Academic Journals

Ab initio design of drug carriers for zoledronate guest molecule using phosphonated and sulfonated calix[4]arene and calix[4]resorcinarene host molecules

The Psychological Record - Sun, 04/01/2018 - 00:00
Abstract

Monomolecular drug carriers based on calix[n]arenes and calix[n]resorcinarenes containing the interior cavity can enhance the affinity and specificity of the osteoporosis inhibitor drug zoledronate (ZOD). In this work, we investigated the suitability of nine different calix[4]arenes- and calix[4]resorcinarenes-based macrocycles as hosts for the ZOD guest molecule by conducting ab initio density functional theory calculations for structures and energetics of eighteen different host-guest complexes. For the optimized molecular structures of the free, phosphonated, sulfonated calix[4]arenes and calix[4]resorcinarenes, the geometric sizes of their interior cavities were measured and compared with those of the host-guest complexes in order to check the appropriateness for host-guest complex formation. Our calculations of binding energies indicated that in gaseous states some of the complexes might be unstable but in aqueous states almost all of the complexes can be formed spontaneously. Of the two different docking ways, the insertion of ZOD with the P–O–P branch into the cavity of host was easier than that with the nitrogen-containing heterocycle of ZOD. The work will open a way for developing effective drug delivering systems for the ZOD drug and promote experimentalists to synthesize them.

Categories: Academic Journals

Defect structures in solution-grown single crystals of the intermetallic compound Ag 3 Sn

The Psychological Record - Sun, 04/01/2018 - 00:00
Abstract

The compound Ag3Sn adopts the ordered orthorhombic D0a Cu3Ti-type structure. It exhibits an unusual low yield stress and high ductility for an intermetallic compound, but the reasons for these effects are not clear. Here, we report an electron microscopy study on the defects present in solution-grown Ag3Sn single crystals that have deformed during the decanting and subsequent handling processes. It is found that the crystals contain two types of lenticular deformation twins: {011}-type and {211}-type. These twins interpenetrate with no evidence of cracking at the intersections. The crystals also contain high densities of dislocations including long straight dipoles with b = ± [010] and shorter curved segments and loops with b = [ \( 10\bar{2} \) ] and [001]. It is inferred that the dipoles are artifacts of specimen preparation that climb in from the cross-sectional sample surfaces, whereas the shorter segments are deformation debris. If a combination of twinning and dislocation glide of the types observed here were to form concurrently during general deformation of Ag3Sn, then they could provide the necessary number of independent deformation modes to accommodate an arbitrary plastic strain, which might help to explain the unusual ductility of this compound.

Categories: Academic Journals

ω -Fe particle size and distribution in high-nitrogen martensitic steels

The Psychological Record - Sun, 04/01/2018 - 00:00
Abstract

Systematical transmission electron microscopy (TEM) studies of the martensitic substructure in quenched Fe–C binary alloys have revealed that the initially formed martensite has twinning structure, and the twin is body-centered cubic {112}<111>-type twin regardless of the carbon concentrations. A metastable hexagonal ω-Fe(C) phase with an ultrafine particle-like morphology is distributed at the twin boundary region. In order to explore the common existence of the ω-Fe in nitrogen steels, the martensitic substructures in high-nitrogen martensitic stainless steels at various conditions (as-quenched, subzero-treated and tempered) have been investigated in detail by means of TEM. The ω-Fe with an ultrafine particle size of 1–3 nm has been observed in all the samples. TEM tilting experiment and electron diffraction analysis have revealed that each martensitic lath or plate is composed of {112}<111>-type twin structure with the ω particles at the twin boundary region. The martensite morphology and the relationship between the twin and the ω phase particles have been discussed crystal geometrically. The ω particle size variation with subzero and tempering treatment has also been discussed based on a proposed dilation and split mechanism. The existence of large amount of twins up to 550 °C simply suggests that the nitrogen atoms have much stronger effect than carbon atoms on the ω phase stability. The present investigation will provide a very clear image about the martensitic substructure in high-nitrogen martensitic stainless steels.

