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Nanocrystalline tungsten-copper composites can favorably combine the outstanding material properties of both elements. This work investigates tungsten-copper composites fabricated from elemental powders with 80 wt.% tungsten and either copper or α-brass containing 20 wt.% zinc, respectively. Moreover, high-pressure torsion is used to compact the powders, strengthen the resulting composite by grain refinement, and tailor the grain-size in the nanocrystalline regime by varying the deformation temperature between RT, 400°C and 550°C, resulting in grain-sizes of 9 nm 14 nm and 28 nm, respectively. Hardness measurements revealed a transition from normal to inverse Hall-Petch behavior for grain-sizes below 11 nm. To examine the fracture properties, micro-cantilever bending beams with a cross-section of 10x10 µm2 were fabricated. Evaluation of these experiments indicated a fracture toughness of 3 MPam. The slight decrease of fracture toughness between a grain-size of 9 nm to 14 nm indicates a reduction of the grain boundary cohesion strength. The grain-size increase to 28 nm reversed the trend in fracture toughness and raised it to 3.4 MPam, which points to activating additional deformation mechanisms, such as dislocation-accumulation and twinning. Additionally, alloying with zinc raised the composites strength and retained the composites fracture toughness, benefiting the damage tolerance.

Multi-principal element alloys (MPEAs) are at the forefront of materials science due to their large variety of compositions, which can yield unexplored properties. Mapping the structure and properties of a compositional MPEA library in a reasonable time can be performed with the help of gradient samples. This type of specimens has already been produced in both bulk and layer forms. However, combinatorial MPEA coatings have not been synthesized by electroplating, although this method has a great potential to deposit a coating on components with complex shapes. In this study, a combinatorial Co-Fe-Ni-Zn coating with the thickness of 4 μm was synthesized by electrodeposition. The material exhibited a well-defined Zn gradient; therefore, the investigation of the effect of Zn concentration on the microstructure and mechanical properties was feasible without the production of an excessively large number of specimens. The Zn concentration was controlled laterally through mass transfer due to the unique geometry of the substrate, and it covered a concentration range of 18–44 at%. The chemical and phase compositions as well as the morphology of the as-processed samples were investigated in multiple locations using X-ray diffraction and scanning electron microscopy. The mechanical performance was characterized by nanoindentation. It was found that for any composition, the structure is face-centered cubic and the lattice constant scaled with the Zn concentration of the deposit. The hardness and the elastic modulus were consistent with values of about 4.5 and 130 GPa, respectively, in the Zn concentration range of 25–44 at%. [ABSTRACT FROM AUTHOR]

Multi-principal element alloys (MPEAs) are at the forefront of materials science due to their large variety of compositions, which can yield unexplored properties. Mapping the structure and properties of a compositional MPEA library in a reasonable time can be performed with the help of gradient samples. This type of specimens has already been produced in both bulk and layer forms. However, combinatorial MPEA coatings have not been synthesized by electroplating, although this method has a great potential to deposit a coating on components with complex shapes. In this study, a combinatorial Co-Fe-Ni-Zn coating with the thickness of 4 μm was synthesized by electrodeposition. The material exhibited a well-defined Zn gradient; therefore, the investigation of the effect of Zn concentration on the microstructure and mechanical properties was feasible without the production of an excessively large number of specimens. The Zn concentration was controlled laterally through mass transfer due to the unique geometry of the substrate, and it covered a concentration range of 18–44 at%. The chemical and phase compositions as well as the morphology of the as-processed samples were investigated in multiple locations using X-ray diffraction and scanning electron microscopy. The mechanical performance was characterized by nanoindentation. It was found that for any composition, the structure is face-centered cubic and the lattice constant scaled with the Zn concentration of the deposit. The hardness and the elastic modulus were consistent with values of about 4.5 and 130 GPa, respectively, in the Zn concentration range of 25–44 at%.

[Display omitted] • Grain-size tailoring of WCu and W-α-brass in the nc-regime by high-pressure torsion. • Young's modulus variation due to significant change of grain-boundary volume. • Assessing fracture characteristics by in-situ micro cantilever bending beams. • Improve of mechanical properties by alloying the copper phase with 10 wt.% zinc. Nanocrystalline tungsten-copper composites can favorably combine the outstanding material properties of both elements. This work investigates tungsten-copper composites fabricated from elemental powders with 80 wt.% tungsten and either copper or α -brass containing 20 wt.% zinc, respectively. Moreover, high-pressure torsion is used to compact the powders, strengthen the resulting composite by grain refinement, and tailor the grain-size in the nanocrystalline regime by varying the deformation temperature between RT, 400°C and 550°C, resulting in grain-sizes of 9 nm 14 nm and 28 nm, respectively. Hardness measurements revealed a transition from normal to inverse Hall-Petch behavior for grain-sizes below 11 nm. To examine the fracture properties, micro-cantilever bending beams with a cross-section of 10x10 µm2 were fabricated. Evaluation of these experiments indicated a fracture toughness of 3 MPa m . The slight decrease of fracture toughness between a grain-size of 9 nm to 14 nm indicates a reduction of the grain boundary cohesion strength. The grain-size increase to 28 nm reversed the trend in fracture toughness and raised it to 3.4 MPa m , which points to activating additional deformation mechanisms, such as dislocation-accumulation and twinning. Additionally, alloying with zinc raised the composites strength and retained the composites fracture toughness, benefiting the damage tolerance. [ABSTRACT FROM AUTHOR]

A nano-scale crack tip around 500 nm wide introduced by femtosecond laser still affects the accuracy of fracture toughness K IC measurements of 3Y-TZP zirconia ceramics with average grain size G from 200 to 500 nm. A simple formula was proposed to estimate the additive effect of crack-tip damage zones from an infinitely sharp crack to a nano-scale blunt notch. The error in fracture toughness measurements is less than 8 % if the nano-scale crack-tip width < 0.5· G. The intrinsic K IC can be deduced from the simple formula if the nano-scale crack tip > 0.5· G. This study shows the same K IC was deduced from two different sets of 3Y-TZP measurements with nano- and micro-scale notches of 500 nm and 18 µm wide. Furthermore, the simple formula specifies the relation between the fracture toughness K IC and intrinsic strength f t via grain size G , which means K IC can also be estimated from f t and G without testing pre-cracked specimens. K IC values of 3Y-TZP from specimens with and without pre-cracks were compared. [ABSTRACT FROM AUTHOR]

