Abstract:Zirconium alloys are used as cladding materials for fuel components in reactors due to their excellent mechanical properties, excellent corrosion resistance and low thermal neutron absorption cross-section. However, Zr-4 can no longer reach the requirements of nuclear power technology under higher burn-up conditions. Therefore, it is of great significance to develop new zirconium alloys by regulating the alloy composition. In this study, Zr-4 and two other new zirconium alloy materials were subjected to conventional tensile tests at room temperature and 315℃. The precipitation phase changes caused by composition differences were analyzed based on the calculation results. And the importance of precipitation strengthening mechanism was proposed for the performance improvement of zirconium alloys. The mechanical properties of zirconium alloy were tested for the first time by using small punch test. The coefficient values related to the zirconium alloy material itself were determined in the empirical formula between the conventional tensile test and the small punch test. The feasibility of the small punch test for the evaluation of the tensile properties of zirconium alloys was verified. Zr-4 and two other new zirconium alloys were hydrogen-charged at 400°C by gaseous hydrogen permeation, and their mechanical properties were tested by SPT. The results show that the hydrogen-charged Zr alloys have a special phenomenon of "platform region" in the plastic instability stage of the load-displacement curve. In this paper, the morphological characteristics of hydrides were characterized by metallographic analysis and their contents was quantitatively estimated. It was speculated that the difference in the fracture toughness between hydrides and matrix, the special long chain configuration of the hydride phase and its strong orientation have an important correlation with this phenomenon.

Abstract:The harsh environment with strong acid, high oxidability and irradiation raises urgent demand for advanced structural materials used for reprocessing dissolver of spent nuclear fuels. In this paper, hot compression behavior of a Zr-1.0Ti-0.35Nb alloy was investigated at the strain rates of 0.01, 0.1, 1 s_^-1 and in the temperature range of 670 ~750 °C. Microstructural evolution during the hot compression was analyzed. The results reveal that the strain rate and deformation temperature both significantly affect the hot deformation behaviour of Zr-1.0Ti-0.35Nb alloy. Flow stress increases with accelerated strain rate, and decreases with elevated temperature. Beyond peak stress, the flow curve exhibits apparent characteristic of dynamic recrystallization characteristics. Elevated deformation temperature favors dynamic recrystallization and grain growth. An Arrhenius-type constitutive model was established based on the obtained peak stress values, in which the activation energy is calculated as 225.8 kJ/mol suggesting a Ti-induced elevation of activation energy and the hardening index is 5.62. A correlation coefficient of 0.97427 and average relative error of 6.15% are obtained between the experimental and predicted values, demonstrating sound applicability of the constitutive model that is expected to guide processing optimization for the new Zr-1.0Ti-0.35Nb alloy.

Abstract:Zirconium cladding absorbs hydrogen in the reactor, and the zirconium cladding will embrittlement in the Loss Of Coolant Accident(LOCA). The hydrogen-containing cladding is more likely to rupture in the process of accident or the subsequent treatment of accident, resulting in the leakage of radioactive products. In this thesis, residual plasticity of zirconium alloys with different hydrogen contents (0 ppm, 195 ppm, 315 ppm, 395 ppm) after simulated LOCA was studied, and the effect mechanism of hydrogen on residual plasticity of zirconium alloys during simulated LOCA was explored. The results show that the residual plasticity of zirconium alloy decreases with the increase of hydrogen content. The increase of hydrogen has little effect on the microstructure of zirconium alloy, and the effect of hydrogen on the microstructure of zirconium alloy is not the reason for the reduction of residual plasticity of zirconium alloy. one of the reasons why the presence of hydrogen leads to the decrease of the residual plasticity of zirconium alloy after simulated LOCA is that the increase of hydrogen leads to the increase of oxygen content absorbed by the prior-β phase after quenching, thus reducing the residual plasticity of zirconium alloy. Secondly, hydrogen may exist in the prior-β phase in the form of saturated solid solution or fine hydride brittle phase, which also leads to the decrease of the residual plasticity of zirconium alloy.

Abstract:Zr-0.75Sn-1Nb-0.35Fe-0.15Cr (wt.%) alloy plates were prepared by smelting, hot rolling, cold rolling and annealing techniques successively. The samples were then irradiated on an electrostatic accelerator with Ar+ to a fluence of 1.02×1015 and 5.1×1015 ions/cm2 (corresponding to 1 and 5 dpa, respectively) at 300 ℃. Both the unirradiated and irradiated samples were exposed to 360 ℃/18.6 MPa/0.01 M LiOH aqueous solution for 90 d. The microstructures of the alloy matrix before and after irradiation and the oxide film formed after corrosion were characterized by scanning electron microscope and transmission electron microscope. The results showed that before irradiation the alloy was fully recrystallized and the grains were equiaxed. The second phase particles were mainly Zr(Fe,Cr,Nb)2 with a fcc or hcp structure, and their size was within the range of 50~100 nm. After irradiation, -type dislocation loops were observed in the irradiated region of the alloy, and the second phase particles were completely amorphous, but the element diffusion from the second phase particles to the matrix was not found. After 90-d corrosion, the oxide film thickness of the irradiated samples was smaller than that of the unirradiated sample, indicating that Ar+ irradiation decreased the corrosion rate of the alloy to some extent at early stage of corrosion. This can be explained by the fact that Ar+ irradiation could delay the microstructural evolution of oxide film, including reducing the proportion of equiaxed grains and the number of cracks in the oxide film, as well as slowing down the oxidation of amorphous second phase particles induced by irradiation, thus enhancing the protectiveness of the oxide film.

