Abstract:Mg-Ti composite with bicontinuous phase structure was prepared by the additive manufacturing (AM) coupled with the melt infiltration. The effects of pore structure type and size parameters on the porosity and mechanical properties of AM-prepared Ti-6Al-4V (TC4) porous scaffold reinforcement were investigated. By adjusting the size parameters, both high porosity and appreciable compressive strength can be achieved for the scaffold. The strengthening effect of titanium alloy scaffold on the mechanical properties of Mg-Ti composite was investigated by analyzing the microstructure and interface bonding mechanism. Results show that the Mg-Ti composite has high compressive strength of 400 MPa, whereas its density is only 2.56 g·cm^-3, presenting the potential as lightweight structural materials. The strength of Mg-Ti composite is higher than that of raw Mg-9Al-1Zn (AZ91) alloy matrix by 51%. This enhancement is attributed to the tight metallurgical bonding interface between the scaffold and the matrix, which promotes the effec-tive transfer of load. Additionally, the mutual constraint effect caused by the bicontinuous phase structure and the fine crystal streng-thening caused by the ultra-fine α'-Ti martensite in TC4 scaffold also significantly contribute to the improvement of mechanical pro-perties. The investigation strategy in this research provides a nouveau path for the development of structural lightweight composites.

Abstract:Titanium-steel composite plates with large sizes of 4260 mm×4260 mm×(6.5+32) mm were prepared by explosive welding technique. Ultrasonic nondestructive testing, phased-array waveform microscopy, optical microscope, and scanning electron microscope were used to analyze the mechanical properties and interface morphologies of the composite plates. Results show that when the detonation velocity, density, explosive height, and stand-off distance are 2200–2270 m/s, 0.80–0.82 g/cm³, 45.0–46.0 mm, and 8.0–11.0 mm, respectively, the mechanical properties of the prepared plates can satisfy ASTM B898-2020 technical requirements. The interface waveform presents a typical periodic combination morphology and the interface is clear and uniform. A small amount of solidified melt exists in the vortex area of waveform. The ratio of amplitude to wavelength ranges from 0.15 to 0.25, and the optimal shear strength can be achieved when the ratio is approximately 0.20. This research provides preparation technique for the large-size titanium-steel composite plates and theoretical guidance for the subsequent optimization of the explosive welding process of composite plants.

Abstract:TC4 titanium alloy specimens were prepared by laser directed energy depositon in different oxygen contents of inert atmosphere. The effects of oxygen content in the argon shielding gas on microstructure, fracture surface and mechanical properties of TC4 titanium alloy by laser directed energy depositon have been investigated by optical microstructure (OM), scanning electron microscopy (SEM) , transmission electron microscope (TEM), microhardness testing and tensile testing. The results show that the oxidation degree of the samples surface increase, and the surface color of TC4 titanium alloy samples gradually change from silver white to yellow, blue and dark gray with the increasing of the oxygen content of the atmosphere. From XRD analysis, the types of oxides on the sample surface increase, and the thickness of the oxide layers also increase gradually. The microstructure of the specimens gradually change from basket structure to acicular martensite α" structure, the laths are coarsened and the aspect ratios are reduced. The hardness and tensile strength at room temperature of TC4 titanium alloy samples increase gradually with the increase of oxygen content in the forming atmosphere. Due to the influence of metal lattice distortion and cooling rate, the tensile strength of the deposition samples increase from 920 MPa to 982 MPa and the elongation decreased from 12.4% to 10.9%.

Abstract:The TC4 bar with a diameter of 30mm for blades was prepared by radial forging. The microstructure, phase composition and texture of the bar from the edge to the center were tested by metallographic microscope, XRD diffractometer and electron backscatter (EBSD) technology. The effects of the microstructure and texture on the uniformity of mechanical properties and the level of ultrasonic flaw detection clutter were analyzed. The experimental results show that the internal grains of radial forging bars are fully refined, and the grain size gradually increases from the edge to the center. The transformed β lamellar structure is broken during radial forging. The bar contains a small amount of equiaxed β grains, which distribute in α_p grain boundary and transformed β structure. The texture of the edge is {0001}<10-10>. The texture of the R/2 and the center is <10-10>//axial direction. The texture strength of the bar weakens gradually from the edge to the center. The coefficient of variation of tensile and yield strength of the bar are only 0.24% and 0.29%, which means the excellent uniformity. The level of ultrasonic flaw detection clutter of small size TC4 bars is ? 0.8-9dB, the clutter level is higher than the rolling bar. That is related to the change of crystal orientation in the non-uniform area of the microstructure of the radial forging bar.

Abstract:Due to excellent mechanical properties combined with low density, good corrosion resistance and weldability, titanium alloy acts as attractive structural materials for aerospace, ship navigation, weaponry and nuclear industry now. However, it`s high cost hinders the wide use of titanium alloy in different fields, and which is the key factor for not huge production as Al and further use of titanium alloy. Aiming at low cost of titanium alloy, three parts of raw materials, alloy preparation technology and cooperation of titanium industry were overviewed. On this basis, the trends and suggestions for the development of low-cost titanium alloys in the future are put forward.