Grain boundary interaction with second-phase particles having different degrees of coherency is investigated using the phase field crystal (PFC) method. Both the enveloping and pass-through mechanisms are studied with regards to grain boundary pressure, passage time and interface evolution. It is found that coherent particles exert a stronger retardation effect on grain boundaries compared to incoherent particles, with regards to both pressure and time, but also that this benefit is limited to a small range of misfit values. The simulations also show that the mobility is not a constant during particle passage, as commonly assumed, which means that grain boundary pressure cannot easily be extracted from the grain boundary velocity. Furthermore, the complex evolution of the pass-through mechanism and the transient behavior for intermediate coherencies is also investigated. The highest drag force is found to occur at the switching point between enveloping and pass-through. As part of the study, the advantages of using PFC for this type of analyses are also highlighted.

Severe plastic deformation changes the microstructure and properties of steels, which may be favourable for their use in structural components of nuclear reactors. In this study, high-pressure torsion (HPT) was used to refine the grain structure of Eurofer-97, a ferritic/martensitic steel. Electron microscopy and X-ray diffraction were used to characterise the microstructural changes. Following HPT at room temperature to a maximum shear strain of 230, the average grain size reduced by a factor of ∼30, with a marked increase in high-angle grain boundaries. Dislocation density also increased by more than one order of magnitude. The thermal stability of the deformed material was investigated via in-situ annealing during synchrotron X-ray diffraction. This revealed substantial recovery between 450 K – 800 K. Irradiation with 20 MeV Fe-ions to ∼0.1 dpa caused a 20% reduction in dislocation density compared to the as-deformed material. However, HPT deformation prior to irradiation only had a minor effect in mitigating the irradiation-induced reductions in thermal diffusivity and surface acoustic wave velocity of the material. Microstructural and material property changes are dominated by deformation compared to irradiation. In light of this, the benefits of using HPT to improve the irradiation resistance of Eurofer-97 are limited. These results provide a multi-faceted view of the changes in ferritic/martensitic steels due to severe plastic deformation, and how these changes can be used to alter material properties. [Display omitted] • High-pressure torsion of Eurofer-97 produced sub-100 nm grains. • Microstructural changes saturated by a shear strain value of 110. • Recovery of the deformed material occurred between 450 and 800 K. • Irradiation caused a reduction in dislocation density of the deformed material. • Deformed materials exhibited less irradiation-induced changes than the reference. [ABSTRACT FROM AUTHOR]

Mg0.5Zr2(PO4)3 is a promising electrolyte for Mg solid-state batteries. But it is difficult to achieve high-density thin films with phase purity. Here, we synthesized Mg0.5(1+x)FexZr2−x(PO4)3 nanopowders using liquid-feed flame spray pyrolysis and used the product to form transparent thin films via simple pressureless sintering at 1100 °C. The influence of Fe on the phase and microstructure were discussed and the bottlenecks during Mg2+ conduction pathway were calculated. The dense and high-purity Mg0.6Fe0.2Zr1.8(PO4)3 exhibited an extremely low ionic area specific resistance of 1.6 kΩ cm2 at 200 °C. This paper presents a method for preparing dense, high-purity solid electrolytes at modest sintering temperatures.

The microstructure and the fracture behavior of TiZrHfCoNiCu high entropy shape memory alloys with two different compositions were investigated. An unusual microstructure featuring pattern-forming nanoprecipitates was observed in dendritic and the interdendritic regions of both alloys. The unique higher-level order of these precipitates does not follow concentration gradients but is influenced by homogeneity and mechanical stress. The results also demonstrate that high entropy alloys are not necessarily homogeneous single-phase solid solutions. Moreover, it appears that solid solution strengthening as the primary mechanism also has to be questioned. Image, graphical abstract [ABSTRACT FROM AUTHOR]

We report a transition to large-strain, multi-slip plasticity in Mg alloys resulting from refinement of a single dimension of the deformation geometry to the ∼ 100 nm-scale. Basal-slip-dominated strain localisation and fracture is suppressed and shear strains greater than 200% are realised at ambient temperatures when one characteristic dimension is refined in an asymmetric wedge indentation, even when the other two dimensions remain macroscopic. The ductility at sub-critical scales of low dimensionality discovered here is independent of crystal orientation, and interfaces and large shear strains result in homogeneous nanocrystallinity in the deformed material under these conditions. [ABSTRACT FROM AUTHOR]

Fracture of metallic thin films during deformation hampers extensive applications of coated engineering components. In this study, the resistance to micro-crack initiation of Niobium (Nb) coatings deposited on stainless steel substrates is improved remarkably by tuning the substrate bias voltages during unbalanced magnetron sputtering. With the tailored nanocrystalline microstructure, the failure strain for coating fracture is increased to 30 %, which is far greater than that of previous metallic coatings (below 10 %). Microstructure characterizations reveal that intergranular nano-pinholes and amorphous phases can be eliminated effectively with a moderate ions bombardment effect to avoid brittle film fracture. At the same time, compact and homogenous nanocrystalline grains with appropriate intragranular defects are obtained via enhanced atom diffusivity during deposition. Therefore, large plastic deformation can be accommodated through both stress-driven grain coarsening and continuous dislocation plasticity, avoiding fracture of the Nb coatings. [Display omitted] [ABSTRACT FROM AUTHOR]

