Abstract:The oxidation behavior, oxidation morphology, and oxidation products of pure Ti joint welded by tungsten inert gas welding technique at 550 °C for different durations (2, 4, 6, and 8 h) and those at different temperatures (650, 750, 850, and 950 °C) for 4 h were investigated. Results show that at 550 °C, the oxidation time has a slight influence on the oxidation behavior of welded joint. The oxidation temperature has a significant impact on the oxidation behavior, and the higher the temperature, the more severe the oxidation of welded joints. The oxidation kinetics is very close to the quasi-linear law at low temperatures. With increasing the temperature, the oxidation rate is increased exponentially. Additionally, the oxidation products generated on the surface of welded joint are TiO₂ with anatase and rutile structures, and the temperature barely has effect on the TiO₂ type. The oxidation process of pure Ti welded joint can be described as follows: oxygen atoms are absorbed on the surface; oxides preferentially nucleate in the defective zone; oxides grow laterally and the oxidation film becomes thicker. At relatively higher temperatures, the cracks or voids appear in the oxidation film, which become the transmission channels of O atoms, leading to the high diffusion rate of O and Ti atoms and high oxidation rate.

Abstract:Ti6Al4V specimens prepared by electron beam selective melting were heat-treated for 1, 3, 5, 7, and 9 h, and the Tafel and electrochemical impedance spectroscopy experiments were conducted to discuss the behavior and mechanism of electrochemical corrosion. Through the modification mechanism analysis of corrosion performance, it is found that the more the <111> crystal orientations, the greater the proportion of small-angle grain boundaries, the larger the grain diameter, and the better the corrosion resistance. The specimen after heat treatment for 5 h has the most uniform <111> crystal orientations. The proportion of small-angle grain boundaries is the highest of 56.2%, the grain intercept is 5.252 μm, and the corrosion resistance is optimal with corrosion current of 0.037 μA/cm².

Abstract:A new type of near-β titanium alloy (Ti555211) was investigated. This alloy has excellent plasticity, high specific strength, and excellent comprehensive properties, which is widely used in the aerospace and chemistry industries. Through the 3×3 orthogonal experiments, the influences of different stages of two-step annealing treatment (solution temperature, aging temperature, aging time) on the mechanical properties and microstructures of Ti555211 titanium alloy were investigated. Results show that with increasing the solution temperature and decreasing the aging temperature, the alloy strength is increased. The elongation is increased with decreasing the solution temperature and increasing the aging temperature. After treatment of 820 °C/2 h/air cooling and 580 °C/12 h/air cooling, the alloy has better plasticity, and its tensile strength reaches 1333 MPa, which is higher than the strength index (1080 MPa) of similar alloys by 20%. The elongation of the Ti555211 titanium alloy is 12%, which is higher than the plasticity index (5%) of similar alloys by 140%.

Abstract:In order to investigate the effect of γ/α₂ phase interface on the deformation mechanism and mechanical properties of TiAl alloy during bombardment process, the supersonic fine particle bombardment of dual-phase TiAl alloy was simulated by molecular dynamics. Results show that the impact deformation mechanisms of γ/α₂ models with different thickness ratios are different, and the deformation is mainly concentrated at the γ phase and interface. With decreasing the γ phase thickness, the dislocations in contact with the phase interface are firstly absorbed by the mismatched dislocation network, then they are nucleated at the phase interface, and eventually the dislocations pass through the phase interface, entering the α₂ phase. Shockley dislocation is the main dislocation type in the impact process, and incomplete stacking fault tetrahedron forms in the specimen. After impact, uniaxial tensile simulation and nano-indentation simulation were conducted to measure the strength and surface hardness of the specimens. The main deformation mechanisms of specimens with different thickness ratios are the phase transformation, twins, and stacking faults during tensile process. Compared with other specimens, TiAl alloy with thickness ratio of 1:3 has the highest yield strength, the highest hardness, and the highest elastic modulus after impact.

