Abstract:The microstructure difference between different parts of the TB9 ingot during hot-working was analyzed, and the microstructure inheritance effect on microstructure evolution and properties of TB9 bar was revealed. The results show that the TB9 ingot can be divided into axial columnar crystal zone at the bottom, equiaxed crystal zone in the core, and columnar crystal zone inclined 45° to the axial direction at the edge. The columnar crystal at the bottom of the ingot with a strong <100> texture is difficult to break and has a strong heredity, resulting in the residual coarse columnar crystal in corresponding bar after hot rolling, and the tensile strength of the bar after aging is only 987 MPa. The equiaxed crystal zone in the core of the ingot has no obvious preferred orientation, and the corresponding bar after hot rolling has fine equiaxed grains with a tensile strength of 1290 MPa.

Abstract:The Ti-6Al-4V titanium alloy was treated with micro-arc oxidation by adding HfO2 into the electrolyte. The effect of adding HfO2 on the characteristics of the micro-arc oxidation film of titanium alloy was studied by characterizing the surface and cross-section morphology of the micro-arc oxidation film, the composition of the film and the electrochemical behavior, and measuring the thickness, hardness, roughness and other parameters of the film. The results show that after adding HfO2, the main components of the micro-arc oxidation film are Al2TiO5,TiO2 and γ-Al2O3.The appropriate concentration of HfO2 can promote the film-forming reaction, improve the microstructure of the micro-arc oxidation film, improve the thickness and hardness of the film and reduce the surface roughness. The film sample has a double-layer film structure, and the corrosion resistance of the film sample is better than the original substrate. When the concentration of HfO2 is 3.0g/L, the comprehensive performance of the micro-arc oxidation coating is the best.

Abstract:This paper investigated the effects of different heat treatment processes (solution aging and double annealing) and pre-stretching on the microstructure and mechanical properties of Ti-6Al-4V-0.55Fe (TC4-0.55Fe) alloy with duplex microstructure and the relationship between microstructure and mechanical properties of TC4-0.55Fe alloy was analyzed. The microstructure and mechanical properties of the duplex microstructure after solution aging and double annealing were compared and it can be found that the thickness of the micron scale lamellar α phase gradually increased with the increase of aging and low temperature annealing temperature under the condition of two kinds of heat treatments, which reduced the strength and increased the plasticity of the alloy. Under the solution aging treatment, the yield strength of the samples decreases from 873MPa at 530℃ to 862MPa at 590℃ and the elongation increases by 3.2% with the increasing aging temperature. The yield strength of the double annealing heat treatment sample decreases gradually with the increase of the low temperature annealing temperature, but the elongation has been greatly improved compared with the solution aging, and the best is 23.6%.Because the strength of titanium alloy is not significantly improved by ordinary heat treatment, the plasticity of the double annealing sample is better than that of the solution aging when the aging and low temperature annealing temperature is 590 ℃, so the sample is selected to introduce the pre-stretching strengthening and pre-stretch it between the solution and low temperature annealing. After the introduction of pre-stretching, the grain deformation is obvious. And a large number of fine secondary α phase (αs) are precipitated in the precipitation-free zone (PFZ) of the alloy structure after aging strengthening. The aging after the introduction of pre-stretching can improve the yield strength of titanium alloy and only reduce a little plasticity. Among them, the sample with 1% pre-stretching deformation has the highest content of equiaxed grains, the strength is increased by 68MPa compared with that before the introduction of pre-stretching, and the elongation is only decreased by 4%, the mechanical properties are the best. According to this study, the comprehensive mechanical properties of TC4-0.55Fe titanium alloy can be improved by pre-stretching and aging strengthening after solution strengthening.

Abstract:In this paper, the repetitive nano-cutting process of single crystal γ-TiAl alloy was simulated by molecular dynamics method. The evolution of cutting force and microstructure defects in the repetitive nano-cutting process was studied. The roughness and residual stress of the machined surface were analyzed, and the difference between repetitive nano-cutting and single-cutting was discussed. The results show that the repeated nano-cutting process is accompanied by the formation and annihilation of dislocations, and the fluctuation of dislocation line length in the second cutting process is less than that in the first cutting process, and the cutting state is more stable; The cutting force increases rapidly in the initial stage of machining, and then the cutting force enters the stable machining stage. At the same time, it is found that the cutting force of the second cutting is less than that of the first cutting. After secondary cutting, the residual stress distribution is more uniform and the residual compressive stress of the machined surface layer increases due to the secondary extrusion of the tool; Secondary machining can improve surface quality and reduce subsurface damage, while the increase of residual compressive stress and the increase of energy required for machining reduce the plasticity of the machined surface, so that the tertiary machining has no obvious improvement on both.

