Abstract:TC4 titanium alloy was treated by microarc oxidation (MAO) with Si₃N₄ nanoparticles into the base electrolyte. The effect of the Si₃N₄ content on the surface morphology, corrosion resistance, and wear resistance of the coatings was studied. The results show that MAO coatings with Si₃N₄ addition present the porous structure, and the coating is the thickest as the Si₃N₄ content is 1 g/L. The coating with the addition of 1 g/L Si₃N₄ after acid corrosion test for 7 d shows excellent corrosion resistance with the lowest corrosion rate of about 0.057 mg·cm^-2·d^-1. With the addition of Si₃N₄, the antibacterial property of MAO coatings is firstly increased and then decreased, which is optimal when the Si₃N₄ addition is 1 g/L. The Si₃N₄ addition can obviously enhance the wear resistance of the coatings in the simulated seawater. When the Si₃N₄ addition is 3 and 4 g/L, the friction coefficient of MAO coatings is low and stable. In addition, MAO coating with the addition of 3 g/L Si₃N₄ shows the excellent wear resistance.

Abstract:The duplex Ti-45Al-7Nb (at%) alloys with equiaxed fine grains were prepared by powder metallurgy method. The high temperature mechanical properties of the alloys at 900, 950, and 1000 °C under the strain rates of 1×10^-3, 1×10^-4, and 5×10^-5 s^-1 were investigated, and the corresponding deformation mechanism was also discussed. Results show that the tensile strength is decreased whereas the elongation is greatly increased at elevated temperatures or under decrescent strain rates. Since the small grains are easy to achieve deformation and coordination, the elongation of the small grain alloys is significantly higher than that of coarse grain alloys. The alloys form a large number of voids at the fractures after high temperature tensile. Long cracks perpendicular to the tensile direction are formed at the front fracture. Besides, the grain boundary sliding, grain twinning, and dynamic recrystallization also lead to the deformation of alloys, thus improving the microstructure ductility.

Abstract:The Al-10wt% Mg alloy was cold-rolled with the thickness reduction ratio of 75% followed by annealing at 75~150 °C, and its microstructure characteristics and mechanical behavior were investigated. The as-rolled and annealed Al-10wt% Mg alloys are characterized by elongated ultra-fine grains, high density of dislocations, a very small amount of Al₃Mg₂ phase, and no dispersed distribution of Al₃Mg₂ phase. With increasing the annealing temperature, the width of elongated ultra-fine grains is increased and the dislocation density is decreased. After annealing at 75~150 °C, compared with those of as-rolled alloys, the yield strength of annealed alloys is decreased by 8%~33%, the ultimate tensile strength is decreased by 1%~12%, and the elongation is increased by 16%~83%. The contributions of various strengthening mechanisms to yield strength and the contributions of preexisting dislocations and Mg solute to ductility were analyzed and discussed.

Abstract:The thick Cr/CrN multilayer coatings with different modulation ratios (1:2, 1:3, 1:5) were deposited on the A100 steel substrate at room temperature by multi-arc ion plating (MAIP). The chamber temperature gradually rose to 160~170 °C during deposition. The modulation structures are designed to optimize the adhesion strength and the mechanical properties. The Cr/CrN multilayer coating with modulation ratio of 1:2 exhibits the highest adhesive strength (L_c=63.8 N), which may be attributed to the highest hardness (H)/elastic modules (E) and H³/E² values of 0.083 and 0.138, respectively. The thicker the Cr layer, the better the plasticity and tribological properties. The dry friction test shows that the mean coefficient of friction and the specific wear rate of Cr/CrN multilayer coating are decreased by 24% and 94% at most, respectively, compared with those of the single-layer CrN coating. As the Cr layer becomes thick, the wear mechanism is transformed from surface fatigue wear to abrasive wear, which may be attributed to the coordinate changes of hardness and plasticity.

Abstract:Direct chill casting (DCC) and twin roll casting (TRC) methods were applied to produce 1XXX series aluminium blanks with different contents of Fe, Si, Cu, and Mn elements. Different treatments, including homogenization, hot rolling, cold rolling, and annealing, were subsequently applied to produce the aluminium foil of 13 μm in thickness. Results show that the casting process barely affects the tensile strength of the aluminium foil, while the fine particles of secondary phase introduced by twin roll casting has a positive effect on the elongation of aluminium foil. The coarse grain boundary intermetallic in ingots after DCC can be refined at homogenization temperature above 580 °C, and subsequently be broken into small particles through the following hot rolling process. The addition of Cu is better than that of Fe, Si, or Mn elements, as Cu solute atoms can increase the strain hardening rate. The foil thickness greatly affects the tensile properties during intermediate annealing process, which is related to the ratio of thickness to grain size. Room temperature storage causes deterioration of tensile properties of thin aluminium foil due to the recovery mechanism after application of very large strain.

Abstract:The in-vitro degradation behavior and corrosion mechanism of Mg-4.0Zn-0.2Mn-0.2Ca (wt%) micro-tube was investigated by the immersion tests and electrochemical tests. The results show that the corrosion resistance of the micro-tubes can be improved by the annealing treatment. The long-term immersion tests reveal that the corrosion process is relatively uniform, and the corrosion rate of the annealed micro-tube in Hank's solution is about 0.30 mm/a. During the initial stage of immersion, Mg(OH)₂ is formed on the surface of the annealed micro-tubes, forming a protective film to hinder the corrosion progress. Although the formed hydroxyapatite (HA) on Mg(OH)₂ film can further reduce the corrosion rate, the coarse secondary phases in Mg matrix can enhance the galvanic corrosion effect. The generated abundant hydrogen may destroy the HA film, thus promoting the corrosion process.

Abstract:The synergetic effects of nitrogen and oxygen impurities on the micro-area chemical composition, microstructure, and hydrogen storage performance of V-Ti-Cr-Fe alloys were investigated through X-ray diffraction, scanning electron microscopy, optical microscopy, and pressure-composition-temperature (PCT) analyses. Results show that the hydrogen storage capacity of V₄₀Ti₂₆Cr₂₆Fe₈ alloy is obviously decreased with increasing the nitrogen and oxygen impurities. The mechanism for the decrease is as follows: the oxygen dissolved in V-based alloys suppresses the formation of the dihydride phase, resulting in the decrease in hydrogen capacity (primary effect); while the nitrogen is bound with titanium forming a new nitrogen-titanium-enriched phase, which results in composition change of the main phase and decreases the lattice parameter (secondary effect).