Abstract:To study the intricate mechanical behavior of ultrafine-grained(UFG) pure titanium under high temperature and high strain rate loading, a model that can accurately describe its dynamic mechanical behavior was established. The dynamic impact test of UFG pure titanium was carried out at loading temperatures of 300~450℃ and strain rates of 2000~3000 s-1, the true stress-strain curves were also obtained. The results show that under the studied conditions, the true stress-strain curves show obvious double stress peaks, the annihilation and rearrangement of dislocations at grain boundaries and the subsequent formation of adiabatic shear bands(ASB) are the main factors for the two stress reduction. UFG pure titanium shows positive strain rate sensitivity and negative temperature sensitivity. Considering strain hardening effect, strain rate hardening and thermal softening effect, a modified Johnson-Cook(J-C) constitutive model and a BP artificial neural network(BP-ANN) model are proposed, and the accuracy of the two models is analyzed. The results show that the BP-ANN model can better predict the dynamic mechanical behavior of UFG pure titanium, the correlation coefficient can reach 0.97065, and the average relative error is only 4.63%.

Abstract:The laser welding processing of 10mm thickness TA5 titanium alloy by using10KW high power fiber laser was syudied. The high speed photography shows that when the laser power reaches 3~4KW, the plume become serious, and the splash and soot increase obviously. The weld metallography test shows that the weld section is "wedge-shaped" when the laser power is low, while the weld section becomes "funnel shaped" when the laser power is more than 6KW.When the laser power is set 10KW~11KW ,and the welding speed is 1100~1500mm/min，an excellent "Key-holding" welding joint is obtained，and the welding seam become typical high-energy beam joint shape with a big ratio of depth to width is up to 2:1. RT and PT test of the weld seam show that NDT standard can be met.The mechanical test shows that the strength of the welded joints can reach 800Mpa, and the bending standard can be met，The fracture dimple is obvious, which indicates a ductile fracture. Metallographic test shows that the section of weld zone is "girdle-shape" morphology and the columnar crystal zones are obvious, with each columnar crystal zone showing obvious competitive growth mode. The weld zone is mainly serrated α+punctate β. The hardness test shows that the hardness of the weld zone is slightly higher than that of base metal, and the hardness of heat-affected zone is the lowest, which meets the hardness requirements of titanium alloy joint.

Abstract:The effects of microstructure and texture on the rotating-bending fatigue anisotropy of an α+β two-phase titanium alloy by β forging was investigated. The microstructure and texture distribution of forged billet in different directions and thicknesses were characterized by OM, SEM, XRD and EBSD, and the effects of microstructure and texture on the rotating-bending fatigue anisotropy were analyzed. The results show that after β forging, the alloy has the characteristics of basket-weave microstructure, the prior β grains are flattened and elongated, and there are recrystallized grains at the grain boundary. The texture of β-phase <100>// axial direction and α-phase <0001>// radial direction formed by forged billet after β forging. The rotarting-bending fatigue strength of radial direction samples is better than that of axial direction samples, which are related to the morphology and texture type of the prior β grains of forged billet. The arrangement of the prior β grains leads to different initiation of cracks and different tortuous degree of crack growth path. In addition, the α and β textures also cause the fatigue strength differences due to the difficulty of slip systems activation of samples in different directions under cyclic loading.

Abstract:The effects of three typical microstructures ( bi-modal microstructure, basketweave microstructure and lamellar microstructure ) on the high cycle fatigue properties of TB17 titanium alloy were studied, and the high cycle fatigue fracture morphology was analyzed. The results show that the TB17 titanium alloy with bimodal microstructure has the highest matching level of strength and plasticity, but its fatigue life has a bilinear relationship with stress, and its fatigue performance is not stable. The strength and plasticity of the basketweave structure are slightly worse, but it has the highest fatigue strength and fatigue ratio. The fatigue strength of lamellar structure is slightly lower than that of basketweave structure, but its fatigue ratio and tensile plasticity are the worst. When the high-cycle fatigue loading stress is in a low stress state, fatigue crack prone to inside the specimen, single source initiation, meanwhile, when it is in a high stress state, the fatigue crack tends to be on the surface of the sample and multi-source initiation. There are more secondary cracks in the basketweave microstructure, and the fatigue bands are clearer and denser, the crack propagation path is more tortuous, and more energy is consumed during propagation.

