Nanoscale Grain Research Articles

Improved low-temperature mechanical properties of FH36 marine steel after ultrasonic surface rolling process

The ultrasonic surface rolling process (USRP) was adopted to improve the low- temperature mechanical properties of FH36 marine steel for strengthening the service performance of marine steel in the low-temperature environment between − 30 °C and − 60 °C, such as polar regions. The results indicated that the surface integrity of FH36 marine steel was restructured as a result of the severe plastic deformation induced by USRP. The surface average grain diameter was refined from 10.92 µm to 5.86 µm with the number of nanoscale grains increased significantly and a nanostructured surface layer formed. The surface roughness decreased greatly with Ra not more than 0.074 µm. The surface residual compressive stress with an affected layer depth of not less than 2.6 mm was produced. The surface microhardness increased significantly with a large-depth work hardening layer of not less than 580 µm. The yield strength and ultimate tensile strength of FH36 marine steel after USRP at room temperature and low temperatures were enhanced. The combined effects of fine grain strengthening, dislocation strengthening, modified surface roughness, induced residual compressive stress, work hardening, and changed heat transfer performance caused by USRP were the main reasons for the improved low-temperature mechanical properties of FH36 marine steel.

Plasticity enhancement mechanism: Effect of the annealing temperature on strain-induced segmented martensitic transformations and Portevin–Le Chatelier bands in 7Mn steel after deep cryogenic treatment

This study investigated the microstructural evolution and strain localization of warm deformed Fe-0.15C-7Mn steel after deep cryogenic treatment (DCT) and intercritical annealing (IA) at 600, 630, and 660 °C. After DCT and IA, the steel contained nanoscale austenite grains with inhomogeneous thermal stability and grain size. Lüders bands appeared in all the samples, whereas the Portevin–Le Chatelier (PLC) effect only occurred in the samples annealed at 630 and 660 °C. The occurrence and initiation position of the PLC bands depended on the IA temperature, which affected the final grain size, retained austenite (RA) stability, and interactions between the solute atoms/C-Mn pairs and mobile dislocations. This indicates that segmented martensitic transformations occurred in the samples annealed at 600 and 630 °C, and the transformation sequence γ → ε → α’ occurred in the samples annealed at 630 and 660 °C. The segmented martensitic transformation depended on the IA temperature, which directly affected the amplitude of fluctuations in the Mn concentration in the RA grains and resulted in the heterogeneous thermal stability of the RA. The excellent uniaxial tensile properties of the samples were ascribed to the transformation of RA with heterogeneous thermal stability to segmented martensite during deformation. The segmented martensite acted as a protective shell that shielded the encapsulated austenite in the core. • Microstructural evolution and strain localization of a medium Mn steel were studied. • The annealing temperature affects the PLC bands and microstructural evolution. • Relationship between heterogeneous stability of RA and martensitic transformations. • Mechanisms underlying the observed physical properties were investigated. • Segmented martensite transformation behavior occurs and plays a protective role in the encapsulated austenite.

Photocatalytic and antibacterial properties of NaTaO3 nanofilms doping with Mg2+, Ca2+ and Sr2+

In this research, we prepared pure and alkaline earth metal elements (Mg2+, Ca2+ and Sr2+) doped NaTaO3 nanofilms by a simple hydrothermal method. Compared with traditional powder photocatalysts, they possess better stability and recycling performance, which makes them more practical in wastewater treatment. The as-prepared NaTaO3 crystals show nanoscale grain size that increases its redox ability owing to the small size effect and surface effect. After further introduction of Mg2+, Ca2+ and Sr2+, the band gaps were reduced to 2.83, 3.01 and 2.96 eV, respectively. Meanwhile, elemental doping induces a phase transition in the crystal structure of NaTaO3, creating an additional energy level that improves its responsiveness to visible light. According to the results, Mg-NaTaO3 catalyst possessed a higher photodegradation efficiency of 80.1 % for methylene blue solution under visible light irradiation. Furthermore, the photocatalytic bactericidal performance of different samples was investigated with Gram-positive and negative bacteria. In particular, the ROS (⋅O2–, ⋅OH, 1O2) induced by Mg-NaTaO3 could effectively destroy cell membranes, and the inhibition effect on E. coli and S. aureus reached 99.99 % within 50 min. Lastly, the results of cyclic photocatalytic experiments showed that Mg-NaTaO3 still had a high photodegradation capacity (75.2 %) and sterilization performance (98.8 %) after three cycles.