Abstract:In this paper, the hot deformation behavior of Ti2AlNb-based alloy was studied by using Gleeble-3500 thermal simulation experiment machine to carry out compression experiments with deformation temperature of 650-850℃ and strain rate of 0.001-1s-1, and the optimal process parameter range of Ti2AlNb-based alloy was obtained. First, the flow stress curve of Ti2AlNb-based alloy is analyzed, and the hot deformation activation energy Q, lnZ and power dissipation factor are calculated η, so as to establish the thermal deformation activation energy Q, lnZ and power dissipation factor η, the second order response surface model of Ti2AlNb-based alloy was established, and the optimal region after optimization was obtained through multi-objective visual optimization, which was verified with the microstructure diagram. The results show that the flow stress of Ti2AlNb-based alloys decreases with increasing deformation temperature and decreasing strain rate. The established response surface model has high accuracy, which can be used for optimization and analysis of process parameters; the results of multi-objective visual optimization show that the optimal region of Ti2AlNb-based alloy after optimization is the deformation temperature of 750-850℃ and the strain rate of 0.01-0.03s-1.

Abstract:High-strength, Low density periodic Ti-6Al-4V lattice materials built with additive manufacturing provide relatively widespread applications for aerospace, biomedicine, marine and other fields. In this paper, the reported compressive properties, failure modes, microstructure and the heat treatment of Selective laser melting (SLM) and Selective electron beam melting (SEBM) additive manufatured Ti-6Al-4V lattice materials are reviewed. According to statistics, the continuous and integrated lattice materials can be manufatured via SLM and SEBM. And more importantly, the compressive strength and yield strength of skeleton-based Diamond TPMS lattice materials can reach to 411.71 MPa and 317.48 MPa respectively, which are comparable to those of magnesium alloys. It is also be found that the main failure modes of Ti-6Al-4V lattice materials are 45° shearing fracture and horizontally fracture. Shearing fractured lattice materials have unique advantages in load-bearing capacity, while horizontally fractured lattice materials with smaller fluctuation in stress-strain curves, showing dominant superiority in energy absorption capacity. Heat treatment is an effective method to eliminate the residual stress, reduce the roughness and transform acicular α "martensite to α+β phase caused by additive manufacturing, and then increase the ductility of lattice materials without reducing or even increasing the strength of Ti-6Al-4V lattice materials. Finally, the existing disadvantages and future development trend of additive Ti-6Al-4V lattice materials are prospected.

Abstract:WC-12Co particles were deposited on polished AA7075 (7075 aluminum alloy) substrate by HVOF (high velocity oxy-fuel) spraying. The microstructure, composition and hardness of the deposits were analyzed by SEM, EDS and nanoindentation hardness tester, respectively. The deposition behavior of six types of particles in three different molten states, including non-molten, semi-molten, and molten particles, was investigated. Results show that different types of particles have great impact on the substrate, which makes the AA7075 substrate deform or causes tears. The surface morphology and cross-sectional morphology of the deposits are different from those of the original powder. The surface of the deposits exhibits certain melting characteristics, and the cross-section is relatively dense. The semi-molten particles and molten particles generate some tearing to the substrate, and have a metallurgical bonding with the substrate to form a mutual meting zone. After the deposition of the particles, a hardened layer is formed on substrate surface with a thickness about 5 μm, and there is a certain gradient change in the hardness. The hardness near the surface is 3420 MPa, which is 1.56 times higher than that of the substrate (2200 MPa). The increase in hardness is originated from two factors: the peening effect of particles at high temperature and high speed, and the work hardening caused by particle extruding substrate.

Abstract:The mechanical properties of 2219 aluminum alloy can be significantly improved by the solution-aging process. Nevertheless, large residual stress is generated during quenching, exerting negative effects on dimensional stability, fatigue strength, stress corrosion, and other properties. A cold bulging process was introduced between quenching and artificial aging to reduce the quenching residual stress of the 2219 aluminum alloy ring. Firstly, the numerical value and distribution law of the residual stress after quenching and cold bulging of the 2219 aluminum alloy ring were analyzed by finite element method (FEM) simulation. Secondly, the residual stress after quenching, artificial aging and solution-cold bulging-artificial aging of the ring was measured by the drilling method. Additionally, the effect of cold bulging process parameters on residual stress value and uniformity was investigated. Experimental results show that quenching residual stress of 2219 aluminum alloy ring is reduced by up to 85% or more.

Abstract:The effects of different deformation annealing processes on the microstructure, texture, and properties of 2A12 aluminum alloy were studied by scanning electron microscope (SEM) equipped with energy dispersive spectrometer (EDS) and electron backscatter diffraction (EBSD). Results demonstrate that after deformation annealing treatment, the 2A12 aluminum alloy grains become longer along the rolling path and smaller in size. The proportion of subgrain boundaries decreases, the proportion of low angle grain boundaries (LAGB) at 2°?15° increases, and the proportion of high angle grain boundaries (HAGB, >15°) first increases and then declines as the deformation annealing treatment cycles increase. The degree of recrystallization rises at this point as the annealing process switches from recovery multi-lateralization to recrystallization. After single-step deformation annealing, the two samples have a similar microstructure and proportion of HAGB and LAGB in total due to the small deformation and less deformation stored energy. Compared to the sample that underwent mild deformation with the same annealing process, the large deformation sample has a lower proportion of subgrain boundaries in total and a higher proportion of LAGBs and HAGBs, and the degree of recrystallization increases. There will be texture evolution pathways of Brass→R-Cu and m-Brass→Goss→R-Goss→Cube, T and P_0°→Near rotated Cube and {102}<201> when the deformation is significant. R-Cu and m-Brass→Goss→R-Cube will become the new route during single-step small deformation annealing. The toughness and plasticity of the 2A12 aluminum alloy diminish while the strength and hardness rise with higher deformation.

