Abstract:The design and mechanical properties of porous titanium alloys has become a hot research topic in the biomedical field. Two types of Gyroid minimal surface monolithic structures, i.e. homogeneous and gradient, were designed and prepared by laser selective melting (SLM). By conducting static compression and tensile experiments on them, and comparing them with traditional truss-like cellular structures, the quasi-static compression models of five different lattice structures were established. The mesh division and analysis were carried out through the co-simulation of Hypermesh and ABAQUS. Five types of porous structure failure forms and deformation mechanisms of hollow cubic, G7, bcc, homogeneous Gyroid and gradient Gyroid were analyzed through the observation of stress-strain nephogram, plastic strain nephogram and compression experiment process. The stress-strain curves obtained by simulation were compared with the experimental results. Results show that the simulation method can better predict the maximum compressive strength of different porous structures. The results of compression and tensile experiments show that the maximum tensile properties of Gyroid lattice materials are much higher than those of truss-like structures, and the compressive properties are also superior. Among them, the G-gradient structure has the best overall mechanical properties.

Abstract:TiAl alloys have become one of the most promising high-temperature lightweight structural materials in aerospace and other fields because of low density, high specific strength, high-temperature oxidation resistance and other properties. However, due to the brittleness of them, it is easy to introduce micro-cracks, holes and other defects in the forming process, which seriously affect the mechanical properties. For this reason, supersonic fine particle bombardment (SFPB), one of the surface modification techniques, was used to investigate the effect of twin boundaries (TBs) on the mechanical properties and deformation behaviour of TiAl alloys. The findings demonstrate that when the number of TBs increases, the yield strength of models with various numbers of TBs falls. The closer the location of TB to the upper surface of model, the lower the yield strength of the material. As the number of TBs increases, the obstruction of dislocation movement by TBs becomes more evident and the degree of plastic deformation of the surface of the model after bombardment becomes greater, making the material more susceptible to fracture. The closer the TB to the upper surface of the material, the more evident the inhibition of dislocation growth by the twin, which in turn affects the strength of the material. Deformation failure of the model is the combination result between dislocations and dislocations, dislocations and twins and other defects.

Abstract:The thermal deformation tests of diffusion-bonded region of TC4 titanium alloy was carried out at deformation temperatures of 920,950,980,1010 ℃ and strain rates of 0.01, 0.1, 1,10 s-1. The effects of deformation temperatures and strain rates on flow stress and microstructure of diffusion-bonded region of TC4 titanium alloy was investigated. The results show that the diffusion-bonded region of TC4 titanium alloy has obvious dynamic softening characteristics at high temperature,and the flow stress decreases with the increase of deformation temperature and increases with the increase of deformation rate; The diffusion-bonded interface disappears after high temperature deformation,and the volume fraction of isoaxial α phase decreases with the increase of deformation temperature,accompanied by the emergence of short rod-like and plate-like secondary α phase, and the volume fraction of secondary α phase decreases with the increase of strain rate; When the deformation temperature reaches 1010 ℃,martensite α ""phase appears; Based on the hyperbolic sinusoidal modified Arrhenius equation,the hyperbolic sinusoidal constitutive equation and the thermal processing diagram of diffusion-bonded region of TC4 titanium alloy were established.The optimal deformation parameters of diffusion-bonded region of TC4 titanium alloy were determined as T=920~950 ℃, ε=0.01~ 0.1 s-1.

Abstract:To reveal the effects of solid solution temperatures (850 °C, 920 °C, 960 °C) on the microstructure and dynamic tensile mechanical properties of TC4 titanium alloy, XRD, SEM and EBSD methods were applied to analyze the characteristics of crystal structure, microstructure, and grain orientation of the material. The separated Hopkinson tension bar (SHTB) experimental device was used for dynamic tensile mechanical property testing of the material, and the Johnson-Cook (J-C) constitutive model was established. Finally, dynamic tensile fracture morphology analysis was performed. Results show that with the increase of solid solution temperature, the content of α/α′phase increases, the content of primary α phase decreases and the content of needle-like α′ phase increases, while the grain size decreases and the strength of selective orientation increases. TC4 titanium alloy exhibits a significant strain rate strengthening effect. With the increase of solid solution temperature, the material yield strength and Vickers hardness gradually increase, and the fracture elongation decreases. The dynamic tensile fracture exhibits ductile fracture characteristics, and with the increase of solution temperature, the plasticity of the material decreases. When the solid solution temperature is 960 ℃, the ductile fracture characteristics of the specimen are not significant. The conclusions of this paper can provide methods and data to support the mechanical property control and impact resistance design of TC4 titanium alloy.

