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This study employs the molecular dynamics method to examine the tensile mechanical properties and failure mechanism of MgAl2O4 spinel along [001] orientation. The results indicate that the mechanical properties of MgAl2O4 are sensitive to temperature. Young's modulus and ultimate tensile strength (UTS) of MgAl2O4 exhibit a linear decrease with increasing temperature from 100 to 2100 K. Specifically, Young's modulus decreases from 237.1 to 154.9 GPa, while the UTS decreases from 23.9 to 11.5 GPa. The failure mechanism of MgAl2O4 under uniaxial tensile loading is a brittle fracture induced by point defects. The propagation of microcracks in MgAl2O4 single crystal during tension is related to the slip band. The temperature does not have a significant effect on the direction of microcrack propagation, but it influences the crack expansion rate. In addition, the effect of strain rate on the mechanical properties of MgAl2O4 has been explored. In the range of 5 × 108 to 2 × 1010 s−1, the strain rate has almost no effect on the elastic modulus and the crack propagation direction and has little influence on the UTS. However, high strain rates delay the initiation of MgAl2O4 cracking. [ABSTRACT FROM AUTHOR]

Through molecular dynamics simulations, this study investigates the orientation and temperature dependence of the tensile mechanical properties, the failure mechanism, and crack propagation characteristics of MgAl2O4 single crystal. The results reveal significant anisotropy and temperature sensitivity in the mechanical properties of MgAl2O4. Particularly, [111]-oriented MgAl2O4 exhibits the highest elastic modulus and ultimate tensile strength but a relatively minor failure strain. In the 300 K to 2100 K temperature range, the elastic modulus, ultimate tensile strength, and failure strain decrease with increasing temperature. At 2100 K, MgAl2O4 exhibits excellent structural stability and high-temperature strength. The failure mechanism is a brittle fracture initiated by the continuous convergence of vacancies into micropores/microcracks. The propagation of microcracks is influenced by crystal orientation and slip bands. Nevertheless, high temperatures significantly accelerate crack propagation, leading to premature failure. This study provides guidelines for preparing MgAl2O4 with excellent mechanical properties. [ABSTRACT FROM AUTHOR]

Preparation of a titanium foil with weak anisotropy is of great significance for the development of bipolar plate materials for hydrogen fuel cell. However, the titanium foil obtained by rolling deformation often suffer from a severe deformation anisotropy due to the formation of a specific texture feature. In this study, the texture feature of pure titanium foil with different cold‐rolling reduction is characterized by electron back‐scattered diffraction (EBSD), and the effect of cold‐rolling deformation on texture evolution and tensile properties of titanium hfoil are systematically investigated. The results show that the cold‐rolling reduction could significantly affect the tensile anisotropy of titanium foil by regulating the texture characteristics. At the low level of cold‐rolling reductions (0%–30%), the texture of titanium foil is mainly pyramid texture, causing the obvious tensile anisotropy. At the medium level of cold‐rolling reductions (50%), strong basal‐plane texture components are appeared, causing that the activated slip system along transverse direction (TD) or normal direction (ND) is almost the same, and thus the tensile anisotropy gradually diminishes. At the high level of cold‐rolling reductions (70%), the intensity of basal‐plane texture becomes weak, and the tensile anisotropy appears in titanium foil again. The findings could provide theoretical guidance and technical support for the preparation of weak anisotropic titanium foil for hydrogen fuel cell. [ABSTRACT FROM AUTHOR]

To understand the hot compression deformation characteristics of the self-developed Al-9.3Zn-2.4Mg-1.1Cu alloy, the hot compression tests of Al-9.3Zn-2.4Mg-1.1Cu alloy were investigated by Gleeble 1500 thermo-mechanical simulator to determine the best hot processing conditions. The hot deformation temperatures were 300, 350, 400, and 450 °C, and the strain rates were 1, 0.1, 0.01, and 0.003 s−1, respectively. Based on the experimental results, the constitutive equation and hot processing maps are established, and the corresponding strain rate and temperature-sensitive index are analyzed. The results show that Al-9.3Zn-2.4Mg-1.1Cu alloy has a dynamic softening trend and high strain rate sensitivity during the isothermal compression process. The hot deformation behavior can be described by an Arrhenius-type equation after strain compensation. The temperature has a negligible effect on the hot processing properties, while a low strain rate is favorable for the hot working of alloy. The processing maps and microstructure show that the optimal processing conditions were in the temperature range of 400–450 °C and strain rate range of 0.003–0.005 s−1. [ABSTRACT FROM AUTHOR]

The interface mismatch and weak bonding between the aluminum matrix and reduced graphite oxide (rGO) limits the reinforcing effect of reduced graphene oxide-reinforced aluminum matrix composites. This study utilized vacuum hot-pressing sintering and hot extrusion methods to fabricate rGO/2024Al composite materials and improved the interface bonding of the composite materials through solution treatment and aging. The research results indicate that the tensile strength of the heat-treated composite material increased to 455 MPa, representing a 19% improvement. Appropriate heat treatment processes can aid in enhancing the interfacial structure of composites, augmenting the interfacial bonding strength, and optimizing load transfer efficiency. The reinforcement mechanisms of composites typically include textured strengthening, fine-grained strengthening, and load transfer strengthening. In addition, the rGO can toughen the composites through crack deflection and bridging effects. Therefore, this technique offers a promising route for optimizing properties and improving the interface of aluminum matrix composites reinforced with graphene, via a heat treatment process. [ABSTRACT FROM AUTHOR]

