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Recently, it was shown that the nanocrystallization of B i 2 O 3 glasses with the addition of S i O 2 and A l 2 O 3 leads to the stabilization of the δ -like B i 2 O 3 phase at least down to room temperature, which is significantly below its stability range in bulk form. In this research, we investigated the properties of bismuthate glasses synthesized with various glass-forming agents such as S i O 2 , G e O 2 , B 2 O 3 , and A l 2 O 3 . It was demonstrated that vitrification of all these systems is possible using a standard melt quenching route. Furthermore, we investigated the crystallization processes in pristine glasses upon increasing the temperature and the thermal stability of arising phases using thermal analysis and high-temperature XRD in situ experiments. It was shown that it is possible to stabilize crystallites' isostructures with δ - B i 2 O 3 embedded in a residual glassy matrix down to room temperature. The temperature range of the appearance of the δ -like phase strongly depended on the nominal composition of the glasses. We postulate that the confinement effect depends on the local properties of the residual glassy matrix and its ability to introduce sufficient force to stretch the structure of the δ -like B i 2 O 3 phase in the nanocrystallites. [ABSTRACT FROM AUTHOR]

Co-Zr amorphous alloys exhibit soft magnetic properties, whereas the Co-rich crystalline magnetic phases in this alloy system displayed a hard magnetic behavior. In this study, an initial two-phase Co-Zr composite with an overall composition of 75 at.% Co and 25 at.% Zr was processed by high-pressure torsion (HPT), and the effects of severe plastic deformation and subsequent thermal treatment on the composite's structural evolution and its magnetic properties were investigated. HPT processing allowed us to achieve an amorphous microstructure with low coercivity in its as-deformed state. To further tune the alloy's magnetic properties and study its crystallization behavior, various annealed states were investigated. The microstructural properties were correlated with the magnetic properties, and a decreasing coercivity with increasing annealing temperatures was observed despite the onset of crystallization in the amorphous alloy. At higher annealing temperatures, coercivity increased again. The results appear promising for obtaining tuneable rare-earth free magnetic materials by severe plastic deformation. [ABSTRACT FROM AUTHOR]

Through surface nanocrystallization and low-temperature ion sulfurization, the nanocrystalline/FeS thin film with excellent friction-reduction and antiwear properties was fabricated on the surface of AISI321 stainless steel. The nanocrystallization treatment formed the high hardness and active nanocrystalline structure on the surface of AISI321, with the harness increased from 4.6 GPa to 7.56 GPa. Furthermore, the significantly refined nanostructure strongly increased the concentration of S element in comparison with the single-sulfurized layer on the substrate. Tribological tests reveal that both the original AISI321 substrate and the single-sulfurizing-treated samples are subject to severe abrasion. Single nanocrystallization treatment can improve the wear resistance of AISI321, while the compound treatment can obviously improve the comprehensive tribological properties. The compound-modified layer presents excellent tribological properties with the lowest coefficient of friction (COF) of 0.33, which is related to the increased hardness of the substrate and increased thickness, density, and homogeneity of the sulfurized layer. Furthermore, a physical model is developed for the vacuum tribological behavior of the samples after different treatments. This model provides a reference for revealing the tribological mechanism of the compound-modified layer treated using surface nanocrystallization-assisted chemical heat treatment. [ABSTRACT FROM AUTHOR]

