Abstract:Isothermal uniaxial tension tests for O phase-based Ti-22Al-25Nb alloys were conducted at 1203–1283 K with temperature interval of 20 K. The strain rates were 2.5×10^-4, 5.0×10^-4, 1×10^-3, 2×10^-3, 4×10^-3, 1×10^-2, and 5×10^-2 s^-1. The microstructures of specimens at different deformation temperatures were characterized. Through the experiment results, the material constants for the constitutive models are determined and the tensile deformation activation energies are 845 165 and 412 779 J/mol at α₂+B2/β+O three-phase region (1203–1243 K) and α₂+B2 two-phase region (1243–1283 K), respectively. Arrhenius-type constitutive models are constructed to characterize the tensile deformation behavior of Ti-22Al-25Nb alloy at different temperatures.

Abstract:The finite element method was adopted to analyze the temperature state of titanium alloy seamless pipe during the multi-stand continuous rolling. The simulation results show that with increasing the rolling passes, the outer surface temperature under the groove vertex is decreased at a gradually reducing rate, the center temperature is basically increased at a gradually reducing rate, and the outer surface temperature under the groove taper is continuously increased. The circumferential unevenness of center temperature is decreased in odd passes and increased in even passes. However, the unevenness of temperature distribution on the outer surface has opposite variation trend. The rolling reduction of the front pass shows a negative correlation with temperature rise at the groove taper of the next pass. In addition, decreasing the rolling reduction of the former pass can significantly improve the circumferential temperature unevenness of the next pass. The results of temperature measurement and grain morphology show that the simulation results are in good agreement with the experiment results.

Abstract:The transient method was used to simulate the argon arc welding process of large-scale thin-walled parts with multiple welds of TC4 alloy as aeroengine based on the SYSWELD professional welding simulation software. The influence of the welding line energy, fixture constraint state, and welding sequence on welding temperature field, welding deformation, and residual stress was analyzed. Results show that the welding deformation is increased exponentially with increasing the line energy, and the optimal line energy for argon arc welding is 310 J/mm. The application of welding fixture constraint can effectively reduce the welding deformation, but causes in the larger welding residual stress and wider distribution area. The decentralized symmetric welding can reduce the overall welding deformation of parts with multiple welds.

Abstract:The hot formability of Ti-22Al-25Nb alloy sheet at elevated temperatures was studied through the gas bulging experiments and numerical simulation. The distributions of bulging shell shape and wall thickness at 930 and 970 °C were analyzed. The microstructure and mechanical properties of the bulging part were discussed. Results show that the bulging shell is close to the spherical surface in the initial bulging stage, and it gradually becomes ellipsoid with increasing the bulging height. At 930 and 970 °C, the final bulging height reaches 46.25 and 49.85 mm, and the curvature radius of shell top reaches 49.33 and 49.19 mm, respectively. The wall thickness of bulging part is inhomogeneous: it gradually decreases from the bottom region to the top region. The deformation temperature strongly affects the shape of bulging part: the partial bulging shape is more inhomogeneous at low temperature of 930 °C. Under the same bulging height, the curvature radius of bulging is lower and the thinning ratio is higher at 930 °C. In addition, the O phase is precipitated and spheroidized during bulging at 930 °C, which causes the generation of O type and V type cavities and the reduction in microhardness. However, the microstructure is uniformly distributed after bulging at 970 °C. O phase is precipitated during the cooling process in lamellar morphology, which strengthens the bulging part.

Abstract:Fluent software was used to simulate the interaction among the temperature field, flow field, and solute field in the vacuum arc remelting process of TC4 titanium alloy. The effects of three process parameters (smelting rate, upper surface temperature of the ingot, and cooling intensity), which are directly related to the ingot, on the ingot macrosegregation were studied. Results show that under different smelting conditions, the radial macrosegregation of Fe element shows a bell-shaped distribution at the ingot height of 1000 mm, i.e., the core of ingot presents the positive macrosegregation whereas the surface area presents the negative macrosegregation, and the degree of negative macrosegregation is greater than that of the positive macrosegregation. The effect of smelting rates on the temperature field and macrosegregation of the ingot is the most obvious: with increasing the smelting rate from 0.15 mm/s to 0.18 mm/s, the ingot height to reach the stable melting stage is increased from 1200 mm to 1600 mm, and the depth of the molten pool is increased from 494 mm to 738 mm. In the area within the distance of 130 mm from the ingot center, the macrosegregation is decreased with increasing the smelting rate, and the maximum value is 3.36% when the smelting rate is 0.15 mm/s. In the area beyond the distance of 295 mm from the ingot center, the macrosegregation is increased with increasing the smelting rate, and the maximum value is 6.23% when the smelting rate is 0.21 mm/s. The effect of upper surface temperature and cooling intensity on macrosegregation and molten pool depth is not obvious. Through the orthogonal analysis, the influence degree of three main process parameters on macrosegregation is as follows: smelting rate>cooling intensity>ingot upper surface temperature. The optimal conditions are smelting rate of 0.15 mm/s, ingot upper surface temperature of 2179 K, and cooling intensity of 500 (bottom)/1000 (side) W·m^-2·K^-1.

Abstract:To investigate the hot flow behavior of Ti-55511 alloy in near-β region, isothermal compression tests were conducted at the temperature of 973-1223 K and the strain rate of 0.001–1 s^-1 by Gleeble-3500 thermomechanical simulation equipment. The flow stress curves obtained from experiments were corrected, and the influence of friction and adiabatic temperature rise on flow stress was reduced. The corrected Arrhenius model with consideration of material parameter evolution and the back-propagation artificial neural network (BP-ANN) model were used for flow stress prediction of Ti alloys during hot deformation process, and the precision of these prediction models were evaluated by statistical analysis. The stress and strain data extended by the two prediction models were implanted into finite element to simulate the hot compression process. Results show that the flow stress of Ti-55511 alloy has a positive correlation with strain rate and a negative correlation with temperature. The alloy softening mechanism is primarily the recrystallization. Both the corrected Arrhenius model and BP-ANN model can describe the flow behavior of fluid, and the fitting accuracy of BP-ANN model is higher than that of corrected Arrhenius model in α+β region but lower than that of corrected Arrhenius model in β region.

