Search

The research of thermoelectric materials is of great significance to solve the energy crisis and environmental problems. In this work, a series of pure SnSe bulk crystals were prepared by melting, high-energy ball milling, and hot pressing processes. The results show that the ZT value of the prepared pure SnSe polycrystalline material is up to 2.1 at 873 K. On the one hand, due to the reduction of grain size and lattice distortion caused by long-time high-energy ball milling, the lattice thermal conductivity is significantly reduced, which is only 0.18 W K-1 m-1 at 873 K. On the other hand, high-energy ball milling leads to the increase of Sn vacancies, which improves the conductivity of SnSe polycrystalline materials. Since the whole process of ball milling was carried out in a closed ball milling tank filled with high-purity argon, no oxidation of the SnSe powder is also a guarantee to obtain pure SnSe polycrystalline materials with high ZT value.

The tensile properties of a Ni-Co-based superalloy were investigated from room temperature to 900 °C. From 25 to 650 °C, the yield strength and tensile strength of the alloy decreased slightly, while the elongation decreased sharply. From 760 °C to 900 °C, the yield strength and tensile strength were greatly reduced, while the elongation also had a low value. With the increase in temperature, the deformation mechanism transformed from anti-phase boundary shearing to stacking fault shearing, and then from deformation twinning to Orowan bypassing, respectively. Deformation twins were generated in the deformed alloy with high-density stacking faults and they can contribute to the high strength. The alloy in this study has good mechanical properties and hot working characteristics below 760 °C and can be used as a turbine disk, turbine blade, combustion chamber, and other aircraft structural parts.

Three-dimensional finite element physical models considering the layered distribution of materials at the interface were developed to study the effect of the coating system on distributions of thermal residual stresses in SiCf/Ti2AlNb composites. Two coating systems were comparatively studied, namely C coating and C/Mo duplex-coating. The thermal residual stresses after 1 080 °C/1 h solution treatment and 800 °C/20 h ageing treatment in the composites were also analyzed. The experimental results show that Mo coating can decrease thermal residual stress magnitude in the matrix. However, it would increase the thermal residual stresses in the interfacial reaction layer of TiC. The change of radial thermal residual stress in TiC layer is inconspicuous after solid solution and ageing treatment, but the hoop and axial thermal residual stresses increase obviously. However, the heat treatment can obviously reduce hoop and axial thermal residual stresses of the matrix, which is benefit to restrain the initiation and propagation of cracks in the matrix.

In this research, high-temperature in situ X-ray diffraction were used to study the high-temperature transformation behavior of the iron-doped titanium dioxide (TiO2). The results show that the pha...

Photothermal/photodynamic therapy (PTT/PDT) and synergistic therapeutic strategies are often sought after, owing to their low side effects and minimal invasiveness compared to chemotherapy and surgical treatments. However, in spite of the development of the most PTT/PDT materials with good tumor-inhibitory effect, there are some disadvantages of photosensitizers and photothermal agents, such as low stability and low photonic efficiency, which greatly limit their further application. Therefore, in this study, a novel bismuth-based hetero-core-shell semiconductor nanomaterial BiNS-Fe@Fe with good photonic stability and synergistic theranostic functions was designed. On the one hand, BiNS-Fe@Fe with a high atomic number exhibits good X-ray absorption, enhanced magnetic resonance (MR) T2-weighted imaging, and strong photoacoustic imaging (PAI) signals. In addition, the hetero-core-shell provides a strong barrier to decline the recombination of electron-hole pairs, inducing the generation of a large amount of reactive oxygen species (ROS) when irradiated with visible-NIR light. Meanwhile, a Fenton reaction can further increase ROS generation in the tumor microenvironment. Furthermore, an outstanding chemodynamic therapeutic potential was determined for this material. In particular, a high photothermal conversion efficiency (η = 37.9%) is of significance and could be achieved by manipulating surface decoration with Fe, which results in tumor ablation. In summary, BiNS-Fe@Fe could achieve remarkable utilization of ROS, high photothermal conversion law, and good chemodynamic activity, which highlight the multimodal theranostic potential strategies of tumors, providing a potential viewpoint for theranostic applications of tumors.

Carbon nanotubes (CNTs)-reinforced Al2O3-matrix nanocomposites were fabricated by a serious of physical dispersion methods and subsequent spark plasma sintering. Crystalline structure, density, mechanical properties and electrical conductivity of the composites were evaluated, and the strengthening and toughening mechanisms were discussed. The results show that there exist angular drifts of the X-ray diffraction peaks for the Al2O3 matrix, which indicates the presence of residual compressive stress in the matrix. The bending strength increased initially with the increase of CNTs content, and reached the maximum with 1.0 wt% CNTs content. The fracture toughness of the nanocomposites also increased with the addition of CNTs, and the composite with 0.5 wt% CNTs has the maximum. The resistivity of composites decreased significantly with the increase in CNTs content, decreasing by seven orders of magnitude when the CNTs content is 2.0 wt%. According to the observations of crack propagation path and fractographs, four toughening mechanisms are summarized: CNTs pull-out, grain interface bridging, crack deflection and crack bridging.