Abstract:Vacuum dissimilar brazing of TC4 alloy and TNM alloy was performed at 900 ~ 1020 °C for 10 min using amorphous Ti-25.65Zr-13.3Cu-12.35Ni-3Co-2Mo (wt.%) filler. The interfacial microstructure and formation mechanism of the TC4/TNM brazed joint and the variation of the interfacial microstructure and shear strength of the brazed joints as brazing temperature were systematically investigated. Results revealed that the interfacial microstructure of the TC4/TNM joints brazed at 900 ~ 980 ℃ were TC4/ fine basket weave (α+β)-Ti/γ-(Ti, Zr)2(Cu, Ni) + α-Ti/Ti3Al/TNM. The brittle γ-(Ti, Zr)2(Cu, Ni) decreases but the ductile α-Ti increases with brazing temperature. Once the brazing temperature increased to 1000 °C and 1020 °C, the interfacial reaction layer of the TC4/TNM brazed joints transformed from three layers into two layers, which consist of coarse acicular (α+β)-Ti with poor ductility and Ti3Al, respectively. And the coarse acicular (α+β)-Ti was further coarsened with brazing temperature. The shear strength of the TC4/TNM brazed joint increased first and then decreased with brazing temperature. The maximum shear strength of 494.83 MPa was obtained at 980 ℃. The brittle fracture primarily occurs in the brazing seam near TNM side regardless of brazing temperature during shear test.

Abstract:The microstructure evolution of TC25G titanium alloy bar with basket microstructure after different deformation degrees were studied and the changes of its thermal stability and creep resistance at 550 ℃ were compared. The results show that the tensile plasticity after thermal exposure increases and the creep resistance decreases with the increase of deformation degree. The two mechanical properties match well at 100% deformation degree and can meet the requirements of engineering application. The increase of deformation degree corresponds to the spheroidizing process of lamellar α phase. Before the lamellar α phase is fully spheroidized, the interface strengthening effect of multi-layer structure makes the alloy have good creep resistance at high temperature. However, after α-phase spheroidization, the alloy has better plasticity because of the microstructure dominated by equiaxed microstructure. With the increase of deformation degree, the size of the fracture dimples becomes smaller and more uniform, and the dimple depth increases, which indicates that the plasticity after heat exposure increases . The results of nano-hardness test show that the microhardness of primary α phase is higher than that of β transforms, and the creep resistance can be improved by adjusting the content and distribution of α phase in the alloy by solution temperature, in order to obtain the best matching of strength and plasticity at high temperature, the extent of lamellar α phase spheroidization can be controlled.

Abstract:The influence of cooling conditions on the temperature field and macro-segregation of Cr element of TC6 alloy ingot was investigated by MeltFlow-VAR. In order to validate the agreement between the model and experiment results, a full-scale TC6 ingot has been prepared. The simulation results show that with increase of the heat transfer between ingot and crucible, the depth of molten pool and mushy zone of ingot becomes shallower, and the whole ingot is solidified in a bottom-up sequence, which leads to the reduction of the segregation range of Cr element. The experimental results show that the solidified macrostructure is composed of full-columnar grains by using the irregular crucible with reduced wall thickness, which is beneficial to reduce segregation and obtain high quality ingot.

Abstract:The effect of different quasi-beta heat treatment processes on the microstructure and mechanical properties of TC4-DT titanium alloy were investigated, and the microstructure and mechanical properties fracture morphology were compared and analyzed. The results show that with the increase of solution temperature from Tβ+10℃ to Tβ+25℃, the ratio of length to width of primary α phase and the content of secondary α phase increased, the plasticity decreased and the tensile strength increased. The decrease of cooling rate has coarsened effect on the primary lamellar α phase, which reduce the aspect ratio of the primary lamellar α phase, Therefore the tensile strength gradually increased, while the plasticity gradually decreased. With the prolongation of solution time, the width of the primary lamellar α phase increases and the aspect ratio decreased, while the aspect ratio of the secondary lamellar α phase increased.There are many dimples with different size on the fracture of TC4-DT alloy. With the increase of solution temperature and the extension of aging time, the size of dimples of tensile fracture samples increased to varying degrees, and a small number of tearing edges appeared at the same time. The fracture mechanism of the samples is mainly ductile fracture with quasi-cleavage fracture.

Abstract:The texture evolution mechanism of TA2 pure titanium under different stress (tensile stress, compressive stress) was studied by tensile and compressive test methods, combined with Schmid factor calculation and crystal plasticity simulation calculation. The results show that, in the process of tensile deformation, it is difficult to change the texture under large strain variables, while in the process of compression deformation, the texture changes is significant. Under different strain paths, there are some differences in the starting deformation mode. Under different strain variables, with the increase of deformation, the increase of grain number of base plane slip or conical slip or {10-12} stretched twin is the main reason for the formation of different textures.

Abstract:By adding rare earth Yb2O3, the superplastic deformation ability of laser weld of TC4 titanium alloy is improved, and the superplastic deformation uniformity of joint is improved. The results show that the addition of Yb2O3 can reduce the flow stress of weld superplastic deformation, improve the elongation and increase the uniform coefficient of joint deformation. With the increase of Yb2O3 content, the longitudinal peak flow stress and elongation of weld first decrease and then increase, and the peak flow stress is 11.9MPa at 6%. The highest elongation was 592.3 %. With the increase of Yb2O3 content in transverse deformation, the joint deformation uniformity coefficient K increases first and then decreases. When the content of Yb2O3 is 6 wt.%, the maximum K value of the sample is 0.209.

