Abstract:Micron tantalum powder (Ta) has broad application prospects in biomedical additive manufacturing and other manufacturing fields. The irregular tantalum powder was spheroidized by RF thermal plasma to improve its fluidity. The tantalum powder before and after plasma spheroidization was characterized, and the formation mechanism of satellite powder in the process of spheroidization was analyzed. The results show that the tantalum powder after plasma spheroidization has ideal sphericity and smooth surface, and its Hall fluidity and apparent density are increased from 13.6 s·(50 g)^-1 to 6.73 s·(50 g)^-1 and from 6.83 g·cm^-3 to 9.06 g·cm^-3, respectively. The spheroidization rate and spherical degree of tantalum powder can reach about 95.2% and 0.92, respectively. The formation of satellite powder in the spheroidization process is mainly caused by the collision of droplets, and with the increase in powder feeding rate, the collision probability of droplets increases, resulting in larger particle size of spherical particles due to the droplet condensation.

Abstract:Nanometer-(70?80 nm) and micrometer-sized (500?600 nm) rare-earth (RE) oxides (La₂O₃, Y₂0₃) were separately mixed with tungsten powder by a mechanical alloying method. Afterwards, the W-1.5La₂O₃-0.1Y₂O₃-0.1ZrO₂ (wt%) was prepared by cold isostatic pressing, medium-frequency induction sintering, rotary forging, and drawing. Then we performed tungsten argon arc welding (TIG) under the same welding current for 0.5, 1, and 2 h on the cathode samples containing, separately, nanometer- and micrometer-sized RE oxides. Results show that the sample with nanometer-sized RE oxides exhibits higher working stability during the welding process, and the burning loss is decreased by nearly 85.4%. Moreover, with prolonging the working time, the aggregation degree of RE oxides in different regions of the tip significantly increases. Combined with the temperature simulation by COMSOL Multiphysics, we found that the diffusion activation energy of the second phase is decreased by nearly 34%. This is because the finer second phase effectively controls the evolution of the tungsten matrix structure, thus preserving many grain boundaries as channels and promoting the diffusion of active substances.

Abstract:The structure and elastic properties of α-Zr and its hydrides were investigated by first-principle calculations and experimental methods. Considering all possible H-atom configurations, different phase models of hydrides were constructed. Results show that the stable structures of γ, δ and ε hydrides are P4₂/mmc, P4₂/nnm and I4/mmm, respectively. Calculation results suggest that ε hydride has the lowest formation enthalpy, and the phase transition sequence of γ → δ → ε is proposed. Compared with those of α-Zr, the c-axis lattice constants of hydrides become smaller, and the expansion volumes of γ, δ and ε unit cell are 12.1%, 14.8% and 17.9%, respectively. The calculated elastic modulus (E) of the three hydrides are lower than that of α-Zr, but their elastic anisotropy is higher than that of α-Zr. The elastic properties of α-Zr matrix and δ hydride were analyzed by nanoindentation experiment and the results show that E of the α-Zr matrix and δ hydride is 116.88 and 111.01 GPa, respectively. Therefore, the stress concentration is easy to occur on the hydride sides near the hydrides/matrix interface, so the hydrides are more likely to be the sources of crack and cause brittle fracture of zirconium alloys.

Abstract:Using powder metallurgy sintered billet as raw material, Mo-47.5Re (wt%) foils with the thicknesses of 0.035 and 0.030 mm were obtained by multi-pass rolling and intermediate annealing. After hydrogen annealing at 1300–1900 °C, metallurgical microscopy, SEM and EDS were used to analyze the effect of annealing temperature on characteristics of σ-phase. EDS analysis indicates that Mo:Re atomic ratio of second phase in the ND direction approaches to 1:1, and that in the RD direction is close to or lower than 1:2, so the majority of second phase in Mo-47.5Re foils is σ-phase; but Mo:Re atomic ratio of second phase in the RD direction is relatively low, even reaching 1:4. The micrograph characteristics of Mo-47.5Re foil includes large grains, few deformation twins, and larger and more σ-phase particles in grains than at the grain boundary. The number of σ-phase in 0.035 and 0.030 mm thick foils increases first and then decreases with rasing annealing temperature. After annealing at 1300 °C, σ-phase number of 0.035-mm- sample reaches the maximum and the grain size is significantly reduced, while 0.030-mm-sample shows this phenomenon at 1500 °C. After annealing at 1900 °C, a few small-sized σ-phase particles remain in the RD direction of 0.030-mm-sample, and all σ-phase particles in the ND direction of 0.030-mm-sample and those in RD and ND directions of 0.035-mm-sample are totally redissolved and disappear. In as-rolled and relatively low-temperature annealed samples, such as 1300 °C, most σ-phase particles have irregular polygonal morphology, and a few of them are spherical. After annealing at 1500 °C and higher temperatures, σ-phase particles in some samples exhibit a cube shape.

Abstract:Different-temperature Cu/NbTi cladding extrusion was put forward where Cu and NbTi are different in temperature during plastic deformation. Different-temperature Cu/NbTi cladding extrusion can significantly lower the deformation temperature of Cu cladding layer so as to reduce the difference in yield stresses between Cu cladding layer and NbTi alloy core, which contributes to accommodating the deformation of the two metals. Rigid viscoplastic finite element method was used to simulate different-temperature Cu/NbTi cladding extrusion in order to reveal the interface compatibility between Cu cladding layer and NbTi alloy core, where various cone angles of bottom die, including 60°, 120° and 180°, were adopted. The results show that increasing the cone angle of bottom die contributes to reducing the relative elongation between Cu cladding layer and NbTi alloy core, which is conducive to the interface bonding between Cu cladding layer and NbTi alloy core. According to the optimal parameters from finite element simulation, Cu/NbTi cladding extrusion die with the cone angle of 180° can be used to implement Cu/NbTi cladding extrusion experiment. The experimental results show that stable flow of metal takes place during Cu/NbTi cladding extrusion, where Cu cladding layer and NbTi alloy core present compatible deformation and the relative elongation between them is small. The experimental results agree well with the simulated ones.

Abstract:In order to investigate the intergranular reaction mechanism during sintering of molybdenum-copper powders with submicron components, a Mo-15Cu composite with an intergranular reaction layer was prepared by a submicron-activated layer method. The histomorphology, connectivity and structural characteristics of Mo-15Cu alloy were characterized by X-ray diffracto-meter (XRD), scanning electron microscope (SEM), energy dispersive spectrometer (EDS), transmission electron microscope (TEM), and high-resolution transmission electron microscope (HRTEM). The effect of submicron-activated layers on the intergranular reaction of Mo-15Cu composites was investigated. The results show that the submicron-activated layer with a thickness of 0.5 μm is formed by adding 8wt% submicron powder. The submicron-sized Mo particles change the intergranular reaction mechanism through flow and diffusion, forming an intergranular reaction layer with a thickness of about 5 nm and achieving metallurgical bonding.