In this work, the interfacial structure, adhesion properties, and electronic structure of the Al(001)/MgAl2O4(001) interface are investigated via density functional theory calculations. Considering different termination atoms and stacking sites, six interfacial models are explored. The results show that the OAlO-terminated O-top stacking configuration has the greatest interfacial adhesion work of 2.51 J m−2. The nature of bonding between atoms at the Al(001)/MgAl2O4(001) interface is determined by analyzing their interfacial electronic structures, such as valence charge density difference, Bader charge, and density of states. The atoms of the Al(001)/MgAl2O4(001) OAlO-terminal exhibit not only the Al-Al metal bonding but also ionic bonding. For the O-top and two hollow configurations, Al-O covalent bonding components are also present, which mainly originate from the coupling between the Al-3p and O-2p orbitals. In turn, the OAlO-terminated O-top stacking configuration possesses deeper negative energy bands in the Al-O resonance peaks of the interfacial atoms than the OAlO-terminated hollow stacking configuration, resulting in stronger interfacial bonding. Finally, the OAlO-terminated O-top stacking interface corresponds to the most stable interfacial structure. [ABSTRACT FROM AUTHOR]

To investigate the compression and deformation behavior of nano-polycrystalline Cu/Al2Cu/Al-layered composites, it was constructed and analyzed using molecular dynamics simulation (MD). The findings indicate that The Cu/Al2Cu/Al materials exhibit sensitivity to changes in the interfacial layer d due to the asymmetry between tensile and compressive deformations. The compressive strain strengthening of the nano-polycrystalline Cu/Al2Cu/Al-layered composites increases as the interfacial layer d increases. During the tensile process, an increase in interfacial layer d leads to an increase in Young's modulus, while the fracture strength and fracture strain first increase and then decrease. The interfacial layer with a value of d = 4.88 nm promotes the delocalization of strain during the tensile and compressive deformation of nano-polycrystalline Cu/Al2Cu/Al materials. It facilitates cooperative deformation behavior between components, leading to improved toughness and strength of the materials. [ABSTRACT FROM AUTHOR]

To study the micromorphology and dynamic evolution law of copper aluminum composite interface evolution, ultra-high temperature laser Confocal microscopy (CLSM) was used to observe and analyze the evolution of copper aluminum interface in situ, and then SEM, EDS and other advanced material analysis methods were used to observe the micromorphology of the composite layer, and study the composition of the interface layer and the formation process of the copper aluminum composite interface. The results indicate that the formation of the copper aluminum composite interface layer is mainly related to the mutual diffusion of copper aluminum atoms and the interface reaction between copper and aluminum. The bonding of the copper aluminum composite interface is mainly related to the melting of the metal surface of the interface layer and the mutual diffusion of copper aluminum atoms, which is the main mechanism of the copper aluminum composite interface bonding. The intermetallic compound is mainly Al2Cu. In situ, observation of copper aluminum composite interface shows that there is a clear and relatively flat boundary between copper and the interface layer, while the boundary between aluminum and the interface layer is not straight, which is caused by the difference in thermal expansion coefficient, Lattice constant and hardness between intermetallic compounds and matrix and between intermetallic compounds. At the same time, it was found that there is a certain relationship between the visual changes of the copper aluminum composite interface image and reaction-diffusion migration during in-situ observation using a confocal laser scanning high-temperature microscope. Moreover, under no pressure, the oxide layer and interface inclusions can seriously affect the interface bonding. [ABSTRACT FROM AUTHOR]

In view of the problem that the top hammer was prone to structural failure caused by cracking hammer and collapse hammer during long-term loading and unloading, taking Ф240 large top hammer as the research object, the stress distribution in sensitive areas of the super large top hammer in the working process was calculated and analyzed by finite element software. The stress situation of the small top hammer under the same working conditions was compared and studied, and the reasons for the super large top hammer easy to break were analyzed from the stress aspect. Then, the elemental mapping analysis was carried out by scanning electron microscopy, and the fracture morphology and chemical composition of the broken top hammer were studied. The results show that the tensile stress and shear stress of the top hammer slope are greater than those of the core, the crack source is easy to occur at the inclined surface, and the crack mainly extends along the WC / WC interface. The high pressure anvil has a higher degree of fracture oxidation and Co phase precipitation accumulation due to the temperature being higher than the slope. [ABSTRACT FROM AUTHOR]

The effect of solution temperature on the microstructure of 5A super duplex stainless steel (SDSS) was investigated by scanning electron microscopy (SEM), energy-dispersive spectrometry (EDS), and transmission electron microscope (TEM). The corrosion resistance of the samples after solution heat treatment is analyzed by chemical immersion and electrochemical test. The experimental results show that with an increasing solution temperature, the ratio of α/γ phase is close to 1:1 at 1080 °C, demonstrating the best anti-corrosion and mechanical properties. When the temperature of solid solution is 950 °C, the content of σ phase is higher than the other samples, which seriously affects the mechanical properties and corrosion resistance. According to the TEM results, it is found that there is a coherent relationship between the σ and α phases, which proves that the eutectoid reaction of the α phase leads to the formation of σ phase. [ABSTRACT FROM AUTHOR]

The microstructure evolution and dynamic softening mechanism of a 00Cr27Ni7Mo5N hyper duplex stainless steel during uniaxial hot compression are investigated based on the electron backscattered diffraction and transmission electron microscopy. The (sub)grains of ferrite are significantly refined at the temperature of 1050 °C using the strain rate of 0.01 to 1 s−1. The softening mechanism within ferrite are classified as continuous dynamic recrystallization (CDRX). However, the dynamic softening within ferrite is diminished at a strain rate of 10 s−1. A softening mechanism analogous to discontinuous dynamic recrystallization (DDRX) is observed in the ferrite/austenite interphase mantle regions. The dynamic softening within austenite is remarkably limited at the temperature of 1050 °C, which appears to be complex‐shaped deformation bands. There are a small number of recrystallized grains within austenite. The dynamic softening of hyper duplex stainless steel is dominated by ferrite. The formation of DRX nuclei and growth of austenite by strain‐induced boundary migration mechanism is observed at the temperature of 1250 °C with different strain rates, indicating its softening mechanism is akin to DDRX. In addition, the increase in temperature and the decrease in strain rate is favorable to the dynamic softening of austenite. [ABSTRACT FROM AUTHOR]