Melanin is an insoluble, amorphous polymer that forms planar sheets that aggregate naturally to create colloidal particles with several biological functions. Based on this, here, a preformed recombinant melanin (PRM) was utilized as the polymeric raw material to generate recombinant melanin nanoparticles (RMNPs). These nanoparticles were prepared using bottom-up (nanocrystallization—NC, and double emulsion–solvent evaporation—DE) and top-down (high-pressure homogenization—HP) manufacturing approaches. The particle size, Z-potential, identity, stability, morphology, and solid-state properties were evaluated. RMNP biocompatibility was determined in human embryogenic kidney (HEK293) and human epidermal keratinocyte (HEKn) cell lines. RMNPs prepared by NC reached a particle size of 245.9 ± 31.5 nm and a Z-potential of −20.2 ± 1.56 mV; 253.1 ± 30.6 nm and −39.2 ± 0.56 mV compared to that obtained by DE, as well as RMNPs of 302.2 ± 69.9 nm and −38.6 ± 2.25 mV using HP. Spherical and solid nanostructures in the bottom-up approaches were observed; however, they were an irregular shape with a wide size distribution when the HP method was applied. Infrared (IR) spectra showed no changes in the chemical structure of the melanin after the manufacturing process but did exhibit an amorphous crystal rearrangement according to calorimetric and PXRD analysis. All RMNPs presented long stability in an aqueous suspension and resistance to being sterilized by wet steam and ultraviolet (UV) radiation. Finally, cytotoxicity assays showed that RMNPs are safe up to 100 μg/mL. These findings open new possibilities for obtaining melanin nanoparticles with potential applications in drug delivery, tissue engineering, diagnosis, and sun protection, among others. [ABSTRACT FROM AUTHOR]

Recently, an interest in NASICON-type materials revived, as they are considered potential cathode materials in sodium–ion batteries used in large-scale energy storage. We applied a facile technique of thermal nanocrystallization of glassy analogs of these compounds to enhance their electrical parameters. Six nanomaterials of the Na3M2(PO4)2F3 (M = V, Ti, Fe) system were studied. Samples with nominal compositions of Na3V2(PO4)2F3, Na3Ti2(PO4)2F3, Na3Fe2(PO4)2F3, Na3TiV(PO4)2F3, Na3FeV(PO4)2F3 and Na3FeTi(PO4)2F3 have been synthesized as glasses using the melt-quenching method. X-ray diffraction measurements were conducted for as-synthesized samples and after heating at elevated temperatures to investigate the structure. Extensive impedance measurements allowed us to optimize the nanocrystallization process to enhance the electrical conductivity of cathode nanomaterials. Such a procedure resulted in samples with the conductivity at room temperature ranging from 1 × 10 − 9 up to 8 × 10 − 5 S/cm. We carried out in situ impedance spectroscopy measurements (in an ultra-high-frequency range up to 10 GHz) and compared them with thermal events observed in differential thermal analysis studies. [ABSTRACT FROM AUTHOR]

The effects of severe plastic deformation (SPD) by means of high-pressure torsion (HPT) on the structural properties of the two iron-based metallic glasses Fe73.9Cu1Nb3Si15.5B6.6 and Fe81.2Co4Si0.5B9.5P4Cu0.8 have been investigated and compared. While for Fe73.9Cu1Nb3Si15.5B6.6, HPT processing allows us to extend the known consolidation and deformation ranges, HPT processing of Fe81.2Co4Si0.5B9.5P4Cu0.8 for the first time ever achieves consolidation and deformation with a minimum number of cracks. Using numerous analyses such as X-ray diffraction, dynamic mechanical analyses, and differential scanning calorimetry, as well as optical and transmission electron microscopy, clearly reveals that Fe81.2Co4Si0.5B9.5P4Cu0.8 exhibits HPT-induced crystallization phenomena, while Fe73.9Cu1Nb3Si15.5B6.6 does not crystallize even at the highest HPT-deformation degrees applied. The reasons for these findings are discussed in terms of differences in the deformation energies expended, and the number and composition of the individual crystalline phases formed. The results appear promising for obtaining improved magnetic properties of glassy alloys without additional thermal treatment. [ABSTRACT FROM AUTHOR]

Nanograins were obtained in the AZ31 Mg alloy bars with different initial grain sizes via cold rotary swaging. Microstructure evolution during deformation was investigated through electron backscatter diffraction analysis and transmission electron microscopy studies. The results indicate that initial grain size had little effect on the mechanism of grain refinement during swaging. The nanocrystallization process of the alloys with different initial grain sizes included extensive twinning followed by the further refinement of the twin lamellae through the formation of massive dislocation arrays. However, as the initial grain size decreased, the formation rate of nanograins increased, resulting in a higher degree of nanocrystallization after the same swaging pass. The mean grain size and yield strength of the sample with the smallest initial grain size were about 91 nm and 489 MPa, respectively. The slower rate and lower degree of nanocrystallization in the alloy with a larger initial grain size were mainly attributed to the less grain boundary areas and higher activity of twinning. [ABSTRACT FROM AUTHOR]