Magnetoelastic coupling behaviour of nanocrystalline ε-Fe2O3

Preparation of a ceramic sample which preserved the nanoscale grain sizes of ∼10–30 nm has allowed elastic and anelastic properties of ε-Fe2O3 to be investigated as functions of temperature and magnetic field strength by Resonant Ultrasound Spectroscopy in the frequency range ∼0.1–1 MHz. Formal analysis of spontaneous strains, e, from previously obtained high resolution lattice parameter data confirmed that magnetic ordering below ∼500 K is accompanied by strains of up to ∼±0.002 due to coupling with the order parameter, m, according to λem2. However, this coupling does not result in elastic softening that would be expected if the order parameter relaxed in response to an induced strain on the timescale of the acoustic resonances. Stiffening or softening during heating through ∼450–480 K of the initial as prepared material, which acquired a distinct magnetisation parallel to the stress applied during Spark Plasma Sintering, is attributed to changes in magnetic domain configurations involving preferred local alignments of individual moments of monodomain crystals. The crystallographic space group, Pna21, and magnetic space group at room temperature, Pna'21', allow ε-Fe2O3 to be both piezoelectric and piezomagnetic. It is postulated that changes in the effective coefficients of these properties for bulk samples are responsible for the observed variations in acoustic resonance frequencies according to the magnetic domain structure present. No elastic or anelastic anomalies were observed at the commensurate-incommensurate transition near 110 K. Instead, acoustic resonance frequencies changed in response to an applied magnetic field, consistent with viscous motion of magnetic domain walls and the effect of poling on piezo coefficients. Ceramic samples of ε-Fe2O3 could have potentially functional piezoelectric and/or piezomagnetic properties that are tunable by choice of magnetic and thermal history.

Nanoscale grain sizes in BNT-based ceramics with superb energy storage performances via coating boron nitride nanosheets

Electronic devices impose higher requirements on the energy storage performances of ceramic capacitors toward miniaturization and integration application in 5G industry. The micron ranges grain size of bulk ceramics severely constrains the improvement of the breakdown strength (BDS), which restricts the applicability of ceramic capacitors in terms of energy storage. However, it is still a long-standing challenge to achieve nanoscale ranges grain size of bulk ceramics. Herein, a novel strategy of all-inorganic nanocomposites ceramics by introducing BN nanosheets (BNNSs) is first time proposed to sharply reduce the grain sizes, leading to significantly enhance BDS. The BNNSs encircling BNST ceramic particles form the nano coating structure, which contributes to the record value of grain sizes ∼68.86 nm and ultrahigh BDS ∼640 kV/cm in Na0.325Bi0.395Sr0.245TiO3-0.005 BNNSs (BNST-0.005BN) ceramic. A combined phase-field simulation and experimental research is further performed to specifically investigate the effect of the ultrafine grain sizes on the BDS. Accordingly, the superior total energy density of 7.34 J/cm3 and recoverable energy density of 5.28 J/cm3 are attained at 640 kV/cm. More importantly, the present work provides an effective solution for the improvement of the energy storage performances of dielectric ceramics as well as the reduction of the co-fired temperature, which is anticipated to achieve extensive application in MLCCs field.

Size Ranges of Magnetic Domain States in Tetrataenite

AbstractPaleomagnetic studies of meteorites provide unique constraints on the evolution of magnetic fields in the early solar system. These studies rely on the identification of magnetic minerals that can retain stable magnetizations over ≳4.5 billion years (Ga). The ferromagnetic mineral tetrataenite (γ''‐Fe0.5Ni0.5) is found in iron, stony‐iron and chondrite meteorite groups. Nanoscale intergrowths of tetrataenite have been shown to carry records of paleomagnetic fields, although the effect of magnetostatic interactions on their magnetic remanence acquisition remains to be fully understood. Tetrataenite can also occur as isolated, non‐interacting, nanoscale grains in many meteorite groups, although the paleomagnetic potential of these grains is particularly poorly understood. Here, we aim to improve our understanding of tetrataenite magnetization to refine our knowledge of existing paleomagnetic analyses and broaden the spectrum of meteorite groups that can be used for future paleomagnetic studies. We present the results of analytical calculations and micromagnetic modeling of isolated tetrataenite grains with various geometries. We find that tetrataenite forms a stable single domain state at grain lengths between 6 and ∼160 nm dependent on its elongation. It also possesses a magnetization resistant to viscous remagnetization over the lifetime of the solar system at 293 K. At larger grain sizes, tetrataenite's lowest energy state is a lamellar two‐domain state, stable at Ga‐scale timescales. Unlike many other magnetic minerals, tetrataenite does not form a single‐vortex domain state due to its large uniaxial anisotropy. Our results show that single domain and two‐domain tetrataenite grains carry an extremely stable magnetization and therefore are promising for paleomagnetic studies.