Abstract:The mechanical properties of the prior-β Zr layer in zirconium alloys in loss of coolant accident (LOCA) are of great significance to nuclear safety. Nb as an important alloying element in zirconium alloys, has an important influence on its mechanical properties. In this paper, the phase transformation behavior of Zr-xNb (x=0, 0.5, 1, 2.5; wt.%) alloy during LOCA quenching and tensile behavior after quenching were investigated by molecular dynamics method, and the Nb"s effect on mechanical properties of Zr-xNb was analyzed. The results show that the simulated phase transformation process of quenching leads to lamellar polycrystals similar to the structure of prior-β Zr , which are mainly composed of fcc and hcp structural atoms. The bcc→fcc phase transformation path follows the Brain phase relationship, while the bcc→hcp phase transformation path follows the P-S phase relationship. During the cooling process, the addition of Nb reduces the difference between the free energy of the bcc and hcp phases, thus making the temperature of β to α + β phase transition lower. In the Zr, Zr-0.5Nb and Zr-1Nb alloy models, Nb promotes the generation of bcc phase at the grain boundaries, which makes the deformation concentrated at the grain boundaries thus leads to the fracture of the grain boundaries. In Zr-2.5Nb, the content of Nb in the grain is also higher for the formation of bcc phase, which makes the deformation homogeneous and improves its plasticity. In addition, the clusters of Zr-2.5Nb alloy models are diffusely distributed, which makes the tensile strength of Zr-2.5Nb improved.

Abstract:The high temperature steam oxidation behaviour of zirconium alloys under Loss of Coolant Accident (LOCA) is one of the issues that needs to be focused on. In this paper, we smelted Zr-xNb (x=0.5, 1.0, 1.5, wt.%) alloys and Zr-1Nb-yCr (y=0.05, 0.2) alloys and prepared them as plate samples. The oxidation behaviour of the five zirconium alloys in steam at 900~1200 °C under simulated LOCA conditions was investigated using a simultaneous thermal analyser. And the microstructure and microhardness of the samples before and after oxidation were studied using a metallographic microscope and a microhardness tester, respectively. The results show that the oxidation resistance to high-temperature steam of Zr-xNb alloys does not vary monotonically with the change of Nb content at 900~1100 °C, and changes with temperature; the addition of Cr makes the oxidation resistance to high-temperature steam of Zr-1Nb alloys worse, and the effect is complicated; overall, the Zr-1.5Nb alloy has the best performance at 900~1100 °C. When oxidized in steam at 1200 °C, the addition of Nb and Cr has little effect on the oxidation resistance to high temperature steam of the alloys.With increasing temperature, the oxidation kinetic of the five alloys undergoes a parabolic → linear transition with multiple transitions. Finally, the mechanism that Nb and Cr affect the high temperature steam oxidation behaviour of zirconium alloys has been investigated from the following perspectives: the solid solution content of O in the Zr matrix, the α?β phase transition of the Zr matrix and the monoclinic (m) ? tetragonal (t) phase transition of the oxide film.

Abstract:The deformation behavior of pure Ti, Ti-0.2wt% O, and Ti-0.4wt% O polycrystals under high strain rate was investigated by quasi-in-situ EBSD and SEM observation. Results show that under dynamic compressive deformation of 5% strain, the twinning behavior in pure Ti is very active, the twins in most grains are activated, and multiple twin variants appear in half of the grains. However, the slip trace analysis shows that the slip systems are activated in only 50% grains. With the increase in oxygen content, the proportion of twins and the twin area ratio are decreased, and multiple slips and cross slip are activated in the meantime. XRD analysis reveals that the solute oxygen atoms cause the lattice distortion and increase the c/a ratio in α-Ti, which is beneficial to the dislocation slip. The active dislocation slip inhibits the twin nucleation, and the oxygen atoms can pin dislocations to hinder the expansion of twinning boundaries. Thus, the twinning behavior is no longer active. In addition, the dynamic yield strength of pure Ti increases by about 390 MPa for every 0.2wt% increase in oxygen content. This solution hardening phenomenon mainly originates from the lattice distortion, and it is also influenced by the pinned dislocations and the jogs resulting from multiple slips and cross slip.