The early stages of nanocrystallization in amorphous Fe73.8Si13B9.1Cu1Nb3.1 ribbons and microwires were compared in terms of their internal stress effects. The microstructure was investigated by the X-ray diffraction method. Classical expressions of crystal nucleation and growth were modified for microwires while accounting for the internal stress distribution, in order to justify the XRD data. It was assumed that, due to the strong compressive stresses on the surface part and tensile stresses on the central part, crystallization on the surface part of the microwire proceeded faster than in the central part. The results revealed more rapid nanocrystallization in microwires compared to that in ribbons. During the initial period of annealing, the compressive surface stress of a microwire caused the formation of a predominantly crystallized surface layer. The results obtained open up new possibilities for varying the high-frequency properties of microwires and their application in modern sensorics. [ABSTRACT FROM AUTHOR]

This study demonstrated for the first time that it is possible to prepare nanocrystalline δ-Bi2O3 that is stable at room temperature by twin-rollers and free cooling methods, using a ceramic crucible. The phase composition of prepared samples and upper limit of the thermal stability of nanograins confined in an amorphous matrix were determined by the X-ray diffraction (XRD) method. The average size of crystallites and the microstructure of studied samples was determined by SEM and XRD methods. The average grain size varied from 38 to 85 nm, depending on the preparation technique; however, it was also observed that agglomerations consisted of smaller crystallites ca. 10–30 nm. Using the EDX method, it was found that a crucial role in the preparation of nanocrystalline δ-Bi2O3 glass-ceramics was played by Si and Al impurities and their glass forming oxides from ceramic crucible. By impedance spectroscopy (IS), the temperature dependencies of electric conductivity (via oxygen ions) were studied and the activation energies of conductivity were determined. [ABSTRACT FROM AUTHOR]

In the field of condensed matter physics, as new quantum materials, topological semimetals have a special topological energy band structure and nontrivial band crossings in the energy band, which will have many excellent topological properties, such as internal insulation of topological insulators and the presence of conduction electrons on the surface; this makes topological semimetals exhibit wider application prospects in electronic devices. So far, the experimental synthesis of topological semimetals was performed using physical methods to synthesize bulk single crystals, which is not conducive to the commercial application of micro and small devices. Weyl semimetal Co3Sn2S2 with shandite structure was successfully synthesized experimentally by a green and environmentally friendly hydrothermal method. Adjusting its reaction temperature, molar atomic ratio of elements and annealing temperature, and other experimental conditions, we analyze the crystal structure and physical properties of Co3Sn2S2, with the nanocrystal size being about 200 nm. We found that the Co3Sn2S2 synthesized by the hydrothermal method has a Curie temperature at 100 K to undergo ferromagnetic transition. [ABSTRACT FROM AUTHOR]

As a promising surface treatment technique, the surface mechanical attrition treatment (SMAT) has been applied to enhance mechanical properties of various materials. Through multidirectional severe plastic deformation, SMAT is able to nanocrystallize the near surface region of materials. The nanostructured layer associated with high compressive residual stresses coupled with a work hardening layer can provide the treated materials with an improved fatigue resistance. The present work gives a comprehensive review on the fatigue strength of SMATed materials. First of all, a brief introduction is given on the basic elements of SMAT and surface modifications induced by this treatment. The fatigue strength of a large variety of SMATed materials with different loading conditions is reviewed, including low-cycle fatigue (LCF), high-cycle fatigue (HCF) and very-high-cycle fatigue (VHCF). Then, the mechanism of enhancement or reduction is explained through a detailed review on the effects of several factors, such as residual stress, surface quality and nanocrystalline grains. In addition, the combined effect of SMAT coupled with other processes is also reviewed. Trends and prospects of the current research are summarized at the end. [ABSTRACT FROM AUTHOR]