In this paper, through high-temperature tensile tests of 55NiCrMoV7 steel, high-temperature fracture behavior, microstructure evolution, and carbide distribution characteristics of both the thermal–mechanical coupling zone (fracture zone) and thermal stress zone (clamping zone) at different temperatures were studied. Intrinsic relationships between high-temperature fractures and carbide types, distribution and size were revealed, and evolution mechanisms of microstructure near cracks in 55NiCrMoV7 hot-working die steel during high-temperature deformation was clarified. Samples were stretched at different temperatures from 25 °C to 700 °C, and microscopic examinations were carried out using SEM and TEM. The results showed the following. With the increase in temperature, tensile strength and yield strength decreased, elongation and reduction of area increased, and fracture mode changed from brittle fracture to ductile fracture by transition temperature at about 400 °C. During high-temperature deformation, the grain dislocation density decreased and the tempered martensite decomposed, recovered, recrystallized, and then grain grew. M7C3 and M23C6 carbides precipitated and grew along the grain boundary, and a small amount of fine granular MC carbides was dispersed in the grain. The work done by the external force on the deformation zone would cause the temperature of it to be higher than the tensile temperature, which provides thermodynamic conditions for the redissolution of small carbides near the fracture zone and the grain growth of large carbides, resulting in a decrease in small carbides and increase in large carbides in thermal–mechanical coupling zones. [ABSTRACT FROM AUTHOR]

In this work, using the high-throughput density functional theory calculation method, the influence of 36 alloying elements on the elastic properties of FCC-Cu was systematically studied, and based on the Labusch model, a linear relationship was fitted between the composition and lattice parameters, and the shear modulus. The solid solution strengthening behavior brought about by alloying was studied quantitatively. The results showed that most alloying elements have solid solution potentiality in copper. The change in the elastic modulus and the strengthening effect of alloying on solid solutions were determined by the elements' positions in the periodic table. In the same period, the alloying elements located in the middle of the period tended to enhance the elastic modulus of copper, while the elements located at both ends have greater solid solution strengthening ability. The predicted results are in good agreement with the experimental values, which provide theoretical guidance for the design of high-performance copper alloys. [ABSTRACT FROM AUTHOR]

In this work, effects of artificial aging temperature on the mechanical properties and precipitation behavior of a pre-strained Al–Cu–Mg–Ag alloy were investigated by hardness and tensile tests, and quantitative transmission electron microscope analysis. Three aging conditions, a single aging at a high temperature (T8H), a single aging at a low temperature (T8L) and an interrupted aging at low temperature following under-aging at a higher temperature (T8I4), were compared. Based on the quantitative analysis of the strengthening phases, the evolution law of the average diameter, thickness and volume fraction of Ω plates with the aging time for a pre-stretched Al–Cu–Mg–Ag alloy aged at 190 °C/160 °C may be predicted by the modified equations. The precipitation behavior of Ω precipitates was confirmed by considering the coarsening kinetics of them. Results show that a higher aging temperature can increase the precipitation kinetics of Ω phase and inhibit the precipitation of θ′ phase. Thus, a new type of interrupted aging treatment, T8I4 (3.2% pre-stretch + 190 °C/1 h + 160 °C/10 h), was proposed to enhance the strength of the pre-stretched Al–Cu–Mg–Ag alloy. [ABSTRACT FROM AUTHOR]

This paper investigated the micromechanical behavior of different 6H-SiC/Al systems during the uniaxial tensile loading by using molecular dynamics simulations. The results showed that the interface models responded diversely to the tensile stress when the four low-index surfaces of the Al were used as the variables of the joint surfaces. In terms of their stress–strain properties, the SiC(0001)/Al(001) models exhibited the highest tensile strength and the smallest elongation, while the other models produced certain deformations to relieve the excessive strain, thus increasing the elongation. The SiC(0001)/Al(110) models exhibited the largest elongations among all the models. From the aspect of their deformation characteristics, the SiC(0001)/Al(001) model performed almost no plastic deformation and dislocations during the tensile process. The deformation of the SiC(0001)/Al(110) model was dominated by the slip of the 1/6 <112> Shockley partial dislocations, which contributed to the intersecting stacking faults in the model. The SiC(0001)/Al(111) model produced a large number of dislocations under the tensile loading. Dislocation entanglement was also found in the model. Meanwhile, a unique defect structure consisting of three 1/6 <110> stair-rod dislocations and three stacking faults were found in the model. The plastic deformation in the SiC(0001)/Al(112) interface model was restricted by the L-C lock and was carried out along the 1/6 <110> stair-rod dislocations' direction. These results reveal the interfacial micromechanical behaviors of the 6H-SiC/Al composites and demonstrate the complexity of the deformation systems of the interfaces under stress. [ABSTRACT FROM AUTHOR]

In this work, first-principles calculations are performed to investigate the interfacial bonding properties of the TiC(001)/TiAl(100) interface. After convergence tests, 5-layer TiC(001) and 5-layer TiAl(100) surface slabs are chosen to construct four kinds of TiC(001)/TiAl(100) interface structures with different atomic stacking characteristics. The adhesive work and interfacial energy are calculated to analyze the interfacial bonding strength and thermodynamic stability. The interfacial electronic structure is revealed by the charge density difference and the partial density of states (PDOS). Research shows that the TiC(001)/TiAl(100) TOP(C) interface stacking structure has the largest interfacial adhesive work (2.966 J/m2) and the lowest interfacial energy (0.233 J/m2), which indicates that it has the greatest interfacial bonding strength and stability, and is the most ideal balanced structure for TiC(001)/TiAl(100) interface. Based on the analysis of the interfacial electronic structure, the interfacial bonding of the TiC(001)/TiAl(100) TOP(C) interface is mainly composed of Ti-C covalent bond and Al-C covalent bond, and these strong interactions contribute to its optimal interfacial bonding properties. [ABSTRACT FROM AUTHOR]

