The thickness dependence of mechanical properties of nacre in Cristaria plicata shell was studied under three-point bending tests. The results show that the mechanical behavior of nacre exhibits a strong thickness dependence. The bending strength firstly increases with the increase of specimen thickness and then becomes roughly constant as the thickness reaches a certain value of ~2.5 mm. However, the mean value of work per unit volume increases constantly with increasing specimen thickness; meanwhile, the cracking mode changes from penetration into the platelets to deflection along the interfaces. The theoretical analyses indicate that the thickness-dependent mechanical properties of nacre are mainly caused by the variation in the number of inter-lamellar interfaces. The more the number of inter-lamellar interfaces is, the higher the strength and work of fracture of nacre under bending tests will be. However, as the number of inter-lamellar interfaces reaches a certain value (e.g., in the present specimen with 2.5 mm thickness), the strength tends to remain constant, while the work of fracture still increases. Therefore, the present research findings are expected to provide a valuable guidance for the interfacial design of nacre-like materials with high strength and toughness.

In this study, three kinds of A380/Al₂O₃ composite coatings were prepared by cold spray (CS) using spherical, irregular and spherical + irregular shaped Al₂O₃ particulates separately mixed in the original A380 alloy powders. The influence of Al₂O₃ particulates’ morphology on the microstructural characteristics (i.e. retention of Al₂O₃ content in coatings, coating/matrix interfacial bonding, pore size distribution and morphology etc.) and wear performance of the coatings was investigated by scanning electron microscopy (SEM), X-ray computed tomography (XCT) and 3-D optical profilometry. Results indicated that the spherical Al₂O₃ shows obvious tamping effect during deposition process. As a result, the interface showed a wavy shape while the matrix and particulates were mechanical interlocked with much improved adhesion. In addition, the porosity of the coating was minimized and the pores exhibited curved spherical structure with reduced dimensions. The irregular Al₂O₃ particles predominantly displayed the embedding effect together with fragmentation of Al₂O₃ particulates. Consequently, poor coating/ matrix interfacial bonding, high porosity and the formation of angular-shaped pores were resulted in the coating. Dry sliding wear tests results revealed that the wear resistance of the coating is directly related with the retained content of Al₂O₃ in the coating. The coating containing irregular Al₂O₃ particulates displayed superior wear performance with its wear rate one seventh of that of the pure A380 alloy coating. The coating containing both kinds of Al₂O₃ particulates showed mixed characteristics of above two kinds of Al₂O₃ composite coatings.

To resolve the strength-ductility trade-off problem for high-strength Mg alloys, we prepared a high performance Mg-8Gd-3Y-0.5 Zr (wt%) alloy with yield strength of 371 MPa, ultimate tensile strength of 419 MPa and elongation of 15.8%. The processing route involves extrusion, pre-deformation and aging, which leads to a bimodal structure and nano-precipitates. Back-stress originated from the deformation-incompatibility in the bimodal-structure alloy can improve ductility. In addition, dislocation density in coarse grains increased during the pre-deformation strain of 2%, and the dislocations in coarse grains can promote the formation of chain-like nano-precipitates during aging treatment. The chain-like nano-precipitates can act as barriers for dislocations slip and the existing mobile dislocations enable good ductility.

In this work, the phase transformation sequence during the continuous heating process (3 °C/min) was investigated in a near β titanium alloy. The results show that the staring formation of ω phase is about 267 °C, and the ending precipitation temperature about 386 °C during the heating process. When the heating temperature is greater than 485 °C, there are no ω phase detected within the β matrix. Combined with the microstructural characterization, it is found that ω phase facilitates the nucleation of α phase nearby the ω/β interface and has a great effect on the refinement for α phase. As compared with the specimens directly aged, the specimens with ω-assisted refinement of α phase possess high tensile strength, but there is no yield stage detected on their stress-strain curve. Combined with the analyses of the fracture morphology, the specimens with ω-assisted refinement of α phase present a brittle fracture. This is mainly ascribed to its relatively lager width of grain boundaries and the absence of widmanstätten α precipitates.

