The influence of the heating rates from 10 to 1000 °C/s and annealing temperatures on the microstructure and mechanical properties of two 0.2%C, 1.9%Mn, 1.4%Si cold-rolled steels with and without the ...addition of carbide-forming elements (Mo, Nb, and Ti) have been investigated. Results show that the increase of the heating rate above 100 °C/s refines the parent austenitic grains in both alloys. The increment of the heating rate led to carbon heterogeneities in the austenite, which after subsequent cooling promoted the formation of a complex mixture of fine-grained constituents. As expected, at the lower heating rates the presence of Nb and Ti-rich carbides and carbonitrides controls the austenite grain growth during the annealing treatment. The tensile test results reveal that high heating rates do not have a significant influence on the tensile strength of the alloy with carbide-forming elements. On the other hand, both the ultimate tensile strength (UTS) and total elongation of the alloy without carbide-forming elements decrease, due to the formation of bands of ferrite and high carbon martensite. However, samples treated at heating rates above 100 °C/s show a combination of UTS in the range of 1400–1600 MPa, and 12–18% of total elongation. The results suggest that the microstructure heterogeneity obtained after high heating rates, especially the ferrite content, has the major effect on the mechanical behavior of the studied steels.
A model is presented for the increase in magnetoelectric (ME) coupling in magnetostrictive-piezoelectric bilayers in the electromechanical resonance region. The ME voltage coefficients αE have been ...estimated for transverse field orientations corresponding to minimum demagnetizing fields and maximum αE. We solved the equation of medium motion taking into account the magnetostatic and elastostatic equations, constitutive equations, Hooke's law, and boundary conditions. The resonance enhancement of ME voltage coefficient for the bilayer is obtained at antiresonance frequency. To obtain the inverse ME effect, a pick up coil wound around the sample is used to measure the ME voltage due to the change in the magnetic induction in magnetostrictive phase. The measured static magnetic field dependence of ME voltage has been attributed to the variation in the piezomagnetic coefficient for magnetic layer. The frequency dependence of the ME voltage shows a resonance character due to the longitudinal acoustic modes in piezoelectric layer. The model is applied to specific cases of cobalt ferrite–lead zirconate titanate and nickel–lead zirconate titanate bilayers. Theoretical ME voltage coefficients versus frequency profiles are in agreement with data.
Magnetoelectric gradient structures Nikitin, A O; Petrov, R V
Journal of physics. Conference series,
11/2021, Volume:
2052, Issue:
1
Journal Article
Peer reviewed
Open access
Abstract
This work is a comprehensive theoretical study of a new class of structures – magnetoelectric gradient structures, which are a product of the integration of magnetoelectric mutliferroic ...layered structures and an artificial dielectric. In this paper, a mathematical model of the behaviour of a layered multiferroic structure in inhomogeneous electric and magnetic fields is built on the basis of solving Maxwell’s equations, taken in the magnetostatic approximation, and the equation of motion of the magnetization. Based on the constructed mathematical model, the influence on the spectrum of eigenwaves of stationary magnetic and electric fields, as well as the values of the dielectric constant of an artificial dielectric layer, are analysed. The results of the study confirm the possibility of designing a new class of electronically controlled microwave devices with a triple control mechanism: magnetic field – electric field – artificial distribution of dielectric constant.
The recrystallization and texture evolution of four Mg–Zn–Ce sheets with a warm-rolled microstructure obtained through two stages that can be characterised as rough rolling and finish rolling were ...investigated at different stages of post-rolling annealing. On annealing, the same regions of the microstructure, located by hardness indentations, were examined and tracked by electron backscatter diffraction (EBSD). Furthermore, intragranular misorientation axes (IGMA) analysis was used to investigate the associated deformation mechanisms in the as-deformed material. By combining these two methods, the development of the recrystallization microstructure was investigated and important aspects, such as preferential nucleation sites, correlation between activated deformation mechanism and initial orientation of the recrystallized grains, were studied. The results showed that the Mg–1Zn–1Ce alloy, which had the highest Ce/Zn ratio, showed the weakest as-rolled texture and the most homogenous distribution of shear banding/twinning. The IGMA analysis also showed that in Mg–1Zn–1Ce, other types of dislocations rather than basal 〈a〉 were activated; in particular, prismatic 〈a〉 type was activated during deformation. Therefore, the weakening of recrystallization texture during rolling resulting from the addition of RE elements was linked with a change in dynamic recrystallization (DRX) behaviour. Since the Mg–1Zn–1Ce alloy corresponds to the highest level of Ce in solid solution, the observed texture weakening was possibly due to decreasing grain boundary mobility as a result of solute partitioning of RE elements to dislocations and grain boundaries.