A model of investment casting of a titanium alloy gearbox based on the ProCAST software was established in this work, and the simulated result was used to optimize the casting process. The flow and temperature field of casting were simulated based on an actual pouring process. Casting defects and the solidification process were analyzed. The results show that the defects can be predicted by the simulation result exactly, and the simulated temperature field is in accordance with the actual process. Shrinkage and porosity are observably alleviated by remodelling the casting mould. The casting temperature field and solidification simulation results show that the casting defects arise from hot spots and heat accumulation. The temperature-time curve of different representative location nodes of casting further confirms the defect simulation results. In addition, the use of low-cost alloy elements reduces raw material costs. Compared with TC4 alloy, the mechanical properties of the casting remain unchanged.

The high-temperature compressive property of Ti2AlN/TiAl composites, which are promising lightweight materials for high-temperature applications, was investigated. In situ high-energy X-ray diffraction (HEXRD) was utilized to analyze the micromechanical behavior at different deformation stages. It is determined {1 1 0}γ fiber texture firstly formed at work hardening stage and {0002}H fiber texture appeared at softening stage. The micro-deformation sequences were related to crystallographic orientations where [2 0 0]//LD, [2 0 2]//LD oriented γ grains were easier to work-hardening while [0 0 2]//LD, [1 1 0]//LD oriented γ grains presented hardening-softening transformation characteristic. The lattice strain wave of [0 0 0 2]//LD oriented H grain reflected an interesting atomic-scale ripples meanwhile [1 0_1 3]//LD oriented H phase presented a unique interface-dislocation mechanism. A significantly higher stress level in H phase demonstrates its strong bearing capacity. Our investigations establish a relationship between macroscopic deformation of composite and the microscopic elastic/plastic deformation of each component meanwhile provide in-depth understanding of the cooperative deformation characteristics in Ti2AlN/TiAl composites.

Synergetic therapy includes the combination of two or more conventional therapeutic approaches and can be used for tumor treatment by combining the advantages and avoiding the drawbacks of each type of treatment. In the present study, truncated tissue factor (tTF)-EG3287 fusion protein-encapsulated gold nanorod (GNR)-virus-inspired mesoporous silica core-shell nanoparticles (vinyl hybrid silica nanoparticles; VSNP) (GNR@VSNP-tTF-EG3287) were synthesized to achieve synergetic therapy by utilizing selective vascular thrombosis therapy (SVTT) and photothermal therapy (PTT). By integrating the targeted coagulation activity of tTF-EG3287 and the high tumor ablation effect of GNR@VSNP, local hyperthermia could induce a high percentage of apoptosis of vascular endothelial cells by using near-infrared light. This provided additional phospholipid sites for tTF-EG3287 and enhanced its procoagulant activity in vitro. In addition, the nanoparticles, which had unique topological viral structures, exhibited superior cellular uptake properties leading to significant antitumor efficacy. The in vivo antitumor results further demonstrated an interaction between SVTT and PTT, whereas the synergetic therapy (SVTT and PTT) achieved an enhanced effect, which was superior to the respective treatment efficacy of each modality or the additive effect of their individual efficacies. In summary, the synthesized GNR@VSNP-tTF-EG3287 exerted synergetic effects and enhanced the antitumor efficiency by avoiding multiple injections and suboptimal administration. These effects simultaneously affected both tumor blood supply and cancer cell proliferation. The data suggested that the integration of SVTT induced by tTF-EG3287 and PTT could provide potential strategies for synergetic tumor therapy.

In order to assess Al–Zn–Mg–Cu alloys as potential high temperature structural materials, the hardness, tensile properties and fracture behaviors of 7085 Al alloy were investigated at various temperatures from room temperature to 175 °C. High-resolution transmission electron microscopy was used to investigate the evolutions of precipitates at different temperatures, particularly on the relationship between microstructural evolution and tensile strength. The results reveal that both the microstructure and mechanical properties of the alloy are quite sensitive to the environmental temperature. As the temperature increases, the hardness and strength decrease while the elongation and reduction of area increase. As tensile testing temperature rises, the strain hardening exponent (n) decreases due to the thermal softening effect. The fracture mode of the alloy transforms from mixture of intergranular and transgranular fracture to completely transgranular dimples when tensile testing temperature reaches 150 °C. The precipitate sequence during high temperature tests is coincident with that of aging. With the increase of tensile testing temperature, the mean precipitate radius grows larger, and the distribution of grain boundary precipitates transforms from continuous to discontinuous. Keywords: 7085 Al alloy, Microstructure evolution, Tensile strength, Fracture mode