Abstract:A novel method to prepare ultrafine WC was proposed: the PbWO₄ prepared by hydrothermal synthesis was used as raw material, and WC was obtained through the carbothermic reduction-carburization process. PbWO₄ was used as the tungsten intermediate product to avoid the introduction of ammonia nitrogen reagent. The carbon reduction method can avoid the generation of water vapor and inhibit the growth of tungsten powder. Results show that more than 99.9wt% of W is extracted in the form of PbWO₄ from the Na₂WO₄ solution under the conditions of initial pH value of 7.0, reaction temperature of 160 °C, and reaction time of 4.5 h. Then, the homogeneous mixture of W and C is obtained by the carbothermic reduction of PbWO₄ at 950 °C for 3 h with the molar ratio of carbon:tungsten as 5. Pre-adding excessive carbon in the mixture can inhibit the agglomeration of tungsten powder. Subsequ-ently, the WC powder with particle size of about 60 nm is obtained by the carburization of the W and C mixture at 1200 °C for 6 h.

Abstract:In order to investigate the influence of different magnetic field strengths on the mechanical property and wear resistance of nickel-based alloy, GH99 nickel-based alloy specimen was subjected to pulsed magnetic treatment by the pulsed strong magnetic field equipment. Through the microstructure observation, the wear mechanism and strengthening mechanism of GH99 nickel-based alloy were analyzed. Results show that the applied pulsed magnetic field improves the material dislocation distribution and reduces the dispersion of residual stress on the specimen surface. At the magnetic field strength of 10 T, the residual compressive stress reaches the maximum value (-223.45 MPa). The tensile fracture of the material is mainly characterized by the ductile fracture. This is because the pulsed magnetic field treatment of the alloy produces sub-structured dislocation cells, which contributes to the fine grain strengthening effect. In addition, the surface microhardness and wear resistance of the specimen are firstly increased and then decreased with increasing the magnetic field strength from 0 T to 15 T. The dislocations inside the alloy proliferate under the pulsed magnetic field, increasing the dislocation density and resulting in the phenomenon similar to the process hardening. However, excessive magnetic field strength may lead to the dislocation plugging, resulting in severe distortion of the cell dot and deterioration of material properties.

Abstract:Amorphous SmCo thin films with thickness of 10–150 nm were deposited on the flexible polyethylene terephthalate (PET) substrates. Tensile/compressive strain was generated in the amorphous SmCo thin film when PET substrate was flattened from concave/convex shape after thin film deposition. Results show that both the normalized remanent magnetization and the squareness of hysteresis loops of SmCo/PET can be tuned by the strain. Compared with that induced by compressive strain, the tunable amplitude induced by tensile strain is larger for the amorphous SmCo thin films. Because the amorphous SmCo thin film has negative magnetostrictive property, the magnetic properties of amorphous SmCo thin film can be controlled by the mechanical strain supplied by flexible substrates. When the negative magnetostriction effect occurs, the magnetization process of amorphous SmCo thin films is hindered by the tensile strain, whereas it is promoted by the compressive strain. The amorphous SmCo/PET shows great potential in the field of flexible spintronic devices and flexible micro-nano electronic devices.

Abstract:Zn-6Sn-5Bi alloy was used to solder DP1180 steel and NdFeB permanent magnet coated with Cu and Ni, and the microstructures and mechanical properties of the soldered joints under different coating conditions were compared and analyzed. Results show that for the soldered joint of sintered NdFeB permanent magnet with Cu coating and DP1180 steel, Cu diffuses in the solder and reacts with Zn and Fe to form brittle intermetallic compounds, resulting in cracks and holes in the soldering seam. The shear strength of the soldered joint of sintered NdFeB permanent magnet with Cu coating and DP1180 steel decreases to 52.3 MPa, compared with that without Cu coating (61.9 MPa). For the soldered joint of sintered NdFeB permanent magnet with Ni coating and DP1180 steel, Ni is concentrated at the interface of NdFeB side, different diffusion layers are formed due to the diffusion of Sn and Bi, and the shear strength of soldered joint increases to 78.1 MPa.