Alluaudite-type materials are systematically attracting more attention as prospective cathode materials for sodium-ion batteries. It has been demonstrated that optimized thermal nanocrystallization of glassy analogs of various cathode materials may lead to a significant increase in their electrical conductivity. In this paper, three alluaudite-like glasses (Na 2 Fe 3 (PO 4 ) 3 —FFF, Na 2 VFe 2 (PO 4 ) 3 —VFF, and Na 2 VFeMn(PO 4 ) 3 —VFM) were synthesized and subjected to an optimized thermal nanocrystallization. This procedure resulted in nanostructured samples with increased electrical conductivity at room temperature: 5 × 10 − 7 S/cm (FFF), 7 × 10 − 5 S/cm (VFM), and 6 × 10 − 4 S/cm (VFF). The nanocrystalline microstructure was also evidenced by ultra-high-frequency impedance spectroscopy (up to 10 GHz) and proposed electrical equivalent circuits. Prototype electrochemical cells were assembled and characterized with voltage cutoffs of 1.5 and 4.5 V. The electrochemical performance was, however, modest. The gravimetric capacity varied between the studied materials, but did not exceed 35 mAh/g. Capacity retention after ca. 100 cycles was satisfactory. Further optimization of the residual-glass-to-nanocrystallite volume ratio would be desirable. [ABSTRACT FROM AUTHOR]

The microstructure evolution of Zr-1.1Nb-1.51Fe-0.26Cu-0.72Ni zirconium alloy, irradiated by 800 keV Kr2+ ions at 585 K using the IVEM-Tandem Facility at Argonne National Laboratory, was observed by in situ transmission electron microscopy. A number of β-Nb precipitates with a body-centered cubic (BCC) structure were distributed in the as-received zirconium alloy with micrometer-size grains. Kr2+ ion irradiation induced the growth of β-Nb precipitates, which could be attributed to the segregation of the dissolved niobium atoms in the zirconium lattice and the migration to the existing precipitates. The size of precipitates was increased with increasing Kr2+ ion fluence. During Kr2+ iron irradiation, the zirconium crystals without Nb precipitates tended to transform to the nanocrystals, which was not observed in the zirconium crystals with Nb nanoparticles. The existing Nb nanoparticles were the key factor that constrained the nanocrystallization of zirconium crystals. The thickness of the formed Zr-nanocrystal layer was about 300 nm, which was consistent with the depth of Kr2+ iron irradiation. The mechanism of the precipitate growth and the formation of zirconium nanocrystal was analyzed and discussed. [ABSTRACT FROM AUTHOR]

High-frequency impacting and rolling was applied on AZ31B magnesium alloy to obtain a gradient nano-structured surface. Surface characteristics were experimentally investigated, and the nanocrystallization mechanism is discussed in detail. Results showed that the gradient nano-structure with the characteristics of work hardening, compressive residual stress and a smooth surface was induced on the treated surface. Grains on the top surface were generally refined to around 20 nm. Twins, dislocations and dynamic recrystallization dominated the grain refinement process. Fatigue strength of the treated specimens corresponding to 107 cycles was increased by 28.6% compared to that of the as-received specimens. The work hardened layer induced by high-frequency impacting and rolling is the major reason to improve fatigue life. [ABSTRACT FROM AUTHOR]

This study showed that thermal nanocrystallization of glassy analogs of LiFe 1 − x Mn x PO 4 (with the addition of vanadium for improvement of glass forming properties) resulted in highly conducting materials that may be used as cathodes for Li-ion batteries. The glasses and nanomaterials were studied with differential thermal analysis, X-ray diffractometry, and impedance spectroscopy. The electrical conductivity of the nanocrystalline samples varied, depending on the composition. For x = 0.5 , it exceeded 10 − 3 S/cm at room temperature with an activation energy as low as 0.15 eV. The giant and irreversible increase in the conductivity was explained on the basis of Mott's theory of electron hopping and a core-shell concept. Electrochemical performance of the active material with x = 0.5 was also reported. [ABSTRACT FROM AUTHOR]