Sodium- and potassium-ion batteries are one of the most promising electrical energy storage devices at low cost, but their inferior rate and capacity have hampered broader applications such as electric vehicles and grids. Carbon nanomaterials have been demonstrated to have ultrafast surface-dominated ion uptake to drastically increase the rate and capacity, but trial-and-error approaches are usually used to find desired anode materials from numerous candidates. Here, we developed guiding principles to rationally screen pseudocapacitive anodes from numerous candidate carbon materials to create ultrafast Na- and K-ion batteries. The transition from pseudocapacitive to metal-battery mechanisms on heteroatom-doped graphene in charging process was revealed by the density functional theory methods. The results show that the graphene substrate can guide the preferential growth of K and Na along graphene plane, which inhibits dendrite development effectively in the batteries. An intrinsic descriptor is discovered to establish a volcano-shaped relationship that correlates the capacity with the intrinsic physical qualities of the doping structures, from which the best anode materials could be predicted. The predictions are in good agreement with the experimental results. The strategies for enhancing both the power and energy densities are proposed based on the predictions and experiments for the batteries.

Long-term thermal stability plays an important role in practical applications of Al-Zn-Mg-Cu alloys. In the present work, thermal stability of the T7452-treated 7085 Al alloy was assessed at temperatures of 100, 125, 150 and 175 °C for 100, 500 and 1000 h, through hardness, electrical conductivity and tensile tests after thermal exposure. The nanoscale precipitates under different thermal exposure conditions were also qualitatively studied by transmission electron microscopy (TEM). The results show that thermal stability of the alloy is more sensitive to thermal exposure temperature than to exposure time. The hardness increases first and then decreases with the increase of exposure temperature while it decreases gradually as exposure time prolongs. However, the variation of electrical conductivity is opposite. The tensile strength, yield strength and hardness after 100 °C/100 h thermal exposure increased by 2.4%, 6.7% and 9.2% than those of the alloy without thermal exposure, respectively. The precipitate sequence during thermal exposure is coincident with that of aging. In addition, as thermal exposure deepens, the average radius of precipitates increases while the volume fraction decreases. Meanwhile, the grain boundary precipitates coarsen and transform from continuous to discrete. The influence of precipitates on properties of the alloy is discussed quantitatively.

A lattice reorienting process is observed in Ti at atomic resolution through in situ transmission electron microscope tensile test. A new orientational relationship is identified between matrix (M) and reoriented (R) lattice: [ 1 ¯ 2 1 ¯ 3]R//[ 1 ¯ 2 1 ¯ 0]M and (0 1 ¯ 11)R//(0002)M, which is distinct from the known twinning and “twinning-like” relationships in hexagonal close-packed metals. Molecular dynamics simulation results suggest that the reorienting process is accompanied by the evolution of grain boundary misfit dislocations to lattice dislocations, as well as by the transformation of (0002) basal to (0 1 ¯ 11) pyramidal plane. Atomic rearrangement analysis shows that the short-distance shuffling of atoms can accomplish the transformation.

The microstructure and texture evolution near the adiabatic shear band (ASB) in TC17 Titanium alloy, during hot compression, were studied by electron back-scattered diffraction (EBSD). The ASB was induced in the bulk cylindrical TC17 Titanium alloy with an initially equiaxed microstructure, by hot compression with a relatively low strain rate. When the equiaxed-microstructure TC17 Titanium alloy was compressed at 600 °C, 700 °C, and 850 °C, two kinds of ASB were observed: D-ASB, which is almost parallel to the diagonal of the longitudinal section, and H-ASB, which is almost parallel to the horizontal of the longitudinal section. Dynamic recrystallization took place in β phase grains at the ASB center, while dynamic recovery dominated at the transition region. The large angle grain boundaries (LAGBs) were mainly concentrated in β phase, while the small angle grain boundaries (SAGBs) were mainly concentrated in α phase distributed along the ASB direction. Meanwhile, both α and β phase grain sizes slightly increased with increasing hot compression temperature and deformation, except for the alloy compressed at 850 °C with 70% deformation due to the phase transformation. At the ASB center, prismatic textures existed in α phase grains except for the basal textures in the alloy deformed at 600 °C. In β phase grains, the {001} planes were always normal to CD, while the {111} planes were normal to CD in the initial microstructure of the TC17 alloy. Furthermore, in β phase grains, the cubic texture {100} 〈001〉 dominated in the TC17 alloy deformed at 600 °C, 700 °C, and 850 °C. With increasing compression temperature, the crystal plane parallel to the ASB direction in α phase grains changed from {0001} to {11 2 ¯ 0} while it was stable in β phase grains, which is not beneficial to the mechanical performance of this alloy.