Abstract:Y modified aluminizing coatings were prepared on pure Nb substrates by aluminizing in the pack mixtures with Y₂O₃ addtion. The effects of Y on the microstructure and growth mechanism of the coatings were studied. The results show that the Y has no obvious effect on the phase constitution of the coating and the grain morphology of NbAl₃ phase. With the increase of Y₂O₃ content in the pack mixtures, the Y content on the coating surface increases. After Y modification, the growth mechanism of the coatings is changed from being controlled by the intergranular diffusion of Al atoms to being controlled by the intragranular diffusion of Al atoms, which reduces the growth rate of the coatings and contributes to the formation of two kinds of silk textures (<010>//ND and<110>//ND) in the columnar crystal area of NbAl₃ phase.

Abstract:Biofouling is an important factor threatening the safe and efficient service of marine engineering materials, so it is of great significance to develop efficient, environmentally friendly and low-cost antifouling materials. In this paper, two kinds of α-MoO3 powder materials were prepared by one-step thermal decomposition at 450 °C and 750 °C, designated as S450 and S750. And the samples were analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM), and infrared spectroscopy (FTIR). It indicated that the α-MoO3 obtained at 450 °C and 750 °C showed nanoscale plate-like structure and micron-sized long plate-like structure, respectively. Plate counting was used to evaluate the antimicrobial effects of two materials on Pseudomonas aeruginosa (P. aeruginosa) in the absence of light. The results showed that the antibacterial rates of S450 and S750 at concentrations of 0.25, 0.5, 0.75, and 1 mg/ml were 27.3%, 99%, 100%, 100% and 16.1%, 30.1%, 52.3%, 73.6%, respectively. It indicated that both α-MoO3 obtained under the two conditions showed good antibacterial properties in the absence of light. The pH value of the solution decreases with the increase of the α-MoO3 concentration, and the concentration of Mo ions increases with the increase of the α-MoO3 concentration. The antibacterial activity of α-MoO3 in the absence of light stems from the synergistic effect of dissolution of H3O+ and Mo ions. Compared to S750, S450 exhibits higher antibacterial rate, which may be due to the higher solubility of S450, resulting in more H3O+ and Mo ions release.

Abstract:A new method of fabricating Ti layer on diamond surface was proposed to obtain the metallization of diamond surface. A Ti bar heated to a certain temperature with induction method was rotated, extruded and rubbed on the surface of shielded polycrystalline diamond. The surface temperature of polycrystalline diamond was measured with infrared thermometer. The interface and inner surface of Ti layer, and the interface between polycrystalline diamond and cemented carbide were observed with scanning electron microscope. The phase composition of the inner surface, the elements of the interface and inner surface of Ti layer were analyzed with X-ray diffractometer and energy spectrum analyzer, respectively. The research results show that the mutual diffusion of C and Ti elements occurs at the interface between polycrystalline diamond and Ti layer, and TiC with spot shape is generated. The chemical bonding between polycrystalline diamond and Ti layer can be realized. Thermal damage at the interface between polycrystalline diamond and the cemented carbide can be effectively avoided by placing polycrystalline diamond in an electromagnetic shielding device. The formation process of Ti layer on diamond surface can be divided into three stages: contact of fresh surfaces, initial diffusion and formation of diffusion band. The proposed method has features of fabricating processes simply, increasing layer efficiency significantly and avoiding diamond thermal damage effectively.

Abstract:Si-Co-Y co-deposited coating was prepared on the surface of TiAl alloy by pack cementation process. The microstructure, formation mechanisms and oxidation performance at 950 ℃ of the coating were analyzed. The obtained Si-Co-Y co-deposition coating is compact and possesses multilayer structure: mainly composed of a TiSi₂ superficial zone, a TiSi₂ and Ti₅Si₄ mixed outer layer, a Ti₅Si₃ middle layer and a TiAl₂ inner layer. The growth of the Si-Co-Y co-deposited coating is controlled by inward diffusion of Si, and followed an orderly process of depositing Si first and then Co. High-temperature oxidation tests show that the Si-Co-Y co-deposited coating has good anti-oxidation resistance, due to the formation of a protective oxide scale that composed a mixture of SiO₂, TiO₂ and Al₂O₃. The growth of the oxide scale on the coating followed a parabolic law, and the parabolic rate constant of oxidation weight gains is about 6.3×10_-2 ^mg₂^/cm₄^h_1/2^, lower than that of the TiAl substrate by about one order of magnitude.

Abstract:Thermal barrier coatings were deposited on the third generation single crystal superalloys DD90.NiCrAlY+NiCoCrAlTaY double-layer bond coatings were prepared by high velocity oxy-fuel spray (HVOF).The ceramic layers were YSZ and MSZ/YSZ structures which were prepared by using atmospheric plasma spray technique, respectively. The oxidation resistance test at 1150℃ shows that the weight gain of the YSZ coating is significantly higher than that of the MSZ coating. After 250 thermal cycles at 1200℃, the two coatings do not occur obvious phase transition and the sintering resistance of the MSZ coating is better. The TGO of the two coatings mainly consists of Al2O3 and a small amount of spinel structure mixed oxides. The double-layer bond layer reduces the diffusion of Al element into the substrate, while due to the concentration gradient diffusion of Cr element leads to the precipitation of topological close-packed (TCP) phases and the increase in the depth of secondary reaction zone (SRZ).

