Search

This study explores the stability of Al–Si–Ca–Mg-Sc melt foams and investigates the melt foam filling process and the dynamic evolution of pore structures in the fabrication of foam aluminum profiles using the melt transfer foaming technique. The results show that Al–Si–Ca–Mg-Sc melt foam maintains high porosity and a stable pore structure even after 30 min of foaming, without any signs of boundary rupture or destabilization. This stability is attributed to the increased viscosity from finely dispersed second-phase particles, which hinder the growth, coalescence, and drainage of the melt foam. Regarding melt foam filling, enhanced filling capability is achieved by elevating the foaming temperature, extending the foaming time, and increasing the TiH2 addition. The melt foam exhibits a smooth flow from the lower part of the mold to the corners, completing the filling process with well-defined edges in the profile. During lateral movement for filling, a gradual increase in porosity, a decrease in pore number, and a slow enlargement of pore size and standard deviation along the lateral (x-axis) are observed. This is due to the slower liquid phase flow compared to the gas phase, resulting in bubble coalescence. After filling is complete, this phenomenon improves, contributing to a slow and stable evolution of the pore structure.Under optimized conditions of 1.4 wt% TiH2 addition at 600°Cfor 9 min of foaming with Al–Si–Ca–Mg-Sc alloy melting, we successfully fabricated foam aluminum profiles with complete filling, a porosity of 81.5%, an average pore size of 2–3 mm, and a uniform pore structure.

CoCrMoW alloys with different nitrogen (N) additions (0, 0.05, 0.1, and 0.2 ​wt%) were prepared via laser powder bed fusion (LPBF). The effects of N content on the microstructure and mechanical properties were investigated. The results indicate that the LPBFed CoCrMoW alloy with 0.1 ​wt% N addition (0.1 ​N alloy) shows the best combination of mechanical properties with a yield strength of ∼983 ​MPa and an elongation of ∼19 ​%. Both the LPBF process and the N addition impose great effects on suppressing the γ to ε martensitic transformation, resulting in a decrease in the width and amount of ε laths/stacking faults. Besides, the N addition promotes the segregation of elements Mo, W, and Si along the cellular sub-grain boundaries (CBs), forming fine and discontinuous precipitates rich in Mo, W and Si along the CBs in the 0.1 ​N alloy, but dense and continuous (Mo,W)5Si3 precipitates along the CBs in the 0.2 ​N alloy. The (Mo,W)5Si3 precipitates with a tetragonal structure were observed and characterized for the first time in the Co–Cr based alloys. The negative mixing enthalpy between the non-metallic elements N, Si and the metallic elements Mo, W, Cr, and the rapid solidification induced segregation of high melting point elements such as Mo and W along CBs during LPBF process, synergistically contribute to the chemical heterogeneity in the alloys. The pure FCC matrix, the slightly increased segregation of Mo, W, Si elements and fine precipitates along the CBs contribute to the good combination of strength and elongation of the 0.1 ​N alloy. However, though pure FCC phase was present in the 0.2 ​N alloy, the dense and continuous (Mo,W)5Si3 precipitates along CBs acted as nucleation sites for cracks, deteriorating the elongation of the alloy. Overall, it is possible to tune the mechanical properties of the LPBFed CoCrMoW alloy by adjusting the local chemical heterogeneity.

This study investigated the influence of Sb addition on the microstructure, thermal behavior, mechanical properties, and interfacial evolution of SAC305-2Bi-xSb/Cu solder joints. Compared with the SAC305-2Bi alloy, the melting temperature and pasty range slightly increased with the increasing of Sb content from 0.2 to 2.0 wt.%, while the undercooling temperature decreased. The research revealed that with the addition of Sb element, the grain size of β-Sn is refined. When the content of Sb is 0.5 wt.%, the grain size of β-Sn reached minimum (19.91 μm). Compared to the SAC305-2Bi alloy, the ultimate tensile strength of SAC305-2Bi–2Sb alloy is increased by 30.10%, contributed to the Sb solid solution strengthening effect and the refinement of β-Sn. With the addition of Sb, the thickness and growth rate of the interface is reduced gradually. The uniform solution of Sb and Sn can significantly inhibit the diffusion rate of Cu atoms and Sn atoms at the interface. The SAC305-2Bi-xSb alloy system has low melting temperature, superior mechanical properties, and reliable solder joints for service. Therefore, it is a potentially reliable lead-free solder for high-stability connections in automotive electronics, communications electronics, and medical devices.

Developing reticular reinforcement and heterogeneous microstructure remains persistent challenges in one-dimensional carbon nanotube (CNT)-Cu system. We herein fabricated dual-heterostructured Cu composite by diazotizing CNT into cross-linked (CL) networks and achieving bimodal grain distribution. The CL-CNT networks uniformly dispersed in Cu matrix, forming strong C–N/O–Cu covalent bonds at the interfaces and effectively retarding grain growth to create ultra-fine grain (UFG) regions around them. The CL-CNT networks/UFG regions, along with the surrounding coarse grain (CG) regions, resulted in a remarkable synergy between mechanical and electrical properties within the composite. Systematic analysis indicates that CL-CNT network acts as a whole to bear loading, remarkably enhances the load-transfer strengthening and promotes the dislocation accumulation around the interface. Meanwhile, hetero-deformation between “hard” CL-CNT networks/UFG regions and “soft” CG regions lead to extra-strengthening and hardening associated with strain partitioning, generation of geometrically necessary dislocation (GND) and strain delocalization. In-situ tensile test further reveals that CL-CNT/Cu with dual-heterostructure introduces the extra-toughening via crack bridging and deflection mechanisms. Besides, CL-CNT network with the robust interface is considered to reduce the interfacial inelastic scattering and provide additional paths for electron transport, accounting for the high electrical conductivity. This work highlights the importance of configuration design of reinforcement in tailoring heterostructured metal matrix composites (MMCs) with outstanding comprehensive performance.