Abstract:Sn2.5Ag0.7Cu0.1RE0.05Ni lead-free solder alloy was used as the research object. Based on the unique structure, excellent physical properties, and good mechanical properties of graphene nanosheets (GNSs), the Ni modified GNSs (Ni-GNSs) were used as the reinforcement phase. The soldering process of Ni-GNSs reinforced SnAgCuRE system composite solder/Cu and thermal aging tests of soldering joints were conducted to investigate the effect of Ni-GNSs on the microstructure and thermal aging fracture mechanism of composite soldering joints. Results show that the addition of Ni-GNSs inhibits the linear expansion of the composite solder, resulting in lattice distortion and dislocation. The intermetallic compound (IMC) particles near the dislocation line interact with the dislocations and hinder their movement, thereby strengthening the composite solder and further improving the soldering joint. With a longer thermal aging time, the thickness of interface IMC layer is increased and the shear strength of soldering joints is decreased. Among them, the shear strength decrement of the composite soldering joints with 0.05wt% GNS addition is the least of only 8.9%. Moreover, after thermal aging for 384 h, its shear strength is still higher than that of the Sn2.5Ag0.7Cu0.1RE0.05Ni/Cu soldering joint before thermal aging. With the addition of Ni-GNSs, the growth coefficient of interface IMC of composite soldering joints is significantly reduced, which effectively alleviates the degradation of mechanical properties of composite solder/Cu soldering joints during the thermal aging process, further changes the thermal aging fracture mechanism of composite solder/Cu soldering joints, and ultimately affects the reliability of joints. The fracture position of the Sn2.5Ag0.7Cu0.1RE0.05Ni/Cu soldering joints moves from the soldering seam before thermal aging to the soldering seam/interface IMC, presenting the ductile-brittle mixed fracture. The fracture position of the Sn2.5Ag0.7Cu0.1RE0.05Ni-0.05GNSs/Cu soldering joints is still in the soldering seam zone, presenting the ductile fracture, which indicates the high reliability of the soldering joints.

Abstract:A series of C₃N₄/CuGaO₂ composites were synthesized by facile hydrothermal method. The prepared samples were characterized by XRD, SEM, TEM, and XPS. The gas sensing properties of the C₃N₄/CuGaO₂ composites were investigated. Results demonstrate that the gas sensor based on C₃N₄/CuGaO₂-0.3 composite (molar ratio of C₃N₄ to CuGaO₂ is 0.3:1) shows better sensing performance to toluene than CuGaO₂ sensor does. Compared with the operating temperature of CuGaO₂ sensor (140 °C), the optimal working temperature of C₃N₄/CuGaO₂-0.3 composite sensor is only 25 °C, the response to 100 μL/L toluene gas reaches 28, and the detection limit is as low as 0.01 μL/L. The response time and recovery time for the detection of 100 μL/L toluene vapor are 114.2 and 27.4 s, respectively. Moreover, the C₃N₄/CuGaO₂-0.3 composite sensor also exhibits excellent long-term stability, good repeatability, and extraordinary humidity resistance for toluene detection.

Abstract:Metal Y was purified by plasma zone melting, and the migration laws of Al, Si, Fe, Ni, Cu, and Mo impurities during the zone melting purification process were obtained. Calculation results show that the equilibrium distribution coefficients of the Al, Si, Fe, Ni, Cu, and Mo impurities in metal Y are 0.2173, 0.2201, 0.5065, 0.1586, 0.1742, and 0.8576, respectively. Because all equilibrium distribution coefficients are less than 1, the solubility of impurities in the liquid phase is greater than that in the solid phase. Therefore, theoretically, with the movement of molten zone, the Al, Si, Fe, Ni, Cu, and Mo impurities will be concentrated in the tail side of Y metal ingot, namely last-to-freeze zone. Experiment results demonstrate the correctness of the theoretical calculation. Besides, the internal relationship between the zone melting times and the impurity migration was investigated. Results show that with the increase in the zone melting time from 5 to 10, the concentration degree of impurities at the tail side of Y metal ingot is increased, i.e., the removal ratio is increased. After 10 times of zone melting, the removal ratios of Al, Si, Fe, Ni, Cu, and Mo impurities are 45.71%, 61.54%, 33.98%, 64.15%, 52.14%, and 46.28%, respectively. Because the saturated vapor pressure of the abovementioned impurities is similar to that of metal Y, impurities are difficult to be removed by the common methods. The investigation of plasma zone melting proposes a new research direction for the preparation of high purity Y.

Abstract:Fe-Al/Al₂O₃ composite coating was prepared through rare earth-modified aluminizing and in-situ oxidation at 760 °C. The microstructure and phase distribution of the aluminizing layer and oxide film were investigated. Results show that the rare earth-modified aluminizing layer can be divided into three layers: an outer aluminizing layer, a transition layer, and an inner diffusion layer. The aluminizing layer is predominantly composed of FeAl phase and Fe₃Al phase. Notably, the FeAl phase is primarily concentrated in the outer layer of aluminizing layer, providing favorable conditions for selective oxidation of the Al₂O₃ oxide film. The surface of oxide film exhibits the α-Al₂O₃ ridge structure. Additionally, the presence of Ce oxide on the surface is attributed to the outward diffusion of Ce and its preferential reaction with O₂ during the initial oxidation stage. The oxide film can be divided into two layers, namely a pure α-Al₂O₃ layer and a transition layer which is mainly composed of α-Fe(Al) and mixed oxides of Al, Fe, and Ce.

