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•Three nanocrystalline (NC) 316 steels with similar grain size have been produced.•These NC states have different parameters of GBs and dislocation structure.•Interplay of GB ...segregations with dislocations governs plasticity in NC steels.•Significant increase in plasticity of the extra-strong NC 316 steel is achieved.
We study three structurally different states of nanocrystalline 316 steel and show that the state, where boundaries containing excess concentration of alloying elements are combined with mobile dislocations in grain interiors, allows maintaining extraordinarily high strength and remarkably enhanced plasticity. Underlying mechanisms featuring interaction between the segregations and mobile dislocations are discussed.
Thermodynamic calculations and experimental studies including transmission electron microscopy (TEM), atom probe tomography (APT), microhardness and specific electrical conductivity measurements, and ...high temperature uniaxial compression tests have been carried out in order to determine the influence of indium trace addition on the structure and precipitation hardening response in Al–Si–Cu based casting alloy. Analysis of the hardness curves for aging at 175 °C has revealed that the peak hardness of the In-containing alloy is about 22% higher compared to the In-free alloy (140 vs 115 HV) and is achieved in a much shorter time of aging (2 h vs 10 h). TEM analysis of the peak aged samples has revealed that much finer precipitates of the θ′ phase with a higher number density are formed in the alloy with trace addition. Furthermore, fine spherical nanoparticles associated with θ′ phase platelets are found in the In-containing alloy structure. Quantitative APT analyses have revealed that the number densities of θ′-phase precipitates and the spherical nanoparticles are equal at the beginning of aging, while in the peak aged state the number density of the θ′-phase is at least two times that of the spherical nanoparticles. APT analyses have also revealed that in the near-peak aged state more than half of copper (∼2.0 wt.%) is still dissolved in the aluminum matrix of the In-free alloy in comparison with only 0.2 at. % (∼0.46 wt.%) copper for the In-containing alloy. The results of uniaxial compression tests of the peak aged samples have shown that the 250 °C yield strength of the alloy with trace solute is about 1.5 times that of the base alloy (259 vs 174 MPa). Thus, indium trace addition catalyzes the decomposition process making it more effective and complete which is beneficial for increasing the alloy strength at low and elevated temperatures.
The effect of 0.1 wt% (0.02 at%) Sn trace addition on the structure and phase composition of Al-Si-Cu based alloy has been studied using thermodynamic calculations (Thermo-Calc software) and ...experimental techniques (transmission electron microscopy (TEM), atom probe tomography (APT), hardness and specific electrical conductivity measurements). The Vickers hardness measurement made after aging at 175 °C revealed that the peak hardness of the Sn-containing alloy is about 22% higher than that of the Sn-free alloy (135 HV vs 115 HV). Moreover, the peak hardness is achieved in a much shorter aging time (4 h vs 16 h). Considerably finer precipitates of the θ′ phase (average length less than 60 nm and thickness 3–5 nm) with a substantially higher number density are observed in the Sn-containing alloy. Tiny, rounded particles most of which are associated with the θ′ phase precipitates are also observed. Atom probe tomography analysis confirmed that the observed nanoparticles consist of tin. Quantitative APT analysis revealed that the number density of the copper-containing precipitates is at least twice that of the tin-containing ones (7.6·104 vs 3·104 µm-3). APT data also revealed a clear evidence of noticeable dissolution of Sn (average concentration from 0.05 to 0.10 at%) and silicon (average concentration from 2.2 to 2.8 at%) at the core of the θ′ phase precipitates, which is consistent with the fact that Sn and to a lesser extent Si act as catalysts in the nucleation of this phase. The data obtained using the proxigram technique suggest that Sn atoms show no tendency to segregate at the coherent θ′/(Al) heterophase interface upon aging, whereas localized Sn segregation is observed at the semi-coherent interface. Both Sn-free and Sn-containing alloys in their peak aged states have been subjected to uniaxial compression tests at an elevated temperature of 250 °С. The results suggest that the yield strength of the Sn-containing alloy is about 1.5 times that of the Sn-free alloy (250 MPa vs 175 MPa). The revealed difference is very big and testifies to a high potential of the new alloys as materials for new-generation engine parts.