The martensitic transformation, kinetics, elastic and magnetic properties of the Ni_2-xMn_1.5In_0.5Co_x (x = 0-0.33) ferromagnetic shape memory alloys were investigated experimentally and theoretically by first-principles calculations. First-principles calculations show that Co directly occupies the site of Ni sublattice, and Co atoms prefer to distribute evenly in the structure. The optimized lattice constants are consistent with the experimental results. The martensitic transformation paths are as follows: PA ↔ FA ↔ 6 M^FIM ↔ NM^FIM when 0 ≤ x < 0.25; PA ↔ FA ↔ 6 M^FM ↔ NM^FIM with 0.25 ≤ x < 0.3 and PA ↔ FA ↔ NM^FM with 0.3 ≤ x ≤ 0.33 for Ni_2-xMn_1.5In_0.5Co_x (x = 0-0.33) alloys. The fundamental reasons for the decrease of T_M with increasing Co content are explained from the aspects of first-principles calculations and martensitic transformation kinetics. The component interval of the magnetostructural coupling is determined as 0 ≤ x ≤ 0.25 by first-principles calculations. Furthermore, the origin of the demagnetization effect during martensitic transformation is attributed to the shortening of the nearest neighboring distances for Ni-Ni (Co) and Mn-Mn. Combining the theoretical calculations with experimental results, it is verified that the T_M of the Co6 alloy is near room temperature and its magnetization difference ΔM is 94.6 emu/g. Therefore, magnetic materials with high performance can be obtained, which may be useful for new magnetic applications.

Flexible sensors have been widely investigated due to their broad application prospects in various flexible electronics. However, most of the presently studied flexible sensors are only suitable for working at room temperature, and their applications at high or low temperatures are still a big challenge. In this work, we present a multimodal flexible sensor based on functional oxide La_0.7Sr_0.3MnO₃ (LSMO) thin film deposited on mica substrate. As a strain sensor, it shows excellent sensitivity to mechanical bending and high bending durability (up to 3600 cycles). Moreover, the LSMO/Mica sensor also shows a sensitive response to the magnetic field, implying its multimodal sensing ability. Most importantly, it can work in a wide temperature range from extreme low temperature down to 20 K to high temperature up to 773 K. The flexible sensor based on the flexible LSMO/mica hetero-structure shows great potential applications for flexible electronics using at extreme temperature environment in the future.

The native oxide thin scale on magnesium (Mg) surface appears continuous and crack-free, but cannot protect the Mg matrix from further oxidation, especially at elevated temperatures. This thermal oxidation process is witnessed in its entirety using a home-made in-situ heating device inside an environmental electron transmission microscope. We proposed, and verified with real-time experimental evidence, that transforming the native oxide scale into a thin continuous surface layer with high vacancy formation energy (low vacancy concentration), for example MgCO₃, can effectively protect Mg from high-temperature oxidation and raise the threshold oxidation temperature by at least two hundred degrees.

Bi doped SrTiO₃ ceramics with Sr deficiency, i.e. Sr_1-1.5xBi_xTiO₃ (x=0, 0.01, 0.05, 0.1), were prepared via conventional solid-state reaction route. A colossal permittivity (CP) over 10⁴ with low dielectric loss less than 0.05 was obtained in x=0.05 Sr_1-1.5xBi_xTiO₃ ceramics. In addition, the dielectric constant is maintained at a value greater than 10⁴ in the range of 10²-10⁵ Hz and almost frequency independent. Phase structure analysis and density functional theory calculations suggest that the Bi_Sr^· - V_Sr^" - Bi_Sr^· defect complex with hole-pinned defect-dipoles maybe responsible for the high-performance CP properties. This work gives a new way to achieve high performance CP materials in ABO₃ perovskite ceramics.

