Abstract:The microstructure and texture evolution of Cu-Nb nanocomposite wire after heat treatment were characterized by the scanning electron microscope and electron backscatter diffractometer (EBSD). The recrystallization, nucleation, large angle boundary, and residual internal stress of the nanocomposite were also discussed. Results demonstrate that after the annealing treatment, the grain recovery and recrystallization occurs in the Cu-Nb nanocomposite and a small number of large angle boundaries appear. The residual internal stress becomes weaker after the annealing treatment. After annealing over 600 °C, the grains in Nb filaments are recrystallized and grow significantly. The Cu-Nb nanocomposite wire has good structural stability at high temperatures.

Abstract:Silver nanowires with different aspect ratios were prepared by adjusting the molar content of polyvinylpyrrolidone (PVP) through the liquid-phase reduction method. X-ray diffractometer, scanning electron microscope, UV-Vis spectrophotometer, simultaneous thermal analyzer, and transmission electron microscope were used to characterize the phase composition, microstructure, light absorption properties, thermal decomposition, and crystal structures of the silver nanowires, and the molecular dynamics was used to simulate the stretching and melting processes of single-crystal silver nanowires. Result shows that the silver nanowires are mainly composed of face-centered cubic silver. When the molar ratio of PVP to AgNO₃ changes from 1.5 to 7.5, the diameter of silver nanowires firstly decreases and then increases, and the minimum diameter of nanowires is 77.7 nm when the molar ratio is 6.0. With decreasing the diameter of silver nanowires from 106.1 nm to 77.7 nm, the melting temperature is decreased, and the lowest melting temperature is 281.2 °C. The yield strength is gradually increased from 0.63 GPa to 0.83 GPa with increasing the aspect ratios of silver nanowires from 6 to 72. The melting temperature of single-crystal silver nanowires is decreased from 690 K to 657 K with increasing the aspect ratio. Therefore, the molar ratio of 6.0 is the optimal condition to synthesize silver nanowires, and the silver nanowires with a large aspect ratio have good resistance to deformation.

Abstract:With graphene quantum dots (GQDs) of unique properties as the secondary phase additive, Ni-based nanocomposite coatings were prepared by supercritical electrodeposition technique. The effect of the addition of GQDs on the microstructure, microhardness, wear resistance, and corrosion resistance of the coatings under supercritical conditions was studied. Results show that the densification and homogenization occur in the coating microstructure after GQD addition. When the GQD content is 1.5 g/L, the surface morphology of the coating is more compact. X-ray diffraction analysis shows that the GQD addition can change the peak positions of (111), (200), and (222) nickel diffraction planes of the composite coatings, and the crystallographic preferred orientation appears in the (111) plane. The GQD addition greatly improves the properties of composite coatings. When the GQD content is 1.5 g/L, the coating microhardness is as high as 7381.4 MPa, which is nearly 980 MPa higher than that of the pure nickel coating. The cross-section area of the wear scar is 3336 μm², which is only 44% of that of the pure nickel coating. Tafel polarization test shows that the corrosion current density is 3.55×10^-6 A·cm^-2, which is 65% lower than that of the pure nickel coating (10.07×10^-6 A·cm^-2). The immersion corrosion tests of 150 h show that when the GQD content is 1.5 g/L, the optimal corrosion resistance occurs with the least pitting corrosion in the composite coating.

Abstract:After the colloidal proton acid treatment, the preparation of titanium carbide Ti₃C₂T_x was achieved. In addition, the single-walled carbon nanotube (SWCNT) was used as reinforcement to improve the mechanical properties of proton acid treated titanium carbide (H-MXene): the tensile property is enhanced by nearly 400% while the electromagnetic shielding performance is retained. This study demonstrates that the H-MXene and carbon nanotube have great potential in electromagnetic interference (EMI) shielding composite materials with excellent mechanical properties.

Abstract:Sn_1-xSm_xO₂ (x=0wt%, 8wt%, 16wt%, 24wt%) micro/nano-fibers were prepared by electrospinning combined with heat treatment. The phase, morphology, infrared emissivity, and laser absorption properties of the products were characterized. The first principles simulation based on density functional theory was used to compare and analyze the photoelectric properties of Sn_1-xSm_xO₂ (x=0wt%, 16wt%) material, and the effect mechanism of Sm³⁺ doping on the infrared emissivity and laser absorption of SnO₂ from the perspective of electronic structure was further clarified. Results show that after calcination at 600 °C, the calcined Sn_1-xSm_xO₂ micro/nano-fibers all present the single rutile structure and show good fiber morphology. The fibers interlace with each other, forming irregular three-dimensional network structure, and the elements are evenly distributed on the fiber. With increasing the Sm³⁺ doping amount, the reflectivity of Sn_1-xSm_xO₂ micro/nano-fibers is decreased gradually at wavelength of 1.06 and 1.55 μm, and the infrared emission is decreased firstly and then increased. When x=16wt%, the reflectivity at wavelength of 1064 nm is 53.9%, the reflectivity at wavelength of 1550 nm is 38.5%, and the infrared emissivity at wave band of 8?14 μm is 0.749, which provides a theoretical and practical basis for the thin, light, wide-band, and high-performance laser-infrared compatible stealth materials.

Abstract:The effects of crystalline states, twin boundary spacing, and Fe doping on the mechanical properties of SLM aluminum are examined by performing molecular dynamics simulations of uniaxial tensile tests. The results show that the strengthening effect of twins on aluminum with different crystalline states and whether or not Fe is quite different. Inserting nano-twin in different crystalline aluminum can increase the tensile strength of single crystal aluminum, but reduce the tensile strength of equiaxed grains and columnar grains aluminum. Among them, the mechanical properties of columnar grains are the most sensitive to twins, especially the tensile strength. There is a critical value of 2.8 nm for the effect of twin boundary distance λ on the tensile strength of the columnar crystal aluminum. When λ is less than this value, the tensile strength of columnar twin aluminum decreases with the increase of λ, while when λ is greater than this value, the tensile strength of columnar grains aluminum gradually increases with the increase of λ, until it is close to that of columnar grains aluminum with twin-free. Compared with the tensile strength of different crystalline twin Al, the tensile strength of different crystalline twin Al doped with 5 at.% Fe is greater, and the strengthening effect of columnar twin Al-5%Fe is the best, indicating that reasonable control of the content of Fe and nanotwinned crystalline, which are expected to improve the mechanical properties of SLM aluminum.