Abstract:The microstructure evolution and super-diffusion mechanism of weld zone of TC11 and TC17 dissimilar titanium alloys after linear friction welding under different frictional pressures (22–47 MPa) were investigated. The joint microstructure was analyzed by scanning electron microscope, and the atomic concentration near the joint interface was analyzed by electron probe. Results show that the temperature in the weld zone exceeds the β-phase transition temperature, the temperature of the joint drops rapidly after welding, and the weld microstructure changes to a fully recrystallized microstructure. Super-diffusion of atoms occurs at the joint interface, and the diffusion coefficient of typical atoms is about 100 times higher than that of diffusion welding atoms. Within the experiment parameter range, increasing the frictional pressure can extend the diffusion distance of typical atoms.

Abstract:TA18 titanium alloy tube has specific radial basal texture due to the requirement of its service environment and the annealing temperature is one of the important factors. In order to reveal the formation mechanism of annealing texture of the tube. In this paper, Ф8×0.6 mm the cold rolled tube and the annealed tube at 450, 500, 550, 600, 650, 700, 750℃/3h were selected as experimental materials. Studied the grain orientation characteristics of the tubes at different annealing temperatures by electron backscatter diffraction (EBSD). As a result, the cold rolling tube had great radial basal texture and <10-10> direction was mainly parallel to the axial direction of tube. The grain recovery, recrystallization and growth occurred at annealing temperature 450-550℃,550-650℃,650-750℃ respectively and the transformation of texture occurred during the stage of grain recrystallization and growth. With the occurrence of recrystallization, the radial texture of tube was enhanced and the <11-20> direction was mainly parallel to the axial direction. The main cause of radial texture enhancement is that the fine grain of original cold rolling tube had more obvious radial orientation than the matrix, and the crystallization grain was prior to nucleation and growth around the fine grain and obtained strong radial orientation. During the following process of grain growth, the grain with strong radial orientation can grow dominantly, so that the tube can perform obvious radial distributed ‘recrystallization texture’.

Abstract:In order to improve the hot workability of TC17 titanium alloy, TC17 titanium alloy was hydrogenated. Through metallographic observation and X-ray diffraction analysis, the microstructure and phase transformation law of TC17 titanium alloy were studied after hydrogenated treatment. Under the conditions of deformation temperature of 800-860℃ and strain rate of 0.001-0.1s_^-1, the isothermal compression tests of hydrogenated TC17 titanium alloy were carried out. The deformation behavior of the hydrogenated TC17 titanium alloy was studied, and the thermal activation energy was calculated and analyzed. The results show that the microstructure of TC17 titanium alloy is a typical net basket structure, which is composed of α+β phase composition. With the increasing of hydrogen content, the volume fraction of acicular α phase decreases, and the volume fraction of β phase increases. When the hydrogen content exceeds 0.40wt%, the γ and δ hydrides separate out. The hydrogenated TC17 titanium alloy is not only a temperature sensitive material, a rate sensitive material, but also a hydrogen content sensitive material. When the hydrogen content is 0.2wt%, the peak stress reaches the minimum value. Compared with the original alloy, the deformation temperature can be deincreased by 40℃ and the strain rate can be increased by one order of magnitude. At the same time, the thermal activation energy of TC17 titanium alloy with 0.2wt% hydrogen content also reaches the minimum value of 162KJ/mol, and its thermal deformation softening mechanism was dynamic recovery.

Abstract:The dynamic three-point bending loading was carried out on Ti6321 titanium alloy to cause mode I (open type) fracture and obtain the waveform curve. Combined with the experimental & numerical method, the mode I crack dynamic fracture properties of Ti6321 titanium alloy with three structures were obtained. The fracture surfaces of three kinds of Ti6321 titanium alloys were observed and analyzed by scanning electron microscope (SEM) and confocal laser scanning microscope (CLSM). The results show that the widmanstatten structure has the highest dynamic fracture performance of mode I crack, followed by the bimodal structure, and the equiaxed structure has the lowest dynamic fracture performance. For mode I crack fracture, equiaxed structure and bimodal structure are mainly ductile fracture mechanism, while widmanstatten structure has the characteristics of partial cleavage fracture. The Widmanstatten structure has the best fracture performance. Because of the largest fluctuation of fracture and the largest specific surface area, the crack propagation needs more energy.

Abstract:In view of the characteristics of narrow hot rolling temperature range, rapid temperature drop and large deformation resistance of titanium alloy , titanium alloy and the new technology of seamlessStube Tandem Skew Rolling was combined and systematic research was carriedSout in this paper. According to the process structure and characteristics, the speed model, tension model and rolling force model of TSR were described,the deformation mechanism and the metal flow law of titanium alloy in TSR process was studied by finite element numerical simulation,the distribution of stress and strain field, temperature field and velocity field were obtained, and the field test was conducted based on finite element simulation. The results show that when the temperature is 1050℃ and the parameters of the piercing section and rolling section are matched reasonably, the seamless titanium alloy tube can be successfully obtained with high dimensional accuracy and no obvious surface defects. The theory and experimental analysis show that the TSR process is completely suitable for the preparation of seamless titanium alloy tube, and the production process is shortened and the production efficiency is improved.

Abstract:As a typical hydrogen storage material, titanium has an important application on hydrogen energy materials and deuterium-tritium fusion neutron source. The various contents and distribution of hydrogen isotopes in titanium will affect the structure and properties of titanium in many ways. The conventional quantitative determination methods of hydrogen isotope content in titanium include pressure-volume method, weighing method and thermogravimetric method, etc. Compared with these conventional methods, the thermal desorption spectroscopy (TDS) method can not only obtain hydrogen isotope contents, but also distinguish between hydrogen and deuterium, and can reveal the position information of hydrogen isotope atoms in the crystal lattice. In this research, by optimizing the hydrogen absorption process of titanium, titanium hydrogenated/deuteride samples with different hydrogen and deuterium contents were successfully prepared. Combined with X-ray diffraction (XRD) analysis, the crystal structure changes of titanium before and after hydrogen absorption are given. Using the TDS technology developed by our research group, the ion current signal intensity of the mass spectrometer was calibrated through a standard leakage, and the quantitative analysis of the amount of hydrogen isotope desorption in titanium was realized. The absolute error between the TDS measurement result and the pressure-volume method measurement value is less than 6%. The total contents of hydrogen and deuterium desorbed in the sample were calculated. The results provide a useful reference for the accurate measurement of hydrogen isotope content in materials in the field of hydrogen energy, nuclear energy and nuclear technology.

