Abstract:The failure of solder joints under thermal cycling is mainly as a result of progressive damage process of solder materials. The objective of this study was to investigate the damage behavior of SnAgCu solder under thermal cycling condition. A damage model was proposed and employed to simulate the thermal cycling behavior of SnAgCu solder. The proposed damage evolution law was based on continuum damage mechanics and an interaction between creep and fatigue. Thermo-mechanical cycling and thermal cycling tests were conducted for model parameter determination. A special bimetallic load frame with single joint-shear solder sample was designed and used to study the damage evolution behavior of SnAgCu solder. The damage variable D=1–R0/R was selected and measured for the single joint-shear solder sample every dozens of cycles during thermal cycling tests to verify the model. The damage evolution law was deduced as power function with thermal cycles and the results show that the experimental damage data can be fitted reasonably well by the relationship as the damage model proposed. The microstructure evolution of SnAgCu solder under thermal cycling was observed by Scanning Electron Microscopy and the damage mechanism was analyzed.

Abstract:An epitaxial Sm0.2Ce0.8O1.9-x (SCO) single buffer layer with thickness of about 250 nm has been deposited via dip-coating polymer-assisted chemical solution deposition (PACSD) approach for YBCO coated conductors on bi-axially textured Ni-5%W (200) alloy substrate. Flat, crack-free SCO films with sharp (200) c-axis orientation and texture have been obtained by carefully controlling the concentration of precursor solution, withdrawing speed, annealing temperature and dwelling time. Leaving other three factors unchanged, focuses on the influence of different withdrawing speeds on the performance of the SCO buffer layer has been focused on. YBCO superconducting layer has been deposited equally via dip-coating PACSD approach on the SCO-buffered NiW, showing a bi-axially texture. Micro-structural investigations revealed a homogeneous surface structure. Both of these indicate that SCO single buffer layer can function well as template. The approach has shown a promising way to fabricate long-length, low-cost YBCO coated conductors.

Abstract:The Gibbs free energy of liquid and crystal, intermetallic compounds, and amorphous phases were investigated by thermodynamic analysis for microstructure of high-entropy alloy (HEA). Results show that the value of ΔSrΔHh(sol.) plays an important role in estimating the microstructure of HEAs. The alloys with lower value of ΔSrΔHh(sol.) have stronger tendency of forming single fcc or bcc solid solution, and the alloy with complicated microstructure always has larger value of ΔSrΔHh(sol.).

Abstract:Effects of ageing with electric pulse treatment on shape memory effect and precipitation of Cr23C6 carbide in a pre-deformed Fe-Mn-Si-Cr-Ni-C alloy were investigated. The results showed that electric pulse treatment could accelerate the migration of Cr and C atoms and precipitation of Cr23C6 carbides, lower ageing temperature, shorten ageing time and induce the nucleation of Cr23C6 carbides. Therefore, the shape recovery ratio was improved to the maximum value 89.2% from 32% of a water-quenching alloy within 30 min in a pre-deformed Fe-Mn-Si-Cr-Ni-C alloy aged with electric pulse treatment compared to alloys aged without electric pulse treatment at 973 K.

Abstract:Using the multi-field coupled analysis model with considering various thermal effects for the hot shear spinning of TA15 titanium alloy thin-walled shells, the deformation mechanism of thermal load conditions and mechanical load conditions have been elucidated. The results show that higher workpiece temperature and mandrel preheat temperature can bring about a smaller temperature gradient in the thickness direction, and the deviation ratio has a complicated effect on temperature difference of the deforming zone and a marked negative effect on the fittability. Moreover, the friction between workpiece and roller has a significant influence on the temperature difference. Increasing roller feed rate increases the temperature difference and decreases the fittability, which is opposite to that of the cold shear spinning, and a larger roller setting angle is favorable to the decrease of temperature difference and the improvement of the fittability.

Abstract:The highly pure nano-silver sols were prepared by an electrolysis method using two highly pure silver flakes as electrodes and deionized water as electrolytic solution, and PVP served as stabilizer. The effects of PVP content, electrolytic time and current density on the colloidal silver nanoparticles were researched. The results indicate that as-synthesized particles were spherical about 1~3 nm in size, and monodispersed and its concentration reached to 130 μg/g under the condition of 5.0 wt% PVP with current density about 1~2 mA/cm2 for 150 min. Moreover, the nano-silver sol had such an excellent stability that it had not any change though it was placed in dark at room temperature for 6 months.