Abstract:Tungsten-fiber toughening is an effective way to improve the brittleness of tungsten materials. In this paper, a continuous tungsten fibers-toughened tungsten composite with refractory metal molybdenum as the interfacial coating was prepared by spark plasma sintering technology. The tensile brittle-to-ductile transition temperature of the composite was studied, and the influence of molybdenum coating on the fracture mode of the Wf/W composite were analyzed and discussed. The tensile test results show that the composite is brittle fracture at 400℃ and below. Many curved cracks are formed until 400℃ at the interface between fibers and matrix, indicating that the coating has signs of weakening the bonding strength of the matrix-fiber interfaces. The composite exhibits toughness at 500°C, which mainly comes from the pseudo-plasticity by fibers. Molybdenum as an interfacial coating helps to stimulate the fiber debonding-fracture toughening mechanism. However, due to the special structural orientation of the coating by magnetron sputtering, there is no expected plastic deformation of molybdenum. The transient thermal shock resistance of fibers and coarse-grained tungsten were analyzed. Tungsten fibers were more resistant to thermal shock than coarse-grained tungsten matrix due to high strength and low DBTT, and incorporation of fiber could reduce cracking areas of tungsten materials.

Abstract:Zirconium alloy is the one and only fuel cladding material for pressurized water reactor (PWR) in full-scale commercial use at present, and its water-side corrosion resistance is the dominant factor for the safety and economy of nuclear reactor. The trace alloying elements (Fe, Nb etc.) are existed in zirconium matrix in the form of dispersive secondary phase precipitates (SPPs), which has a crucial influence on the corrosion behavior of zirconium alloy. The type of SPP for various zirconium alloys was compared in this article, and then the corrosion behaviors and influence factors of typical SPPs were reviewed. The corrosion procedures of principal alloying elements Fe and Nb within the binary and/or ternary SPPs were compared respectively, and the difference of SPP corrosion products under different water chemistry and the further effects on the corrosion behavior of zirconium matrix were also summerized. Meanwhile, the deficiencies of current studies on SPP corrosion behavior were indicated. Finally, the future research vision of SPP in zirconium alloy was enunciated herein, and advanced microstructure characterization methods will further refine the mechanism study on corrosion of SPPs bearing Fe and/or Nb, which will provide theoretical support for the corrosion resistance improvement of domestic novel zirconium cladding materials.

Abstract:Tungsten and vanadium was separated from Ti in waste selective catalytic reduction (SCR) catalyst by roasting with waste NaCl salts (WNCS). Results show that the leaching efficiency of tungsten and vanadium reaches 84.63% and 66.42%, respectively, under the optimal conditions (roasting temperature 900 °C; roasting time 3 h; mass ratio of WNCS to waste SCR catalysts 0.5; reaction temperature 80 °C; reaction time 60 min), and the loss rate of titanium is 1.3%. The waste NaCl salts and roasting temperature play a positive role in converting anatase TiO₂ to rutile TiO₂. And the rutile TiO₂ is obtained. The valence of rutile TiO₂ is quadrivalent, and the lattice oxygen and chemisorbed oxygen occupy 57.26% and 42.74%, respectively.

Abstract:Vanadium and ruthenium were introduced into NiS₂ via solvothermal method and ruthenium drop method (room temperature) to prepare (V, Ru)-co-doped NiS₂ microspheres coated on Ni foam ((V, Ru)-NiS₂/NF) as electrocatalysts. The rough golf-like structure allowed the exposure of abundant active sites via sulfuration process. Moreover, the cooperation of vanadium and ruthenium could optimize the electronic structure of NiS₂, provide extra catalytically active sites, and further strengthen the intrinsic catalytic activity. Besides, the addition of nickel foam could support the catalytic material, avoid the aggregation, and enhance the conductivity. Results show that the obtained (V, Ru)-NiS₂/NF electrocatalysts exhibit excellent electrocatalytic performance and superior stability for hydrogen evolution reaction (HER) in alkaline media. At the current density of 10 mA·cm^-2, the presented (V, Ru)-NiS₂/NF delivers an overpotential of 38 mV, which is smaller than that of commercial Pt/C, and possesses lower Tafel slope (80.3 mV·dec^-1), higher relative electrochemical active surface area (ECSA) and excellent durability in 1 mol/L KOH for 24 h.

Abstract:The structural characteristics and thermal protection mechanism of a certain type of auxiliary power unit (APU) turbine guide vane in service were analyzed by scanning electron microscope (SEM) and energy dispersive analyzer (EDS). Then, the thickness variation and failure mode of the high temperature protective coating after removal from aircraft were investigated. The results show that there are two different coating structures in the aircraft APU guide vanes: aluminized coating+MCrAlY coating and mono aluminized coating. The MCrAlY coating thickness of the scrapped APU guide vane components increases first and then decreases from the area of trailing edge to the pressure side and then to the leading edge. Affected by the configuration and the service environment of APU guide vanes, the coatings at the trailing edge and pressure side present an oxidation-predominant damage mode. The oxidation degree of the coating on the trailing edge is more serious, while the closer the pressure-side region to the leading edge, the less severe the oxidative damage. However, due to the coupling effect of CMAS (CaO, MgO, Al₂O₃, SiO₂) corrosion and high temperature oxidation, the damage to the coating at the leading edge of vanes is the most serious.

Abstract:The formation process of nodules (small black projections) on the surface of tin-doped In₂O₃ (ITO) targets during magnetron sputtering was studied by observing the surface morphologies of ITO films prepared within etching time of 2?50 h. The effects of etching time on the electrical and optical properties of the deposited ITO films were explored. Results show that the distribution of In and Sn on the surfaces of the ITO targets changes with the etching time, resulting in uneven ITO films. The electrical and optical properties of the films are degraded significantly due to nodule formation. The photoelectric properties of the ITO films are not affected significantly by etching time within 40 h. However, a rapid deterioration is recorded when longer etching time is applied.