Abstract:The effect of magnetic compound fluid (MCF) slurry on the gallium arsenide (GaAs) wafer surface after nano-precision polishing was investigated. MCF slurry was prepared by mixing CS carbonyl iron particles (CIPs), Al₂O₃ abrasive particles, α-cellulose, and magnetic fluid. Firstly, a polishing device was assembled by designing MCF unit for the generation of revolving magnetic field. Then, the spot polishing experiments were performed on GaAs wafer surface to clarify the effects of MCF components on the surface roughness R_a and material removal (MR) at different polishing positions. Finally, the scanning polishing experiments were conducted using water-based MCF slurry containing particles with different diameters. Results show that after spot polishing with water-based and oil-based MCFs, the initial surface roughness R_a of 954.07 nm decreases to 1.02 and 20.06 nm, respectively. Additionally, the depth of MR is increased linearly with prolonging the polishing time. It is worth noting that the MR depth of surface after polishing with water-based MCF is 2.5 times higher than that with oil-based MCF. Meanwhile, the cross-section profile of the polished zone shows the W shape, which indicates the non-uniform MR on the workpiece surface after spot polishing. After scanning polishing, the cross-section profile of the polished zone shows the U shape, which indicates that MR is uniform under specific experiment conditions, regardless of the MCF types. The smoothest work surface with R_a=0.82 nm is achieved using MCF with abrasive particles of 0.3 μm in diameter, and MR rate is 13.5 μm/h.

Abstract:A sliding-pressure additive manufacturing technique with low cost and high accuracy based on Joule heat (SP-JHAM) was developed for the small metal parts. The temperature field and thermal history of the system are important for the experiment analysis. In this research, a thermal-electrical-structural coupling finite element simulation model for three-dimensional SP-JHAM process was established. The temperature field variation law during manufacturing, the temperature distributions inside the wire and substrate, and the shape of isothermal surfaces were analyzed. Results show that the Joule heat is generated between the wire and roller, and the internal temperature of wire rises to 2700 °C within 0.1 s. The position of the maximum temperature is moved with the roller moving. The temperature gradient inside the wire presents the arching shape, and that inside the substrate presents the semi-ellipsoidal shape. The simulated cross-section melting regions are in good agreement with the experimental ones. Thus, the established finite element model can accurately simulate the temperature field of SP-JHAM process, which is of great significance for the guidance of mechanism investigation and actual production.

Abstract:The microstructure of materials has an effect on the properties of components. In this study, the effect of deformation on the microstructure and properties of semi-solid CuSn10 alloy was investigated. Semi-solid CuSn10 slurry was made by a self-developed enclosed cooling slope channel (ECSC) and cast into thin plates by rheological squeeze, then rolled at 350°C. The results showed that as deformation increased, casting defects such as shrinkage porosity and shrinkage cavities gradually decreased, with grains compressed and elongated, and their average thickness reduced, from 30.58 μm (undeformed) to 22.12 μm (ε=0.4). In addition, more deformation twins were found inside the primary phase with increasing deformation . As deformation increased from 0 to 0.4, a large amount of substructures and dislocation density was introduced into the CuSn10 alloy microstructure. At ε=0.4, textures [101], [111], and [001] were found in pole figures {110} and {111}. The mechanical properties of the plate, including yield strength, tensile strength, and hardness increased. At the deformation of 0.4, the three properties reached 443 MPa, 554 MPa, and 194 HBW, respectively, up by 106.1%, 66.4%, and 41.6%, compared with those without receiving deformation. But the plasticity of the plate was on the decline, and its elongation decreased to 0.82%. The changes in the alloy are mainly attributed to work hardening and refined grains produced during the rolling deformation.

Abstract:The lifespan of carbon cathode is affected by the corrosion of molten salt and molten aluminum in aluminum reduction cell, and TiB₂ coating is an ideal cathode material for aluminum reduction cells.SIn this paper, TiB₂ coatings were electrodeposited on graphite in KF-KCl-K₂TiF₆-KBF₄molten salt at 700-800 _o^C with the current density of 0.4-0.7A.cm_-2^{. T}he coatings prepared at different current densities and temperatures were analyzed by XRD, SEM-EDS, surface roughness tester and adhesion tester.SThe results show that the obtained TiB₂ coating is uniform and coherent well to the graphite substrate. Increasing the current density and the electrolysis temperature can refine the grain size of the coating and improve the compactness of the coating. A TiB₂ coating thickness of 229 μm, the preferred orientation of <110>, the surface roughness of 14.85 μm, and the adhesion between the coating and graphite substrate of 6.39 MPa is prepared by electrodeposition under the optimum condition of 0.6 A.cm_-2 ^{and 750} ℃.