Abstract:The annealing behaviors of hot and cold rolled Zr705 were investigated in a wide temperature range of 200~850 °C. Compared to the cold rolled specimens, the hot rolled specimens exhibited lower hardness at temperatures < 500 °C and a shift of the temperature for the maximum hardness to a higher value. Microstructural examination showed that the transformation rate from β to ω phase in the hot rolled specimens was lower than that in the cold rolled specimens. Recovery and recrystallization occurred at a lower temperature in the hot rolled specimens than in the cold rolled specimens. Partial recrystallization occurred in both the specimens at 500 °C, and more recrysatllized grains were observed in the hot rolled specimens. The recrystallization process was completed at 700 °C in both the specimens.

Abstract:Novel coated Pt@SnO2/Al2O3 supported catalyst was prepared by a continuous reduction-ultrasonic loading approach. The peculiar coated structure enables it to have better aggregation and sintering resistance and was characterized by transmission electron microscope. When used in the propane dehydrogenation reaction, coated Pt@SnO2/Al2O3 with a Pt/Sn molar ratio of 1:1.5 exhibited excellent catalytic activity and high-temperature stability compared with that using the conventional impregnation method, which further verified intense synergistic interactions between SnO2 shell and Pt core.

Abstract:The alloy with composition Ni-45.61Al-7.8Mo (at%) has been directionally solidified by liquid metal cooling (LMC) process. The effect of growth rate on the solidified microstructure such as interface morphology, dendrite growth and primary β phase precipitation, was experimentally investigated. The interface morphology of the β phase undergoes the evolution from plane front, cellular, thick dendrite to thin dendrite with increasing of growth rate for a given temperature gradient. The first dendrite spacing λ1 of the primary β phase increases gradually during the cellular growth, and decreases during the dendrite growth, while the second dendrite spacing λ2 decreases with increasing of the growth rate. The amount of primary β phase increases with the growth rate. And the analysis results show that the varieties of nucleation rate of NiAl caused by melt undercooling variation with different growth rates are responsible for the phenomenon.

Abstract:The grain topology was investigated by the topological data from serial sectioning experiment on pure iron and simulation of grain growth with Monte Carlo method. The results show that the mean number of faces of pure iron =12.46 is different from other experimental data in literatures, such as β-brass, Al-Sn alloy, β-titanium, austenite grains of steel, etc. The reason is likely due to the variable surface tension and mobility, which are assumed to play an important role in the evolution of polycrystalline grain systems and thus exert influence on the topological characteristics of the grain network. For the distribution of the number of faces per grain and the grain size distribution, the data from Monte Carlo simulation is consistent with the data from pure iron, but different with the data from Al98Sn2 due to the segregation of Sn atoms to the grain boundary that possibly alter the grain growth process.

Abstract:Based on the heat processing technology of 7085 aluminum alloy aircraft parts, 7085 aluminum alloy in the temperature range of 300~450 °C and strain rate range of 0.0001~1 s-1 have been studied by hot compressing testing. Processing map of 7085 aluminum alloy was generated and hot formability was analyzed. The results demonstrate that the temperature range of 340~450 °C and strain rate range of 0.0001~1 s-1 is the processing safety area for hot deformation of the 7085 aluminum alloy. The flow instability region occurs in the temperature range from 300 °C to 340 °C and strain rate range from 0.01 s-1 to 1 s-1. The adiabatic shear bands are generated when 7085 aluminum alloy is deformed in the flow instability region. The structure of adiabatic shear banding is violently elongated grain. The potential processing dangerous area is in the temperature range from 300 °C to 340 °C and strain rate range from 0.0001 s-1 to 0.01 s-1. The optimal deformation processing parameters are the deformation temperatures ranging from 340 °C to 410°C and strain rates ranging from 0.0004 s-1 to 1 s-1.

Abstract:The compressive property and microstructure of Mg-3Al-6Zn-2Y alloy at the strain rates of 0.001, 900, 1300 s-1 were studied. The hardening rate, ultimate strength, and yield strength increased with strain rate increasing, while the reinforcement phases of Al2Y and Al12Mg17 and the transition phase MgZn2 decreased. The {102}<100> twinning occurred with higher density of dislocation which tangled and piled up on the interface of crystal twin. The weakening effect on intensity caused by decreasing of reinforcement phases competes with the intensifying effect caused by the higher density of dislocation piling up on the interface of crystal twin.

Abstract:The numerical model of temperature filed for micro-droplet deposition manufacture was established by adopting finite element method and element birth and death technology. The transient evolution of temperature filed was simulated during fabricating 7075 aluminium alloy thin-wall part by micro-droplets. The results show that the forming temperature filed of thin-wall part presents circumferentially dynamic change along with the moving of droplet depositing position; the thermal cyclic curves of different droplet element nodes include different number of temperature peak and valley values. With increasing the height of deposited layer, the cooling rate of adjacent overlapping droplets from the first to the tenth layers was decreased gradually, the high temperature region in deposited layer was enlarged gradually and the variable temperature gradient was shown in part building orientation, which causes the grain size of adjacent overlapping droplets to change. Experiments were carried out to validate the proposed numerical model in this paper. The simulated result and the experimental results are in good accordance.