Abstract:In this study, nanocrystalline La1-xEuxB6 powders were successfully fabricated using a novel calcium thermal reduction and acid leaching technique (CTR&AL) for the first time, and the effect of Eu-doping on the structure and optical properties of La1-xEuxB6 and the mechanism were also systematically investigated. The XRD, FE-SEM and TEM analyses all confirm that the nanocrystalline La1-xEuxB6 exhibits a single-phase CsCl-type cubic structure, good crystallinity and a cubic morphological characterization with an average grain size of 40 nm. The results of optical absorption show that the transmission light wavelength of nanocrystalline La1-xEuxB6 shifts from 595 nm to 825 nm with increasing Eu-doping content, indicating a "red shift" phenomenon of transmission light. And the Eu doping causes the enhancement and broadening of absorption spectrum of LaB6 in the near-infrared region. Furthermore, the first principle calculations reveal that the Eu-doping strengthens the localization of energy bands at near Fermi level of LaB6 and reduces the number of conduction electrons in the conduction band, which in turn decreases its plasmon resonance frequency energy, which qualitatively explains the continuous tunable characteristic of La1-xEuxB6 transmission light.

Abstract:In this paper, three kinds of organic/inorganic hybrid flame retardant coatings were prepared by sol-gel method using water-based nano-aluminum sol as the inorganic component (ALS), methyltriethoxysilane (MTES) and phenyltriethoxysilane (PhTES) as the organic precursors. The three kinds of coatings are nano-aluminum sol hybrid methyltriethoxysilane (ALS/MTES), nano-aluminum sol hybrid phenyltriethoxysilane (ALS/PhTES), and nano-aluminum sol hybrid methyltriethoxysilane and phenyltriethoxysilane (ALS/MTES/PhTES). The flexibility test of the coatings showed that the flexibility of ALS / PhTES and ALS / MTES / PhTES coatings containing phenylsilane were better than that of ALS / MTES coatings, indicating that the addition of PhTES could improve the flexibility of the coating. The thermal stability test of the coatings illustrate that the Tg of ALS/MTES/PhTES coating is 205.78°C, which is the highest, besides, the residual mass reaches 72.57% when the temperature is 900 °C. It illustrates that the addition of PhTES promotes the thermal stability of the coating in some extent. The SEM figure of the samples show that the surface of coating is uniform, dense and without obvious phase interface. Otherwise, the XRD test results of the coating before and after ablation show that its mechanism of fire-resistant is attributed to the decomposition of boehmite (AlO(OH)), random depolymerization of the main chain Si-O-Si in coating and the decomposition of side chain alkyl.

Abstract:V/UiO-66 catalyst and modified Sn-V/UiO-66 catalyst were prepared by impregnation method with UiO-66 as carrier, and their potassium poisoning was simulated. The reaction and deactivation mechanisms of vanadium-titanium catalyst were analyzed. Results demonstrate that the crystallographic form of catalysts barely changes after K-loading, and the specific surface area of the catalysts has an irregular fluctuation. The catalyst activity is decreased rapidly after the alkali metal was loaded due to the degraded metal redox performance and the rapidly decreased surface acid content of the catalysts. The addition of Sn can enhance the interaction between VO_x and other components, which thereby increases the V⁵⁺ content and reducibility of VO_x. Thus, VO_x on the surface of Sn-V/UiO-66 catalysts can provide more acid sites. The poisoned K-Sn-V/UiO-66 catalyst still has high total acid content and strong redox property, presenting the high resistance of Sn-V/UiO-66 catalyst against alkali metal poisoning.

Abstract:To further improve the high-temperature service performance of DZ125 alloy, the rare earth element Y-modified Cr-Al co-deposition coating was prepared via the pack cementation method on the DZ125 alloy surface. The effects of Y₂O₃ content on the oxidation resistance at high temperature and the microstructure and phases of the co-deposition coating were studied. Results show that the Cr-Al-Y coatings prepared under different conditions have a triple-layered structure, which is arranged from the outside to the inside as follows: the Cr+Ni₃Cr₂ outer layer, the Ni₃Cr₂+Al₁₃Co₄ middle layer, and the Ni₃Al inner layer. Both the coating thickness and the density are strongly increased with the addition of 0wt%?2wt% Y₂O₃, and they are decreased when the content of Y₂O₃ is further increased to 5wt%. The results of oxidation tests at 1100 °C demonstrate that the Cr-Al-Y coating significantly improves the oxidation resistance of DZ125 alloy at high temperatures.

Abstract:The microstructure and mechanical properties of Mg-2Zn-1Mn-xY (x=0, 1, 3, 5, 7, wt%) alloy were studied by optical microscope (OM), X-ray diffractometer (XRD), X-ray fluorescence spectrometer (XRF), electron probe microanalyzer (EPMA), scanning electron microscope (SEM), electron backscatter diffractometer (EBSD), transmission electron microscope (TEM), and uniaxial tensile tests. Results show that the secondary phases of as-cast alloys are changed from Mg₇Zn₃ to Mg₃Zn₃Y₂ and finally transformed to Mg₁₂ZnY with the addition of Y element. Although Y addition hinders the dynamic recrystallization process and therefore refines the grains, the excess Y addition cannot further refine the grains. Meanwhile, the ductility of as-extruded Mg-2Zn-1Mn alloy is increased and then decreased with the addition of Y element, which may be attributed to the synergistic effect of texture orientation and grain coarsening. Besides, the strength enhancement is mainly attributed to grain refinement strengthening and secondary phase strengthening. The Mg-2Zn-1Mn-7Y alloy has the optimal mechanical properties: the ultimate tensile strength is 357 MPa, yield strength is 262 MPa, and elongation is 14%.

Abstract:The dynamic and static recrystallization behavior of GH4760, GH4738, and AD730 typical Ni-based superalloys during hot deformation was investigated. The compressive hot deformation and solution annealing experiments were conducted. Results show that the nucleation mechanism of dynamic and static recrystallizations is dominated by the discontinuous mechanism of grain boundary bulging. Different types of stepped grain boundaries are generated during the dynamic and static recrystallizations due to the transformation from ordinary crystal planes into low-index crystal planes. This transformation results in lower energy of more grain boundaries. The morphology of the stepped boundaries on Σ3 grain boundaries mostly decompose into {111}₁/{111}₂ and 90°{112}₁/{112}₂ facets. The stepped grain boundaries promote the migration of grain boundaries, accelerating the recrystallization process. After recrystallization, partial stepped grain boundaries remain, the interfacial energy reduces, and the further grain growth is promoted.

Abstract:The internal relationship between the microstructure and service stability of NdFeB magnets was investigated. Results show that the NdFeB magnets after low-pressure sintering have significantly finer grains and more uniform distribution of the Nd-rich phase among the grains, which is beneficial to obtain smaller coercivity temperature coefficients of magnets, thereby improving the temperature stability. Compared with that of the magnets after vacuum sintering, the coercivity temperature coefficient of low-pressure-sintered magnets is reduced from -0.488%/°C to -0.472%/°C. However, the flow of the Nd-rich phase from the triangular grain boundary to the main phase intergranular area promotes the formation of complete network structure, which degrades the corrosion resistance of the magnets. The low-pressure-sintered magnets show more serious corrosion mass loss after immersion in 3.5wt% NaCl solution, presenting a stronger corrosion tendency.