Abstract:The as-cast CuSn10P1 copper alloy was pre-annealed and then prepared into semi-solid billets by cold rolling isothermal treatment strain-induced melting activation method (CRITSIMA). Using metallographic microscope, scanning electron microscope (SEM) equipped with energy dispersive spectrometer, X-ray diffractometer, electron probe and Brinell hardness tester, the effects of pre-annealing temperature on the microstructure evolution and mechanical properties of semi-solid copper alloy billets were studied. The results show that with the increase of the pre-annealing temperature, the average grain size of the semi-solid copper alloy billet increases, and the shape factor and liquid phase rate decrease; with the increase of the pre-annealing temperature, the solid solution in the α-Cu phase increases with more Sn element, the segregation of Sn element is weakened, the content of intergranular brittle and hard phase δ phase decreases, and the Brinell hardness gradually decreases. The existence of a new phase Cu_13.7Sn was detected in the semi-solid copper alloy billet, which is related to the high segregation of the intergranular Sn element. The semi-solid copper alloy billet prepared by pre-annealing at 600 ℃ for 2 h has fine and uniform microstructure and good mechanical properties. The average grain size is 68.34 μm, the shape factor is 0.78, the solid solubility of Sn in α-Cu matrix is 4.21wt%, and the Brinell hardness is 128 HBW.

Abstract:Molybdenum has high melting point, low thermal expansion coefficient and excellent stability. It has broad application prospects in plasma propulsion and electric vacuum devices so that its secondary electron emission characteristics have gradually attracted the attention of researchers. Firstly, the secondary electron yield (SEY) and secondary electron spectrum (SES) of molybdenum were studied experimentally. Then the test data were analyzed by the relevant model. Finally, the SEY model of molybdenum is established by Monte Carlo method to analyze the influence of work function on SEY. The results show that the maximum value of SEY is 1.77, which is significantly lower than that of silver-plated aluminum alloy. When the incident electron energy changes, the most probable energy of the true secondary electron peak of the SES is basically unchanged, while the position and intensity of the elastic backscattered electron peak change accordingly. Among all kinds of secondary electrons, true secondary electrons are most affected by the work function.

Abstract:Automatic riveting is an important assembly technology in the aviation manufacturing industry. The distribution of residual stress around the rivet hole after the riveting process is closely related to the fatigue performance of the riveting structure. In this paper, ABAQUS software was used to establish the finite element model of the press riveting process of the 2060-T8 Al-Li alloy plate. It was found that the residual stress on the wall of the rivet hole after the riveting process gradually decreased from the place close to the rivet head to the place close to the rivet head. With the pressure riveting force increasing from 28.5kN to 46kN, the average residual stress of the hole wall of the riveted plate with the rivet material of 2117-T4 increases by 33%, and the uniformity of the residual stress distribution along the thickness of the wall plate increases by 180%. The average residual stress of the hole wall of the riveted plate with 7050-T73 rivet material is increased by 58%, and the uniformity of the residual stress distribution along the thickness of the wall plate is increased by 184%. The fatigue crack originated near the hole wall of the riveted lower plate. With the increase of the riveting force from 32.5kN to 42kN, the fatigue life of the riveted plate with the rivet material of 2117-T4 increased by 31%~80%, and the fatigue life of the riveted plate with the rivet material of 7050-T73 increased by 6%~161%. Compared with the riveted plate with rivet material of 7050-T73, the fatigue life of the riveted plate with rivet material of 2117-T4 under the same process conditions is increased by 12%~44%.

Abstract:In this paper, a rapid and low-cost method was suggested to fabricate carbon nanomaterials-soot particles (C_H), and lead/soot (Pb/C_H) composite anode materials were prepared by powder metallurgy and mechanical alloying techniques. Oxygen evolution of lead-based anodes was improved due to high activated surface and catalytic activity of carbon nanomaterials. C_H was characterized using field emission scanning electron microscopy (FE-SEM), Fourier infrared spectroscopy (FTIR), cyclic voltammetry curve (CV) and linear scanning voltammetry curve (LSV). C_H shows a shape of many chains of nanosized with abundant carbonyl and hydroxyl groups as a excellent transfer carrier of electron and proton. The overpotential of composite anodes decreased with the conten of C_Hin lead/soot materials.The apparent exchange current density of the Pb/1.5 wt.% C_H composite anode was increased by 3 and 2 orders of magnitude compared to the pure Pb and conventional Pb/0.75 wt.% Ag anodes, respectively. The oxygen evolving overpotential of Pb/1.5 wt.% C_H composite anode was lower than that of the Pb/Ag anode and pure Pb anode by 20 mV and 133mV, respectively, under the simulated zinc electrowinning conditions, showing excellent electrocatalytic activity of oxygen evolution.

