Nanostructured metallic materials having nanocrystalline and ultrafine-grained structures show exceptional mechanical properties, e.g. superior strength, that are very attractive for various ...applications. However, superstrong metallic nanomaterials typically have low ductility at ambient temperatures, which significantly limits their applications. Nevertheless, several examples of nanostructured metals and alloys with concurrent high strength and good ductility have been reported. Such strong and ductile materials are ideal for a broad range of structural applications in transportation, medicine, energy, etc. Strong and ductile metallic nanomaterials are also important for functional applications where these properties are critical for the lifetime of nanomaterial-based devices. This article presents an overview of experimental data and theoretical concepts addressing the unique combination of superior strength and enhanced ductility of metallic nanomaterials. We consider the basic approaches and methods for simultaneously optimizing their strength and ductility, employing principal deformation mechanisms, crystallographic texture, chemical composition as well as second-phase nano-precipitates, carbon nanotubes and graphene. Examples of achieving such superior properties in industrial materials are reviewed and discussed.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
Mechanical strength and electrical conductivity are the most important properties of conducting metallic materials used in electrical engineering. Today, there is a growing need in this field for ...innovative conductor materials with improved properties. Meanwhile, the main issue is that high electrical conductivity and high strength are usually mutually exclusive due to physical nature of these properties. Alloying of pure metals results in significant increase of their mechanical strength, whereas electrical conductivity dramatically drops due to the scattering of electrons at solutes and precipitates. Recent studies have shown that intelligent nanostructural design in Al, Cu, and their alloys can improve combination of high mechanical strength with enhanced electrical conductivity. It was demonstrated that mechanical strength and electrical conductivity of these materials are primarily controlled by their microstructure, of which grain size, morphology of second phases, and their distribution, as well as dislocation structure, are the most important parameters. Rapid development of the state-of-the-art methods for the microstructural characterization at nano- and atomic scale has allowed a deeper insight into microstructure–properties relationship. The approach of intelligent nanostructural design of Al and Cu alloys has even enabled to increase the material strength with simultaneous improvement of its electrical conductivity. In this case, recent works on nanostructuring alloys by severe plastic deformation are of special interest, which gives rise to fundamental questions dealing with new mechanisms of strength and electrical conductivity as well as innovation potential of practical application of nanostructured materials. These issues are considered and discussed in the present progress article.
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DOBA, EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, IZUM, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, SIK, UILJ, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
Despite rosy prospects, the use of nanostructured metals and alloys as advanced structural and functional materials has remained controversial until recently. Only in recent years has a breakthrough ...been outlined in this area, associated both with development of new routes for the fabrication of bulk nanostructured materials and with investigation of the fundamental mechanisms that lead to the new properties of these materials. Although a deep understanding of these mechanisms is still a topic of basic research, pilot commercial products for medicine and microdevices are coming within reach of the market. This progress article discusses new concepts and principles of using severe plastic deformation (SPD) to fabricate bulk nanostructured metals with advanced properties. Special emphasis is laid on the relationship between microstructural features and properties, as well as the first applications of SPD-produced nanomaterials.
A novel method for calculating rate constants for internal conversion (
k
IC
) that simultaneously accounts for Duschinsky, anharmonic and Herzberg-Teller effects has been developed and implemented. ...This method has been applied to robust planar molecules like tetraoxa8circulene (
4B
), free-base porphyrin (
H
2
P
) and pyrometene (
PM567
) with small Duschinsky rotation (
i.e.
with almost identical normal coordinates in the ground and excited states) and to poly
n
fluorenes (
P
n
F
) (
n
= 2-14) with a substantial Duschinsky rotation. The obtained results show that the Duschinsky effect is large in the harmonic approximation, whereas it is in general much smaller in the anharmonic approximation. The Duschinsky effect is found to be large for high frequency vibrational modes with energies of ∼3300 cm
−1
such as the X-H (X = C, N and O) stretching modes that mix in the S
1
→ S
0
electronic transition. However, even in this case, the increase in
k
IC
due to the Duschinsky effect does not exceed one order of magnitude. The calculations show that anharmonic contributions to
k
IC
are larger than Herzberg-Teller contributions which in turn are larger than contributions from the Duschinsky effect ANH > HT > Du. We also show that an approximation, where only X-H bonds are considered in the
k
IC
calculation, is accurate even for
P
n
F
(
n
= 2-14).
A novel method for calculating rate constants for internal conversion (
k
IC
) that simultaneously accounts for Duschinsky, anharmonic and Herzberg-Teller effects has been developed and implemented.
•Physical-vapor deposited (PVD) coating was applied to Ultra-fine grained (UFG) Ti alloy.•PVD coating improves protective properties and provides higher endurance of UFG Ti alloy.•PVD coating on UFG ...Ti alloy has large increase in adhesive strength vs. when on coarse-grained alloy.•PVD-coated UFG Ti alloy exhibits high erosion resistance under gas-abrasive wear.