Abstract:Reactive plasma spray (RPS) technique is frequently used to prepare high-performance coating materials with different application requirements. Based on the classical thermite reaction, the Al-Fe₂O₃ coatings were fabricated by RPS under atmosphere and low-pressure ambient. The phase compositions and microstructures of the obtained coatings were characterized by XRD, SEM and EDS. Moreover, the reaction mechanisms of thermite reaction of Al and Fe₂O₃ in sintering and RPS process were elucidated. The DTA analysis results indicate that the main sintering products are Fe, Al₂O₃ and FeAl phases under prolongated reaction condition with Ar gas protetion. However, low oxygen partial pressure leads to the formation of FeAl₂O₄ hercynite phase as an intermediate product during spraying. In atmosphere-reactive plasma spraying (A-RPS), such phase can be retained in the final coating under extremely fast cooling rate. Furthermore, it can also be continuously reduced to FeAl phase in the low pressure Ar-H₂ ambience due to the deoxidation effect and long in-flight distance of plasma jet.

Abstract:Silica aerogel films were fabricated on five substrates, i.e., Ti, SiO₂, GaN, Al and Si, by ambient pressure dry method. The influence of the substrate type on the morphology of the silica aerogel films was investigated. X-ray photoelectron spectroscopy (XPS) was used to observe the interfacial bonding states between silica aerogel films and the substrates. The refractive index of each film was measured by fitting the reflectance spectrum using spectroscopic ellipsometry. The morphology and cross-section of each film were observed by atomic force microscope and field emission scanning electron microscope. Results show that the binding energy offset of 0.07 eV of the Al-O center peak and 0.43 eV of the Ti 2p_3/2 center peak are caused by the fabrication of the silica aerogel films, which suggests the formation of chemical bonds between the substrates and the silica aerogel films. The silica aerogel film prepared on the Ti substrate has the lowest refractive index of the films (1.17), and an approximate average porosity of 63.8% which is higher than that of the film on the Si substrate (57.2%). Effect of substrate type on the morphology of silica aerogel film is attributed to hydrophilicity. Owing to the best hydrophilicity of Ti substrate, more particles are accumulated on the Ti substrate to nucleate and grow, producing a silica aerogel film with larger surface roughness, particles and pores than other films.

Abstract:The interfacial reactions and growth kinetics of Sn-20Bi-0.7Cu-xAg (x=0.1, 0.4, 0.7, 1.0, 1.5, wt%) were investigated during solid-state aging. The effects of chemical composition on the structure and the growth of interface under high temperature and high humidity conditions were studied experimentally and numerically. In order to determine the long-term reliability of the solder joints, thermal accelerated aging tests were performed for 0, 10, 30, 50, 100, 200 and 500 h under 85 °C and 85% relative humidity conditions. The surface morphology, thickness, and distribution of interface compounds were observed by scanning electron microscope. The nucleation surface and growth direction of β-Sn were clarified. The phases were determined at the interface and the alloy matrix. Results show that with increasing the Ag content, the growth of the Cu₆Sn₅ layer is suppressed. The growth kinetics of intermetallic compound (Cu₆Sn₅+Cu₃Sn) remains a diffusion-controlled process during the isothermal aging. The scallop-type Cu₆Sn₅ phase disappears at later aging stages, suggesting that the growth mechanism changes to the steady growth in the direction perpendicular to the interface. Besides, the results reveal that Ag₃Sn effectively slows down the growth kinetics of Cu₆Sn₅.

Abstract:The effect of hot extrusion with different extrusion temperatures (340, 360, 380, and 400 °C) on the microstructure evolution and properties of the as-cast Mg-1Zn-0.3Zr-1Y-2Sn magnesium alloy was investigated by optical microscopy (OM), scanning electron microscopy (SEM), immersion experiments, electrochemical experiment, and tensile test. The results show that after hot extrusion, the second phase of the alloy is broken into particles along the extrusion direction, while the grain size is significantly reduced, and dynamic recrystallization and deformation grains exist in the microstructure. As the extrusion temperature increases, the content of the second phase changes less, and the size of the dynamic recrystallization grain gradually increases. The mechanical properties of the extruded alloys are improved, but their corrosion resistance is weakened. The hot extrusion treatment can improve the corrosion resistance of the alloy in the early stage of corrosion, while as the corrosion proceeds, the corrosion resistance of the alloy in the later stage is weakened. When the hot extrusion temperature is 360 °C, the extruded alloy has relatively good mechanical properties and corrosion resistance.

Abstract:The dynamic recrystallization behavior of a novel Ni-based superalloy was investigated by means of isothermal compression tests in the temperature range of 1040?1120 °C, and the strain range of 0.35?1.2 with a strain rate of 0.1 s^-1. The microstructure evolution and nucleation mechanism of dynamic recrystallization (DRX) were investigated by optical microscope (OM), scanning electrical microscope (SEM), and electron backscattered diffraction (EBSD). Results show that the critical stress and strain for the initiation of DRX are determined from the work hardening rate curves. The volume fraction of DRX grains increases with increasing the temperature and strain. Both discontinuous dynamic recrystallization (DDRX) and continuous dynamic recrystallization (CDRX) coexist at low deformation temperature and low strain. The effect of CDRX becomes weaker with increasing the deformation temperature, and DDRX is the dominant nucleation mechanisms of DRX at higher temperatures. With increasing strain, the effect of DDRX becomes stronger, and CDRX can only be considered as an assistant nucleation mechanism of DRX at the latter stage of deformation for the studied superalloy. Additionally, Σ3 twin boundary contributes to the nucleation of DRX grains.

Abstract:The tribological properties of (AlCrNbTiVCe)N coating at 500 ℃ fabricated by co-sputtering of Ce and AlCrNbTiV alloy were investigated. Scanning electron microscopy (SEM), X-ray diffraction(XRD) and X-ray photoelectron spectroscopy(XPS) were used to characterize the microstructure, composition and crystal structure of the coatings. The mechanical properties and tribologiccal properties of the coatings were tested by nano indentation, tribometer and white light interfering profilometer.The results show that the (AlCrNbTiVCe)N coatings were perfectly prepared by magnetron sputtering. The addition of Ce can improve the structure,and makes grains refined. Meanwhile,the addition of Ce markedly increases the hardness of coatings, which makes the coatings have excellently resistance to plastic deformation and elastic deformation,leading to considerably enhance the friction and wear properties of the coating.The friction coefficient and wear rate of (AlCrNbTiVCe)N coating are significantly lower than that of free Ce (AlCrNbTiV)N coating at room temperature, and the wear mechanism is slight abrasive wear and adhesive wear; at 500 ℃, the friction coefficient of (AlCrNbTiVCe)N coating is lower than that at room temperature, and wear mechanism is mainly oxidation wear. It is indicated that the introduction of Ce contributes to the formation of CeO₂ on the coating surface, and thus improves the tribological properties of (AlCrNbTiVCe)N coatings.