In this study, Cu–9Ni–6Sn-xCr alloys (x = 0, 0.3, 0.6, or 1.0) were designed and prepared. The influence of Cr content on the microstructure, the precipitation behavior, and the mechanical properties of the alloys was systematically investigated. The results show that the Cu–9Ni–6Sn-0.6Cr alloy exhibits outstanding mechanical properties and higher level electrical conductivity after aging at 400 °C for 8 h: The peak-aged hardness reaches 323.6 ± 8.4 HV, with a tensile strength of 876.4 MPa and an electrical conductivity of 12.59 ± 0.33% IACS. These excellent comprehensive properties of Cu–9Ni–6Sn-0.6Cr alloy are attribute to the refinement effect and the precipitation of DO22 phase within the Cu matrix grains. Further analysis reveals that the addition of an appropriate amount of Cr refines the microstructure of the alloy and promotes the precipitation of the DO22 phase. At the same time, Cr also suppresses the precipitation of the DO3 phase at grain boundaries, achieving an excellent combination of plasticity, electrical conductivity, and strength. This work suggests that the potential application prospects of Cr in the multi-component design of Cu–Ni–Sn alloy, and the addition of 0.6 wt% Cr can achieve good strengthening effects and provide outstanding comprehensive performance for Cu–Ni–Sn alloys.

Deformation twins (DTs) and stacking faults (SFs) are rarely found in Cu-20Ni-20Mn alloy, which limits further strengthening of alloy. Here, we report ultra-strong Cu-20Ni-20Mn alloy prepared by introducing a high density of coherent nanoprecipitates. The ultimate tensile strength (UTS) of alloy can be largely enhanced to 1624.7 ± 14.7 MPa, while maintaining an acceptable elongation of 7.3 ± 0.5%. We find that the coherent nanoprecipitates contribute to an ultra-high true stress up to about 1740 MPa, which facilitate the formation of DTs. The strength and ductility improvement stems from the synergistic effect of dislocations, nanoprecipitates and DTs.

In this work, an in-situ boride-reinforced Ti6Al4V compositionally graded material was prepared successfully by spark plasma sintering (SPS), and exhibited a good potential for military application because of its stepwise transition properties from a high-toughness end to a high-strength end along the thin-thickness direction. Microstructure characterization shows the chemical gradient ranged from 0 to 30 wt% TiB2 along the thickness direction, which was correlated with increasing micro-hardness values ranging from 565±5HV to 1270±5HV, respectively. The strength-toughness matching mechanisms of the gradient composites with different compositional gradients were discussed based on the static compression experiments and the dynamic Hopkinson compression rod experiments. The primary phases of the gradient composites included the α-Ti phase, β-Ti phase, remained TiB2 and in-situ formed whisker-like TiB phases. The composites with a compositional gradient of G84 (0, 0, 15, 30 wt%) exhibited the best impact resistance which achieved a good balance of high toughness and strength, and exhibited a compressive strength of 2148±5 MPa and a good elongation of 20 ± 0.5%. The strength-toughness matching mechanisms can be explained by the dispersion strengthening effect due to the presence of the in-situ formed TiB phase, and the consumption of more fracture energy by dislocation defects, which can prevent the crack propagation. Moreover, the pull-out of the whisker-like TiB phases toughened the gradient composites furthermore. This research demonstrated a reliable method for preparing TiB2/Ti–6Al-4Vgradient composites with high-impact resistance.

The hot deformation behavior of the solutionized Cu–15Ni–8Sn alloy is investigated by hot compression tests at temperatures of 750–900 °C and strain rates of 0.001–1.0 s−1. The flow stress curves of the alloy are analyzed, and the constitutive equations are developed to predict the flow behavior of the alloy. In addition, the optimal deformation conditions are proposed through the constructed hot processing map and microstructure analysis, revealing the impact of the deformation mechanism under different deformation parameters on the microstructure evolution. The results show that temperature and strain rate have a great influence on the hot deformation of the alloy. The strain-compensated constitutive equation can well predict the peak flow stress of the alloy, with a correlation coefficient of 0.993 between experimental and predicted values. The high power consumption region is mainly caused by dynamic recovery and partial dynamic recrystallization, while flow localization is the main reason for the appearance of the unstable region. The optimum hot processing conditions for the alloy are at a temperature range of 750–780 °C and the strain rate is 0.001–0.0025 s−1.

The graphite-reinforced epoxy resin composite (Gr/EP) is considered one of the promising solid lubricating materials. However, the low thermal conductivity and correlated poor wear resistance cause limitations to its tribological applications. With the expectation to improve the thermal conductivity and wear property, carbon nanotube (CNT)-reinforced copper foams (CNTs/Cuf) are introduced as 3-dimensional skeletons to reinforce Gr/EP composites. Herein, comprehensive testing was conducted to assess the wear resistance, thermal conductivity, microstructure, and wear morphology of the composites. The results revealed that incorporating Cu or CNTs/Cu foams into the Gr/EP matrix significantly enhanced thermal conductivity and wear resistance, with only minor elevation of the friction coefficients, which showed a consistent decline trend with increasing CNTs contents. Notably, with the CNT content of 0.159 wt%, the composites reached the favorable combination of a 25.4 % improvement in thermal conductivity and a 34 % reduction in wear rate compared to pure copper foam-reinforced Gr/EP composites.