Low material cost and high extrudability for ensuring price competitiveness with Al alloys, as well as excellent mechanical properties, are essential for expanding the application range of Mg extrudates. Bi is a promising alloying element for developing extruded Mg alloys that satisfy such requirements. Bi is inexpensive, exhibits a high solubility limit, and forms a thermally stable Mg₃Bi₂ phase, which improves the commercial viability and enables the high-speed extrusion of Mg-Bi alloys. In this study, the effects of Bi addition on the dynamic recrystallization (DRX) and dynamic precipitation behaviors during hot extrusion of a pure Mg and the resultant microstructure and mechanical properties of the extruded materials were investigated. The addition of 6 wt% and 9 wt% Bi to a pure Mg yielded numerous fine Mg₃Bi₂ precipitates during the early stage of hot extrusion. Consequently, the area fraction of dynamic recrystallized (DRXed) grains decreased because of DRX-behavior suppression by the Zener pinning effect. However, the DRXed grain size was substantially reduced through the grain-boundary pinning effect. The size and number of undissolved Mg₃Bi₂ particles in the homogenized billets increased when the Bi content was increased, which resulted in increased DRX fractions owing to the enhanced levels of particle stimulated nucleation. Bi addition yielded considerable strength improvement of the extruded pure Mg. However, the extruded Mg-Bi binary materials were less ductile than the extruded pure Mg material. This lower ductility resulted from the cracking at twins formed in the coarse unDRXed grains of the Mg-6Bi material and the cracking at large undissolved Mg₃Bi₂ particles in the Mg-9Bi material.

Due to the outstanding creep performance, nickel-based single crystal superalloys (Ni-SXs) are extensively applied in modern aero-engine and industrial gas turbine. Apart from the special single crystal structure which is disadvantageous to extension of creep cracks, Ni-SXs derive the creep strength from intrinsic two-phase microstructure (γphase and γ’ phase). Main microstructural parameters including volume fraction of γ’ phase and the lattice misfit, and the formation and distribution of precipitated phase are determined by the compositions of alloys. Besides, the creep properties are greatly influenced by these microstructural parameters and precipitated phase. This review has summarized the relationships between different alloying elements and microstructures and indicated their influence on creep properties of Ni-SXs. In addition, with the improvements of experimental methods and characterization technique, some recent discoveries have provided additional evidence to support or challenge the pervious creep theories of superalloys. In view of these new discoveries, this review has provided some perspectives which can be referenced in future compositional design of Ni-SXs.

The strategy of a reliable transition temperature control of vanadium dioxide (VO₂) is reported. Rectangular VO₂ nanobeams were synthesized by a thermal chemical vapor deposition (TCVD) system. The metal-insulator transition (MIT) temperature increases to above 380 K when the TiO₂ ratio of the source is 5 at.%, although the Ti source is not physically doped into VO₂ nanobeams. The XPS spectra of the V 2p orbital reveal the excessive oxidation of V after the TCVD processes with a higher TiO₂ ratio, indicating that the TiO₂ precursor is important in the O-doping of the surface V—O bonds when forming volatile Ti-O gas species. Thus, TiO₂ reactants can be used as a VO₂ surface chemical modifier to manipulate the MIT transition temperature and maintain a homogenous VO₂ phase, which is useful for a Mott device application with a record on/off switching ratio > 10⁴ and Mott transition temperature > 380 K.

A synergistic inhibition study was carried out on an aluminium/copper galvanic coupling model in neutral aerated NaCl solution using scanning vibrating electrode technique (SVET). The approach allows the simulation of the local micro-galvanic cells of AA2024-T3 obtained from the potential difference between the intermetallic particles (IMPs) and the aluminium matrix. The inhibition effect of CeCl₃ and 3-Amino-1,2,4-triazole-5-thiol (ATAT) was demonstrated by the reduction in the galvanic current density over Al and Cu surfaces. An improved inhibition from positive synergistic effect was revealed by the combination of the two inhibitors after 24 h of immersion, with the best inhibition recorded for Ce_1.5ATAT_3.5. Scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and time of flight secondary ion mass spectrometry (ToF-SIMS) were used to characterize the Ce- and ATAT-based complex film formed and to illustrate the mechanism of inhibition.

In this work, the computational complexity of a spin-glass three-dimensional (3D) Ising model (for the lattice size N = lmn, where l, m, n are the numbers of lattice points along three crystallographic directions) is studied. We prove that an absolute minimum core (AMC) model consisting of a spin-glass 2D Ising model interacting with its nearest neighboring plane, has its computational complexity O(2mn). Any algorithms to make the model smaller (or simpler) than the AMC model will cut the basic element of the spin-glass 3D Ising model and lost many important information of the original model. Therefore, the computational complexity of the spin-glass 3D Ising model cannot be reduced to be less than O(2mn) by any algorithms, which is in subexponential time, superpolynomial.