Multiphase Fe-based hardfacing alloys, for example Tristelle 5183 Fe-21%Cr-10%Ni-7.5%Nb-5%Si-2%C in wt.%, are extensively used for tribological applications, including valves, bearings and drive mechanisms, where two surfaces are unavoidably subjected to loaded sliding contact within engineering systems. In this study, transmission electron microscopy (TEM), scanning electron microscopy (SEM), and X-ray diffraction (XRD) were used to characterise, for the first time, the tribologically affected material induced by the self-mated sliding contact of HIPed Tristelle 5183. This provided novel insight into the deformation modes which permit the accumulation of the high levels of subsurface strain required for plasticity dominated (adhesive) wear in a commercial hardfacing. In the subsurface regions furthest from the sliding contact, plastic deformation is accommodated by deformation induced martensitic transformation to ϵ -martensite and α ′ -martensite, twinning, the generation of planar dislocation arrangements (generated by planar slip) and the generation of dislocation tangles. Closer to the sliding contact, the subsurface becomes unstable, and nanocrystallisation driven by grain boundary mediated deformation mechanisms and crystallographic slip completely engulf the near surface microstructure. It is postulated that nanocrystalisation within the subsurface is a needed in order to accommodate the extremely high strains required in order to permit tribological degradation via plasticity dominated wear. The extrusion of metallic slivers via plastic ratcheting generates ductile shear cracks governed by plastic strain, and the failure of these slivers generates plate/flake-like wear debris. [Display omitted] [ABSTRACT FROM AUTHOR]

Abstract A ternary immiscible nanostructured Cu-Al-Nb alloy was fabricated by friction stir processing of mechanically compacted pellets. Subsequently, aging was carried out at 563 K for various times. The material exhibited hardness of ~4.3 ± 0.1 GPa in the peak-aged condition (aging for 6 h), which is remarkable among Cu-based ternary immiscible alloys. The excellent strength of the material is attributed to Hall-Petch strengthening due to the extremely refined nanocrystalline structure, coupled with precipitation strengthening due to a uniform distribution of nano-scale Al- and Nb-rich precipitates or clusters, as confirmed by X-ray diffraction and microstructural characterization. Graphical abstract Unlabelled Image [ABSTRACT FROM AUTHOR]

Abstract Driven by bottom-up microstructure design approaches to enhance glass-ceramic mechanical performance, extensive molecular dynamics simulations on binary aluminosilicate (50Al 2 O 3 -50SiO 2) glasses with embedded circular and ellipsoidal nanocrystals have been conducted. Enhancement of fracture toughness K IC is widely observed and correlates with nanocrystal size, aspect ratio, relative position and angle of crystal surface to the crack tip. Crack penetration, deflection and nanocrystal cleavage are activated in different samples, leading to distinct variations in numerically measured K IC. The results provide building blocks for establishing a statistical model to encapsulate the cumulative effect of heterogeneous crystalline microstructures on the fracture behaviors in aluminosilicate glass-ceramics. Graphical abstract Unlabelled Image [ABSTRACT FROM AUTHOR]

Abstract Using first-principles computations we provide comprehensive energetics at zero Kelvin of Guinier-Preston zone (GPZ) formation and topologies of GPZs in two classical Al binaries: Al-Cu and Al-Ag. Without a priori geometric and morphological assumptions, we conclusively show that GPZs in Al-Cu prefer a planar arrangement of {100} layers while GPZs in Al-Ag consist of clusters with {111} facets. We expand the model to 34 additional elements from the fourth and the fifth rows of the periodic table. The morphologies can be entirely related to directional nature and hybridization of Al 3 s and 3 p orbitals in the presence of secondary elements. Graphical abstract Unlabelled Image [ABSTRACT FROM AUTHOR]

Abstract Conventional arc-melting and casting is the most widely used synthesis method of high-entropy alloys (HEAs). However, the extremely high melting temperature and repetitious melting processes cause the evaporation of some constituent elements with a low melting temperature, resulting in inaccurateness of composition. In this work, in-situ high throughput synthesis of FeCoNiCrCuAl x was carried out in the transmission electron microscope. The dynamic melting process of FeCoNiCrCu with Al was recorded, and the composition of FeCoNiCrCuAl x was examined by an energy dispersive spectrometer. The in-situ high throughput method provides a novel way to prepare HEA samples efficiently. Graphical abstract Unlabelled Image [ABSTRACT FROM AUTHOR]

An innovative multistage heat treatment, that combines Bainitization and Quenching & Partitioning processes (BQ&P) can be applied to obtain multiphase microstructure in the carburized surface layer comprising nanobainite, ultra-fine martensite and retained austenite. In this study, a carburized medium-carbon Cr-Si-Mn alloyed steel was treated by BQ&P treatments with 20%, 40% and 100% of advancement of bainitic transformation in the top surface to investigate the effect of isothermal holding time on microstructure evolution and properties.Extending the bainitization time leads to an increase in the bainitic ferrite content in the microstructure and more significant fragmentation of the residual austenite blocks. It was shown that multiphase microstructure consisting of nanobainite, ultra-fine martensite and retained austenite results in the higher hardness and wear resistance of the case as compared to the fully bainitic microstructure. The enhanced properties results from the strengthening effect of additional martensite fraction and higher amount of stabilized austenite prone to transformation under friction (transformation induced plasticity, TRIP effect). Furthermore, adjusted parameters of the process lead to favorable mechanical properties in a medium-carbon core (YS ∼ 1430 MPa, UTS ∼ 1820 MPa, KV ∼ 20 Jcm−2). The ability to tailor mechanical and service properties of steel by controlling the fraction of particular phases along with a significant reduction of heat treatment time might designate the BQ&P process to industrial application, e.g. carburized gear wheels. [Display omitted] • Bainitization Quenching&Partitioning treatment was proposed for carburized steel. • Shortening time of Bainitization enhances properties of carburized surface and core. • The addition of martensite due to BQ&P improves wear resistance of nanobainite. • During friction retained austenite transforms into martensite increasing hardness. [ABSTRACT FROM AUTHOR]