Abstract:_{:TiAl alloy are high-profile advanced structural material because of its high strength-to-weight ratio and high service temperature, which has great potential in aerospace,automotiveandotherfields. However, TiAl alloy has poor thermal workability and is difficult to be formed by traditional methods. Powder metallurgy has a significant advantage in preparing complex TiAl alloy parts due to the characteristics of near-net forming.In recent years, researchers have done a lot of work on sintering technology of TiAl alloy powder and made some progress.The Process, microstructure,mechanical propertiesandparts of TiAl alloy using spark plasma sintering (SPS), hot isostatic pressing(HIP), hot pressing sintering,spray depositionand injection moldingin recent years were reviewed. The features and existing problems of above preparation methods were discussed. Meanwhile, some suggestions on powder metallurgy forming TiAl alloy parts and its future development were proposed.}

Abstract:AlCoCrFeNiMo_x (x=0, 0.5, 1.0, 1.5, 2.0) high entropy alloy (HEA) coatings were prepared by laser cladding method. The effect of Mo content on the microstructure, hardness, and corrosion resistance of the coatings was studied. Results show that with increasing the Mo content, the microstructure is changed from (Al, Ni)-rich body-centered cubic (bcc) phase+(Mo-Cr-Fe)-rich σ phase into (Fe, Ni)-rich bcc phase+(Mo-Cr-Fe)-rich σ phase+(Al-Fe-Mo)-rich σ phase+a little AlN (aluminum nitride). Additionally, the coating hardness (HV₁) is increased from 6514.4 MPa to 10652.6 MPa. With increasing the Mo addition, the self-corrosion potential of the coating in 3.5wt% NaCl solution is also increased. The coating presents the optimal corrosion resistance at x=1.0.

Abstract:FeCrAl coating with thickness of 18 μm was deposited on Zr-4 alloy substrate by magnetron sputtering in order to improve the high-temperature oxidation resistance of Zr alloys. The oxidation resistance of FeCrAl coating with low Al content was investigated by air oxidation tests. Field emission scanning electron microscope, energy dispersive spectrometer, and grazing incidence X-ray diffraction were used to evaluate the relationship between interfacial evolution and element migration. Results show that although the FeCrAl coating is layered and gradually peels off after air oxidation at 1000 °C, the coating still effectively protects the Zr-4 substrate from oxidation. The performance degradation of FeCrAl coatings is mainly caused by the severe outward diffusion of Al element and the inward diffusion of Fe and Cr elements at high temperatures, which results in the layering and peeling inside the coating. The air oxidation behavior of FeCrAl coating at 800, 900, and 1000 °C was also discussed.

Abstract:A CeO₂-modified aluminide coating was prepared on 309 stainless steel by pack cementation method with NH₄Cl as activator. The surface and cross-section of the coating before and after cyclic-oxidation at 900 °C for 50 cycles were analyzed by X-ray diffractometer and scanning electron microscope coupled with energy dispersive spectroscope. The microstructure analysis results show that the modified coating consists of Fe₄Al₁₃ phase. A few CeO₂ nanoparticles are entrapped due to the outward diffusion of base metal. Compared with the normal aluminide coating without the addition of CeO₂ nanoparticles, the aluminide coating modified by dispersed CeO₂ nanoparticles has better scale spallation resistance in air at 900 °C. Some Fe₂Al₅ phases can be found on CeO₂-modified aluminide coating even after 50 cycles of oxidation. Additionally, the outward-diffused Al layer, the intermediate FeAl layer, and the external Fe₂Al₅+FeAl mixed layer exist in the coating, suggesting that CeO₂ nanoparticles can retard the degradation of aluminide coatings.

Abstract:This work studies the influence of characteristic parameters on the heat transfer and stress distribution for the thermal barrier caotings used in a novel 700℃ dual-pipe system. The finite element sequential coupling method was used and revealed that the thickness ratio of the ceramic layers, thermal conductivity of the outer ceramic layer, thermal expansion coefficient, cooling steam temperature, and pressure simutaneously have significant effects on the temperature and stress distribution of the coated steam dual-pipe system. On this basis, a structural optimization method for the multilayer heterogeneous coating system was developed by using MATLAB and ABAQUS platforms. And the optimal geometric sizes and material properties were identified. Furthermore, it was discovered that the inner surface temperature of P91 steel pipes can be decreased by about 27℃ and the maximum Mises stress at the interface between thermal growth oxide and bond coat can be decreased by about 151MPa, respectively. The results show that the proposed systematic optimization method can be used to automatically determine the optimal key characteristic parameters of multilayer heterogeneous coating systems, resulting in improved thermal management and reduced stress on critical components. These findings have important implications for the design and optimization of thermal barrier coatings in high-temperature applications.