Given that graphene features high electrical conductivity, it is a kind of material with corrosion-promotion activity. This study aimed to inhibit the corrosion-promotion activity of graphene in coatings. Here, we report an exciting application of epoxy matrix (EP)/F-doped reduced graphene oxide (rGO) coatings for the long-term corrosion protection of steel. The synthesized F-doped rGO (FG) did not reduce the utilization of rGO by a wide margin and possessed distinctive electrically insulating nature. The electrical conductivity of rGO was approximately 1500 S/m, whereas those of FG-1, FG-2 and FG-3 were 1.17, 5.217 × 10^-2 and 3.643 × 10^-11 S/m, respectively. FG and rGO were then dispersed into epoxy coatings. The chemical structures of rGO and FG were investigated by transmission electron microscopy (TEM), scanning probe microscopy (SPM), X-ray photoelectron spectroscopy (XPS), Fourier-transform infrared spectroscopy (FT-IR), and X-ray diffraction (XRD). EP/FG coatings exhibited outstanding corrosion protection in comparison with blank EP and EP/rGO coatings mainly because the corrosion-promotion effect of rGO was eliminated. The anticorrosion ability of EP/FG coatings was improved with increased F-doped degree of FG. In addition, electrochemical impendance spectroscopy (EIS) results indicated that the R_c values of EP/FG-2 and EP/FG-3 were four orders of magnitude higher than those of EP/rGO in diluent NaCl solution (3.5 wt.%) after immersion for 90 days.

We report first-principles results of the point defect properties in a V-Ta-Cr-W high-entropy alloy (HEA) with the body-centered cubic (bcc) structure. Different from the widely-investigated face-centered cubic (fcc) HEAs, the local lattice distortion is more pronounced in bcc ones, which has a strong influence on the defect properties and defect evolution under irradiation. Due to the large size of Ta, the exchange between vacancies and Ta exhibits lower energy barriers. On the other hand, interstitial dumbbells containing V and Cr possess lower formation energies. These defect energetics predicts an enrichment of V and Cr and a depletion of Ta and W in the vicinity of defect sinks. Besides, we find that interstitial dumbbells favor the [110] orientation in the HEA, instead of [111] direction in most nonmagnetic bcc metals, which helps to slow down interstitial diffusion significantly. Consequently, the distribution of migration energies for vacancies and interstitials exhibit much larger overlap regions in the bcc HEA compared to fcc HEAs, leading to the good irradiation resistance by enhancing defect recombination. Our results suggest that HEAs with the bcc structure may bear excellent irradiation tolerance due to the particular defect properties.

Ti₂AlNb-based intermetallic compounds are considered as a new category of promising lightweight aerospace materials due to their balanced mechanical properties. The aim of this study was to evaluate monotonic and cyclic deformation behavior of an as-cast Ti-22A1-20Nb-2V-1Mo-0.25Si (at.%) intermetallic compound in relation to its microstructure. The alloy containing an abundant fine lamellar O-Ti₂AlNb phase exhibited a good combination of strength and plasticity, and superb fatigue resistance in comparison with other intermetallic compounds. Cyclic stabilization largely remained except slight cyclic hardening occurring at higher strain amplitudes. While fatigue life could be described using the common Coffin-Mason-Basquin equation, it could be better predicted via a weighted energy-based approach. Fatigue crack growth was characterized mainly by crystallographic cracking, along with fatigue striation-like features being unique to appear in the intermetallics. The results obtained in this study lay the foundation for the safe and durable applications of Ti₂AlNb-based lightweight intermetallic compounds.

