Fractographic Analysis of Mechanical Properties of Microalloyed Steel

Extensive efforts made over the past few decades have enhanced the rising performance of High-Strength Low-Alloy steels. Use of thermomechanical processing was considered for this research. However, the desired mechanical properties are obtained by formulating alloys. Further, to enhance mechanical properties, impact energy, the subsequent quenching and tempering are used. The metallurgical transformation caused by deformation followed by cooling and/or heat treatment has added influences on steels’ mechanical properties. The rational decrease in impact energy value is complex.

FEATURES OF STRUCTURE FORMATION IN THE JOINING ZONE OF COPPER-STEEL COMPOSITE COPPER M3 + STEEL 30CRMNSIA AFTER EXPLOSION WELDING AND THERMAL IMPROVEMENT

The results of optical and electron microscopic metallographic studies and energy-dispersive analysis of the structure and composition in the zone of connection of copper M3 with steel 30 CrMnSiA after explosion welding, subsequent quenching from a temperature of 880 ° C and high tempering at a temperature of 520 ° C are presented. The change in the distribution of hardness and chemical elements over the cross section of the bimetal, the formation of martensite in melts after quenching and its decomposition during high tempering are shown.

A DNA sensor based on upconversion nanoparticles and two-dimensional dichalcogenide materials

We demonstrate the fabrication of a new DNA sensor that is based on the optical interactions occurring between oligonucleotide-coated NaYF4:Yb3+;Er3+ upconversion nanoparticles and the two-dimensional dichalcogenide materials, MoS2 and WS2. Monodisperse upconversion nanoparticles were functionalized with single-stranded DNA endowing the nanoparticles with the ability to interact with the surface of the two-dimensional materials via van der Waals interactions leading to subsequent quenching of the upconversion fluorescence. By contrast, in the presence of a complementary oligonucleotide target and the formation of double-stranded DNA, the upconversion nanoparticles could not interact with MoS2 and WS2, thus retaining their inherent fluorescence properties. Utilizing this sensor we were able to detect target oligonucleotides with high sensitivity and specificity whilst reaching a concentration detection limit as low as 5 mol·L−1, within minutes.

SYNTHESIS OF HIGH-STRENGTH CERAMICS BASED ON TECHNOGENIC WASTE CONTAINING ALUMINUM OXIDE

The aim of this work is to synthesize wear-resistant and heat-resistant ceramics based on aluminum oxide. The manmade aluminum-containing waste of the Shurtan gas chemical complex was used as a source of aluminum oxide. In the work, the dependences «composition-structure», «composition-property» and «property-size of particles» were obtained, obtained by the method of heliomaterials science, namely by melting raw materials in a stream of concentrated solar radiation of high density (350 W/cm2) with subsequent quenching of the melt into water (103 deg/s). It is shown that the wear resistance and heat resistance of the material sharply increase when the content in the mass is more than 80% of aluminum oxide.

Local texture analysis of structure non-uniformity in low carbon high-strength steel after direct quenching

The direct quenching of high-strength steels after hot rolling, which enables discard of the reheating operation, is economically efficient but necessitates a careful analysis of corresponding structural features. In particular, this treatment sometimes results in extended domains of coarse bainite decreasing the fracture toughness of steel. To reveal dependence of such effects on ausforming conditions, local textures of the parent γ-phase have been reconstructed from EBSD orientation data with allowance for the inter-phase orientation relationship. According to the obtained results, the unfavorable structural non-uniformity appears in the direct quenching due to excessive work hardening of austenite at the finish rolling stage; however, the structure and properties of steel can be improved by the reheating and subsequent quenching.

Effects of Sintering Conditions on Structures and Properties of Sintered Tungsten Heavy Alloy

Probably the most advantageous fabrication technology of tungsten heavy alloys enabling the achievement of required performance combines methods of powder metallurgy and processing by intensive plastic deformation. Since the selected processing conditions applied for each individual processing step affect the final structures and properties of the alloys, their optimization is of the utmost importance. This study deals with thorough investigations of the effects of sintering temperature, sintering time, and subsequent quenching in water on the structures and mechanical properties of a 93W6Ni1Co tungsten heavy alloy. The results showed that sintering at temperatures of or above 1525 °C leads to formation of structures featuring W agglomerates surrounded by the NiCo matrix. The sintering time has non-negligible effects on the microhardness of the sintered samples as it affects the diffusion and structure softening phenomena. Implementation of quenching to the processing technology results in excellent plasticity of the green sintered and quenched pieces of almost 20%, while maintaining the strength of more than 1000 MPa.