Abstract:Interface optimization is an effective way to improve the performance of aluminum matrix composites. Basalt fibers (BF) modified by Ni-Co-P alloy coatings with about 0.2 μm in thickness were prepared by electroless plating firstly, and then Ni-Co-P coated basalt fibers reinforced 2024Al matrix composites (BF(Ni-Co-P)/Al) and uncoated basalt fibers reinforced 2024Al matrix composites (BF/Al) were fabricated by vacuum hot pressing sintering process. The effects of Ni-Co-P coatings on the interface microstructure and tensile properties of BF(Ni-Co-P)/Al composites were studied. The results show that stable Ni-Co-P intermediate layer is formed in BF(Ni-Co-P)/Al composites, which can not only restrain harmful interface reaction but also optimize the interface bonding state between matrix and basalt fiber. The density and hardness of BF(Ni-Co-P)/Al composites are superior to those of BF/Al composites, and yield strength (252 MPa) and ultimate tensile strength (360 MPa) of BF(Ni-Co-P)/Al composites with basalt fibers content of 30vol% have a significant improvement compared with those of BF/Al composites and 2024Al matrix, and the fracture mode is progressive accumulative failure.

Abstract:The effect of Al doping on microstructure, crystal structure, martensitic transformation, mechanical properties and corrosion resistance of Ni₄₈Co₁Mn₃₇In_14-xAl_x (0≤x≤2) magnetic shape memory alloys was studied by the material preparation method of arc melting. The results show that the grain size of the alloy is reduced by replacing part of In with Al, and the average grain size is reduced to about 10 μm when 2at% Al element is doped, which is about 1/35 of that of the undoped sample. When the doping amount of Al is 0.25at%?2at%, the metal Al is completely dissolved into the matrix, and the solid solubility of Al in the alloy increases with the increase in the doping amount; when the doping amount is 2at%, the solid solubility of Al in the matrix is close to 2at%. With the substitution of Al for In, the alloy changes from the two-phase structure of L2₁ cubic austenite and monoclinic 6M martensite to a single 6M at room temperature, the unit cell volume gradually decreases, and the martensitic transformation temperature shows an upward trend. The compressive strength of the alloy continues to increase, and compared with that of Ni₄₈Co₁Mn₃₇In₁₄, the compressive fracture strength of Ni₄₈Co₁Mn₃₇In₁₂Al₂ is increased by 160%, and the compressive strain also increases from 5.46% to 6.36%. After an appropriate amount of Al replacing In, the corrosion resistance of the alloy in artificial seawater generally shows an increasing trend. The corrosion resistance of Ni₄₈Co₁Mn₃₇In₁₂Al₂ alloy is significantly higher than that of Ni₄₈Co₁Mn₃₇In₁₄ alloy, and its corrosion resistance is close to that of 304 stainless steel.

Abstract:In high magnetic field magnets, especially those with high stability requirements, superconducting joints with ultra-low resistances play an important role in magnet fabrication. The Nb₃Sn and NbTi joints were fabricated by the resistive welding technique. The Nb₃Sn joint was fabricated by sintering the Nb-Sn precursors after mechanical alloying. Then the Nb₃Sn bulk in the Nb₃Sn joint was welded to the NbTi conductor. The microstructure and grain sizes of Nb₃Sn bulk after long periods of time at high temperature were investigated. After welding, the joint was analyzed using X-ray nano-CT technology to display the connecting status and the defects between the Nb₃Sn and NbTi conductor without destroying the joint. The electrical characteristics of the joints were measured under background fields through the field decay method. Results show that compared with the ones prepared by the commonly used solid matrix replacement technique, the prepared joint exhibits better magnetic field resistance and lower resistance at 1.5 T background field.

Abstract:A mathematic model based on influence function method was established and the plan view pattern evolution rules of plates during angular rolling were studied by simulation and experimental methods. Results show that the difference in the elongation between the area near the angular point and other parts of the plate increases with the increase in the rotation angle of the first pass, which is the main reason why the length-width angle shows a downward trend with the increase in the rotation angle of the first pass. The length-width angle shows an upward trend with the increase in the rotation angle of the second pass, which can be attributed to the fact that the difference in the elongation between the area near the angular point (obtuse angle) and other parts of the plate increases with the increase in the rotation angle of the second pass. ε_w (the deformation in the width direction) increases with the increase in the rotation angle of the first or second pass, which is the primary reason why the width spread increases with the increase in the rotation angle of the first or second pass. Considering the same absolute reduction amount of the two passes, when the rotation angle of the second pass is two times the rotation angle of the first pass, the plates can return to almost rectangular. The predicted length-width angle and width spread values are in good agreement with the experimental ones, indicating that the established computational model based on influence function method can accurately estimate the length-width angle and width spread.