Abstract:The layered double hydroxides (LDHs) were prepared on 6061Al alloy by in-situ synthesis. The effects of LDHs on the corrosion behavior of 6061Al alloy in 3.5wt% NaCl solution with different dissolved oxygen (DO) contents (1~16 mg/L) were analyzed through the polarization curves (Tafel) and electrochemical impedance spectroscopy (EIS). The results indicate that the polarization processes of 6061Al and LDHs/6061Al alloys are controlled by DO diffusion. With increasing the DO content, a large number of pits appear on the 6061Al alloy surface, and the pit is gradually deepened. The corrosion current is increased from 1.273 μA to 1.743 μA, and the pit depth is increased from 12 μm to 19 μm. However, no pits can be observed in LDHs/6061Al alloy at different DO contents, which is attributed to the inhibition of DO diffusion and the polarization process. In addition, the resistance of 6061Al alloy is increased with increasing the DO content, which is related to the formation of Al₂O₃. However, the resistance of LDHs/6061Al alloy has no obvious change at different DO contents, showing excellent isolation performance against DO.

Abstract:The silver nanobowls were prepared by self-template method, and the structure and growth mechanism of Ag nanobowls were investigated. Results show that the Ag₂O clusters result from the reaction of AgNO₃ and NaOH. After adding the reductant methanal, Ag nano-shell is obtained on the Ag₂O cluster surface with the by-product CO₂ inside the Ag nano-shell. With the reaction further proceeding, the increasing pressure breaks through the Ag nano-shell, thereby forming the Ag nanobowls with the size of approximately 200 nm. This unique synthesis method provides theoretical and experiment basis for the noble metal nanomaterials with special structure.

Abstract:The nano/submicron scaled spraying powders of lanthanum titanium aluminum oxide LaTi₂Al₉O₁₉ (LTA) toughened by yttria stabilized zirconia Zr_0.92Y_0.08O_1.96 (YSZ) were prepared via spray drying and then calcined at different temperatures. The effect of heat treatment on the flowability, apparent density, and morphology of the spray-dried powders was investigated. Results show that the spray-dried powders have loose structure with the size of 40~80 μm. The cohesion between LTA-YSZ particles becomes stronger after calcination. The spray-dried powders calcined at 1100 °C achieve the optimal spraying characteristics and morphology, and therefore are deposited via air plasma spraying (APS) to obtain LTA-YSZ coatings which show a good lamellar structure with defects.

Abstract:The Al-10Mg composites containing 10wt% Mg reinforced by 6.8vol% continuous carbon fibers (CFs) were prepared by twin-roll casting method at different pouring temperatures (943, 963, 983, and 1003 K). The Ni coating on the CF surface was used to inhibit the formation of Al₄C₃ brittle phase. Results show that CFs and Al-10Mg matrix are well bonded without the formation of Al₄C₃ brittle phase. The ultimate tensile strength (UTS) of the composites is firstly increased and then decreased with increasing the pouring temperature. When the pouring temperature is 963 K, UTS of CFs/Al-10Mg composites reaches 185 MPa, which is increased by 41.2% compared with that (131 MPa) of the substrate. Meanwhile, the fracture surface of CFs/Al-10Mg composites was also investigated. The good interface bonding between CFs and Al matrix can be observed. Thus, the twin-roll casting is an effective method to prepare CFs/Al-10Mg composites with a promising prospect.

Abstract:The effect of cutting temperatures on the hole quality in multi-layered carbon fibre reinforced polymer (CFRP)/Ti stacks was investigated. The cutting force, cutting heat, hole surface, and subsurface quality of CFRP during drilling with and without Ti alloy supporting layer were analyzed, and the evaluation method for subsurface damage was proposed. The results show the cutting temperature and subsurface quality are greatly influenced by the existence or absence of Ti alloy supporting layer, whereas the cutting force and surface quality are slightly affected. A large amount of cutting heat is generated during cutting process of CFRP and Ti alloy simultaneously, resulting in the significant increase in temperature at the exit part of CFRP holes. The high temperature reduces the rigidity and bonding performance of CFRP resin matrix, leading to serious subsurface damage of the fibre layers around the exit part of CFRP holes. The subsurface damage was also evaluated by the proposed method, and the fibre layer at the exit part of holes is the most damaged, and the farther the distance away from the exit part of holes, the less damaged the subsurface. Therefore, the cutting temperature significantly influences the subsurface quality of CFRP hole during the drilling of multi-layered CFRP/Ti stacks, and subsurface damage is crucial to evaluate the machining quality of CFRP.

Abstract:The corrosion behavior of different regions of AA2219-T87 aluminum alloys after self-reacting friction stir welding was investigated through the electrochemical corrosion and immersion corrosion tests. The results show that the weld nugget zone (WNZ) has the optimal corrosion resistance, while the base material shows the worst corrosion resistance. In the base material, the volume fraction of precipitated phase is the largest. The closer the area to the nugget center, the more the dissolving precipitated phase. WNZ is composed of fine equiaxed grains with a small amount of θ phase.

Abstract:The effect of phosphating temperature on formation, microstructure, and corrosion resistance of the phosphate chemical conversion (PCC) coatings and that on the magnetic property of the sintered Nd-Fe-B permanent magnets were investigated. The results show that the coating mass is increased slightly with increasing the phosphating temperature. The scanning electron microscope observation demonstrates that PCC coatings have blocky structure with the grain size of 5~10 μm. The analyses of energy dispersive spectra and Fourier transform infrared spectrometer spectra reveal that the coatings are mainly composed of neodymium phosphate hydrate, praseodymium phosphate hydrate, and a small amount of iron phosphate hydrate. The oxygen and phosphorous elements in PCC coatings are mainly distributed on the grain surface, while the iron element is mainly concentrated at the grain boundaries. The distribution of neodymium and praseodymium is relatively uniform. The electrochemical analysis and static immersion corrosion test show that PCC coatings prepared at different temperatures can effectively improve the corrosion resistance of the sintered Nd-Fe-B permanent magnets. The coatings prepared at 70 °C exhibit a better corrosion resistance due to the uniform and dense microstructure. Although the magnetic properties of the sintered Nd-Fe-B permanent magnets with PCC coatings are decreased, those with PCC coatings prepared at 70 °C are relatively fine. The optimal phosphating temperature of 70 °C for the sintered Nd-Fe-B permanent magnets is determined.

Abstract:The mechanical properties at room temperature and the dynamic mechanical properties at different temperatures of Ti₄₈Zr₂₀Nb₁₂Cu₅Be₁₅ metallic glass composite were investigated. Results show that the tensile strength at room temperature of this metallic glass composite is about 1350 MPa and its fracture strain is approximately 0.13. With increasing the temperature, the state of the metallic glass composite changes from elastic to viscoelastic. The physical parameters, such as loss factor and correlation coefficient, are introduced to analyze the dynamic mechanical behavior under the framework of quasi-point defects model, and the theoretical curve fits well with the experiment data. Therefore, the quasi-point defects model can well describe the dynamic mechanical behavior of Ti₄₈Zr₂₀Nb₁₂Cu₅Be₁₅ bulk metallic glass composite at different temperatures.