Abstract:Abstract: In bone tissue engineering, the studies on porous structures of Triply Periodic Minimal Surfaces (TPMS) are increasingly extensive. At present, the studies at home and abroad mainly focus on conventional TPMS porous structures, while the studies on deformed TPMS porous structures are few. The porous structure of deformed TPMS element has the advantage of mechanical properties in a certain direction. In this paper, a parametric design method of deformed Gyroid cell porous structure with radial and axial aperture gradients is studied. The deformed Gyroid cell porous structure samples with 60% and 75% porosity of titanium alloy are prepared by Selective Laser Melting (SLM) technology. The Finite Element Method (FEM) was used to carry out static simulation analysis on four kinds of gradient porous scaffold models and two kinds of uniform models, and the mechanical properties of the prepared titanium alloy gradient porous samples were tested, and the mechanical properties were compared and analyzed with those of the tested uniform samples. Finite element calculation results and the mechanical performance test result shows that the mechanical properties of porous structure deformation Gyroid unit decreases with porosity increased, while the porosity is the same,the radial gradient of mechanical properties of porous scaffolds is better than that of uniform porous scaffolds, more suitable for cortical bone defects of bone repair,and axial gradient of mechanical properties of porous scaffolds compared with uniform porous scaffolds weakened, more suitable for the cancellous bone.

Abstract:Pure aluminum foil (dilute Al-Fe-Si alloy series) with Cu or Mn addition was prepared by severe cold-rolling deformation, and the effect of room temperature storage or low temperature annealing on the tensile properties and microstructure was investigated through tensile tests, optical microscope, scanning electron microscope, electron back scatter diffraction, and atom probe microscope. Results show that the ultimate tensile strength and elongation simultaneously decrease after room temperature storage. The recovery mechanism of substructure, such as subgrain coalescence, leads to the decrease in tensile properties. The decrease in plasticity is more significant for the Mn-containing alloy due to the more significantly increased subgrain size. The atom cluster strengthening can compensate for the strength loss to some extent, whereas the effect of the secondary phases is negligible.

Abstract:The Al_0.5Nb_1.5TiV₂Zr_0.5 high entropy alloy was prepared by vacuum arc melting, and its microstructure, density, and mechanical properties were investigated. Results show that Al_0.5Nb_1.5TiV₂Zr_0.5 alloy consists of 90.6vol% body-centered cubic phase and 9.4vol% C14-Laves secondary phase. The matrix phase of the alloy is rich in Ti and V, and the secondary phase is rich in Al and Zr. The alloy has a low density of 6284 kg/m³ and Vickers hardness of 5197.9 MPa. The yield strength of alloy is decreased with increasing the temperature: it decreases from 1082.9 MPa at room temperature to 645.0 MPa at 1073 K. The compressive strain decreases from 27.20% at room temperature to 14.94% at 873 K, which is related to the decrease in atomic interaction force when the temperature rises. At 1073 K, the compressive strain of alloy exceeds 50%, indicating the good plasticity without fracture. The results of compression tests show that the ductile-brittle transition temperature ranges from 873 K to 1073 K.

Abstract:The self-made hollow porous micro/nano-fiber structure Sn_0.84Sb_0.08Sm_0.08O₂ and thermoplastic polyurethane (TPU) were used as raw materials to prepare the Sn_0.84Sb_0.08Sm_0.08O₂/TPU (the addition content of Sn_0.84Sb_0.08Sm_0.08O₂ is 0wt%, 3wt%, 6wt%, and 9wt%) composite micro/nano-fiber films by electrostatic spinning method. Results show that the microstructures of composite films all present a fibrous 3D network structure. The tensile strength and elongation of the composite film are increased firstly and then decreased with increasing the addition content. When the addition amount is 6wt%, the tensile strength and elongation of the film are 2.68 MPa and 573%, which are 1.5 and 8.3 times higher than those of TPU film, respectively. The addition of Sn_0.84Sb_0.08Sm_0.08O₂ increases the thermal decomposition temperature and contact angle of the composite films to 303 °C and 120°, respectively. The infrared emissivity of the composite film is decreased with increasing the filler content. When the addition content is 9wt%, the infrared emissivity of the specimens at wavelength of 3–5 and 8–14 μm is 0.576 and 0.652, respectively. This composite film has good hydrophobicity, thermal stability, flexibility, and infrared stealth performance, providing experimental basis for the research of lightweight infrared stealth materials and showing certain application potential in the infrared stealth field.

Abstract:The 316L stainless steel part was prepared by the selective laser melting method at different scanning speeds. The effects of scanning speed on phase constitution, molten pool morphology, surface roughness, density, and mechanical properties of the part were investigated by phase analyses, metallographic microscopy, tensile test, Vickers hardness test, and surface roughness test. Results show that all specimens are successfully prepared at different scanning speeds (800–1200 mm/s). In addition, with increasing the scanning speed, the ratio of depth to width of molten pool without remelting is decreased, and the surface roughness is increased from 5.78 μm to 22.79 μm. The cracks appear at scanning speed of 800 mm/s, while the molten line shrinkage occurs when the scanning speed exceeds 1100 mm/s. When the scanning speed is 800 mm/s, specimens have relatively high porosity due to the overhigh laser input energy. When the scanning speed is 900 mm/s, the specimens have the optimal Vickers hardness (2401 MPa) and high relative density (99.2%).

Abstract:The effects of the heating rate and peak temperature on the springback, mechanical properties, and corrosion resistance of Al-Zn-Mg-Cu alloy were investigated. The precipitation behavior and aging strengthening mechanism of the alloy were analyzed by transmission electron microscope. Results show that with decreasing the heating rate and increasing the peak temperature, the springback of the alloy is decreased; the size of intragranular precipitates is increased; the volume fraction of intragranular precipitates is firstly increased and then decreased; the grain boundary precipitates become discontinuous and the precipitate-free zone is expanded. After nonisothermal creep aging (NICA) treatment (20 °C/h, 180 °C), the main precipitates of alloy are compact η' phase, the grain boundary precipitates are discontinuous, and the free zone width is approximately 44.2 nm. The mechanical properties and corrosion resistance of the alloy treated by NICA (20 °C/h, 180 °C) are better than those of the alloy treated by common isothermal creep aging (120 °C, 24 h), and the aging time is shortened by 67%.