Abstract:A new method to produce graphene-coated aluminum composite powder by graphene aerosol prepared by electrical explosion was proposed. This method solves the problems of uneven dispersion and weak interfacial bonding of graphene in the metal composite powder without damaging the intrinsic properties of graphene. The graphene aerosol of specific content was prepared by the electrical explosion, and the obtained graphene had two structures, namely the flake graphene and the gel graphene. The graphene had 5?8 layers, and the graphene aerosol was uniformly dispersed in the chamber. Then, the graphene aerosols were mixed with spherical aluminum particles by stirring under the air flow, and the graphene-coated aluminum composite powders with different graphene contents were prepared. When the content of graphene aerosol is 1.5wt%, the graphene is uniformly dispersed in the aluminum composite powder and the graphene sheets adhere to the metal particles. Finally, the mechanism of in-situ formation of graphene-coated metal composite powder by dispersing of graphene aerosols was analyzed.

Abstract:A novel method for the preparation of α-alumina foams with P-γ-Al₂O₃ modified coating for the palladium catalysts was proposed. The polyurethane template method was used and the preparation parameters were optimized. The apparent porosity of the ceramic foam is 90.28%, the bulk density is 0.45 g·cm^-3, and the strength of ceramic foam is satisfying. The P-modified γ-Al₂O₃ coating was prepared on the α-alumina foam, and then the active catalytic phase (Pd) was loaded by ultrasound-assisted impregnation. Results show that the P-containing coating increases the surface area and weakly acidic sites of the inert foam while decreasing the proportion of strongly acidic sites. Compared with the uncoated foam, the foam with modified coating can easily load the active phase. In addition, the loaded Pd metal can hardly be oxidized, and the catalytic conversion temperature (T₅₀, T₉₀) of CO reduces by about 50 °C. This research presents the great practical potential of low-cost modified α-Al₂O₃ ceramic foams in the palladium catalyst production.

Abstract:Corrosion resistance of as-extruded and as-annealed binary Mg-xLi (x=1, 3, 5, wt%) alloys was investigated via immersion tests, electrochemical tests, corrosion morphology observation, and scanning Kelvin probe tests. Results reveal that the annealing twins form in the as-extruded alloys after annealing at 350 °C for 4 h, and the corrosion resistance of the as-annealed alloys is obviously worse than that of as-extruded alloys in 0.1 mol/L NaCl solution. Typical filiform corrosion appears in as-extruded alloys at the initial corrosion stage, according to the analysis results of scanning electron microscope and laser confocal 3D morphology observation. Some corrosion pits are gradually formed with prolonging the corrosion duration. The rapid corrosion damage occurs on the as-annealed alloy surface, and meanwhile the relatively large and deep corrosion pits appear on the alloy surface. Besides, the distribution of isopotential line of corrosion indicates the occurrence of preferential corrosive degradation in the annealing twin areas. Thus, the micro-galvanic effect is formed between the annealing twins and parental grains with annealing twins as anode and parental grains as cathode, which decreases the corrosion resistance of as-annealed Mg-Li alloys.

Abstract:The NiCrBSi coating was sprayed onto the 45 steel under a steady magnetic field. The microstructure, mechanical properties, and friction and wear properties of coatings were studied. In the steady magnetic field, the coating porosity decreases dramatically. No new phase forms, but the preferred orientation occurs for the γ-Ni, FeNi₃, and Ni₃Si₂ phases. Moreover, the magnetic domains within the coating become more active and more ordered with subtle variations in external magnetic fields. The microhardness of the cross section of coating increases significantly, the residual stress on the surface fluctuates obviously, and the wear amount of the coating decreases by nearly 13.6%. Results show that a steady magnetic field can improve the coating quality effectively. Besides, the mechanism of property enhancement of Ni-based coating by spraying under steady magnetic field was discussed.

Abstract:FeCrMnAlCu high-entropy alloy (HEA) coatings were prepared on the surface of 45# steel by cold spraying-assisted induction remelting and cold spraying-assisted laser remelting. The phase composition, microstructure, microhardness, and wear resistance of the HEA coatings were characterized, and the effects of the two processes on the wear resistance of HEA coatings were studied. Results show that the FeCrMnAlCu HEA coatings synthesized by these two methods are composed of body-centered cubic (bcc) and face-centered cubic (fcc) phases. The coating microstructure is dense and the elements are evenly distributed. The microstructures of coatings consist of dendrite+interdendrite structures, and the dendrite region is mainly enriched with Mn, Cr, and Fe elements, while the interdendrite region is rich in Cu. In addition, the Al element is evenly distributed between the dendrite and interdendrite. The lattice strain of bcc phase in FeCrMnAlCu HEA coating synthesized by cold spraying-assisted induction remelting is greater than that by cold spraying-assisted laser remelting. The microhardness of the FeCrMnAlCu HEA coating synthesized by cold spraying-assisted induction remelting is 1.2 times higher than that by cold spraying-assisted laser remelting and 3.5 times higher than that of the 45# steel matrix. The friction process of FeCrMnAlCu HEA coating is mainly the abrasive wear. The FeCrMnAlCu HEA coating synthesized by cold spraying-assisted induction remelting has good wear resistance, and its wear rate is 29% lower than that by cold spraying-assisted laser remelting.

Abstract:Nearly spherical NaCl particles prepared by a disc granulator were used to produce open-cell aluminum foams via infiltration casting. The average compressive strength of the salt balls is 3.9 MPa, and they can be completely collapsed within 5 min in the ultrasonic cleaner. By controlling the hot-pressure sintering duration as 0.5?2 h and the hot-pressing temperature at 700 °C, the preforms with bulk density of 0.66?0.83 g/cm³ can be prepared. Prolonging the duration of hot-pressure sintering can increase the pore size of the open-cell aluminum foams from 0.48 mm to 1.16 mm, and also increase the porosity from 64% to 82%. Compression test results show that the macroscopic deformation characteristics of the foams with different pore structures are basically the same, and they all exhibit the deformation characteristic of layer-by-layer collapse. In addition, the densification strain value, elastic modulus, plateau yield stress, and energy absorption capacity of open-cell aluminum foams are al decreased with increasing the porosity. The energy absorption capacity is the largest (15.0 MJ·m^-3) when the porosity is 64%.

Abstract:To study the deformation twins and plastic anisotropy of AZ31 magnesium alloy, based on the plastic constitutive theory of rate-correlated crystals, a magnesium alloy model with different initial textures, including slip and twin deformation mechanisms, was established by the finite element method. Besides, the volume fraction of twin crystals was introduced into the model. The relationship among texture evolution, twins, and mechanical properties during compression was studied. Results show that the plastic behavior of crystal depends largely on the initial texture, and the difference in the initial texture leads to the obvious anisotropy of compression behavior: high axial yield and tensile strength and low radial yield and tensile strength. During the compressive plastic deformation process, with increasing the deformation, the volume fraction of activated twin crystal is increased. In addition, the higher the volume fraction of radial compressive activated twin crystal, the lower the volume fraction of axial compressive activated twin crystal. The points of obvious twin crystal appearance in the simulation coincide with those of stress mutation. When the volume fraction of twin crystal reaches a certain value, the stress suddenly changes, the crystal orientation changes significantly, and the new slip system is activated, reflecting the influence of the coupling of slip and twin crystal mechanisms on the mechanical properties of AZ31 magnesium alloy.