Abstract:The first-principles theory calculation was used to investigate the structural, electronic, mechanical, and thermodynamic properties of intermetallics ZrBe₂, ZrBe₅, ZrBe₁₃, and Zr₂Be₁₇ in Zr-Be binary alloy system, based on the density functional theory with generalized gradient approximation (GGA) approach. Results show that the optimized lattice parameters at 0 K are in agreement with the available experimental results, indicating the calculation reliability. The calculated formation enthalpy and cohesive energy indicate that all the intermetallics are formed spontaneously at 0 K, among which ZrBe₅ has the strongest alloying ability and ZrBe₂ has the best structural stability. Subsequently, the electronic density of states (DOS) was also used to investigate the intermetallic stability. The stress-strain method was adopted to calculate the independent elastic constants of the intermetallic. Based on that, the mechanical parameters of polycrystal, such as bulk modulus B, shear modulus G, Young's modulus E, Poisson's ratio ν, and anisotropy value A can be deduced by Voigt-Reuss-Hill approximation. In addition, according to Pugh's criterion, Poisson's ratio, and Cauchy pressure, the ductile behavior of intermetallic was analyzed. As for the thermodynamic properties, all the phonon dispersion curves illustrate the dynamic stability of the intermetallic, and the lattice vibration energy, bulk modulus, thermal expansion coefficient, and specific heat varying with temperature change were calculated by the quasi-harmonic approximation (QHA).

Abstract:The molecular dynamics simulations were conducted to investigate the effects of random roughness on nano-cutting of γ-TiAl alloys. To simulate the actual workpiece surface, the random surface roughness was generated by a multivariate Weierstrass-Mandelbrot (W-M) function under the condition of different rake angles of cutter and depths of cutting. The equivalent height of the workpiece was used to quantify the depth of cutting. The molecular dynamics simulation results reveal that the roughness has a profound effect on the nano-cutting quality of the workpiece. Besides, the effects of roughness are also different under different cutting parameters.

Abstract:The thermal barrier coatings (TBCs) are employed to protect metallic components from high temperature gas, and their microstructure and service performance are closely related to and have the mutual effect with the preparation process and service condition. This research reviews TBCs failure mechanisms caused by different stress inducements from the perspective of thermally grown oxide (TGO) thickening, phase transformations, and sintering. Subsequently, the preparation methods of TBCs with columnar structure are summarized, as well as their functions of releasing stress during TBC service. Although the preparation process and service conditions are different, the lifetimes of TBCs prepared by different methods are evaluated by comparing with that of the standard TBCs. The long lifetime service mechanism of TBCs with column structure is summarized. This research reviews the interaction effects among the stress source, microstructure, preparation process, and service performance of TBCs, providing guidance for the advanced and durable TBCs design.

Abstract:In this paper, the local mechanical properties of the welding joint for 15CrMoR base metal and nickel based welding metal were systematically studied by means of microstructure analysis, digital image correlation (DIC) test and hardness test. Based on DIC method, the whole field strain nephogram was obtained for the welding joint of nickel based welding metal during tensile process. It was found that the strain in the welding area was small and inhomogeneous, but it was large in base metal area, while it was uniformly variated in the heat affected zone. Then, the local stress-strain curves of different regions for the welding joint were constructed, and the distribution of local mechanical properties parameters in the welding joint was revealed. Based on the microstructure analysis of welding joint, the distribution of local mechanical properties parameters was closely correlated to the distribution of microstructure. Finally, combining the distributions of microhardness and strength parameters in the welding joint, the correlation equations of them were established, which were convenient to estimate the local mechanical parameters for the welding joint of nickel based welding metal.

Abstract:The relationship between the microstructure and the creep behavior of metal films at room temperature was evaluated by nanoindentation experiment. Nanocrystalline body center-cubic (BCC) metal Mo, nanocrystalline face center-cubic (FCC) metal Ni and amorphous CuZr were selected as the study materials, and the loading rates were 0.005, 0.05, 0.1 and 0.2s-1.According to research, the creep deformation of BCC-Mo, FCC-Ni and amorphous CuZr exhibits strong loading strain rate dependence, and the main reason is related to the dominant deformation mechanism.The creep behavior of BCC-Mo is dominated by the mixed dislocation movement dominated by screw dislocation, the creep behavior of FCC-Ni is dominated by the grain boundary emission incomplete dislocation, and the creep behavior of amorphous CuZr is dominated by the shear deformation transition zone (STZ).

Abstract:In order to verify the feasibility of directly preparing high entropy alloy using natural ferrochrome ore powder, Cr, Fe, Ni, Al, Si close to the ferrochrome ore powder was selected as the base element and suppressed into billet after mixed with Ti elements doped with non-equimolar ratio, and CrFeNiAlSiTix (x=0-1.2) high entropy alloy was prepared by laser self-spreading sintering. It was characterized by OM, XRD, SEM and EDS, Vickers microhardness tester and electrochemical workstation, and its phase structure, microstructure,density and porosity, hardness, wear resistance, corrosion resistance and high temperature oxidation properties were analyzed. The results show that with the Ti content, the alloy increases BCC phase and confirms the results of intrinsic parameters.The results show that the Ti content and the experimental parameters are consistent with the experiment. Dendritic tissue decreases, petal-like tissue increases, and elements with strong Ti binding forces are mainly present in dendritic crystals. When x=1.0, the maximum alloy microhardness of 935.62 HV, maximum density of 5.01 g/cm3, porosity of 24.01%, minimum per area wear of 34 mg·cm-2, oxidation rate of 5.92×10-6 mg2·cm-4·s-1, corrosion current of 0.98 μA/cm2, annual corrosion depth of 1.01×10-2 mm/a..

Abstract:Ti6Al4V alloy is the most widely used titanium alloy in orthopaedics. Selective laser melting of porous Ti6Al4V alloy can reduce its elastic modulus, reduce the stress shielding phenomenon, and promote the growth of bone tissue, but the plasticity of the formed parts is usually low. Therefore, rhombohedral dodecahedron porous structures with unit size of 1~2 mm, aperture of 500~1200 μm and porosity of 60%~90% are designed, and the compression specimens are formed by selective laser melting technology. The mechanical properties are studied by compression simulation and experiments, and the effects of annealing heat treatment on their mechanical properties and microstructure are also studied. The simulation results show that more accurate results can be obtained by error compensation for the strut diameter of the model. The experimental results show that when the unit size is 1.5 mm, the compressive strength and elastic modulus of specimens are between 78.16~242.94 MPa and 1.74~4.17 GPa, which are similar to the mechanical properties of human cortical bone. After annealing at 820 ℃ for 2 hours, the compressive strength and elastic modulus of the specimens are basically the same as those of the formed specimens, while the plasticity is improved, so they are more suitable for orthopedic implants.