Modeling ablator grain structure impacts in ICF implosions

High-density carbon is a leading ablator material for inertial confinement fusion (ICF). This and some other ablator materials have grain structure which is believed to introduce very small-scale (∼nm) density inhomogeneity. In principle, such inhomogeneity can affect key ICF metrics like fuel compression and yield, by, for example, acting as a seed for instabilities and inducing mix between ablator and fuel. However, assessments of such effects are uncertain due to the difficulty of modeling this small-scale structure in ICF simulations, typically requiring reduced-resolution modeling that scales these features. We present a grain model and show both the impact of de-resolving grains and the complex mixing dynamics such structures can induce. We find that different methods for de-resolving grains can yield both different total deposition of kinetic energy perturbations and different fuel–ablator mixing. We then show a simple-to-implement approach for approximately conserving the deposition of perturbed kinetic energy and demonstrate that, for the present grain model and test cases, this approach yields a reasonably matched time history of mix width between less and more resolved grain models. The simulations here also demonstrate the complex interaction history between grain-induced mixing and instability around the fuel–ablator interface, showing, for example, that the grain-induced perturbations typically trigger instability of conduction-driven density gradients in the DT fuel, enhancing mix penetration early in the acceleration of the shell. Simulating both microscale and nanoscale grains, we find initial evidence for larger mixing in the microscale case of the present model, despite smaller deposited kinetic energy perturbation.

Microstructure and photoluminescence properties of Er3+/LaBiO3 co-modified (K0.5Na0.5)NbO3 transparent textured ceramics via tape-casting method

A trade-off contradictory relationship between texturization and optical transparency exists in ferroelectric ceramics, so to achieve transparency in textured ferroelectrics is quite difficult. Here, Er3+ and LaBiO3 co-modified (K0.5Na0.5)NbO3 (1Er-KNN-yLB) transparent textured ceramics were successfully prepared by the tape-casting method. Doping of LaBiO3 enables the textured ceramics to exhibit excellent up-conversion photoluminescence properties, and the red emission is significantly improved. Meanwhile, with certain amount of LB content, the textured ceramics show nanoscale grains and approaching pseudo-cubic phase, resulting in high density and obvious relaxor-like behavior. This result indicates high local symmetry and less light scattering centers within the textured ceramics, finally bringing about enhanced optical transparency, with the highest transmittance of ∼ 39% in the visible region at y = 0.025. Additionally, the observable piezoelectric and ferroelectric performances were obtained. These multifunctional properties endow KNN-based textured ceramics with promising application prospects in optoelectronic devices.

Effects of hot rolling and annealing temperature on microstructure and tensile properties of a Zr-containing Ni-based ODS superalloy

A Ni-based ODS superalloy with composition of Ni-20Cr-0.5Ti-0.3Al-0.6Y2O3-0.6Zr (in mass%) was prepared by mechanical alloying and hot isostatic pressing. Hot rolling was carried out at 1100 °C with different reduction ratio (40 %, 50 % and 60 %) and different annealing temperature (1200 °C, 1250 °C and 1300 °C) to investigate their influence on nanoscale oxides, grain and high temperature tensile properties. The results showed that high-density nanoscale oxides Y4Zr3O12 are formed in the Zr-containing Ni-based ODS alloy. Hot rolling and annealing result in the slight increase of oxide size and decrease of oxide density. The growth rate of oxides obeys fifth-law, which is called pipe diffusion along dislocation. The diffusion activity energy is derived as 827 kJ/mol. Average oxide size decreases and number density increases by decreasing rolling reduction ratio or annealing temperature. The size of columnar grain and grain aspect ratio increase with increase of annealing temperature which results into enhanced ultimate tensile strength and improved ductility at 800 °C. In addition, increasing rolling reduction ratio refines grain size and reduces grain aspect ratio in the alloy. The strength of the alloy annealed at 1300 °C with a reduction ratio of 50 % is the highest which is approximately 300 MPa at 800 °C.