Abstract:Friction stir channel pressing (FSCP) is a new solid-state method for producing metal matrix composite, which was invented by the authors based on the principles of friction stir welding and equal channel angular pressing. The carbon nanotubes (CNTs) reinforced 7075 aluminum alloy composites (CNTs/Al-7075) were fabricated by FSCP, with different volume percentages of CNTs (0%, 2% and 4%). The distribution of CNTs in Al-7075 matrix and the microstructures including fine grains and second-phase particles were analyzed by optical microscope, scanning electron microscope and transmission electron microscope. The solution and aging treatments were used for improving the microstructures and the mechanical properties of the CNTs/Al-7075 composites. The results show that the CNTs/Al-7075 composite with a uniform distribution of CNTs is fabricated by FSCP. The grain refinement of Al-7075 is realized by FSCP, and further finer grains are obtained by introduction of CNTs. The grains of CNTs/Al-7075 composite become finer with increasing the volume percentage of CNTs. The precipitation behavior of second-phase particles of the Al-7075 produced by FSCP and the CNTs/Al-7075 composite is improved by the solution and aging treatments, resulting in an increase in micro-hardness. The strengthening mechanisms of the CNTs/Al-7075 composite include fine-grain strengthening, dislocation strengthening, load transfer mechanism and second-phase strengthening, among which the second-phase strengthening plays a leading role.

Abstract:5A06 aluminum alloys are widely used in the precise manufacturing structures such as liquid-cooling and waveguide components because of high strength, excellent corrosion resistance as well as good thermal conductivity and machinability. In this paper, spark plasma brazing by using Al-Cu-Si-Ni solder foil is performed to realize the joining of 5A06 aluminum alloy. The influence of brazing temperature on microstructure and mechanical properties of brazed 5A06 alloy joints was investigated. The results show that at the bonding temperature of 510~530℃, pressure of 4MPa and holding time of 10min conditions, the tensile strength of welded joint increase with temperature increasing. The maximum tensile strength is 152 MPa, wherein ductile fracture surface mainly composed of fine and homogenous dimples is obtained. Under the combined effect of low melting point solder, welding pressure, pulse electric field and short holding time, the brazing zone is getting thinner while matrix grains are finer and brittle phases are more dispersed. Meanwhile, the interfacial atomic diffusion and reaction are enhanced that the microscopic metallurgical bonding strengthened by Mg2Si, Si particles is obtained.

Abstract:Al-Zn-Mg-Cu and Al-Zn-Mg-Cu-Yb alloys were prepared by melting casting and hot extrusion. The effect of rare earth Yb microalloying on the microstructure of Al-Zn-Mg-Cu alloy was observed by optical microscope, scanning electron microscope and transmission electron microscope, and the properties were tested by differential thermal analyzer, tensile tester and electrochemical workstation. The results show that the addition of Yb can obviously refine the grains, and the microhardness and tensile strength increase from 125.6 HV and 562.9 MPa to 154.9 HV and 616.3 MPa respectively. The tensile fracture mode also changes from intergranular and dimple coexisting mixed fracture to complete dimple fracture. However, the precipitation of coarse Al8Cu4Yb phase in the matrix and the continuous distribution of η phase on grain boundary are unfavorable to the corrosion resistance.

Abstract:The microstructure evolution responsible for significant change of mechanical properties during low-temperature aging of U-Nb alloys was investigated by phase-field method. Results show that spinodal decomposition may occur at the early stage only when its thermodynamic condition is satisfied. Possibilities of general precipitation widely exist at low-temperature region, where the Nb content difference between the stable nucleus and the matrix can be significantly small, no matter the matrix of aging is cubic-like phase or in the orthorhombic-like phase, because the alloy composition is close to the critical composition of structural transition. At low diffusion rate and the relatively high mobility of phase interface, the Nb content of growing precipitates is far away from equilibrium composition. It is suggested that the Nb redistribution caused by phase decomposition may be responsible for the low-temperature aging hardening effect in U-Nb alloys.

Abstract:In order to study the differences in microstructure and mechanical properties of three kinds of electrodeposited cobalt plates, the preferred orientation, crystal structure, and microstructure of each plate were analyzed by X-ray diffractometer and scanning electron microscope. Furthermore, the mechanical properties of electrodeposited cobalt plates were tested, including their strength, hardness, and toughness. The results show that all of the plates are pure cobalt phases with a close-packed hexagonal structure (hcp) and random grain orientation. The deposition layer of the A-Co plate is uniform and dense with few holes, while those of the B-Co and C-Co plates grow apart and has a large number of holes. Meanwhile, the average grain size on the surface of the A-Co plate is the smallest, and the grain size distribution of the deposited layer is uniform, while that of the B-Co plate is the largest, and the grain size distribution of the deposited layer is not uniform. The starting sheets of the three electrodeposited cobalt plate cross-sections are all columnar crystal structures, and the growth patterns of the two sides of the starting sheets are different. From the analysis of mechanical properties, it is found that the tensile strength and hardness of the A-Co plate are higher than those of other two cobalt plates, but the toughness is lower. In conclusion, the quality of A-Co plates is significantly better than that of B-Co plates and C-Co plates.