Abstract:Using 3D simulation software DEFORM-3D, the semi-solid forming process of 7075 aluminum alloy deep cavity cylinder was simulated,the effects of billet temperature, die temperature and loading speed on the forming process of cylinder were analyzed.The results show that,increasing the die temperature and billet temperature can significantly reduce the deformation resistance of billet during cylinder forming;increasing the mold temperature and loading speed can reduce the heat loss and improve the filling capacity of semi-solid billet.The optimal process parameters are as follows: billet temperature 610℃, die temperature 350 ~ 400℃, punch loading speed 15mm/s,at this time, the maximum equivalent stress value of the material is 69.9MPa.Tests have shown that,semi-solid forming is carried out under optimized process parameters. The shape of the cylinder is complete, the surface quality is high, the structure is compact and there is no forming defect.

Abstract:In traditional industries, niobium plates are usually obtained by Unidirectional-Rolling. The niobium plates obtained by Unidirectional-Rolling often show strong unevenness in grain size and texture distribution, which leads to their use in modern industries. The above has certain limitations. In this experiment, 135° Clock-Rolling and Unidirectional-Rolling were used to obtain niobium plates, and the differences in the thickness direction of the niobium plates obtained under the two process conditions were studied. The results show that 135° Clock-Rolling can help reduce the texture gradient of the high-purity niobium sheet in the thickness direction. In addition, niobium plates with a higher degree of {001} preferred orientation can be obtained under the conditions of 135° Clock-Rolling process, and after recrystallization, they still have a strong {001} preferred orientation. This texture The dominance of niobium helps to obtain a more uniform niobium plate, which is confirmed by the microhardness curve, microscopic characterization of recrystallized structure, and semi-quantitative calculation results of storage energy in this experiment. It is also worth noting that compared to Unidirectional-Rolling, the niobium plate obtained under 135° Clock-Rolling has a smaller difference in the storage energy of {111} and {100} orientations in the thickness direction, and does not show a significant energy gradient. This also helps to optimize the uniformity of high-purity niobium.

Abstract:The corrosion behavior of as-cast GH3625 alloy were studied in different corrosive media (Air、75 wt% Na₂SO₄+25 wt% NaCl and 2% SO₂+H₂O+Air) at 900 ℃ for 120 h, utilizing XRD, SEM, EDS, weight-gain measurement and thermodynamic calculation. The formation and destruction mechanism of the oxide film under different corrosive media were discussed. Results show that from the top layer to the internal structure of GH3625 alloy is divided into loose oxide layer, dense oxide layer, Cr poor zone and alloy matrix after corrosion in different media, which is mainly composed of NiO, Cr₂O₃ and NiCr₂O₄. In addition, the depth of Cr-poor zone after corrosion in corrosive medium (14μm and 11μm) is greater than that after oxidation in air (8μm). The damage degree of corrosion medium to the surface oxide film of the alloy is molten salt medium, acidic atmosphere medium and air medium in descending order. The corrosion of GH3625 alloy is mainly due to the competition between the formation and dissolution of the surface oxide film in different media. When GH3625 alloy is corroded in 75 wt.% Na₂SO₄+25 wt.% NaCl medium, the corrosion mechanism is mainly that the oxide film reacts with Cl^_- to form gas phase Cl₂ and reacts with Na₂O to form chromate Na₂Cro₄. However, when GH3625 alloy is corroded in 2% SO₂+H₂O+Air, the corrosion mechanism is mainly the continuous sulfurization and oxidation reaction of Cr, Ni and SO₂ and O₂.

Abstract:Dissolution behaviors of Cu-20%Sc master alloy in liquid Al-0.12%Zr alloy was studied in this paper. It was found that both size and areal fraction of particles bearing Sc and Al₃Zr particles decreased,the solubility of Sc,Cu and Zr in α Al increased with increase in holding time and temperature. Part of Sc atoms was odsorbed on the surface of Al₃Zr particles so that Al₃Zr particles rich Sc on surface were formed. The microstructure of the alloy with Sc and Zr after solidification was fine observably. Average grain size of the alloy increased slightly with increase in holding time and temperature. Fine microstructure of the alloy with Zr and Sc is resulted from the a lot of stable nuclei of Al₃(Zr,Sc) particles rich Sc on surface. Same as adding Al-Sc-Zr master alloy Al₃(Sc,Zr) precipitated in the Al-Zr alloy added by Cu-Sc master alloy after homogenization.

Abstract:Fe_41.5Co_41.5Zr₇B₉Cu₁ and Fe_38.5Co_38.5Zr₇B₁₅Cu₁ amorphous alloys were prepared by adding 1at.% Cu based on Fe₄₂Co₄₂Zr₇B₉ with low B content and Fe₃₉Co₃₉Zr₇B₁₅ alloy with high B content. Crystallization curves and structure of crystalline phase of the alloys by synchronous thermal analyzer (STA), X-ray diffraction (XRD) And TEM (TEM). The effects of Cu addition on the thermal stability and crystallization process of Fe₄₂Co₄₂Zr₇B₉ and Fe₃₉Co₃₉Zr₇B₁₅ amorphous alloys were investigated. The results show that the addition of Cu slightly improves the thermal stability of Fe₄₂Co₄₂Zr₇B₉ amorphous alloy, and significantly improves the thermal stability of Fe₃₉Co₃₉Zr₇B₁₅ amorphous alloy. For Fe₄₂Co₄₂Zr₇B₉ and Fe₃₉Co₃₉Zr₇B₁₅ amorphous alloys, there is obvious peak shift(XRD) at the initial stage of crystallization. For Fe_41.5Co_41.5Zr₇B₉Cu₁ and Fe_38.5Co_38.5Zr₇B₁₅Cu₁ alloys, there is almost no peak shift during the crystallization process. TEM results show that the addition of Cu improves the distribution uniformity of nanocrystals and slightly increases the grain size. The effect of Cu addition on the thermal stability and crystallization process of Fe₃₉Co₃₉Zr₇B₁₅ alloy with high B content is greater than that of Fe₄₂Co₄₂Zr₇B₉ alloy with low B content.