X-ray computed tomography (CT) has been widely used in clinical practice, and contrast agents such as Iohexol are often used to enhance the contrast of CT imaging between normal and diseased tissue. However, such contrast agents can have some toxicity. Thus, new CT contrast agents are urgently needed. Owing to the high atomic number (Z = 83), low cost, good biological safety, and great X-ray attenuation property (5.74 cm2 kg−1 at 100 keV), bismuth has gained great interest from researchers in the field of nano-sized CT contrast agents. Here, we synthesized BiF3: Ln@PVP nanoparticles (NPs) with an average particle size of about 380 nm. After coating them with polyvinylpyrrolidone (PVP), the BiF3: Ln@PVP NPs possessed good stability and great biocompatibility. Meanwhile, compared with the clinical contrast agent Iohexol, BiF3: Ln@PVP NPs showed superior in vitro CT imaging contrast. Subsequently, after in situ injection with BiF3: Ln@PVP NPs, the CT value of the tumor site after the injection was significantly higher than that before the injection (the CT value of the pre-injection and post-injection was 48.9 HU and 194.58 HU, respectively). The morphology of the gastrointestinal (GI) tract can be clearly observed over time after oral administration of BiF3: Ln@PVP NPs. Finally, the BiF3: Ln@PVP NPs were completely discharged from the GI tract of mice within 48 h of oral administration with no obvious damage to the GI tract. In summary, our easily synthesized BiF3: Ln@PVP NPs can be used as a potential clinical contrast agent and may have broad application prospects in CT imaging.

The atomic-scale evolution routes of stacking faults (SFs) interacting with non-screw dislocations were revealed by in situ tensile tests on Cu. SFs impinged by lattice dislocations tend to shrink to form stair-rod dislocations which may either be stable or unstable, depending on the dislocation reactions. Also, stacking fault can transform from intrinsic to extrinsic, which provides a new route of twin nucleation in face-centered cubic metals.

The atomic-scale dynamic evolution process of an isolated nanograin embedded within matrix under stress is recorded through in situ transmission electron microscopy tensile experiment on Al. the results reveal a 〈110〉 tilt grain boundary (GB) between the matrix and nanograin, with the misorientation angle increasing and GB shrinking during loading. A sudden annihilation of the nanograin occurs when the grain size reduces to ~4 nm. We then employ a dislocation dipole model to describe the GB structure in which the rotation, shrinkage and annihilation of nanograin can be interpreted as the approach and combination of opposite-sign dislocation pairs.

As an important reinforcement for metal matrix composites, the microstructure and mechanical properties of W-core SiC filament have drawn increasing attentions among researchers. In this work, the growth behavior of polycrystalline 3C-SiC on W-wire substrate in the chemical vapor deposition (CVD) process and the evolution of mechanical properties in preparation of W-core SiC filament, were investigated as a function of gas-phase supersaturation. Kinetic studies revealed that the growth of 3C-SiC grains was limited by surface reactions at both 850 °C and 1050 °C, and the deposit experienced similar morphological changes from a porous structure to large clusters, with the increase in supersaturation. Structural analyses and mechanical tests show that the production of pores and the amorphous phase with a low supersaturation, of 9.6 × 107 at 850 °C, resulted in a reduction in the modulus and hardness of the polycrystalline deposits, to 270.3 GPa and 33.9 GPa, while the reduced structural defects (e.g., stacking faults and twins) in highly (111) orientated 3C-SiC grains, as well as the improved surface quality obtained with the medium supersaturation of 1.6 × 107 at 1050 °C, enhanced the tensile strength and the Weibull modulus of W-core SiC filament to 2.88 GPa and 11.2, respectively. During the growth of 3C-SiC grains, the variation in structural defects density is controlled by the critical nucleation energy of the two-dimensional (2D) nucleus.

A twinning-induced void initiation mechanism at grain boundary is revealed in Cu through in situ tensile tests. Two microcracks connected by a twin boundary (TB) are formed following the growth of the void, which then develop via the relative sliding of the two crystals beside the migrating TB. The experimental observations of TB migration and dislocation activities are corroborated by performing molecular dynamics simulations.

In this study, the rolling technique of aluminum alloy was investigated, and the effects of deformation temperature on the edge cracks and mechanical properties of aluminum alloy were studied through a hot compression experiment on high magnesium aluminum alloy. Based on the test, DEFORM-3D software was introduced to optimize the selection of the influence conditions of the experiment. The research results suggested that the crack length of the as-cast aluminum alloy samples decreased with the increase of temperature when the deformation temperature was between 300 °C and 450 °C; the tensile strength and elongation after fracture increased with the increase of temperature when the deformation temperature was between 300 °C and 500 °C. Therefore it is concluded that the cracks of high magnesium aluminum alloy can be reduced through controlling deformation temperature, which provides an idea for the optimization of aluminium alloy.