•0.1% Sn addition in Al8Si3.5Cu alloy increases hardness by 22 % and catalyzes aging.•Fine Sn-containing particles attached to some θ′ precipitations are observed.•Number density of θ′ precipitates is three times that of the Sn-containing particles.•A noticeable dissolution of Sn (~0.1 at%) at the core of θ′ precipitates is observed.•Long-term aging decreases in the Sn core concentration down to 0.05 at%.
The effect of high pressure torsion (HPT) on the structure and microhardness of Al3Ca2La1·5Mn alloy containing 13 vol% of Al4(Ca,La) eutectic phase has been studied using electron microscopy, X-ray ...analysis and atom probe tomography (APT). We show that HPT causes the formation of a nanocrystalline structure resulting in a 4-fold increase in the microhardness (to 2.5 GPa) of the alloy. Post-deformation low-temperature annealing further increases the microhardness to ~3.1 GPa. The APT data suggest that the increase in the microhardness after annealing is caused by precipitation hardening due to the decomposition of the calcium and manganese supersaturated aluminum solid solution.
•The microhardness of the Al3Ca2Ca1·5Mn alloy after high-pressure torsion increases to 2.5 GPa.•Atom probe tomography showed that the Ca solubility in Al solid solution increases 10-fold to 0.06 at.% after HPT.•Annealing at 150–175°С showed an additional increase in the microhardness by 25% (up to ~3.1 GPa).•Ca and Mn concentration in the Al solid solution after aging decreases by ~2 and ~6 times, respectively.•The annealing-induced hardening can be caused by the precipitates hardening with formation of 5–10 nm precipitates.
Abstract
The lead-free ferroelectric 0.4Ba
0.85
Ca
0.15
Zr
0.10
Ti
0.90
O
3
–0.6BaTi
0.89
Sn
0.11
O
3
(0.4BCZT–0.6BTSn) ceramics were successfully prepared by the sol–gel process. Raman spectroscopy ...was used to examine the structural properties of the 0.4BCZT-0.6BTSn sample. The findings indicate that the sample was well crystallized into a single perovskite structure. The phase transitions of the studied sample have been investigated using the DSC technique. The electrocaloric effect (ECE) properties were indirectly determined using the Maxwell approach. Under a relatively low applied electric field of 30 kV cm
−1
, the results show enhanced electrocaloric temperature change and entropy change of ΔT = 1.32 K and ΔS = 1.41 J/kg.K, respectively. Besides, the electrocaloric responsivity (
ξ
max
= 0.45 K·mm/kV) obtained is among the highest reported values in pb-free ferroelectrics near room temperature. These findings demonstrate that the lead-free 0.4BCZT–0.6BTSn ceramic is a promising candidate for solid-state cooling applications.
Abstract
Multilevel devices demonstrating switchable polarization enable us to efficiently realize neuromorphic functionalities including synaptic plasticity and neuronal activity. Here we propose ...using the ferroelectric logic unit comprising multiple nanodots disposed between two electrodes and coated by the dielectric material. We devise the integration of the ferroelectric logic unit, providing topologically configurable non-binary logic into a gate stack of the field-effect transistor as an analog-like device with resistive states. By controlling the charge of the gate, we demonstrate the various routes of the topological switchings between different polarization configurations in ferroelectric nanodots. Switching routes between different logic levels are characterized by hysteresis loops with multiple branches realizing specific interconnectivity regimes. The switching between different types of hysteresis loops is achieved by the variation of external fields and temperature. The devised ferroelectric multilevel devices provide a pathway toward the novel topologically-controlled implementation of discrete synaptic states in neuromorphic computing.