Abstract:In view of the urgent need of the new generation of aero-engine and heavy duty gas turbine for long life and high toughness thermal barrier coatings, a ZrO2 whisker composite YSZ spray powder with a aspect ratio of 10 has been prepared by spray granulation. The YSZ/ZrO2 whisker toughened ceramic composite coating has been prepared by SAPS technology, and the process parameters of the composite coating have been optimized. The effect of melt index on the microstructure of ceramic composite coating was studied; The formation mechanism of YSZ ceramic coating toughened by ZrO2 whisker was elucidated through the experiment of collecting single slice by slit method. The internal relationship between microstructure and thermodynamic properties of YSZ ceramic coating toughened by ZrO2 whisker was established. Based on the characteristics of whiskers dispersed in the unmelted particle area of the composite coating, the fracture toughness and thermal cycle life of YSZ / ZrO2 whisker toughened ceramic composite coating are doubled compared with nanostructured YSZ coating.

Abstract:In this paper, 6.5 mm thick Al/Cu composite plates composed of the Cu cladding plate with 30% were selectedfor friction stir welding（FSW）.The influence of welding position（Cu cladding plate was placed upon and Al base plate was placed upon the Cu cladding plate）on the welding process was investigated emphatically. In addition, the influence of thermo-mechanical coupling on the material flow of Cu clad plate, the microstructure evolution mechanisms in the welded joint, especially the interfacial microstructure were analyzed combined with numerical simulation technology. The results show that when Al base plate was placed upon the Cu cladding plate, the tunnel defect was created under the process parameters that were the plunge depth of 0.2 mm, the rotation speed of 900 r/min and the welding speed of 150 mm / min in the weld joint, because of the weakly influence of the action of thermal mechanical coupling on the Cu clad plate, the weakly interaction of upward migration, the lower temperature effect on high-melting point high-conductivity copper clad plate. When Cu cladding plate was placed upon the Al base plate, the joint with perfect appearance could be prepared under the same welding parameters. Due to the temperature variations of the advancing side and the treating side during the FSW process, the small number of Al-Cu intermetallic compound interlayer were formed in the Cu/Al interface of the lower temperature treating side and hook zone the thick Al-Cu intermetallic compound interlayer were formed in the Cu/Al interfacein the advancing side. The average tensile strength of the joint is 85.2 MPa, which is about 62.7 % of the tensile strength of the base metal.

Abstract:In the cryogenic temperature environment, the movable parts of traditional crystalline components or equipment will be stuck, cracked, characteristic change and even brittle fracture. The influence of cryogenic extreme environment such as temperature mutation and high strain rate shocks on metallic glass severely restricts its application in industry. Due to special properties of higher strength and better plasticity at cryogenic temperature, bulk metallic glass has great application advantages in extreme conditions such as polar scientific research and aerospace. A (Zr_0.6336Cu_0.1452Ni_0.1012Al_0.12)₉₇Tm₃ bulk metallic glass was chosen in this paper, and the effect of cold-heat treatment time on the microstructure, mechanical properties and electrochemical corrosion resistance were studied. It is found that when the treatment time is set from 30 min to 90 min, the crystallization volume fraction of specimens increases from 2.3% to 4.0%, and the yield strength increases from 1701 MPa to 1810 MPa. The smaller self-corrosion current density and larger electrochemical impedance in 3.5 wt.% NaCl solution indicate that the bulk metallic glass has excellent corrosion resistance after cold-heat treatment. This study provides a strong theory support for the application of bulk metallic glasses in cryogenic temperature extreme environment fields.

Abstract:The mechanical properties and microstructure evolution of novel Al-Mg-Zn alloy during quasistatic and dynamic impact processes were investigated by Gleeble-1500, separated Hopkinson pressure bar(SHPB), optical microscope, scan electron microscope and transmission electron microscope. The Al-Mg-Zn alloy exhibited a global strain hardening effect in quasistatic impact. The dynamic yield strength increased first and then decreased slightly with the increase of strain rate. The grains of alloy deformed to different degrees with the change of strain rate, and the grains deformation inhomogeneity became more serious with the increase of strain rate. The morphology, density and size of precipitates varied significantly before and after dynamic impact with 4800s_^-1.

Abstract:In this paper, two coatings (Zr(84.61 at.%)Cr/Zr(17.39 at.%)Cr/Al₂O₃ and Al₂O₃ without ZrCr gradient interfacial layer) were fabricated by intermediate frequency magnetron sputtering and supersonic plasma spraying on zirconium alloy (Zr-4) substrate. The influence of ZrCr gradient interfacial layer on the interface microstructure, adhesiveSstrength and thermal shock resistance of two coatings was studied by XRD,SEM and HRTEM. The results show that the adhesiveSstrength of Zr-4/ZrCr /Al₂O₃ system can be significantly increased to 50.3±2.52 MPa about 46% higher than that of Zr-4/Al₂O₃ system by adding ZrCr gradient interfacial layer. In the process of thermal shock test, It is found that the interface of Zr-4/ZrCr/Al₂O₃ system remian intact because of its higher adhesiveSstrength and formation of dense Cr₂O₃ in ZrCr gradient transition layer protecting Zr-4 substrate from oxidation. The interface of Zr-4/Al₂O₃ system, however, appears obvious cracking or even peeling behavior, the main reason is that thermal stress concentration in the interface of Zr-4/Al₂O₃ system leads to Zr-4/Al₂O₃ interface cracking. In the process of subsequent thermal shock test, the formation of loose ZrO₂ at the Zr-4/Al₂O₃ interface cracking confirmed by HRTEM and line scanning results was the root cause for aggravating the large-scale peeling to failure of the coating.

Abstract:The Mg2Sn thermoelectric films with a tiny metal Mg phase are prepared using a Mg-Sn alloy and a high pure metal Mg target by magnetron sputtering alternately. The phase composition, surface and cross-sectional morphology, element content and distribution of the deposited films were studied by X-ray diffraction (XRD) pattern, scanning electron microscope (SEM), and energy diffraction spectrometer (EDS). The resistivity and Seebeck coefficients of the deposited films were measured by using the Seebeck coefficient/resistance analysis system LSR-3. And the power factor of the Mg2Sn film with different Mg contents was studied. The XRD shows that the deposited film is composed of nano-sized Mg2Sn phase with cubic anti-fluorite structure and a small number of nano-sized metal Mg phase. The content of nano-sized metallic Mg phase increases with increasing Mg target sputtering time, and the resistivity and Seebeck coefficient increase first and then decrease, which is due to the phase interface between the nano-sized metallic Mg phases and substrate phases.The nano-sized metal Mg phase with proper quantity exists in the Mg2Sn film, which is beneficial to improve the Seebeck coefficient. The deposited Mg2Sn films containing proper quantity nano-sized metallic Mg phase possess a higher power factor due to their high Seebeck coefficient and an appropriate resistivity. The layered Mg2Sn film can significantly increase the Seebeck coefficient and the power factor of the film is significantly improved even if the resistivity increases.