Abstract:A novel low-nickel duplex stainless steel of 21Cr-DSS with excellent hot workability was prepared by the alloying design of "C/N+Mn instead of Ni", while the effects of solid solution treatment on its microstructure, strength-toughness and pitting corrosion resistance were studied. The ferrite of 21Cr-DSS during hot-rolling was more susceptible to dynamic softening than austenite. The effect of solid solution treatment temperature on the ferrite/austenite ratio in 21Cr-DSS was more obvious than that of holding time, and the stability of austenite grain size was better than that of ferrite. The strength and toughness of 21Cr-DSS were improved with an increase in solid solution temperature, but when the temperature exceeded 1100°C, its strength and toughness were decreased. The 21Cr-DSS solid solution treated at 1050 °C for 30min had the excellent comprehensive properties, with the PSE (product of strength and plasticity), -40°C impact energy and pitting potential in 3.5% sodium chloride solution having been measured to be about 58.9GPa%, 84J and 0.43V, respectively. The 21Cr-DSS has the more excellent hot workability and strength-toughness than LDX2101, and the similar pitting corrosion resistance. Compared with AISI 304 austenitic stainless steel, the 21Cr-DSS has the higher strength and pitting corrosion resistance.

Abstract:High quality Mg₃Sb₂ crystals were successfully prepared by directional solidification method. The critical velocity of planar interface of single-phase Mg₃Sb₂ crystal was predicted according to the solidification theory, and the precipitated Sb phase can be inhibited below this rate. Microstructure analysis of Mg₃Sb₂ crystals at different solidification rates indicates that, the quantity of Mg vacanices can be effectively reduced. The excess Mg atoms in the crystals is conducive to the improvement of thermoelectric performance. Carrier mobility and concentration of Mg₃Sb₂ crystal is tincreased by grain boundry eliminated and Ag doping. On the premise of keeping a high Seebeck coefficient, the maximum electric conductivity is 309Scm^_-1 at the testing temperature range of 300-800K. As a result, a better electronic transport properties of PF=1.2mWm^_-1K^_-2 is obtained. This result is verified by Hall testing and first-principle calculations. Correspondingly, the maximum ZT value is 0.67 at the doping concentration of 25at%. This method developed in this pape provides a new path for the performance optimization of Mg₃Sb₂-based thermoelectric materials, and also provides a reference for the preparation of high-performance ternary Mg₃(Sb, Bi)₂ alloy.

Abstract:In this paper, based on the CoCrNi medium-entropy alloy with equal atomic ratio, the CoCrxNi (x=1.0, 1.5, 1.6, 1.7, 1.8, 1.9, 2.0) medium-entropy alloy was prepared by a vacuum arc melting furnace, and the effect of Cr element content on the alloy microstructure was studied. The influence of organization and mechanical properties. The results show that CoCrxNi (x=1.0, 1.5, 1.6) medium-entropy alloy is a single face-centered cubic phase (FCC); With the increase of Cr content, Cr rich strip structure of body centered cubic phase precipitated in FCC phase matrix of entropy alloy in CoCrxNi (x=1.7, 1.8, 1.9, 2.0) medium-entropy alloy; the strength and hardness of the alloy continue to increase with the increase of the Cr element content, but the plasticity deteriorates; compared with the equal atomic ratio CoCrNi medium entropy alloy, While maintaining high plasticity, the strength and hardness of CoCr1.7Ni medium-entropy alloy are significantly improved.

Abstract:Plasma arc welding experiments were performed on 4mm nickel-based superalloy Inconel625 thin plates, and the microstructure of each part of the welded joint under three different welding heat inputs, the mechanical properties of the joint, the fracture morphology, and the high-temperature corrosion behavior of the base metal and the weld were compared.The results show that the structure of Inconel625 plasma welded joint is composed of the austenite equiaxed crystal of the base material and the cell crystal near the weld fusion line and the dendritic crystal in the center of the weld.There is a large amount of carbide and a small amount of Laves phase precipitation at the weld, making the mechanical properties of the welded joint reduced, the toughness of the weld becomes a weak link in the joint.In the welding heat input of 10.175KJ/cm when the mechanical properties of the joint is optimal, the tensile strength of 765.3MPa and the parent material of 785.4MPa equivalent, elongation of 31.9% compared to 42.8% of the parent material has decreased.Specimens fracture by ductile fracture occurring at the weld seam.Base metal and weld metal at 750°C after 24h molten salt corrosion corrosion products are basically the same: the outer layer of granular NiO and Cr2O3 and NiCr2O4 corrosion layer.

Abstract:Effect of Zn on the corrosion properties of homogenized Mg-3Sn-Ca alloy was investigated in this paper. The second phase is composed of CaMgSn and Mg₂Sn in the Mg-3Sn-Ca alloy. The grains are significantly refined by the addition of Zn. The volume fraction of the second phases increase and exist dispersed distribution. Mg₂Ca phase is precipitated. In addition, the corrosion rate of Mg-3Sn-Ca(TX31)and Mg-3Sn-Ca-Zn(TXZ311)alloys were analyzed by immersion and hydrogen evolution test. The corrosion resistance of TX31 and TXZ311 alloys was analyzed by electrochemical polarization curves and impedance spectroscopy. The results show that TXZ311 alloy has smaller grain size, more uniform distribution CaMgSn phases and more dense corrosion film, which cause the higher corrosion resistance of TZX311 alloy.

Abstract:A series of Cu Modified AgSnO₂In₂O₃ electrical contact materials were prepared by alloy melting—internal oxidation method. The temperature rise and electrical life testing system were used to evaluate the performance of Cu Modified samples. The 3D microstructure, phase composition, micro morphology and chemical composition of Cu Modified samples were characterized by ex-situ VR 3D projection technology, XRD and SEM/EDS, and the failure mechanism of electrical life endurance was explored. The results show that with the increase of Cu doping content, the microstructure of the modified samples changes from short whisker like oxide to slender fibrous like oxide. However, when the Cu doping content is as high as 6.8 wt.%, the phenomenon of "dissolution-segregation" occurs, a large number of oxide particles preferentially segregate at the grain boundary. The temperature rise behavior of the modified AgSnO₂In₂O₃ contact material decreases first and then increases with the increase of Cu doping. When the copper doping is 2.15 wt.%, the average temperature rise is as low as 76.558k. The order of electrical life service capability of series Cu Modified AgSnO₂In₂O₃ materials is as follows: Cu (2.15) > Cu (1.65) > Cu (1.1) > Cu (3.4) > Cu (4.0) > Cu (6.8). The corresponding electrical life failure mode is fusion welding, which is mainly due to the failure characteristics such as microcracks, enrichment of high proportion (Ag, Cu) microstructure or (Sn, Cu) microstructure and large-area splashing in the process of arc erosion.