This paper uses ANSYS Workbench platform to simulate the casting and rolling composite process, taking the horizontal type casting and rolling machine as the research object, and conducts the numerical simulation study of copper-aluminum composite solid-liquid casting and rolling heat-flow coupling, mainly to study different walking speed, aluminum pouring temperature, casting and rolling zone length, heat transfer coefficient on the temperature field, liquid phase rate influence law, and use it as a theoretical guide for copper-aluminum solid-liquid casting. The experiments of copper-aluminum solid-liquid casting-rolling composite were carried out to optimize the process parameters and to verify the experiments, so as to prepare a well-bonded copper-aluminum composite plate. The composite mechanism in the preparation of copper-aluminum composite plate was analyzed, and it was clarified that the interfacial layer was formed through four stages: contact between copper and aluminum surfaces, contact surface activation, mutual diffusion of copper and aluminum atoms, and reaction diffusion. [ABSTRACT FROM AUTHOR]

In this work, the effect of secondary-phase precipitation on the microstructure, mechanical properties, and corrosion resistance of 00Cr27Ni7Mo5N hyper-duplex stainless steel (HDSS) during solution treatment was investigated. The results reveal that σ-phase precipitates at the interface between the α and γ phase when the solution treatment temperature is lower than 1070 °C. It is not only brittle, but also prone to create a Cr-depleted zone, which significantly deteriorates the mechanical properties and corrosion resistance. With the increase in the solution treatment temperature, the volume fraction of ferrite gradually increases. The yield strength and tensile strength increase slightly, but the elongation decreases. At the same time, the impact toughness shows a trend of first increasing and then decreasing. When the solution treatment temperature is higher than 1130 °C, Cr2N precipitates in the ferrite. The precipitation of Cr2N causes a decrease in the plastic toughness, but it does not deteriorate the mechanical properties as significantly as the σ phase. However, it can also cause the formation of a Cr-depleted zone that significantly decreases the corrosion resistance. There is no secondary-phase precipitation in the sample after solution treatment at 1100 °C, which shows the best mechanical properties and corrosion resistance. [ABSTRACT FROM AUTHOR]

Herein the present work, the thermodynamic, physical, and mechanical properties of different random solid solution structure models are first calculated based on first‐principles calculation method, and the optimal composition ratio of 5Ti5Zr5Nb1Sn is quickly selected as a new biomedical high‐entropy alloy (HEA) with a low elastic modulus and high strength–ductility balance. Then, 5Ti5Zr5Nb1Sn HEA is prepared by vacuum‐melting method. The microstructure characterization results show that the actual composition of 5Ti5Zr5Nb1Sn HEA corresponds to the calculated target composition, and the HEA consists of two phases BCC1 and BCC2 with distinct color and structure. The compressive yield strength and compressive elongation of the 5Ti5Zr5Nb1Sn HEA are 1171.2 MPa and 29.03%, respectively. The compressive elastic modulus is 22.4 GPa, which is within the range of human bone elastic modulus (10–30 GPa). There are many tiny dimples and small tearing edges in the compression fracture, showing obvious plastic deformation characteristics. The analysis results of potentiodynamic polarization curve show that the corrosion resistance of 5Ti5Zr5Nb1Sn HEA is equivalent to that of pure titanium. Therefore, 5Ti5Zr5Nb1Sn HEA possesses the characteristics of high strength and ductility, low elastic modulus, and excellent corrosion resistance, and has the potential to be used as metallic biomedical materials. [ABSTRACT FROM AUTHOR]

TiAl alloys are regarded as ideal lightweight structural materials above 600 °C and show remarkable application prospects in the field of aerospace materials. However, many potential TiAl alloy engineering applications have been limited by their low room-temperature tensile plasticity and insufficient high-temperature capability. Composite technology is an effective method for enhancing the comprehensive properties of TiAl alloys. In this paper, recent research progress in TiAl matrix composites is reviewed to highlight the scientific and technological investigation of TiAl matrix composites with excellent properties. The content includes four aspects of TiAl matrix composites: reinforcement selection, configuration design, interfacial microstructure, and processing technology. The aim of this work is to provide a reference for the preparation and research of TiAl matrix composites and open up a novel design direction for TiAl matrix composites with excellent comprehensive properties. [ABSTRACT FROM AUTHOR]

The Ti2AlC/TiAl composite with a homogenous architecture was fabricated via spark plasma sintering (SPS) using Ti/Al/GNSs composite powders, after ultrasonic mechanical stirring, as raw materials. The phases, microstructure, compressive properties and Vickers hardness of the composite were methodically characterized. We observed the transformation of graphene nanosheets from multi-layer to few-layer by the ultrasonic dispersion and the uniform distribution of few-layer graphene nanosheets in composite powders by ultrasonic mechanical stirring. The composite is mainly composed of rod-shaped Ti2AlC particles and a TiAl matrix, and the formation of rod-shaped morphology with the long axis along the (0001) plane is due to the fact that the growth rate of Ti2AlC parallel to the (0001) plane is much higher than the growth rate along the [0001] direction. The compressive stress and strain of the as-prepared Ti2AlC/TiAl composite reach 1451.2 MPa and 19.7%, respectively, which are better than some Ti2AlC/TiAl composites using graphite as the carbon source, and the Vickers hardness remains between 400~500 HV. The fracture morphologies show the deformation and fracture features of Ti2AlC particles, i.e., lamellae kinking and laminated tearing, which could increase the toughness of TiAl alloys. [ABSTRACT FROM AUTHOR]