Abstract Metallic phthalocyanines are promising electrocatalysts for CO2 reduction reaction (CO2RR). However, their catalytic activity and stability (especially under high potential) are still unsatisfactory. Herein, we synthesized a covalent organic polymer (COP‐CoPc) by introducing charge‐switchable viologen ligands into cobalt phthalocyanine (CoPc). The COP‐CoPc exhibits great activity for CO2RR, including a high Faradaic efficiency over a wide potential window and the highest CO partial current density among all ligand‐tuned phthalocyanine catalysts reported in the H‐type cell. Particularly, COP‐CoPc also shows great potential for practical applications, for example, a FECO of >95% is realized at a large current density of 150 mA/cm2 in a two‐electrode membrane electrode assembly reactor. Ex situ and in situ X‐ray absorption fine structure spectroscopy measurements and theory calculations reveal that when the charge‐switchable viologen ligands switch to neutral‐state ones, they can act as electron donors to enrich the electron density of Co centers in COP‐CoPc and enhance the desorption of *CO, thus improving the CO selectivity. Moreover, the excellent reversible redox capability of viologen ligands and the increased Co–N bonding strength in the Co–N4 sites enable COP‐CoPc to possess outstanding stability under elevated potentials and currents, enriching the knowledge of charge‐switchable ligands tailored CO2RR performance.

The effects of Ag addition on the microstructure of Sn–9Zn alloy and its corrosion behaviour in neutral and static 3.5 wt% NaCl solutions were investigated using surface characterization techniques and electrochemical techniques. The results show that in Sn–9Zn-xAg alloys, Ag reacts with Zn to form AgZn3 intermetallic compounds (IMCs), which refined the microstructure of the alloys and changed the corrosion mode of the alloy surfaces from pitting corrosion to surface corrosion. The addition of Ag effectively improved the corrosion passivation film structure and electron transfer characteristics of the alloy, increased the self-corrosion potential (Ecorr) and reduced the self-corrosion current (Icorr), thus improving the corrosion resistance of the alloy. The study explained and verified the corrosion mechanism of the alloy from both experimental and theoretical perspectives. It is concluded that Sn–9Zn-0.4Ag alloy shows relatively the best corrosion resistance.

Insight into the well-balanced mechanical-electrical properties of copper composites is requisite to provide an understanding for the development of novel structure–function integrated materials. In this study, the multi-dimensional hybrid reinforcements, carbon nanotube and zero-dimensional carbonized polymer dots (abbreviated as: CNT + CPD), were incorporated within copper matrix via spraying pyrolysis dispersion and segmented ball milling routes. A novel strategy was developed to simultaneously introduce intragranular CPD and intergranular CNT by controlling the spatial configuration. Characterization results show that the dispersibility and interface wettability of CNT-Cu were improved by the spraying pyrolysis. Intragranular CPD facilitated the trapping and accumulation of dislocations inside grain interior, which enhanced the strain hardening capability. 3.0 vol% CNT-CPD/Cu composites achieved good strength-plasticity compatibility (410 MPa and 19.8 %, i.e., 146.6 % and 139.3 % of the CNT/Cu composites, respectively). Meanwhile, composites had also displayed good electrical conductivity (96.5% IACS), which was attributed to the creation of conductive graphitic channels locally around intragranular CPD and produced a potent electric field with little charge loss. This work presented an effective route for the design of advanced copper composites and demonstrated potential in applications as progressive multi-functional materials.

The hot deformation behaviour of an as-cast Cu–20Ni–20Mn alloy was investigated by isothermal compression tests in a TA-DIL 805 phase change thermal expansion instrument with a temperature ranging from 800 to 950 °C and a strain-rate ranging from 0.001 s−1 to 1 s−1. The results showed that Cu–20Ni–20Mn presented a stress drop at the beginning of the strain, and the flow stress decreased with increasing temperature and decreasing of strain rate. In particular, the hot deformation activation energy was determined to be 277.958 kJ/mol. The hot compression constitutive equation was established, and the processing maps of the alloy were constructed. The stress-strain values predicted by the proposed model were coincident with the experimental results, which confirmed that the deformation principal equation gives an accurate and precise estimate of the flow stress in Cu–20Ni–20Mn. The established processing maps and microstructure analysis determined the rolling process parameters in which the optimum range of temperature for the hot-working deformation of the as-cast Cu–20Ni–20Mn alloy is 810–900 °C with a strain rate of 0.001–0.002 s−1.

Ni60/60% WC composite coatings with a good surface roughness and high mechanical properties were successfully prepared on 316L stainless steel substrate by laser-directed energy deposition (LDED) technology. The effects of laser power on the microstructural evolution and mechanical properties of the Ni60/60% WC composite coating were investigated. The relationships between the chemical composition, the microstructure, the hardness, and the friction wear resistance of the composite coatings were characterized and investigated. The results show that the laser power had a significant effect on the energy input, which determined the melting extent of the Ni60 phases around the WC particles and the bonding strength between the reinforcements and the matrix, as well as the bonding strength between the substrate and the coatings. With an increase in the laser power from 800 W to 1400 W, the average hardness of the coating surface increased due to the increased densification of the deposited coatings and then decreased due to grain coarsening under a high energy input. The average coefficient of friction of the coatings decreased gradually to 0.383 at 1000 W, showing a minimum wear of 0.00013 mm2 at 1200 W. The main wear mechanisms on the coated surfaces were adhesive wear and abrasive wear. Moreover, the coatings deposited at 1200 W exhibited better forming quality and wear resistance. This work suggests that the processing parameters during LDED can be optimized to prepare Ni60/60% WC wear-resistant coatings with excellent mechanical properties.