Abstract:In order to improve the corrosion resistance of aluminum alloy, a porous anodizing film was prepared on the surface of aluminum by anodizing method, and a magnesium-aluminum hydrotalcite (MgAl-LDH) with layered bimetallic structure was constructed on the surface by the in situ growth method using the anodic oxide film as the skeleton. For the first time, zinc dibenzyl dithiocarbamate (ZBEC) was used to modify the prepared MgAl-LDH film layer, and the morphological composition of the modified MgAl-LDH film layer was studied by SEM, EDS, XPS and ft-IR, and the effects of ZBEC concentration, modification temperature and modification time on the corrosion resistance of the modified film were studied by electrochemical impedance spectroscopy (EIS).The results show that the hydrotalcite film layer is a flaky staggered structure perpendicular to the surface of the matrix, the ZBEC molecule can successfully bind to the MgAl-LDH film layer, and the modified film layer has a good binding force. When the concentration of ZBEC modified solution was 0.03 mol/L, the temperature was 45°C, and the time was 15 min, the EIS low-frequency modulus value of the modified film layer increased from about 7.94×100000 Ω?cm2 to 1.995×1000000 Ω?cm2, indicating that the ZBEC modification improved the corrosion resistance of the MgAl-LDH film layer.

Abstract:Molecular dynamics simulations were used to investigate the effect and mechanism of the angle (θ) between the plane of void center formation and the loading direction on void growth and coalescence behavior in single-crystal nickel under uniaxial tension. The results show that the yield stress and average flow stress of single-crystal nickel decrease with increasing θ, and the rate of stress decrease accelerates with increasing θ. When θ=90° (loading direction perpendicular to the plane of void center), the independent growth time of voids in single-crystal nickel is the shortest and void coalescence occurs first, leading to the most easily entering the softening stage. This is due to the fastest growth rate of void volume fraction and damage evolution rate in single-crystal nickel when θ=90°. When θ=90°, the significant reduction of 1/6<112> (Shockley) dislocation length and the maximum transformation rate of atomic number from FCC crystal structure to Other and HCP crystal structures in single-crystal nickel lead to the fastest damage evolution rate and the most severe damage level when θ=90°. It is worth noting that voids in single-crystal nickel are most likely to coalesce when θ=90°, due to the larger tensile stress on the void surface under this condition. Through this work, the aim is to reveal the void coalescence behavior and mechanism of metallic materials under high strain rates, and to provide theoretical guidance for understanding their softening behavior and fracture mechanism.

Abstract:The spheroidization behavior and kinetic model of plate-like δ phase of DP-GH4169 alloy during hot deformation were investigated by OM, TEM and isothermal compression tests. The results show that the dissolved spheroidization behavior of plate-like δ phase is mainly controlled by the diffusion of Nb from δ/γ phase boundaries to matrix γ. In the process of hot deformation, the dissoloved spheroidization has little effect on the spheroidization behavior of plate-like δ phase. The spheroidization critical strain εc of plate-like δ phase depends on the deformation temperature and strain rate. The spheroidization critical strain εcof plate-like δ phase is from 0.04 to 0.10 in the isothermal compression tests, and it decreases with the deformation temperature increasing or the strain rate decreasing. The relationship between the spheroidization volume fraction of plate-like δ phase and the thermal deformation parameters is accord with the Avrami equation.

Abstract:K4750 alloy is a new cast nickel-based superalloy with excellent mechanical properties at 700-750℃ and is expected to replace K4169 alloy. However, the tensile plasticity of K4750 alloy at room temperature fluctuates, and the relationship among room temperature tensile properties, solidification microstructure, and casting parameters is still unclear for this alloy. In this work, several K4750 alloy test bars were prepared with various casting temperatures and shell cooling conditions, and tested at room temperature by uniaxial tension. Sensitivity of the alloy"s room temperature tensile properties to changes in casting temperature and shell cooling rate was evaluated, and the mechanism was elucidated by microstructure characterization. Results show that the grain size of alloy drops significantly with decreasing casting temperature, and the yield strength of alloy slightly increases while the plasticity remains stable. When cooling rate of the shell decreases, the fracture elongation of alloy decreases significantly at room temperature. This is mainly because the cooling condition of mold shell significantly affects the precipitation characteristics of MC carbides. When the cooling rate is low, MC carbides tend to precipitate at grain boundaries in coarse and strip-like shapes. MC carbides are prone to internal cracks under stress, accelerating the intergranular failure of material and reducing the plasticity of alloy. In order to optimize the tensile properties of K4750 alloy at room temperature, more attention should be paid to the cooling rate of mold shell after casting and the precipitation morphology of intergranular carbides, prohibiting the formation of coarse intergranular carbides to improve the grain boundary plasticity of alloy.