Abstract:A thermodynamic coupling finite element model of tungsten selective laser melting was established by using the ‘birth and death element’ technique to simulate the powder laying process, taking into account the material parameter characteristics and latent heat of phase transition. The temperature and stress fields of the forming parts during selective laser melting were simulated. The effects of different preheating temperatures of substrate and different support structures on the residual stress of formed parts was investigated. The simulation results show that tungsten has undergone many heating and cooling processes during selective laser melting, and the temperature distribution is not uniform. Both substrate preheating and applying support structures can reduce the residual stress of the formed part. When the preheating temperature of the substrate is 1273.15K, the residual stress of the intermediate joint of the forming part is reduced by 118.99MPa (9.96%). When the four-layer grid support structure is adopted, the residual stress of the middle joint of the forming part is reduced by 413.33MPa (34.61).

Abstract:The microstructure, mechanical properties and fracture mechanism of SP2215 austenitic heat-resistant steel tube after aging at 650 ℃ for different times were studied by OM, SEM, TEM, microhardness, room temperature impact and high temperature tensile tests. The results show that the microstructure of solid solution treated SP2215 steel is composed of austenite, a small amount of twins and undissolved NbN and Z phases. Cr23C6 preferentially precipitates at austenite grain boundaries during aging at 650 ℃, and gradually increases, coarsens and forms a continuous network with the extension of aging time. The spherical Cu-rich phase is precipitated in the austenite grains, when the aging time reaching 2012 h, the size of Cu-rich phase is about 15 nm. The room temperature microhardness in grains of SP2215 steel reaches the maximum value after aging for 50 h, and then tends to be stable, which is related to the precipitation strengthening effect of stable Cu-rich phase. SP2215 steel has obvious tendency of high temperature aging embrittlement. The room temperature impact absorption energy of sample aging for 2012 h is about 78.5 % lower than that of solid solution treated sample. The impact fracture mechanism at room temperature changes from ductile fracture to intergranular brittle fracture with the extension of aging time, which is caused by the precipitation, aggregation and coarsening of Cr23C6 at austenite grain boundary. Portevin-Le Chatelier (PLC) appears when SP2215 steel was stretched with the strain rate of 2.5×10-4 s-1 at 650 ℃, and the serrated type is Type ( A + B ). With the increase of aging time, the PLC gradually “weakens”, but the serrated type remains unchanged. With the extension of aging time, the high temperature tensile yield strength of SP2215 steel remains basically stable, the tensile strength and reduction of area gradually decrease, and the high temperature tensile fracture mechanism changes from ductile fracture to quasi cleavage brittle fracture.

Abstract:Si-modified NiAl coating has been studied by researchers due to its good performance in high temperature corrosive environment, but the effect of Si content on the high temperature oxidation resistance of the aluminide coatings has seldom studied systematically. To figure out this issue, three modified NiAl coatings with different Si contents were prepared by varying the Si/(Si+Al) ratios eg. 8 wt.%, 17 wt.% and 30 wt.% in the slurry. Phase structures and microstructures of the simple NiAl coatings and three Si-modified NiAl coatings before and after oxidation were analyzed using XRD, SEM and EPMA etc. Results show that the δ-Ni₂Al₃ and β-NiAl are the primary phases of the four aluminide coatings. Si mainly locates in the upper zone of the Si-modified NiAl coatings in the form of slilicides as CrSi₂, Cr₅Si₃ and Ni₂Si. After oxidation at 1000 °C for 500 h, the simple NiAl coating has the maximum weight gain of 1.93 mg/cm^₂, while the Si-modified NiAl coating with Si/(Si+Al) ratio of 8 wt.% has the smallest weight gain. The dopant of Si into NiAl coatings can promote the formation of protective α-Al₂O₃ film, retard the outward diffusion of refractory metal elements and improve the surface quality of the oxide film, resulting in reduced oxidation rate. However, the addition of Si reduces the Al content on the surface layer of the coating and may make the Al reservoir β phase insufficient to maintain the selective oxidation of Al in the later period of long-time oxidation. Therefore, when the Si/(Si+Al) is 8 wt.% and the Si content is 9.0 at.%, the Si modified NiAl coating possesses the best oxidation resistance.