The paper presents the results of a study of the service properties of an ion-plasma protective coating deposited on a titanium substrate with an ultrafine-grained structure in the process of Physical vapor deposition (PVD). Data on the microhardness, adhesion strength, and erosion resistance of the ion-plasma coating on the Ti-6%Al-4%V alloy with the initial Coarse-grained (CG) structure and Ultrafine-grained (UFG) state produced by Severe plastic deformation (SPD) are presented. Data were also obtained on the long-term strength of cylindrical specimens in the UFG state with and without coating at the operating temperatures of this alloy. A significant increase in the service properties of the coating on the titanium alloy with an UFG structure was established in comparison with the properties of this coating on the original coarse-grained alloy. The physical nature of the increase in the properties of the coating on the UFG alloy is discussed and a hypothesis about the influence of the UFG state of the substrate on the fine microstructure and properties of the protective coating is considered.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
An efficient method for estimating non-adiabatic coupling matrix elements (NACME) and rate constants for internal conversion (
k
IC
) is presented. The method, based on Plotnikov's theory, requires ...only calculations of the electronic wave functions and the corresponding electronic excitation energies. Computationally expensive calculations of the derivatives of the electronic wave function with respect to the nuclear coordinates are avoided. When the main accepting modes of the electronic excitation energy are X
-
H vibrations, the present method can be used for estimating the efficiency of the energy transfer between donor and acceptor molecules. It can also be used in studies of the influence of hydrogen bonding or solvent effect on fluorescence quenching, in studies of vibronic effects of TADF (thermally activated delayed fluorescence) emitters, and for calculating
k
IC
. Here,
k
IC
and NACME are calculated for free-base porhyrin, magnesium porphyrin, azulene, naphthalene, pyrene and fluorenone interacting with a solvent molecule. Reverse
k
IC
and NACME are further calculated for the T
1
→ T
2
transition of dibenzothiophene-
S
,
S
-dioxide (PTZ-DBTO2), which is used in TADF applications. Finally, we estimate the efficiency of the energy transfer between two large porphyrinoid dimers.
An efficient method for estimating non-adiabatic coupling matrix elements (NACME) and rate constants for internal conversion (
k
IC
) is presented.
Lanthanide-doped upconversion nanoparticles (UCNPs) are promising for applications as wide as biological imaging, multimodal imaging, photodynamic therapy, volumetric displays, and solar cells. Yet, ...the weak and narrow absorption of lanthanide ions poses a fundamental limit of UCNPs to withhold their brightness, creating a long-standing hurdle for the field. Dye-sensitized UCNPs are emerging to address this performance-limiting problem, yielding up to thousands-fold brighter luminescence than conventional UCNPs without dye sensitization. In their configuration, organic dyes with spectrally broad and intense absorption are anchored to the surface of UCNPs to harvest the excitation light energy, which is then transferred via Förster and/or Dexter mechanisms across the organic/inorganic interface to the lanthanides incorporated in UCNPs (with or devoid of a shell) to empower efficient upconversion. This tutorial review highlights recent progress in the development of dye sensitized UCNPs, with an emphasis on the theory of energy transfer, the geometric classification of the dye sensitized core and core/shell nanocrystals, and their emerging photonic and biophotonic applications. Opportunities and challenges offered by dye sensitized UCNPs are also discussed.
The high strength and increased electrical conductivity of the Al alloys are highly desirable for their applications in power transmission lines. However, high strength and high electrical ...conductivity are mutually exclusive in metallic materials. A novel nanostructuring strategy is reported that achieves Al–Mg–Si alloys with superior tensile strength and enhanced electrical conductivity. The new strategy is based on a combination of grain refinement down to ultra-fine scale with accelerated formation of nanosized precipitates during severe plastic deformation.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
A new method for calculating internal conversion rate constants (
k&cmb.b.line;
IC
), including anharmonic effects and using the Lagrangian multiplier technique, is proposed. The deuteration effect ...on
k&cmb.b.line;
IC
is investigated for naphthalene, anthracene, free-base porphyrin (
H
2
P
) and tetraphenylporphyrin (
H
2
TPP
). The results show that anharmonic effects are important when calculating
k&cmb.b.line;
IC
for transitions between electronic states that are energetically separated (Δ
E
) by more than 20 000-25 000 cm
−1
. Anharmonic effects are also important when Δ
E
< 20 000-25 000 cm
−1
and when the accepting modes are X-H stretching vibrations with a frequency larger than 2000 cm
−1
. The calculations show that there is mixing between the S
1
and S
2
states of naphthalene induced by non-adiabatic interactions. The non-adiabatic interaction matrix element between the S
1
and S
2
states is 250 cm
−1
and 50 cm
−1
for the normal and fully deuterated naphthalene structure and this difference significantly affects the estimated fluorescence quantum yield. Besides aromatic hydrocarbons
H
2
P
and
H
2
TPP
, the
k&cmb.b.line;
IC
rate constant is also calculated for pyrometene (PM567) and tetraoxa8circulene (4B) with a detailed analysis of the effect of the vibrational anharmonicity.
A new method for calculating internal conversion rate constants (
k
IC
), including anharmonic effects and using the Lagrangian multiplier technique, is proposed.
Lanthanide-doped upconversion nanoparticles hold promises for bioimaging, solar cells, and volumetric displays. However, their emission brightness and excitation wavelength range are limited by the ...weak and narrowband absorption of lanthanide ions. Here, we introduce a concept of multistep cascade energy transfer, from broadly infrared-harvesting organic dyes to sensitizer ions in the shell of an epitaxially designed core/shell inorganic nanostructure, with a sequential nonradiative energy transfer to upconverting ion pairs in the core. We show that this concept, when implemented in a core–shell architecture with suppressed surface-related luminescence quenching, yields multiphoton (three-, four-, and five-photon) upconversion quantum efficiency as high as 19% (upconversion energy conversion efficiency of 9.3%, upconversion quantum yield of 4.8%), which is about ∼100 times higher than typically reported efficiency of upconversion at 800 nm in lanthanide-based nanostructures, along with a broad spectral range (over 150 nm) of infrared excitation and a large absorption cross-section of 1.47 × 10–14 cm2 per single nanoparticle. These features enable unprecedented three-photon upconversion (visible by naked eye as blue light) of an incoherent infrared light excitation with a power density comparable to that of solar irradiation at the Earth surface, having implications for broad applications of these organic–inorganic core/shell nanostructures with energy-cascaded upconversion.
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IJS, KILJ, NUK, PNG, UL, UM
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