Abstract:For the stray grain problem of 18 single crystal blades in high efficiency preparation due to the non-uniform temperature field, three different module structures ensure to have same production capacity were designed. The high rate solidification of DD6 Ni-based superalloy under different module structures was simulated by using ProCast software and CAFE model, the influence of the temperature field evolution and the withdrawal rate on stray grains was analyzed. The result showed that the solid-liquid interface of the single-layer module became curved seriously because the cooling efficiency of side close to the center pillar is higher than the side close to the furnace body for the heat preservation effect of center pillar is weak, and it had a large undercooling and tendency to form stray grains. By adding a sleeve to the single-layer module to increase the heat preservation effect, the temperature field can be changed effectively, the degree of bending was reduced to avoid the nucleation of stray grain. The double-layer superimposed module had a uniform thermal and a low undercooling, which could decrease the tendency of stray grain effectively. Both the double-layer superimposed module and the sleeve module could form a complete single crystal when the withdrawal rate was below 100 μm/s, however the diameter of the double-layer superimposed module reduces to a half of the other two, which could reduce the requirement of size of furnace body, it could achieve efficient preparation of single crystal blades.

Abstract:To investigate the effects of alloying Ta and Mo elements on the strength and morphology of the γ′ phase of Co-Al-W-based high-temperature alloys, the γ′-L12 supercell structure was constructed, doping calculations were performed at six nonequivalent sites, and the energy structure and mechanical properties were analyzed; and Co-8.8Al-9.8W-2X (X = Ta, Mo) alloys were prepared, and the alloys were deformed in 5% and 10% compression. The γ′ phase morphology and dislocation morphology of the alloy were analyzed using transmission electron microscopy (TEM) technique. The results show that the Ta atoms preferentially occupy the Al2 position and the Mo atoms preferentially occupy the W6 position during alloying, and the Ta atoms occupy the Al2 position, which increases the strength and tissue stability of the γ′-L12 doped structure, while the Mo atoms doping at the W6 position has the opposite effect. The γ′ phase shape can be maintained as cubic when the alloy is compressively deformed, and the dislocation damage to the γ′ phase is more limited, while the strength of the γ′ phase of the 2Mo alloy is reduced due to the preferential occupation of the Mo atoms in the W6 position, and the γ′ phase shape is changed from cubic to raft when the alloy is compressively deformed, and the dislocation damage to the γ′ phase is more serious.

Abstract:In order to ameliorate the microstructure characteristics and degradation behavior of the medical Mg alloys, the extrusion process was conducted to change the grain size characteristics and the distribution law of secondary precipitates/intermetallic compounds, and the microstructure characteristics and degradation behavior of as-extruded Mg-2Zn-0.5Gd-1Y-0.5Mn Mg alloy were analyzed. Results show that different hot-extrusion deformation methods do not change the types of the secondary phases in Mg-2Zn-0.5Gd-1Y-0.5Mn Mg alloy, but change their distribution and morphology. The main components of Mg-2Zn-0.5Gd-1Y-0.5Mn Mg alloy are α-Mg and W-Mg₃Y₂Zn₃ phases. The electrochemical tests demonstrate that the corrosion current densities are 2.498, 3.656, and 1.012 μA·cm^-2 for as-cast, extruded/370 °C, and extruded/390 °C Mg alloys, respectively. The precipitates/intermetallic com-pounds of strip shape are distributed in the matrix of as-cast Mg alloy, which can act as the micro-cathode, thus forming the galvanic-corrosion sites and accelerating the corrosion rates. Partial coarse precipitates cannot completely dissolve into the α-Mg matrix due to the low actual temperature of the Mg alloy during extrusion at 370 °C. With the disordered distribution and the increasing precipitates, the area proportion of micro-cathode is increased, which accelerates the corrosion rate. However, for the Mg alloy during extrusion at 390 °C, the extrusion speed is fast, the dissipation behavior is slow, and the friction between ingot and extruder is intense, indicating the occurrence of sufficient dynamic recrystallization, which reduces the number/area of micro-cathode and improves the corrosion resistance.

Abstract:CeN powder was prepared through the carbothermal reduction nitridation reaction assisted by sol-gel method. Citric acid (CA) was used as the chelating agent, indicating that the organic material is used as the carbon source. The whole process could be divided into an aqueous phase process and a heat treatment process. The aqueous phase process mainly involved the chelation and polyester of Ce³⁺ and CA to form stable Ce³⁺-CA chelate precursors. Homogeneous mixing at the molecular level of Ce and C sources could be achieved by the aqueous phase process. The heat treatment process included the in-situ carbonization and carbothermal reduction nitridation reaction. The in-situ carbonization process formed CeO₂/C powder, promoting the close contact between CeO₂ and C. The diffusion distance between the atoms of Ce and C sources is reduced to facilitate the carbothermal reduction nitridation process.

Abstract:To improve the hard and brittle mechanical characteristics of single crystal germanium (Ge), the molecular dynamics (MD) simulation was used to study the mechanism of surface modification on single crystal Ge by ion implantation with three different doses. Results show that the ion implantation causes amorphous phase damage to Ge matrix, and the nano-indentation process shows the lattice evolution. The nano-indentation results reveal that the existence of amorphous phase can reduce the hardness and brittleness of single crystal Ge and enhance its plasticity. Additionally, the degree of amorphous phase damage and the hardness of Ge matrix are related to the ion dose. With increasing the ion dose, the amorphous damage is deepened, and the hardness is decreased.