Abstract:A novel method of electromagnetic coupling treatment (EMCT) was proposed to control the residual stress of 2A02 aluminum alloy blade forging in compressor, aiming at solving the industrial problem of machining deformation of large-size thin-wall parts due to residual stress releasing. The effects of electric and magnetic field treatment on the residual stress and mechanical properties of forgings were studied. The microstructure was analyzed by quasi-in-situ EBSD. The results show that compared with a single physical field, the EMCT has the most significant relaxation effect on residual stress. When the magnetic field intensity is 1.5 T and the electric field intensity is 750 V/m, the maximum reduction of residual stress of blade forging is 53%. EMCT can improve the plasticity of aluminum alloy without damaging the strength. Under the above parameters, the elongation is increased by 14.3% and the resistance is decreased by 4.9%. EBSD quasi-in-situ analysis shows that after EMCT, the geometric dislocation density of forgings is reduced by 58.2%, the small-angle grain boundaries are reduced, the plug dislocations are dispersed and annihilated, the local strain is reduced, and the macroscopic stress is relaxed.

Abstract:The influence of steel's recrystallization on the stability of intermetallic compounds (IMCS) layer was investigated in molten Al at 700 °C. Results show that high degree of structural rearrangement leads to the formation of non-protective IMCS layer on the 304SS surface and its corrosion kinetics coincides with linear law. Compact and stable Fe₂Al₅ layer delays the failure of the 410SS in liquid Al. The stability of IMCS is affected by steel's recrystallization in three aspects: (1) energy for IMCS nucleation and growth are reduced, especially for Fe₄Al₁₃; (2) grain orientation transforms to close-packed direction which slows down the diffusion rate of Al ion; (3) stress mismatch is increased at the IMCS/steel interface, especially for the austenitic 304SS.

Abstract:The hot deformation behavior of ZL270LF aluminum alloy under a strain of 70%, deformation temperatures ranging from 300 °C to 550 °C, and strain rate ranging from 0.01 s^-1 to 10 s^-1 was studied by hot compression tests. A constitutive equation for flow stress was constructed, and the hot processing map was drawn, thus determining the optimal hot processing region. An electron back scattered diffractometer (EBSD) and a transmission electron microscope (TEM) were used to explore microstructural evolution of the alloy. The results show that the flow stress of ZL270LF Al alloy decreases with increasing deformation temperature and decreasing strain rate. The deformation activation energy is 309.05 kJ/mol, and the optimal processing region is the area where the temperature is from 470 °C to 530 °C and the strain rate is from 0.01 s^-1 to 1 s^-1. Three different dynamic recrystallization (DRX) mechanisms are involved in the hot deformation process of the alloy, namely continuous dynamic recrystallization (CDRX), discontinuous dynamic recrystallization (DDRX), and geometric dynamic recrystallization (GDRX). Among them, CDRX is the main DRX mechanism of ZL270LF Al alloy.

Abstract:The nickel-based ODS alloy could be applied to nuclear reactor and aerospace. The dissolution and precipitate of the oxide particles or the Ostwald repining in the nickel-based ODS alloy resulting from the grain boundary migration affect the mechanical properties of the nickel-based alloy by increasing the size and decreasing the number density of the oxide particles during the cold working and heat treatment. In this paper, the microstructure of the cold-rolled nickel-based ODS alloy annealing at different temperature were characterized by XRD, EBSD, and TEM. The influence of the annealing process on the microstructure of the cold-rolled nickel-based ODS alloy was studied. It is indicated that the dislocation density of the nickel-based ODS alloy decreased and part of the oxide particle coarsened with the annealed temperature rising. Besides, there were the uniform microstructure and the fine oxide particles in the nickel-based ODS alloy after annealing at 900 ℃. According to the calculation, the tensile strength of the nickel-based ODS alloy after annealing at 900 ℃ is mainly contributed by the dispersion strengthening and dislocation strengthening which were the theoretical basis and the effective method to improving the properties of the nickel-based ODS alloy.

Abstract:The effects of Hf addition on the microstructure, solidification behavior and porosity of a nickel-based high-boron cast superalloy were studied. The results of microstructure analysis, differential thermal analysis (DSC) and isothermal solidification quenching test showed that Hf segregated in interdendritic regions during the solidification process of the alloy, and precipitated from the residual liquid phase in the form of Ni5Hf phase at the end of the solidification process. The addition of Hf reduced the precipitation temperature of liquid/solidus , γ/γ′ eutectic phase and boride, delayed the solidification process of the alloy, widened the solidification temperature range from 166.3 ℃ to 200.5 ℃, and significantly increased the content of γ/γ′ eutectic phases. A thin-walled tube cast was independently designed by ourselves. Penetration test results showed that the addition of Hf significantly reduced the porosity of the thin-walled tube, and the tendency of porosity forming of the alloy was significantly reduced.