Влияние термообработки на деформационные свойства кристаллов сплава Ni-=SUB=-49-=/SUB=-Fe-=SUB=-18-=/SUB=-Ga-=SUB=-27-=/SUB=-Co-=SUB=-6-=/SUB=- при их сжатии вдоль оси [011]

Stress–strain diagrams (σ–ε curves) have been studied during uniaxial compression of Ni_49Fe_18Ga_27Co_6 alloy single crystals in the [011] axis direction for the initial samples and those after 15-min annealing at 1373 K with subsequent quenching in water. It was established that the σ–ε curves of initial crystals exhibited a one-stage character and showed a single stress decay, whereas the curves of heat-treated and quenched crystals displayed two stress decays. The shape-memory (SM) strain recovery on heating the compression-strained crystals showed an anomalous (burstlike) character. Investigation of the reproducibility of burstlike recovery of SM strain in a series of thermomechanical treatment cycles showed that the recovery took place in quenched crystals, whereas the temperature interval of SM recovery in the initial crystal grew from 1 to 12 K with increasing number of thermomechanical treatment cycles.

Кристаллографические особенности структуры литых и закаленных сплавов кобальт--ниобий

By the means of metallography, scanning and transmission electron microscopy, and EBSD-analysis, the features of the structure formation upon β→α (fcc-hcp) - polymorphic transformation in Co - Nb binary alloys were studied. It was shown that upon gradual cooling of the crystallized ingot, in each β-grain of the alloy nucleation of the α-phase crystals of several orientations out of 4 possible in accordance with the Wasserman’s orientational relations occurs. The formation of any of the 4 possible orientations of the α-phase is equally probable. At room temperature, only α (hcp)-martensite was found in the structure of the studied alloys. The misorientation of the substructure in the martensitic crystals length-wise in cast alloys does not exceed 1 deg. After the homogenization and the subsequent quenching in salted water, the structure of Co-Nb alloys does not undergo neither morphological, nor crystallographic changes, but becomes noticeably more fine-grained. In this case, the misorientation of the substructure elements of the martensitic crystals length-wise increases several times, consequent to the high level of quenching microstresses in martensite. No phases with multilayer lattices such as NR martensite were found.

Synthesis and crystal structure of (E)-1,2-bis[2-(methylsulfanyl)phenyl]diazene

The title compound, C14H14N2S2, was obtained by transmetallation of 2,2′-bis(trimethylstannyl)azobenzene with methyl lithium, and subsequent quenching with dimethyl disulfide. The asymmetric unit comprises two half-molecules, the other halves being completed by inversion symmetry at the midpoint of the azo group. The two molecules show only slight differences with respect to N=N, S—N and aromatic C=C bonds or angles. Hirshfeld surface analysis reveals that except for one weak H...S interaction, intermolecular interactions are dominated by van der Waals forces only.

Post-starburst galaxies in SDSS-IV MaNGA

ABSTRACT Post-starburst galaxies, identified by their unusually strong Balmer absorption lines and weaker than average emission lines, have traditionally been selected based on their central stellar populations. Here we identify 360 galaxies with post-starburst regions from the MaNGA integral field survey and classify these galaxies into three types: 31 galaxies with central post-starburst regions (CPSB), 37 galaxies with off-centre ring-like post-starburst regions (RPSB), and 292 galaxies with irregular post-starburst regions (IPSB). Focusing on the CPSB and RPSB samples, and comparing their radial gradients in Dn4000, HδA, and W(H α) to control samples, we find that while the CPSBs have suppressed star formation throughout their bulge and disc, and there is clear evidence of rapid decline of star formation in the central regions, the RPSBs only show clear evidence of recently rapidly suppressed star formation in their outer regions and an ongoing central starburst. The radial profiles in mass-weighted age and stellar v/σ indicate that CPSBs and RPSBs are not simply different evolutionary stages of the same event, rather the CPSB galaxies are caused by a significant disruptive event, while the RPSB galaxies are caused by disruption of gas fuelling to the outer regions. Compared to the control samples, both CPSB and RPSB galaxies show a higher fraction of interactions/mergers, misaligned gas, or bars that might be the cause of the gas inflows and subsequent quenching.