Advanced microstructure investigations of the high-burnup structure (HBS) in UO 2 produced by high-dose 84 MeV Xe ion irradiation are reported. Spark plasma sintered micro-grained UO 2 was irradiated to 1357 dpa at 350 °C. The characteristic nano-grains and micro-pores of the HBS were formed. The grain size and grain boundary misorientation distributions of the HBS were measured using transmission electron microscopy based orientation imaging microscopy. Grain polygonization due to accumulation of radiation-induced dislocations was found to be the mechanism of nano-crystallization. The morphology of Xe bubbles was quantitatively investigated. This study provides crucial references for advanced fuel performance modeling of high-burnup UO 2 . [ABSTRACT FROM AUTHOR]

The early stage athermal electromigration behavior at the heterogeneous interface of a Cu/Sn couple was investigated at room temperature. The material interaction formed an interphase consisting of an amorphous Cu-Sn matrix, enriched with Cu (87.6–93.4 at.% Cu) and embedded with a few nano-crystalline Cu cells. The Cu-rich characteristic of the interphase indicates atypical interdiffusion behavior. The formation of the interphase was governed by the electrodisruption of the cathode Cu lattices accompanying the interdiffusion between Cu and Sn atoms. The occurrence of the meta-stable interphase is believed to be a preliminary stage prior to the subsequent intermetallic formation. [ABSTRACT FROM AUTHOR]

Zn-Ni and Zn-Co alloy coatings were electrodeposited on mild steel from sulphate-based baths. The morphology, microstructure, microhardness and tribological behaviours of the coatings have been studied and discussed. While the Zn-5wt-% Co layers presented a nanocrystalline simple nodular structure (45 ± 5 nm), the Zn-14wt-% Ni showed a particular structure called cauliflower morphology (30 ± 7 nm). The X-ray diffraction analysis showed that each of the electrodeposits was formed from zinc solid solution with a uniform zinc-cobalt intermetallic phase γ2 (CoZn13) for Zn-5wt-% Co alloy. However, a single γ-phase (intermetallic compound Ni5Zn21) was presented for the Zn-14wt-% Ni alloys. The Zn-14wt-% Ni films were found to be harder and rougher than the Zn-5wt-% Co layers. Plastic deformation and oxide layers production were the main wear mechanisms for the investigated coatings. The Zn-14wt-% Ni coatings were found to have the best wear resistance due to their microhardness and particular structure. [ABSTRACT FROM AUTHOR]

We report the first successful densification of polycrystalline α-quartz. The innovative hydrothermal sintering process was used as a low temperature route on sol-gel silica nanoparticles (350 MPa, 300 °C, 90 min) in presence of water or aqueous sodium hydroxide solution (from 0.2 M up to 5 M). For the lowest NaOH concentrations, amorphous silica densification is observed, reaching a compactness of 86%. The basic physical-chemical mechanism proceeds through dissolution-precipitation. When NaOH concentration increases, the kinetics of dissolution are faster, nanoparticles totally dissolve and α-quartz is stabilized during precipitation. 98% dense α-quartz is obtained, the crystallite size increases with NaOH concentration. [ABSTRACT FROM AUTHOR]

In-situ transmission electron microscopy (TEM) is developed to observe the microstructure evolution during ultrasonic bonding. It was found that many nanoparticles were generated and moved around between the Al sheets' contact regions in a random way. Gaps between the joining partners were buried by the nanoparticles, which facilitated the formation of the bonded interface. It was shown that the in-situ TEM observation technique provides a new way to investigate the ultrasonic bonding process. [Display omitted] [ABSTRACT FROM AUTHOR]

Lithium-ion batteries with graphite anode have been utilized in a condition close to the theoretical capacity of graphite, and thus the application of current collector-free aluminum anode has been attempted for further increase in capacity because theoretical capacity of aluminum is 2.7 times larger than that of graphite. In this study, Al-2mass%Fe alloy was applied as a noble anode material, and found to possess better discharge capacity retention and Coulomb efficiency than those of 4N-purity aluminum. Such improvement of battery performance in Al-2mass%Fe anode is attributed to the formation of more stable reaction layers of randomly oriented nanocrystalline AlLi owing to finely dispersed intermetallic compounds of Al 6 Fe and Al 3 Fe. This result would expand application ranges of recycled aluminum containing larger amounts of impurity iron, with less future demand from foundry industries to be partly compensated. [Display omitted] [ABSTRACT FROM AUTHOR]

A Co Fe Ni Zn multi-principal element alloy (MPEA) film with the thickness of about 2.5 μm is processed by electrodeposition. The layer has a nanocrystalline microstructure with the grain size of about 12 nm as determined by transmission electron microscopy. The structure of the majority of the film is face-centered cubic (fcc); however, body-centered cubic (bcc) and amorphous phases with small fractions are also detected. The average hardness and elastic modulus of the coating are 9.2 and 197 GPa, respectively, as determined by nanoindentation. The hardness value is superior compared to other fcc MPEA layers processed by different deposition methods. The enhanced hardness can be attributed to the strengthening effect of the very small grain size and the presence of nanocrystalline bcc and amorphous minority phases. This study demonstrates the ability of electrodeposition for producing hard MPEA layers with the desired composition. • A Co–Fe–Ni–Zn multi-principal element alloy film was processed by electrodeposition. • The layer has a nanocrystalline microstructure with the grain size of about 12 nm. • Beside the major FCC phase, BCC and amorphous minority phases were detected. • The hardness was superior compared to other fcc MPEA layers. • The ability of electrodeposition for producing hard MPEA layers was demonstrated. [ABSTRACT FROM AUTHOR]