Abstract:The strategy of sintered closed-hole followed by reopening was proposed to prepare the microporous nickel material with high porosity through the powder metallurgy and subsequential treatments. The carbonyl nickel powder with particle size of 1 μm was used as raw material, and the effects of sintering process parameters on the pore properties and mechanical properties of microporous nickel were studied. Results show that the porosity measured by mercury injection method of microporous nickel is 53.7%, and the average pore diameter is 612.25 nm at the sintering temperature of 400 °C. After machining, the porosity measured by mercury injec-tion method is 54.0%, and the average pore diameter is 511.37 nm, which still satisfies the requirements of engineering application. The strategy provides providing a new approach for the preparation of microporous nickel and other porous metal materials.

Abstract:A novel explosive welding method was proposed to prepare the indium/iron composite plate by inserting a velocity-control plate between the explosive and composite plate to achieve the ideal welding condition. The experiments were conducted to investigate the effects of explosive load, and the parameters of explosive welding were calculated by the theoretic method. Numerical simulation of the smoothed particle hydrodynamics (SPH) method was used to verify the parameters and to investigate the formation mechanism of the bonding interface. The distributions of pressure and plastic strain were also studied. Results show that the wave structures become more obvious when the explosive thickness increases. The shear test results indicate that the shear strength of indium/iron composite plate is 16 MPa, which is higher than that of the indium material. After the three-point bending test, no cracks can be observed at the bonding interface. The modified explosive welding method can effectively prepare the high quality indium/iron composite plate.

Abstract:By ameliorating the contact heat transfer measurement device and simulating the transient heat exchange characteristics of roll gap by finite element model, the coupling influence of temperature, pressure, and roughness on the contact heat transfer coefficient was analyzed. Results show that there are two obvious critical thresholds for the contact heat transfer. When the interface pressure is less than 22.1 MPa at temperature<150 °C, there is a good linear relationship. When the interface pressure exceeds the first threshold, the contact heat transfer is significantly enhanced, presenting the obvious nonlinear characteristic. In addition, once the interface pressure exceeds 50 MPa and the temperature is higher than 300 °C, the contact heat transfer quickly tends to be stable. Obviously, the second threshold is directly related to the elastic-plastic deformation of friction peaks on the surface of magnesium alloy strip. The contact heat transfer at high pressure is caused by the increased micro-contact area and the interactive diffusion of friction peak. Based on these characteristics of the phenomena, it is beneficial to accurately control the contact temperature of roll gap, and therefore to design suitable rolling parameters and optimize the rolling technique.

Abstract:Asymmetrical rolling is an important way to improve the deformation quality of aluminum alloy sheet as a severe plastic deformation technology. The deformation mechanism in thickness direction is difficult to be analyzed due to the characteristics of multivariable, strong coupling and nonlinearity in asymmetrical rolling of plate. In order to deeply study the deformation in the thickness direction of asymmetrical rolling, a strain calculation model along the thickness direction after asymmetrical rolling is established. The deformation zone is divided into rigid plastic rigid zone according to the kinematic characteristics of rolling process. On this basis, the boundary conditions of the deformation zone are modified, and the stream function method is used to establish the near-real velocity field. According to the minimum energy principle and linearized integration method, the rolling power consumption model is established, the multi-field and multi-parameter nonlinear coupling problem in the calculation process is solved, and the rapid calculation of the boundary model of the deformation zone is realized. Finally, the strain calculation model of asymmetrical rolling is established by combining the velocity components and strain rate components. In order to verify the asymmetrical of the theoretical model, numerical simulation and asynchronous rolling experiments were carried out. Compared with the experimental results, the maximum relative error of the calculation results is 13.44%, and the minimum relative error is 1.33%. The overall calculation time is reduced to less than 1 second. The establishment of this calculation model can provide an important theoretical reference for the quality control and prediction of asymmetrical rolling.

Abstract:Effective prediction and evaluation of sheet deformation degree has practical guiding significance for bending forming process and product precision control, and neutral layer offset is an important parameter to measure the degree of uneven deformation in the tension and compression area of bending sheet. In this paper, based on the microelement stress balance condition in the plastic deformation theory and the Yoon2014 yield criterion which can reflect the tension and compression asymmetry of magnesium alloy, the neutral layer offset calculation model in the bending process of AZ31B magnesium alloy sheet was obtained, and the neutral layer offset model was verified by finite element simulation and corresponding experiments. The results show that the model can reliably predict the neutral layer migration phenomenon of magnesium plate. During the bending process of magnesium plate, the neutral layer shifts to the tensile side due to the influence of tension and compression asymmetry. The smaller the Angle after bending, the larger the neutral layer offset. The neutral layer offset is the most obvious when the bending Angle is 90° and the pressure is between 40mm and 47mm.

Abstract:In order to study the effect of heat treatment system and alloy composition on the mechanical properties of Al-Mg-Si alloys, the strength prediction model (ANN-GA model) of Al-Mg-Si alloys was constructed by using the combination of artificial neural network (ANN) and genetic algorithm (GA). The effects of alloying element content and heat treatment process parameters on the strength of aluminum alloy were studied by single factor and double factor analysis. The results show that the tensile strength of aluminum alloy decreases first and then increases with the increase of Si content; With the increase of Mg content, the increase of Cu content or the decrease of Fe content, the tensile strength of aluminum alloy increases as a whole. Two factor analysis can better reflect the influence of input parameters on the tensile strength of aluminum alloy. Mg/Si ratio, total amount of Mg+Si and aging time have significant effects on the mechanical properties of Al-Mg-Si alloys. The variation trend of hardness of aluminum alloy with time was consistent with the calculation results of ANN-GA model. The peak aging time was 29h and the relative error was 11.86%.