Abstract:The effects of Mn microalloying on the microstructure and mechanical properties of new near-α Ti-Al-Mo-Zr-Fe-B alloy were studied by OM, EBSD, and TEM. Results indicate that the addition of 0.5wt% Mn can refine the casting microstructure of the alloy from 3.28 μm to 2.65 μm, which leads to the increase in ultimate tensile strength from 882 MPa to 966 MPa. However, the elongation decreases from 7.8% to 5.1%. After forging, the grain size of two alloys tends to be similar, and the microstructure is more equiaxed. Besides, the microstructure becomes more homogeneous after Mn microalloying. The ultimate tensile strength and elongation of Ti-Al-Mo-Zr-Fe-B alloy increase to 966 MPa and 16.4%, respectively, whereas the alloy containing 0.5wt% Mn element possesses higher ultimate tensile strength, reaching 1079 MPa. Meanwhile, the elongation reaches 15.8%. These results suggest that the increase in strength can be attributed to the solid solution strengthening effect of Mn element. Additionally, the Mn microalloying promotes the enrichment of Al element in alloy into the α phase, which is beneficial to improve the strength and plasticity of the alloy.

Abstract:The nanoscale (VNbTaZrHf)C high-entropy carbide (HEC) powders with face-centered cubic structure were prepared by electro-deoxidation of metal oxides and graphite in CaCl₂ at 1173 K. Appropriate temperature conditions are favorable for suppressing the in-situ sintering growth of HEC particles. Electrochemical performance tests were conducted in 1 mol/L KOH solution to investigate the catalytic performance of (VNbTaZrHf)C HEC. The catalytic performance of (VNbTaZrHf)C HEC for hydrogen evolution reaction (HER) was evaluated through polarization curves, Tafel slope, electrochemical impedance spectroscopy, and double-layer capacitance value cyclic voltammetry tests. Results show that the double-layer capacitance value of (VZrHfNbTa)C HEC is 40.6 mF/cm². The larger the double-layer capacitance value, the larger the electrochemically active surface area. Due to the high-entropy effect and nanoscale structure of (VNbTaZrHf)C HEC, it exhibits superior catalytic performance to HER. This research provides a novel method for the preparation of HECs via molten salt electro-deoxidation.

Abstract:In order to explore the effects of Ti doping on the optical and mechanical properties of Ta₂O₅ coatings prepared by Ar/N₂-Ar co-sputtering, Ta₂O₅, N₂-Ta₂O₅, Ti-Ta₂O₅, and N₂-Ti-Ta₂O₅ coatings were prepared on the glass substrate surface by radio frequency and direct current magnetron co-sputtering techniques. The microstructures and surface morphologies of Ta₂O₅, N₂-Ta₂O₅, Ti-Ta₂O₅, and N₂-Ti-Ta₂O₅ coatings were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), and atomic force microscope (AFM). The optical parameters of the coatings were tested by ultraviolet-visible spectrophotometry. The hardness and Young's modulus of the coatings were tested by nanoindentation. XRD test results show that the Ta₂O₅, N₂-Ta₂O₅, Ti-Ta₂O₅, and N₂-Ti-Ta₂O₅ coatings mainly consist of amorphous phase structure with Ta₂O₅ as the main body. SEM and AFM results show that the coatings deposited on the glass substrate do not have extensive voids. The sputtered particles are uniformly piled and grow on the substrate surface. The coating thicknesses are basically the same and the thickness error is within 5%. The separate introduction of N₂, Ti, and N₂-Ti co-doping can reduce the roughness of Ta₂O₅ coatings. The optical test results show that the separate introduction of N₂ and Ti element can increase the average transmittance of Ta₂O₅ coatings to more than 81%, whereas the average transmittance of N₂-Ti-Ta₂O₅ coatings prepared by N₂-Ti co-doping reduces. Mechanical test results show that compared with that of Ta₂O₅ coating, the hardness of N₂-Ta₂O₅ and N₂-Ti-Ta₂O₅ coatings increases significantly. The hardness of Ti-Ta₂O₅ coatings is basically the same. The elasticity index (H/E) and plasticity index (H³/E²) indicate that the N₂-Ta₂O₅ and N₂-Ti-Ta₂O₅ coatings possess better fracture toughness and plastic deformation resistance. The preparation of N₂- and Ti-doped Ta₂O₅ coatings on glass surface can obtain the multifunctional coatings with both excellent optical and mechanical properties, which is represented by N₂-Ta₂O₅ and N₂-Ti-Ta₂O₅ coatings.

Abstract:In order to solve the problems of insufficient forming of complex box part in the single deep drawing, a precise hot forming process of deep drawing and gas bulging was proposed, and the shape and thickness of the formed parts could meet the design requirements. TC2 titanium alloy complex box part was selected as the research object in this research. The high temperature formability of TC2 titanium alloy was investigated at 550–800 °C and 0.001–0.1 s^-1. A set of mold for deep drawing and gas bulging at one time was designed. The forming process of the complex box part was simulated based on the finite element simulation software PAM-STAMP, and the optimized process parameters were obtained and verified by experiments. Results show that the simulation software PAMSTAMP can effectively predict the part defects during deep drawing and gas bulging. The process parameters and mold shape are ameliorated and verified by experiments. Complex box part with thickness and height meeting the design requirements can be obtained under the conditions of 800 °C and gas pressure of 2.5 MPa, which verifies the feasibility of the composite process of deep drawing and gas bulging.