Abstract:Different crystal structures of CrB were obtained bythe CALYPSO software. The electronic structure and mechanical properties of CrB were analyzed through first-principles calculations. The results show that the structure of CrB transits from α-CrB to β-CrB phase at 90 GPa. The β-CrB phase exhibits both covalent and ionic bonds, while α-CrB phase is dominated by ionic bonds. The modulus and hardness of both phases increase with increasing pressure. However, the hardness of β-CrB is less than that of α-CrB, indicating that the comprehensive mechanical properties of CrB are optimized at 90 GPa. From the perspective of electronic structure, the reasons for the changes in the mechanical properties of CrB under different pressures were explained.

Abstract:The undercooled solidification of (Co₆₀Sn₄₀)_100-xNb_x(x=0, 0.4, 0.6, 0.8, at%) single phase alloys was performed to investigate the changes of Co₃Sn₂ phase growth morphology.Results show that the Co₃Sn₂ phase grows with fractal seaweed morphology at small undercooling (x=0, 0.4), and transits to dendrite as the content of added Nb increases to 0.6at%, and then returns to fractal seaweed (x=0.8) as a response to the changes in interfacial energy anisotropy and kinetic anisotropy. With the increase in undercooling, the growth morphology of Co₃Sn₂ phase in (Co₆₀Sn₄₀)_99.4Nb_0.6 alloys returns from dendrite back to factual seaweed at undercooling larger than 28 K and then transits to compact seaweed at undercooling more than 143 K. The minor Nb addition slightly increases the growth velocity of Co₃Sn₂ phase at low and intermediate undercooling but obviously decreases the growth velocity at large undercooling. The sharp increase in the growth velocity is corresponding to the transition of Co₃Sn₂ phase growth morphology from fractal seaweed to compact seaweed.

Abstract:The preparation of spherical scandium oxide powders by ammonium bicarbonate precipitation was investigated. The carbonate containing scandium was prepared in the solution with ScCl₃·XH₂O as precursor. The effect of reaction temperature, amount of precipitant and stirring speed on the recovery of scandium was discussed. The effect of pH on the crystalline structure and particle size of carbonate containing scandium was characterized by the powder X-ray diffraction and laser particle sizer. Results demonstrate that the structure of carbonate containing scandium changes from non-crystalline structure to crystalline structure with increasing the reaction pH value. It indicates that when the initial change pH value is about 6, the crystalline structure of scandium oxide is cubic structure. Meanwhile, scandium sediment particles with 3.756?103.8 μm in size can be obtained in a certain condition, depending on the pH value,. When the feasible pH value is 7, the D₅₀ of scandium sediment can be 6.634 μm. The carbonate containing scandium is used as a precursor for the preparation of scandium oxide. The TG-DTA result indicates that the decomposition temperature of the carbonate tends to about 600 ℃. Based on the XRD and IR analysis, it can be concluded that the appropriate calcination temperature for obtained relatively pure scandium oxide is 1000 ℃. Meanwhile, the obtained scandium oxide powders were characterized by the laser particle size analyzer, BET and SEM-EDS. The crystallite size of spherical scandium oxide powders is less than 10 μm with a surface area of about 373.952 m²/g. The microstructure is very homogeneous with spherical structure.

Abstract:Combined with digital image correlation (DIC) technique, in-situ fatigue tests with different stress ratios (R = 0.1 and R = -1) at room temperature were carried out to analyze the mesoscopic surface crack propagation mechanism of selected laser melted Ni-based superalloy (SLM-IN718) in the very high cycle fatigue regime. The results show that: firstly, the DIC analysis results indicated that a plastic strain zone, similar to a butterfly shape, appeared at the crack tip when SLM-IN718 was loaded, which is consistent with the adoption of the Von Mises yield criterion; Secondly, the strain field characteristics and displacement field characteristics in front of the crack tip were analyzed to determine the existence of crack closure effect in SLM-IN718. The crack closure effect was also evaluated, i.e., for SLM-IN718, crack opened when the load reached 53% and 29% of the maximum load under R = 0.1 and R = 0, respectively; In addition, a considered the crack closure effect model was developed to evaluate the size of the plastic zone in front of the crack tip. The calculated values were in good agreement with the measured values; Finally, the surface crack propagation mechanism of SLM-IN718 under low stress conditions was suggested based on DIC analysis results.

Abstract:The dynamic microstructure evolution and fracture mechanism of Ni-based cast superalloy MAR-M247 are investigated during tensile test at room temperature, 400 °C and 760 °C by an in-situ SEM high temperature tensile stage. The in-situ tensile test results show that the yield strength and ultimate tensile strength decrease slightly, and the tensile plasticity increases slightly from room temperature to 760 °C. There is no slip band during in-situ tensile test at room temperature; and there is only a small amount of slip bands near the fracture surface at 400 °C and 760 °C. With the increase of tensile temperature, the fracture mechanism is not change, and all of them are ductile transgranular fracture. Microcracks mainly originate from the rupture of carbides which dispersed in the grains and on the grain boundaries.