As a new generation of Al-Zn-Mg-Cu alloy, 7085 aluminum alloy is a promising structural material in the field of aerospace industry. However, research on its thermal stability is still lacking. In the present work, thermal exposure was carried out on the T7452-treated 7085 aluminum alloy under different temperatures (100 °C, 125 °C, 150 °C and 175 °C) for 500 h. Variations of tensile properties and hardness were exhibited. The microstructure, nano-scale precipitates and fracture characteristics of the alloy were investigated using optical microscopy (OM), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results show that with the increase of exposure temperature, the strength and hardness increase first and then decrease while the elongation and the reduction of area increase continuously as compared to those of the non-thermal exposed alloy. The transformation from η′ phase to η phase during thermal exposure occurs continuously during thermal exposure. In addition, as the exposure temperature increases, the average dimensions of precipitates and the average spacing of neighbor precipitates become larger. The influence of precipitates on mechanical properties of the alloy is discussed.

Two dynamic processes were revealed in Cu by in situ tensile tests at the atomic scale: a lattice screw dislocation forming by the combination of two twinning dislocations; and two 60° full dislocations evolving from an extended screw dislocation. The results indicate that screw dislocation can trigger the transition of dislocation slip mode by its formation and dissociation, and also nucleate non-screw dislocations.

In situ tension tests in a transmission electron microscope and molecular dynamics simulations were carried out on pure Al, revealing a localized twinning-responded cracking mechanism. The dynamic twinning at crack tip was suggested to impose dual effects on fracture. On one hand, the intrinsic brittleness of coherent twin boundary (CTB) and the dislocation activities along it could facilitate cracking; on the other, twinning in Al could impede cracking mainly by effectively releasing the concentrated stress at crack tip. The competition between twin growth and CTB brittleness under stress was responsible for the behaving of crack.

Novel Al2O3 nanoparticle-reinforced heterogeneous CrCoNi-matrix composites (CrCoNi–Al2O3P) with 10–30 wt% of coarse grain (CG) matrix were prepared by multi-step mechanical milling plus hot pressing sintering. The relationships between microstructure and mechanical properties of the composites were studied in detail. The results reveal that the heterogeneous structure in CrCoNi–Al2O3P composites is composed of CG region and ultrafine grain (UFG) region with uniform distribution of Al2O3 nanoparticles. With increasing content of CG matrix in the nanocomposite, the hardness first decreases but then increases, and the increase of hardness may be due to the formation of carbides. Compared with homogeneous CrCoNi–Al2O3P composite, the compressive fracture strain of heterogenous composite increases by 53.2% at most, while sacrificing a small amount of strength, among which the 20 wt% CG heterogeneous composite exhibits an excellent strength-ductility synergy. For the mechanisms of strengthening and toughening, hetero-deformation induced (HDI) hardening makes the heterogeneous composites almost as strong as the homogeneous composite. Meanwhile, the CrCoNi matrix with low stacking fault energy can be deformed by dislocation slipping and twinning at room temperature, which improves the plasticity of the composite. Furthermore, the heterogeneous structure with soft and hard domains increases the work hardening ability of the composite.

Continuous fiber-reinforced TiAl-matrix composites are a potential structural material to satisfy the service requirements in space industry. Ta fiber with outstanding plasticity and toughness is regarded as a promising reinforcement. In this work, a 10 vol% Ta fiber-reinforced TiAl composite was prepared by combining slurry casting and vacuum hot pressing under condition of 1150 °C/ 35 MPa/ 2 h. Microstructure of interfacial reaction zone of the composite was investigated; meanwhile, thermodynamic calculation and theoretical analysis were conducted to explain the formation mechanisms of the reaction products. Three types of reaction products σ-Ta2Al, B2 and α2 phases were formed between Ta fiber and TiAl matrix. σ phase was adjacent to Ta fiber with a fine grain structure, which was formed due to the lowest formation free energy. The aggregation of β stabilizers in Ti-rich region resulted in the formation of B2 phase that was close to σ phase. α2 phase relied on B2 phase to nucleate and grow based on the Burgers relationship and their structure symmetry. Three-point bending tests show the fracture toughness (KIC) of the Taf/TiAl composite was 58% higher than that of pure TiAl matrix. The main toughening mechanism of the Taf/TiAl composite was plastic deformation of the Ta fiber, meanwhile the interfacial debonding also had a contribution to toughening the TiAl alloy. The interfacial debonding location was mainly at the Ta / LI-σ interface due to the existence of thermal residual stress.