Abstract:In this work, an A356 Al alloy based composite reinforced by core-shell structured (CS) particulates was prepared by powder thixoforming, and then further improved the comprehensive mechanical properties of the composite by T6 heat treatment. The results show that the CS particulates not only improved the ultimate tensile strength and yield strength of the composite (increased by 18.0% and 32.7%, respectively), but also rendered the composite an excellent elongation of 12% equivalent to that of the A356 alloy (10.8% and 11.3%, respectively). During the T6 heat treatment, the strength and hardness of the composite increased firstly (1-7h, i.e., under-aging) and then decreased (9-12h, i.e., over-aging) with the extension of the aging time, reaching the maximum value at 8h (i.e., peak aging). The ultimate tensile strength, yield strength and hardness of the composite at peak aging were 325.4 MPa, 254.4 MPa and 104.0 HV, respectively, which were 33.7%, 74.0% and 48.5% higher than those without the heat treatment, and the elongation was 9.4%, which was almost no decrease compared with that without heat treatment. In other words, after the T6 heat treatment, the CS particulates can improve the strength of the composite while retaining its good plasticity. Finally, the strengthening mechanisms of the composite are discussed by analyzing the size, density and type of the precipitates in the matrix of the composites aged for 8h and 12h.

Abstract:For nuclear radiation n-γ mixed field, a kind of environment-friendly ray flexible synthetic shielding material is developed. The material uses Gd as the core shielding particle and SEBS as the matrix. It has the characteristics of environmental protection, production energy saving, comprehensive protection, flexible plastic, recyclable and so on. Scanning electron microscopy (SEM) shows Gd2O3 powder distributes uniformly in granular form and has excellent dispersion in the matrix. X ray diffraction spectroscopy (XRD) and fourier-transformed infrared spectroscopy (FT-IR) show that Gd2O3 and SEBS are essentially physico-mechanical mixtures, and do not involve changes of chemical bond. The shielding results of γ ray and thermal neutrons show that with the increase of Gd areal density, the transmittances of γ ray and thermal neutrons follow the exponential attenuation law. When the Gd areal density is 0.018 4 ~ 0.291 3 g/cm2, the γ ray transmittances of material at 39 keV, 59 keV and 122 keV are 11.48%~83.73%, 2.73%~75.43% and 51.64%~93.03%, respectively. When Gd areal density is 0.018 9 ~ 0.070 9 g/cm2, the neutron transmittance of material is 35.78%~45.74%. This flexible ray shielding material effectively makes up the disadvantages of traditional shielding materials. It has potential application values in the biological shielding in ships, nuclear medical diagnosis and treatment, radiographic testing and other fields.

Abstract:As a common precious metal, Au nanoparticles (NPs) perform excellent physical and chemical properties. It’s properties are related with the microstructure, morphology and size of Au NPs. The structure and morphology of Au NPs determine their properties. The function and applications depend on properties. In the paper, the properties and applications of Au NPs were briefly introduced firstly, and the method for synthesis of common spherical Au NPs were elucidated. In addition, it is highlighted the versatile morphologies of Au NPs with different function, including rod-shaped, tubular, lamellar, flower-shaped, sea urchin shaped, polyhedron, and core/shell, etc. The approaches for synthesis of the Au NPs with different morphologies and their application were summarized in detail, respectively. Finally, the development of Au NPs in the future was prospected.

Abstract:The traditional Ag sheath has both good chemical compatibility and plastic processing characteristic with iron-based superconductors (IBS), but it possesses too low mechanical strength. Employing composite sheathes is a direct, efficient and low-cost method to prepare high strength Ba1-xKxFe2As2 conductors. In this paper, the Ba1-xKxFe2As2 multifilamentary wires/tapes with stable structure and large ductility were obtained through optimizing the sheath size, cold deformation and intermediate annealing. It is found that the shape distribution of multi-cores is uniform, and the superconducting filling factor is about 25.3-28.0% for our Ag/Nb/Cu composite sheathed Ba1-xKxFe2As2 superconductors. The magnetic critical transition temperature Tc of Ba1-xKxFe2As2 tape is up to 37.5 K, meanwhile the magnetization of hysteresis loops (M-H) shows a strong flux pinning ability. The transport critical current density Jc of Ba1-xKxFe2As2 tape is about 1.0×104 A/cm2 at 4.2 K and 2 T, and still holds 8.7×103 A/cm2 at 10 T.