A quantum paraelectric SrTiO3 is a material situated in close proximity to a quantum critical point (QCP) of ferroelectric transition in which the critical temperature to the ferroelectric state is ...suppressed down to 0 K. However, the understanding of the behavior of the phase transition in the vicinity of this point remains challenging. Using the concentration x of Pb in solid solution Sr1−xPbxTiO3 (PSTx) as a tuning parameter and applying the combination of Raman and dielectric spectroscopy methods, we approach the QCP in PSTx and study the interplay of classical and quantum phenomena in the region of criticality. We obtain the critical temperature of PSTx and the evolution of the temperature-dependent dynamical properties of the system as a function of x to reveal the mechanism of the transition. We show that the ferroelectric transition occurs gradually through the emergence of the polar nanoregions inside the non-polar tetragonal phase with their further expansion on cooling. We also study the ferroelastic cubic-to-tetragonal structural transition, occurring at higher temperatures, and show that its properties are almost concentration-independent and not affected by the quantum criticality.
The crystal structure and lattice dynamics of quantum paraelectric BaxSr1−xTiO3 (x = 0, 0.01, 0.02) solid solutions are studied using X‐ray diffraction (XRD), Raman and terahertz‐infrared (THz‐IR) ...spectroscopies in a temperature range of 4–300 K. XRD and Raman spectroscopy reveal the cubic‐to‐tetragonal nonpolar structural phase transition at about 100 K. At the same time, Raman spectra manifest the presence of polar modes, TO2 and TO4, normally prohibited in paraelectric phase. Emergence of these modes indicates the appearance of the polar nanoregions in a broad temperature range. The modes become more intensive at low temperatures, and temperature dependence of their intensities on cooling reveals the kink‐like change of the slope from flat to steep, indicating on activation of polar nanoregions. The transmission THz‐IR spectra show that squared frequency of the polar TO1 soft mode, responsible for ferroelectric transition, follows Cochran's behavior at high temperatures. However, at low temperatures, it doesn't vanish at extrapolated Curie temperature but saturates, demonstrating the plateau feature below 20 K. This behavior, coherent with known saturation of the dielectric constant, indicates that transition to ferroelectric phase in BaxSr1−xTiO3 is suppressed by quantum fluctuations and the system stays in quantum paraelectric state at very low temperatures.
Crystal structure and lattice dynamics of quantum paraelectric BaxSr1−xTiO3 are studied at temperatures 4–300 K. Polar nanoclusters appear in a broad temperature range and extend with increasing concentration of Ba ions. Clusters’ activation locally stabilizes the ferroelectric phase and reduces the temperature of structural transition. Quantum fluctuations suppress the ferroelectric state, conserving the paraelectric state at very low temperatures.
The crystal structure of BiFeO3/BaxSr1-xTiO3 (BFO/BST) heterostructures with x = 0.2, 0.6 and 0.8, grown on single-crystal MgO (001) substrate was investigated by x-ray diffraction and Raman ...spectroscopy in order to determine the influence of mismatch-induced strains and spontaneous polarization in BST buffer layers on BFO layers. The lattice parameter of the BFO layers was shown to decrease with increasing concentration of Ba ions, despite the increasing in-plain lattice parameters of tetragonal unit cells of BST layers. The rhombohedral angle of the crystal structure of BFO layers demonstrates an increase towards the ideal cubic perovskite structure with the appearance of the built-in electric field, induced by the spontaneous polarization in buffer layers. This result provides a remarkable tool for the control of polarization in BFO layers and other ferroelectric films in general, by changing the built-in electric field from ferroelectric buffer layer without changing a single crystal substrate.
•Oriented multiferroic/ferroelectric heterostructures were grown by RF-sputtering.•Distortion of the BiFeO3 decreases with increasing polarization in buffer layers.•Built-in electric field induces polarization rotation in the BiFeO3 layers.
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