Abstract:The texture evolution of Cu-1.6Ni-1.2Co-0.65Si alloy sheet during the production process was studied by EBSD. The results show that the texture composition of the solid solution sample of the alloy is mainly the Brass texture of the α fiber texture, the Goss texture, the S texture and a small amount of Copper texture; the direct aging treatment after solution does not change the sample The type of texture, but it will significantly reduce the strength of the Brass texture and slightly increase the strength of the Copper texture. As the cold-rolled deformed sample increases, the Brass texture will gradually replace other original textures. The texture pole density increases, and the increase in hardness of the alloy by work hardening is positively correlated with the increase in texture pole density. The texture type remains unchanged at the initial stage of aging at 500°C, and the overall texture pole density increases slightly as the aging time increases. Extending, the extreme density of the overall texture gradually decreases, and the texture types tend to be dispersed. During the aging process, the texture density first increases and then decreases, the same as the hardness change rule；With the increase of the aging temperature, the cold-rolled samples recrystallized and the grains grew, the Brass texture tended to disperse, the strength gradually weakened, the recrystallized texture formed and gradually concentrated, and the extreme density strength gradually increased.

Abstract:Ba(Zn1/3Ta2/3)O3 (BZT) ceramic was synthesized by a solid-state reaction method using BaCO3, ZnO, and Ta2O5 powders as the raw materials. The phase structure, high-temperature phase stability, thermal conductivity, coefficient of thermal expansion, and adaptability of spraying process of BZT were investigated and characterized, and compared with Ba(Mg1/3Ta2/3)O3 (BMT), Ba(Ni1/3Ta2/3)O3 (BNT), and Ba(Sr1/3Ta2/3)O3 (BST) to evaluate the potential application of BZT as a top coating material for thermal barrier coatings. The results indicate that no phase transition occurred during the heating from room temperature to 1500 oC, and BZT was quite stable up to 1600 °C for 48 h, without the occurrence of decomposition, showing excellent high-temperature phase stability; The thermal conductivity of BZT was only 1.65 W·m-1·K-1 at 1200 oC, which is significantly lower than that of BMT (2.59 W·m-1·K-1), BNT (2.56 W·m-1·K-1) and BST (2.11 W·m-1·K-1), showing better high-temperature heat insulation ability; The average coefficient of thermal expansion of 11.3 × 10-6 k-1 for BZT from 200 to 1400 oC was higher than that of BNT (10.7 × 10-6 k-1) and BST (8.1 × 10-6 k-1); The plasma-sprayed BZT coating had single perovskite structure, and the adhesion between the layers was compact for YSZ/BZT double-ceramic-layer coatings. Therefore, BZT ceramic might be a promising candidate material for novel thermal barrier coatings.

Abstract:The Sc-doped La0.6Sr0.4Co0.2Fe0.8-XScxO3-? (LSCFScx, x=0, 0.04, 0.08) cathode powders were synthesized by a sol-gel method. The crystal structure, chemical morphology of surface elements, catalytic activity and electrochemical properties of LSCFSc cathode material were systematically analyzed.XRD results show that LSCF has a cubic structure, and the LSCFSc cathode material changes from cubic to hexagonal structure.The conductivity of LSCFSc cathode material decreases with the Sc3+-doping, and the conductivity of LSCFSc0.08 cathode sample is still greater than 100 S/cm in the temperature range of 300-800.XPS results show that Sc3+-doping increases the content of adsorbed oxygen (OAds) on the surface of LSCFSc cathode material, and the RASR of polarization surface of LSCFSc0.08 cathode material measured at 800℃ is 0.026 Ω·cm2, which is about 87.6% lower than RASR of LSCF cathode material, which significantly improved the adsorption/dissociation ability of LSCFSc cathode material to oxygen, and enhanced the catalytic activity of oxygen.Ni-SDC as the anode material, SDC as electrolyte, and LSCFSc0.08 as cathode material assembled into Ni-SDC|SDC|LSCFSc0.08 anode-support single cell, the maximum power density is 806 mW/cm2 at 800 ℃, indicating that Sc3+-doping can significantly improved the electrochemical performance of cathode materials.

Abstract:Al-Mg alloy (5xxx aluminum alloy) has good processability, corrosion resistance and weldability, but their medium-hardness limits their wear resistance. Based on the main alloy elements of 5xxx aluminum alloys, 0.14wt.% Zr and 0.35wt.% Er were added into Al-xMg-0.5Mn; the effects of different contents of Mg (Mg content up to 9.28wt.%) on the microstructure and friction and wear properties of high Mg aluminum alloy were studied. With the increase of Mg content from 2.96wt.% to 9.28wt.%, the (Al, Mg, Mn, Er, Zr) composite phases formed in Al-xMg-0.5Mn-0.14Zr-0.35Er alloy increased gradually; the size also increased gradually; their morphology changed from rod shape to fine fishbone shape, and finally forms uniformly coarse fishbone shape. When Mg content increases from 2.96wt.% to 9.28wt.% Mg, Er and Mg are often "concomitant segregation", mainly in the form of Al (ErxMg1-x) and Al (Erx(Mg, Mn)1-x). These composite phases change from massive to uniformly distributed (Al, Mg, Mn, Er) phases, which have a certain strengthening effect and can significantly improve the friction and wear performance of the alloy. After compound addition of 0.14wt.%Zr and 0.35wt.%Er, the wear mode of the alloy changes from the mixed wear (adhesive wear and abrasive wear: Mg content is 2.96wt.% - 5.15wt.%) to abrasive wear (Mg content is 5.7wt.% - 9.28wt.%). With the increase of Mg content from 2.96wt.% to 6.8wt.%, the wear resistance of the alloy increases gradually; when the Mg content increases to 8.0wt.% - 9.28wt.%, the wear resistance of the alloy tends to be stable, and the instantaneous friction and wear coefficient μ reaches the stable value of 1.11-1.15.

Abstract:In this work, the irregular TA1 powder was spheroidized by DC arc thermal plasma. Metallographic microscope, scanning electron microscope, particle size analyzer, Hall flowmeter and oxygen-nitrogen analyzer were used to study the particle size of raw material powder and the power of plasma generator in the process of spheroidization, and the effects on the microstructure, particle size, sphericity, fluidity, bulk density and oxygen content of the spheroidized powder. The results show that the irregular TA1 powder was spheroidized into solid spherical powder with uniform particle size after thermal plasma spheroidization. The surface was coated with a layer of nanoparticles. After spheroidization, the internal structure of the powder changed from the initial equiaxed α phase to the long strip α phase. The average particle size and oxygen content of TA1 powder decreased and the sphericity increased by thermal plasma spheroidization. The smaller the particle size of raw powder and the greater the power of plasma generator, the smaller the average particle size of spheroidized powder and the higher the sphericity, too small particle size of raw material powder and too high power of plasma generator will lead to the increase of nano-particle content in the powder after spheroidization, the deterioration of powder fluidity and the decrease of bulk density. After removing nanoparticles can improve the fluidity of powder.