Categories: Academic Journals

Nucleation behavior of ω o phase in TiAl alloys at different elevated temperatures

The Psychological Record - Sun, 04/01/2018 - 00:00
Abstract

In this study, the location, morphology and composition of the ωo phase, which transformed from B2 phase in Ti–45Al–8.5Nb-(W, B, Y) (at.%) alloy, were investigated by short-time heat treatments in an intermediate temperature range. The results showed that the characteristics of B2 → ωo phase transformation differ with the reduction in temperature. Below the ωo solves, the B2 → ωo phase transformation will take place within B2 area. There are existing two stages in the phase transformations during cooling from 850 to 700 °C. When the temperature is high (850 °C), granular ωo populated along the dislocations existing in B2 phase and B2 grain boundaries, due to higher energy and the enrichment of Nb element at the B2/γ boundaries. It is worth noting that only two ωo variants nucleate at 850 °C. With the decrease in temperature, the nucleation sites of ωo phase would be migrated from the B2 boundaries to the inner area. At the temperature of 700 °C, four ωo variants with different orientations nucleate homogenously within B2 grain. The ordered ωo formation process of Ti–45Al–8.5Nb-(W, B, Y) alloy during cooling was postulated in this study.

Categories: Academic Journals

Enhancing the reactivity of aluminosilicate materials toward geopolymer synthesis

The Psychological Record - Sun, 04/01/2018 - 00:00
Abstract

Geopolymers are alternative materials to portland cement, obtained by alkaline activation of aluminosilicates. They exhibit excellent properties and a wide range of potential applications in the field of civil engineering. Several natural aluminosilicates and industrial by-products can be used for geopolymer synthesis, but a lot of starting materials have the disadvantage of poor reactivity and low strength development. This paper presents a comprehensive review of the main methods used to alter the reactivity of aluminosilicate materials for geopolymer synthesis, as reported recently in the literature. The methods consist of mechanical, thermal, physical separation and chemical activation, of which mechanical activation is the most commonly employed technique. The reactivity of the activated aluminosilicate materials is mainly related to the activation method and the treatment parameters. Chemical activation by alkaline fusion is a promising method allowing preparation of one-part geopolymer materials, an alternative class of geopolymeric binders. However, the resulting alkaline-fused geopolymer products are vulnerable to attack by excessive alkalis.

Categories: Academic Journals

A three-dimensional porous hydroxyapatite nanocomposite scaffold with shape memory effect for bone tissue engineering

The Psychological Record - Sun, 04/01/2018 - 00:00
Abstract

It is known that scaffold is a key factor in bone tissue engineering. The aim of this study was to improve the design of scaffold in order to achieve an effect of precisely matching the irregular boundaries of bone defects as well as facilitate clinical application. In this study, controllable three-dimensional porous shape memory polyurethane/nano-hydroxyapatite composite scaffolds were successfully fabricated. Detailed studies were performed to evaluate its structure, porosities, and mechanical properties, emphasizing the effect of different apertures of scaffolds on shape recovery behaviors and biological performance in vitro. Results showed its compression recovery ratios and shape recovery ratios of all scaffolds could reach more than 99 and 90%, respectively, which could let it more accurately match the irregular boundaries of bone defects. And also its cell proliferation ability was improved with the increase in the apertures. Thus, these scaffolds have potential applications for the bone tissue engineering.

Categories: Academic Journals

Improved electrochemical performance of bagasse and starch-modified LiNi 0.5 Mn 0.3 Co 0.2 O 2 materials for lithium-ion batteries

The Psychological Record - Sun, 04/01/2018 - 00:00
Abstract

Organic carbon-coated LiNi0.5Mn0.3Co0.2O2 materials are prepared by mixing 2 or 5% starch or bagasse evenly with the synthesized LiNi0.5Mn0.3Co0.2O2 material and calcining for 10 h at 750 °C. The microstructures and electrochemical performance are investigated by X-ray diffraction, scanning electron microscopy, carbon/sulfur analysis, transmission electron microscopy and electrochemical testing. The results indicate that the organic carbon coated on the surface of LiNi0.5Mn0.3Co0.2O2 material does not change the surface morphology and crystal structure, but greatly improves the conductivity, rate and cycle performance of the LiNi0.5Mn0.3Co0.2O2 cathode in a Li-ion battery. The initial discharge capacity of the synthesized LiNi0.5Mn0.3Co0.2O2 material is 147.8 mAh g−1, which increases to 152.4 and 153.3 mAh g−1 for 2% starch and bagasse, respectively. After 100 cycles, the capacity retention rates are 70.7% (uncoated), 83.3% (coated with 2% starch), 90.1% (coated with 2% bagasse), 83.1% (coated with 5% starch) and 91.1% (coated with 5% bagasse). The influence of the percentage of coated carbon and its dispersion uniformity on the performance of the battery is analyzed. A small coating capacity and uniform carbon film can achieve better performance. Rational organic carbon coating technology is an effective way to improve the electrochemical performance of LiNi1−xy Mn x Co y O2-based material.