The medium carbon-medium alloy steel was developed for the manufacture of large ball mill liners and sports equipment. In this study, the continuous cooling transformation curve of a novel type of medium carbon-medium alloy steel was measured with a thermal simulation machine; based on this curve, the hardening and tempering processes were optimized. The steel was then complex modified with alkaline earth and rare earth alloys. The mechanical properties of the treated steel were tested. The microstructure of the steel was analyzed by metallographic microscopy, X-ray diffraction, scanning electron microscopy and transmission electron microscopy, and the wear surface of the steel was analyzed by a three-dimensional morphometer. After high-temperature tempering, the microstructure transformed into tempered sorbite, which possesses good mechanical properties and can adapt to working conditions that require high strength and toughness. Rare earth or alkaline earth modification of the medium carbon-medium alloy steel promoted microstructural uniformity and grain refinement and improved the mechanical and anti-wear properties. [ABSTRACT FROM AUTHOR]

To improve the antibacterial properties of the non-woven fabric (Tel), the antibacterial Tel composed of chitosan and silver ions composite antibacterial agents (CS-Ag/Tel) was prepared by a facile impregnation method in this work. The morphology, surface composition, microstructure, stability and mechanical properties of the as-prepared antibacterial non-woven fabrics were characterized by FT-IR, SEM, ICP, contact angle and universal testing machine, respectively. The antibacterial performance was evaluated by agar diffusion method and viable bacteria counting method. The results showed that the chitosan-silver ions was successfully impregnated on the surface of the Tel, and endowed the Tel with good stability and antibacterial performance. The ICP test showed that the maximum release concentration of silver in CS-Ag/Tel was 0.142 ppm. The antibacterial tests showed the modified CS-Ag/Tel had an obvious inhibition zone and the antibacterial rate arrived at 96.33%. At the same time, the mechanical properties of the as-prepared CS-Ag/Tel was comparable to the raw Tel. These findings suggested that the as-prepared CS-Ag/Tel had an excellent antibacterial performance, which showed important value in the development and application of the non-woven fabric in the fields of cosmetics and medicine. [ABSTRACT FROM AUTHOR]

In the present work, the effects of vacancy in graphene on the bonding strength, electronic characteristics and thermal conductance of Cu/graphene/Al interface are deeply studied by first-principles calculation. It is found that the introduction of appropriate vacancies could simultaneously enhance the Cu/graphene/Al interfacial bonding strength and thermal conductance. The Cu(111)/perfect graphene/Al(111) interfacial bonding strength is very low because of the limited interface charge transfer. However, when the vacancy is introduced in the graphene, the Cu(111)/graphene/Al(111) interfacial bonding strength could enhance several times, the enhancement effect increases with the vacancy concentration, and the increasement of vacancy area has a better effect for the enhancement of Cu(111)/graphene/Al(111) interfacial bonding strength at the same vacancy concentration. The reason why the vacancy in graphene could significantly improve the interfacial bonding strength is that the Cu-p and Al-p state of interfacial Cu and Al atom are more delocalized and could effectively hybridize with the p states of C atom near the vacancy in graphene. In addition, the introduction of vacancy could effectively increase the phonon density of states matching degree between the interfacial Cu, Al atoms and C atoms in graphene, and thus could effectively enhance the thermal conductance across the Cu(111)/graphene/Al(111) interface. [ABSTRACT FROM AUTHOR]

Nanofriction with few layers of graphene as lubrication is an interesting issue recently, and it provides a quite important guide for modeling the nanofriction properties of nanodevice. Based on the molecular dynamics (MD) simulations, nanofriction properties of a silicon tip sliding on different graphene layers with or without substrate were studied systemically. We revealed that the friction of these systems exhibits clearly the even-odd oscillations with different thickness of graphene, and we further demonstrated that such even-odd oscillations behavior is totally independent of the size of the silicon tips, as well as applying normal loadings. The underlying physics of this intriguing phenomenon is attributed to the oscillations of indirect-contact-atom-number between top and sublayers of suspended graphene. Furthermore, we showed that such indirect contact oscillations would be reflected by the direct contact oscillations between the tip and the top-layer graphene when graphene lubrication layers on a rigid substrate. Overall, our new findings not only enrich the nanofriction mechanism of graphene lubrication systems, but also introduce a new way to design the nanofriction systems with two-dimensional (2D) van der Waals materials as lubrications. [ABSTRACT FROM AUTHOR]

Most of the molybdenum (Mo) bilayer films are deposited by direct current (DC) magnetron sputtering at the bottom and the top layer (DC/DC). However, the deposition of Mo bilayer film by radio frequency (RF) Mo bottom layer and DC Mo top layer magnetron sputtering has been less studied by researchers. In this paper, the bottom layer of Mo bilayer film was deposited by RF magnetron sputtering to maintain its good adhesion and high reflectance, and the top layer was deposited by DC magnetron sputtering to obtain good conductivity (RF/DC). Generally, the bottom layer sputtering pressure is relatively random, in this paper, the effects of the bottom layer RF sputtering pressures on the microstructures and properties of Mo bilayer films were first studied in detail. Next, in order to further improve their properties, the as-prepared Mo bilayer films at 0.4 Pa bottom layer RF sputtering pressure were annealed at different temperatures and then investigated. Specifically, Mo bilayer films were deposited on soda-lime glass substrates by RF/DC magnetron sputtering at different bottom layer RF sputtering pressures in the range of 0.4–1.2 Pa, the powers of bottom layer RF sputtering and top layer DC sputtering were 120 W and 100 W, respectively. Then, Mo bilayer films, prepared at a bottom layer sputtering pressure of 0.4 Pa and top layer sputtering pressure of 0.3 Pa, were annealed for 30 min at various temperatures in the range of 100–400 °C. The effects of bottom layer sputtering pressures and the annealing temperatures on the microstructures, electrical and optical properties of Mo bilayer films were clarified by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), atomic-force microscopy (AFM), and ultraviolet (UV)-visible spectra, respectively. It is shown that with decreasing bottom layer sputtering pressure from 1.2 to 0.4 Pa and increasing annealing temperature from 100 to 400 °C, the crystallinity, electrical and optical properties of Mo bilayer films were improved correspondingly. The optimized Mo bilayer film was prepared at the top layer sputtering pressure of 0.3 Pa, the bottom layer sputtering pressure of 0.4 Pa and the annealing temperature of 400 °C. The extremely low resistivity of 0.92 × 10−5 Ω.cm was obtained. The photo-conversion efficiency of copper indium gallium selenium (CIGS) solar cell with the optimized Mo bilayer film as electrode was up to as high as 13.5%. [ABSTRACT FROM AUTHOR]