Abstract:The severe deterioration of thermal plasticity for nickel-base wrought superalloys with high Al and Ti contents during cogging has become the bottleneck for their wide application, and their thermal plasticity can be significantly affected by the γ′ precipitation. However, previous studies about the role of γ′ on hot deformation behaviors of such alloys did not consider the interference of grain boundary strengthening elements. In this paper, a high Al+Ti nickel-base superalloy ingot without adding grain boundary strengthening elements C, B and Zr was prepared and fully homogenized. Afterwards, the hot deformation behaviors of this as-homogenized ingot at 1060 ℃ (γ/γ′ dual-phase range) and 1170 ℃ (γ single-phase range) were investigated. The results show that, the deformation resistance in γ single-phase range is much lower than that in γ/γ′ dual-phase range, and the plasticity of γ single-phase range is much better. Interestingly, in γ single-phase range a typical yield drop phenomenon appeared, while no such phenomenon appeared in γ/γ′ dual-phase range. This may be because the release of more Al and Ti solutes in γ single-phase range hinders the movement of dynamic dislocations and finally locks them. Both the γ single-phase and γ/γ′ dual-phase ranges showed intergranular cracking, which indicates that initial grain boundaries are the weakest link in hot working process of such alloys. When the logarithmic strain reaches 0.36, discontinuous dynamic recrystallization (DDRX) has occurred in both the γ single-phase and γ/γ′ dual-phase ranges, and with the increase of strain the number of DRX grains increases significantly, but the DRX grain size has no obvious change. Owing to the pinning effect of γ′ to grain boundaries, the DRX grain size in γ single-phase range is much greater than that in the γ/γ′ dual phase range, but the number density of DRX grains in the γ single-phase range is much smaller. The main reason for the lower deformation resistance and better thermal plasticity in the γ single-phase range is that the rapid growth of DRX grains rapidly can reduce the dislocation density near the initial grain boundary.

Abstract:This paper studies the stress distribution of a 700℃ novel coated steam dual pipe system under thermal-mechanical loading. By running the sequentially coupled simulation, it is shown that Mises stress distribution is strongly correlated with the TGO thickness and morphology, particularly that at the peaks of TGO/BC interface is more sensitive to the roughness. In addition, under the constant amplitude and wavelength of TGO, the maximum value of Mises stress at the peak of TGO/BC interface is directly determined by the local curvature of the interface rather than the arrangement of various waveforms. It is revealed that TGO"s amplitude and wavelength are the crucial parameter controlling the stress distributed at the TGO/BC interface in the coated dual pipe system.

Abstract:The paper introduced the fabricating technology of tungsten plasma facing material (W-PFM), such as plasma spraying technology and powder metallurgy with dispersed Lanthanum oxide (La₂O₃). And it was studied that the micro-structure and the main performances of tungsten materials as PFM. The results indicate that VPS-W coating has the better properties compared to APS-W coating: the lower porosity, the better thermal conductivity, the lower impurity content and the better heat flux performance. It can withstand 100 fatigue cycles under the heat flux of 10MW/m^₂ and is more appropriate for plasma facing material. La₂O₃ particles can hold back W particle growing and enhance the strength of tungsten, which are helpful to improve thermal performance of W PFM. And W-1wt.%La₂O₃ as PFM is suitable under the heat flux of no more 6MW/m^₂.

Abstract:ZnSn(OH)₆ cubes with the hollow structure of 250 nm in size were prepared by hydrothermal method with zinc acetate , Na₂SnO₃ and ammonium fluoride as raw materials using NH₄F etching. The crystal structure, morphology, and optical properties of ZnS(OH)₆ were characterized by X-ray diffraction (XRD), infrared spectroscopy (FTIR), Raman spectroscopy (Raman), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and Photoluminescence (PL). The photocatalytic properties of ZnSn(OH)₆ prepared at different hydrothermal reaction duration were investigated by degrading methylene blue (MB). It was found that ZnSn(OH)₆ prepared by hydrothermal treatment for 2 h had a complete hollow structure, and its degradation efficiency of methyl blue (MB) was 97.4 % in 150 min under visible light. The hollow ZnSn(OH)₆ cubic photocatalytic material is a promising photocatalytic material for visible light degradation.

Abstract:In this paper, the low-cycle fatigue behavior of Ti-6Mo-5V-3Al-2Fe-2Zr alloy under two different heat treatment processes of solution + isothermal aging and solution + furnace cooling was studied. The results show that the microstructure of M1 alloy after solution + isothermal aging treatment contains short rod-like intracrystalline α phase and continuous grain boundary α phase, The microstructure of M2 alloy obtained after solid solution + furnace cooling treatment contains elongated acicular intragranular α phase, continuous grain boundary α phase and WGB α phase. M1 and M2 alloys exhibit cyclic stability at low strain amplitudes of 0.6 %, 0.7 % and 0.8 %, and M2 alloys exhibit higher stress amplitudes with smaller intracrystalline α phase spacing. At a high strain amplitude of 1.0 %, due to the competitive mechanism of back stress and friction stress, both M1 and M2 alloys exhibit cyclic softening. Under high strain amplitudes of 0.9 % and 1.0 %, the back stress hardening rate of M2 alloy is relatively small, the cyclic softening phenomenon is more obvious, and the stress amplitude is relatively low. The intracrystalline α phase of M2 alloy divides the matrix into several " closed units " and forms a WGB α phase parallel to the intracrystalline at the β grain boundary, resulting in lower low cycle fatigue life than M1 alloy.

Abstract:Al0.3CoCrFeNiBx(x= 0,0.01, 0.05, 0.1) high entropy alloys were fabricated by cold crucible levitation melting. The effect of addition of B on the microstructures of Al0.3CoCrFeNiBxalloys were studied using X-ray diffraction, electron backscatter diffraction, scanning electron microscopy with wavelength dispersive X-ray spectroscopy. The microhardness, friction and wear properties and compression properties of Al0.3CoCrFeNiBxalloys at room temperature were analyzed. The results show that Al0.3CoCrFeNi alloy is FCC structure. With increasing B content, the Cr2B precipitated phase increases gradually at the grain boundaries of FCC phase matrix, and the Cr2B phase gradually changes from granular distribution to continuous network distribution, resulting in the alloy microhardness, wear resistance and yield strength are gradually improved. It can be seen that the precipitation of Cr2B has significant dispersion strengthening effect, and the comprehensive performance of Al0.3CoCrFeNiB0.1is better.

