Advanced Multiphase High Strength Steels are generally obtained by applying isothermal treatments around the martensite start temperature (Ms). Previous investigations have shown that bainitic ...ferrite can form from austenite in isothermal treatments below Ms, where its formation kinetics is accelerated by the presence of the athermal martensite. That athermal martensite is tempered during the isothermal treatment, and fresh martensite may form during the final cooling to room temperature. The distinction between product phases present after the application of this type of heat treatments is difficult due to morphological similarities between these transformation products. The aim of this study is to characterize the structural and morphological features of the product phases obtained in isothermal treatments below the Ms-temperature in a low-carbon high-silicon steel. Multiphase microstructures, having controlled fractions of product phases, were developed by applying isothermal treatments above and below Ms, and were further studied by electron back scatter diffraction (EBSD) and scanning electron microscopy (SEM). The bainitic or martensitic nature of these product phases is discussed based on this characterization. Results showed that bainitic ferrite appears in the form of acicular units and irregularly shaped laths. Tempered martensite appears as laths with a sharp tip and as relatively large elongated laths with wavy boundaries containing protrusions.
•Bainitic/Martensitic structures were systematically characterized in isothermal treatments below Ms.•Bainite and martensite were distinguished by combining dilatometry, SEM and EBSD.•Bainitic ferrite appears as thin acicular units and irregularly shaped laths below Ms.•Tempered martensite appears in the form of laths with wavy boundaries and ledge-like protrusions.•Ledge-like protrusions can be related to the formation of bainite from martensitic laths.
Herein, a Mn‐based metal–organic framework is used as a precursor to obtain well‐defined α‐MnS/S‐doped C microrod composites. Ultrasmall α‐MnS nanoparticles (3–5 nm) uniformly embedded in S‐doped ...carbonaceous mesoporous frameworks (α‐MnS/SCMFs) are obtained in a simple sulfidation reaction. As‐obtained α‐MnS/SCMFs shows outstanding lithium storage performance, with a specific capacity of 1383 mAh g−1 in the 300th cycle or 1500 mAh g−1 in the 120th cycle (at 200 mA g−1) using copper or nickel foil as the current collector, respectively. The significant (pseudo)capacitive contribution and the stable composite structure of the electrodes result in impressive rate capabilities and outstanding long‐term cycling stability. Importantly, in situ X‐ray diffraction measurements studies on electrodes employing various metal foils/disks as current collector reveal the occurrence of the conversion reaction of CuS at (de)lithiation process when using copper foil as the current collector. This constitutes the first report of the reaction mechanism for α‐MnS, eventually forming metallic Mn and Li2S. In situ dilatometry measurements demonstrate that the peculiar structure of α‐MnS/SCMFs effectively restrains the electrode volume variation upon repeated (dis)charge processes. Finally, α‐MnS/SCMFs electrodes present an impressive performance when coupled in a full cell with commercial LiMn1/3Co1/3Ni1/3O2 cathodes.
The composite of α‐MnS and S‐doped carbon derived from Mn‐based metal organic frameworks enables outstanding lithium storage performance in half/full Li‐ion cells, benefiting from its structural and compositional features. The study of the lithium storage mechanism reveals that alongside the conversion reaction of α‐MnS, CuS, which is formed during the electrode coating on Cu foil, is also undergoing the conversion process.
Microstructure modulation is of great significance for the practical application of TiAl alloys. Here, the optimal annealing temperature to obtain modulated microstructure containing nanoscale α2 + O ...lathes for high Nb-TiAl alloy is determined as 625 °C by dilatometry (DIL) and transmission electron microscopy (TEM) analysis. The results show that the compressive strength and plastic strain increased by 5% and 15.8% after annealing at 625 °C for 5 h, respectively. The improvement of both strength and ductility owing to the improved elastically mediated strain transfer ability related to refined microstructure in modulated structure. Geometric phase analysis (GPA) and HRTEM results show that the rough interface between tweed laths and γ lamella provides nucleation sites for dislocations which release the local elastic strain energy. What's more, the formation of nanoscale deformation twins as well as extensive twin intersections also played an important role in the improvement of both strength and ductility.