Multistable shells that have the ability to hold more than one stable configuration are promising for adaptive structures, especially for airfoil. In contrast to existing studies on bistable shells, which are well demonstrated by the Venus flytrap plant with the ability to feed itself, this work experimentally studies the aerodynamic response of various stable configurations of a nanostructure-induced multistable shell. This multistable shell is manufactured by using nanotechnology and surface mechanical attrition treatment (SMAT) to locally process nine circular zones in an original flat plate. The aerodynamic responses of eight stable configurations of the developed multistable shell, including four twisted configurations and four untwisted configurations with different cambers, are visually captured and quantitively measured in a wind tunnel. The results clearly demonstrate the feasibility of utilizing different controllable configurations to adjust the aerodynamic performance of the multistable shell. [ABSTRACT FROM AUTHOR]

Alluaudite-type materials are systematically attracting more attention as prospective cathode materials for sodium ion batteries. In this paper, we strove to optimize various synthesis parameters of three alluaudite compositions (Na 2 Fe 3 (PO 4 ) 3 —FFF, Na 2 VFe 2 (PO 4 ) 3 —VFF, and Na 2 VFeMn(PO 4 ) 3 —VFM) to obtain nanostructured alluaudite-type glass-ceramics with high phase purity. We systematically investigated the role of the chemical reactions, temperature and time of melting, cooling rate, and reducing factors on the quality of the final products. A detailed synthesis protocol along with X-ray diffractometry, thermal analysis, scanning electron microscopy imaging, and electrical conductivity measurements (with impedance spectroscopy) are reported. As a result, a significant increase of the conductivity was observed in the nanomaterials. The highest value was reached for the VFF composition and was equal to 6 × 10 − 4 S/cm at room temperature. [ABSTRACT FROM AUTHOR]

This review article presents recent studies on nanostructured glass-ceramic materials with substantially improved electrical (ionic or electronic) conductivity or with an extended temperature stability range of highly conducting high-temperature crystalline phases. Such materials were synthesized by the thermal nanocrystallization of selected electrically conducting oxide glasses. Various nanostructured systems have been described, including glass-ceramics based on ion conductive glasses (silver iodate and bismuth oxide ones) and electronic conductive glasses (vanadate-phosphate and olivine-like ones). Most systems under consideration have been studied with the practical aim of using them as electrode or solid electrolyte materials for rechargeable Li-ion, Na-ion, all-solid batteries, or solid oxide fuel cells. It has been shown that the conductivity enhancement of glass-ceramics is closely correlated with their dual microstructure, consisting of nanocrystallites (5–100 nm) confined in the glassy matrix. The disordered interfacial regions in those materials form "easy conduction" paths. It has also been shown that the glassy matrices may be a suitable environment for phases, which in bulk form are stable at high temperatures, and may exist when confined in nanograins embedded in the glassy matrix even at room temperature. Many complementary experimental techniques probing the electrical conductivity, long- and short-range structure, microstructure at the nanometer scale, or thermal transitions have been used to characterize the glass-ceramic systems under consideration. Their results have helped to explain the correlations between the microstructure and the properties of these systems. [ABSTRACT FROM AUTHOR]

In this work, a small amount of Nb has been added in a Zr52Cu42.5Al5.5 bulk metallic glass, and a Zr52Cu42Al5.5Nb0.5 bulk metallic glass composite with dual-amorphous and nanocrystal structures has been developed for the first time. This in situ formed bulk metallic glass composite has a larger room compressive plasticity of above 13% than that of the Zr52Cu42.5Al5.5 bulk metallic glass. The excellent plasticity of the bulk metallic glass composite is attributed to the phase-separated matrix with micro-nanocrystal and the nanocrystallization during the deforming process. This work may give a new sight into design bulk metallic glass composites and the underlying mechanism for deformation. [ABSTRACT FROM AUTHOR]

Wear failures of components often occur and cause great economic losses in modern industry production. To obtain excellent wear resistance surface will help reduce the abrasion. Herein, a wear-resistant iron-based alloy coating was deposited on a low-carbon steel substrate by argon arc overlaying, and sequentially surface nanocrystallized through ultrasonic impact treatment (UIT). Micro-structural, mechanical property (including nanohardness and elastic modulus) and wear behavior changes of the coating before and after UIT were experimentally investigated. In addition, the wear mechanism variation owing to the application of UIT was discussed. The results show that a highly deformed nanocrystalline layer with an average grain size in the range of ~100 nm was generated at a depth of approximately 34 μm from the treated coating surface, which contains a certain amount of the deformation-induced α'-martensite phase. Compared with the as-deposited coating, the coating after UIT processing exhibits considerable improvements in the ratio of nanohardness (H) to elastic modulus (E) and better wear resistance under the same wear test conditions. The wear mechanism has also changed from the adhesive type of the as-deposited coating to an abrasive type on the introduction of a nanocrystalline microstructure. [ABSTRACT FROM AUTHOR]