Multi-step nucleation catalyzed by a Ni–Si master alloy in Al–Si liquids was investigated. Instead of enhancing heterogeneous nucleation, the master alloy triggers pre-nucleation clusters before initiating stable phase nucleation. The pre-nucleation clusters manifest themselves by a high number density of nano-sized silicon particles with rhombohedral (9R, ABCBCACAB…) and hexagonal (2H, ABAB…) stacking sequences, which have higher energies than diamond-cubic phase. Thermal analysis in Al–Si alloys with different Si concentration and inoculation time shows the effect of pre-nucleation clusters varying with the amount of local ordering (NiSi) clusters. In addition, the growth of silicon crystal is changed due to the presence of pre-nucleation clusters by suppressing the twin plane re-entrant mechanism. [ABSTRACT FROM AUTHOR]

The evolution of the CP titanium microstructure at deformation by rolling at the temperature of 77 K in the range of 0.06–3 true strain has been investigated using light microscopy, transmission electron microscopy and X-ray analysis. Role of deformation twinning as the main mechanism responsible for the fragmentation of grains and formation of the bulk nanocrystalline state is determined. We discovered a three-stage character of the grain refinement with increase in cryorolling reduction. It corresponds to stages of twinning process development. The limit of grain refinement in the processing of nanocrystalline titanium using the method of cryomechanical grain fragmentation is ~ 40 nm. It is due to a low probability of occurrence of twins in the grains with a size less than ~ 100 nm. The coincidence of the grain size and the crystallite size (coherent scattering regions) indicates that grains have a sufficiently perfect internal structure. It demonstrates that dislocations known to be a source of lattice distortion cannot be accumulated in nanoscale grains. It was shown that cryomechanical grain fragmentation (CMGF) is the effective method of processing a bulk nanocrystalline titanium (as well as zirconium). The mechanical properties of titanium have been characterized in three structural states: coarse-grained, ultrafine-grained and nanocrystalline. [ABSTRACT FROM AUTHOR]

Cubic and hexagonal zinc sulphide nanoparticles were prepared by hydro/solvothermal decomposition of Zinc N,N-diethyldithiocarbamate by using different experimental conditions such as pH values, solvents and the presence of a particle stabilizer, sodium polyacrylate. The effect of these different experimental conditions on the microstructure and photocatalytical efficiency of ZnS was investigated in this work. Microstructural parameters, such as, apparent mean crystal size, microstrain and crystal size distribution were determined by analysis of experimental X-ray diffraction. Apparent mean crystal sizes were in the range of 6.5–44 nm and the lattice microstrain varied from 0.24% to 0%. Dimethylformamide showed to be more suitable than water to form small particles with a very narrow size distribution. The obtained optical band gaps and Urbach energies were in range of 3.32–3.60 eV and 0.09–0.15 eV, respectively. Photoluminescence spectra showed strong visible light emissions (green, blue and white) associated to the electronic levels introduced by the presence of superficial defects. The photocatalytic efficiency of these samples was investigated towards methylene blue degradation and a correlation between this efficiency and the PL intensity was observed. This correlation was associated to the formation of surface active centres at catalyst surfaces and the local potential fluctuations of valence and conduction bands. [ABSTRACT FROM AUTHOR]

The microstructure and chemical composition of white layers (WLs) formed during hard turning of AISI 52100 steel were studied using atom probe tomography (APT) and transmission electron microscopy (TEM). APT analyses revealed a major difference in the re-distribution of the carbon (C) atoms between WLs formed above and below the A c1 temperature, i.e. T-WL and M-WL, respectively. In T-WL, the C-atoms segregate to grain boundaries (GBs) forming interconnected or isolated C-rich clusters, ∼5 nm, with a concentration of 9.8 ± 0.3 at.%C. Apart from the GB segregation, in M-WLs, large C-rich regions were found with 24.8 ± 0.4 at.%C. Owing to the chemical composition (stoichiometry) and element partitioning of such regions, they were assigned as θ -carbides (cementite). The APT results reveal that the original θ -carbides remain un-dissolved in the M-WLs, but might be plastically deformed due to the excessive strain that exists in hard machining process. The obtained results are in good agreement with the temperatures that are reached during formation of M-WLs. The isolated nano-sized C-clusters were assigned as off-stoichiometric carbides whereas the interconnected C-rich clusters were attributed to Cottrell atmospheres, evident by the linear shape of the C-enrichment as observed in the APT reconstructions. The C-contents in the nano-sized martensitic and ferritic grains were estimated to 0.50 ± 0.06 at.%C and ∼0.46 ± 0.02 at.%C, respectively. The C-content in the ferritic grains, beyond the C-solubility limit in ferrite (<0.1 at.%) is governed by the high dislocation density inside the grains, supported by the favorable binding energy between dislocations and C-atoms compared to C-atoms and Fe in carbides. No other evidence of redistribution of the substitutional alloying elements was observed. TEM analyses showed that T-WLs comprises of an equiaxed and nano-sized grains with well-defined cell boundaries, whereas the structure in the M-WLs comprised of elongated sub-grains formed via re-orientation of the original martensite followed by breakage/partitioning into elongated sub-grains. [ABSTRACT FROM AUTHOR]

For the control and study of the post-implantation biomechanical processes of TiAl6V4 implants, the ability of wireless in vivo measurement of various parameters (i.e., temperature in this case) at the tissue–implant interface is required. Compared with other types of sensors, which consist of sensing and transmitting elements, nanocrystalline magnetic glass-coated microwires combine both of these features into unit. Thanks to a Pyrex coating, the microwires are biocompatible, and due to their size, they do not intervene into the surface structures of implants. The studied as-cast microwire has a low Curie temperature due to the high amount of molybdenum, and is not magnetically bistable at room temperature. In order to create its bistability at room temperature and enhance its temperature sensitivity in the range from 37 °C up to 42 °C, the microwire is specially annealed under axial stress above crystallization temperature. Extreme temperature sensitivity in the required temperature range is achieved using the superparamagnetism effect; moreover, due to this effect, the switching field increased in an almost linear way. The temperature dependence of the switching field is employed to sense the temperature in two TiAl6V4 samples produced by additive manufacturing and representing implants with different types of fixations of the microwire onto the surface. Sensitivity up to 0.01 K is achieved. [ABSTRACT FROM PUBLISHER]