Abstract:The core-shell composite nanomaterials composed of magnetic particles and dielectric materials have excellent microwave absorption properties and have become a research hotspot in the field of microwave absorption. The absorbing mechanism of different types of absorbers in composite materials is different, so their proportion has an important influence on the comprehensive absorbing performance. In this paper, a facile method is proposed to prepare core-shell FeBP@SiO₂ nanoparticles. This method combines chemical reduction and sol-gel to realize the controllable shell-core structure of composite particles. By changing the thickness of SiO₂ shell, the effect of shell thickness on microwave absorption performance was studied, and the microwave absorption mechanism was analyzed and explained. With the increase of SiO₂ shell thickness, the microwave absorption capacity of the particles increases first and then decreases. When the thickness of the SiO₂ shell is 38 nm, the FeBP@SiO₂ sample has a nice microwave absorption performance, and the reflection loss at a thickness of 2.19 mm obtains better absorption performance ( -52.66 dB ). This enhanced microwave absorption performance mainly comes from the new magnetic-dielectric interface, thereby improving the impedance matching and dielectric loss of the material. By designing the shell-core structure of the composite particles, the performance regulation of the composite absorber can be achieved. Therefore, this work might provide an important reference for the design of the next generation of new composite microwave absorbing materials.

Abstract:A novel flowable tritium breeder is a tritium breeder composite material which can flow through the combination of liquid metal matrix and liquid dispersion insulating phase. Such a liquid-liquid dual-phase composite can not only inhibit the magnetohydrodynamic (MHD) resistance effect of the current liquid metal or molten salt tritium breeders, but also address the problems of solid tritium breeders such as low tritium release efficiency, low heat transfer, fragile and easy blockage of gas channel. In this paper, the liquid metal GaInSn alloy was used to simulate the flowable behavior of lithium-based liquid tritium breeder, and composite with quenching oil simulating liquid dispersion insulation phase to form a flowable tritium breeder material. In this paper, a flowable metal with low conductivity characteristics was prepared, and the liquid metal GaInSn alloy and liquid dispersed insulating phase quenching oil were mixed into a new fluid. The influence of magnetic flux, mixing ratio and temperature on its viscosity was studied, and the change of conductivity of fluid with the quenching oil of the added dispersed insulating phase was tested. The results showed that When the magnetic induction intensity exceeds a certain value, the viscosity of the fully liquid metal is significantly higher than that of the composite material with quenched oil, indicating that the addition of quenched oil can effectively reduce the MHD effect, and the quenched oil composite material will have lower flow resistance under a strong magnetic field. The conductivity of the fluid was tested and it was found that the conductivity decreased approximately exponentially with the increase of quenching oil. The conductivity of the flowable tritium breeder increased abruptly after standing for a period of time, and then stabilizes again at the new conductivity level. On condition that it was re-sonicated, it could be restored to its original conductivity again, which meant that it could be recycled in practical applications.

Abstract:In order to obtain high quality copper cathodes, a comparative study of microstructure and mechanical properties of copper cathodes produced by conventional electrolytic method from four domestic companies was carried out. The microstructure, grain size, grain orientation and fracture morphology of copper cathodes were analyzed by XRD, OM and SEM, and the mechanical properties of electrolytic copper sheets were analyzed by universal testing machine, impact testing machine and micro hardness tester. The results show that the surface of copper cathodes produced by the traditional electrolytic method of the four companies all show strong selective orientation on the (220) crystal surface, and the homogenization of the weave has a certain effect on the grain refinement, while there is a certain connection between the grain size and mechanical properties, which shows that the smaller the grain size, the higher the strength, hardness and toughness of the material, but the grain refinement affects the plastic deformation ability of the material and reduces the elongation. In addition, all four companies" copper cathodes show characteristics typical of ductile fracture, and the abnormal fracture phenomenon during the tensile process indicates that the presence of defects such as nodules can have a great impact on the performance of copper cathodes.

Abstract:In this paper, dendritic silver powders were prepared by electrolysis and the growth mechanism of tartaric acid on the morphological evolution of silver particles during electrochemical deposition was investigated. The effect of tartaric acid on the morphology and structure of the silver powder during deposition was analysed by field emission scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray diffraction (XRD). In addition, cathodic polarisation (LSV), cyclic voltammetry (CV) and chronoamperometry (CA) were used to investigate the effect of tartaric acid on the electrochemical behaviour of dendritic silver powders prepared by electrolysis. The results showed that when 0 g/L tartaric acid was added to the solution, the silver ions formed a sphere-like structure at a current density of 850 A/m₂ ^, while when 0.05 g/L tartaric acid was added to the solution, the silver ions formed a rod-like structure at the same current density, and the cathodic polarization increased and the overpotential increased as the amount of tartaric acid added increased. When the amount of tartaric acid added to the solution was increased to 0.5 g/L tartaric acid, a dendritic silver powder with a particle size of about 3-4 um, a loose packing density of 1.1 g/cm₃ ^{and a vibrational density of 0.6 g/cm}₃ ^{and good} crystallinity was successfully prepared. The chrono-current results showed that the solution systems all followed a transient nucleation process, but the addition of tartaric acid affected the nucleation and growth kinetics of the silver and inhibited cathodic polarisation.