Abstract:With the consideration of the influence of arc driving forces, a 3D transient numerical model was established for the ripple formation process during pulsed tungsten inert gas (TIG) welding. To avoid the influence of droplet caused by the melting of welding wire on the surface fluctuation of molten pool, the wire-feeding process did not proceed when the arc was scanning the 2024 aluminum alloy substrate. Results show that the molten pool surface fluctuates periodically when the current is switched between the base value and the peak value. With the arc movement, the rear side of molten pool is solidified gradually. The molten pool surface is solidified before flattening under the cooling with large temperature gradient, resulting in the welding ripples. The formation frequency of the welding ripples is equal to the current pulse frequency. The distance between adjacent welding ripples is approximately equal to the product of the arc scanning velocity and the current pulse frequency.

Abstract:As a kind of light and high strength material, SiC/Al composite has been widely concerned because of its excellent physical and chemical properties. In this study, molecular dynamics methods were used to construct SiC/Al composite material models with different SiC particle sizes. The results of tensile deformation simulation show that smaller SiC particle size is beneficial to higher tensile strength. As the tensile deformation gradually increases, the SiC particles are separated from the Al matrix on both sides along the tensile direction to generate voids, and then dislocations are generated from the void defects to nucleate and expand into the matrix to form plastic deformation. After adjusting the occupancy of C and Si on the SiC/Al interface, it is found that the bonding is stronger when the interface is rich in Si, and the generation of voids is more difficult, which strengthens the SiC/Al composite material.

Abstract:Zr-0.3Cu-xCr (x=0.2, 0.5, 1.0, wt.%) alloys were prepared to investigate the effect of Cr on the corrosion behavior of Zr-0.3Cu alloy in 360 ℃/18.6 MPa/0.01 M LiOH aqueous solution. The results showed that with the increase of Cr content, the number of ZrCr2 secondary phase particles (SPPs) increased, while the number of Zr2Cu SPPs were nearly unchanged. After exposure to the aqueous solution, the corrosion resistance of Zr-0.3Cu-0.2Cr alloy was relatively high compared to other alloys probably due to the thick ZrO transition layer at the oxide/matrix interface. When the Cr content was higher than 0.5 wt.%, the number of SPPs increased, which can generate more defects like micropores and microcracks during oxidation, and consequently, accelerate the corrosion of Zr-0.3Cu-xCr alloys.

Abstract:In this paper, the high temperature mechanical properties and the associated deformation mechanism of CoCrNi-based entropy alloy with rich-CoCr content were studied. It is found that the alloy with the compostions of Co_33.3Cr_30.6Ni_26.1Al₅Ti₅ (at. %) exhibited excellent instantaneous tensile properties in the temperature range of 600℃ to 800℃ after hot forging and aging heat treatment. In particular, the yield strength anomaly occurs at 700℃, the tensile yield strength is as high as 944 MPa and the elongation at break is 16%, which is better than most nickel-base and nickel-cobalt-base superalloys. By means of X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscope (TEM) and three-dimensional atomic probe (3D-APT), it is found that the strong ordered strengthening of high-volume fraction multi-principal γ" [(Ni, Co, Cr)₃(Al, Ti)] phase combined with grain boundary strengthening aring from the formation of FCC phase with rich-CoCr is the main factor for the excellent high temperature properties of the alloy.

Abstract:In this paper, the oxidation behavior of Ti-15Mo-xO (x=0.1, 0.2, 0.3, 0.4, 0.5, mass fraction, %) alloys at 873 K and 1073 K, and the precipitation behavior of α phase at 837 K were investigated by using OM, XRD, EPMA, Vickers hardness tester and first-principles calculation. The results showed that the oxidation products were all composed of TiO2, Ti3O and Ti6O at 873 K, the oxygen contents had no significant effect on the oxidation behavior of the alloys, which was mainly controlled by the diffusion of Titanium out of the substrate. At 1073 K, the oxidation products of each alloy were TiO2, but the oxygen contents had a significant effect on the oxidation behavior of the alloys: in low oxygen-added alloy, the oxidation process was controlled by the oxidation reaction between oxygen and substrate combined with the oxygen diffusing into the substrate, while with the oxygen contents increased, it was controlled by the oxygen diffusing into the substrate, which enhanced the oxidation resistance. The α phase precipitated by ageing at 873 K for 10 h and 100 h increased with the increase of oxygen contents and ageing time, the lattice parameter of molybdenum-rich and oxygen-poor β phase decreased, and the c axis of oxygen-rich and molybdenum-poor α phase increased, while the a axis was basically unchanged, and the c/a radio increased. The hardness of the alloys increased with the increase of oxygen contents before and after ageing, however, under the condition of the same oxygen content, molybdenum and oxygen elements were redistributed in the two phases with the precipitation of α phase, which leaded to the decrease of the hardness of the alloys after ageing.

Abstract:Titanium alloy has become a promising candidate material for oil country tubular goods(OCTG) and offshore components in rigorous service environment, owing to its high specific strength, low density, low elastic modulus, excellent toughness，fatigue and corrosion resistance. However, there is a lack of research on the friction and wear properties of titanium alloy drill pipes under ultra-deep drilling conditions, and the comparison research on the tribology performance and mechanism of titanium alloy drill pipes and steel drill pipes is few. In this paper, the friction and wear properties of three titanium alloy drill pipes and steel drill pipes are compared and analyzed through hardness test, impact wear test, reciprocating friction test, simulated condition wear test and microscopic analysis in simulating ultra-deep well conditions, and the wear mechanism of titanium alloy drill pipe under drilling conditions were also investigated, the results showed that the impact and wear resistance of titanium alloy drill pipes was lower than that of steel drill pipe materials, especially the impact resistance of titanium alloy drill pipe materials under medium-frequency impact. In the air reciprocating wear test, the friction coefficient of titanium alloy drill pipe was lower than that of steel drill pipe, when titanium alloy drill pipe wear against rock, it was a typical abrasive wear mechanism, and it is typical Adhesive wear when it wear against steel pipe. Under the simulated working condition of drilling fluid, the friction coefficient of titanium alloy drill pipe was significantly lower than that in air, and the friction coefficient of titanium alloy was the lowest when friction with rock under water-based drilling fluid conditions, and the wear resistance was the strongest, which was due to the fact that it was easier to form a dense passivation film with a lower friction coefficient on the surface of the titanium alloy in the water-based drilling fluid. It is recommended to use water-based drilling fluid when drilling with titanium alloy drill pipes, but because the wear of titanium alloy drill pipes under working conditions was still not as good as that of steel drill pipes, the next step is to conduct surface treatment on titanium alloy drill pipes to improve the wear resistance of titanium alloys.