We report herein the successful synthesis of in situ nanocomposite W-30Cu as powder via the hydrothermal approach combined with the co-reduction process, having sodium tungstate and copper nitrate as starting materials. The cold isostatic pressing, vacuum sintering and canned hot extrusion technology have been employed in order to improve the properties of the W-30Cu alloy. The impact of preparation's methodologies on the microstructure, mechanical and physical properties have been investigated by the means of X-ray diffractometry (XRD); scanning electron (SEM); field emission electron (FE-SEM) and high-resolution electron (HRTEM) microscopies; conductivity meter and Brinell hardness tester. The results indicate that the precursor powder had a coating structure leading to W and Cu elements in situ symbiosis during the co-reduction period. The W-Cu reductive powder displayed an unstable core-shell structure of W coated Cu. During hot extrusion, the rapid mass transport, sintering mode conversion and bridge effect elimination enhance the density and properties of the W-Cu composites. The microstructure of the W-Cu composite exhibited a uniform distribution of W within the Cu phase with intact Cu network structure as well as fine W particles. The relative density, conductivity and hardness of the final product have reached 99.2%, 43.3% IACS and 214 HB, respectively, which are superior compared to those obtained by the traditional powder metallurgy methods. [ABSTRACT FROM AUTHOR]

In this paper, the bilayer Mo films with a constant thickness were deposited by direct current and direct current (DC/DC), radio frequency and direct current mixed (RF/DC) magnetron sputtering, respectively. Changing thickness ratios of bottom layer to total thickness of bilayer film in the range from 10% to 50%, ten types of bilayer Mo thin films were deposited. The purpose is to improve the photo-conversion efficiency of Cu(In, Ga)Se2(CIGS) solar cells by changing the sputtering modes and thickness ratio. The microstructures, electrical and optical properties of the bilayer Mo thin films were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), atomic force microscope (AFM), Hall Effect measurement system, ultraviolet-visible spectrophotometer (UV-vis) and four-point probe resistance system. It was found that with the increase of thickness ratios in two sputtering modes, both the crystallinity and grain size decreased, while the reflectance increased. Especially, when the thickness ratio was 40%, the resistivity of Mo film prepared in RF/DC mode was as low as 3.365 ×10-5 Ω·cm and the highest reflectance was above 60%. Using this optimized Mo thin film as electrode, the highest photo-conversion efficiency for the CIGS thin film solar cells was as high as 11.5%. [ABSTRACT FROM AUTHOR]

The arc erosion under medium direct currents in the argon flow was tested on tungsten-copper (W-Cu) contacts which were processed by hot extrusion and heat treatment. The scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were used to study the microstructure of the W-Cu powders and compacts. The contact resistance, arcing energy, and arcing time were continuously measured by JF04C contact materials test system. Changes in tungsten-copper contact surface were observed by SEM. The test results showed that the arcing time and arcing energy all increase with current and voltage, but the changes of average contact resistance are more complicated. For a short arcing time, the average contact resistance decreases with increasing current due to the vaporization of Cu. However, for a longer arcing time, it slightly increases due to the formation of high resistant films, compound copper tungsten. The formation of compound copper tungsten was confirmed by the increased Rc kept in the range from 1.1 to 1.6 mΩ. The compound copper tungsten is first exposed with a tungsten and copper-rich surface, and then totally exposed due to evaporation of copper from the surface. At last a stabilized surface is created and the crystals decrease from 8 μm to 2 μm caused by the arc erosion. [ABSTRACT FROM AUTHOR]

SiCp/2024 aluminum alloy matrix composite was prepared by powder metallurgy method. Effects of heat treatment on the microstructure and mechanical properties of composite were investigated by SEM, EDS, XRD, HREM, tensile and hardness tests. The experimental results showed that SiC particles distributed uniformly in the matrix and were in good combination with matrix. The tensile strength and hardness were improved significantly after heat treatment. With the increase of solid solution temperature, the alloy phases dissolved in the matrix gradually. When the solid solution temperature arrived at 505 °C, the alloy phases dissolved thoroughly, and the composite exhibited the highest tensile strength and hardness ( δ=360 MPa, HBS=104). The main strengthening phase was AlCu, which was granular and distributed dispersively in the matrix. Effect of T6 was better than that of T4 at the same solid solution temperature. [ABSTRACT FROM AUTHOR]

An adequate hardness of MoS/Cu composites has not been achieved if these materials are applied under the extreme wear conditions. Therefore, Mo-reinforced MoS/Cu composites were prepared by powder metallurgy (P/M) methods. The electrical sliding wear properties in the absence or presence of Mo-reinforced MoS/Cu composites were tested by HST-100 high speed electric-tribometer. The hardness, electrical conductivity, density, and microstructure of MoS/Cu composites were observed. Mo-reinforcement MoS/Cu composites are of good electrical conductivity, while the hardness of Mo-reinforcedment MoS/Cu composites is about 33.3% higher than that of MoS/Cu composites. With the addition of Mo, composites show better wear properties under high speed and large electric current due to the improvement of hardness. The effects of current intensity and sliding velocity on the wear properties of the tested materials are complicated, and the wear mechanisms of MoS/Cu composites are mainly abrasive wear and adhesive wear with arc erosion. [ABSTRACT FROM AUTHOR]