Abstract:In order to reduce cost and to fully utilize the excellent corrosion resistance of nickel materials, pure nickel N6 with thickness of 1 mm was selected as the flyer plate, and the medium carbon steel 45# with thickness of 3 mm was used as the base plate for explosive welding tests. The dynamic parameters were calculated through the explosive welding window, and the interface bonding morphology and elements were analyzed by metallographic optical microscope and scanning electron microscope. The mechanical properties of the composite plate were tested through shear tests, and the explosive welding process was simulated by AUTODYN. Results indicate that there is a boundary effect near the explosion point, and the bonding interface along the explosion welding direction changes from the flat state to the stable wavy interface. The thickness of the element diffusion layer near the interface is 20 μm, and the wavy diffusion layer increases the bonding area, which is conducive to the metallurgical bonding. The shear strength of the composite plate reaches 325.5 MPa. Numerical simulation analysis results demonstrate that the simulated interface morphology is consistent with the experiment results. The simulation results show that the velocity and plastic deformation degree of the characteristic points are basically consistent with the experimental results.

Abstract:The microstructure evolution of Al7(CoCrFeMnNi)93 high-entropy alloy was studied by directional solidification technology. Then single crystals of high-entropy alloy with cellular and dendritic substructures were prepared by the natural competitive growth method. Finally, the effect of substructure and orientation on the nano-mechanical properties of high-entropy alloy single crystals was studied. The results show that the growth interface of Al7(CoCrFeMnNi)93 high-entropy alloy is more prone to destabilization during directional solidification. Its planar-cellular solidification interface morphologies transition rate is less than 1 μm/s, and the cellular-dendritic solidification interface transition rate ranges from about 2 to 5 μm/s. The primary dendrite arm spacing and the secondary dendrite arm spacing of the alloy decrease gradually with the increase of directional solidification rate and satisfy the exponential relationship with the withdrawal rate respectively. After directional solidification, the elements of Co, Cr, and Fe were enriched in the dendrite region, while the elements of Mn, Ni, and Al with lower melting temperatures tend to be enriched in the inter-dendrite region. The orientation of the cellular and dendritic substructures single crystal obtained by the natural competition method are [2 1 4] and [2 1 3], respectively. The data of nano-indentation mechanical properties show that the substructure caused by segregation behavior has little effect on the elastic modulus and hardness of single crystals, while the crystal orientation has a greater influence on the elastic modulus of single crystals, but has little effect on the hardness value.

Abstract:Silver-based electrical contact materials are the core of low-voltage electrical connection in the fields of new energy power vehicles, industrial electrical appliances and other fields, with the widest range of applications and the largest demand. The Ag/SnO2 contact material system has made great progress due to its excellent electrical contact performance and arc erosion resistance. However, the material system still has problems such as higher temperature rise and shorter electrical life under service. Once it fails, it will lead to major safety accidents such as power system paralysis and out-of-control communication facilities, and economic and social losses are difficult to estimate. Herein, in order to explore the impact of the type and content of the modified components on the preparation process, microstructure, microhardness, temperature rise and electrical life of the modified Ag/SnO2In2O3 contact materials, the modified AgSnIn alloys are synthesized by medium-frequency smelting and casting process, and then the corresponding Ag/SnO2In2O3 contact materials are prepared by internal oxidation method. The AC-4 electrical life type testing platform is used to evaluate the temperature rise and electrical life performance of the materials. The results shows that the optimum parameters of internal oxidation process of the modified Ag/SnO2In2O3 materials are 700℃, 5MPa, 48h. Compared with the binary modification of Ni, Cu or Zn, there exists larger micro-strain in the Ni-Cu-Zn ternary modified AgSnIn alloys, and the microhardness of the corresponding modified Ag/SnO2In2O3 material increases first and then decreases sharply with indium content decreased. The modified AgSnIn alloy, composed of 0.47wt.% nickel, 0.4wt.% copper, 0.43wt.% zinc and 2.1wt.% indium element, could achieve complete internal oxidation. The corresponding modified Ag/SnO2In2O3 material presents the optimum microhardness (1382.49 MPa), the longest cycle number (28989 operations) and the appropriate temperature rise (43.69 K), which is attributed to some larger micro-strain (19×10-3) and grain boundary structure with strengthening effect. By comparison analysis, A positive correlation has been established between the electric life cycle number and the microhardness of the modified Ag/SnO2 material Within In element content ranged from 2.1 to 3.1 wt.%, which will provide a new idea for the formulation design and electric life performance prediction of the Ag/SnO2 contact material.