•The optimal annealing temperature to obtain orthorhombic phase for Ti-45Al-8Nb alloy is 625 °C.•After annealing at 625 ℃ for 5h, the compressive strength and plastic strain increased by 5% and 15.8%, respectively.•The improved “elastically mediated” strain transfer ability in modulated alloy results in improved mechanical properties.
This paper reports on the charging mechanism of an activated carbon electrode in a symmetric electrochemical capacitor operating in an ionic liquid electrolyte (EMIm+TFSI−). With the application of ...step potential electrochemical spectroscopy (SPECS) and electrochemical dilatometry, it is determined that the electrical double-layer formation mechanism strongly depends on the porous structure of the electrode material. Furthermore, SPECS calculations allow us to separate and quantify the charge component responsible for the ionic movement.
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Knowledge of the martensite start temperature in low and medium alloy steels is of critical importance for steel makers, or any industry involved in the transformation of hardenable steels. Its ...determination is often carried out by length change measurements in quenching dilatometers. The present paper focuses on the meaning of the information obtained in these experiments and discusses two alternative methods and their respective benefits, particularly with respect to the phenomenon sometimes referred to as 'slow start' for the martensite transformation.
Information on the sintering activation energy is currently focused on evaluation of single-phase ceramic systems. This work shows the results of high-temperature dilatometry measurements of layered ...and particle composites based on alumina and zirconia. Layered composites with different layer thickness ratios and particle composites with variable composition in the entire concentration range were prepared by electrophoretic deposition allowing manufacturing composites with precious design and strongly bonded interfaces. The phenomena observed during the high-temperature dilatometry measurements are discussed, and the data were used to calculate the sintering activation energies of composites using the modified Master Sintering Curve concept. By covering a wide range of composite designs, it was possible to determine differences in activation energies and to show their dependence on the direction in the case of laminate composites given by the directionally dependent sintering behaviour. Sintering activation energies of layered composites were always higher than for monoliths due to constrained sintering showing maximum sintering activation energies at lower volumes of zirconia in the layers for longitudinal and transversal orientation of the samples. A similar trend was identified in particle composites due to slowed down alumina densification by the pinning effect. Additionally, mechanical properties represented by Vickers hardness and indentation elastic modulus were related to the microstructure developed during sintering. The effects of interconnectivity of phases present in the composites together with other parameters of the microstructure were described.
Nanostructured birnessite exhibits high specific capacitance and nearly ideal capacitive behaviour in aqueous electrolytes, rendering it an important electrode material for low-cost, high-power ...energy storage devices. The mechanism of electrochemical capacitance in birnessite has been described as both Faradaic (involving redox) and non-Faradaic (involving only electrostatic interactions). To clarify the capacitive mechanism, we characterized birnessite's response to applied potential using ex situ X-ray diffraction, electrochemical quartz crystal microbalance, in situ Raman spectroscopy and operando atomic force microscope dilatometry to provide a holistic understanding of its structural, gravimetric and mechanical responses. These observations are supported by atomic-scale simulations using density functional theory for the cation-intercalated structure of birnessite, ReaxFF reactive force field-based molecular dynamics and ReaxFF-based grand canonical Monte Carlo simulations on the dynamics at the birnessite-water-electrolyte interface. We show that capacitive charge storage in birnessite is governed by interlayer cation intercalation. We conclude that the intercalation appears capacitive due to the presence of nanoconfined interlayer structural water, which mediates the interaction between the intercalated cation and the birnessite host and leads to minimal structural changes.
We investigated the effect of the MgO-CaO-Al2O3-SiO2 (MCAS) additive on the densification of Al2O3 ceramics. MCAS wassynthesized using a polymeric-complex method. We analyzed the densification ...behavior, using dilatometric analysis up to1600 oC, and the results showed that sinterability increased with increasing MCAS content. Al2O3 samples were prepared byisothermal sintering at 1400, 1500, and 1600 oC. The microstructure, phase formation, and hardness of the samples wereanalyzed and discussed in relation to both the MCAS content and sintering temperature. The density of the MCAS-dopedsamples sintered at 1500 and 1600 oC was over 98%, and the maximum relative density was 99.7%. The highest hardness (18GPa) was achieved for the sample prepared with 3 wt.% MCAS and sintered at 1500 oC for 1 h because further dopingresulted in excessive grain growth. These results elucidate the conditions required for pressure-free sintering. KCI Citation Count: 0
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