The paper reports microstructures (revealed by transmission electron microscopy) in various zones of laser welds of the X70 and X80 low-carbon steels with different initial microstructures, as well ...as chemical and phase compositions. In the X70 steels with 0.13% C, the microstructure refinement has been achieved through helical rolling at temperatures of 920 °C and 850 °C (designated as X70-920 and X70-850, respectively). For all studied cases, both initial steel microstructures and phase compositions have determined the formation of different microstructures with various microhardness levels in the weld metal and heat-affected zones. For the X70-850 steel with a more dispersed and homogeneous microstructure (dF = 3.3 μm), a lower microhardness level of 340 HV has been observed in the weld metal, compared with the X70-920 one (dF = 5.5 μm, 370 HV). The reason has been the formation of both bainite and martensite laths in the X70-850 weld metal, while only lath and lamellar martensite has formed in the X70-920 one. For the X80 steel (0.55% C), lowering the carbon content and additional microalloying with chromium, molybdenum and nickel have enabled to decrease the microhardness level down to 295 HV in the weld metal due to the degenerate upper bainite formation and the carbon level reduction in martensite. The dispersed and homogeneous initial microstructures of the X70-850 and X80 steels has provided the formation of granular ferrite-bainite microstructures in the intercritical heat-affected zone. They have possessed a lower proportion of residual austenite regions and small sizes of twinned martensite areas. The welded X80 steel specimen has been characterized by higher ductile properties compared to both X70 ones.
•The M(H) magnetization curves of NiO nanoparticles (NPs) measured in pulsed fields of up to 250 kOe have been studied.•A model of NiO NP obtained from analysis of M(H) data have been ...proposed.•Surface and size effects as well as the origin and the magnitude of uncompensated magnetic moment have been revealed.
-The analysis of the M(H) magnetization curves of antiferromagnetic nanoparticles yields information about magnetic subsystems formed in these objects, which are characterized by a large fraction of surface atoms. However, in the conventionally investigated experimental magnetic field range of up to 60–90 kOe, this analysis often faces the ambiguity of distinguishing the Langevin function-simulated contribution of uncompensated magnetic moments μun of particles against the background of a linear-in-field dependence (the antiferromagnetic susceptibility and other contributions). Here, this problem has been solved using a pulsed technique, which makes it possible to significantly broaden the range of external fields in which the μun contribution approaches the saturation. Nanoparticles of a typical NiO antiferromagnet with an average size of ~ 4.5 nm have been investigated. Based on the thorough examination of the M(H) magnetization curves measured in pulsed fields of up to 250 kOe, a model of the magnetic state of NiO nanoparticles of such a small size has been proposed. The average moment is ~130 μB (μB is the Bohr magneton) per particle, which corresponds to 60–70 decompensated spins of nickel atoms localized, according to the Néel hypothesis (μun~ 3/2), both on the surface and in the bulk of a particle. A part of the surface spins unrelated to the antiferromagnetic core form another subsystem, which behaves as free paramagnetic atoms. Along with the antiferromagnetic core, an additional linear-in-field contribution has been detected, which is apparently related to superantiferromagnetism, i.e., the size effect inherent to small antiferromagnetic particles.
In this paper, the heat affected zone (HAZ) of laser welded joints of the X70 steel were studied by the transmission electron microscopy method. The effect of the initial microstructure ...(coarse-grained hot-rolled and fine-grained after cross-helical rolling) on the HAZ formation and the mechanical characteristics of the welded joints were shown. It was found that the microstructure in the inter-critical HAZ of the steel after cross-helical rolling was more dispersed, homogeneous, and uniform compared to that of the coarse-grained hot-rolled one due to the initial fine-grained ferrite-bainitic-pearlite microstructure and the absence of pronounced ferrite-pearlite banding in the base metal. The character of the microhardness value distribution in the HAZ of the steel after cross-helical rolling was smooth with the gradual decrease from 370 down to 185 HV as shifted towards the base metal. In the HAZ of the coarse-grained hot-rolled steel, the heterogeneous microhardness value (up to 640–670 НV) distribution was revealed. The reason was the upper degenerate bainite microstructure with high residual stresses, characterized by laths up to 2.0–2.5 μm long and a high martensitic-austenitic constituent fraction (10–16%) of a slender shape along the boundaries of bainite laths. The conclusion was drawn that one of the ways to reduce the brittleness of the laser welded joints could be using the initially fine-grained steels possessing the homogeneous (mainly bainitic) microstructure.