During the laser-based directed energy deposition (DED-LB) processing, a WC-12Co composite coating with high hardness and strong wear resistance was successfully prepared on a 316L stainless steel substrate by adopting a high-precision coaxial powder feeding system using a spherical WC-12Co composite powder, which showed a large number of dendritic carbides and herringbone planar crystals on the substrate-binding interface. The influences of laser power on microstructural and mechanical properties (e.g., hardness, friction resistance) of WC-12Co composite surfaces were investigated. The results show that laser power has a significant effect on determining the degree of Co phase melting around the WC particles and the adhesion strength between the matrix and the coating. Lower laser power does not meet the melting requirements of WC particles, thus weakening the molding quality of the composite coating. At high laser power, it is possible to dissolve the WC particles and melt the metal powder between the particles, thus improving the material properties. The laser power increased from 700 W to 1000 W and the average hardness of the coating surface gradually increased from 1166.33 HV to 1395.70 HV, which is about 4–5 times higher than the average hardness of the substrate (about 281.76 HV). In addition, the coatings deposited at 1000 W showed better wear resistance. This work shows that the processing parameters during laser-directed energy deposition can be optimized to prepare WC-12Co composite coatings with excellent mechanical properties.

The laser drilling of carbon steel is always suffered from the formation of slag, the presence of cutting burrs, the generation of a significant quantity of spatter, and the incomplete penetration of the substrate. In order to avoid these defects formed during the laser drilling of carbon steel, the COMSOL multi-physics simulation method was used to model and optimize the laser drilling process. Considering the splash evolution of the material during the complex drilling process, the transient evolution of the temperature field, the flow of the molten fluid, the geometrical changes, and the absorption of the laser energy during the laser drilling process were investigated. The simulated borehole dimensions are consistent with the experimental results. The process parameters have a great influence on the fluid flow pattern and material slag splashing. The laser power has a significant effect on the laser processing compared with the process parameters. With the increase in laser power and the decrease in laser heat source radius, the time required for perforation is reduced, the flow of melt is accelerated, the perforation efficiency is increased, and the hole wall is smoother, but the degree of spattering is greater. The optimized process parameters were obtained: laser heat source radius of 0.3 mm, laser power of 3000 W. These findings can help reduce the machining defects in carbon steel with excellent mechanical properties by optimizing the laser drilling processing parameters.

Reinforcement architecture and interfacial structure are two key factors affecting the performance of composites. Herein we attempted to achieve a comprehensive improvement of mechanical properties of carbon nanomaterials (CNMs) reinforced Cu matrix composites by means of reinforcement structure construction and interface structure optimization. Graphene oxide (GO) and acid-treated carbon nanotubes (AT-CNTs) were self-assembled into a GO-CNT hybrid structure through an ultrasonic mixing method, and then used as reinforcement of Cu matrix composite through the powder metallurgy method. The strengthening efficiency of GO-CNT hybrid was significantly higher than that of individual CNTs or GO, which could be attributed to the stable interconnected architecture of GO-CNT hybrid formed through sp3 hybridized C–C bonds and the larger interfacial area between them and Cu matrix. In addition, aiming at the issue of poor interfacial adhesion between the GO-CNT hybrid and Cu matrix, TiC nanoparticles were introduced onto the surface of GO-CNT hybrid through a pressureless spark plasma sintering strategy. The TiC nanoparticles can improve the interfacial wettability and optimize the interfacial bonding state. TEM results confirmed a semi-coherent interfacial lattice matching relationship between TiC nanoparticles and Cu matrix, which was conducive to forming robust interfacial bonding. Through the construction of hybrid reinforcement and the introduction of nanosized interfacial TiC, the GO-CNT hybrid reinforced Cu matrix composite has obtained ultra-high strengthening efficiency, and exhibited satisfied combination of strength and ductility. This study can provide a referential strategy for the comprehensive performance optimization of CNMs reinforced metal matrix composites.

The thermo-mechanical and failure behavior of the burning-free Al2O3 –C–SiO2 slide gate plate materials during the steel casting process are investigated. Firstly, the instantaneous coefficient of thermal expansion and the Young's modulus of the slide gate plate materials with different component contents at high temperature are measured. Secondly, a material constitutive model and a concrete damage plasticity mode are established based on the experiments, and adopted to simulate the failure behavior of the burning-free Al2O3–C–SiO2 slide gate plate during casting based on Finite Element Method (FEM) analysis. Results show that temperature gradient in the slide gate plate near the casting hole increased significantly and had a significant influence on cracking. The area near the casting hole of the slide gate plate is under tensile stress conditions, and then changes towards compressive stress conditions. Under those severe thermal stress conditions, crack formation is evaluated and an optimized composite structure of the slide gate plate combining advantages of reducing the risk of cracking and extending the service life is proposed. Moreover, the thermal shock test further verified that the microcrack extension was significantly alleviated due to the SiC distributed in whisker form and formed an interlocking structure in material. This work provides a reliable theoretical and experimental basis for the design and optimization of high performance Al2O3–C–SiO2 slide gate plates.