The requirement for 7085 Al alloy as large airframe parts has been increasing due to its low quenching sensitivity and high strength. However, the relationship between high temperature mechanical properties and the evolution of precipitates in hot environments is still unclear. In this work, thermal exposure followed by tensile tests were conducted on the 7085 Al alloy at various temperatures (100 °C, 125 °C, 150 °C and 175 °C). Variations of hardness, electrical conductivity and tensile properties were investigated. The evolution of the nano scale precipitates was also quantitatively characterized by transmission electron microscopy (TEM). The results show that the hardness and electrical conductivity of the alloy are more sensitive to the temperature than to the time. The strength decreases continuously with the increase of temperature due to the transformation from η′ to η phase during the process. Furthermore, the main η phase in the alloy transformed from V3 and V4 to V1 and V2 variants when the temperature was 125 °C. Additionally, with increasing the temperature, the average precipitate radius increased, meanwhile the volume fraction and number density of the precipitates decreased. The strengthening effect of nano scale precipitates on tensile properties of the alloy was calculated and analyzed.

Improving surface properties can effectively expand the industrial application of aluminum alloys. In this study, a gradient nanostructured surface layer was successfully fabricated in an aged Al–Zn–Mg–Cu alloy by ultrasonic surface rolling processing (USRP). The microstructure and microhardness of the gradient nanostructured surface layer were investigated. The results show that a perfect gradient lamellae structure was fabricated in the surface layer. The average structural size in the topmost surface layer is approximately 41 nm, and the depth of nanostructure lamellae layer is up to 50 μm. After the USRP and two years of natural aging, the gradient distribution of precipitates was formed in gradient lamellae structure. A large number of discontinuous coarse η phase are formed on the lamellae boundary throughout the lamellae structure. However, the precipitates inside the lamellae have gradient distribution. The volume fractions of precipitates increase gradually from nanostructure to ultrafine-grained structure, and the main precipitates are GPII zones. The microhardness in the topmost surface is increased by 40% and gradually decreases from the surface to the matrix. The increase in microhardness is attributed to the fact that the enhancement of the hardness by the grain refinement is greater than the decrease due to the reduction of the precipitates inside the gradient lamellae structure from the surface to the matrix. This study provides technical method and theoretical basis for improving the surface hardness of Al–Zn–Mg–Cu alloy.

Heat treatment can change the matrix microstructure of metal based composites, which leads to the change of mechanical properties of the composites. In the present work, the variation of microstructure and hardness of the matrix of SiCf/Ti–6Al–4V composites prepared by foil-fiber-foil (FFF) method were investigated after quenching from 950, 980 and 990 °C. The results indicated that the β transus temperature of the matrix was close to 990 °C, which is slightly higher than that of the Ti–6Al–4V alloy, which is between 950 and 970 °C. This increase was attributed to the diffusion effect of carbon atoms. Some carbide particles were precipitated at the prior β grain boundaries when full martensite was obtained. Transmission electron microscopy examination observed three α′ variants that obeyed the Burgers orientation relationship with the β phase in the sample quenched from 950 °C. The hardness of the matrix increased with the increase in quenching temperature, and the highest hardness of 420 HV was obtained after quenching from 990 °C, which is much higher than that of the Ti–6Al–4V alloy. The high hardness was resulted from phase transformation strengthening by martensite, solid solution strengthening of carbon atoms and the dispersion strengthening of TiC precipitates.

The real-time 10 1 ¯ 1 twinning process at the crack tip of Ti is captured by carrying out the in situ tension tests in a transmission electron microscope. Both the atomic-resolution observations and the molecular dynamics simulations reveal that the 10 1 ¯ 1 twinning deformation is accomplished by the twinning mode corresponding to the b2 twinning dislocations instead of the conventional b4 mode. The sessile steps in twin boundaries which induced by pyramidal stacking faults extending across the twin are observed acting as the nucleation sources of b2 twinning dislocations. The nucleation mechanism is verified by determining the Burgers vectors of the sessile steps.

Surface sliding friction treatment of Al-Zn-Mg-Cu alloy generally introduces a large number of depth-dependent gradient deformation bands (DBs), which are approximately parallel to {111} Al and penetrated deeply into the coarse grain matrix. The DB segment adjacent to the ultrafine grain (UFG) layer is composed of a string of nanograins and generally shows a bamboo-like morphology. The intersected nanograin boundaries (INBs) and parallel DB boundaries (DBBs) are more often low angle dislocation boundaries. Compared with precipitates in the surrounding matrix, the precipitates at DBBs are much coarser, whereas those within DBs are smaller and scarcer. With increasing depth from the UFG layer, the INBs gradually disappear along with the decrease in the size differentiation between precipitates within DBs and at DBBs. Such deformation banding induced grain refinement and precipitate redistribution were fundamentally attributed to intense dislocation activities and possible dynamic recovery and recrystallization, which can be significantly affected by the gradient shear strain component as well as the randomly encountered coarse dispersoids and precipitates. Additionally, a variant selection phenomenon during mechanically induced precipitate dissolution process was pointed out, and the crystallographic orientation of equivalent variants with respect to the DBB plane was considered to be responsible for this orientation dependent precipitate dissolution. Deformation banding is of great benefit to work hardening, although there are probably some detrimental effects on mechanical properties.