Abstract:To explore the influence of randomness of materials and loads on the crack driving force of TP304 stainless steel, a probability prediction for crack driving force through the elastic-plastic finite element method (EPFEM) coupled with the Kriging surrogate model was proposed. To improve the efficiency of finite element analysis, MATLAB was used to further develop the pre-processing and post-processing procedures of ABAQUS software to realize the automatic change of random specimens, batch calculation, and automatic analysis of probability prediction results. The statistical distribution law of the crack driving force of TP304 stainless steel material under the action of random factors was obtained, as well as other probability characteristics, including failure probability, failure probability density function, cumulative probability density function, etc. The sensitivity of each random factor was analyzed. Finally, the effectiveness and efficiency of the proposed method were analyzed, compared with those of the Monte Carlo method. Results show that the randomness of load and material parameters can significantly influence the driving force of crack tips of TP304 stainless steel, thereby affecting the failure probability of TP304 stainless steel. The load and strain hardening exponent present the most obvious effect on the dispersion of crack driving force of austenitic TP304 stainless steel.

Abstract:The first-principles calculation was used to investigate the influence of doping fourth-period transition metal elements on the structural, mechanical, and thermal properties of Mo₂CoB₂. Through the calculation of cohesive energy and formation enthalpy as well as the calculation comparison between the obtained results and Born-Huang criterion, all doped compounds are thermodynamically and mechanically stable. Point defect theory was employed to determine the occupation sites and occupation preference of doped elements in the Mo₂CoB₂ crystal cell. Results show that Sc and Ti exhibit strong preference for Mo sites, and V has a weak preference for Mo sites. Additionally, Cr, Mn, Fe, Cu, and Zn have a weak preference for Co sites, and Ni has a strong preference for Co sites. Debye temperatures were obtained by the contrast calculation. The results reveal that except Mo₇TiCo₄B₈, Mo₇VCo₄B₈, and Mo₇CrCo₄B₈, the doped models all have lower Debye temperatures than the undoped model, suggesting that except Ti, V, and Cr elements, the addition of transition metal elements of large quantity into the Mo₂CoB₂ hard phase should be avoided. Furthermore, except that of the Cr-doped model, the hardness of the doped models is lower than that of the undoped model, and the models with doped elements at preferential sites normally exhibit higher hardness than those at non-preferred sites do. This research provides theoretical basis for the development of Mo₂CoB₂-Co cermet with improved properties.

Abstract:Horizontal continuous casting is a common method to produce copper strip. It is very important to explore the influence of process parameters on the quality of the billet. The influence of drawing speed on temperature field, liquid hole depth and cooling rate in mold was analyzed by numerical simulation, and the influence mechanism of drawing speed on the structure of billet was revealed by process test. The results show that with the continuous increase of the billet drawing speed, the depth of the liquid hole in the mold continues to increase, and the cooling rates of the surface and core of the billet along the traction direction gradually decrease, and the difference between the two cooling rates gradually decreases. When the drawing speed was 149mm/min, the cooling rates of the two parts reach the same. With the continuous increase of the billet drawing speed, the angle θ between the grain growth direction and the traction direction on the section of the billet increases gradually, the grain growth distance was shortened, the number of grains on the surface of the billet increases, and the average grain diameter decreases from 1.96mm to 1.05mm, and the overall microstructure uniformity was obviously improved.

Abstract:Aimed at improving the performance and compactness of the heat pipe heat exchangers, different forms of double-pipe heat exchanger units with densely longitudinal fins are obtained by metal additive manufacturing method. The manufacturing deviation is summarized, which shows that the internal structure is complete. The optical measurement shows that the roughness distribution on both sides of the inclined fin is not uniform. The steady state experiments are implemented to investigate the heat transfer characteristics of four densely longitudinal fins enhanced compact double-pipe heat exchanger units. The configurations are classified into two categories of straight fin type (DPHE-1) and periodically arranged fin type (DPHE-2). Within the Re ranging from 2000 to 15000, the tested results show that, due to the increase of heat transfer area and the enhancement of flow mixing effect, the DPHE-2 gives 1.3~1.4 folds averaged Nusselt number and 12.6~28.6 averaged friction factor than the DPHE-1. Comparing their overall heat transfer performance, the long fin scheme in DPHE-1 type performs best.

Abstract:Two 100-m MgB2 wires with different conductor structures (Cu core and CuNb core) were designed and successfully fabricated by the central Mg diffusion process (IMD), and the mechanical and transport superconductivity of the wires were tested. The uniformity of MgB2 superconducting layer distribution along the longitudinal direction of the two wires was analysed by different methods, and it was found that the distribution of superconducting layer tended to be more uniform as the diameter of the wire decreased, and the MgB2 FF fluctuation range of the wire with Φ 0.8 mm was the smallest, and the extreme difference of the base super ratio was 0.02. The results of the uniformity of MgB2 layer distribution showed that the Mg and B densities in the wire were well distributed. The results of the superconductivity tests show that the critical current Ic of the Cu replacement core wire is 19 A (4.2 K, 4 T) higher than the critical current Ic of the CuNb replacement core wire, while the Jc performance is basically the same. The Mg/B/Nb/Monel matrix composite enable to manufacture high performance MgB2 wires with 100-m class.