The microcavity in the form of a liquid crystal defect layer embedded in a one-dimensional photonic crystal is considered. The microcavity mode has a tunable radiation decay rate in the vicinity of a ...bound state in the continuum. It is demonstrated that coupling between the microcavity mode and a Tamm plasmon polariton results in hybrid Tamm-microcavity modes with a tunable
Q
factor. The measured spectral features of hybrid modes are explained in the framework of the temporal coupled mode theory.
It is demonstrated that coupling between a Tamm plasmon polariton and the microcavity mode in the vicinity of a bound state in the continuum results in hybrid Tamm-microcavity modes with a tunable
Q
factor.
Ferrite-bainite microstructures and impact toughness of the X65 low-carbon microalloyed steel were investigated after helical rolling at 1000, 920, 850, and 810 °C followed by continuous cooling in ...air. After helical rolling at 1000 °C, granular bainite with large areas of the massive-shape martensite-austenite constituent (d = 1.5 μm) and a high fraction of twinned martensite (d > 2.0 μm) were observed in the steel. This caused a decrease in impact energy at low test temperatures (for example, 70 J at –70°С). Lowering the helical rolling temperature contributed to a reduction of dimensions of both ferrite-bainite and martensite-austenite constituent areas, as well as the replacement of the latter by a slender type one and an improvement in fracture toughness at the low temperatures. The highest impact energy level (210 J at –70 °C) was achieved after helical rolling at 850 °C due to the formation of a homogeneous microstructure, which included dispersed ferrite grains, granular bainite and small fractions of the slender type martensite-austenite constituent (d = 0.1–0.7 μm). In this case, areas of twinned martensite were absent.
Microstructure of laser welds of the X70 low-carbon pipe steel was studied. High cooling rates after laser welding and non-uniform distribution of carbon in the ferrite-pearlite base metal caused ...formation of regions with increased microhardness (up to 650 НV) in inter-critical heat affected zone (ICHAZ). These regions consisted of finely dispersed degenerate upper bainite and martensite-austenite constituents of a slender shape and small fraction of a massive shape along the boundaries of bainite laths, as well as twinned martensite. High concentration of martensite-austenite constituents (10–16%) and residual stresses in ICHAZ, as well as a dendritic martensitic structure with carbide interlayers along the boundaries of martensite laths in fusion zone were the main reasons of sharp decrease in charpy impact energy of the welded samples. High microhardness of the laser welds was decreased down to 320 HV and their brittleness was improved by annealing. Also, in ICHAZ, degenerate upper bainite and the regions of martensite-austenite constituents decayed forming tempered sorbite and Fe2C and Fe3C carbides, respectively. Charpy impact energy of the welds doubled after annealing compared to the welds without annealing, and ductile-brittle transition temperature decreased down to –60°С.
•Synthetic and biogenic ferrihydrite nanoparticles are synthesized.•Analysis of the Mössbauer spectra and magnetometry revealed the interparticle magnetic interactions in synthetic ...ferrihydrite.•Collective processes of freezing the magnetic moments of particles take place in synthetic ferrihydrite.
