formation quenching mechanism. Since the effects of environmental quenching are more pronounced in denser structures that form at later times, we seek to constrain environmental quenching processes using cluster galaxies at z We explored seven clusters from the Local Cluster Substructure Survey (LoCuSS) at 0.15 3727, Hβ , [O III] λ 5007, Hα , and [N II] λ 6584 emission lines of cluster members, enabling us to unambiguously derive O/H gas metallicities. We also measured star formation rates (SFRs) from extinction-corrected Hα fluxes. We compared our cluster galaxy sample with a field sample of 705 galaxies at similar redshifts observed with Hectospec as part of the same survey.Results. We find that star-forming cluster and field galaxies show similar median specific SFRs in a given mass bin of 1 − 3.2 × 1010 M ⊙ and 3.2 − 10 × 1010 M ⊙ , respectively. But their O/H values are displaced, in the lower mass bin, to higher values (significance 2.4σ ) at projected radii of R 200 compared with galaxies at larger radii and in the field. The comparison with metallicity-SFR-mass model predictions with inflowing gas indicates a slow-quenching scenario in which strangulation is initiated when galaxies pass R ∼ R 200 by stopping the inflow of gas. We find tentative evidence that the metallicities of cluster members inside R 200 are thereby increasing, but their SFRs are hardly affected for a period of time because these galaxies consume available disk gas. We use the observed fraction of star-forming cluster galaxies as a function of clustercentric radius compared to predictions from the Millennium simulation to constrain quenching timescales to be 1−2 Gyr, which is defined as the time between the moment the galaxy passes R 200 until complete quenching of star formation. This is consistent with a slow-then-rapid quenching scenario. Slow quenching (strangulation) starts when the gas inflow is stopped when the galaxy passes R 200 with a phase in which cluster galaxies are still star forming, but they show elevated metallicities tracing the ongoing quenching. This phase lasts for 1−2 Gyr, and meanwhile the galaxies travel to denser inner regions of the cluster. This is followed by a “rapid” phase, i.e., a rapid complete quenching of star formation due to the increasing ram pressure toward the cluster center that can also strip the cold gas in massive galaxies.

SDSS-IV MaNGA: Inside-out vs. outside-in quenching in different local environments

Abstract: The large Integral Field Spectroscopy (IFS) surveys have allowed the classification of ionizing sources of emission lines on sub-kpc scales. In this work, we define two non-parametric parameters, quiescence (f$_{q}$) and its concentration (c$_{q}$), to quantify the strength and the spatial distribution of the quenched areas, respectively, traced by the LI(N)ER regions with low EW(H$\alpha$). With these two measurements, we classify MaNGA galaxies into inside-out and outside-in quenching types according to their locations on the f$_{q}$ vs. c$_{q}$ plane and we measure the fraction of inside-out (outside-in) quenching galaxies as a function of halo mass. We find that the fraction of galaxies showing inside-out quenching increases with halo mass, irrespective of stellar mass or galaxy type (satellites vs. centrals). In addition, high stellar mass galaxies exhibit a greater fraction of inside-out quenching compared to low stellar mass ones in all environments. In contrast, the fraction of outside-in quenching does not depend on halo mass. Our results suggest that morphological quenching may be responsible for the inside-out quenching seen in all environments. On the other hand, the flat dependence of the outside-in quenching on halo mass could be a mixed result of ram-pressure stripping and galaxy mergers. Nevertheless, at a given environment and stellar mass, the fraction of inside-out quenching is systematically greater than that of outside-in quenching, suggesting that inside-out quenching is the dominant quenching mode in all environments.