Abstract:Single-layer sandwich panels and six kinds of multilayer sandwich structures were prepared using closed-cell aluminum foam and aluminum alloy sheets. The cellular and macroscopic deformation modes were analyzed to study the influence mechanism of the plates and layer number on the quasi-static mechanical properties and energy absorption characteristics. The results show that the plates can adjust the stress state and make the cores collapse layer by layer, which reduces the multilayer synchronous deformation, lateral and bilateral slip caused by the formation and extension of the inclined deformation bands, so that the structure has higher collapse stress, platform stress, energy absorption per unit volume and smaller densification strain. The increase of the layer number leads to the increase of the length and number of the deformation bands in the structures without plate, thus changes the macroscopic deformation mode, results in the aggravation of the slip phenomenon on both sides, leads to the accumulation of cellular defects in the structures with plate, affects the stable deformation, results in the increase of densification strain, the reduction of collapse stress, platform stress and energy absorption per unit volume, and the decrease of energy absorption efficiency at densification strain. Compared with other structures, the three-layer structure with plates has the best compression resistance and energy absorption properties.

Abstract:In this paper, a series of Ni3Al films were successfully prepared by magnetron sputtering at different bias voltage, and then the bias voltage-dependent composition, deposition rate, microstructure, hardness and fracture toughness were studied in detail by XPS, XRD, SEM, AFM, nanoindentation and digital microhardness tester. The results showed that introducing the bias voltage could increase the kinetic energy of the ionized charged ions during sputtering, thus significantly improve the deposition rate, the density of the internal structure and the surface smoothness of Ni3Al films; In addition, the introduction of appropriate bias voltage could induce the formation of amorphous/nanocrystalline composite structure to improve the crystallinity of the films. The wrapped nanocrystalline composite with biphasic structure could provide a large number of grain boundaries, which strengthen the blocking effect on dislocations, leading to the dislocation stacking at the grain boundary and resulting in the increasement of hardness. Meanwhile, the existence of the large number of grain boundaries could also consume the energy of crack propagation to inhibit the generation of macrocracks, and significantly enhance the fracture toughness of Ni3Al films.

Abstract:Novel Ni-W-Co-Ta heavy alloys were cold rolled under room temperatures to characterize the microstructural evolution and mechanical properties by using optical microscopy, scanning electron microscopy, transmission electron microscopy, X-ray diffractometry, electron back scattered diffraction, tensile testing and microhardness testing. The results show that equiaxial grains were elongated along the rolling direction and a fibrous texture could be observed with an increase in deformation, in which a large number of slip bands were generated to coordinate the intensive plastic deformation. The sharp increase in dislocation density significantly promoted the dislocation interaction, which, in turn, refined the grain size down to 25.2 nm. After 90% severe plastic deformation, the tensile strength is increased to 1953 MPa. The yield strength is increased to 1806 MPa, the hardness is increased to 534 HV, and the elongation is sharply decreased by 9.1%. The fracture morphology changed from a typical ductile fracture to quasi-cleavage and ductile mixed fractures.

Abstract:Laser filamentous wire additive manufacturing technology is a manufacturing technology that can rapidly form small parts. However, due to the influence of thermal accumulation effect in the manufacturing process, it is often unable to ensure the precision shape control of formed parts. In order to solve this problem, this paper uses the calibrated infrared thermography to collect the surface temperature of single pass multi-layer thin-walled parts, and studies the characteristic variation law of temperature field and heat accumulation effect in the manufacturing process, which provides a basis for the optimization of forming process. The results show that the infrared thermal thermography can be used to study the evolution of temperature field in the process of thin wall stacking. With the increase of cladding height, the area of high temperature area gradually increases, and the heat accumulation effect is significantly enhanced. In the process of cladding, the heat is conducted downward, the heat dissipation condition becomes worse gradually, and the cooling rate of each layer decreases with the increase of the number of layers until it becomes stable. In addition, when the number of cladding layers is more than 15, the thermal accumulation effect will no longer affect the cladding layers below 15.

Abstract:The oxidation behaviors of new-type Fe-Ni-Cr-Al alloys with different Y contents in air atmosphere at 1300 ℃ were studied by isothermal oxidation test. The type and distribution of oxidation products were studied by X-ray diffraction (XRD) and scanning electron microscopy (SEM). It is found that the addition of Y element is beneficial to the oxidation resistance of Fe-Ni-Cr-Al alloy. The reason is that the Y element can promote the formation of a dense composite protective layer of spinel and chromium oxide on the surface of Fe-Ni-Cr-Al alloy, and then slow down the diffusion of the elements in the matrix. At the same time, Y element can accelerate the transformation mode of Al₂O₃ from internal oxidation to external oxidation and slow down the internal nitridation process. In summary, the oxidation resistance increases.