Categories: Academic Journals

A highly active bio-based epoxy resin with multi-functional group: synthesis, characterization, curing and properties

The Behavior Analyst - Sun, 04/01/2018 - 00:00
Abstract

A bio-based epoxy resin, triglycidyl ether of resveratrol (TGER), was synthesized based on the renewable resveratrol deriving from tannins. The structure and properties of TGER have been characterized by 1H NMR, 13C NMR, FTIR, GPC and viscosity measurement. Besides, systematical investigation was carried out on the curing reaction of TGER and diaminodiphenylmethane (DDM), assisted by the characterization of mechanical properties and thermal properties of cured TGER/DDM by means of differential scanning calorimetry, thermogravimetric analysis, dynamic mechanical analysis (DMA), flexural and impact measurement. Non-isothermal and isothermal curing analysis showed that TGER/DDM system, deriving from autocatalytic curing reaction, possessed 40 °C lower curing temperature (84 °C) than bisphenol A diglycidyl ether (DGEBA) (124 °C) and much lower activation energy than DGEBA/DDM system calculated by Kissinger equation. DMA revealed that TGER possessed high glass transition temperature (T g = 148 °C) and glassy storage modulus (2.391 GPa@23 °C). Meanwhile, TGER/DDM thermosets also exhibited good mechanical properties and heat resistance, illustrating that multi-phenol group and stilbene group of resveratrol endowed polymer with high cross-linking density and rigidness. Therefore, TGER could be a promising alternative to petroleum-based epoxy resin.

Categories: Academic Journals

Temperature-dependent space-charge-limited conduction in BaTiO 3 heterojunctions

The Behavior Analyst - Sun, 04/01/2018 - 00:00
Abstract

We have investigated the space-charge-limited conduction (SCLC) in two different metal–insulator–metal junctions of the form: Au/BaTiO3 (BTO)/Nb:SrTiO3 (Nb:STO) and Au/BTO/La0.67Ca0.33MnO3 (LCMO) at various temperatures. The SCLC model has been employed to determine various parameters relevant to the charge conduction in these systems. While the trap density increases with decreasing temperature, the ratio of free to trapped carriers (θ) reduces for both the junctions, which can be understood as the thermally activated process. The extracted activation energies of 0.071 eV for Au/BTO/Nb:STO and 0.154 eV for Au/BTO/LCMO indicate the presence of shallow trap level. Moreover, the Fermi level at thermal equilibrium approaches the intrinsic limit with increasing temperature. Comparing both the junctions, we observe lower θ and deeper trap level in BTO/LCMO junction.

Categories: Academic Journals

Preparation and evaluation of superparamagnetic core–shell dummy molecularly imprinted polymer for recognition and extraction of organophosphorus pesticide

The Behavior Analyst - Sun, 04/01/2018 - 00:00
Abstract

In this paper, we reported a simple and effective strategy to synthesize core–shell dummy template magnetic molecularly imprinted polymers (Fe3O4@DMIPs) using ethyl paraoxon as a template for the recognition and selective extraction of organophosphorus pesticide. Initially, monodisperse Fe3O4 nanoparticles were synthesized directly through a facile one-pot hydrothermal method. Then, the imprinted layer was synthesized directly on the surface of the magnetic core by means of a one-pot sol–gel copolymerization which avoided further modification of the external part of the magnetic core. The structure and morphology of the materials (Fe3O4@DMIPs) were characterized by SEM, TEM, FTIR, XRD, and VSM. It was observed that Fe3O4@DMIPs showed regular morphology, good dispersibility, and superparamagnetism. The synthesis conditions for the formation of Fe3O4@DMIPs were systematically investigated. It was found that the morphology and monodispersity of Fe3O4@DMIPs were highly influenced by the ratio of the mixture solvent of methanol and water and the volume ratio of functional monomer (APTES) and cross-linker (TEOS). The binding performance of the imprinted polymers was investigated through a series of adsorption experiments, which indicated that the Fe3O4@DMIPs had a fast adsorption rate (15 min) and high adsorption capacity (195.7 mg g−1) to methyl parathion and phoxim. Meanwhile, real wine sample tests demonstrated a good extraction effect. This study provides a possibility for the selective extraction of organophosphorus pesticide residue in a complex matrix.