Impact tension behavior of heavy-drawn nanocrystalline CoCrNi medium entropy alloy wire

High-strength metallic wire is a vital bearing structure used in many industrial fields. Impact loads often challenge the service safety of metal wire in engineering applications. However, few studies have been made on the dynamic mechanical behavior of metallic wires, especially for newly developed high-entropy alloy wires. By equipping split Hopkinson tension bar (SHTB) with specially designed test fixtures, we have carried out a systematic study on the dynamic deformation behavior of the heavily-drawn CoCrNi medium-entropy alloy (MEA) wire in impact tension at both room and cryogenic temperatures. We show that these millimeter-diameter MEA wires with nano-scale grains can achieve an excellent combination of impact tensile strength and ductility at 293 K and 77 K. More interestingly, we find that the strength and ductility of the MEA wire were enhanced simultaneously with decreasing temperature and increasing strain rate. Detailed microstructure characterizations and molecular dynamics simulations reveal that the increased strength and ductility at coupled high strain and low temperature resulted from the multiplication and thinning of nanoscale twins, which further caused additional strengthening and toughening mechanisms such as stack faulting net and secondary twin. This study highlights the advantage of CrCoNi MEA wire for cryogenic temperature and impact applications and provides an experimental reference for the design and evaluation of high-strength metal wires under such extreme conditions.

Facile dynamic current deposition of high tensile gradient Cu foil with (110) preferred orientation

The conductive copper (Cu) foil is an important raw material in the electronic industry. However, the traditional Cu foil with low tensile strength (∼350 MPa) and poor toughness is prone to breakage during production and usage, which is not conducive to its application in high-density printed circuit boards and high-energy-density batteries. In this work, we report a facile dynamic current deposition (DCD) method for preparing a gradient Cu foil with adjustable thickness (9–50 µm) and a highly preferred crystal orientation of Cu (110). The gradient Cu foil transitions gradually from micron-scale coarse grains to nano-scale fine grains, which promotes its tensile strength (∼840 MPa) while maintaining toughness (∼3.6%). Particularly, the gradient Cu foil shows a high conductivity of 3.3 × 107 S m−1, indicating its promising application in negative electrode current collectors of lithium-ion batteries and printed circuit boards. The facile DCD method can also provide guidance for the fabrication of other metallic materials.

Control of mechanical properties of a high-entropy alloy Cantor CoCrFeMnNi

A brief analysis of the work on changing the mechanical properties of the high-energy alloy (HEA) Cantor CoCrFeMnNi in various ways has been performed. The article describes the influence of alloying with aluminum, vanadium, manganese, titanium, silicon, carbon, copper on the hardening of wind turbines obtained by vacuum arc melting, laser melting, arc melting and drip casting, mechanical alloying with subsequent plasma sintering, gas sputtering followed by shock wave and static compaction. It is shown that additives of 2.5 % TiC and 5 % WC significantly improve the tensile strength, but reduce the elongation to failure. The effect of grain size in the range of 4.4 – 155 µm is to increase the tensile strength with a decrease in grain size. Lowering the temperature increases the strength and yield limits for grains of all sizes. Intensive plastic deformation forming nanoscale (~50 nm) grains significantly increases the tensile strength up to 1950 MPa and hardness up to 520 HV. Subsequent isochronous and isothermal annealing allows varying the strength and ductility of wind turbines. The formation of nanostructured-phase states during shock compounding, mechanical alloying and subsequent spark plasma formation significantly increase the tensile strength at room temperature, maintaining excellent plasticity (elongation of approximately 28 %). As one of the methods of modifying the mechanical properties of wind turbines, the authors propose electron-beam processing (EPO). The analysis of the deformation curves of the wind turbine, obtained by the technology of wire-arc additive production, after EPO with an electron beam energy density of 10 – 30 J/cm2, has been carried out; assumptions about the reasons for the decrease in strength and ductility characteristics have been found and substantiated. A comparative analysis of mechanical properties of the Cantor wind turbine obtained by various methods was carried out, and the reasons for discrepancy in the values of strength and plastic parameters were noted.