Abstract:Effects of disproportionation time and dehydrogenation pressure on the magnetic properties and anisotropy of HDDR magnetic powders were studied. The phase structures of the samples were identified by X-ray powder diffraction. The microstructure was investigated using scanning electron microscope. The magnetic properties of NdFeB were measured by AMT-4A magnetic measuring instrument. The results showed that the disproportionation time determines the content of the disproportionated phase and the residual parentNd₂Fe₁₄BH_1.04 phase in the material after the HD process. The residual parent Nd₂Fe₁₄BH_1.04 can inherit the texture information of the original Nd₂Fe₁₄B phase, which results in strong c-axis texture of new phase Nd₂Fe₁₄B. When the disproportionation time extends to 40 min, the anisotropy of the magnetic powder reaches the maximum, DOA=0.55. The dehydrogenation pressure mainly acts as the driving force for the crystal growth. The low pressure of 0.01 Mpa will cause over large driving force, which leads to the weak anisotropy of the generated new phase Nd₂Fe₁₄B. The magnetic powder has the optimum anisotropy when the dehydrogenation pressure is at 0.03 Mpa, DOA=0.53.

Abstract:A Cu-Sn-Fe-Ni alloy was prepared by melt casting and thermomechanical treatment The static corrosion behavior in NaCl solution was characterized by scanning electron microscope and X-ray photoelectron spectroscopy. Finally, the corrosion mechanism of the alloy was discussed and analyzed. The results show that the static corrosion rate of the alloy in 3.5 wt.% NaCl solution is 0.0473 mm/a, and the corrosion resistance is good; The corrosion resistance of the alloy increases first and then decreases with the increase of immersion time; The alloy has an obvious preferential corrosion tendency in the immersion process. At first, Fe removal corrosion occurs, and then Cu oxidizes to form a relatively dense passivation film, which reduces the corrosion rate of the alloy. Later, Sn and Ni begin to dissolve and corrosion, forming an oxide film, which makes the passivation film denser. However, at the time, Fe removal corrosion still occurs in the lower layer of the passivation film, which promotes the local destruction of the dense passivation film, leading to the decline of the corrosion resistance of the alloy.

Abstract:For Al/Mg friction stir welded (FSW) joints, when the thickness of base metal is too large, thicker brittle and hard intermetallic compounds (IMCs) are easily formed along the interface, which makes joint formation extremely difficult. In this paper, the interface interlocking composite Zn interlayer is innovatively used to study the evolution of IMCs at the interface of thick plate Al/Mg FSW joint and the change rule of joint performance, which provides theoretical and practical basis for subsequent high-strength joining of Al/Mg FSW joints. The results show that a low melting point eutectic layer (Mg+ Al12Mg17) with an average thickness of 69.7μm is formed at the upper part of the magnesium side interface of the oblique butt joint, and IMCs with an average thickness of 42.7μm and 21.2μm are formed at the middle and lower part. The IMCs layer consists of Al12Mg17 and Al3Mg2。Compared with oblique butt joints, when interfacial interlocking compound Zn interlayer is used, Al-Mg-Zn phase (Al5Mg11Zn4) and Mg-Zn phase (MgZn2, Mg2Zn3) are generated locally at the interface, replacing the original Al-Mg IMCs with a minimum IMCs thickness of 3.9μm. The tensile strength of the joint is increased from 2.7MPa of oblique butt joint to 32.3MPa of interfacial interlocking composite Zn interlayer joint, which is related to interfacial interlocking effect and thickness reduction of IMCs.

Abstract:The corrosion behavior of copper pipes buried in tropical rain forest soil environment for a long time was studied by weight-loss method, morphology analysis, composition analysis and electrochemical test in this paper. The results show that the average corrosion rate of the copper pipe after 16 years of burial is 2.5 μm/y, the law of corrosion weight loss conforms to the power function model, and its fitting equation is C=0.4273t_^-0.246. The corrosion products on the surface of the copper tube show a light green dense scale structure, which is well combined with the metal matrix. XPS、EDS and FTIR analysis results show that the main component of the corrosion product is copper green (Cu₂ (OH) ₂CO₃). The electrical test results show that after 16 years of burial, the corrosion rate of the copper tube decreases and the impedance value increases significantly, indicating that the corrosion product film has a good protective effect on the substrate and can effectively slow down the continuous development of the corrosion process.