In the present study, the tested hypereutectic Al-21wt.%Si alloys were prepared by modifying the melt using different proportions of P and Ce, and then applying T6 heat treatment. The modification effects and mechanism of P+Ce complex modifier on the Si phase of hypereutectic Al-21wt.%Si alloy were studied, and the aging precipitation behavior after modification was characterized by means of tensile strength measurement, OM, SEM and TEM analysis. The results show that the massive primary silicon phase particles are significantly refined after modification, while the needle-like eutectic silicon crystals become fibrous and short. It was found that the mechanism of phosphorus modification on the primary silicon can be attributed to heterogeneous nucleation of AlP, while the modification mechanism of Ce can be explained by adsorbing-twinning theory. In the aged microstructure of the modified hypereutectic Al-21wt.%Si alloy, there existed some strengthening phases such as Al4Cu9, Al2Cu, AlCu3, and Al57Mn12. The P+Ce complex modifier not only affected the size of primary silicon and eutectic silicon, but also the aging behavior of alloys under the heat treatment process. When Al-21wt.%Si alloy was modified using 0.08%wt.P + 0.6wt.% Ce, the aging precipitates were dispersed uniformly in the alloy, and its mechanical properties at room and elevated temperatures are optimized (Rm = 287.6 MPa at RT, Rm = 210 MPa at 300°C). [ABSTRACT FROM AUTHOR]

Middle reinforcement content SiCp/Al composites ( V=30%, 35% and 40%) for precision optical systems applications were fabricated by powder metallurgy technology. The composites were free of porosity and SiC particles distributed uniformly in the composites. The mean linear coefficients of thermal expansion (20-100 °C) of SiCp/Al composites ranged from 11.6×10 to 13.3×10 K and decreased with an increase in volume fraction of SiC content. The experimental coefficients of thermal expansion agreed well with predicted values based on Kerner's model. The Brinell hardness increased from 116 to 147, and the modulus increased from 99 to 112 GPa for the corresponding composites. The tensile strengths were higher than 320 MPa, but no significant increasing trend between tensile strength and SiC content was observed. [ABSTRACT FROM AUTHOR]

Metal matrix composites manufactured by the powder metallurgy route often exhibit different tensile strength due to particle geometrical reasons. The tensile strength tendency was studied in 2024 Al/30% SiCp composites as a function of relative particle size (RPS) ratio between the matrix and reinforcement particles. Dry blended composite powders, with different RPS ratios, were hot-pressed in vacuum, their microstructures were observed, and their tensile properties were measured. It was found that a decrease in RPS ratio resulted in a decrease in tensile strength, as a result of improved distribution of the SiCp. Despite their low density and heterogeneous distribution, 3-μm SiCp-reinforced composites had maximum tensile strength. The main reasons were due to the few fracture for small SiCp and the strengthening of the matrix microstructure from small particle effects. Solution treatment plus aging of the composites with the RPS ratio of 10:3 resulted in a significant improvement (42%) in strength due to the smaller diffusion path length for the alloying element. [ABSTRACT FROM AUTHOR]

The effect of CeO2 content on the microstructure and properties of SiCp/Al-Si composites prepared by powder metallurgy was studied, and the mechanism of CeO2 in composites was deeply analyzed. The results show that the addition of the appropriate amount of CeO2 can refine the Si particles and improve the tensile properties of the SiCp/Al-Si composites. As the CeO2 content increases from 0 to 0.4 vol%, the particle size of the Si phase shows a tendency to decrease first and then increase, while the tensile strength, yield strength, and elongation of the composites show a trend of first increasing and then decreasing. When the CeO2 content is 0.2 vol%, the refining effect of CeO2 and the tensile properties of composites are the best. The fracture mode of SiCp/Al-Si composites with a rare earth addition is a mixed fracture. There are three main mechanisms for CeO2 in SiCp/Al-Si composites. One is when CeO2 serves as the nucleation substrate of Si phase to refine Si particles. The second is when CeO2 reacts with the alloying elements in the aluminum matrix to form a new phase, CeCu2Si2, which can not only play a role of dispersion strengthening, but also improve the bonding strength between Al matrix and Si particles. The third is the pinning effect of CeO2 and CeCu2Si2 particles on grain boundaries or phase boundaries to refine aluminum grains. [ABSTRACT FROM AUTHOR]

In this work, the effects of 20 transition element additions on the interfacial adhesion energy and electronic structure of Al(111)/6H-SiC(0001) interfaces have been studied by the first-principles method. For pristine Al(111)/6H-SiC(0001) interfaces, both Si-terminated and C-terminated interfaces have covalent bond characteristics. The C-terminated interface has higher binding energy, which is mainly due to the stronger covalent bond formed by the larger charge transfer between C and Al. The results show that the introduction of many transition elements, such as 3d transitional group Mn, Fe, Co, Ni, Cu, Zn and 4d transitional group Tc, Ru, Rh, Pd, Ag, can improve the interfacial adhesion energy of the Si-terminated Al(111)/6H-SiC(0001) interface. However, for the C-terminated Al(111)/6H-SiC(0001) interface, only the addition of Co element can improve the interfacial adhesion energy. Bader charge analysis shows that the increase of interfacial binding energy is mainly attributed to more charge transfer. [ABSTRACT FROM AUTHOR]

The effect of cooling rate on the microstructure of ZA48 alloy was investigated. The alloy was prepared using a relatively simple technique, i e, rapid cooling of the melt in a steel wedge mould. The dependence of microstructure on the cooling rate (about 40 to 10 K/s) was determined by the secondary dendrite arm space size measurement, optical microscopy(OM), and transmission electron microscopy (TEM). It is found that the matrix structure over a large cooling rate is composed of α-Al dendrite and eutectoid ( α+ η), the size of α-Al dendrite decreases with increasing cooling rate. The relationship between the cooling rate and the secondary dendrite arm space size has been established. TEM shows that a large number of small and dispersed precipitations can be seen in the primary α phase of tip region. Electron diffraction pattern shows that the precipitate phase is ZnMg phase. [ABSTRACT FROM AUTHOR]