Abstract:The liquid phase diffusion bonding between CuW alloy and 20 steel was studied. The brittle Fe2W intermetallic compound thin layer was formed at the interface of CuW near the transition layer of the monolithic material, which seriously deteriorated the mechanical properties of the joint. The CuW/20 steel monolithic material containing copper chromium interlayer was prepared in the range of 1200 ℃~1380 ℃. After the interlayer was added, a complete metallurgical transition layer was formed at the interface between CuW alloy and 20 steel, eliminating the thin layer of Fe2W brittle intermetallic compound produced in the process of direct diffusion bonding. It was observed under the optical microscope that the interface transition layer was composed of dark worm like structure surrounded by a light colored matrix. The results of XRD and EDS analysis showed that, The light colored matrix is divided into copper phase and the black vermicular structure is rich in iron phase. With the increase of diffusion bonding temperature, the dark worm like structure in the interface transition layer extends from one side of 20 steel to the copper matrix and grows continuously. When diffusion bonding at 1250 ℃, dark wormlike tissue is evenly distributed in the entire transition layer. The mechanical properties of CuW/20 steel composites at different temperatures were tested at room temperature. It was found that the interface strength reached the maximum of 145Mpa at 1250 ℃. The tensile fracture morphology was observed by SEM, and it was found that the overall interface was flat without dimples, consisting of Cu phase ductile tear edges and flat iron rich phase area.

Abstract:In this study, high-density CoCrMo and Cr3C2/CoCrMo alloys were prepared by selective laser melting (SLM) to investigate the effect of Cr3C2 particles on the microstructure, strength and wear resistance of the CoCrMo alloys. It was found that the phases of the alloy were γ-Co and ε-Co, and the M23C6 phase was generated due to the addition of Cr3C2. The organization of both CoCrMo and Cr3C2/CoCrMo alloys consisted of epitaxial columnar crystals and homogeneous cellular crystals, and the addition of Cr3C2 reduces the number of columnar crystals. The mechanical characteristics of specimens were tested through experiments, Cr3C2/CoCrMo specimens have a hardness of 514±18 HV and an ultimate tensile strength of 1520 MPa, an increase of 27 % and 39 % respectively compared to CoCrMo specimens. Under the same load, Cr3C2/CoCrMo alloy demonstrates superior wear resistance and less wear loss than CoCrMo alloy, and the wear resistance is improved by 30%. During the SLM process, the added Cr3C2 particles melt rapidly, Cr generates a solid solution strengthening in the matrix; Cr3C2 transforms at the grain boundaries to generate M23C6-type carbides with precipitation strengthening, improving the strength and wear resistance of the alloy.

Abstract:The diffusion welding (DFW) processing for commercial pure tungsten and CuCrZr alloy was carried out at 900 ~ 980℃ with pressure of 80MPa and holding time of 2h. The high-pressure torsion (HPT) processed for tungsten and CuCrZr alloy with 5 ~ 20 turns were also DFW processed at 900℃, and the W/Cu composite materials with noble interfacial bonding and mechanical property were obtained. The effects of lattice defects induced by HPT on the element diffusion, microstructure evolution and microhardness improvement were analyzed by optical microscopy (OM), energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD). The results show that the diffusion depth for W and Cu respectively increase from 0.4μm and 0.9μm to 0.9μm and 1.7μm with the increasing DFW temperature, the high temperature leads to the obvious grain coarsening and microhardness decreasing. The high-density dislocations and ultrafine grains induced by HPT accelerate the element diffusion and immigration during DFW. After 20 turns of HPT followed by DFW, the diffusion depth for W and Cu reach to 2.4μm and 3.1μm, which is the 6 times and 3.4 times higher than the initial. The deformation microstructure of tungsten remained after DFW with slight grain growth to 62μm×25μm and the dislocation density was about 1.5×10₁₄^m_-2^{, which is 36% higher than the initial.} The coarse mixture microstructure of CuCrZr alloy after DFW with HPT composite with annealing twinning grains and equiaxed grains, and the high temperature of DFW lead to complete recovery of dislocations accumulated by HPT. The microhardness of W and CuCrZr after DFW with HPT are about 469 ~ 473Hv_0.5 and 62 ~ 73Hv_0.1 respectively, which is 48% and 9% higher than the value of initial sample with DFW. The results illustrate that HPT processing followed by DFW is benefit to fabricate high performance W/Cu composite materials.

Abstract:In this study, the (Fe50Mn30Co10Cr10)97Al3 high-entropy alloy (HEA) was designed by adding the Al element based on the two-phase metastable Fe50Mn30Co10Cr10 HEA. Then the HEA was treated by rolling and annealing, and the effects of annealing temperature on recrystallization behavior, annealing twin evolution and the mechanical properties of the alloy were studied. The results show that with the increase of annealing temperature, partial recrystallization, full recrystallization and grain growth occur in the alloy. After annealing, the HEA exhibits the high recrystallization temperature (0.59 Tm) and the grain coarsening temperature (700 ℃) due to the severe lattice distortion effect and hysteresis diffusion effect of the HEA. A Large number of annealing twins are formed in the alloy annealed at 600~700 ℃; with the further increase of annealing temperature (800~900 ℃) , the content of annealing twins drop significantly due to the migration of grain boundaries or twin boundaries. Uniaxial tension results show that the alloy annealed at 700 ℃ has good comprehensive mechanical properties, with a tensile strength of 730 MPa and a uniform elongation of 50.5%. At the same annealing temperature, the number of annealing twin variants in a single grain is related to its grain size, it is easy to form single annealing twin variant in the small-sized grains, and to form multiple annealing twin variants in the large-sized grains.