Abstract:Base on finite element method, the stress field evolution of zirconium alloys with different oxidation degrees during the Loss of Coolant Accident process is analyzed in this paper, in which the Zr-4 cladding with three-layer structure after Loss of Coolant Accident process has been modeled, with representing different oxidation degrees of the zirconium alloy cladding by the volume fraction of α-Zr (O). The simulation of two-step cooling from 1200 ℃ to 800 ℃ then to room temperature is carried out. The results show that the stress in the oxide film is compressive stress, and the stress gradient of oxide film with the decrease of temperature is the largest, which leads to a larger residual stress at the interface between α-Zr (O) layer and matrix, and the larger the proportion of matrix volume, the smaller the internal residual stress after cooling. In the low oxidation model, the stress of α-Zr (O) layer is basically unchanged at the end of cooling,。However, there is obvious stress concentration when the oxidation degree is higher. The larger compressive strain has been produced in the high oxidation degree model, which leads to greater deformation of the matrix when cooling down. Accordings to the analysis on the corresponding constitutive equations of each structure in different oxidation degree models, it is found that the stress of each layer in the early stage of quenching decreases first and then increases. There is difference of mechanical properties between the matrix close to the edge of α-Zr(O) layer and that close to core structure. For the model with higher oxidation degree, the core compressive stress of matrix structure is higher than that of edge structure under the same strain.

Abstract:In this paper, a TiBN nano-powder was synthesized by boronizing sintering method to form a solid solution of B in TiN crystalline structure. TiBN powder exhibits a specific micro-nano composite structure composed of TiBN crystals and an amorphous nanometer-sized layer. The amorphous structure is mostly distributed along particle boundaries with a minimum thickness of 2 nm. TiBN powder shows combined ceramic and metallic properties, and its electrical resistivity is 2.986×10-5 Ωm (better than that of TiN, TiC, TiCN, and TiB2). Solid dissolution of B into TiN increases number of valence bands and conduction bands near Fermi level, contributing to excellent electrical conductivity of TiBN powder. This proposed method can synthesize single-phase TiBN powder at 580 ℃ in 1 h, a synthesis temperature 500 ℃ lower than existing TiN synthesis temperatures. This TiBN powder synthesis route can be used to prepare bulk materials in engineering materials industry. In addition, it has attractive research value and broad application prospects in photovoltaic cells and energy storage collector applications including lithium batteries, supercapacitors, and fuel cells.

Abstract:MAX phases have the potential to be used as accident tolerant fuel (ATF) cladding materials. In order to fully understand the corrosion behavior of MAX phases under the simulated normal service conditions,the MAX phase ceramic tube with Ti3SiC2 matrix was exposed to 400 ℃/10.3 MPa superheated steam, 360 ℃/18.6 MPa deionized water, 3.5 ppm Li + 1000 ppm B solution and 70 ppm Li solution for corrosion tests. The microstructure, crystal structure and composition of the samples before and after corrosion were observed by XRD, SEM and FIB/TEM. The results show that the corrosion rates of Ti3SiC2 under the four corrosion conditions are all much higher than that of reference Zr-4 alloy, TiO2 was characterized as the main corrosion product; loose and no protective oxide film was formed on the surface of Ti3SiC2 tube.

Abstract:Modulated pulsed power magnetron sputtering (MPPMS) and pulse direct current magnetron sputtering (PDCMS) were employed to deposit CrNx coatings by controlling the nitrogen/argon flow ratio and sputtering power, respectively. The influence of nitrogen flow ratio as well as sputtering power of MPPMS and PDCMS were systematically studied to learn the roles of process parameters on CrNx coatings composition, phase, microstructure and mechanical properties. The composition, phase, microstructure, morphology, hardness as well as fracture toughness of coatings were characterized through electron probe micro analysis (EPMA), X-ray diffractometer (XRD), scanning electron microscope (SEM), nanoindentation device. As the PDCMS sputtering power increased from 700 W to 1000 W, the peak power of MPPMS showed an increase of 43.5%. The Cr elements in the coatings were ranging from 61.0 at.% to 65.4 at.%, while N contents decreased from 39.0 at.% to 34.6 at.%. The CrNx coatings were mainly composed of Cr2N phase without obvious changes. With the increase of the sputtering power, the hardness of the CrNx coatings was about 20 GPa, while the fracture toughness of the coatings was improved significantly. Changing the flow ratio from 15% to 50%, the peak current of MPPMS first decreased followed by an increase, the phase structure of the coatings gradually varied from Cr2N to CrN. When the nitrogen flow ratio was about 35%, the CrNx coatings were mainly composed of Cr2N and CrN. And the hardness, residual compressive stress and fracture toughness of the CrNx coating all attained their maximum values of 20.5 GPa, -901.8 MPa and 6.5 MPa·m1/2, respectively. The electron temperature should be the driving force for phase structure variation for CrNx coatings, and the dense and two-phase microstructure controlled the toughness of CrNx coatings.

Abstract:W has high thermal inertia and low adiabatic flame temperature, which makes it difficult to burn in air. To change the combustion characteristics of W, 20 wt.% Zr was introduced into W by mechanical alloying. XRD, SEM and STEM analysis showed that after ball milling for 30 h, the diffraction peak of Zr disappeared completely, and the W(Zr20) super-saturated solid solution powders with single BCC phase were obtained. Subsequently, WZrZn alloys were prepared by hot pressing with Zn powder as binder. The results of quasi-static mechanical properties tests and ballistic gun experiments showed that the compressive strength and energy release characteristics of W(Zr20)-Zn30 alloy prepared by W(Zr20) alloy powder were significantly better than those of W/Zr20-Zn30 alloy prepared by conventional mechanical mixing. Under the impact velocity of 1200?m/s, the reaction overpressure of W(Zr20)-Zn30 alloy reached?0.21 MPa.?In the analysis of reaction products, a large amount of WO3 were found, indicating that the solid solution of Zr induced the combustion reaction of W, which effectively improved the impact initiated reaction characteristics of the WZrZn alloy.

Abstract:In order to ensure the accuracy of internal dimension, core supports made of Pt are normally used in the complex hollow single crystal turbine blades. However, the influence of core supports on the microstructure and property of DD5 single crystal turbine blades has not been reported. In this paper, core supports made of Pt were inserted into DD5 thin-wall plate specimens to observe the effect of core support on the microstructure and element segregation. In addition, the typical properties of DD5 thin-wall plate specimens with core support made of Pt were tested to clarify the influence of core support on alloy properties. The results showed that core support made of Pt had great bonding with DD5 alloy without obvious heterogeneous interface. The core support made of Pt was completely alloyed, the microstructure of core support was consistent with DD5 alloy, no new phase was observed. Core support made of Pt had no influence on the microstructure of DD5 alloy, but the degree of element segregation of DD5 alloy was increased. Moreover, core support made of Pt had no negative effect on the tensile property at room temperature, tensile property at 870℃ as well as stress rupture property at 1093℃/158MPa of DD5 thin-wall plate specimens. The fracture mode of DD5 thin-wall plate specimens with core support was interdendritic rupture, and cracks initiated and propagated along the interface between carbide and matrix.