Abstract:Pure tin (β-Sn) has attracted significant attention due to its excellent chemical properties and plasticity. It is widely used in many fields as solder material and coating material. Presently, there are relatively few investigations on the grain refinement behavior and strength toughness strengthening mechanism of bulk polycrystalline pure tin during rolling. In this work, the evolution of microstructure and mechanical properties and the grain refinement law of polycrystalline pure tin (99.99%) under different rolling processes are studied, which is expected to lay a theoretical foundation for adjusting and optimizing the strengthening and toughening properties of pure tin. The results show that different rolling processes have obvious effects on the microstructure and properties of pure tin. The process of twin excitation and twin induced recrystallization in the deformation process are realized by regulating the factors of temperature, speed and path in the rolling process, in which the rolling speed is the most important factor. The grain refinement mechanism of rolling process is as follows: 60°<100> deformation twins are induced at the initial stage of deformation, and the twins gradually evolve into recrystallized banded structure and divide and refine grains in the subsequent deformation process. Recrystallized grains and twins usually randomize the texture and therefore weaken the concentrated texture produced by the original coarse grain. Rolling deformation can significantly increase the strength of pure tin. The yield strength and tensile strength in TD direction are significantly higher than that in RD direction under unidirectional rolling.

Abstract:The influence of deep cryogenic treatments (DCT) on the microstructure and properties of a cold rolled Cu-1.34Ni-1.02Co-0.61Si alloy was investigated using scanning electron microscopy (SEM), transmission electron microscopy (TEM), an X-ray diffractometer (XRD), a mechanical testing machine and a low resistance tester. The DCT refined and homogenized the microstructure of the alloy after cold rolling at 30 % reduction. The grain refinement of the alloy became more obvious and the microstructure distribution became more uniform with increasing DCT time. The DCT promoted the precipitation of the solid solution elements Ni, Co and Si from the Cu matrix to form many fine and evenly distributed 0.1?m~1?m spherical and strip second phase particles in the grain and grain boundary. The tensile strength, conductivity and elongation of the alloy before and after cold rolling at 30 % reduction increased with increasing DCT time, and tended to be stable at about 36 h. After DCT for 48 h, the tensile strength, conductivity and elongation of the alloy before and after cold rolling increased by 5.4% and 4.4%, 6.7% and 8.0%, 13.2% and 18.7% respectively. The tensile strength of the alloy after cold rolling was higher than that before cold rolling. The conductivity and elongation of the alloy after cold rolling was lower than that before cold rolling. However, the both differences decreased with increasing DCT time. The dimple quantity and depth of the alloy with DCT were larger, and the dimple distribution was more uniform than those without DCT.

Abstract:TiAl alloy is a lightweight superalloy with broad application prospects in aerospace field. Electron beam selective melting(EBM) additive manufacturing technology is an effective way to prepare TiAl alloy with complex structure. However, there are few studies on high temperature properties of TiAl alloy. In this paper, the microstructure, high-temperature hardness and high-temperature oxidation behavior of Ti-48Al-2Cr-2Nb alloy fabricated by electron beam selective melting additive are mainly studied. The results show that the Ti-48Al-2Cr-2Nb alloy formed by EBM exhibits a unique layered structure composed of equiaxed γ grains and double phase regions. After isothermal oxidation at 800 °C for 100 h, this alloy shows a low oxidation rate constant, and the formed oxide film is mainly composed of TiO2, Al2O3 and TiO2 / Al2O3 mixed alternating layers. The oxidation resistance is better than that of Ti-48Al-2Cr-2Nb alloy and other TiAl alloy prepared by traditional methods. In addition, this alloy has good high temperature hardness at below 900 ℃, and the microhardness does not decrease significantly with the increase of temperature.

Abstract:Rhenium is a rare refractory metal with unique characteristics and has been widely used. In the case of insufficient rhenium resources, recycling rhenium from rhenium-bearing scraps is considered to be one of the important ways to obtain rhenium. In this paper, W-Re alloyed scraps in the form of powder, block and wire were selected to recycle rhenium by a pyrometallurgical method, and the properties of the recycled intermediate NH4ReO4 obtained by oxidation roasting, ammonia leaching, evaporative crystallization and the rhenium powder obtained by hydrogen reduction under different process parameters were analyzed. The results show that the form of W-Re alloyed scraps has a significant effect on the recycling process and recovery rate of rhenium powder. The W-Re alloyed scraps in unalloyed powder form, alloyed block and alloyed wire form have different oxidation temperatures, and the volatilization rate of Re2O7 were different at different temperatures. The purity of rhenium powder recycled from three different forms of W-Re alloyed scraps in powder, block and wire were 99.952%, 99.939% and 99.915% respectively, and the recovery rate of rhenium were 95.62%, 94.57% and 91.59% respectively.

Abstract:The effects of single cold rolling annealing, three times cold rolling annealing and subsequent aging on the microstructure and mechanical properties of self-designed metastable β titanium alloy Ti-7.46V-5Mo-3.13Cr-1Zr-3Al were investigated by optical microscope (OM), X-ray diffractometer (XRD), scanning electron microscope (SEM) and room temperature tensile tests. The results show that: compared with single cold rolling annealing, the grain size of the alloy after triple cold rolling annealing is finer, the strength and plasticity are improved, the yield strength reaches 815 MPa and the elongation is 27%. After single cold rolling annealing and aging treatment, the secondary α phase with fine and dispersion is precipitated, the yield strength of the alloy reaches 1280MPa, and the yield strength increases at first and then decreases with the increase of aging time, showing higher strength and lower elongation; However, the strength of the sample after triple cold rolling annealing and aging is slightly lower, but the plasticity is significantly improved, and it has a better match between strength and plasticity. Based on the comprehensive comparison of the experimental results, it can be determined that the alloy can achieve a good match of strength and plasticity after triple cold rolling annealing at 800℃/20min and aging at 500℃/10h, the tensile strength is 1380MPa and the elongation is 10.8%.

Abstract:Superalloy that can serve above 800 °C is urgently needed for the development of high-performance aero-engine turbine disk. Increasing the content of γ′ phase could significantly improve high temperature machinal properties, and GH4151 alloy is the typical representative of superalloys with more γ′ phase, and its γ′ phase content is about 55 wt.%. Besides, GH4151 alloy could serve at 800 ℃ and presents a broad application prospect. However, the higher content of γ′ phase also increases the difficulty of deformation. Cogging process of the homogenized ingot is an important part in preparation of turbine discs. However, there is still a lack of systematic research on the hot deformation behavior of homogenized GH4151 alloy. Therefore, the deformation behavior of homogenized GH4151 alloy was studied by isothermal hot compression test and hot processing maps were established based on flow curves. In addition, FESEM and coupled EBSD/EDS methods were utilized to analyze deformed microstructure. Based on the results of hot processing map, the domains with good workability are 1060 ~ 1090 ℃,0.1 ~ 0.2 s-1 and 1060 ~ 1070 ℃,0.1 ~1 s-1. A large amount of primary γ′ phase (γ′Ⅰ) in initial structure hinders the movement of dislocations to promote recrystallization, and pins the grain boundaries to refine the grains. An increasing deformation strain contributes to a larger instability domain. The main form of GH4151 alloy deformation instability is that the tensile stress at the bulging zone of deformed sample induces cracking of grain boundary and γ/γ′Ⅰ phase boundary. Increasing deformation temperature and deformation rate will promote cracking.