The molecular dynamics simulation method is used to investigate the tensile deformation mechanism of Cu-Ag core-shell nanowires. The results for the actual structure of the Cu-Ag core-shell nanowires after energy minimization processes indicate that the atoms in shell Ag are reconstructed when the shell thicknesses smaller than 1.0 nm, while the shell thickness increases from 1.0 nm to 1.5 nm, the shape of NWs change into irregular circle. And then the tension strain is performed along the [0 0 1] direction under the conditions of varying the shell thickness and the temperature, respectively. It is found that, in low temperature region

This paper focused on the correlations between the texture and mechanical properties of hexagonal Ti6Al7Nb films prepared by magnetron sputtering. The texture evolution was controlled under a combination of substrate temperature and sputtering power. It was found that the substrate temperature was the key factor to dominate the texture evolution. At constant sputtering power 275 W, the films show an increasing (0002) growth from 100 to 300 °C, and then transforms into a random growth at 500 °C. According to two kinds of structure zone models, the intrinsic image of structure evolution from zone T, zone 2, to finally zone 3 was discussed. Nanoindentation measurements indicated that the texture strengthening contributes to the improvement of mechanical properties.

In this paper, imitation basalt compounds using red mud, fly ash or coal gangue as raw materials were designed and prepared with the help of thermodynamic calculations. Thermodynamic calculations were used to obtain the suitable chemical composition. Then, the imitation compounds were prepared and their phase/compositions were analyzed. Finally, their high-temperature melting performance and crystallization ability were evaluated. The results show that the characteristic temperature and crystallization ability of the imitation basalt compounds were similar to those of basalt. Moreover, the viscosity of red mud imitation basalt compound approached the viscosity of basalt with the increase in temperature. This work suggests that red mud, fly ash and coal gangue can be mixed with quartz and other source materials to produce imitation basalt fiber. Therefore, thermodynamic calculation is an effective method to design and prepare high-performance imitation basalt compounds.

Uniaxial tension of pure Al is studied at different loading rates by molecular dynamics simulation to understand the initial nucleation processes for amorphous structures and twinning, especially, the competition between twinning partial dislocation and Lomer one. There exists a transition point K I =0.205 eV A −2.5 between twinning partial dislocation and Lomer one, with Lomer dislocation preferable at high loads. A modified Peierls analytic model is established to describe the transition process. The analytic model reflects that a transition from twinning partial dislocation to Lomer one will occur when stress intensity factor K I reaches 0.205 eV A −2.5 , which is similar to the simulation trends. In addition, amorphization behaviours are observed at crack tip in pure Al by in-situ straining transmission electron microscopy. Both the experiment and simulation results are demonstrated that amorphization behaviours occur at crack tip in FCC Al.

Precipitate redistribution and texture evolution are usually two concurrent aspects accompanying grain refinement induced by various surface treatment. However, the detailed precipitate redistribution characteristics and process, as well as crystallographic texture in the surface refined grain layer, are still far from full understanding. In this study, we focused on the microstructural and crystallographic features of the sliding friction treatment (SFT) induced surface deformation layer in a 7050 aluminum alloy. With the combination of transmission electron microscopy (TEM) and high angle angular dark field scanning TEM (HAADF-STEM) observations, a surface ultrafine grain (UFG) layer composed of both equiaxed and lamellar ultrafine grains and decorated by high density of coarse grain boundary precipitates (GBPs) were revealed. Further precession electron diffraction (PED) assisted orientation mapping unraveled that high angle grain boundaries rather than low angle grain boundaries are the most favorable nucleation sites for GBPs. The prominent precipitate redistribution can be divided into three successive and interrelated stages, i.e. the mechanically induced precipitate dissolution, solute diffusion and reprecipitation. The quantitative prediction based on pipe diffusion along dislocations and grain boundary diffusion proved the distribution feasibility of GBPs around UFGs. Based on PED and electron backscatter diffraction (EBSD) analyses, the crystallographic texture of the surface UFG layer was identified as a shear texture composed of major rotated cube texture {001} 〈110〉 and minor {111} 〈112〉, while that of the adjoining lamellar coarse grained matrix was pure brass. The SFT induced surface severe shear deformation is responsible for texture evolution.