Abstract:The semi-solid deformation behavior of Ti14 alloy was investigated by Gleedle1500 at strain rate of 0.05 s-1 and 0.5 s-1, and the deformation temperature 1273~1423 K. The results show that the strain rate and deformation temperature have strong effects on the flow stress. The maximum compressive stress was greatly depended on fraction solid, and a stress relaxation occurred between 0.95 and 0.98 (the temperature from 1323 K to 1373 K), which was related to the decrease in amount of solid bridges between grains. Because of the partial solid/liquid segregation during deformation, the experimental strain rates are much lower than those calculated by the flow of liquid incorporating solid particles (FLS), which suggested that the main deformation mechanism between 1323 K and 1373 K is still plastic deformation of solid particles (PDS).

Abstract:The nanocomposites consisting of α-Fe and a small quantity of Nd2Fe14B have been prepared using rapid quenching from Nd6Fe91B3 melt with low rare earth content and ball milling for 25 h. The effect of rapid quenching speed on the phase composition, microstructure, and microwave electromagnetic properties of α-Fe/Nd2Fe14B nanocomposites have been investigated. Results show that the microwave complex permeability increases and the resonance frequencies (fr) of as-spun Nd6Fe91B3 alloys shifts to lower values with the increase of quenching speed, due to the decrease of Nd2Fe14B with the large anisotropy field (HA). The real part of complex permeability of Nd6Fe91B3 alloy reaches the maximum μmax′=7.88 at 1.55 GHz and imaginary part of permeability reach the maximum at 4.17 GHz μmax″=4.66. Furthermore, the α-Fe/Nd2Fe14B nanocomposites with low Re content shows an excellent microwave permittivity, and its resonance appears at about 2 GHz. Therefore, the α-Fe/Nd2Fe14B nanocomposites are beneficial to be applied to electromagnetic wave absorber in GHz, due to the cooperation effect of magnetic loss and dielectric loss.

Abstract:The formation of copper nanowires inside a carbon nanotube (CuNW@CNT) and boron-nitride nanotube (CuNW@BNNT) and the compressing behavior of the resulting composite structure were studied using molecular dynamics. After optimizing C(5,5) and BN(5,5) nanotubes filled with copper atoms, coaxial CuNW with an axial monatomic chain is formed inside the C(5,5) and BN(5,5). Analysis of the radial distribution function on the CuNWs shows that the CuNW inside CNT has better one-dimensional uniform distribution, whose crystallinity is better. And the CuNW inside BNNT has larger atomic distribution density, which can effectively enhance electrical conductivity for one-dimensional nanowire. Comparison of the axial compressing behavior of CuNW@C(5,5), CuNW@BN(5,5), C(5,5) and BN(5,5) reveals that the critical buckling strains and the total potential energy loss of CuNW@C(5,5) composite structure are bigger than that of CuNW@BN(5,5). The results indicate that the compressive resistance of CuNW@C(5,5) is stronger, but the protective effect on CuNWs at buckling is inferior to that of CuNW@BN(5,5).

Abstract:Employing MA-FAPAS and using TiAl as exothermal mediate layer, gradient cermets (TiC)pNi and TiAl were synthesized from element reactants in one step as well as the structure of (TiC)pNi/TiAl/Ti was accomplished. The effect of temperature, current and pressure on the process was analyzed. Microstructure observation and composition determination were made by FE-SEM, TEM and XRD. It reveals that well formed and crack-free bond were achieved with strong mutual diffusion of elements across both interfaces. Fracture toughness, thermal shock resistance and bonding strength were evaluated and residual stress distribution was simulated by finite element method. It indicates that the interface between TiAl/Ti has higher thermal resistance and shear resistance than that between (TiC)PNi/TiAl.

Abstract:The microstructure and hydrogen absorption and desorption properties of (VFe)48Ti26Cr26-xMox (0≤x≤5) alloys were investigated. XRD and PCT testing results show that both the lattice constants and plateau pressure increase with the rising of Mo content, and the hydrogen absorption/desorption capacities have no significant change when 0≤x≤2. While the effective desorption capacities maintain more than 2%. When x=1, the alloy shows the maximum hydrogen absorption capacity of 3.59% and the maximum desorption capacity of 2.08%, with a plateau pressure of 0.337 MPa at room temperature. SEM and EDS analyses show that all of the alloys consist of bcc main phase, Laves phase and rare earth oxide phase. Mo mainly distribute in the bcc main phase, and a small amount of Mo exist in the Laves phase.