A common cause for premature bearing failures in wind turbine gearboxes are the so-called White Etching Cracks (WEC). These undirected, three-dimensional cracks are bordered by regions of altered ...microstructure and ultimately lead to a cracking or spalling of the raceway. An accelerated WEC test was carried out on a FE8 test rig using cylindrical roller thrust bearings made of martensitic 100Cr6 steel. The resulting WECs were investigated with several characterisation techniques. Ultrasonic measurements showed the WEC were mainly located in the region of the overrolled surface in which negative slip occurs, which agrees with hypotheses based on an energetic approach for a prognosis. SEM orientation contrast imaging of the area around WEC revealed an inhomogeneous structure with varied grain sizes and a large amount of defects. Microstructure characterization around the WEA using EBSD showed significant grain refinement. Atom probe tomography showed the microstructure in the undamaged zone has a plate-like martensitic structure with carbides, while no carbides were detected in the WEA where the microstructure consisted of equiaxed 10nm grains. A three dimensional characterisation of WEC network was successfully demonstrated with X-ray computerized tomography, showing crack interaction with unidentified inclusion-like particles.
•Accelerated laboratory WEC test successfully carried out.•Electron backscatter diffraction of WEC region.•3D characterization of nanocrystalline WEA using atom probe tomography.•3D characterisation of WEC network using X-ray tomography.
The reaction of 1,2‐dipiperidinoacetylene (1) with 0.5 equivalents of SnCl2 or GeCl2⋅dioxane afforded the 1,2,3,4‐tetrapiperidino‐1,3‐cyclobutadiene tin and germanium dichloride complexes 2 a and 2 ...b, respectively. A competing redox reaction was observed with excess amounts of SnCl2, which produced a tetrapiperidinocyclobutadiene dication with two trichlorostannate(II) counterions. Heating neat 1 to 110 °C for 16 h cleanly produced the dimer 1,3,4,4‐tetrapiperidino‐3‐buten‐1‐yne (3); its reaction with stoichiometric amounts of SnCl2 or GeCl2⋅dioxane furnished the 1,3,4,4‐tetrapiperidino‐1,2‐cyclobutadiene tin and germanium dichloride complexes 4 a and 4 b, respectively. Transition‐metal complexes containing this novel four‐membered cyclic bent allene (CBA) ligand were prepared by reaction of 3 with (tht)AuCl, RhCl(CO)22, and (Me3N)W(CO)5 to form (CBA)AuCl (5), (CBA)RhCl(CO)2 (6), and (CBA)W(CO)5 (7). The molecular structures of all compounds 2–7 were determined by X‐ray diffraction analyses, and density functional theory (DFT) calculations were carried out to rationalise the formation of 3 and 4 a.
Cyclic bent allenes as ligands: The thermal dimerisation of 1,2‐dipiperidinoacetylene affords 1,3,4,4‐tetrapiperidino‐3‐buten‐1‐yne, which provides access to main‐group and transition‐metal complexes of a strongly electron‐donating four‐membered cyclic bent allene ligand. The formation of these complexes as well as the dimerisation of 1,2‐dipiperidinoacetylene were also studied by computational methods.
The microtexture of secondary α plates in Ti–4.5Fe–6.8Mo–1.5Al has been investigated by electron backscatter diffraction (EBSD) to obtain more insight in the nucleation and variant selection of these ...α plates. A statistical analysis of the EBSD data shows that for most β grain boundaries the variant selection of the α plates is in agreement with a commonly used variant selection criterion yielding that the α-{0
0
0
1} pole is nearly parallel to the closest β-{1
1
0} poles of the two adjacent β grains. For a small angle between the β-{1
1
0} poles nucleation is predominantly observed at both sides of the grain boundary, while with increasing angle some β grain boundaries exhibit nucleation of α plates at only one side. In the β grain interior many so-called Type 2 α–α grain boundaries are observed which are thought to originate from autocatalytic nucleation when a new α plate is formed at an existing α–β interface.