Morphology‐controlled synthesis and structural features of ultrafine nanoparticles of Co3O4: An active electrode material for a supercapacitor

AbstractIn this study, the authors present a morphology‐controlled synthesis strategy for the preparation of Co3O4 nanoparticles. The importance of the fuel (ascorbic acid) to oxidiser (cobalt nitrate) ratio (F/O ratio) in obtaining evenly distributed nanoscale grain Co3O4 with pure crystalline phases using the solution combustion method is proposed. The structural features of all the as‐formed cobalt oxide nanoparticles were studied using the powder X‐ray diffraction technique, a field emission scanning electron microscope and Raman spectroscopic techniques. The electrochemical characteristics of all the as‐formed cobalt oxide nanoparticle‐embedded electrodes were examined by cyclic voltammetry, galvanostatic charge–discharge studies and electrochemical impedance spectroscopy in a 2 M KOH solution. The electrochemical data demonstrated that the Co3O4 nanoparticles showed good capacitive behaviour. The morphological changes in the Co3O4 nanoparticles affect the charge storage mechanism, and Co3O4 nanoparticles with an F/O ratio equal to 1 (COO2) showed the highest electrochemical property, with a specific capacitance of 166 F g−1 at a current density 0.5 A g−1. The COO2 electrode material showed capacitance retention of 90% after 5000 cycles.

Introducing Spontaneously Phase‐Separated Heterogeneous Interfaces Enables Low Power Consumption and High Reliability for Phase Change Memory

AbstractPhase‐change memory is one of the most promising candidates for the next generation nonvolatile memory, but their high power consumption and low reliability remain bottleneck problems that limit the data storage density and its storage‐class memory application. Here, an innovative phase change material with embedded self‐precipitated interfaces, where the nanoscale grains of phase change material are cut into interconnecting “crystal islands” by thermally stable self‐precipitated material with low thermal conductivity, is proposed. The precipitated material provides both thermal and atomic migration confinements in three dimensions. The thermal confinement enables low power consumption, and the atomic migration confinement enables high device reliability. The devices based on spontaneously phase‐separated O‐doped Sb2Te3 verify the material design, where Sb oxide acts as the precipitated heterogeneous phase and Sb–Te alloy as the phase change material. O‐doped Sb2Te3 device with 250 nm hole diameter shows an ultralow power consumption, down to a few hundreds of femtojoule, which is comparable with those of phase change nanowires. Besides, good thermal stability and low resistivity drift (drift coefficient 0.005) as well as excellent cycle endurance up to 108 times are also obtained at the same time. The doping fabrication process is quite compatible with current semiconductor industry.

Preparation of nanoscale [(Ba0.85Ca0.15)0.995Nd0.005](Ti0.9Hf0.1)O3 ceramics via hydrothermal method and effect of grain size on multifunctional performance

Nanoscale [(Ba0.85Ca0.15)0.995Nd0.005](Ti0.9Hf0.1)O3 (Nd-BCTH) ceramics were prepared via the hydrothermal method, and the effects of sintering temperature and holding time on the phase structure, micromorphology, electrical and optical properties of the Nd-BCTH ceramics were explored. All the Nd-BCTH ceramics present rather pure perovskite structure with composition approaching rhombohedral phase around the morphotropic phase boundary (MPB) region. The highest relative density is obtained for the sample sintered at 1220 °C for 10 h. The existence of Ba2+, Ca2+, Ti4+, Hf4+ and Nd3+ is confirmed and the elements distribute rather uniformly detected by X-ray photoelectron spectrometer (XPS) and energy dispersive X-ray (EDX) analysis. The ceramics present nanoscale grain size, which tends to increase with the increase of sintering temperature and holding time, and significantly affects dielectric constant and Curie temperature. Very thin and narrow ferroelectric hysteresis loops are observed, where a considerable energy storage density (173.88 mJ/cm3) and high energy storage efficiency (80.68%) are obtained at low electric field. The increase of sintering temperature and holding time induces a red shift at 400 nm absorption edge and a blue shift at 300 nm absorption edge in the Nd-BCTH ceramics, and all ceramics have a maximum absorption value at around 260 nm. Under the excitation of 269 nm light, the Nd-BCTH ceramics show the strongest fluorescence peak at 473 nm, corresponding to the 4G3/2→4I9/2 transition, emitting indigo blue fluorescence. When the ambient temperature is above 400 °C, grains conduction dominates the conductive mechanism in the nano-sized Nd-BCTH ceramics. Such conduction can be attributed to oxygen vacancies caused due to the evaporation of alkaline-earth metals during high temperature sintering, and show typically thermally excited relaxation process.