Samples of synthetic ferrihydrite with an average nanoparticle size of 2.7 nm have been examined by magnetometry and Mössbauer spectroscopy. Ferrihydrite is characterized by the antiferromagnetic interactions between the magnetic moments of iron atoms. In ferrihydrite nanoparticles, as in any other antiferromagnetic ones, structural defects induce the formation of an uncompensated magnetic moment, which determines the magnetic properties typical of single-domain ferro- and ferrimagnetic particles. The manifestation of the magnetic interactions between ferrihydrite nanoparticles in the magnetic properties of the material and in the temperature evolution of Mössbauer spectra has been in focus. The results obtained on synthetic ferrihydrite have been compared with the data for the biogenic ferrihydrite sample with a similar average size of particles surrounded by a polysaccharide shell, which weakens and screens the interparticle magnetic interactions. A clear manifestation of the effect of the interparticle magnetic interactions on the transition to the blocked state is the presence of a significant contribution of the relaxation component in the Mössbauer spectra at temperatures of the transition from the superparamagnetic to blocked state. The temperature dependence of the particle relaxation time obtained from the Mössbauer spectra points out the collective effect of freezing of the magnetic moments of particles due to the magnetic interactions between them.
•Magnetite nanoparticles coated with arabinogalactan and chitosan were synthesized.•Immobilization of biospecific molecules on the nanoparticle surface was studied.•The obtained samples are ...characterized by a high density of immobilized molecules.•Such nanoparticles can be used in bioanalytical systems or as affinity sorbents.
In this work, magnetite nanoparticles coated with polysaccharides were synthesized. Arabinogalactan and chitosan were used as polysaccharides. The possibilities of immobilization of biospecific molecules on the surface of the obtained composites were studied. Experiments on covalent immobilization of biospecific molecules on magnetic nanoparticles coated with a polysaccharide showed a high density of immobilized molecules. This suggests the use of such materials in bioanalytical systems or as affinity sorbents.
•Melt-spun (Sm0.9Zr0.1)Fe11Ti alloy with ThMn12-type structure was synthesized.•Structural and phase transformations of the alloy were studied with heat treatments.•Optimal regime of the alloy ...annealing was determined providing coercivity of 4.8 kOe.•Temperature dependence of the alloy coercivity was measured in the range of 2–570 K.
Rapidly increasing demand for high-energy permanent magnets and volatility of the rear-earth market encourage a search of hard magnetic materials that can compete with those based on the Nd2Fe14B phase. Sm-Fe compounds with the ThMn12-type crystal structure are considered as promising candidates for it. However, their synthesis and achievement of theoretically predicted magnetic properties are still challenging tasks that have not been solved yet. This paper addresses this problem. Its aim was to synthesize and to study magnetic properties of the (Sm0.9Zr0.1)Fe11Ti compound with ThMn12-type structure. Initially amorphous alloy was obtained by melt spinning and its subsequent heat treatments were performed. Structural and phase transformations of the (Sm0.9Zr0.1)Fe11Ti alloy with annealing temperatures were studied along with magnetic properties. For the optimally annealed alloy features of magnetization reversal were discussed and temperature dependences of coercivity and maximum energy product were obtained.
•Stress-induced transitions occur in all orientations of strain-glass TiNi crystals.•Orientation determines strength properties and strain reversibility.•Superelasticity is observed only in ...high-strength 001-orientation.•Superelasticity degradation is associated with the formation of {113}B2 twins.•Stabilisation of B19′-martensite is observed only in low-strength 111--orientation.
The orientation dependence of the functional and mechanical properties of quenched Ti-51.8at.%Ni single crystals, undergoing a strain-glass transition upon cooling/heating was investigated. It was found that a compressive stress above 800 MPa leads to the B2-B19′ martensitic transformation (MT), regardless of orientation. In the high-strength 001-orientation, superelasticity (SE) was observed at 203–248 K, with a reversible strain of 2.3%. Degradation of SE at deforming stresses σ > 1000 MPa was associated with the formation of {113}B2 twins during the reverse MT. In the low-strength 111--orientation, the formation of stress-induced B19′-martensite occurred simultaneously with the plastic deformation of the B2-phase (due to the formation of reorientation bands and dislocation slip) and a reversible strain was not observed.