In the present investigation, an austenitic AISI 304 stainless steel was subjected to high strain rate surface deformation by Pipe Inner-Surface Grinding (PISG) technique. The depth-dependent deformation parameters (strain, strain rate and strain gradient) were evaluated and the microstructures were systematically characterized. Microstructural evolution from millimeter- to nano-scale was explored, with special attention paid to the localized deformation. Microstructural evolution begins with the formation of planar dislocation arrays and the twin-matrix lamellae, which is followed by the localized deformation characterized by the initiation and the development of shear bands. A twinning-dominated process that was supplemented with dislocation slip-dominated one governed the microstructural evolution inside shear bands. The twin-matrix lamellae transform into extended/lamellar structure and finally the nano-sized grains. Austenitic grains were substantially refined and martensitic transformation was effectively suppressed, of which the underlying mechanisms were analyzed.

The porous titanium with a channel-like pore structure fabricated by infiltration casting followed by selectively dissolving the precursor woven three dimensional (3D) structure technique was comprehensively investigated by means of mechanical tests, in vitro and in vivo evaluation. Such porous structure exhibited superiority in compressive, tensile strength and osseointegration. At 40% porosity, the average compressive and tensile strength reached about 145 MPa and 85 MPa, which was superior to that of other porous titanium, e.g., Selective Laser Melting or powder sintered ones, and was comparable to that of the human cortical bone. Without any bioactive surface treatment, this porous titanium exhibited good cell adhesion, rapid cell proliferation and excellent osseointegration. Based on the study, the 0.4 mm pore size resulted in the most rapid cell proliferation and the maximal BV/TV ratio and trabecular bone number of the new bone that ingrew into the porous titanium. To balance the excellent osseointegration and adequate mechanical properties, the optimal structural parameters were 0.4 mm pore size with 40% porosity. This porous titanium is very promising for orthopedic applications where compressive and tensile load-bearing is extremely important.

Magnesium and its alloys are significant superior metallic materials for structural components in automobile and aerospace industries due to their excellent physicomechanical properties. The Mg-rare earth (RE) systems have attracted great interests because RE additions can improve both the deformability and the strength of Mg alloys through solid solution strengthening and precipitation hardening mechanisms. This paper focuses on the interface stability, together with thermodynamics and kinetics of nucleation and growth of the key phases and matrix phases in Mg-RE alloys. In this paper, the theory and recent advances on Mg-RE alloys, especially for the interface stability, thermodynamics and kinetics of nucleation and growth of the key phases and matrix phases, together with their relationships with micro-structures, and macroscopic properties, are reviewed. By combining the thermodynamics/kinetics integrated simulations with various advanced experimental techniques, “reverse” design of Mg-RE alloys starting from the target service performance is put forward as a kind of scientific paradigm with rational design.

The temperature and stress profiles of porous cubic Ti-6Al-4V titanium alloy grids by additive manufacturing via electron beam melting (EBM) based on finite element (FE) method were investigated. Three-dimensional FE models were developed to simulate the single-layer and five-layer girds under annular and lateral scanning. The results showed that the molten pool temperature in five-layer girds was higher than that in single-layer grids owing to the larger mass and higher heat capacity. More energies accumulated by the longer scanning time for annular path than lateral path led to the higher temperature and steeper temperature gradient. The thermal stress drastically fluctuated during EBM process and the residual stress decreased with the increase of powder layer where the largest stress appeared at the first layer along the build direction. The stress under lateral scanning was slightly larger but relatively more homogeneous distribution than those under annular scanning. The stress distribution showed anisotropy and the maximum Von Mises stress occurred around the central node. The stress profiles were explained by the temperature fields and grids structure.

The immiscible Cu-Fe alloy was characterized by a metastable miscibility gap. With the addition element Zr, the miscibility gap can be extended into the Cu-Fe-Zr ternary system. The effect of the atomic ratio of Cu to Fe and Zr content on the behavior of liquid-liquid phase separation was studied. The results show that liquid-liquid phase separation into Cu-rich and Fe-rich liquids took place in the as-quenched Cu-Fe-Zr alloy. A glassy structure with nanoscale phase separation was obtained in the as-quenched (Cu_0.5Fe_0.5)₄₀Zr₆₀ alloy sample, exhibiting a homogeneous distribution of glassy Cu-rich nanoparticles in glassy Fe-rich matrix. The microstructural evolution and the competitive mechanism of phase formation in the rapidly solidified Cu-Fe-Zr system were discussed in detail. Moreover, the electrical property of the as-quenched Cu-Fe-Zr alloy samples was examined. It displays an abnormal change of electrical resistivity upon temperature in the nanoscale-phase-separation metallic glass. The crystallization behavior of such metallic glass has been discussed.