Abstract:The selective laser melting (SLM) 3D printing method was applied to design and manufacture tungsten materials with lattice structures. The changes in the mechanical properties of tungsten materials under different lattice structures were investigated through finite element analysis, scanning electron microscopy, and quasi-static uniaxial compression tests. The influence of microstructure on mechanical properties was analyzed.The results indicate that the ARC lattice structure can effectively reduce stress concentration at the nodes, while maintaining the lightweight and low porosity characteristics of the lattice structure, as well as the high-strength mechanical properties of tungsten materials. The average compressive strength reaches 535MPa, while the average mass is only 1.25g. After laser printing, the ARC lattice has an average compressive strength increase of 93% compared to the cubic lattice, with the Body-Centered arc lattice (BCA) showing superior compressive performance, reaching a maximum compressive strength of 721MPa, and a theoretical structural density of 12.8%. The mechanical performance of 3D printed W is close to plastic processed sample. Compared with the cubic lattice, the arc lattice has good ability absorption characteristics, and the total energy absorption value of the latter is increased by 223% compared with the former, and the average energy absorption of the arc lattice reaches 1664J/cm3. In addition, the SEM image shows that the arc lattice reduces the hanging distance of the oblique pillar in the printing due to its arc characteristics, and the forming effect is better than that of the cubic lattice.

Abstract:Platinum iridium bonding wire is a high-strength wire bonding material used in the packaging of special microelectronic devices, and heat treatment is the key method for the cold-deformed platinum-iridium alloy microfilament to control the lifetime service performance of the bonding wire. Based on the Φ25 μm Pt-10Ir ultrafine bonding wire, the microstructure and deformation of ultrafine filaments under different annealing processes were analyzed and measured by high-resolution FIB-EBSD linkage characterization technology, and the evolution of their mechanical and electrical properties was statistically studied. The results show that with the increase of annealing temperature, the microstructure gradually changes from fine fibrous grains to partial equiaxed grains. The equiaxed grains preferentially grow at the grain boundary. Simultaneously, the intensity of the silk texture gradually decreases, the breaking force gradually decreases, the elongation gradually increases, and the resistivity shows a trend of first decreasing and then increasing. After the annealing of Pt-10Ir ultra-fine bonding wire at 600°C/30 min, recovery rather than recrystallization occurs in the microstructure, the texture orientation evolves into a deformation texture parallel to the wire drawing direction of <111> with a breaking force of 37.06 cN, a tensile strength of 755.29 MPa, an elongation of 1.30%, and a resistivity of 22.81 μΩ·cm, showing an excellent mechanical/electricity comprehensive performance. This study will provide a theoretical and experimental basis for the optimization of microstructures and properties in high-strength precious metal ultra-fine bonded wire.

Abstract:The surface of nanodent and nanopore structured alumina membranes with different periods were directly modified by Angelica sinensis polysaccharide (ASP) or covalently modified by ASP via γ-aminopropyl triethoxysilane (KH550). After that, the morphology and cell viability of breast cancer cells MDA-MB-231 grew on the modified nanostructured surfaces were systematically studied. It was found that nanodent and nanopore structure directly modified by ASP could effectively inhibit the viability of breast cancer cells, and had little effect on cell morphology. However, the inhibitory effect of nanodent structure on cell viability was superior to that of nanopore structure. Nanodent structure with period of 300 nm had the best inhibitory effect on cell viability, and the inhibitory rate is 27.7%. The nanodent and nanopore structures covalently modified by ASP via KH550 had a better inhibitory effect on cell viability than that directly modified ASP, and the cell morphology changed obviously. A large number of lamellipodia were generated around the cell body. However, the inhibition effect of the nanodent structure on cell viability was better than that of the nanopore structure. Nanodent structure with period of 300 nm had the best inhibitory effect, and the inhibition rate is 28.2%. These results have a certain function for the design and delivery of drugs.

Abstract:Aluminum alloy castings exhibit versatile prospects in critical aircraft, aerospace, and lightweight of automobile owing to their ultralow density and excellent specific strength. The optimization of forming and mechanical properties of cast Al alloys can significantly expand their applications. In this work, the research progress of Al-Zn high strength cast aluminum alloy are reviewed. The strengthening mechanism and research results on (micro-)alloying, grain refinement, structure purification, and heat treatment optimization of high-strength as-cast aluminum alloys are summarized. The existing problems are also discussed. At last, the development trends of as-cast aluminum alloys with high strength and toughness were prospected, which has certain practical and theoretical significance for the aluminum alloys.

Abstract:High-entropy alloys based on the multiple components design concept exhibit excellent comprehensive properties such as high strength, high toughness, good wear resistance, oxidation resistance and thermal stability, making it prospective to become an excellent new structural material. As for the composition design, high-entropy alloys can adjust its stacking fault energy and microstructure by changing the concentration of each principal element, doping interstitial atoms and so on, and then introduce multiple strengthening and toughening mechanisms such as precipitation strengthening, fine grain strengthening, phase transformation or twinning-induced plasticity effect, thereby improving its comprehensive mechanical properties. In this paper, the effects of composition design with non-equiatomic and interstitial C/N atom additions on the microstructure, mechanical properties and deformation mechanism of face-centered cubic high-entropy alloys are summarized, so as to provide the theoretical basis for the design of the new high-performance face-centered cubic high entropy alloys.