Abstract:Nickel diamond-like (Ni-DLC) composite electrodes with different Ni contents were prepared on pure Ti substrate by high power pulsed magnetron sputtering technology, which was used to construct enzyme-free glucose sensor. The surface morphology, microstructure and electrochemical performance of Ni-DLC composite electrode were characterized by X-ray diffractometer, atomic force microscope, Raman spectrometer and electrochemical workstation. The results show that: (1) with the increase of Ni content, the particle protrusion on the surface of Ni-DLC film increases gradually, and the diameter of agglomeration particles also increases, which significantly increases the active sites on the surface of Ni-DLC film. The content of sp2 bond in Ni-DLC film increases, the order degree of the film increases, and the conductivity of the film is improved. No obvious Ni-C bond is formed in the film, and Ni mainly exists in elemental form. (2) Glucose sensor made of Ni-DLC composite electrode was placed in glucose solution for testing, and the results showed that: Ni-DLC composite electrode has a good catalytic effect on glucose, electrode reaction is mainly controlled by diffusion, oxidation peak current density and glucose concentration has a good linear relationship, Ni-DLC composite electrode for glucose detection sensitivity of 796 μAmM-1cm-2, the lower limit of detection LOD = 0.5 μM, The response time is 5 s, and the electrode has good anti-interference performance for uric acid and ascorbic acid. The electrode has a broad application prospect in the construction of enzyme-free glucose sensor.

Abstract:V-5 (Al-5Ti-1B) alloys (V-5ATB) were prepared by in vacuum electric arc melter. The effects of solution treatment temperature and time on the microstructure, hardness and rollability of V-5ATB alloys were studied by optical microscope, X-ray diffractometer, hardness testing and rollability testing technology. The results showed that, when V-5ATB alloys were solution treated at 800 and 900 ℃, TiB phases gradually dissolved into V–based solid solution (Vss) and the grains grew with the increasing temperature. The strengthening effect of TiB second phase and fine grains of the alloys is weakened more than the increase of solid solution strengthening effect, resulting in the hardness decrease of the alloys with the increasing temperature. When the alloys were solution treated at 1000 ℃, the TiB phases in the alloys were almost completely dissolved into Vss, and the solid solution strengthening effect is dominant, resulting in the hardness increase of the alloys. When V-5ATB alloys were solution treated at 900 ℃, TiB phases gradually dissolves into Vss and the grains grew with time. The weakening degree of the strengthening effect of the second phase and fine grain of the alloys is greater than the increase degree of the solid solution strengthening effect, resulting in the hardness decrease of the alloys after solution treatment with the extension of time. The optimum solution treatment parameter of V-5ATB alloys is 900 ℃/2 h. The rollability of the solution treated V-5ATB alloys is improved by about 24% compared with those of the as-cast alloys.

Abstract:In order to improve the strength and wear resistance of the copper, ZrB2-SiC/Cu composite coating was prepared on the surface of a copper substrate by laser cladding with the raw materials of Zr, Si, Ni-B4C, Cu composite powders. The surface morphology, microstructure, phase composition and interface combination of the composite coating were analyzed by OM, XRD, SEM and TEM, And the hardness and wear resistance of coatings with different reinforcement phase content were tested. The results showed that the micron-sized needle-like ZrB2 and nano-sized granular SiC were successfully synthesized in the copper matrix by the designed in-situ synthesis reaction. A clean and impurity-free interface formed between the reinforcements and the copper matrix. Mechanical properties of the composite coating were improved by two reinforcements with different dimensions and sizes through a variety of strengthening mechanisms. The size of the reinforcement could be controlled by adjusting the laser process parameters, with the content of the reinforcements increased, the average hardness and wear resistance of the composite coating gradually increased. The average hardness of the composite coating with the reinforcing phase content of 30 wt% was 309 HV0.2, which was about 5.6 times that of pure copper. The current-carrying wear rate of the 30 wt% composite coating was about 80% lower than that of the 10 wt% coating. The higher content of the composite coating showed excellent current-carrying wear resistance.

Abstract:In order to solve the problems of large stomata， coarse grain and poor mechanical properties of the aluminum alloy joints， the welding of the 7075 aluminum alloy thin sheet was completed by using the CMT welding method， and the ultrasonic wave was introduced in the welding process.The influence of different ultrasonic power on welded joint stomata， microstructure and mechanical properties were investigated by gold phase，EBSD，and mechanical properties.The results show that ultrasonic vibration can significantly reduce the number of stomata and increase the melting width， and the width of HAZ decreases with the microhardness of welding joints at 1200W by about 8.93HV， tensile strength 5by about 85MPa and fracture elongation by 1.4%.According to EBSD results， the average grain size of the weld was 36.89 μm when the ultrasonic power is 1200W，9.99 μm and the large angle boundary ratio of the welding joint to some extent.

Abstract:In order to study the influence of WC addition on the microstructure evolution and use security of selective laser melted metal, economical spherical WC powders produced by granulation-sintering-deoxygenation (GSD) method were chosen as reinforcements to manufacture powder reinforced 18Ni300 steel matrix composites via selective laser melting under the given forming parameters after powder mixtures in this paper. The effects of reinforcement contents on the microstructures and impact properties were analyzed. The results reveal that the WC powder contents are the key factor of determining relative density and impact toughness of the composites. The relative density of the composite has few changes, but the dense composites with no defects can not be manufactured when the WC content is higher than 25% under the given forming parameters. Under the forming parameter, metallurgical bonding can be formed between WC powders and the matrix. The W and C elements in the matrix of the composites increase due to partial fusion of WC particles. α-Fe phase formation is restrained, and the grain size and orientation change. With increasing WC contents, α-Fe phase gradually transforms into γ-Fe phase, and grain sizes increase. The average impact energy of the samples decreases from 49.25 J to 8.5 J with WC weight contents increasing form 0% to 20%. The SLMed 18Ni300 exhibit plastic fracture characterization, and the fracture characterization gradually transforms form the mixture of plastic and brittle fracture characterization to brittle fracture characterization.