Upon non-equilibrium solidifications, dendrite growth, generally as precursor of as-solidified structures, has severe effects on subsequent phase transformations. Considering synergy of thermodynamics and kinetics controlling interface migration and following conservation of heat flux in solid temperature field, a more flexible modeling for the dendrite growth is herein developed for multi-component alloys, where, two inherent problems, i.e. correlation between thermodynamics and kinetics (i.e. the thermo-kinetic correlation), and theoretical connection between dendrite growth model and practical processing, have been successfully solved. Accordingly, both the thermodynamic driving force ΔG and the effective kinetic energy barrier Qeff have been found to control quantitatively the dendrite growth (i.e. especially the growth velocity, V), as reflected by the thermo-kinetic trade-off. Compared with previous models, it is the thermo-kinetic correlation that guarantees quantitative connection between the practical processing parameters and the current theoretical framework, as well as more reasonable description for kinetic behaviors involved. Applied to the vertical twin-roll casting (VTC), the present model, realizes a good prediction for kissing points, which influences significantly alloy design and processing optimization. This work deduces quantitatively the thermo-kinetic correlation controlling the dendrite growth, and by proposing the parameter-triplets (i.e. ΔG - Qeff - V), further opens a new beginning for connecting solidification theories with industrial applications, such as the VTC.

Topological crystalline insulator (TCI) as a new type of topological materials has attracted extensive research interests for its tunable topological properties. Due its symmetry topological protection essence, the structure investigation provides a solid basement for tuning its topological transport properties. On SrTiO₃ (111) substrate, the SnTe film was found to be epitaxial growth only along [001] while not [111] direction. The detailed structural study was performed and a structural model was proposed to elucidate epitaxial growth of the SnTe (001) film. The transport properties of SnTe (001) film were further investigated and a typical weak anti-localization effect was observed. By Pb-doping into SnTe, the bulk carriers were inhibited and its topological surface states were strengthened to induce the enhanced surface transport contribution. With tunable multiple transport channels from the even Dirac cones, the TCI SnTe film systems will have the potential application in future spintronics devices.

Uniform Fe₃C/N-doped carbon nanofibers were successfully synthesized through a facile self-catalyzed CVD method by using acetylene as carbon source and Fe₃O₄ as iron source and autocatalytic template for the reaction under moderate preparation conditions. The experimental and theoretical calculation results demonstrate that Fe₃C can improve the lithium storage performance of carbon nanofibers. Besides, the addition of PPy can not only control the growth rate of carbon fibers but also help to form uniform carbon fibers. As a result, the obtained Fe₃C/N-doped carbon nanofiber composites display favorable electrochemical performance as an anode for lithium-ion batteries, which including satisfactory rate performance of 402 mA h g^-1 under 1.2 A g^-1, and good cycling stability of 502.3 mA h g^-1 under 200 mA g^-1 over 400 cycles. The introduction of Fe₃C species and the uniform carbon fiber morphology are responsible for the long-cycling and high rate performance of materials.

The constant increase in global energy demand and stricter environmental standards are calling for advanced energy storage technologies that can store electricity from intermittent renewable sources such as wind, solar, and tidal power, to allow the broader implementation of the renewables. The grid-oriented sodium-ion batteries, potassium ion batteries and multivalent ion batteries are cheaper and more sustainable alternatives to Li-ion, although they are still in the early stages of development. Additional optimisation of these battery systems is required, to improve the energy and power density, and to solve the safety issues caused by dendrites growth in anodes. Electrolyte, one of the most critical components in these batteries, could significantly influence the electrochemical performances and operations of batteries. In this review, the definitions and influences of three critical components (salts, solvents, and additives) in electrolytes are discussed. The significant advantages, challenges, recent progress and future optimisation directions of various electrolytes for monovalent and multivalent ions batteries (i.e. organic, ionic liquid and aqueous liquid electrolytes, polymer and inorganic solid electrolytes) are summarised to guide the practical application for grid-oriented batteries.