Categories: Academic Journals

Visible light photocatalytic oxidative desulfurization using Ti-MCM-41-loaded iron phthalocyanine combined with ionic liquid extraction

The Behavior Analyst - Sun, 04/01/2018 - 00:00
Abstract

Iron phthalocyanine (PcFe) was loaded on Ti-MCM-41 as visible light photocatalyst (R-PcFe/Ti-MCM-41). Dibenzothiophene (DBT) was photooxidized using R-PcFe/Ti-MCM-41 as a photocatalyst, air as an oxidant, and ionic liquid as the extraction agent during visible light irradiation at room temperature and ambient conditions. The results indicated that photocatalytic efficiency of the amino iron phthalocyanine (NH2-PcFe)/Ti-MCM-41 was superior to the other substituent groups. The DBT content in the model oil decreased from 1000 to 44 μg/mL with 95.6% removal rate under the optimal reaction conditions (model oil 10 mL, photocatalyst NH2-PcFe/Ti-MCM-41 0.02 g, loading amount of NH2-PcFe 0.3 g/g, air flow rate 100 mL/min, reaction time 2 h, room temperature). The kinetics of photocatalytic oxidation of DBT follows first-order kinetics with a rate constant of 1.319 h−1 and halftime of 0.525 h. The photocatalyst NH2-PcFe/Ti-MCM-41 was reused for five times, and the catalytic activity decreased slightly. The photocatalytic oxidation system demonstrated significant desulfurization effects on different sulfur compounds and real gasoline, and the sulfur content of the actual gasoline could be reduced from 1000 to 78 ppm.

Categories: Academic Journals

PTFE/SPEEK/PDDA/PSS composite membrane for vanadium redox flow battery application

The Behavior Analyst - Sun, 04/01/2018 - 00:00
Abstract

How to solve the crossover of vanadium ions through ion exchange membrane is a key issue in vanadium redox flow battery (VRB), especially for ultra-thin membranes used for VRB to obtain a lower cell resistance. Herein, an ultra-thin (~ 30 μm) PTFE/SPEEK [polytetrafluoroethylene/sulfonated poly(ether ether ketone), P/S] membrane is successfully prepared and modified by using layer-by-layer (LBL) self-assembly technique with polycation poly(diallyldimethylammonium chloride) (PDDA) and polyanion poly(sodium styrene sulfonate) (PSS). P/S membranes are alternatively immersed in positively and negatively charged polyelectrolyte to form 2 to 8 bilayers onto its surface. Consequently, a series of P/S-[PDDA/PSS] n (n is the number of multilayers) membranes are fabricated. Both the physicochemical properties and VRB performances of the P/S-[PDDA/PSS] n membranes are then investigated in detail. Results show that the ion selectivity of the P/S-[PDDA/PSS] n membranes is much higher than that of pristine P/S membrane, especially for P/S-[PDDA/PSS]6 membrane. As a result, the VRB with the P/S-[PDDA/PSS]6 membrane exhibits the highest coulombic efficiency (CE) of 96.5% at 80 mA cm−2, the highest voltage efficiency of 94.7% at 40 mA cm−2 and the highest energy efficiency of 87.7% at both 40 and 50 mA cm−2, respectively. In addition, 80 times charge–discharge test proves that the P/S-[PDDA/PSS]6 membrane possesses high stability and no obvious CE decay after running. All the results show that the LBL technique is an effective way to prepare ultra-thin membrane with high ion selectivity for VRB application.

Categories: Academic Journals

Preparation and evaluation of magnetic field-induced orientation on magnetic nanoparticles on PVA nanocomposite films

The Behavior Analyst - Sun, 04/01/2018 - 00:00
Abstract

Magnetite Fe3O4 particles (M) were dispersed in polyvinyl alcohol (PVA) and oriented successfully by applying low external magnetic field. Observed orientation was verified by image analysis using ImageJ software. Crystallinity of the M/PVA samples was examined using DSC, showing a lower crystallinity by addition of particles and higher crystallinity resulting from orientation. Orientation of 0.05 and 0.1 wt% of M particles increased crystallinity of nanocomposites 39 and 57%, respectively. Tensile tests were also measured to examine the mechanical properties of oriented and non-oriented samples. Results show that the mechanical properties of samples including elongation at break and modulus had improved in the direction of oriented particles. Afterward, graphene oxide particles were magnetized [magnetic graphene oxide (MGO)] and dispersed in PVA resulting in improved mechanical properties. PVA/MGO nanocomposites showed better mechanical properties than PVA/M, although no improvement in the crystallinity was observed.