Abstract:In this work, GH3536 alloy specimens were fabricated by selective laser melting (SLM). The microstructure, high temperature tensile properties and fatigue crack growth rate of the specimens were investigated after hot isostatic pressing and solution treatment. The results show that there are two kinds of equiaxed grains of different sizes in the alloy samples after hot isostatic pressing and solution treatment, and there are continuous lamellar distribution of M23C6 and M6C carbides between the grains. The tensile properties of the alloy specimens decreased continuously with the increase of temperature, and the fracture mode changed from ductile fracture at room temperature to brittle fracture at 900℃. Under different stress ratios, the crack propagation mode of the specimens is transgranular propagation. The increase of stress ratio will accelerate the crack growth rate, which is caused by the inclination of fatigue crack propagating through these grains with low grain boundary misorientation.

Abstract:Ni-6W alloy strip with 70μm thick was used as substrate, nanoporous NiW was prepared by anodic oxidation method, and then CeO2 was deposited by chemical decomposition method on nanoporous NiW to prepare NiW-nano-CeO2 electrode. The morphology structure of the NiW, nanoporous NiW and NiW-nano-CeO2 three electrodes were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD) and XPS. The electrochemical hydrogen evolution behaviors of the three electrodes were characterized by cathodic polarization curves, cyclic voltammetry curves and electrochemical impedance techniques. The results show that NiW-nano-CeO2 electrode has the highest electrocatalytic hydrogen evolution performance, which is mainly due to the three-dimensional nanoporous structure, small mass transfer impedance, large electrochemically active specific surface area and the synergistic effect between NiW and CeO2. When used as an electrocatalyst for hydrogen evolution, the current density reaches 100 mA cm-2 in 1M NaOH solution, it is 55 mV and 81 mV lower than that of NiW-CeO2 lectrode and NiW electrode, respectively. The impedance spectra obtained were fitted and analyzed, and the influence of CeO2 on the electrochemical process of the whole hydrogen evolution process was analyzed. The results show that the hydrogen evolution performance of the (200) crystal-exposed nano-porous NiW-CeO2 electrode is better than that of the Ni (111) crystal-exposed NiW-CeO2 electrode and the non-preferential orientation Ni-S/ CeO2, Ni-Zn/ CeO2 electrode. The composite electrode has a higher exchange current density of 1.7 × 10-1A cm-2 than the co-deposited Ni-CeO2 reported in the literature. In this paper, the morphology of CeO2 was controlled by this method, and then the (200) crystal face was selectively exposed to control the catalytic performance of NiW-CeO2 composite electrode for hydrogen evolution.

Abstract:A composite Ni-based coating with diamond mass fraction of 10% was prepared on the surface of 65Mn steel by induction heating. The microstructure and phase composition of the brazing joint were analyzed by SEM, EPMA and XRD. The element diffusion mechanism and formation mechanism of diamond/filler interface in induction brazing were studied. The wear resistance of the coating was tested by dry sand rubber wheel wear tester, and the wear resistance enhancement mechanism of diamond/Ni-based coating was analyzed. The results show that the main phases of filler alloy in brazing coating are Ni4B3, (Ni, Fe) solid solution, Ni3Si2 and CrB. The diamond and the filler alloy react in metallurgy, and the distribution of C element at the interface of diamond/filler alloy causes the appearance of double layer carbide structure on diamond surface, which are Cr3C2 on diamond side and Cr7C3 on the surface of Cr3C2 respectively. The wear resistance of the diamond composite coating is significantly better than that of the steel substrate. The wear weight loss of the coating is only 0.25g in 60min, which is 1/12 of that of the steel contrast sample. Diamond plays a role in preventing furrow expansion during the wear process, and the failure mechanism of the coating is Ni-based alloy wear and diamond shedding.

Abstract:In order to identify the damping and vibratio-reduction characteristics of metallic cylindrical sandwich shell under high temperature condition, a metal-rubber material with excellent temperature resistance and viscoelastic damping characteristics was adopted as the sandwich core for damping layer. The effects of internal structural parameters and external excitation conditions on the dynamic mechanical characteristics of cylindrical sandwich shell with metal-rubber under different temperature gradients were studied. Firstly, the traditional metal-rubber stamping preparation process and vacuum brazing connection process were combined to realize the reliable metallurgical combination on the panel/core interface of sandwich cylindrical shell structural. The persistent temperature resistance of the prepared sample can be up to 500℃. Secondly, the effects of key parameters such as the core density, the thickness ratio of panel and core and the gradient temperature on the high-temperature damping characteristics by using different exiiation conditions were analyzed. The main performance evaluation indexes include the secant stiffness, the natural frequency, the vibration acceleration level and the high temperature damping ratio. Comparing to the non-sandwich cylindrical shell with equal quality, the stiffness of cylindrical sandwich shell with metal-rubber is positively correlated with the panel thickness and the core density. The damping effect decreases in the temperature range of 0-300℃, but increases in the temperature range of 300℃-500℃. The temperature-induced damping characteristic exhibits the obvious nonlinear.

Abstract:Magnesium alloys own excellent biocompatibilities and unique degradation characteristics. However, the poor corrosion resistance in physiological environment seriously restricted its development in clinical applications. In this study, Mg-Zn-Sr-Zr-Mn alloys were prepared by pre-tensile process. XRD (X-ray diffraction), OM (optical microscopy) and SEM (scanning electron microscopy) were used to investigate the relationship between the pre-tensile type variables and the microstructure, corrosion rate and film layer morphology. The results showed that with the increase deformation of pre-stretching, the grain sizes were gradually elongated, the numbers of twins were increased, and the dispersion degrees of precipitated phases were gradually increased. The corrosion rate of the three pre-stretching alloys in electrochemical (0.39→0.25 →0.74mm·y-1) and weight-loss (2.85→1.83→5.88mm·y-1) were both decreased firstly and then increased. Therein, the 4% pre-stretching alloy has high corrosion resistance, which indicated that appropriate pre-tensile deformation could improve the continuity of the precipitated phase at the interface, hinder the corrosion process, and play a positive role in the corrosion properties of the alloys. However, when the pre-tensile deformation continues to increase, a large number of dislocations will be generated and hydrogen diffusion path will be created, which was conducive to hydrogen enrichment and leads to the decrease of corrosion resistance. Moreover, appropriate pre-tensile deformation could improve the corrosion uniformity, densification and continuity of the film-layer, and delay the corrosion process by changing the redistribution of residual-stress.