The deposition characteristics of titanium coating on SiC fiber using TiCl4-H2-Ar gas mixture in a cold-wall chemical vapor deposition were studied by the combination of thermodynamic analysis and experimental studies. The thermodynamic analysis of the reactions in the TiCl4-H2-Ar system indicates that TiCl4 transforms to titanium as the following paths: TiCl4 → TiCl3 → Ti, or TiCl4 → TiCl3 → TiCl2 → Ti. The experimental results show that typical deposited coating contains two distinct layers: a TiC reaction layer close to SiC fiber and titanium coating which has an atomic percentage of titanium more than 70% and that of carbon lower than 30%. The results illustrate that a carbon diffusion barrier coating needs to be deposited if pure titanium is to be prepared. The deposition rate increases with the increase of temperature, but higher temperature has a negative effect on the surface uniformity of titanium coating. In addition, appropriate argon gas flow rate has a positive effect on smoothing the surface morphology of the coating.

The Yb3+ and Er3+ co-doped yttrium molybdenum oxide upconversion phosphors were prepared by the solid state combustion method using urea as fuel at ignition temperature of 550 °C. The upconversion phosphors were characterized by X-ray diffraction (XRD), scanning electronic microscope (SEM), and photoluminescence spectra. XRD results revealed the samples were pure monoclinic Y2Mo4O15 phases when the sintering temperature was 700 °C. SEM micrographs illustrated particle size distribution was almost uniform with an average particle diameter of about 0.5–1.0 m. The obtained Y2Mo4O15:Yb3+, Er3+ presents bright and pure green upconversion luminescence during daylight pumping under 980 nm LD. According to the analysis of upconversion luminescent mechanism, the cross relaxation processes of Er3+ ions restrained the electron population of red emission energy level, which not only increased the green light upconversion emissions fluorescent branching ratio (IG:IR = 153:1) but also enhanced the efficiency and purity of green light emissions.

Although deformation processes in single-phase nano-polycrystalline alloys at different temperatures are well described, the deformation mechanism in two-phase nano-polycrystalline alloys at different temperatures is still unclear. Here, the deformation behaviour of the two-phase TiAl+Ti3Al nano-polycrystalline alloys is investigated at different temperatures by molecular dynamic simulation. For a comprehensive understanding of the processes, mechanical properties of the single-phase TiAl and Ti3Al nano-polycrystalline alloys are explored as well. The results of numerical simulations indicate that temperature has a strong influence on the deformation mechanism of the alloys. When temperature is below 800 K, the critical grain size (~8.3 nm) becomes a dominant factor controlling the deformation process in the single-phase TiAl. In the two-phase TiAl+Ti3Al nano-polycrystalline alloys, the motion of dislocations in the TiAl phase with the grain size smaller than the critical size dominates the deformation process. On the other hand, no obvious phenomena linked with the critical size occur in the Ti3Al phase. Once the strain exceeds 18.0%, the dislocation emission is observed in the Ti3Al grains. At high temperatures (≥800 K), in the two-phase nano-polycrystalline alloy, the deformation mechanism changes from the plastic deformation to the boundary slip and recrystallization.

Cryogenic treatment is an effective method that can improve the material's performance by changing the microstructure, such as shrinking the crystal lattice. It is usually used in combination with the annealing treatment of the material. In this article, the effects of cryogenic and annealing treatment on the microstructure and mechanical properties of TA15 friction stir welded joints are investigated. The results show that the base material's microstructure has no noticeable change after cryogenic and annealing treatment. However, the microstructure of the stirred zone has an apparent structural transformation. It indicates a selected influence of cryogenic and annealing treatment on the microstructure under severe plastic deformation of the friction stir welding. The weight fraction of the α phase increases from 78.7% to 84.8%, and the aspect ratio of the β phase becomes smaller. These changes improve the mechanical properties of the friction stir welded joints. The ultimate tensile strength and elongation of the TA15 welded joints treated by cryogenic and annealing treatment are 943.4 MPa and 5.5%.

Carbon-based pseudo-supercapacitors are one of the most promising electrical energy storage devices with high power density and long cycle life which is strongly desired for electric vehicles but their capacitance needs to be improved. Here, a new approach and design principle to enhance the energy density have been developed with the density functional theory methods. The results reveal that compared with pure carbon, the energy density could be enhanced significantly via heteroatom-doping. An intrinsic descriptor is discovered to establish a volcano-shaped relationship that correlates the capacitance with the heteroatom-doping structures of carbon nanomaterials, from which the best electrode structures are identified, which are in good agreement with the experimental results. Th strategies for further enhancing energy densities are proposed for rational design and fabrication of high-energy-density supercapacitors.