Analysis of a Gel-like State of Nickel Hydroxide Created By Electrochemical Aging

As global energy demands increase, the need for clean energy and energy storage is evident. Water electrolysis has shown promise as a clean energy storage solution and can be coupled with other clean energy techniques (e.g., wind, solar) to store chemical energy in the form of hydrogen. Alkaline systems are of particular interest as they are more cost effective compared to acidic systems that require precious metal-based catalysts. Alkaline water electrolysis suffers from inefficiencies that include the oxidative half reaction known as the oxygen evolution reaction (OER). Nickel-based electrocatalysts are being developed for the electrochemical transformations of organic species and used in gas evolution reactions, such as the OER. Nickel-based materials are sought after in part for their lower cost relative to precious metal catalysts (e.g., Pt, Ru, Ir), but they lack the higher electrochemical activity achieved by their precious metal counterparts. To develop more active and durable materials and to better understand the mechanisms involved in electrochemical transformations on nickel-based materials, it is essential to understand how these materials evolve and age as a result of electrocatalytic use.In this study, we have preserved the hydrated form of Ni electrocatalysts aged under alkaline conditions relevant to the OER. We prepared a series of electrocatalysts with nano- and micro-scale grains that were polished to a similar nano-scale roughness. First, we electrochemically aged Ni electrocatalysts with nanoscale and microscale grains by potential cycling techniques (i.e., cyclic voltammetry). Following electrochemical aging, the Ni electrocatalysts were preserved by immersion in liquid nitrogen and sublimed in a lyophilizer. After this freeze-drying process, the electrocatalysts were imaged under cryogenic conditions using scanning electron microscopy (SEM) techniques. A comparison was made to aged electrocatalysts where freeze-drying was implemented and those that were allowed to air dry. The surfaces of aged Ni electrocatalysts were all observed to contain an electrochemically active layer with a gel-like form. When the catalysts were air-dried, the layer appeared to have a collapsed, web-like texture. Through the use of transmission electron microscopy analyses, it was determined that these gel-like layers contained predominantly nanocrystalline β-phase nickel hydroxide (β-Ni(OH)2), which likely formed due to relaxation of the OER active beta-phase nickel oxyhydroxide [β-NiOOH] prior to the imaging process. The formation of the gel-like layer covering these electrocatalysts has implications for dynamic processes taking place at their interface with the electrolyte. Processes influenced by the gel-like form of this active layer include the rates of diffusion of electrolyte, the mechanism of O2 bubble nucleation, and the mechanics of bubble release. The results of these studies also have implications for the electrocatalytic activity and stability of other types of electrocatalysts. Further, this work can be extended for the design of new electrocatalysts for a variety of electrocatalytic processes, such as the hydrogen evolution reaction and other gas evolution reactions. Figure 1

Quasi-in-situ observation of the grain growth and grain boundary movement in sintered Cu nanoparticle interconnects

Sintered Cu interconnection for power electronics has attracted considerable interest recently. Investigation of grain growth during Cu nanoparticle sintering provides insight into the strengthening mechanism of the sintered structure. Currently, the literature on Cu nanoparticle sintering mechanism is limited and mainly focuses on the transmission electron microscopy (TEM) observation of a limited number of nanoparticles with an ultrathin region. This study employs a quasi-in-situ method to investigate the mechanism of grain growth and twin formation in the bulk sintered Cu nanoparticle structure. The grains were found to continuously grow accompanied by orientation unification which is attributed to grain boundary (GB) migration or dislocation motion at elevated temperature. Two mechanisms governing twin formation have been observed and detailed. The grain and pore size and porosity in the sintered Cu structure under different sintering conditions were measured and correlated to the joint strength. Porosity was found to be the dominant factor affecting joint strength rather than grain or pore size. The original bonding interface between the sintered structure and the Cu substrate has high porosity. However, subsequent GB movement during heating causes this interface to shift into the sintered structure, eliminating the high porosity interface. Meanwhile, a model predicting porosity evolution was used to identify the dominant diffusion mechanism. This study constitutes the first detailed experimental observation of nanoscale grain growth, twin formation and GB movement at the interface and in the bulk sintered Cu structure. This novel mechanism of GB shifting could provide new guidance for strengthening the sintered Cu interconnections for power electronics.