Abstract:WC-WB-CoCr coatings were prepared by high velocity oxy-fuel spraying (HVOF), and the effect of temperature on the frictional wear properties of WC-WB-CoCr coatings was investigated. The microstructure and mechanical properties of the coatings were characterized by scanning electron microscopy, X-ray diffraction and microhardness tester. The high-temperature tribological properties and oxidation products of WC-WB-CoCr coatings were investigated by friction and wear testing machine and Raman spectroscopy, and the abrasion scar morphology was scanned and the wear rate of WC-WB-CoCr coatings was calculated by a surface profiler. The results showed that the WC-WB-Co-Cr coating mainly consisted of WC and CoW₂B₂, and the coating structure was dense and tightly bonded to the substrate. The friction coefficient of the coating decreased from 0.66 to 0.57 as the temperature of the wear test increased, and the wear rate of the coating increased with the increase of temperature, but the growth rate of its wear rate decreased with the increase of temperature. During high temperature wear, the oxide film on the surface of the wear marks mainly consisted of WO₃ and CoWO₄, and CoWO₄ showed better high temperature wear resistance than WO₃. The main wear mechanisms of the coating are fatigue wear and adhesive wear.

Abstract:The high-temperature steam oxidation behavior of zirconium alloys is one of the issues that need to be focused on under loss of coolant accident (LOCA). To study the effect of Sn on the high-temperature steam oxidation behavior of zirconium alloys, SH12(Zr-0.75Sn-0.2Fe-0.1Cr, wt.%) and Zr-4(Zr-1.5Sn-0.2Fe-0.1Cr) alloys with different Sn contents were used for high-temperature steam oxidation tests at 1000, 1050, 1100 and 1200 ℃, under simulated LOCA conditions. The microstructure of the oxidized samples and the microhardness of the samples before and after oxidation were analyzed by optical microscope, electron probe microanalyzer, and microhardness tester. The results show that SH12 with low Sn content has better oxidation resistance to high-temperature steam than Zr-4 alloy with high Sn. This indicates that reducing the Sn content can improve the oxidation resistance to high temperature steam of zirconium alloys. Before oxidation, the microhardness of the SH12 alloy is lower than that of the Zr-4 alloy, while after oxidation the microhardness of the SH12 alloy matrix is significantly higher than that of the Zr-4 alloy, which is consistent with the result that the oxygen content in the matrix of the SH12 alloy is higher than that of the Zr-4 alloy after oxidation. This indicates that Sn has the effect of inhibiting the diffusion of oxygen in the Zr matrix. Through first-principles calculations, it is found that Sn is easily combined with O, thereby inhibiting O diffusion in the zirconium matrix, which reasonably explains the higher oxygen content in the oxidized SH12 alloy compared to the Zr-4 alloy.

Abstract:Single-phase V-based alloy membranes have potential applications in the field of hydrogen separation purification due to their higher hydrogen permeability and lower cost than Pd alloy membranes. The effect of Cr content on the hydrogen solubility and diffusivity, hydrogen permeability and hydrogen embrittlement resistance of single-phase V90-xTi10Crx(x=0,5,10,20) alloys has been investigated in this paper. The results show that the increase of Cr content decreases the hydrogen dissolution and hydrogen diffusion in V90-xTi10Crxalloy, thus decreasing the hydrogen permeability, but V90-xTi10Crx alloy still shows better hydrogen permeation performance than Pd and Pd-Ag alloys. Moreover, the fracture temperature of the V90-xTi10Crx alloy decreases from 184°C (x=5at%) to 141°C (x=10at%) with increasing Cr content, while x=20at% the membrane maintaines its integrity when air-cooling to room temperature, exhibiting excellent resistance to hydrogen embrittlement.

Abstract:The direct metallurgical bonding of C45 steel/tin-lead alloy bimetallic structures was achieved by the hybrid TIG arc and droplet deposition manufacturing. The microstructure, interface element distribution and main phases of the steel/lead bimetallic structure were studied by metallurgical microscopy, scanning electron microscopy and X-ray diffraction. The results indicated that the steel/lead bimetallic structure interface formed by the droplet deposition composite TIG arc additive manufacturing process are no obvious cracks, pores and other macroscopic metallurgical defects; According to the distribution of intermetallic compounds (IMCs) at the steel/lead interface, there is both "reactive wetting" and "inert wetting" during the impact and spreading of lead alloy droplets on the C45 steel substrate, where the reactive wetting interface has small fluctuations and the IMCs at the interface are FeSb₂ and FeSn₂, and the inert wetting interface does not precipitate reaction products and has tiny pore defects. The IMCs layer thickness at the center of the molten pool is the largest, and the IMCs layer thickness is about 6 μm. The IMCs layer thickness at the interface shows a non-linear decreasing trend as the test position gradually moves away from the center of the molten pool.

Abstract:The present study is devoted to research the effect of process parameters on processability, and aging treatment on microstructure and mechanical properties of selective laser melting (SLM) high Mg-content Al-Si-Mg-Zr alloy. The results show that alloy forms a large number of fine equiaxed grains at the boundary of the molten pool, which can avoid the generation of cracks during the SLM forming process and increase the processability of the sample. The porosity of the samples obtained under different process conditions is less than 0.3%. The yield strength (YS) and ultimate tensile strength (UTS) of the as-built samples are 426 ± 8 MPa and 464 ± 12 MPa respectively. After aging treatment, due to the increase in the number of nanoparticles embedded in α-Al cells, the strength of the sample increases obviously. The maximum YS and UTS of aged samples reach 482 ± 11 MPa and 522 ± 10 MPa, respectively. The strength of present samples is much higher than that of commercial SLM-formed Al-Si-Mg alloy.