Abstract:2 mm thick 5A02 aluminum alloy plate and 2 mm thick TC4 titanium alloy plate were jointed by refill friction stir spot welding (FSpW). The effects of different process parameters on the microstructure and mechanical properties were investigated by changing dwell time and refilling speed. Results show that within the selected process parameters, the sound joints were formed. The fine grains are formed in the stir zone and the grains in the heat thermo-mechanically affected zone are limited to satisfying extent. The atomic diffusion distance at the interface of the sleeve affected zone is larger than the pin affected zone. The atomic diffusion distance and the intermetallic compound (IMC) layer thickness at the interface of the joint are about 1 μm when dwell time is 6s. With the increase of the refilling speed, the tensile shear load of the joint increases. However, the changing trend is not obvious as the dwell time is kept constant at 2s. The tensile shear load strength is the minimum of 4861N at the welding condition of the refilling speed 30mm/min and dwell time 6s. When the refilling speed is 90 mm/min and dwell time is 6s, the tensile shear strength reaches the maximum of 6617N. The shear fracture mode is observed while the macroscopic fracture surface is relatively flat. The microscopic fracture is consisted of dimples.

Abstract:In order to improve the high temperature oxidation resistance of niobium alloy, a molybdenum layer was firstly prepared on the surface of niobium alloy by electrodeposition method with uniform rotating cathode, and then the silicide composite coatings were obtained by the halide activated pack siliconizing. The formation and microstructure of as-deposited molybdenum layer and silicide coating were studied, and the high temperature oxidation behavior of C103 alloy with or without coating was compared and analyzed. The results showed that the current efficiency during electrodeposition was twice as high as that by conventional electrodeposition. The prepared molybdenum layer was amorphous with a cellular structure. After pack siliconizing, mainly MoSi2 and NbSi2 predominated the surface layer and intermediate layer of the composite coatings, respectively, and the composite coatings exhibited a strong interfacial bonding to the substrate. Thermally exposed to 1200 °C, the coated samples showed parabolic rate constants of 1.83×10-2 mg2cm-4h-1 and 8.08 mg2cm-4h-1, respectively. By comparison, a higher parabolic rate constant about 5.87×103 mg2cm-4h-1 was detected in the bare alloy, and pesting oxidation was found in the bare alloy only 10 h exposure. The composite coatings present excellent resistance to high temperature oxidation due to the formation of SiO2 surface scales during thermal exposure.

Abstract:Al-Ti-Ce master alloy was prepared by aluminothermic reduction of TiO2 and CeO2 in Na3AlF6-NaCl-KCl electrolytic system. The effects of reaction time, reaction temperature, electrolytic composition (mass percent of Na3AlF6) and K2TiF6 dosage on the phase structure and chemical composition of Al-Ti-Ce master alloy were studied, respectively. The experimental results show that there are only three phases in the Al-Ti-Ce master alloy, which are ɑ-Al, Al3Ti and Ti2Al20Ce, at the range of process parameters used in each experiment, and the optimal single-factor parameters in preparing Al-Ti-Ce master alloy by aluminothermic reduction are as follows: reaction time 90 min, reaction temperature 850 ℃, mass percent of Na3AlF6 40 wt%, K2TiF6 dosage 20 mol%. The results of thermodynamic analysis further show that the main several chemical reactions proposed in this study are feasible on the checked experimental conditions.

Abstract:The temperature curves and the images of solidification for Fe40Ni40B20 (at%) eutectic alloys were detected and recorded by using the infrared pyrometer and the high speed video (HSV). Combining with the previous DSC results，three evolution regions can be deduced for the microstructure with initial melts undercoolings (ΔT): ΔT =170K-230K, the rod eutectic colonies of metastable phase (Fe, Ni)23B6 and γ-(Fe, Ni) forms initially which gives birth to the first recalescence in temperature curve and HSV Images. Subsequently, the stable phases γ-(Fe,Ni) and (Fe,Ni)3B solidify from remaining melts and the metastable phases remelt which causes the second recalescence; ΔT=230K-260K, the rod eutectic colonies or near uncoupled two phases with metastable phase solidify from undercooled melts initially and transform into stable phases during further cooling, the stable phase form epitaxially from the matrix phase of the initial colonies almost simultaneously. Therefore only one sharp recalescence peak can be obtained from temperature curve which corresponding to one brightening process from HSV. ΔT=260K-300K, The uncoupled growth between γ-(Fe, Ni) and (Fe,Ni)23B6 appears and forms the anomalous eutectic structure. The severe decomposition of metastable give rise to the inflexion on the temperature curve and the second recalescence in HSV images. The solidification rates of metastable phase were calculated by using BCT model which coincide with the rates first recalescence in the region of medium and large ΔT. With further increasing ΔT, the recalescence rates deviate from the model results and keep almost steady values due to uncoupled growth of two phases.

Abstract:The efficient extraction of iron from nickel slag have attracted more recent attention in the recycling of nickel slag. In this paper, FACTSAGE software was used to predict the formation and preferential precipitation behavior of magnetite crystal in molten nickel oxide slag. The precipitation and growth of magnetite crystal in molten nickel oxide slag during continuous cooling were in-situ observed by high temperature laser confocal microscope (HT-CLSM), and the growth characteristics of magnetite crystal under 5~50 ℃/min cooling rate was studied. The morphology, phase and composition of the samples were characterized by SEM-EDS, XRD and ICP. The results show that magnetite crystals are preferentially precipitated from the melt during continuous cooling, and the initial precipitation temperature is between 1430~1450 ℃. At low cooling rate (5~15 ℃/min), the initial nucleation and precipitation of the crystals are slow, and the grains grow stably at 1200~1400 ℃, with an average growth rate of 0.141 μm/s, the final grain size is more than 100 μm. High cooling rate (25~50 ℃/min) can promote the rapid nucleation and precipitation of magnetite crystal at the initial stage of growth, but the stable growth rate is small, and the final grain size is 20~30 μm.

Abstract:In order to study the influence of the grain orientation and grain morphology of Zr-4 on the stress distribution of the alloy matrix at 500℃, the grain deformation of the Zr-4 has been simulated by the finite element method according to three different grain morphology models with a variable of the different (11-20) oriented grains’ proportion. And the stress that acts on the matrix when the oxide film is formed is applied to the simulation as the load. The simulated results show that the grain morphology and the proportion of oriented grains have obvious influence on the internal stress distribution of the matrix grains. With the increase of the proportion of (11-20) oriented grains (14.6%-85.4%), the stress concentration in the Zr-4 matrix becomes more obvious, and the stress concentration will promote the failure of the Zr-4 during corrosion. The more likely to the equiaxed crystal of the grain, the more homogeneous the stress distribution is in the model, and the less of the stress value is, which is beneficial to improve the corrosion resistance of the alloy.