Categories: Academic Journals

Preparation and droplet impact dynamics of superhydrophobic nano-aluminum films on metal substrates

The Behavior Analyst - Sun, 04/01/2018 - 00:00
Abstract

A simple electrophoretic deposition method followed by stearic acid modification was developed to prepare superhydrophobic multiscale nano-aluminum films on a series of metal substrates such as nickel, copper, titanium and stainless steel. The surface morphology and chemical compositions were characterized by a field emission scanning electron microscopy, X-ray diffraction, energy-dispersive X-ray spectroscope, Fourier-transform infrared spectrophotometer and white light interferometer. The resultant nano-aluminum films exhibited excellent superhydrophobicity with a water contact angle of 168.5° and a water sliding angle of 2°. Furthermore, the obtained nano-Al films showed the desirable stability and durability after the related testing. In addition, the impact dynamic behaviors of water droplet on the superhydrophobic nano-Al films were described via the corresponding parameters, such as Weber number (We), spreading factor (β), contact time (tc), etc. Based on these characteristics, the superhydrophobic nano-Al films presented excellent water-repellent property. The EPD process is an efficient method to prepare superhydrophobic nano-Al films on common engineering metal materials, which can be applied to various industrial or manufacturing fields, including oil–water separation, anti-icing, self-cleaning, anti-corrosion, microelectronic fabrication and so forth.

Categories: Academic Journals

Mechanical behavior of porous Si 3 N 4 ceramics manufactured with 3D printing technology

The Behavior Analyst - Sun, 04/01/2018 - 00:00
Abstract

The paper focuses on experimental measurement and analytical and numerical modeling of the elastic moduli of porous Si3N4 ceramics obtained by 3D printing and pressureless sintering. The pores in such a material have complex irregular shape and porosity varies over a wide range (up to 50%), depending on the technological parameters used. For analytical modeling, we use effective field methods (Mori–Tanaka–Benveniste and Maxwell homogenization schemes) recently developed for pores of superspherical shape. For FEM simulation, we used microstructures generated by overlapping solid spheres and overlapping spherical pores. It is shown that elastic properties of ceramics are largely determined by the granular structure and the concave pore shape, which have been observed in the ceramics microstructure after sintering of the 3D-printed powder green bodies.

Categories: Academic Journals

Influence of slag composition on the stability of steel in alkali-activated cementitious materials

The Behavior Analyst - Sun, 04/01/2018 - 00:00
Abstract

Among the minor elements found in metallurgical slags, sulfur and manganese can potentially influence the corrosion process of steel embedded in alkali-activated slag cements, as both are redox-sensitive. Particularly, it is possible that these could significantly influence the corrosion process of the steel. Two types of alkali-activated slag mortars were prepared in this study: 100% blast furnace slag and a modified slag blend (90% blast furnace slag + 10% silicomanganese slag), both activated with sodium silicate. These mortars were designed with the aim of determining the influence of varying the redox potential on the stability of steel passivation under exposure to alkaline and alkaline chloride-rich solutions. Both types of mortars presented highly negative corrosion potentials and high current density values in the presence of chloride. The steel bars extracted from mortar samples after exposure do not show evident pits or corrosion product layers, indicating that the presence of sulfides reduces the redox potential of the pore solution of slag mortars, but enables the steel to remain in an apparently passive state. The presence of a high amount of MnO in the slag does not significantly affect the corrosion process of steel under the conditions tested. Mass transport through the mortar to the metal is impeded with increasing exposure time; this is associated with refinement of the pore network as the slag continued to react while the samples were immersed.

Categories: Academic Journals

Theoretical study of phosphorene multilayers: optical properties and small organic molecule physisorption

The Behavior Analyst - Sun, 04/01/2018 - 00:00
Abstract

Phosphorene is an emerging 2D-like material with direct energy band. In this work we report the results of a theoretical study on the electronic structure of phosphorene multilayers. A particular emphasis is put on the investigation of the optical absorption and the functionalization of phosphorene layers with organic molecules such as benzene and fullerene. The investigation is carried out employing the density functional theory, and the effect of using different exchange-correlation functionals for the interlayer van der Waals interaction is discussed. Fundamental quantities like lattice constants, interlayer distance and energy band gap are reported in phosphorene monolayers, bilayers and trilayers. The features of the interband optical absorption are studied from the calculated imaginary part of the dielectric function. The results of the numerical simulation of the phenomenon of the small organic molecule physisorption onto phosphorene indicate that the direct band gap is preserved. In the case of the fullerene physisorption, a deformation in the phosphorene monolayer is induced, leading to a shift of the associated band structure. It is shown that such a modification depends on the particular exchange-correlation functional employed. In the case of benzene physisorption, the electronic structure of the phosphorene remains unchanged and is independent of the position of the benzene molecule. This suggests that benzene would be a good candidate for a molecular coating of phosphorene to shield it against oxidation under ambient conditions.