Abstract:Abstract: In this study, the continuous extrusion is combined with an equal-channel die. The microstructure evolution of Al-Sr master alloy under large strain extrusion is analyzed by finite-element simulation, metallographic microscopy, X-ray diffraction, and transmission electron microscopy. Results show that the maximum effective strain in the equal-channel die can reach 16, which appears on the a-path passing through the outer corner of the first die angle, and the refinement effect of Al4Sr phase is the best. The refinement effect of each path on Al4Sr phase is as follows: inner a-path > middle b- path > outside c-path. Using the extrusion method with one die of double hole, the coarse Al4Sr phase particles in the center of cavity inlet can pass through the a-path with largest strain in the equal-channel die, so that they can be effectively refined. Finally the particles of Al4Sr phase in the center and edge of the product are effectively refined, with an average length of about 4.5 μm. Transmission electron microscopy observation shows that after large plastic deformation, due to the increased cumulative strain and increased microscopic strain, the internal dislocations of Al4Sr phase are entangled and delivered, forming a dislocation wall that interacts with the external dislocations to break Al4Sr phase particles. The fragmentation exerts a significant refining effect on Al4Sr phase particles. At the same time, due to the increased interfacial energy, a small amount of Al4Sr phase dissolves.

Abstract:Drived by the need to develop the key components with multifunctional performances such as lightweight, vibration-reduction and electrical conductivity for aviation aircraft, electic control box of vehicle, a copper-steel wire composite metal rubber with double-helix structure was designed and fabricated. The internal crosslinked meso-structure evolution of composite metal rubber was analysed by means of finite element simulation. In order to better understand the dynamic mechanical and the electrical properties of the copper-steel wire composite metal rubber, the experimental platforms for the dynamic loading test with variable excitation condition and the electrical resistance test were established. The damage factor was proposed to evaluate the fatigue failure of composite metal rubber. The effects of copper-steel mass ratio on the dynamic vibration reduction performance, fatigue damage and static/dynamic electrical resistance were invesitigated. The results show that the dynamic stiffness increases and the loss factor decreases with the increase of frequency and amplitude. The larger damage factor, the more sensitivity of dynamic stiffness fluctuation and loss factor fluctuation. The larger copper-steel mass ratio leads to the more serious dynamic wear of internal crosslinked wires. The electrical resistance decreases with the increase of static compression. With the increase of dynamic vibration cycle, the electrical resistance exhibits the increasing evolution, especially for the larger ratio of copper wire.

Abstract:Using the chemical coprecipitation method, the comparative experiments were carried out by changing the process parameters such as growth temperature, pH of coating environment, cleaning and dispersion mode of Fe3O4 nanoparticles. The best parameters and conditions of Fe3O4 nanoparticles in growth stage, coating stage and dispersion stage were summarized and the previous preparation process was optimized to improve the dispersion stability of oleic acid coated magnetic particles in kerosene. The samples were characterized by XRD, TEM and VSM and the rheological properties of the kerosene based magnetic fluid were analyzed by rotating rheometer. The results show that the average particle size of the modified Fe3O4 nanoparticles is about 14 nm, showing a regular sphere. The saturation magnetization of modified Fe3O4 nanoparticle is 60 emu/g and high-density kerosene based magnetic fluid with a mass fraction of 60% was prepared. Compared with ordinary magnetic fluid, the high-density kerosene based magnetic fluid obtained by this preparation process has a great improvement in saturation magnetization and oxidation resistance and has higher application value.

Abstract:In recent years, modern industry has put forward increasingly stringent requirements on the properties of materials, and surface modification has gradually become an effective means to improve the surface properties of materials. CrAlN coating has attracted extensive attention in the field of protective coatings because of its good mechanical properties and excellent high-temperature oxidation resistance. This paper reviews the latest research progress of CrAlN based coatings in recent ten years, including the structure and properties, preparation optimization, alloying, the design and advantages of CrAlN based nano multilayer structure coatings and nano composite structure coatings, Finally, the potential development direction of CrAlN coating is discussed, in order to promote the development and application of CrAlN coatings in the field of protective coatings.

Abstract:Ta and Ta alloys have been used in high-tech fields such as aerospace, metallurgical chemical industry and nuclear industry due to their excellent chemical stability, high temperature mechanical properties, corrosion resistance and processing and forming ability. In view of the huge application potential of Ta and its alloys, scholars have carried out extensive research on it, and have achieved rich research results. According to the existing research results, this paper systematically summarizes the material system types and application fields of Ta alloys, the existing alloy preparation methods and their advantages and disadvantages, the mechanical properties of the main alloy systems and their influencing factors, the high temperature protective coating system and its preparation methods. Finally, the future research directions are prospected according to the shortcomings of the current research.

Abstract:Nickel-rich layered oxides have become the preferred cathodes for high-energy-density Li-ion batteries due to their relatively high specific capacity, further increasing the Ni content, the material properties tend to be LiNiO2, and the electrochemical and structural stability deteriorate. Lattice element doping is an effective strategy to improve the stability of LiNiO2. Clarifying the structure of LiNiO2 cathode material and clarifying the influence and regularity of doping elements on it is of great significance for the development of nickel-rich cathode materials with Ni content greater than 90%. In this paper, the structure of LiNiO2 material and the stability problems it faces are firstly introduced. Then, the influences and laws of typical doping elements such as Co, Mn, Al, Mg, Ti, Zr, and W on LiNiO2 are reviewed, and anionic and multi-element doping and potential doping elements are discussed. This paper aims to provide a new perspective on LiNiO2 doping with a view to developing high-capacity stable Ni-rich cathode materials for power batteries using more efficient doping schemes.

Abstract:A batch of turbine blade castings were produced by using a third generation single crystal superalloy. After solution heat treatment, a large number of bright white spots with irregular shapes were observed on the blade surface. Through metallographic detection of the blade sections, a distinct surface layer was exhibited, in spite of the uniform γ phase structure in the internal area of the castings. The bright white substrate of the surface layer is determined to be continuous γ’ phase composed of Ni, Al and Ta elements. In the surface layer, a lot of lamellar TCP phases precipitated from the γ’ phase matrix. The element distribution near the surface of the casting was measured and analyzed. It was confirmed that the surface layer of the casting was a typical Cr-poor layer, leading to the phase transition from γ to γ’ and the coupled growth of γ’ and TCP phases. The depletion of Cr in the surface layer also resulted in the residual of γ/γ’ eutectic between the surface layer and the internal area.