Abstract:Zr-0.75Sn-0.35Fe-0.15Cr-xNb (x=0, 0.15, 0.50, 1.00, wt.%) alloys were smelt and parpared to plate specimens a in this paper. The high temperature steam oxidation behavior of four zirconium alloys at 800~1200 ℃ under simulated LOCA conditions was studied, and the cross-sectional microstructure was analyzed by metallographic microscope. The results show that the gain weight after oxidation of the four zirconium alloys does not have consisitent trend with the change of Nb content, and the oxidation kinetics is mostly linear. Only the oxidation kinetics of the alloy with 0.5% Nb at 1000 ℃ has two transitions, that is, from linear law to power exponential law and then to linear law. The transformation temperature of the matrix in zirconium alloy decreases with the increase of Nb content, while the phase transition behavior of its oxides does not show consisitent trend with the change of Nb content, it shows that the influence of Nb content on the phase transformation behavior of zirconium alloy and oxide is more complicated than that of the alloy. When the oxidation temperature is 800 ℃, 1000 ℃ and 1200 ℃, the cross-sectional structure of the oxidized sample is: ZrO2 and α-Zr(O), ZrO2, α-Zr(O) and prior β-Zr layer, ZrO2 and α-Zr(O). The thickness ratio of each layer of the cross section of the 800 ℃ oxidized sample does not change with the Nb content. The proportion of the thickness of the α-Zr(O) layer in the cross-section of the oxidized sample at 1000 ℃ increases with the increase of the Nb content. The proportion of the thickness of the prior β-Zr layer is just the opposite, and there is a finger-like intrusion of α-Zr(O). The ratio of the thickness of the microstructure of the cross-section of the oxidized sample at 1200 ℃ varies with the Nb content more complicated. It shows that Nb can promote the transformation of β→α-Zr(O).

Abstract:The effects of Ti-Nb microalloying on the microstructure and mechanical properties of an ultra-pure 30% Cr super ferritic stainless steel were studied by means of optical microscope (OM), scanning electron microscope (SEM) and transmission electron microscope (TEM). The results show that the inclusions in the matrix of ultra-pure material are mainly composed of Cr-rich oxides with approximately size of 2~6 μm. With Ti-Nb addition, Cr-rich oxides are transformed into Ti-O-N-rich composite oxides with approximately size of 1~4 μm. Moreover, the nano-scale (Ti, Nb)(C, N) precipitations are formed in the matrix with Ti-Nb microalloying. It is worthy of noting that the strongly growth inclination of ferrite grain is the unique feature for the ultra-pure material during microstructure evolution. Ti-Nb microalloying can apparently refine the microstructure by weakening the migration rate of grain boundary, and it can also promote the room temperature strengthen and hardness. Meanwhile, the sensation of room temperature elongation of material on grain size is enhanced by Ti-Nb microalloying. In addition, Ti-Nb microalloying has the double effect on the impact toughness for the ultra-pure material. On the one hand, the toughness can be improved by refining the grains, on the other hand, brittle inclusions formed in matrix apparently deteriorate the toughness of ultra-pure material, especially for the toughness at low temperature。

Abstract:Al₂O₃ ceramics have received widespread attention due to their high strength and corrosion resistance. However, its wide application is limited due to its relatively poor toughness. There are many ways to toughen Al₂O₃ ceramics. This article uses micron ZrB₂ to toughen alumina ceramics, discusses the sintering process of composite ceramics, and studies the influence of process parameters on the mechanical properties and toughness of composite ceramics. The results show that the best process parameters of the two ceramics obtained by the single factor method are pure α-Al₂O₃ ceramic sintering temperature of 1500℃, molding pressure of 450MPa, holding time of 8h, ball-to-battery ratio of 1/2, and holding time of 10min; ZrB₂ (wt, 20%)+α-Al₂O₃ (wt, 80%) multiphase ceramic sintering temperature is 1450℃, molding pressure is 450MPa, holding time is 8h, ball-to-battery ratio is 1/2, and pressure holding time is 10min. Among them, the molding pressure, sintering temperature and holding time have the greatest influence on the hardness and density of the composite ceramics. The addition of ZrB₂ can increase the fracture toughness of pureα-Al₂O₃ ceramics from 5.2±0.3MPa.m^_1/2 to 6.7±0.2MPa.m^_1/2 while lowering the ceramic sintering temperature.

Abstract:The effect of different heat treatment temperatures on microstructure and fracture toughness of TC4 titanium alloy fabricated by Selective Laser Melting (SLM) was studied. The results show that the microstructure is characterized by a large number of acicular martensite α" phase and β phase. The longitudinal section is characterized by columnar crystals growing along the forming direction. The angle between the acicular martensite α" phase and the forming direction is about 45o. After heat treatment, the acicular α "phase is transformed into lamellar α phase, forming α+β lath structure. With the increase of heat treatment temperature, the α lamellar coarsened gradually, the zigzags of crack propagation path increased, and the fracture toughness gradually increased from 43.1 MPa?m1/2 to 109 MPa?m1/2。.

Abstract:As a new generation of semiconductor materials, CdMnTe material has high application value in the field of nuclear radiation detection. In this paper, Te solution vertical Bridgman method was used to grow Cd0.9Mn0.1Te: V crystal to study the optical and electrical properties and the distribution of deep-level defects of the Cd0.9Mn0.1Te: V crystal. UV-VIS-NIR spectroscopy analysis shows that the band gap in the middle and tail of the ingot is 1.602 eV and 1.598 eV. The photoluminescence spectral analysis shows that the (D0,X) peak of the crystal is sharp and the half-width is small, indicating that the defect or impurity content is low and the crystal quality is superior. The room temperature I-V test, shows that the resistivities of the middle and tail crystals are 2.85×1010 Ω?cm and 9.54×109 Ω?cm, and leakage currents 3 nA and 8.5 nA, respectively. The Hall test shows that the conductivity type of the crystal is n-type. The energy of the trap peak and the defect concentration in the Cd0.9Mn0.1Te: V crystal are studied by heat induced current spectroscopy. The values of the deep donor levels (EDD) derived from the Te2+ Cd in the middle and tail samples of the ingot are 0.90 eV and 0.812 eV, respectively. Does the deep donor level EDD make the Fermi level in the center of the forbidden band and thus to present a high resistivity.