We have investigated the physical origin of anomalous in-plane thermal expansion (TE) anisotropy leading to invar-like behavior and negative TE in nanostructured NiTi sheets manufactured via severe cold-rolling. The roles of grain size (GS), crystallographic texture, thermally-induced phase transformation, and intrinsic (lattice level) TE of austenite (B2) and martensite (B19′) phases on the macroscopic TE behavior are addressed. It is shown that by controlling the cold-rolling thickness reduction and heat-treatment temperature the coefficient of thermal expansion (CTE) can be controlled in a wide range from positive ( α ∼ 2.1 × 10 −5 K −1 ) to negative ( α ∼ −1.1 × 10 −5 K −1 ) via in-plane anisotropy of TE. A very small CTE of α ∼ −5.3 × 10 −7 K −1 (invar-like behavior) in a wide temperature window of 230 K (353–123 K) is obtained at an angle of 33.5° to the rolling direction (RD) of the severely cold-rolled sheet. TEM and XRD studies show that the microstructure underlying such anomalous TE behavior consists of a mixture of B2 nano-grains and retained/residual deformation-induced martensite and that the observed anomalous TE anisotropy is due to the intrinsic anisotropic TE of residual martensite. The invar-like behavior is the result of the cancellation of the positive TE of austenite phase with the negative TE of residual martensite along 33.5° to the RD. A simple rule of mixture model incorporating the intrinsic TE of B2 and B19′ lattices and the texture coefficients of the sample is proposed which successfully captures the anomalous in-plane TE anisotropy. The discovery of high dimensional stability over a wide temperature window along with temperature insensitive non-hysteretic linear superelasticity of the severely-deformed NiTi opens up a new route for designing stable SMAs for applications in ragged environments. [ABSTRACT FROM AUTHOR]

Low Young's modulus β-type titanium alloys, such as the Ti–45Nb alloy, with elastic properties close to that of human bone containing non-toxic elements are very desirable for load bearing implants. Their relatively low hardness and strength can be significantly increased by severe plastic deformation (SPD) methods, for example high pressure torsion (HPT). To gain a better understanding of the fatigue characteristics, the fatigue crack growth (FCG) behavior of Ti–45Nb was investigated in various microstructural states (as-received, HPT-deformed, HPT + cold-rolled, HPT + heat-treated). Compact tension (CT) specimens with different crack orientations were tested at different load ratios under tension-tension loading. The microstructure of the HPT and HPT + cold-rolled material shows highly elongated grains parallel to the principal deformation direction with grain sizes in the nanocrystalline regime. Compared to the majority of studies on FCG of SPD-processed materials this titanium alloy exhibits a remarkably weak anisotropy in the FCG-behavior in all material states but especially in the HPT and the cold-rolled state. This is mainly attributed to the transcrystalline fracture mode. The threshold of fatigue crack growth was found to decrease with increasing load ratio. This is related to a lower contribution of plasticity-induced crack closure at higher load ratios. [ABSTRACT FROM AUTHOR]

Surface templating of nano-multilayers is a promising step for the advanced industrial application of these nanomaterials. In the present work, the effect of focused ion beam modification of Ag/AlN nano-multilayer near-surface region on the Ag surface outflow is revealed. Surface patterning by ion beam irradiation leads to the formation of a higher amount of Ag crystals in relation to the intact surface region. Heat treatment initiates grooving of Ag grain boundaries, resulting in the formation of channels in the nano-multilayer volume. These channels act as pathways for mass transport of Ag to the film surface. Ion bombardment creates regions of high concentration of non-equilibrium defects, which locally increase the driving force for grooving and channeling, thereby promoting creation of more pathways for Ag surface migration. The obtained experimental results indicate that surface modification by focused ion beam can be used for production of nano-multilayers with designed templates of surface outflow. • Ag crystals are formed on the nano-multilayer surface upon high-vacuum annealing. • The HeFIB surface modification results in a higher density of Ag crystals. • Annealing induces formation of channels in the nano-multilayer volume. [ABSTRACT FROM AUTHOR]

W pracy przedstawiono wyniki badań mikrostruktury i wybranych właściwości polikrystalicznego aluminium i jego stopów: AlMg5, AlCu4Zr0.5, AlZn6Mg2.5CuZr ściskanych dynamicznie za pomocą młota spadowego. Próbki odkształcano w zakresie odkształceń rzeczywistych = 0-0.62 z prędkością odkształcenia z zakresu 1.77-6.06x102 s-1. Na tak odkształconych materiałach przeprowadzono pomiar mikrotwardości oraz badania mikrostruktury przy zastosowaniu transmisyjnego mikrosko- pu elektronowego (TEM) i mikroskopu świetlnego (LM), dodatkowo przeprowadzono pomiar dezorientacji w mikroobszarach metodą linii Kikuchiego przy zastosowaniu oprogramowania KILIN. Cechą charakterystyczną mikrostruktury badanych materiałów były licznie obserwowane pasma i pasma ścinania. Wyniki uzyskane przy zastosowaniu transmisyjnego mikroskopu elektronowego dowiodły występowania licznych mikropasm i mikro- pasm ścinania, które w zależności od materiału przebiegały na tle różnych układów dyslokacyjnych. Obserwowane mikropasma wykazywały dużą dezorientację względem osnowy. Stwierdzono wzajemnie przecinanie się mikropasm. W zakresie wyższych wartości odkształcenia, mikropasma wypełniały niemal całą objętość próbek. Zaobserwowano zależność zmniejszania się średniej szerokości i mikropasm wraz ze wzrostem wielkości odkształcenia i prędkości odkształcenia. Praca miała na celu określenie wpływu prędkości odkształcenia (1.77x10' - 6.06xl02s_1) na możliwość rozdrobnienia mikrostruktury polikrystalicznego aluminium A199.5 i jego stopów (AlMg5, AlCu4Zr0.5, AlZn6Mg2.5CuZr) odkształcanych w procesie dynamicznego ściskania za pomocą młota spadowego.