In this paper, inhomogeneous copper matrix composite with carbon nanotube reinforced copper foam (CNTs/Cuf) as the three-dimensional (3-D) skeleton is designed to overcome the paradox between strength and ductility or conductivity. The open cell composite foams with uniformly embedded CNTs are filled with dense copper phase in the foam pores by spark plasma sintering (SPS) to form the inhomogeneous composites. The inhomogeneous composite reinforced with CNTs/Cuf shows a combination of high electrical conductivity (93.4% IACS), tensile strength (366.7 MPa), and fracture elongation (31.78%) with a quite low CNTs content (0.2414 vol%). In addition, the polarization curves and AC impedance (EIS) tests show that the best corrosion resistance is achieved with the CNTs content of 0.2414 vol%, and the corrosion rate is reduced by 71.9% and 49.1% compared with the Cu and Cuf®Cu samples, respectively.

As-cast CrCoNi Medium Entropy Alloy (as-casted MEA) was obtained by vacuum arc melting. The as-casted MEA was rolled 3 times at the temperature of liquid nitrogen (77 K), the sum of the total deformation was 50%. Then, the rolled CrCoNi Medium Entropy Alloy (as-rolled MEA) were annealed with different parameters, the annealing parameters were 923 K/30min, 973 K/30min and 1073 K/30min respectively. The experimental samples were characterized by uniaxial tensile test at room temperature, electron back scatter diffraction (EBSD) and transmission electron microscopy (TEM). The tensile test results showed the CrCoNi MEA was deformed by Liquid Nitrogen rolling, the tensile strength increased from 421 MPa to 1312 MPa, but the elongation was only 7.4%. The as-rolled MEA annealed at moderate temperature and short time, the ductility of the CrCoNi was improved significantly. When the as-rolled MEA annealed at 1073 K/30 min, the elongation of CrCoNi increased to 65.3%, while the tensile strength maintained 800 MPa. The EBSD and TEM results showed that the CrCoNi MEA was deformed by Liquid Nitrogen rolling, there were a lot of high density dislocation regions in the alloy. At the same time, a large number of bunches of stacking faults (SFs), intersected SFs and deformation twins (DT) were found in the rolled MEA. The EBSD and TEM results also showed that when the CrCoNi MEA was annealed, a large number of type B and type C annealing twins and 9 R structures were found in the alloy. The growth of annealing twins were achieved by the mechanism of grain boundary migration caused by stacking faults annexation. After annealing, the transformation of FCC→9 R structure was occurred, and the 9 R structure caused more boundary nucleation of annealing twins. The annealing twins and 9 R structure played a key role in improving the ductility of the annealed CrCoNi MEA. Adopt the technology of moderate temperature combining short time annealing process, can effectively control the properties of CrCoNi MEA.

With a unique cellular structure to enhance the multi-reflection and multi-absorption properties of electromagnetic waves, metal foam is considered a new type of electromagnetic shielding material that can also be used for lightweight structural applications such as energy absorption and shock attenuation. This work introduces reduced graphene oxide (RGO) to reinforce Cu foam for the purpose of improvement of the foam's mechanical and electromagnetic shielding properties. After the preparation stage of the electrodeposition and heat treatments, the RGO was observed to uniformly disperse in the Cu foam matrix and nano-sized Cu2O particles formed at the interface. This resulted in improved mechanical properties and electromagnetic shielding performance compared to the pure Cu foams. The primary shielding mechanism was deduced as absorption loss.

Ammonia (NH3), as main industrial gas emissions, are extremely harmful to the human beings. So the detection of NH3 concentrations in special environments at room temperature (25 °C) is essential. Herein, the composite MXene Ti3C2Tx-TiO2-CuO was successfully prepared by one-step in-situ oxidation method using Cu(NO3)2·6H2O as a precursor. The morphology of Ti3C2Tx-TiO2-CuO shows layered accordion-like structure. Ti3C2Tx-TiO2-CuO sensor exhibits improved NH3 gas sensing response of 56.9 toward 100 ppm NH3 at room temperature under ultraviolet (UV) light exposure, which is 89.8 % higher than that of pristine Ti3C2Tx material. The improved gas sensing performance is attributed to the irradiation of UV light, the retention of Ti3C2Tx layered structure and the construction of TiO2-CuO heterojunction. Further, the possible gas sensing mechanism of the material was proposed and discussed.

In order to uniformly disperse the ceramic reinforcements synthesized in-situ in the copper matrix composites, this study used Carbon Polymer Dot (CPD) as the carbon source and Cu–1.0%Ti alloy powder as the matrix for supplying Ti source to prepare in-situ synthesized TiC/Cu composites. The results show that TiC nano-precipitates, having the similar particle sizes with the CPD, form at the grains interior and grain boundaries, and maintain a uniform distribution state. Compared with the matrix, 0.3 ​wt% CPD/Cu composite displays the best strength-plastic compatibility, the ultimate tensile strength achieves 385 ​MPa accompanied with a corresponding elongation of 21%, owing to the dislocation hindrance caused by nano-carbide and excellent interface bonding between nano TiC and the Cu matrix. The density function theory calculation supports our experimental results by showing a tighter and stronger interface contact. This work presents a new approach for studying in-situ carbide precipitates.