Abstract:Ta/Ta0.5Hf0.5C laminated composite shows great potential to be used as wing leading edges and nose caps due to its good mechanical properties and ablation resistance. However, the thermal shock behavior of the composite is rarely reported for now, as such, it is hard to evaluate whether the composite can serve as a structural material stably. In this paper, the plasma flame and finite element method (FEM) were employed to investigate the thermal shock behavior of Ta/Ta0.5Hf0.5C laminated composite. By analyzing the morphologies and microstructure of the tested sample, it is found that Ta/Ta0.5Hf0.5C laminated composite possesses great thermal shock resistance since no cracks were observed on the internal and external surfaces of the composites after 120 cycles of plasma flame pulse assessment. Based on the measured temperature results during thermal shock testing, the thermal stress distribution field inside the testing sample was built successfully, and it reveals the maximum thermal stress (207 MPa) caused by plasma flame occurs at the moment of cooling. After 120 cycles of stress cycling, the retention rates of strength and toughness of the composites are 70.1% and 73.9%, respectively. High strength and excellent crack propagation resistance are the main reasons for the excellent thermal shock resistance of Ta/ Ta0.5Hf0.5C laminated composite.

Abstract:This article investigates the effects of electrolyte temperature and pH on the electrochemical crystallization behavior of copper through cyclic voltammetry (CV) and chronoamperometry (CA) experiments. The effects of electrolyte temperature and pH on the phase composition, preferred orientation, microstructure, roughness, and hardness of copper electrodeposited layers were analyzed using X-ray diffraction (XRD), scanning electron microscopy (SEM), three-dimensional ultra depth of field microscopy and microhardness tester. The results indicate that the copper electrocrystallization process is a three-dimensional nucleation and growth mode controlled by diffusion. When the electrolyte temperature is 35 ℃, the electrodeposition efficiency of copper is the highest; When the pH value of the electrolyte is 9, the promotion effect on copper electrodeposition is optimal. The final nucleation mechanism of different electrolyte temperatures and pH values is three-dimensional instantaneous nucleation growth. With the decrease of electrolyte temperature and the increase of pH value, the preferred orientation changes from (111) crystal plane to (220) crystal plane. When the electrolyte temperature is 35 ℃ and pH is 9, a flat, dense, rough and hard electrodeposited copper layer can be obtained.

Abstract:In order to achieve a more uniform temperature distribution during electromagnetic induction heating of titanium plate rolled at different temperature of titanium and aluminum, different induction heating coil sets are designed to heat the titanium plate, and the influence of the structural parameters of the induction coil on the temperature field in electromagnetic induction heating is simulated by using finite elements, and the temperature difference between the width of the titanium plate is controlled within 50 °C by adjusting the induction heating parameters to form a more uniform temperature of the titanium plate. The induction heating and temperature measurement experiments of the titanium plate were carried out, and the average temperature of the titanium plate was formed under a short heating time of 635 °C, and the temperature difference within 45 °C was formed, which verified the correctness of the simulation results. A titanium/aluminum composite plate with an interface shear strength of 63.3MPa was prepared by rolling the high-temperature titanium plate and the room-temperature aluminum alloy plate with good uniformity, and the distribution of the bonding performance of the prepared titanium/aluminum composite plate was analyzed by temperature uniformity.

Abstract:In this study, the effect of different number densities of O-phase on the mechanical properties of the matrix B2 phase in Ti2AlNb alloy was investigated based on molecular dynamics. The results show that the yield strength and plasticity of the B2 phase are improved when the O phase is contained. This is because the precipitated phase hinders the start of the slip system in the matrix during the tensile deformation process, thereby improving the plastic deformation resistance of the B2 phase of the matrix. It is found that the improvement of material plasticity is mainly related to the release of internal stress, in which the release of internal stress by the B2 phase through martensitic phase transition is dominant, and the release of internal stress by dislocation is secondary. When the matrix B2 phase contains the O phase, the O relative dislocation hindrance will lead to stress concentration, thereby inducing martensitic phase transition of a large number of BCC structures, and the degree of stress concentration in this process decreases, delaying the growth of pore nuclei. On the other hand, since the O phase is a ductile phase, the growth of holes at the boundary between the O phase and the B2 phase is inhibited, so that the plasticity and toughness of Ti2AlNb alloy are greatly improved. And with the increase of the density of the number of precipitated phases, the yield strength and yield strain of the material decrease, but its strength and plasticity are still improved compared with those without the O phase. This is because, with the increase of O phase number density, the proportion of martensitic phase transition of the matrix atoms during the deformation process decreases, so the release degree of the stress concentration by the phase transition decreases, and the generation and expansion rate of the holes increases, so that the material is more prone to fracture failure.

Abstract:Based on the real microstructure of composite materials and introducing cohesive element units at the interface between particles and matrix, four finite element models with different particle aggregation distributions (uniform distribution, aggregation at three locations, aggregation at two locations, and aggregation at one location) were established to investigate the influence of particle aggregation on the crack initiation and propagation mechanisms of SiC/AZ91D composite materials. The results show that when the crack initiates, stress distribution in the matrix is highly uneven, with the maximum stress occurring at the corners of the particle group. The more severe the particle aggregation, the greater the maximum stress value during crack initiation. As the crack propagates, the greater the degree of particle aggregation, the higher the maximum stress value in the matrix and the greater the extent of crack propagation. When the crack completely fractures, the maximum stress value of the particles gradually increases with the aggravation of particle aggregation, while the maximum stress value of the matrix remains relatively constant. Particle aggregation accelerates the process of crack initiation and propagation, and particles are uniformly distributed in the matrix. The crack initiation and propagation mechanism of composite materials is due to the severe stress concentration at the boundaries and corners of the SiC particle group, which causes damage to the matrix, initiates microcracks, and then propagates along the direction of maximum shear stress to form the main crack.