Abstract:In this study, the diamond-like carbon (DLC) coating was deposited on magnalium diaphragm by pulsed plasma enhanced chemical vapor deposition technology. The morphology and composition of the DLC coating deposited by different processes were characterized by SEM, RAMAN and AFM, and the mechanical properties of magnalium diaphragm with DLC coating were studied. Compared with magnalium diaphragm, the DLC coating improved the surface roughness, hardness and elasticity modulus. The frequency response curve and harmonic distortion showed that the DLC coating increased the upper limit of frequency response and imparts high fidelity to the loudspeaker. Audio equipment fabricated with magnalium diaphragm with DLC coating had good timbre naturalness, sound field expression, vocal performance and overall evaluation, which can effectively improve the human subjective listening effect.

Abstract:AgCu alloy powder has both the advantages of Ag powder and Cu powder, and has broad application prospects in electronic manufacturing, catalysis and medical fields. Powder samples were prepared by pulse laser etching of AgCu eutectic alloy targets. The particle size, appearance, composition and microstructure of the powder samples were studied by scanning electron microscope, X-ray energy dispersive spectrometer and differential thermal analysis. The results show that the particle size distribution of AgCu alloy powder prepared by pulsed laser etching is in the range of 1 ~ 6 μm. The powder particles are spherical and have a smooth surface. The average Ag content of the powder particles is close to that of the target, the composition is uniform on the cross section, and the Ag content fluctuation is less than 3 at%. The microstructure of the powder is Ag-rich phase and Cu-rich phase. The onset melting temperatures of the powder and target were 773°C and 779.5°C, respectively. The melting temperature range of the two is similar, but the temperature range of the former is shifted to a lower temperature than the latter, which is presumed to result from the presence of metastable structures in the powder particles. The research results provide a feasible way for the preparation of high-performance ultrafine spherical AgCu alloy powders.

Abstract:As the core structural material of water-cooled nuclear reactors, nuclear grade zirconium alloys are mostly processed by hot extrusion process. However, in the harsh hot extrusion environment such as high temperature and high pressure, the lubricating layer is very easy to fail, resulting in defects or even scrapping of finished parts. As a crucial part of the extrusion process, the effect of lubrication on the internal structure and properties of zirconium alloy extrusions has not been systematically reported. In this study, Zr-4 alloy coated with molybdenum disulfide lubricant was hot extruded at 620 ℃, 680 ℃ and 740 ℃, and the microstructure of the longitudinal section of the extrusion was characterized by electron backscatter diffraction technique. The analysis shows that the coating has the best lubricating effect at 680 ℃, which can promote the starting of the internal cylindrical slip and cone slip of the zirconium alloy, and the internal grain deformation is uniform, showing a significant <01-10>//ED extruded silk texture. The research results have a certain guiding role in improving the extrusion lubrication process of zirconium alloy and optimizing the structure and performance of extrusion parts.

Abstract:The effects of single and hybrid reinforcement of carbon nanotubes (CNTs) and TiB2 particles on the microstructure, density, electrical conductivity, hardness and tensile strength of copper matrix composites were studied. Firstly, CNTs/Cu composites with brick structure were prepared by the combined preparation technology of ball milling, surface adsorption and hot-pressing sintering, which solved the problem of agglomeration of CNTs. The density and electrical conductivity of the sintered CNTs/Cu composites decreased with the increase of the CNTs content, while the tensile strength and elongation first increased and then decreased with the increase of the CNTs content. The comprehensive performance is the best when the content is 0.1 wt.%, and the density, electrical conductivity and tensile strength are 97.57%, 91.2 %IACS and 252 MPa respectively. Meanwhile, the density, electrical conductivity and tensile strength of the sintered 1 wt.% TiB2/Cu composite after ball milling are 97.61%, 58.3 %IACS and 436 MPa, respectively. Finally, hybrid reinforced (CNTs+TiB2)/Cu composites were prepared by introducing in situ TiB2 particles into CNTs/Cu composites with brick structure. Compared with single CNTs (or TiB2) reinforced copper matrix composites, the strength of CNTs and TiB2 hybrid reinforced composites is significantly improved. When 0.1 wt.% CNTs and 1 wt.% TiB2 were mixed, the composite density, electrical conductivity and tensile strength were 97.21%, 56.4 %IACS and 531 MPa, respectively. And the electrical conductivity decreases by 3.3%, while the tensile strength increases by 21.8% when compared with 1 wt.% TiB2/Cu. It is mainly attributed to the role of CNTs in carrying and transferring loads, and the pining dislocations of the dispersed TiB2 particles. The two strengthening mechanisms work together to significantly improve the tensile strength of (CNTs+TiB2)/Cu composites.