Abstract:HA/TiO2 composite coatings were prepared on Ti-13Nb-13Zr alloy by micro-arc oxidation. By changing the Ratio of Ca/P in the electrolyte, the phase composition and microstructure changes, as well as the effects of different Ca/P ratios on the wear resistance, corrosion resistance and in vitro biological activity of micro-arc oxidation coating were studied. The results show that the coating roughness and porosity increase with the increase of electrolyte Ca/P ratio. The coating phase is mainly composed of anatase and rutile, and the rutile phase content increases with the increase of Ca/P ratio of electrolyte. The coating thickness of CA35 prepared with 35g/L calcium acetate electrolyte is 80.59 μm and the surface Ca/P ratio is 1.98, showing the best wear and corrosion resistance. Compared with the substrate, the average friction coefficient of CA35 coating is about 0.19, which decreases by 43%. The corrosion resistance of the coating was tested by Pt reference electrode and 0.9 wt % NaCl test solution. The corrosion current density of CA35 coating is 4.94 μA/cm2, and the corrosion potential is -221.71 mV. The CA35 coating produced the fastest mineralized products in Kokubo solution. It is proved that increasing the Ca/P ratio of electrolyte can effectively promote the formation of HA and improve the wear resistance. In addition, the influence mechanism of Ca/P ratio on coating properties was discussed.

Abstract:Multidirectional isothermal forging (MIF) experiments of Ti₂AlNb-based alloy was carried at 800°C. The microstructure evolution and hardness of the alloy under different deformation cycles were quantitatively analyzed by SEM, XRD, EBSD and hardness testing. The dynamic spheroidization behavior of the lath O and alloy hardening mechanism was revealed. The results show that as the number of deformation cycles increases, the initial coarse lath O has undergone two refinement mechanisms, namely dynamic mechanical breaking and dynamic recrystallization. The globalization of the lath mainly occurs in 3 cycles deformation process. The dynamic spheroidization process is accompanied by four deformation behaviors: bending, kinking, shearing and grain tearing. The mechanism of the latter two types of deformation can be summarized as: O/O phase boundary separation、penetration of B2 phase、O phase separation and O phase spheroidization. The initial lath O phase is refined to 1.3 μm equiaxed structure, and the percentages of fine equiaxed O phase is as high as 68.84% after 3 cycles of MIF. At this time, the hardness of the alloy is 103.55HV higher than the initial sample, and the contribution of grain boundary hardening mechanism is 64%.

Abstract:In this investigation, the friction stir processing (FSP) method was adopted to improve the cavitation erosion-corrosion resistance of as-cast Mg-Zn alloy. The microstructure, element distribution, phase identification and microhardness were observed and estimated by using SEM, EDS, XRD and micro-sclerometer. Moreover, cavitation erosion-corrosion resistance was investigated by ultrasonic vibratory apparatus and electrochemical system. The results show that the microstructure becomes finer and more homogeneous. The element distribution also becomes more uniform, and the microhardness is improved by the FSP method. The corrosion product films with a high protective property are easy to form on the surface of the FSP Mg-Zn alloy, resulting in the improvement of corrosion resistance. In addition, owing to the low hardness of the FSP Mg-Zn alloy, the cavitation erosion resistance of the FSP Mg-Zn alloy is not improved in distilled water test. However, FSP samples possess a better cavitation erosion resistance in artificial seawater tests due to their higher corrosion resistance.

Abstract:The paper investigated the influence of sub-solvus heat treatment processes on the γ" phase microstructure of a novel third-generation nickel-based powder superalloy FGH4113A(WZ-A3). The temperature, soaking time, cooling rate of sub-solvus heat treatment, and the effects of super-solvus + sub-solvus, sub-solvus + sub-solvus on γ" phase were mainly explored. The results indicate that: the volume fraction of γ" phase is inversely proportional to the sub-solvus heat treatment temperature; the tendency of γ" phase dissolve back intoγ phase is inversely proportional to the size, and the quantity is inversely proportional to the soaking time; the size of grain boundary γ" phase increases with the increase of soaking time; the overall volume fraction of γ" phase does not change significantly with the increase of soaking time; a fast cooling rate can re-precipitate an intergranular fine unimodal γ" phase structure; a slower cooling rate can re-precipitate intergranular multimodal γ" phase structure; the size of the reprecipitated γ" phase is inversely proportional to the cooling rate; the microstructure after super-solvus + sub-solvus heat treatment is mainly affected by the temperature and cooling rate of the sub-solvus heat treatment, the lower the temperature, the more rectangular γ" phases are in the grain; the small size spherical γ" phase will be coarsened into a rectangle shape at high temperature, which is affected by the absolute value of the mismatch degree of the γ/γ" phase; the γ" phase microstructure of sub-solvus + sub-solvus heat treatment is greatly affected by temperature.

Abstract:Subcritical β solution treatment of TB17 titanium alloy was carried out at the solution temperature range from 800℃ to 835℃ and the solution time range from 0.5h to 9h, and the distribution of Al, Mo and Nb elements in the primary α phase and β matrix was studied by Electron Probe Microanalysis (EPMA). Effect of subcritical β solution on precipitation of primary α phase and secondary α phase of the alloy was investigated. . The experimental results show that primary α phase presents two typical morphologies of needle-type and lamellae-type structure, which the needle-type α phase is distributed at grain interior and lamellae-type α phase is distributed at grain boundaries. The amount of primary α phase decreases with the increasing of solution temperature. No primary α phase is observed at the solution temperature higher than 825℃. The amount of primary α phase increases with the decreasing of solution temperature. The precipitation of primary α phase will reach a steady state at the solution time higher than 2h. Al element tends to be enriched in the primary α phase, and Mo and Nb element tend to be enriched in the β matrix. The Al concentration in the center of the α phase is higher than that in the edge, while the Mo and Nb concentration in the center is lower than that in the edge. Increasing the amount of primary α phase will decrease Al concentration and increase Mo and Nb concentration in the β matrix. When the amount of primary α phase is low, the secondary α phase near primary α phase presents the morphologies of needle-type or lamellae-type structure, and a morphology of the basketweave structure for the secondary α phase far from primary α phase. When the amount of primary α phase is high, the secondary α phase presents the morphologies of needle-type or lamellae-type structure.

Abstract:: TiZrHf medium entropy alloy and pure Ti were prepared in vacuum arc furnace. The equiaxed grains were obtained by cold rolling and annealing, and their phase composition was studied by X-ray diffraction. Scanning electron microscope and Electron back scattered diffraction was performed to study the microstructure and in-grain slip activities of TiZrHf alloy and pure Ti. The results show that both TiZrHf alloy and pure Ti are single-phase HCP structure with approximately the same axial ratio, and their texture are basal texture after recrystallization. The pyramidal slip of TiZrHf alloy occupy a high fraction of～26% at 10% tensile strain along RD, which is twice the proportion of pyramidal slip in pure Ti, and the number of {10-12} tensile twins is significantly more than that of pure Ti.