Abstract:In this paper, rhenium-tungsten core-shell powder was prepared by solid-liquid mixing method and then osmium powder was added to prepare ternary mixed powder with special coating structure after pretreatment. After the powder was pressed, sintered, impregnated with salt, washed and annealed, a ternary mixed-base cathode of tungsten-rhenium osmium was prepared. After impregnation with 411 salt, the pulse emission test found that W2Re1Os1 cathode which is a ternary mixed-base cathode has the best electron emission performance and the current emission density can reach 35 A/cm² at 1050℃, which is slightly higher than that of the same type of binary mixed-base cathode, reaching the level of the ternary film cathode covered with tungsten, rhenium and osmium. It is verified by experiments that neither Re nor Os reacts with the active salt during the impregnation process of the ternary tungsten-rhenium-osmium mixed-base cathode, and the active substance is produced by the reaction of W and the active salt.

Abstract:S110 cast steel shot and Z300 ceramic shot were used to do the shot peening experiment, the morphology of shot peening surface was observed by scanning electron microscopy (sem) and three-dimensional contour instrument. The residual stress of shot peening surface was tested by X-ray diffraction method, the microstructure of cross section of shot peening layer was analyzed by optical microscope(OM) and electron backscattered diffraction(EBSD). The reselut shows that with the increase of shot peening intensity the roughness of shot peening surface is increased. The roughness of ceramic shot peened surface is lower than that of cast steel shot peened. Residual compressive stress on the cast steel shot peening surface is between - 860 Mpa to -1000 Mpa and with the increase of shot peening intensity of residual compressive stress is slightly reduced. Residual compressive stress on the ceramic shot peening surface is between - 1000 Mpa to -1100 Mpa and with the increase of shot peening intensity of residual compressive stress is slightly insreased. After shot peening, projectile pits are formed on GH4096 alloy surface, plastic deformation occurs, grain boundaris are curved, lattice deformation appears, cause a lot of dislocation set and low angle grain boundaries, and the grain orientation changes. The 650 ℃ high temperature fatigue life of GH4096 alloy can improve by shot peening, double shot peening promotion of fatigue life is the most obvious, ceramic shot peening strengthen effect is better than that of cast steel shot. The strengthening effect of shot peening are mutual influenced by residual stress, surface roughness and depth of strengthening layer.

Abstract:This article uses metallographic and EBSD techniques to study the effects of equal channel angular pressing on the microstructure and mechanical properties of two binary alloys, Mg-1Gd and Mg-2Zn. The results show that under the same pressing conditions, Mg-2Zn alloy fully recrystallized, resulting in grain growth and coarsening, and the strength and plasticity did not change with the number of pressing passes. Mg-1Gd alloy only partially recrystallized after pressing, with a microstructure consisting of fine dynamic recrystallized grains and deformed grains. With an increase in the number of pressing passes, the degree of recrystallization increased, leading to a doubling of the alloy"s tensile strength and plasticity. This was related to the greater inhibition of recrystallization and grain growth by the solute atom Gd compared to Zn. The recrystallized grains had a dispersed orientation, while the grains that did not recrystallize in Mg-1Gd alloy had a c-axis orientation that deviated 45° from ED to TD, which was consistent with the detection of macroscopic texture. A large number of small-angle grain boundaries formed within the grains, and rotations around the c-axis occurred on both sides of these boundaries, gradually evolving into large-angle boundaries.

Abstract:Indium tin (InSn) alloy nanowires were prepared using anodic aluminum oxide (AAO) film as template through vacuum mechanical injection method. Ru particles were then coated on the surface of InSn nanowires using the "in situ discharge reduction" method. Subsequently, the tin oxide nanowires (ITO NWs) was obtained by heat treatment of the composite material. Finally, RuO₂/ITO NWs were reduced in H₂ atmosphere to obtain Ru/ITO NWs. The results indicate that the diameter of InSn nanowire is about 40 nm and Ru nanoparticles of 2-5 nm are uniformly coated on the surface of ITO NWs. In addition, the catalytic pyrolysis of cellulose by Ru/ITO NWs was tested and the main products were 1,6-anhydropyranose, glycoladehyde, and hydroxyacetone. Compared the catalysate of ITO NWs without catalysts, Ru/ITO NWs catalyst reduces the production of 1,6-anhydropyranose, indicates that Ru nanoparticles exacerbate the fracture of oxygen bridges during pyrolysis, accelerate the generation of glycoladehyde and hydroxyacetone, and improve the pyrolysis efficiency. At the same time, the pyrolysis of nonylphenol polyoxyethylene ether with ether bonds is also carried out, and the result shows that Ru/ITO NWs plays a role in the fracture of ether bonds.