Grain growth in two- and three-dimensional nanocrystalline materials is modeled by modifying the Monte Carlo Potts method based on the assumption that grain boundaries as well as triple junctions can be rate limiting during coarsening. To that aim each type of junction-associated lattice points (grain boundary-associated and triple junction-associated) is assigned an own specific mobility and energy. For the first time the influence of triple point (in 2D) and triple line (in 3D) energy and mobility on the grain growth kinetics is shown in detail. The results deviate clearly from normal grain growth kinetics but are in agreement with experimental studies as well as theoretical predictions. [ABSTRACT FROM AUTHOR]

Complex investigations of the thermal stability as well as Mn-dopant distribution depending on chemical composition and processing condition have been performed in heavily doped SrTi 1-x Mn x O 3 nanoparticles with x = 0.2 and 0.4. Prepared nanopowders reveal stable enough cubic perovskite structure even after treatment in oxidizing atmosphere up to 1000 °C. At the same time treatment in reducing atmosphere leads to decrease of the Mn solubility limit. Mn distribution evidences a weak tendency of Mn ions to migrate to surface. This migration increases in air and decreases at treatment in oxygen atmosphere. [ABSTRACT FROM AUTHOR]

The correlation between the thermoluminescence (TL) response of nanocrystalline LiF and its microstructure was studied. To investigate the detailed TL mechanism, the glow curves of nanocrystalline LiF samples produced by high-energy ball-milling were analyzed. The microstructure of the prepared samples was analyzed by synchrotron X-ray powder diffraction (XRPD) at room temperature. Then, the microstructure of a representative pulverized sample was investigated in detail by performing in situ XRPD in both isothermal and non-isothermal modes. In the present study, the dislocations produced by ball-milling alter the microstructure of the lattice where the relative concentration of the vacancies, responsible for the TL response, changes with milling time. An enhancement in the TL response was recorded for nanocrystalline LiF at high-temperature traps (after dislocations recovery starts >425 K). It is also found that vacancies are playing a major role in the dislocations recovery mechanism. Moreover, the interactions among vacancies-dislocations and/or dislocations-dislocations weaken the TL response. [ABSTRACT FROM AUTHOR]

A local electrode atom probe has been employed to trace the onset of Cu clustering followed by their coarsening and subsequent growth upon rapid (10 s) annealing of an amorphous Fe 73.5 Si 15.5 Cu 1 Nb 3 B 7 alloy. It has been found that the clustering of Cu atoms introduces heterogeneities in the amorphous matrix, leading to the formation of Fe rich regions which crystallizes pseudo-homogeneously into Fe–Si nanocrystals upon annealing. In this paper, we present the data treatment method that allows for the visualization of these different phases and to understand their morphology while still quantifying them in terms of their size, number density and volume fraction. The crystallite size of Fe–Si nanocrystals as estimated from the atom probe data are found to be in good agreement with other complementary techniques like XRD and TEM, emphasizing the importance of this approach towards accurate structural analysis. In addition, a composition driven data segmentation approach has been attempted to determine and distinguish nanocrystalline regions from the remaining amorphous matrix. Such an analysis introduces the possibility of retrieving crystallographic information from extremely fine (2–4 nm sized) nanocrystalline regions of very low volume fraction (< 5 Vol%) thereby providing crucial in-sights into the chemical heterogeneity induced crystallization process of amorphous materials. [ABSTRACT FROM AUTHOR]

The analytic modeling and one experimental assess of the ultrasonic surface mechanical attrition treatment are presented. The bombarding ball speed, induced energy, hardness and grain size are incorporated into this model, based on harmonic longitudinal vibration motion of ultrasonic-wave-driven impact. There appear some optimum attrition working parameters for the best attrition effect; beyond which, the sample surface would be subject to bombarding microcracking and the grain size would not be further reduced. The benefits from attrition would become lower. [ABSTRACT FROM AUTHOR]

The strategy of diatomic synergy is applied to the in-situ synthesis of electrode catalyst material for methanol fuel cells. During the one-pot synthesis in hydrothermal conditions, the doped Bi and Mn atoms are highly dispersed on and immobilized into the SOD zeolite cage structure as nanocrystals with trace amounts to form the novel Bi/Mn/SOD composite catalyst. The as-synthesized Bi and Mn NPs were confined in a rigid SOD nano-cage to maintain the stability and catalytic activity of the monodisperse state. Several key problems to be solved in methanol fuel cell applications are its energy density, catalytic efficiency, stability, and cost. Through the combined action of Mn and Bi, the composite electrode performed high activity in the methanol oxidation reaction (MOR) with a high current density of 45.9 mA cm−2 without precious metal and with high stability in 10 M methanol without any catalyst poisoning. [ABSTRACT FROM AUTHOR]

[Display omitted] • Grain boundary and particle interaction is studied by the phase field crystal method. • Novel details on grain boundary passage by particle cutting are provided. • Grain boundary retardation is found to be stronger for coherent particles. • The highest drag force occurs at the switching point between the two mechanisms. Grain boundary interaction with second-phase particles having different degrees of coherency is investigated using the phase field crystal (PFC) method. Both the enveloping and pass-through mechanisms are studied with regards to grain boundary pressure, passage time and interface evolution. It is found that coherent particles exert a stronger retardation effect on grain boundaries compared to incoherent particles, with regards to both pressure and time, but also that this benefit is limited to a small range of misfit values. The simulations also show that the mobility is not a constant during particle passage, as commonly assumed, which means that grain boundary pressure cannot easily be extracted from the grain boundary velocity. Furthermore, the complex evolution of the pass-through mechanism and the transient behavior for intermediate coherencies is also investigated. The highest drag force is found to occur at the switching point between enveloping and pass-through. As part of the study, the advantages of using PFC for this type of analyses are also highlighted. [ABSTRACT FROM AUTHOR]