Abstract:In order to realize the stable control of rare earth content in rare earth single crystal superalloy and clarify the crucible interface reaction mechanism that rare earth elements participate in the melting process, the effect of melting time on the interfacial reaction of Y-containing superalloy CMSX-4 and Al2O3 ceramic crucible during vacuum induction melting and the residual amount of rare earth Y were studied. The results show that with the extension of melting time, the interfacial reaction becomes more severe. During the melting process, yttrium first reacts with the Al2O3 matrix to form Y2O3, and Y2O3 will continue to react with Al2O3 to form yttrium aluminate reaction layer with different atomic ratios of Y and Al. The final interface reaction product formed on the crucible surface is composed of YAlO3 in the outer layer, Y3Al5O12 (Y3Al2(AlO4)3) in the inner layer and the attached superalloy. The residual amount of rare earth Y in the alloy was 41.023, 4.566 and 5.368 ppm when melting for 10~30 min.

Abstract:For energetic deposition, ion bombardment was an important factor independent of grain size for influencing the residual stress, and the energy and flux were critical parameters to determine the residual stress evolution. In this work, Modulated Pulsed Power magnetron sputtering (MPPMS) and Deep Oscillation magnetron sputtering (DOMS) were employed to control the energy and flux to modulate the ion bombardment for intrinsic stress generation under similar average power. The films thickness was selected at 0.1, 0.2, 0.5, 1.0, 1.5 and 3.0 μm to give a comparative study of the intrinsic part of residual stress. All Cr coatings were textured along Cr(110) preferred orientation with dense T-zone columnar microstructure of equivalent grain size. Compared with MPPMS, Cr thin films deposited by DOMS showed a compressive residual stress tendency. When the Cr thin films were under 0.5 μm, Cr thin films deposited by DOMS showed higher compressive residual stress. Further increasing the film thickness, the compressive residual stress first showed a sudden decrease in a sharp slope, and then turn to relative slow decrease and gradually turn to show tensile stress. In the film continuous growing process, the ion bombardment showed limited effect in the early growth stage, but high bombardment effect will directly influence the grain size. At early growth stage, ion bombardment showed limited contribution to residual stress formation. For thick Cr thin films, energy of the bombardment ions relied on residual stress. Ion energy was an important factor influencing the formation of compressive residual stress, and ion bombardment with high energy assisted the generation and control of compressive residual stress.

Abstract:Biomedical materials have excellent mechanical properties, stability and biocompatibility, and are widely used in dentistry, orthopedics, medical devices and other fields. However, various infection problems are obviously occurred in the current use of biomedical materials, which are severely harmful human health and life safety. Micro-arc oxidation technology can construct antibacterial film on the surface of biomedical metal materials such as titanium and magnesium, which is one of the surface modification technologies to effectively solve the infection problem. In this paper, the research status and mechanism of particle incorporation into micro-arc oxide film are summarized. On this basis, the latest development of antibacterial surface constructed by the incorporation of Ag, Ag2O, Cu, CuO, ZnO and other metal particles into micro-arc oxidation film in recent years was reviewed. The effects of particle incorporation on corrosion resistance and wear resistance of micro-arc oxidation film are described. Meanwhile, the application and development of micro-arc oxidation antibacterial film with particle incorporation are prospected.

Abstract:Microstructure and texture evolution of as-drawn and annealed Cu-Nb microcomposite wires were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray diffraction (XRD). The variation of hardness of the wires with the annealing temperature was investigated using nanoindentation. The results show that the Nb fibers begin to spheroidize and the nanoscale Cu matrix to recrystallize when annealed at 400-500 ℃. The texture of wires changes insignificantly after annealing, maintaining a strong <111>_Cu//<110>_Nb fiber texture along the wire axis. Nanohardness was analyzed by the rule of mixtures and the confined layer slip (CLS) model, respectively. The nanohardness is fitted well with the CLS model before the spheroidization of the Nb fibers, while the nanohardness conforms to the rule of mixtures when the annealing temperature is above 800 ℃.

Abstract:The effects of different bonding temperatures on the microstructure and mechanical properties of TC11 alloy diffusion bonded joints were investigated and compared with the original base metal. The experimental results show that the optimal parameter for direct diffusion bonding of TC11 alloy was 900 ℃/30 min/60 min. There are no holes at the interface of the diffusion bonded joint, and the tensile strength of the joint was close to that of the original TC11alloy base metal. In addition, the plasticity of TC11 alloy diffusion bonded joint was better than that of the original base metal. High cycle fatigue properties tests were performed at room temperature for the original TC11 alloy base metal and the diffusion bonded joints under optimal process parameter. Compared with the original TC11 alloy base metal, the fatigue property of the direct diffusion bonding of the TC11 alloy was reduced, and all the diffusion bonded joint fractures occur at the diffusion bonded interface. By observing the microstructural characteristics of the fatigue fracture and interface, it is concluded that the difference in the crystal orientation of the base metal on both sides of the interface of the diffusion joint caused fatigue crack initiation, which is the main reason for reducing the fatigue property of the diffusion bonded joint.

Abstract:FeCrAl alloy is one of the candidate materials for reactor fuel cladding due to its excellent oxidation resistance at high temperature. However, the presence of Cr and Al has negatively effects to the mechanical properties and pose a potential risk to the safy of reactor operation. In order to analyze the deformation mechanism of FeCrAl alloy system in microscale, the mechanical properties of FeCrAl single crystal under the influence of temperature and strain rate were studied by molecular dynamics method. The defects distribution, dislocation density change and deformation mechanism are discussed, and analyzed the solute atoms on the result of simulation. The results show that the increase of temperature increases the thermal motion of atoms, promotes the formation and growth of defects, reduces the interaction between atoms, and results in the decrease of elastic modulus and tensile strength. The increase of strain rate leads to the decrease of elastic modulus and tensile strength. The plastic deformation mechanism of low strain rate is mainly deformation twinning, of middle strain rate is dislocation slip, and of high strain rate is deformation with atomic arrangement disorder. The effect of temperature and strain rate on α-Fe and FeCrAl is similar, but Cr and Al in FeCrAl cause significant lattice distortion and stress concentration, promoting the formation and movement of defects and dislocations and reducing the yield strength and tensile strength. Based on the calculated results, a constitutive model for FeCrAl crystal system was established based on Field-Backofen equation, which extended the application of the simulation results.