Al-Ti-C-(Ce) grain refiners were prepared by combining in-situ reaction, hot extrusion, and adding CeO2. The effects of second phase TiC particle size and distribution, extrusion ratio, and Ce addition on the grain-refining performance of grain refiners were investigated. The results show that about 10 nm TiC particles are dispersed on the surface and inside of 100–200 nm Ti particles by in-situ reaction. The Al-Ti-C grain refiners, which are made, by hot extrusion, of a mixture of in-situ reaction Ti/TiC composite powder and Al powder, increase the effective nucleation phase of α-Al and hinder grain growth due to the fine and dispersed TiC; this results in the average size of pure aluminum grains to decrease from 1912.4 μm to 504.8 μm (adding 1 wt.% Al-Ti-C grain refiner). Additionally, with the increase of the extrusion ratio from 13 to 30, the average size of pure aluminum grains decreases further to 470.8 μm. This is because the micropores in the matrix of grain refiners are reduced, and the nano-TiC aggregates are dispersed with the fragmentation of Ti particles, resulting in a sufficient Al-Ti reaction and an enhanced nucleation effect of nano-TiC. Furthermore, Al-Ti-C-Ce grain refiners were prepared by adding CeO2. Under the conditions of holding for 3–5 min and adding a 5.5 wt.% Al-Ti-C-Ce grain refiner, the average size of pure aluminum grains is reduced to 48.4–48.8 μm. The reason for the excellent grain-refining and good anti-fading performance of the Al-Ti-C-Ce grain refiner is presumedly related to the Ti2Al20Ce rare earth phases and [Ce] atoms, which hinder agglomeration, precipitation, and dissolution of the TiC and TiAl3 particles.

The preparation method of advanced ceramics that serve as target materials, has been the key challenge to produce high quality thin film transistors (TFTs) with the desired properties. In this study, a novel two-step sintering (TSS) process was successfully applied to fabricate indium gallium zinc oxide (IGZO) ceramics. The sintering behaviour of the IGZO compacts was investigated in detail and it was established that the first step optimum temperature should be in the range of 1400–1500 ℃, while for the second step should be 1350℃ with a dwell time of 12 h. Using this method, the relative density, average grain size and resistivity of the IGZO ceramics could reach 99.5%, 4–5 μm and 2.31 mΩ⋅cm, respectively. The corresponding IGZO thin films produced from the ceramic through sputter deposition had an average transmittance of over 88% and a low resistivity of 3.56 mΩ⋅cm. These excellent properties suggest that TSS has considerable potential as a viable approach for the preparation of ceramic target materials, which find application in the fabrication of TFTs.

The intrinsic properties and the damage behavior of powder metallurgy (P/M) connecting rod preform have significant effects on its metal flow behavior during flashless forging into its final complex shape with substantial densification. The P/M material constitutive equation were established using isothermal compression tests, and then used to study the metal flow behavior of a P/M connecting rod preform during flashless forging based on finite element modelling (FEM). Moreover, the preform geometry was designed based on these metal flow mechanisms. Experiments and flashless forging of P/M connecting rod preforms were performed in order to verify the accuracy of the simulations. The simulated results are well consistent with the experimental results. Results showed that the shank is much more prone to cracking due to the higher deformation rate and the faster cooling rate. The optimal dimensions of the P/M preform were obtained. When the preform geometry are optimized, the average density of the connecting rod increases homogeneously, and becomes superior to that of the original shape. This work suggests that the geometry of the preform can be designed efficiently based on our models. This work can help to derive a P/M connecting rod preform optimization methodology, which can offer the possibility of improving the quality of the connecting rods efficiently. Keywords: Connecting rod, Numerical simulation, Optimization, Powder metallurgy

The homogeneous distribution of carbon nanotubes (CNTs) in the Cu matrix and good interfacial bonding are the key factors to obtain excellent properties of carbon nanotube-reinforced Cu-based composites (CNT/Cu). In this work, silver-modified carbon nanotubes (Ag-CNTs) were prepared by a simple, efficient and reducer-free method (ultrasonic chemical synthesis), and Ag-CNTs-reinforced copper matrix composites (Ag-CNTs/Cu) were fabricated by powder metallurgy. The dispersion and interfacial bonding of CNTs were effectively improved by Ag modification. Compared to CNTs/Cu counterparts, the properties of Ag-CNTs/Cu samples were significantly improved, with the electrical conductivity of 94.9% IACS (International Annealed Copper Standard), thermal conductivity of 416 W/m·k and tensile strength (315 MPa). The strengthening mechanisms are also discussed.

Element segregation in the as-cast medium-entropy alloy (MEA), CrCoNiAl0.014, has a significant influence on its mechanical properties. This study focused on aluminum segregation in the as-cast CrCoNiAl0.014 MEA at room temperature (300 K). The element distribution, morphology, and type of precipitates formed by the elemental segregation were identified by optical microscopy, X-ray diffraction, electron probe microanalysis, and transmission electron microscopy. Al segregation existed at the dendritic boundary in the face-centered cubic (FCC) MEA matrix. Hybrid molecular dynamics and Monte Carlo simulations were conducted to analyze the diffusion behavior and the chemical affinity of Al, as well as understand the segregation mechanism of Al at the atomic scale. Al displayed a faster diffusion speed and a higher chemical affinity than Ni, Cr, and Co at the same temperature. Al segregated at the dendritic boundary to form the Al-rich phase. Furthermore, as the temperature was increased, the atomic thermal vibration of these four elements became more intensive, and Al segregation was more serious. However, Al segregation improved the uniform diffusion of Cr, Co, and Ni. Therefore, this study provides a reference for subsequent reductions in element segregation and improvements in the mechanical properties of MEA.