Abstract:four different heat treatment processes were used to heat treat the welded joints,which were prepared by the pulse Tig welding. We compared the unheated joint and the joints under four different heat treatments on microstructure and mechanical Properties. The results show that after four kinds of heat treatment processes, some phases dissolve, the joint tensile strength at room temperature and high temperature is improved, and the joint hardness is significantly increased, but the joint plasticity is significantly reduced after heat treatment. Among them, after 1020℃ solution treatment + two-stage aging, the Laves phase in the joint weld partially dissolved, and the tensile strength of the joint at room temperature and high temperature increased to the maximum.

Abstract:Two kinds of ink-jet printing conductive inks were prepared with silver nanoparticles and silver nanowires as conductive components, byk-333 as surface additive and ethylene glycol as solvent respectively. The conductive lines were printed on the flexible transparent substrate by micropltter II micro nano deposition system. The effects of printing process, thermal sintering curing and packaging on the conductivity, weather resistance and interference of the two printing circuits were studied. The results show that the diameter of printer nozzle and the contact angle between ink and substrate are the key factors to determine the linewidth accuracy of conductive circuit. Thermal sintering treatment can improve the conductivity of silver nanoparticle flexible circuit. When sintered at 160 ℃ for 30 minutes, the resistivity decreases to 16.4 μ Ω. cm, keep the conductivity unchanged after being placed in the air for 90 days, and the resistivity increases by 12.4% after 1000 bends; With the increase of printing times, the conductivity of the silver nanowire printing circuit continues to increase. The unit resistance of the printing line obtained by printing 9 times is 88.9 Ω /cm. With the increase of sintering temperature and time, the conductivity of the circuit decreases. PDMS packaging can greatly improve the stability of the printing circuit. After being placed in the air for 90 days and bent for 1000 times, the conductivity remains unchanged, It shows that conductive ink based on silver nano materials and micro nano deposition system can achieve stable printing of high-performance and high-precision flexible circuits.

Abstract:Mg-Zn-Ca alloys are expected to be widely used in human bone tissue implant materials due to its excellent mechanical properties, good biocompatibility and excellent degradability. However, the poor bio-corrosion resistance of magnesium alloys limits its further clinical application. The surface of Mg67Zn28Ca5 alloys with eutectic composition was modified by laser amorphization. The effect of laser scanning speed on the microstructure and phase composition of Mg67Zn28Ca5 alloys amorphous coating were studied. The bio-corrosion behavior of the alloy surface before and after laser amorphization in artificial body fluid was tested. The results show that a large amount of amorphous and a small amount of crystalline materials were formed on the surface of the specimens after laser amorphization. With the increase of laser scanning speed, more amorphous phases were formed on the alloy surface. The formation of crystal phase was mainly caused by thermal activation due to the thermal influence of subsequent laser processing, and some amorphous phases nucleated and grew up. Compared with the as-cast magnesium alloy, the corrosion potential of the amorphous layer in the artificial body fluid was positively shifted by 0.16 V, and the corrosion current density decreased about 13 times. The existence of a small amount of crystalline phase on the alloy surface became an active channel form surface corrosion, which had a slight impact on the corrosion performance of the alloy surface. The biological corrosion resistance of Mg67Zn28Ca5 alloy can be effectively improved by laser amorphization treatment, which shows a good application prospect in biomedical implants.

Abstract:The effect of medium and coarse WC content on the microstructure and grain distribution of Ni-Co coarse crystalline cemented carbide was studied, and then the effect of grain distribution on the mechanical properties of cemented carbide was discussed. The effect of medium and coarse WC content on the grain size and adjacency of the cemented carbide was analyzed by metallographic analysis, and the distribution pattern of the grains in the microstructure was investigated by using the truncation method; the effects of grain size and grain distribution on the magnetic force, density and other mechanical properties were studied. The results show that the medium and coarse WC grains can be uniformly distributed around the coarse WC grains to hinder the contact between the coarse grains and the bonding phase, which inhibits the rapid coarsening of the coarse grains, reduces the average grain size and average free range of the alloy, and gradually transforms the grain distribution into a bimodal distribution; the relative densities of all the alloys under pressure sintering are above 99.5%, and the bimodal distribution of the grains in the microstructure is verified by the analysis of the coercivity magnetism. The accuracy of the bimodal distribution of grains in the microstructure was verified by the analysis of coercivity magnetism; the decrease of average grain size gradually increased the hardness and decreased the fracture toughness of the alloy; the gradual decrease of super coarse grains in the microstructure was beneficial to the improvement of flexural strength and wear resistance of the carbide. The addition of some medium coarse WC particles to the Ni-Co coarse grain cemented carbide is beneficial to reduce the grain coarsening and thus improve the wear resistance, and the best overall performance is achieved with 30% medium coarse WC particles.

Abstract:The Spherical and densified of tungsten-based (W-Ni-Fe) alloy powder is of great significance to the improvement of physical properties such as the strength of powder-formed components for additive manufacturing. The effects of spray granulation and radio frequency (RF) thermal plasma treatment on the morphology and porosity of W-Ni-Fe alloy powder were studied by the spray granulation and radio frequency thermal plasma densification and spheroidization with high temperature. The research shows that the 96W-2.5Ni-1.5Fe ternary alloy powder formed by spray granulation has a loose microstructure, many internal voids and a rough surface. The comprehensive properties of the spray granulated powder can be significantly improved after the radio frequency thermal plasma treatment. The holes and looseness on the surface of spherical powder are alleviated, but there are also some micropores on the surface and internal with a few particles. The Ni and Fe phases between the W grains of the densified and spheroidized particles contain a relatively high content of W element.