SiCp/Al-Si composites with different CeO2 contents were prepared by a powder metallurgy method. The effect of CeO2 content on mechanical properties, friction and wear properties of the composites was studied. The results show that with the increase in CeO2 content from 0 to 1.8 wt%, the density, hardness, friction coefficient of the composites first increases and then decreases, the coefficient of thermal expansion (CTE) and wear rate of the composites first decreases and then increases. When the content of CeO2 was 0.6 wt%, the density and hardness of the composite reached the maximum value of 98.54% and 113.7 HBW, respectively, the CTE of the composite reached the minimum value of 11.1 × 10−6 K−1, the friction coefficient and wear rate of the composite reached the maximum value of 0.32 and the minimum value of 1.02 mg/m, respectively. CeO2 has little effect on the wear mechanism of composites, and the wear mechanism of composites with different CeO2 content is mainly abrasive wear under the load of 550 N. Compared with the content of CeO2, load has a great influence on the wear properties of the composites. The wear mechanism of the composites is mainly oxidation wear and abrasive wear under low load. With the increase in load, the wear degree of abrasive particles is aggravated, and adhesive wear occurs under higher load. [ABSTRACT FROM AUTHOR]

SiCp/Al-Si composites with different CeO2 contents were prepared by a powder metallurgy method. The effect of CeO2 content on the microstructure of the composites was studied. The mechanism of CeO2 on the precipitation of Si during sintering was analyzed by theoretical calculations. The results show that the appropriate amount of CeO2 can significantly refine the size of precipitated Si particles in the composite and increase the number of Si particles. With the increase of CeO2 content from 0 to 0.6 wt%, the number of Si particles precipitated in the composites increases gradually, and the average particle size of Si particles decreases gradually. When the CeO2 content is 0.6 wt%, the number of Si particles precipitated in the composites reaches the maximum, and the average particle size reaches the minimum. However, with the increase of CeO2 content from 0.6 wt% to 1.8 wt%, the number of Si particles precipitated in the composites began to decrease, and the average size of Si particles gradually increased. CeO2 can be used as heterogeneous nucleation substrate of precipitated Si, and the nucleation rate of precipitated Si on a CeO2 substrate is higher than that on an aluminum substrate. The proper addition of CeO2 can improve the nucleation efficiency of precipitated Si, thus increasing the amount and refining the size of precipitated Si. [ABSTRACT FROM AUTHOR]

The research elaborates on the mechanical properties at the Al (111)/6H-SiC (0001) interface based on the density functional theory. Because of the difference in atom category at the interface of 6H-SiC (0001), it takes the C-terminated interface and Si-terminated interface into account. As indicated by the gross energy computing results at the two interfaces, the C-terminated Al (111)/6H-SiC (0001) interface demonstrates a greater adhesion force than the Si-terminated counterpart. Throughout detailed analysis on the bonding mechanism, surface hybridization and charge transfer at the Al (111)/6H-SiC (0001) reaction interface, the research reveals its strong covalent characteristics. According to the comparative study on the ideal tensile strength and general stacking fault energy at varying cleavage surfaces, a conclusion can be fitly reached that the fracture at the Al (111)/6H-SiC (0001) interface is easily seen in Al-Al bonds in the Al matrix instead of C(Si)-Al bonds at the interface. Despite the greater adhesion energy of the C-Al bond than the Si-Al bond, Al-Al bonds close to the C-terminated Al (111)/6H-SiC (0001) interface easily fracture due to the low ideal tensile strength. [ABSTRACT FROM AUTHOR]

Hot deformation at elevated temperature is essential to densify particle-reinforced aluminum matrix composites (AMCs) and improve their performance. However, hot deformation behavior of the AMCs is sensitive to the variation of hot-processing parameters. In this paper, optimal processing parameters of dual-scale SiCp/A356 composites were determined to explore the control strategy of the microstructure. Hot-compression tests were conducted at temperatures ranging from 460 to 520 °C under strain rates from 0.01 to 5 s−1. Constitutive equation and processing maps were presented to determine the hot-processing parameters. Microstructure evolution of the dual-scale SiCp/A356 composites was analyzed. The strain rate of 0.62–5 s−1 and deformation temperature of 495–518 °C is suitable for the hot processing. The number of dynamic recrystallization (DRX) grains in the "safe" domains is larger and the dislocation density is lower compared to those of instability domains. DRX grains mainly occurred around SiC particles. The presence of SiC particles can promote effectively the DRX nucleation, which results in the dynamic softening mechanism of the dual-scale SiCp/A356 composites being dominated by DRX. [ABSTRACT FROM AUTHOR]

The hot deformation behavior of nano-SiCp/Al-Si composites was studied by isothermal compression tests at 470–530 °C and strain rates of 0.01–5 s−1. A strain-compensation constitutive model was developed with a Z parameter and an Arrhenius function, and its accuracy was verified by error analysis. The results show that the flow stress of the composites decreased with the increase in deformation temperature and the decrease in strain rate. The average activation energy for nano-SiC particle-reinforced Al-Si matrix composites was 277 kJ/mol, which was larger than the activation energy for self-diffusion of pure aluminum. The average relative error was calculated as 2.88%, indicating the strain-compensated constitutive equation could accurately predict the hot deformation behavior of nano-SiCp/Al-Si composites. [ABSTRACT FROM AUTHOR]

Pure Zn and Zn–ERGO composite coatings were prepared by direct current electrodeposition on 304 stainless steel. Samples were characterized by X-ray diffraction (XRD), scanning electron microscopy coupled with energy dispersive X-ray spectroscopy (SEM/EDS), and laser Raman spectroscopy (Raman). Results obtained have shown that the concentration of GO sheets in zinc sulfate electrolyte has an important effect on the preferred crystal orientation and the surface morphology of Zn–ERGO composite coatings. A study of the corrosion behavior of the coatings by Tafel polarization and electrochemical impedance spectroscopic (EIS) methods leads to the conclusion that the Zn-1.0 g/L ERGO composite coating possesses the best corrosion resistance compared to the pure Zn coating and other composite coatings in this study. [ABSTRACT FROM AUTHOR]