In this study, the interfacial structure and abnormal long-term increase of tensile strength in the interfacial intermetallic compounds (IMCs) between SnAg3Cu0.5 solder and Cu substrates during isothermal aging were investigated. After reflow soldering, the IMC layer at the interface was thin and scallop-type. The interfacial layer became thicker with the increase in aging time. After 200 h of aging at 150 °C, the thickness of the interface gradually increased to 3.93 μm and the interface became smooth. Compared with the unaged Cu-Sn interface, the aged joint interface contained more Cu3Sn. The top of the IMC being reflown was relatively smooth, but became denser and prismatic in shape after 200 h of aging at 150 °C. The tensile strength of the joint, immediately after the reflow, reached 81.93 MPa. The tensile properties of the solder joints weakened and then strengthened as they aged. After 200 h of aging at 150 °C, the tensile strength was 83.86 MPa, which exceeded that of the unaged solder joint interface, because the fracture mode of the solder joints changed during aging.

Titanium alloy is a key supporting material in the field of engineering technology and high-tech, and also an extremely important national defense strategic metal material. However, the high cost limits its wider application. Direct rolling of titanium alloy melted by electron beam cold hearth melting (EBCHM) technology is considered to be an important low-cost plate production process. The rolling process has a considerable influence on the microstructure and mechanical properties of the alloy. Therefore, Ti-6Al-4V alloy melted by EBCHM technology was investigated in this study. The effects of different rolling processes on the microstructural evolution and mechanical properties of titanium alloy plates were evaluated. The results show that with the increase of deformation amount and rolling temperature, the more obvious the disintegration of lamella α and the higher the degree of equiaxation when the deformation is below the β transus. However, only dynamic recovery occurs when rolling temperature above the β transus, and lamella α does not undergo disintegration and equiaxation. With ultimate tensile strength (UTS) of 1076 MPa and elongation (EI) of 11%, the plate with 90% deformation at 950 °C has good strength and plasticity.

High-energy ball milling and spark plasma sintering (SPS) are used to create high-strength Ti-25Nb-6Zr biomedical alloys with β structures. The Ti-25Nb-6Zr alloy microstructure and mechanical properties were examined as a function of the sintering temperatures. The results showed that as the sintering temperature was raised, the densification process was expedited, and the comprehensive mechanical characteristics increased at first, then dropped slightly. Moreover, under high temperatures, the fracture morphology of the Ti-25Nb-6Zr biomedical alloys exhibited more dimples, indicating enhanced plasticity of the material. Evaluating the mechanical properties of the Ti-25Nb-6Zr biomedical alloy sintered at 1623 K indicated a high compressive strength of 1678.4 ± 5 MPa and an elongation of 12.4 ± 0.5%. The strengthening mechanisms are discussed in terms of the formation and distribution of bcc-Ti in the matrix as well as the homogeneous distribution of Nb and Zr. This research presents a new method for fabricating Ti-25Nb-6Zr biomedical alloys with high strength and low modulus values. The theoretical grounds for the development of high-performance Ti-Nb-Zr alloys will be laid by detailed research of this technology and its strengthening mechanisms.

Carbonized polymer dots (CPDs) have been paid a lot of attention by researchers because of their excellent properties due to their unique structure. However, few studies have researched the impact of the CPD structure on composite applications. Herein, CPD and heat-treated CPD (h-CPD) are used to fabricate a reinforced Cu matrix composite. There was a semi-coherent interface between h-CPD and Cu. However, functional groups and polymer chains of CPDs decomposed during heat treatment, weakening the mechanical and electrical properties of the composites. These findings show that CPD structural integrity is vital to composites.

Interface optimization is the most important and eternal research issue in preparation of the metal matrix composites (MMCs). For nano sp2-carbon material (NSCM)/metal composites, interfacial precipitates are usually formed intentionally or unintentionally, however, the effect of the interface structure and precipitates on the electron transport properties is still unclear, which is especially important for Cu-based material due to the electronic and electrical applications. In this paper, a series of interface models were constructed based on the transmission electron microscopy (TEM) observation of NSCM/Cu composite and calculated through density functional theory (DFT). The geometric structure, interfacial charge transfer, work function, Bader charges, electron differential density distribution and electronic density of states of Cu/graphene (GR), Cu2O/GR, Cu/Cu2O and Cu/Cu2O/GR interfaces were discussed in detail, we conclude that the Cu2O precipitates at the Cu/GR interface can reduce the average distance and increase the binding energy between Cu and GR. Besides, the formation of Cu2O can improve the electronic transport between Cu2O and copper instead of the weak binding of the Cu and graphene, but Schottky barrier at the interface remains an obstacle need to be overcome. The results can provide reference for the interface design of MMCs and the improvement of the composite properties.

Inhomogeneous structures with carbon nanotubes (CNTs), reinforced with Cu composite foams as the reinforcing skeletons (CNTs/Cuf®Cu), have been designed to overcome the paradox between strength and ductility or conductivity in copper matrix composites. The interface between CNTs and the copper matrix is usually weak, due to poor wettability and interaction. In this study, nickel nanoparticles are decorated onto CNTs to improve interfacial bonding. The broader interface transition area between CNTs and copper with Ni3C interfacial products formed, and a combination of improved electrical conductivity (95.6% IACS), tensile strength (364.9 MPa), and elongation (40.6%) was achieved for the Ni-decorated CNTs/Cuf®Cu (Ni-CNTs/Cuf®Cu). In addition, the strengthening mechanisms are discussed in this study.