Abstract:Direct band gap semiconductor gallium antimonide (GaSb) has applications in fiber optic communication and optoelectronic devices because of its excellent performance. In order to explore the potential applications of GaSb in optoelectronic devices and new spintronics materials, the electrical, magnetic and optical properties of GaSb at different Ti doping concentrations (denoted as Ga1-xTixSb, where X is the atomic percentage concentration of Ti) were calculated by first-principles. The calculated results show that the energy band structure and the density of states of Ga1-xTixSb generate spin splitting near the Fermi level and form a net magnetic moment, making the Ga1-xTixSb (x=0.25, 0.5, 0.75) show half-metal ferromagnet, dilute magnetic semiconductor and magnetic metallic, respectively. The lattice constant of Ga1-xTixSb increases after optimization. The refractive index, reflectivity and absorption coefficient of Ga1-xTixSb are red-shifted and have a higher optical absorption coefficient than that of undoped GaSb in the middle and far infrared band. The absorption of Ga1-xTixSb become better in the middle and far infrared band as the Ti doping concentration increases. The calculation results provide a theoretical reference for the expansion of GaSb-based semiconductor materials for applications in infrared detectors, infrared semiconductor lasers and the discovery of new materials for spintronics.

Abstract:The pure nickel N6 plasma arc weld was subject to U-shaped bending deformation heat treatment.The grain boundary characteristic distribution (GBCD) of Non GBE and GBE samples and its influence on corrosion behavior were studied by grain boundary character distribution (EBSD) and orientation image microscopy (OIM). The results show that the proportion of lowΣCSL grain boundaries increase to more than 54.1% by the TMP after U-shaped bending deformation and subsequent annealing at 900℃ for 10 min, and simultaneously the large-size highly-twinned grain-cluster microstructure is formed.The recrystallization nucleation point increased and the grain size decreased to 146 um during annealing.The corrosion resistance of GBE sample is higher than that of Non GBE sample. The self corrosion current density of GBE sample is less than that of Non GBE sample, and the capacitive arc radius, impedance modulus and phase angle of GBE sample are greater than those of corresponding Non GBE samples.Pitting corrosion occurr on the surface of samples.The passivation film on the surface of the coating is destroyed by C1-in the solution and forms pitting pits at the initial stage.With the prolongation of immersion time, the concentration of Ni2+near the anode metal reaches saturation or supersaturation. the bound water in the corrosion product film reacts with Ni2+ forms Ni(OH)2, and then the Ni(OH)2 are dehydrated and decomposed into NiO.Corrosion products cover the surface of the sample and form a corrosion product film, which are composed of NiO and Ni(OH)2. The corrosion product film has a protective effect,which prevents Cl- from penetrating through the corrosion products to the sample surface and the pitting is controlled.

Abstract:In this paper, the tensile creep behavior in vacuum of W-4Re-0.27HfC alloy prepared by powder metallurgy was studied. The creep temperature was 1500~1700℃ and the creep stress was 40~60MPa. SEM, EBSD and TEM observations were used to observe the microstructure, characterize the evolution of grain size and dislocation during the creep process. The results show that the steady creep rate of W-4Re-0.27HfC alloy ranges from1′10-7~5′10-6, which is two orders of magnitude lower than that of pure tungsten (W). The creep resistance of W-4Re-0.27HfC alloy is higher than that of pure W due to the dislocation pinned by HfC particles and the lattice distortion caused by Re replacing W atoms. The creep mechanisms of W-4Re-0.27HfC is mainly dislocation slip, accompanied by grain boundary slip at 1500℃. Dislocation climb becomes the main creep mechanism with increasing temperature. The dislocations were blocked by the HfC particles, which leads to the debonding of the HfC/ matrix interface. Moreover, the desquamation of HfC particles forms pores, which results in the great degradation in the creep properties of the alloy.

Abstract:Recent research in three-way catalyst development for natural gas vehicles (NGVs) exhaust gas purification has been focusing on the high dispersibility of loaded noble metal of catalysts. In this paper, nanostructured CeCoOx composited oxide support was prepared by metal organic frameworks (MOFs) template method and compared with cerium-cobalt oxides prepared by the conventional sol-gel method (SG), which were used to investigate the dispersion state of noble metal Pd on the two catalyst supports and its influence on the catalytic performance. The results showed that the CO, NO and CH4 three-way catalytic performance of Pd/CeCoOx(M) catalyst derived from CeCo-MOFs material was about 100 ℃ lower than that of Pd/CeCoOx(SG) catalyst with the same composition prepared by sol-gel method, and it has lower low-temperature activity. The cerium-cobalt composite oxide derived from CeCo-MOFs had smaller crystal particles and uniform crystalline phase structure with larger specific surface area, which promoted the improvement of the dispersion state of Pd components and also enriched the oxygen vacancies and structural defects of the catalysts, so significantly improving the low-temperature three-way catalyst performance. The results indicated that the composite oxide obtained by thermal decomposition of MOFs precursor can be used as a good material for the dispersion of the active components of noble metal of three-way catalyst.