Abstract:Al-Cu-Li alloy is a critical lightweight structural material in aviation and aerospace industry, which has become one of the key materials to manufacture the large aircraft structures in China. When the aircraft is in service in humid environments such as the ocean, it is vulnerable to be eroded by corrosive halide anions, and especially under the Cl^- ion erosion, its surface of Al-Cu-Li alloy components is prone to pitting corrosion, intergranular corrosion and exfoliation corrosion. The local corrosion of Al-Cu-Li alloy is mainly attributed to the potential difference between the alloy phase and the alloy matrix, which leads to the formation of micro-corrosion battery in the corrosive medium. The corrosion behavior of Al-Cu-Li alloy in NaCl solution and the effect of heat treatment on the corrosion resistance of the alloy were reviewed. The effects of coarse second phase particles and aging precipitates on the corrosion properties of Al-Cu-Li alloy were analyzed. In addition, the corrosion behavior in NaCl solution of different contents and electrochemical behavior in 3.5wt% NaCl solution of typical third generation Al-Cu-Li (2A97-T3, 2A97-T6, 2060-T8 and 2099-T83) alloys and conventional high strength aluminum alloy 2024-T4 used in aviation were studied in NaCl solution. The micro-corrosion morphology, corrosion electrochemical parameters and corrosion degree of each sample were analyzed. Finally, the corrosion resistance of each sample was obtained, from strong to weak in an order of: 2A97-T3>2A97-T6>2024-T4>2060-T8>2099-T83. Finally, the corrosion mechanism of Al-Cu-Li alloy in a corrosive medium was revealed, and the anti-corrosion measures of aluminum alloys in marine environments were summarized. This reseach progress provides reference for the subsequent development of the Al-Cu-Li alloy corrosion protection process and the enhancement in the corrosion resistance of aircraft in humid environments.

Abstract:High-entropy ceramics with five or more cations have attracted great interest due to their excellent properties in various structural and functional applications. After the introduction of the concept of entropic stability, significant efforts have been made to increase the entropy, minimize the Gibbs free energy, and achieve stable single-phase high-entropy ceramics. This paper reviews the recent research progress on high-entropy ceramic films and coatings in recent years. Firstly, the microstructure of high-entropy ceramic films and coatings is introduced from the concept of high entropy in them; then the preparation methods of high-entropy ceramic films and coatings are outlined, and the research results on their excellent properties are summarized in detail; finally, the prospects of high-entropy ceramic films and coatings are presented on this basis.

Abstract:Nano-multi-structured antibacterial coatings on the surface of bone implants possess multiple advantages. They can effectively enhance the antibacterial rate of materials and prevent the bacterial resistance associated with antibiotic use. Compared with single-layer coatings, nano-multi-structured antibacterial coatings simultaneously provide various properties required for bone implants, promoting the proliferation and differentiation of bone cells while effectively reducing adverse reactions caused by cytotoxicity. Therefore, they are currently the focal point in research on surface coatings for bone implants. This article reviews the research progress of nano-multi-structured antibacterial coatings, including their performance, fabrication methods, and antibacterial mechanisms, and discusses the future directions of nano-multi-structured antibacterial coatings, which holds promise in addressing bacterial infections and bone integration.

Abstract:For the creep behavior of lead-free solders and solder joints in recent years, the creep deformation behavior and its application in reliability of solder joint were reviewed. Firstly, the creep behavior of lead-free solders was systematically introduced, and the creep modification mechanism of lead-free solders bearing alloying elements or particles was discussed. Secondly, the creep behavior of solder joints was reviewed, and the research progress about the influence of solder joint composition and substrate materials on the creep behavior of solder joints was analyzed. Furthermore, for specific electronic devices, the creep response and fatigue life prediction of solder joints based on finite element method were analyzed by using finite element simulation, and the reliability of solder joints was evaluated. Finally, the future development of lead-free solder and solder joint creep behavior is prospected, and the existing problems and solutions are analyzed to provide theoretical support for further research on solder joint reliability.

Abstract:This paper mainly introduces several biomaterials with multi-layered porous structures and excellent mechanical properties in nature, and their macroscopic properties are closely related to the multi-layered micro-nanostructures on their surfaces. Through the construction of multi-layered porous structures, biomaterials not only greatly reduce their own density, but also often maintain excellent mechanical properties, such as light weight, high strength, sound absorption and noise reduction. Through the imitation of the porous structure of biomaterials, it is expected to provide important enlightenment and help for the development of artificial materials with biomimetic porous structure and excellent performance.