For the casted CrCoNi medium entropy alloy melted by magnetic levitation, the deformation was carried out in 4 passes under the condition of liquid nitrogen temperature (−196 °C), the total reduction was 50%, The microstructure and properties were analyzed after liquid nitrogen low temperature rolled. The experimental data showed that the phase structure of the alloy was not changed under the low-temperature rolling. The grains, crushed and refined, were elongated along the rolling direction. With the increasing of passes and reduction, the tensile strength increased from 585 MPa to 1359 MPa, while the elongation decreased from 37.8% to 5.9%. work With the increasing of work hardening, the tensile strength of the CrCoNi medium entropy alloy gradually increased, while the plasticity dramatic decreased. At the same time, the corrosion resistance of the CrCoNi medium entropy alloy was improved by low temperature cold rolled. The corrosion resistance of as-cast and rolled CrCoNi was much better than 304 stainless steel.

The ladle nozzle is one of the most important components in metal smelting. The cracking phenomenon occurs due to excessive thermal stress, which seriously affects the performance and life of the ladle nozzle. In this paper, a new composite structure of ladle nozzle is proposed, which consists of two materials with different properties and costs. The thermal physical parameters of the material are measured by high temperature dynamic Young’s modulus test method, thermal expansion test and flashing method. Based on the new structural model of the composite ladle nozzle, finite element simulation is used to combine the material ontology model, contact mechanics model and heat transfer model to study the temperature and thermal stress distribution inside the composite structure of the ladle nozzle during the casting process by taking representative key points inside the ladle nozzle. There is a large temperature gradient in the area near the casting hole, and the farther away from the casting hole, the smaller the temperature change. The ladle nozzle structure was optimized and compared with the existing ladle nozzle structure. The results show that the optimized composite structure of the ladle nozzle has significantly lowered thermal stress extremes under thermal shock, while the thermal stress distribution tends to be more uniform, which can largely reduce the chance of crack generation. This study is of great significance for improving the reliability and service life of the ladle nozzle and reducing its production cost.

Carbon nanotubes (CNTs) reinforced double-layered Cu-Ni composite foams (Cu-Ni/CNT foams) were prepared through chemical plating and electrodeposition, for the purpose of combining enhanced mechanical and electromagnetic shielding properties. The microstructure characterization revealed a quite uniform dispersion of the CNTs embedded in the metal layers, even after heat treatments. The property testing showed the compressive strength, energy absorption capacity and electromagnetic shielding effectiveness (SE) of Cu-Ni/CNTs foams were significantly improved, as compared to Cu-Ni foams. The heat treatments of the composite foams resulted in an interdiffusion of the Cu and Ni layers, causing an increase of compressive strength and a slight decrease of average SE. The possible mechanisms of the property evolution are discussed.

The multi-wall carbon nanotube (MWCNT) reinforced alumina (Al _2 O _3 ) matrix composites were fabricated by spray drying and vacuum hot-pressing sintering. The mechanical properties of the composites with different mass fractions of MWCNT were studied. The flexural strength and fracture toughness of the composite were 498.3 MPa and 5.69 MPa·m ^1/2 , respectively, which were about 55.3% and 84.7% higher than that of pure Al _2 O _3 . With the increase in the content of MWCNT, the Vickers hardness and relative density of the composite decreased gradually. The correlation between the microstructure and the mechanical properties of the composite was analyzed.

In this study, carbon nanotube-reinforced silver composites (CNT/Ag) were prepared by the powder metallurgy process via spark plasma sintering (SPS) and hot pressing sintering (HP) with composite powders through an improved electroless plating method assisted by ultrasonic spray atomization. The dispersion of CNTs was effectively improved by ultrasonic spray atomization, and uniform silver layers were deposited on the surface of CNTs by electroless deposition. The property testing results showed significant improvements of the electrical conductivity, hardness, and tensile strength in the samples prepared by SPS, as compared to their HP sintered counterparts. When the volume fraction of CNTs reached 2.5%, the tensile strength reached a maximum value of 221 MPa, which was more than twice that of the pure silver samples. The structural analysis indicated different degrees of CNT agglomeration and matrix mean grain sizes in the composites prepared by SPS and HP, which are responsible for the differences in properties.

Carbon nanotube (CNT)-reinforced metal matrix composites (MMCs) face the problems of dispersion and interfacial wetting with regard to the matrix. A synergetic method of spray pyrolysis (SP) and flake powder metallurgy (FPM) is used in this paper to improve the dispersibility and interfacial bonding of CNTs in a Cu matrix. The results of the interface characterization show interface oxygen atoms (in the form of Cu2O) and a high density of dislocation areas, which is beneficial for interfacial bonding. The tensile results show that the tensile strength of the SP-CNT-Cu composites is much higher than that of the CNT-Cu composites when the mass fraction of the CNTs does not reach the critical value. This can be explained by the nanoparticles which are found on the surface of the CNTs during the SP process. These nanoparticles not only increase the tensile strength of the SP-CNT-Cu composites but also improve the dispersion of the CNTs in the Cu matrix. Thereby, uniform dispersion of CNTs, interfacial bonding between CNTs and the Cu matrix, and the enhancement of tensile strength are achieved simultaneously by the synergetic method.

The molecule of the title compound, C20H20Br2N2O2, lies on a twofold axis. It contains two stereogenic C atoms with R chirality and thus it is the enatiomerically pure R,R-diastereomer. There is an intramolecular O—H...N hydrogen bond.