Abstract:The research and development of additive manufacturing technology in superalloy composites are comprehensively summarized in this paper. The powder mixing, material metallurgical process and strengthening mechanism of superalloy composites made by additive manufacturing are systematically reviewed. Moreover, the microstructure, defects and the properties of superalloy composites of additive manufacturing are analyzed and compared in detail. On this basis, the research status of additive manufacturing superalloy composites is summarized, the directions of development in future are forecasted, including: the design of new strong phase, the addition mode of reinforcing phase and the influence mechanism of creep and fatigue properties of superalloy composites by laser additive manufacturing. This paper will be beneficial to the research and development of superalloy composites by additive manufacturing.

Abstract:Magnesium and magnesium-based alloys are important lightweight metal materials, which are widely used in automobile, communication, aviation and other fields. Due to the high thermal expansion coefficient of magnesium alloy, the assembly precision and mechanical properties of magnesium alloy are easily reduced when it is applied to precision devices. Therefore, low thermal strain magnesium-based materials need to be developed to meet the requirements of such applications. In this paper, the principles and methods of reducing the thermal expansion coefficient of magnesium alloy are reviewed, and the main methods of adjusting the thermal expansion coefficient of magnesium alloy, such as alloying, composite materials and special processing technology, are summarized and compared. The methods of reducing the thermal expansion coefficient of magnesium alloys, such as alloying with high melting point elements, doping with high hardness particles, doping with low thermal expansion coefficient fiber and heat treatment combined with extrusion processing, were summarized, and the future research trends in this field were prospected.

Abstract:The frequent occurrence of oil spill accidents and the illegal discharge of industrial oily sewage not only cause a waste of natural resources, but also seriously damage our ecological environment. Intelligent oil/water separation materials are feature with the cyclically reversible wettability between hydrophilicity and hydrophobicity, which can flexibly deal with various oil/water mixtures and shows an excellent oil-water separation ability. In this paper, the phenomenon of surface wettability and mechanism of switching wettability are introduced, and the research progress of intelligent oil/water separation materials is reviewed according to the different external stimuli, such as pH, temperature, light, gas and etc. Finally, the main problems and challenges in this field are presented, and its future development direction is prospected.

Abstract:Lead-bismuth eutectic (LBE) alloy has a wide application prospect in the nuclear fields because of its excellent characteristics such as low chemical activity, excellent thermal properties and radiation resistance. It is the first choice material for the fourth generation nuclear energy system lead-cooled fast reactor (LFR) coolant. However, the densified liquid LBE with high temperature and turbulent flow rate will cause serious corrosion to the structural materials of the reactor, threatening its service safety. Thereby, a comprehensive understanding and analysis of the challenges faced by the application of LBE is of great significance not only for solving the key scientific and practical engineering problems of the compatibility between LBE and structural materials, but also for the sustainable development of nuclear energy. This work briefly introduces the characteristics of LBE coolant, systematically reviews the statu of the LBE corrosion mechanism and influencing factors in recent years. The basic principles, protection mechanisms and the latest research progress of the three main solutions, including controlling dissolved oxygen concentration, modification of structural materials and surface protective coating technology, are comprehensively analyzed. Finally, the main problems and shortcomings in the current research are summarized, and the future development prospect is discussed.

Abstract:Abstract: Cd2SnO4 was prepared by hydrothermal calcination, and a series of g-C3N4- Cd2SnO4 composites with different mass ratios were prepared by sonication mixing method. The materials were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and other methods. The gas-sensing properties of g-C3N4-Cd2SnO4 composites in different proportions were studied. The results show that when the addition amount of g-C3N4 was 2.5 wt% (mass fraction), the sensitivity of g-C3N4-Cd2SnO4 composites to gas was the highest, and the response of 100 μL/L isopropanol gas was up to 117 at the optimal working temperature of 170°C, which was 78 times higher than that of pure Cd2SnO4 with a sensitivity of 1.4, and the low detection limit was 0.1 μL/L.

Abstract:La(Fe, Si)₁₃ alloys exhibit first order magnetic transition showing large magnetocaloric effect, and is considered as a magnetocaloric effect material with the great applied prospect. La_0.7Ce_0.3Fe_11.54-xCu_xMn_0.16Si_1.3(x=0, 0.05, 0.1, 0.15)alloys with different proportion of Cu were prepared by high frequence induction melting furnace. With the aid of powder XRD and scanning electron microscope (SEM), the phase composition and microstructure were investigated. The magnetic properties were measured by using VersaLab. Curie temperature increases after partial substitution Cu for Fe, however an opposite result is obtained after hydrogenation. Although the magnetocaloric effects decrease with the increase of Cu content, the max magnetic entropy change of La_0.7Ce_0.3Fe_11.44Cu_0.1Mn_0.16Si_1.3H_1.68alloy is still as high as 8.5 J/kg.K(0 ~ 2 T), the relative cooling capacity improved (118 J/kg) and the hysteresis decrease evidently.