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► The grain scale strain distribution during bending was studied in AA5754 CC sheets. ► DIC based strain mapping from SEM images of in situ bent samples was applied. ► Tendency for ...strain localization due to the presence of particle stringers was found. ► Facilitated matrix shearing and decreased local fracture strength were observed. ► Maximum Mises strain of 2.0 was calculated within dominant shear bands.
The mechanism triggering failure during deformation in Al–Mg alloys often includes localization of the plastic flow into narrow and intense transgranular shear bands propagating through the microstructure with little evidence of damage prior to the final fracture event. The cracks initiate in the sheared zones and propagate by conventional ductile mechanism of fracture, including nucleation of voids at second-phase particles, followed by their growth and ultimate coalescence. In an attempt to fully understand the mechanism of damage in continuous cast (CC) AA5754 aluminium alloy sheet, a methodology for characterization of the microscopic fracture strain distribution during bending was adopted in this work. A batch of digital images representing the deformation history of the samples bent during in situ V-bending tests performed in a scanning electron microscope (SEM) was recorded and later used as an input to a digital image correlation system (DIC) for strain calculations. Local strain maps of the tensile through-thickness cross-section of the bent sheets were built. The results clearly reveal development of spatial inhomogeneity of the strain at microscopic level. The strain concentration inside the formed intensive shear bands, which were the predecessors of the subsequent crack propagation, was found to be considerably larger than the macro-strains typically suggested by the forming limit diagrams for aluminium sheet materials. The presented results are consistent with previously published results on the general forming characteristics of continuous cast AA5754 aluminium alloy sheet materials.
In this article, we probe the strain partitioning between the microstructural features present in a continuously cooled carbide-free bainitic steel together with damage nucleation and propagation. ...These features mainly comprise of phases (bainitic ferrite, martensite, and blocky/thin film austenite), interfaces between them, grain size and grain morphology. A micro Digital Image Correlation (μ-DIC) technique in scanning electron microscope is used to quantify the strain distribution between these microstructural features. The results show a strong strain partitioning between martensite, bainitic ferrite and retained austenite that provides weak links in the microstructure and creates conditions for the crack initiation and propagation during deformation. Blocky austenite islands accommodate maximum local strains in the global strain range of 0–2.3% and undergo strain-induced austenite to martensite transformation governing the local strain evolution in the microstructure. However, the local strains are minimum in martensite regions during entire in-situ deformation stage. Narrow bainitic ferrite channels in between martensitic islands and martensite-bainitic ferrite interfaces are recognised as primary damage sites with high strain accumulation of 30 ± 2% and 20 ± 3% respectively, at a global strain of 9%. The inclination of these interfaces with the tensile direction also affects the strain accumulation and damage.
ABSTRACT
Differential Interferometry allows to obtain the differential visibility and phase, in addition to the spectrum. The differential phase contains important information about the structure and ...motion of stellar photosphere such as stellar spots and non-radial pulsations, and particularly the rotation. Thus, this interferometric observable strongly helps to constrain the stellar fundamental parameters of fast rotators. The spectroastrometry mainly uses the photocentre displacements, which is a first approximation of the differential phase, and is applicable only for unresolved or marginally objects. We study here the sensitivity of relevant stellar parameters to the simulated photocentres using the scirocco code: a semi-analytical algorithm dedicated to fast rotators, applied to two theoretical modelling stars based on Achernar and Regulus, in order to classify the importance of these parameters and their impact on the modelling. We compare our simulations with published VLTI/AMBER data. This work sets the limits of application of photocentre displacements to fast rotators, and under which conditions we can use the photocentres and/or the differential phase, through a pre-established physical criterion. To validate our theoretical study, we apply our method of analysis on observed data of the edge-on fast rotator Regulus. For unresolved targets, with a visibility V ∼ 1, the photocentre can constrain the main stellar fundamental parameters of fast rotators, whereas from marginally resolved objects (0.8 ≤ V < 1), mainly the rotation axis position angle ($\rm PA_{\rm rot}$) can be directly deduced from the vectorial photocentre displacement, which is very important for young cluster studies.
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