Abstract:The Cr-coated Zr alloy materials appear to be one promising short-term accident tolerant fuel cladding concept, due to their outstanding high-temperature oxidation resistance and improved resistance to fretting wear. In addition, there are few barriers or challenges to be applied to nuclear reactors for coated Zr alloy claddings. In this paper, 12-15 μm-thickness coatings have been deposited by magnetron-sputtering process on the outer surface of Zr-1Nb alloy tubes. Two-sided isothermal oxidation tests were performed in flowing steam by synchronous thermogravimetric analyzer, at temperatures ranging from 1000°C to 1200°C and for oxidation times ranging from 300 s to 5000 s, with the object of systematically studying the behavior during accidents. Scanning electron microscopy equipped with energy dispersive X-ray spectroscopy and X-ray diffraction were utilized to characterize the microstructure, element distributions and phase of oxide scale to study the oxidation kinetics and mechanisms of Cr coating. Based on these analyses, dense chromia scale was developed on the outer surface of cladding during steam oxidation, preventing the oxygen atoms from diffusing into the substrate, to improve the high-temperature resistance of the composited claddings. In addition, the oxidation kinetics of the Cr coating was nearly parabolic and the rate constants was at least two orders of magnitude lower than the Zr alloy, enhancing high-temperature steam oxidation resistance of Zr alloy claddings.

Abstract:The particle size distribution of copper powder produced by the domestic electrolysis method is generally above 30 μm, and most of the copper powder obtained is concentrated in the low-end and low-end fields with low added value, which cannot meet the higher requirements of the electronic information field. This paper uses chemical-electrochemical synergistic reaction to prepare electronic grade ultrafine copper powder, and discusses the influence of chemical reaction time, current density and cathode composition on the particle size, morphology and structure of copper powder. The results showed that with the extension of the chemical reaction time, the particle size of the copper powder gradually increased, and the dendritic shape gradually became dense; with the increase of the current density, the particle size gradually decreased, showing a well-dispersed dendritic shape. The optimal process conditions are determined as follows: the chemical reaction time is 1 min, the current density is 300 A.m_^-2, and the aluminum alloy cathode plate. Under this process, a dendritic ultrafine copper powder with an average particle size of 6.44 μm, a bulk density of 0.828 g.cm_^-3 and good dispersibility can be obtained. It is further proved that the chemical-electrochemical coordinated reaction mechanism is that the substitution reaction generates crystal nuclei in advance, and electrochemical deposition grows in situ on the crystal nucleus to form dendritic crystals.

Abstract:The graphite/vanadium oxide composites were prepared by a carbothermal reduction method using V2O5 as the raw material and graphite powder as the reducing agent. The Methylene blue was used as a simulated pollutant, the adsorption properties of the prepared samples in different reduction conditions were systematically evaluated, and the samples prepared at the reduction temperature of 650 ℃, reduction time of 60 min and graphite ratio of 18.03% were selected for characterization and as the target adsorbent. The microstructure and surface morphology were characterized by X-ray diffraction, scanning electron microscopy, X-ray photoelectron spectroscopy, Raman spectroscopy, high-resolution transmission electronic microscope and BET microporous analysis. The characterization results showed that the phase of the samples consisted of graphite, VO2 and a small amount of V6O13, the vanadium oxides were dispersed on the lamellar graphite surface in the form of lumps, strips and radiations, the particle sizes of the samples ranged from a few microns to tens of microns. The BET specific surface area box pore volumes of the graphite/vanadium oxide were 6.84 m2/g and 0.02 cm3/g, respectively, and most of the pore sizes were distributed in the mesoporous and macroporous regions. The adsorption experiments results showed that the graphite/vanadium oxide had good adsorption performance on methylene blue in the pH range of 3-8, and the equilibrium adsorption amounts were above 200 mg ? g-1. The adsorption process was in accordance with the Langmuir isotherm and quasi-secondary kinetic equations.

Abstract:La(Fe, Si)₁₃H_Y based alloy is regarded as the candidate of the room temperature magnetic refrigeration materials. However as the poor mechanical property of the hydride which is difficult to be used in the magnetic refrigerator. How to prepare the magnetic refrigrant with large magnetocaloric effect is the key problem to be solved. In this paper La_0.8Ce_0.2Fe_11.51Mn_0.19Si_1.3master alloy was prepared by medium frequency induction furnace and annealed, followed by milling to powder. The alloy podwer was hot pressed at 650 ℃, 850 ℃ and 1050 ℃ respectively. The resulted La_0.8Ce_0.2Fe_11.51Mn_0.19Si_1.3alloy was cut into plates and then hydrogenated until saturated. The phase constitution, microstructure and magnetocaloric effect of samples was determined by XRD, SEM and VersLab. The porosity is the lowest and the volumetric magnetic entropy change is the alrgest (144.7 mJ/cm^₃?K) for the sample hot pressed at 1050 ℃. The Curie temperature increase to near room temperature, the large magnetocaloric effect of the first order phase transition is still maintained for the sample hot pressed at 1050 ℃ after hydrogenation. No cracks on the surface are found on the hydride and keep integrity.

Abstract:Titanium alloys and nickel-based alloys have unique properties. The bimetallic structure formed by them has a broad application prospect in the aerospace field. However, due to the large differences in physical and chemical properties between the two metals, cracking is easy to occur at the bonding zone. Based on directed laser deposition (DLD) technology, TC4/IN718 bimetallic structures without interlayer and Cu interlayer were fabricated, respectively. The resuslts of test and analysis results indicate that the TC4/IN718 bimetallic structure without interlayer has cracking due to the formation of the Ti-Ni brittle phases at the bonding zone, which leads to the increase of crack sensitivity. In the bimetallic structure with Cu interlayer, the Cu transition zone formed between TC4 and IN718, which inhibited the direct combination of TC4 and IN718 and reduced the crack sensitivity. Due to metallurgical reaction and element diffusion, a small amount of Ti-Cu and a very small amount of Ti-Ni compound phases are formed in the Cu transition zone. Due to the formation of the compound phase, the Vickers hardness of the transition zone of TC4/IN718 bimetallic structure with Cu interlayer is about 592 HV. However, it is much lower than the Vickers hardness of the bonding zone of TC4/IN718 bimetallic structure without Cu interlayer (about 845 HV).

Abstract:The undercooled solidification experiment of Ag-Cu/Co-Sn eutectic alloy was performed by means of molten glass purification and cyclic overheating, and the effects of undercooling and minor Nb addition on the formation of anomalous eutectic were systematically studied. The results show that anomalous eutectic is formed by remelting in the eutectic dendrite during rapid solidification. With the increase of undercooling, the morphology of eutectic phase changes from vermicular to spherical particles. The solid particles formed by remelting will be used as the substrate for the nucleation of residual liquid phase. The nucleation of two-phase in Ag-Cu eutectic is non reciprocal. With the addition of Nb to Co-Sn eutectic alloy, the critical undercooling of anomalous eutectic formation inside the sample decreases from 23 K to 15 K, and from 45 K to 30 K in the surface microstructure. Because the sample surface contact with the crucible wall which is conducive to the dissipation of latent heat of solidification, the critical undercooling of anomalous eutectic formation is higher. The duration of slow solidification stage on the temperature recalescence curve of Ag-Cu eutectic alloy is longer than that of Co-Sn eutectic alloy.