Sugar-Derived Isotropic Nanoscale Polycrystalline Graphite Capable of Considerable Plastic Deformation.

Obtaining large plastic deformation in polycrystalline van der Waals (vdW) materials is challenging. Achieving such deformation is especially difficult in graphite because it is highly anisotropic. The development of sugar-derived isotropic nanostructured polycrystalline graphite (SINPG) is discussed herein. The structure of this material preserves the high in-plane rigidity and out-of-plane flexibility of graphene layers and enables prominent plasticity by activating the rotation of nanoscale (5-10nm) grains. Thus, micrometer-sized SINPG samples demonstrate enhanced compressive strengths of up to 3.0GPa and plastic strains of 30-50%. These findings suggest a new pathway for enabling plastic deformation in otherwise brittle vdW materials. This new class of nanostructured carbon materials is suitable for use in a broad range of fields, from semiconductor to aerospace applications.

Features and regularities in formation of diffusion nickel-copper coatings on steels in the medium of low-melting liquid-metal solutions

The paper considers the features and regularities of formation of Ni-Cu based diffusion coatings on the surface of steel products obtained as a result of diffusion metallization from the medium of low-melting liquid metal solutions. It was found out that a solid solution of Ni, Cu, Fe was formed in the main layer of coatings after applying the Ni-Cu coating on armco-iron, steel 20 and tool steel Kh12MF; it was characterized by approximately equal concentration of nickel and copper on the coating surface, it made 55 % Ni and 27 % Cu. As soon as the depth of the base layer increases, concentration of Ni and Cu in it gradually decreases, while the iron content also increases. During formation of Ni–Cu coatings on alloyed steels, selective diffusion of steel alloying elements deep into the coating is observed. It is established that the coatings have two layers – the main and the transition ones. At the same time, the maximal coating thickness constitutes 55 μm at the saturation temperature of 1150 °C and 6 hours duration. It was revealed that the main layer consists of Ni, Cu, Fe solid solution, also contains steel alloying elements and consists of columnar grains elongated in the direction of diffusion of the coating elements, as well as in its surface layer with thickness of about 5 μm. The layer of nano-scale grains with a cross-section size of 80-100 nm is forming. During formation of Ni-Cu based coatings, the phenomenon of displacement of the coating carbon and the steel alloying elements into the transition layer is confirmed; these carbon and steel elements do not interact with the coating elements.  The innovation project was conducted under financial support of the Kuban scientific fund within the framework of the Competition of scientific-innovation projects directed on commercialization No. NIP-20.1-62/20.

Bimodal grain size structure design to optimize the mechanical properties of TiZrNbTa high entropy alloys/Ti composites

Grain refinement is perfectly efficient for improving strength, but accompanies by a dramatic loss of ductility. Here we report a bimodal grain size structure design by inducing ultra-high strength TiZrNbTa high entropy alloy (HEA) with nanoscale grain size into pure Ti with coarse grain size to achieve the strength-strain balance by establishing bimodal grain size distribution (BGSD). Through optimizing the TiZrNbTa HEA content, the 60 wt.% TiZrNbTa/Ti titanium matrix composite (TMC) exhibits a yield strength of 1426 ± 30 MPa, ultimate compressive strength of 2133 ± 88 MPa, and an acceptable compressive strain of 22.3% ± 1.8%, respectively. The compressive yield strength of 60 wt.% TiZrNbTa/Ti TMC is 3.6-fold for c.p. Ti (393.0 ± 7.1 MPa). The unusual high strength is attributed to the nanoscale grain size provided by TiZrNbTa HEA, and the acceptable compressive strain is obtained from the co-effect of coarse grain Ti and TiZrNbTa HEA. The excellent mechanical properties of 60 wt.% TiZrNbTa/Ti TMC undoubtedly greatly increase the possibility of its application as an orthopedic implant in the biomedical field.