Abstract:In order to illustrate the evolution process and working mechanism of the cerium–tungsten electrode of the high-power pulsed xenon lamp during operation, the cathode surface morphology of the high-power pulsed xenon lamp running for different times, the evolution of the valence state of cerium and its concentration–depth distribution have been studied using a metallurgical microscope, scanning electron microscope (SEM), X-ray photoelectron spectroscopy (XPS) and other methods. The results show that a large number of cracks and ablation of different degrees appear on the working surface of the cerium–tungsten electrode; the degree and depth of the cracks and the ablation depend on the running times; and the crack and ablation are more serious with more working times. As the running time increases, the cerium on the cathode surface diffuses to the working surface of the cerium–tungsten electrode, with the content of cerium increased for a uniform distribution. Through the analysis of Ce3+/ Ce4+ ratio, it has found that the surface activity of the cerium–tungsten cathode running 6466 and 10083 times is in a better state; and the surface activity layer of the cerium–tungsten cathode running 14486 times is significantly reduced, and the electrode is approaching its service life.

Abstract:Powder sherardizing has the advantages of good corrosion resistance, high bonding strength with the matrix, and low melting point of the material. However, improving the quality of the powder zinc layer and optimizing the performance of powder zinc layer are still the aspects that need to be studied. In this paper, different doping amounts of rare earth element La (mass fractions of 0%, 1.3%, 2.7%, 4.0%, 5.3%) were added to the sherardizing agent for surface sherardizing treatment of metal structural parts. Use SEM to observe surface morphology, XRD to determine phase and proportion, confocal laser scanning microscope (CLSM) to generate ultra-high resolution 3D surface morphology images to evaluate surface roughness characteristics, nanoindentation (Nano Indenter G200) study the hardness of the powder zinc layer to evaluate its mechanical properties.The results show that adding 4.0% rare earth element La to the sherardizing agent can better improve the microstructure of the infiltrated layer, increase the columnar and compact δ phase in the permeable layer to make the structure of the layer fine and compact, and reduce the occurrence of defects such as pits and cracks, thereby improving the uniformity of the layer. The hardness of the layer in the thickness direction is improved, and the hardness distribution is more uniform.By measuring the open circuit potential (OCP), polarization curve (Tafel) and electrochemical impedance spectroscopy (EIS) of the material, it is shown that the corrosion resistance of the layer formed by adding 4.0% La element is better.

Abstract:By increasing the surface area of a material, the highly dispersed active components can be promoted, the electron migration of the catalyst can be accelerated, the acid level on the material’s surface can be changed, and the catalytic activity can be greatly improved. As a result, the preparation of catalytic materials with large specific surface area has become a research hotspot. Although many studies have emphasized the importance of material surface changes for catalytic performance, there is currently a lack of systematic research that can reveal the structure–activity relationship between specific surface area and catalytic activity. Furthermore, several studies have proven the structure of the large specific surface area material evolution mechanism and the performance impact. The construction of key structural characteristics affects catalytic activity, thus, realizing the controllable preparation of catalytic materials. In this review, the different preparation methods, physicochemical mechanism, characteristic analysis, and preparation challenges of catalytic materials with a large specific surface area are systematically summarized, and future development is prospected. In addition, the influence and limitation of morphology, scale, and elemental characteristics on the preparation of catalytic materials with a large specific surface area were emphasized.

Abstract:Titanium and its alloys with low density, high strength, good corrosion resistance, good biocompatibility and so on are widely used in the fields of aerospace, marine engineering, petrochemical industry, biomedical, electronic engineering etc., and it is a very important strategic metal after steel and aluminum, known as the "third metal", "space metal" and "marine metal". Porous titanium is a kind of structural and functional integrated material with dual properties of both porous material and titanium, and it is also an indispensable key supporting material in modern high-tech field. The paper reviewed the preparation processes of porous titanium, including powder metallurgy techniques (loose sintering, die compaction process, space holder method, slurry forming technique and additive manufacturing process), and chemical synthesis (reaction sintering, combustion synthesis, calciothermic reduction, dealloying), and the application status of porous titanium was briefly described in the fields of biomedical, filtration & separation, and electrochemistry, etc. Pore structure of porous titanium is the key factor affecting its applied properties, so it should be strengthened to control accurately the pore structure and to study its coupling mechanism with the applied conditions. Furthermore, the design and preparation technology of porous titanium with ultra-lightweight and ultra-high strength should be developed through the interdisciplinarity of materials, mechanics and mathematics.

Abstract:A novel flux-containing 4047 composite brazing filler metal was prepared by powder forging method. The microstructure and brazing performances of the self-made composite filler metal, commercial flux-cored and imported brazing filler metal were investigated comparatively. Experimental results showed that there are two endothermic peaks in the melting curve of the self-made composite filler metal, and the melting point of flux was relatively lower than that of the 4047 filler alloy. The spreading area of the self-made composite filler metal was 363 mm2, which was close to that of imported filler metal (353 mm2) and was significantly larger than that of flux-cored ones (311 mm2). Under the environmental conditions of 85% humidity and 35 ℃, the self-made and imported filler metals showed excellent moisture absorption resistance, while the flux-cored one showed a remarkable increase in mass due to moisture absorption of flux. The moisture absorption rates of the flux-cored ones placed in humid environment for 72 h, 144 h and 216 h were 3.88%, 4.02% and 4.27%, respectively. The results of microstructure analysis showed that the flux particles of the self-made composite filler metal were small in size and evenly distributed, which were firmly wrapped in the matrix of the 4047 filler alloy. The average fracture strength of the brazed AA6061/AA3003 dissimilar lap joints was 107.5 MPa, and the fracture position was located in heat-affected zone of the AA3003 side. The dense structure of the brazed seam showed that the self-made composite filler metal has good brazing performance and high brazed rate.

Abstract:To explore the optical functional characteristics and bionic application potential of morpho menelaus wing scale, the responsive optical performance test and microstructure characterization were carried out, and the visual bionic model of wing scale was constructed. Furthermore, the mapping relationship between the multi-scale hierarchical micro/nano structure and the response functional characteristics in the visible and near infrared bands was revealed. The upper and lower scales of the wing have periodic fine structures, and the ridge structures are stacked into comb-like stack structure and tower-like grating structure by chitin lamellae, respectively. Rayleigh scattering, multilayer interference, photonic band gap and other optical effects make it with sensitive color changing response characteristics to the changes of external media filling and light incidence angle. Moreover, the reflectivity of near infrared band is adjustable. The unique optical properties of morpho menelaus wing scale can provide a new idea for the development of bionic stealth functional materials and components with adaptive color change and variable emissivity.