Effect of Al2Cu constituent layer thickness discrepancy on the tensile mechanical behavior of Cu/Al2Cu/Al layered composites: a molecular dynamics simulation.

Nano-polycrystalline Cu/Al2Cu/Al layered composites with different layer thicknessesdof single-crystal Al2Cu constituent are constructed. The effects ofdon the strength and fracture modes of nano-polycrystalline Cu/Al2Cu/Al layered composites are systematically investigated by molecular dynamics simulations. The uniaxial tensile results show that the ultimate strength and fracture mode of the nano-polycrystalline Cu/Al2Cu/Al layered composites do not change monotonically with the change of single crystal Al2Cu constituent layer thicknessd, the ultimate strength peaking atd= 2.44 nm, and the toughness reaching the optimum atd= 4.88 nm. The improvement of deformation incompatibility between Cu, Al and Al2Cu components increases the ultimate strength of polycrystalline Cu/Al2Cu/Al laminated composites. Due to the high activity of Cu dislocation and the uniformity of strain distribution of single crystal Al2Cu, the fracture of nano-crystalline Cu/Al2Cu/Al layered composites changes from brittleness to toughness. This study is crucial to establish the organic connection between microstructure and macroscopic properties of Cu/Al layered composites. To provide theoretical basis and technical support for the application of Cu/Al layered composites in high-end fields, such as automotive and marine, aerospace and defense industries.

Molecular Dynamics Study of Interfacial Micromechanical Behaviors of 6H-SiC/Al Composites under Uniaxial Tensile Deformation.

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.

Low-dimensional transition metal sulfide-based electrocatalysts for water electrolysis: overview and perspectives.

Hydrogen prepared by electrocatalytic decomposition of water ("green hydrogen") has the advantages of high energy density and being clean and pollution-free, which is an important energy carrier to face the problems of the energy crisis and environmental pollution. However, the most used commercial electrocatalysts are based on expensive and scarce precious metals and their alloy materials, which seriously restricts the large-scale industrial application of hydrogen energy. The development of efficient non-precious metal electrocatalysts is the key to achieving the sustainable development of the hydrogen energy industry. Transition metal sulfides (TMS) have become popular non-precious metal electrocatalysts with great application potential due to their large specific surface area, unique electronic structure, and rich regulatory strategies. To further improve their catalytic activities for practical application, many methods have been tried in recent years, including control of morphology and crystal plane, metal/nonmetal doping, vacancy engineering, building of self-supporting electrocatalysts, interface engineering, etc. In this review, we introduce firstly the common types of TMS and their preparation. Additionally, we summarize the recent developments of the many different strategies mentioned above for efficient water electrolysis applications. Furthermore, the rationales behind their enhanced electrochemical performances are discussed. Lastly, the challenges and future perspectives are briefly discussed for TMS-based water dissociation catalysts.

Numerical Simulation of Copper-Aluminum Composite Plate Casting and Rolling Process and Composite Mechanism.

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.

Effect of Secondary-Phase Precipitation on Mechanical Properties and Corrosion Resistance of 00Cr27Ni7Mo5N Hyper-Duplex Stainless Steel during Solution Treatment.

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.

Investigation on the In Situ Ti2AlC/TiAl Composite with a Homogenous Architecture by Adding Graphene Nanosheets.

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.

Investigation of the Thermodynamic Transformation and Rare Earth Microalloying of a Medium Carbon-Medium Alloy Steel for Large Ball Mill Liners.

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.

Effect of CeO2 Content on Microstructure and Properties of SiCp/Al-Si Composites Prepared by Powder Metallurgy.

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.

Effects of Transition Element Additions on the Interfacial Interaction and Electronic Structure of Al(111)/6H-SiC(0001) Interface: A First-Principles Study.

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.

Effects of CeO2 on the Si Precipitation Mechanism of SiCp/Al-Si Composite Prepared by Powder Metallurgy.

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.

Effects of CeO2 Content on Friction and Wear Properties of SiCp/Al-Si Composite Prepared by Powder Metallurgy.

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.

Hot-Deformation Behavior and Microstructure Evolution of the Dual-Scale SiCp/A356 Composites Based on Optimal Hot-Processing Parameters.

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.

Hot Deformation Behavior and Strain-Compensated Constitutive Equation of Nano-Sized SiC Particle-Reinforced Al-Si Matrix Composites.

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.

Effects of Heating Mode and Temperature on the Microstructures, Electrical and Optical Properties of Molybdenum Thin Films.

In this paper, molybdenum (Mo) thin films are deposited on soda-lime glass (SLG) substrates by direct current magnetron sputtering and heated in three different modes at different temperatures, including substrate heating, annealing treatment, and both substrate heating and annealing treatment. The effects of heating temperature and heating mode on the structures, morphology, optical and electrical properties of Mo thin films were systematically investigated by X-ray diffraction (XRD), Scanning electron microscopy (SEM), atomic force microscope (AFM) and UV-visible spectrophotometer (UV-vis spectra). It is shown that as the substrate and annealing temperature increase, the crystallinity of Mo thin films is improved, and the grain sizes become bigger. Especially in the mode of both substrate heating and annealing treatment at higher temperature, the obtained Mo thin films show higher crystallinity and conductivity. Moreover, with the increase of substrate and annealing temperature in different heating modes, both the surface compactness of Mo films and the optical reflectance increase correspondingly. Furthermore, the Mo film, prepared at the substrate heating temperature of 400 °C and annealed at 400 °C, showed excellent comprehensive performance, and the resistivity is as low as 1.36 × 10-5 Ω·cm. Using this optimized Mo thin film as an electrode, copper indium gallium selenium (CIGS) solar cells have a maximum photo-conversion efficiency of 12.8%.