Abstract:In this study, the relationship between different medium-temperature deformation heat treatment processes and the microstructure and room-temperature mechanical properties of a novel Ni-based superalloy was investigated using EBSD, SEM and quasi-static room-temperature uniaxial tensile tests. It is shown that the length fraction of annealed twins of the novel Ni-based superalloy can be significantly increased up to 40.6% after the medium temperature deformation heat treatment. The formation of annealed twins is mainly based on the "growth accident" mechanism of the grains. At the same time, compared with the mechanical properties of the solid solution + double-stage aging specimens (σ_y = 1018 MPa, ε_f = 17.44 %), the alloy annealed at 1120 °C for 30 min after 30 % roll deformation at 750 °C and double-aged, the σ_y increased by 499 MPa to 1517 MPa, while the ε_f decreased by only 4.69 %. After rolling at 750 °C for 50 % of the deformation and annealing at 1120 °C for 30 min with double-stage aging, the σ_y increases by 352 MPa to 1370 MPa, while the ε_f remains essentially unchanged. This increase in strength is mainly attributed to the combined effect of grain refinement and annealing twinning, which provides a new strengthening strategy for high performance Ni-based superalloys.

Abstract:Uranium metal and its alloys played important roles in the files of nuclear industry, working as configurational or functional materials. The corrosion behavior of them attracted people"s interest because it would greatly affect the materials" performance. Material factors, including components, microstructures, defects in body and on the surface, were the internal causes to affect the corrosion resistance of uranium materials. This paper conducted a review on how the defects of uranium materials affected their corrosion behavior. We summarized the reported works from four aspects: impurity, inclusions, microstructures and surface states. Strategies to improve the corrosion resistance of uranium materials by means of modulating these defects were also briefly discussed.

Abstract:The magnetic refrigeration as a potential alternative refrigeration technique to the conventional vapor-compression techniques is highly regarded for its high energy efficiency and environmental friendliness. The magnetic refrigeration is based on the magnetocaloric effect of magnetocaloric materials which is the critical component of a magnetic refrigerators. The application of the magnetic refrigerators depends on the performance of magnetocaloric materials, among which Mn-Fe-P-Si alloys have been attracting a great deal of attention. Mn-Fe-P-Si alloys are considered to have great promising magnetic refrigerants near room temperature due to their giant magnetocaloric effect, low material cost and tunable magnetocaloric performance. Therefore, this work reviews the recently research progress on the magnetocaloric effect and its performance modulation of Mn-Fe-P-Si alloys in order to provide a reference for the further research on the Mn-Fe-P-Si alloys as magnetic refrigerants.

Abstract:The single crystal blade laser repair technology reduced considerable cost in the aviation field. This technology is based on the additive manufacturing process, in order to grow an ideal single crystal structure through directional solidification on the single crystal substrate. At present, the mainstream single crystal blade repair technology includes the following two categories: Directed Energy Deposition (DED), Powder Bed Fusion (PBF). In this paper, the research progress of two main repair technologies is reviewed, the influence of process parameters and the mechanism of single crystal growth in the repair process are summarized, and the application potential of single crystal repair technology in the aerospace field is clarified. In addition, this paper also discusses the main challenges currently faced by single crystal blade repair then looks forward to its future development trend.

Abstract:Molybdenum is a refractory metal, which has good high temperature strength, creep resistance, thermal conductivity, corrosion resistance and low sputtering rate. Molybdenum is an important candidate material to meet the development of new generation nuclear energy technology. In the irradiation environment, ion irradiation will change the microstructure of molybdenum metal. This paper reviews the recent studies on the damage behavior of molybdenum metal by irradiation. The effects of different ion irradiation on the microstructure, surface morphology, mechanical properties and optical properties of molybdenum are analyzed. On the basis of the existing research, the future research direction of ion irradiation on the damage behavior of molybdenum metal is prospected, so as to provide reference for the development of metal molybdenum and the application of nuclear reactors.