Categories: Academic Journals

Ab initio design of drug carriers for zoledronate guest molecule using phosphonated and sulfonated calix[4]arene and calix[4]resorcinarene host molecules

The Behavior Analyst - Sun, 04/01/2018 - 00:00
Abstract

Monomolecular drug carriers based on calix[n]arenes and calix[n]resorcinarenes containing the interior cavity can enhance the affinity and specificity of the osteoporosis inhibitor drug zoledronate (ZOD). In this work, we investigated the suitability of nine different calix[4]arenes- and calix[4]resorcinarenes-based macrocycles as hosts for the ZOD guest molecule by conducting ab initio density functional theory calculations for structures and energetics of eighteen different host-guest complexes. For the optimized molecular structures of the free, phosphonated, sulfonated calix[4]arenes and calix[4]resorcinarenes, the geometric sizes of their interior cavities were measured and compared with those of the host-guest complexes in order to check the appropriateness for host-guest complex formation. Our calculations of binding energies indicated that in gaseous states some of the complexes might be unstable but in aqueous states almost all of the complexes can be formed spontaneously. Of the two different docking ways, the insertion of ZOD with the P–O–P branch into the cavity of host was easier than that with the nitrogen-containing heterocycle of ZOD. The work will open a way for developing effective drug delivering systems for the ZOD drug and promote experimentalists to synthesize them.

Categories: Academic Journals

Defect structures in solution-grown single crystals of the intermetallic compound Ag 3 Sn

The Behavior Analyst - Sun, 04/01/2018 - 00:00
Abstract

The compound Ag3Sn adopts the ordered orthorhombic D0a Cu3Ti-type structure. It exhibits an unusual low yield stress and high ductility for an intermetallic compound, but the reasons for these effects are not clear. Here, we report an electron microscopy study on the defects present in solution-grown Ag3Sn single crystals that have deformed during the decanting and subsequent handling processes. It is found that the crystals contain two types of lenticular deformation twins: {011}-type and {211}-type. These twins interpenetrate with no evidence of cracking at the intersections. The crystals also contain high densities of dislocations including long straight dipoles with b = ± [010] and shorter curved segments and loops with b = [ \( 10\bar{2} \) ] and [001]. It is inferred that the dipoles are artifacts of specimen preparation that climb in from the cross-sectional sample surfaces, whereas the shorter segments are deformation debris. If a combination of twinning and dislocation glide of the types observed here were to form concurrently during general deformation of Ag3Sn, then they could provide the necessary number of independent deformation modes to accommodate an arbitrary plastic strain, which might help to explain the unusual ductility of this compound.

Categories: Academic Journals

ω -Fe particle size and distribution in high-nitrogen martensitic steels

The Behavior Analyst - Sun, 04/01/2018 - 00:00
Abstract

Systematical transmission electron microscopy (TEM) studies of the martensitic substructure in quenched Fe–C binary alloys have revealed that the initially formed martensite has twinning structure, and the twin is body-centered cubic {112}<111>-type twin regardless of the carbon concentrations. A metastable hexagonal ω-Fe(C) phase with an ultrafine particle-like morphology is distributed at the twin boundary region. In order to explore the common existence of the ω-Fe in nitrogen steels, the martensitic substructures in high-nitrogen martensitic stainless steels at various conditions (as-quenched, subzero-treated and tempered) have been investigated in detail by means of TEM. The ω-Fe with an ultrafine particle size of 1–3 nm has been observed in all the samples. TEM tilting experiment and electron diffraction analysis have revealed that each martensitic lath or plate is composed of {112}<111>-type twin structure with the ω particles at the twin boundary region. The martensite morphology and the relationship between the twin and the ω phase particles have been discussed crystal geometrically. The ω particle size variation with subzero and tempering treatment has also been discussed based on a proposed dilation and split mechanism. The existence of large amount of twins up to 550 °C simply suggests that the nitrogen atoms have much stronger effect than carbon atoms on the ω phase stability. The present investigation will provide a very clear image about the martensitic substructure in high-nitrogen martensitic stainless steels.

Categories: Academic Journals

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