Stress-induced martensite always exhibits an oriented microstructure, which leads to mechanical anisotropy in NiTi alloys. In this study, the effects of grain size on the microstructure and mechanical anisotropy of stress-induced-martensitic NiTi were investigated. Nanocrystalline NiTi exhibited single-variant and twin-free nanograins; ultrafine-grained NiTi exhibited (111) m type І, (2 ‾ 01) deformation twins, (100) deformation twins and (001) m compound twins. Microstructural differences suggest that the nanocrystalline and ultrafine-grained alloys had different textures, grains were reoriented, and alloy deformed plastically upon indentation loading. Stress-induced nanocrystalline martensitic NiTi exhibited considerably stronger elastic-modulus anisotropy than ultrafine-grained NiTi when a lower indentation load was applied, whereas stress-induced ultrafine-grained martensitic NiTi exhibited stronger hardness anisotropy. [ABSTRACT FROM AUTHOR]

A phenomenological approach to model the size effect observed during grain growth in nanocrystalline materials is presented. To that aim, the standard Monte Carlo Potts model is modified such that the mobility of grain boundaries depends on their triple junction distance. For initially very small grains growth kinetics are observed that are in agreement with experimental results, theoretical predictions and another simulation approach using a direct modification of the triple junction mobilities. [ABSTRACT FROM AUTHOR]

Abstract: Rapid annealing (4–10s) induced primary crystallization of soft magnetic Fe–Si nanocrystals in a Fe73.5Si15.5Cu1Nb3B7 amorphous alloy has been systematically studied by atom probe tomography in comparison with conventional annealing (30–60min). It was found that the nanostructure obtained after rapid annealing is basically the same, irrespective of the different time scales of annealing. This underlines the crucial role of Cu during structure formation. Accordingly, the clustering of Cu atoms starts at least 50°C below the onset temperature of primary crystallization. As a consequence, coarsening of Cu atomic clusters also starts prior to crystallization, resulting in a reduction of available nucleation sites during Fe–Si nanocrystallization. Furthermore, the experimental results explicitly show that these Cu clusters initially induce a local enrichment of Fe and Si in the amorphous matrix. These local chemical heterogeneities are proposed to be the actual nuclei for subsequent nanocrystallization. Nevertheless, rapid annealing in comparison with conventional annealing results in the formation of ∼30% smaller Fe–Si nanocrystals, but of identical structure, volume fraction and chemical composition, indicating the limited influence of thermal treatment on nanocrystallization, owing to the effect of Cu. [Copyright &y& Elsevier]

The mechanical properties of tilted AlN fiber structure caused by self-shadowing are investigated using gigahertz vibration induced through the piezoelectricity of AlN itself. We observed significant shear elastic softening in a highly tilted fiber nanostructure, but only a slight decrease in compressive elasticity. Abnormal 1/4 wavelength thickness mode resonance, indicating the decrease in the shear acoustic wave velocity, is reproducibly observed. We attribute this phenomenon to the weak fiber-to-fiber connection seen in a cross-sectional scanning electron microscopy image. [ABSTRACT FROM AUTHOR]

Abstract: This work quantifies the effect of grain size on grain boundary diffusivity. Diffusion of Au into Cu thin films of varying grain size is measured using secondary ion mass spectroscopy depth profiles. Appropriate models for fitting the composition profiles to analytical solutions to diffusion equations are identified by characterizing the microstructure both before and after the diffusion anneal. Finite-element numerical simulations are also employed to extract the diffusion coefficients directly from fits to experimental data. The results indicate that factors such as non-columnar grains, migrating grain boundaries, dislocations and stress gradients must be appropriately accounted for in order to obtain meaningful results. Overall, a strong scaling effect is not observed, which suggests that the atomic structure of boundaries in nanocrystalline thin-film materials probably resembles that of their coarse-grained counterparts. [Copyright &y& Elsevier]

Abstract: The process of mechanically activated disproportionation by ball milling in hydrogen and subsequent desorption–recombination has been proved to be a promising method to produce nanocrystalline NdFeB-type magnets. To ensure a fully recombinated microstructure with homogeneous nano-sized Nd2Fe14B grains, the desorption–recombination processing temperature and time should be properly selected or optimized. Thus, Monte Carlo (MC) simulation was performed to elucidate the effect of processing temperature on the kinetics of the recombination reaction to form Nd2Fe14B phase as well as the growth of the recombinated Nd2Fe14B grains. Based on the recombination reaction and grain growth mechanism of the disproportionated NdFeB alloy, a modified Monte Carlo (MC) model was introduced to simulate the kinetics of the reaction and grain growth behavior under various desorption–recombination processing conditions. The results show that the kinetics of both the recombination reaction and the growth of the newly formed Nd2Fe14B grains accelerate with increasing temperature. In particular, the recombination reaction of the disproportionated stoichiometrical Nd2Fe14B (atomic ratio) alloy can be completed in 30min at 800°C, with the grain size of the recombinated Nd2Fe14B phase being 35nm in average. After the finish of the recombination reaction, the growth of the Nd2Fe14B grains will proceed, with the growth rate or kinetics depending on the processing temperature. This paper presents an effective way to simulate the reaction progress and the grain growth during the desorption–recombination processing of nano-structured as-disproportionated NdFeB alloy, which is useful for process control and optimization. [Copyright &y& Elsevier]

Abstract: The non-isothermal kinetics of primary crystallization processes is studied from numerically generated curves and their predictions have been tested in several nanocrystallization processes. Single processes and transformations involving two overlapped processes in a non-isothermal regime have been generated and deviations from isokinetic behavior are found when the overlapped processes have different activation energies. In the case of overlapped processes competing for the same type of atoms, the heating rate dependence of the obtained Avrami exponent can supply information on the activation energies of each individual processes. The application to experimental data of nanocrystallization processes is consistent with a limited growth approximation. In the case of preexisting crystallites in the as-cast samples, predictions on the heating rate dependence of the obtained Avrami exponents of multiple processes have been confirmed. [Copyright &y& Elsevier]