Abstract:The trapezoidal continuous casting billet Al-5Ti-1B-0.2Cu intermediate alloy was investigated by solid solution treatment at different solid solution temperatures, followed by transverse and longitudinal hot compression deformation at different deformation temperatures, different deformation rates and different deformation directions. To study the effects of Cu element addition, solid solution treatment and hot compression on the microstructure and dimensional inhomogeneous deformation of second phase particles. The results show that there are four types of second phase particles (Ti_1-X,Al_X)B₂, Al₇Cu₂Fe, TiB₂ and TiAl₃ after solid solution treatment at 600 ℃/4h. When Cu is present, the Al-Cu-Fe phase is generated to increase the number of particles in the second phase. At the same deformation degree and deformation temperature, the average size of TiAl₃ particles decreases with increasing deformation rate (0.01, 0.1, 1s_-1^{), while TiB}₂ particles tend to be more diffusely distributed. The second phase particles TiAl₃ are more uniform after transverse compression deformation, but the TiAl₃ particles are finer after longitudinal compression deformation, while the size and distribution of TiB₂ particles in transverse compression and longitudinal compression are basically the same. The dimensional inhomogeneous plastic deformation of the trapezoidal continuous casting billet is more favorable to the size and distribution of the second phase particles TiAl₃ and TiB₂.

Abstract:In order to study the effect of vacancy defects on the damping performance of γ-TiAl coating, molecular dynamics (MD) was used to simulate the reciprocating vibration of γ-TiAl coating with different vacancy concentration. The changes of stress-strain, stored potential energy, dislocation line density, defect area and microstructure were compared and analyzed. The results show that with the increase of vacancy concentration, the energy consumption of γ-TiAl coating increases gradually, and the damping performance is enhanced obviously. The stored potential energy of γ-TiAl coating with different vacancy concentration changes periodically, and the range of variation decreases gradually with the increase of vacancy concentration. In the process of vibration simulation, vacancy defects will evolve into dislocation lines and other defects, resulting in increased dislocation density and defect area. The movement, evolution and annihilation of different defects are the main sources of energy consumption of γ-TiAl coating. In addition, the high altitude concentration of γ-TiAl coating produces more plastic deformation, neck shrinkage and more holes, which further increases the energy dissipation.

Abstract:Thermal barrier coatings (TBCs) are one of the effective ways to raise the upper limit operating temperature of aero-engine hot end components. Rare earth zirconate (RE2-xZr2+xO7+x/2) is considered as a candidate material for the new generation of thermal barrier coatings due to its low thermal conductivity and good high-temperature phase stability. In this paper, given to the strong performance designability, domestic and international research progress on mechanical, thermophysical and corrosion resistance of conventional alloying modified and high entropy modified rare earth zirconate coating have been reviewed based on the alloying design idea, and the prospect future for subsequent research has been proposed based on the deficiency of current research.

Abstract:Carbon nanotubes (CNTs) are tubular structures composed of highly graphitized atoms. Due to the sp2 hybrid electron orbital structure, CNTs possess a variety of fancy physical and chemical properties, such as high mechanical strength, excellent optical anisotropy and good electrical conductivity. Therefore, CNTs are promising advanced materials that can be used in areas of material strengthening, energy conversion and electronic devices. The structures and properties of CNTs can be tuned by regulating the growth environment of CNTs. Nevertheless, the growing process of CNTs is very complicated, and highly depended on raw material, preparation method and growth environment, which consequently determine the growth rate, microscopic morphologies and final properties of CNTs. Here, the effects of fabrication methods, substrates, catalysts, and growth environment on the microscopic morphologies and properties of CNTs are reviewed, and the growth mechanisms of CNTs are discussed. We also pay attention on the application of CNTs in the areas of energy storage, material toughening and catalytic hydrogen production. The present deficiencies and future development directions on the preparation and controlled growth of CNTs are figured out, which provides guidance for the controlled growth and large-scale preparation of CNTs.

Abstract:The Ti-Al system intermetallic compounds and composites fabricated through Ti and Al，such as TiAl3, γ-TiAl and α-Ti3Al intermetallic compounds, and Ti/Al, Ti/Ti3Al, Ti/TiAl, Ti/TiAl3 and Al/TiAl3 metal-metal and metal-intermetallic compound composites, have good application prospects in aerospace, automotive and other fields owing to their excellent physical, chemical and mechanical properties. The preparation of the above materials involves a variety of Ti-Al reaction diffusion processes. Therefore, an in-depth understanding of the Ti-Al reaction diffusion mechanism and kinetics will help to prepare Ti-Al intermetallic compounds and composites reasonably and efficiently. At present, the Ti-Al reaction diffusion mechanism and kinetics has been extensively studied, but there are still many divergences on some conclusions. In this paper, the research progress of the reaction diffusion mechanism and kinetics involved in the preparation of Ti-Al intermetallic compounds and composites is reviewed, and the future research direction of Ti-Al reaction diffusion is prospected.