Abstract:The damage behavior under low-energy and high-flux helium ions irradiation condition of the W28Ta28V28Zr8Sc8 high-entropy alloy, prepared by spark plasma sintering (SPS), is studied. The results show that the high-entropy alloy reveals better resistance to irradiation damage than pure W under the same He ions irradiation condition. Under different He ion energies, the He ions threshold energy when the serious “fuzz” structure appears in high-entropy alloy is much higher than that of pure W. With the same irradiation parameters, the “fuzz” layer thickness of high-entropy alloy is obviously smaller than that of pure W. After irradiation, the different phase regions of W28Ta28V28Zr8Sc8 high-entropy alloy show different surface morphology characteristics, which are related to the He ion irradiation behavior of the main elements constituting the phase region. An excellent irradiation damage resistant material could be achieved by designing the microstructure of the high entropy alloy.

Abstract:The acid washing solution of copper smelting flue gas was adsorbed by D296 anion exchange resin, and then Sb was desorbed by ammonia, Bi was desorbed by NaOH and tartaric acid mixed solution, and Re was desorbed by NH₄SCN solution. The step-by-step desorption of Re/Sb/Bi was realized and rhenium enrichment solution was obtained. The results show that the potential of acid washing solution has no significant effect on the adsorption rates of Re, Sb and Bi. The appropriate concentration of H₂SO₄ in acid washing solution is about 43 g.L^_-1, and the adsorption rates of Re, Sb and Bi are 100%, 6.55% and 89.05%, respectively. The breakthrough capacity and saturation capacity of D296 resin for adsorption of Re are 1.308 g.L^_-1 and 1.773 g.L^_-1, respectively, and the utilization rate of resin is 73.77%. Firstly, 12.5% ammonia is used to desorb sb, and 16% NaOH + 140 g.L^_-1 tartaric acid mixed solution is used to desorb Bi. The hydrolysis of Bi can be effectively inhibited by adding tartaric acid, and then 10% NH₄SCN solution is used to desorb Re to obtain rhenium enrichment solution. The concentration of Cu, As, Sb and Bi in rhenium enrichment solution decrease to less than 1 mg.L^_-1. Re concentration in acid washing solution is enriched four times.

Abstract:Cold spray additive manufacturing technology is a solid-state additive manufacturing method that relies on the plastic deformation of powder particles to form bonds. As the additive components has almost no defects such as oxidation, phase transformation, grain growth, cracks, etc. The lower deposition temperature has little effect on the heat of the matrix, and has the advantages of high additive efficiency and the manufacture of large components. It has attracted the attention of many national research teams and is recognized as a powerful and useful additive manufacturing and additive repair technology. In view of the increasing attention of scholars and industry at home and abroad to the cold spraying additive manufacturing technology, this paper attempts to summarize the microstructure and properties of typical cold spraying deposits (Cu, Al, Ti, Ta and other materials) on the basis of describing the cold spraying equipment, with emphasis on the application and new progress of cold spraying additive manufacturing technology in the field of national defense. At the same time, the challenges of cold spraying additive manufacturing technology are also pointed out.

Abstract:In recent years, magnesium alloy as a "degradable medical metal material" is more and more favored by researchers. However, the rapid corrosion degradation of magnesium alloys leads to significant mechanical attenuation and weakened suitability of the materials for bone healing, which is a bottleneck limiting its clinical application at present. As an effective measure to slow down the degradation rate of magnesium alloys, micro-arc oxidation has the advantages of simple process, high film forming efficiency and good overall performance index of the film, and realizes the dual functions of regulating the degradation rate and improving biocompatibility. The research progress of micro-arc oxidation coatings on biomedical magnesium alloys was reviewed. The essential relationship between micro-arc oxidation process parameters and biocompatibility of coating degradation performance was systematically summarized. The formation/rupture mechanism of micro-arc oxidation coating magnesium alloy was described in detail. The growth mechanism of the self-sealing porous oxide film the deposition process of the porous material and the reason of its retention in the micro-pores were revealed. The phase characteristics of composite surface treatment film and its degradation behavior in bionic solution environment were summarized. Finally, the future development direction of micro-arc oxidation coating for medical magnesium alloy was prospected.

Abstract:The "Re effect" makes the physical and chemical, thermoelectric, mechanical, and processing and welding properties of Mo have been comprehensively improved. Mo-Re alloys are widely used in advanced nuclear energy, aerospace, electronics, biomedical and other fields due to their good comprehensive properties. In particular, its excellent radiation resistance, compatibility with nuclear fuels and alkali metal coolants, neutron characteristics and other nuclear physical properties make it the first choice for core structural materials in space nuclear reactors. In this paper, the research status of Mo-Re alloys is systematically reviewed from four aspects: crystal structure, microstructure, properties, preparation, processing and application, and its development prospect is prospected.

Abstract:In this paper, the magnetic absorbing coating is integrated into the structural design of metamaterials, and a new low-frequency composite metamaterial absorber is obtained. The absorber is composed of annular resistance film, double-layer magnetic absorbing coating and metal back plate. The absorption properties of the metamaterial absorber are calculated by CST simulation software, and the effects of various structural parameters of the absorber on the absorption properties are studied. The simulation results show that when the thickness of the designed metamaterial absorber is 2.5mm, there are two absorption peaks at 1.9GHz and 4GHz, the reflection loss is less than -8dB and the absorption bandwidth is 5GHz in the frequency range of 1.59-6.59GHz. The absorbing mechanism is discussed through the electromagnetic field distribution of the absorber. The results show that the increase of the absorption bandwidth of the absorber is due to the change of the electromagnetic field distribution of the metamaterial absorber and the loss of the magnetic dielectric layer. Finally, the absorber samples are prepared and tested. The physical test results are basically consistent with the simulation results, which shows that the designed and prepared absorber has excellent low-frequency absorbing performance, and the absorbing bandwidth is greatly improved compared with the magnetic absorbing coating.

Abstract:Cu-Ag alloy is a kind of high-strength and high-conductivity alloy with important application prospects. The improvement of the properties of Cu-Ag alloy depends on the development of the deformation and heat-treatment process. However, the effect of pre-deformation before the heat treatment has not been investigated. The effects of pre-deformation on microstructure and properties after solid solution were investigated using XRD analysis, Vickers hardness, conductivity, metalloscope and scanning electron microscopy. The results show that pre-deformation promotes the recrystallization of Cu-6Ag alloy, and the grain size is obviously reduced. Meanwhile, the pre-deformation reduces the amount of Ag in Cu-6 wt% Ag alloy after aging treatment. Discontinuous precipitates are observed in samples with or without pre-deformation. The discontinuous precipitation in the pre-deformed alloy has a smaller spacing of 95±9.5nm. The hardness in pre-deformation alloy is 85.8 HV lower than that in unpre-deformation alloy. The conductivity of pre-deformed alloy is almost equal to unpre-deformation alloy which is, 90.3%IACS.