Red-flesh apples are known as functional fruits because of their rich anthocyanin. The anthocyanin content of the red flesh apple cultivar ′QN-5′ we bred can reach 361 mg·kg−1 (FW), and showed higher scavenging capacity to DPPH radicals, hydroxyl radicals, and superoxide anion radicals, with scavenging rates of 80.0%, 54.0%, and 43.3%, respectively. We used this particular anthocyanin-rich ′QN-5′ apple as material to examine how nanocrystallization affects the antixodiant effect of anthocyanin. The anthocyanin extract was encapsulated with biocompatible zein to form zein-anthocyanin nanoparticles (ZANPs). Transmission electron microscopy (TEM) scanning showed that ZANPs had a regular spherical shape with an average diameter size of 50–60nm. When the ratio of the zein and the anthocyanin was 1:0.5, the results suggested that the encapsulation efficiency (EE) of the ZANPs could reach as high as 92.8%, and that scavenging rate for DPPH radicals was increased from 87.1% to 97.2% compared to the non-nanocrystallized anthocyanin extract. Interestingly, treatment under alkaline conditions (pH 9.0), high temperature (90 °C), and a storage time of 7 days could decrease the scavenging capacity of the ZANPs for DPPH radicals, but this scavenging capacity loss for ZANPs was significantly lower than that observed in the non-nanocrystallized anthocyanin, suggesting the higher stability of ZANPs is caused by encapsulation. These results would provide a theoretical basis for the application of the anthocyanin in scavenging free radicals under stress conditions. [ABSTRACT FROM AUTHOR]

As an innovative surface technology for ultrahigh strain-rate plastic deformation, laser shock peening (LSP) was applied to the dual-phase TC11 titanium alloy to fabricate an amorphous and nanocrystalline surface layer at room temperature. X-ray diffraction, transmission electron microscopy, and high-resolution transmission electron microscopy (HRTEM) were used to investigate the microstructural evolution, and the deformation mechanism was discussed. The results showed that a surface nanostructured surface layer was synthesized after LSP treatment with adequate laser parameters. Simultaneously, the behavior of dislocations was also studied for different laser parameters. The rapid slipping, accumulation, annihilation, and rearrangement of dislocations under the laser-induced shock waves contributed greatly to the surface nanocrystallization. In addition, a 10 nm-thick amorphous structure layer was found through HRTEM in the top surface and the formation mechanism was attributed to the local temperature rising to the melting point, followed by its subsequent fast cooling. [ABSTRACT FROM AUTHOR]

The microstructure evolution of Zr-1.1Nb-1.51Fe-0.26Cu-0.72Ni zirconium alloy, irradiated by 800 keV Kr 2+ ions at 585 K using the IVEM-Tandem Facility at Argonne National Laboratory, was observed by in situ transmission electron microscopy. A number of β-Nb precipitates with a body-centered cubic (BCC) structure were distributed in the as-received zirconium alloy with micrometer-size grains. Kr 2+ ion irradiation induced the growth of β-Nb precipitates, which could be attributed to the segregation of the dissolved niobium atoms in the zirconium lattice and the migration to the existing precipitates. The size of precipitates was increased with increasing Kr 2+ ion fluence. During Kr 2+ iron irradiation, the zirconium crystals without Nb precipitates tended to transform to the nanocrystals, which was not observed in the zirconium crystals with Nb nanoparticles. The existing Nb nanoparticles were the key factor that constrained the nanocrystallization of zirconium crystals. The thickness of the formed Zr-nanocrystal layer was about 300 nm, which was consistent with the depth of Kr 2+ iron irradiation. The mechanism of the precipitate growth and the formation of zirconium nanocrystal was analyzed and discussed.