Abstract:The La0.6Eu0.4B6 nanopowders were prepared by high-energy ball milling, and then the ball-milled nanopowder were used to prepare the high-density La0.6Eu0.4B6 polycrystalline bulks by spark plasma sintering (SPS). The influence of sintering temperature and pressure on the sample density and mechanical properties were investigated. The results show that this method reduces the sintering temperature more effectively than the conventional hot-pressing method. The sample density, Vickers hardness and flexural strength are 4.71 g/cm3, 23.37 GPa, and 295.14 MPa, respectively, which ??are also higher than those of conventional hot-pressing methods. The thermionic emission results show that when the cathode temperature is 1873 K, the maximum emission current density of La0.6Eu0.4B6 is 33.74 A/cm2. Under the same sintering condition, the Vickers hardness, flexural strength and thermionic emission current density of ball-milled nanopowder are increased by 28%, 58% and 32% compared with coarse-powder-sintered sample. These results indicate that refining the powder grain size to nano level is beneficial for reducing the sintering temperature and promoting the thermionic emission and mechanical properties.

Abstract:Young’s modulus and hardness of Cu6Sn5 intermetallic compounds (IMC) were measured by nanoindentation. The samples were prepared according to actual reflow soldering condition and service. The microstructure and chemical composition of the samples were characterized by scanning electron microscopy (SEM) equipped with energy dispersive X-ray analysis (EDX). With continuous stiffness measurement (CSM) technique and difference strain rates, continuous values of hardness and elastic modulus for Cu6Sn5, which belong to lead-free solder joints (Sn3.0Ag0.5Cu, Sn0.7Cu and Sn3.5Ag), were measured. The load, Young’s modulus and hardness-displacement curves were obtained. The creep stress exponents for Cu6Sn5 were determined by nanoindentation.

Abstract:The appearance of the discontinuous strain in the outer surface of a specimen does not indicate the just formation of the adiabatic shear band. The phenomenon is believed to be a result of the further development of the deformed adiabatic shear band. For calculating the peak temperature in the adiabatic shear band, the elastic shear strain should be extracted from the local shear strain because the elastic part does not contribute to the plastic work. The peak temperature in the adiabatic shear band in a Ti-6Al-4V specimen (TA-50) in dynamic torsion is calculated. It is divided into 3 parts: ambient temperature and temperatures caused by homogenous and inhomogenous shear strains, respectively. In two cases (the elastic shear strain is extracted from the local shear strain or not), the calculated temperature values are 669 °C and 665 °C, which are in the range of the thermal recovery/recrystallization temperature and do not exceed the phases transformation temperature. The calculated results in the paper are higher than the calculated result of 630 °C by Liao and Duffy (1998). If the relation between the shear stress and the local plastic shear strain is not completely clear, an appropriate approximation is necessary.

Abstract:The microstructure and creep mechanisms of FGH95 nickel-base superalloy were investigated by full heat treatment, microstructure observation, lattice parameters determination and creep curves. Results show that after the alloy is HIP treated, coarse g ￠ phase discontinuously distribute along the previous particle boundaries. After solution treatment at high temperature and twice aging, the grain size has no obvious change, and the amount of coarse g ￠ phase decreases. Moreover, the fine g ￠ phase and MC carbides dispersedly precipitate in the grain, which can enhance the creep resistance of the alloy. Because the formation elements of g ￠ phase (Al and Ti) are dissolved into the g matrix, the lattice parameter of g ￠ phase increases while the g phase decreases at the same time by XRD spectral line measurement, which results in the lattice misfit of g/g ￠ phases decreasing. In the ranges of experimental temperatures and applied stresses, the creep activation energy is about 630.4 kJ/mol. During creep, the mechanisms of FGH95 alloy are dislocation moving in the matrix or shearing into the g ￠ phase. Thereinto, the creep dislocations move over the g ￠ phase by Orowan mechanism; however, the <110> super-dislocation shearing into the g ￠ phase is decomposed to form the configuration of (1/3)<112> super-Shockleys partials plus the stacking fault.

Abstract:The dense Zr-N alloying layers were prepared on the surface of Ti6Al4V alloy by two kinds of surface alloying processes to improve the wear resistance of Ti alloy at elevated temperature. One process is Zr-diffusing with nitriding simultaneously (synchronous surface alloying), and the other is nitriding after Zr-diffusing (asynchronous surface alloying). The microstructure and tribological property at elevated temperature of the modified surface layers were investigated. Results show that both the Zr-N diffusion layers consist of ZrN phase, and the asynchronous surface alloying with thick Zr-Ti solid solution layer is beneath the surface. The surface microhardness of the Ti6Al4V alloy was significantly increased by both Zr-N alloying layers. With the same time and temperature, the thickness of the asynchronous surface alloying layer was about 6 times of the synchronous surface alloying layer, because the asynchronous surface alloying has excellent solution and low diffusion inhibition. The results of the ball-on-disc wear tests indicate that the wear resistance at 300 °C of the synchronous surface alloying layer was not significantly improved because of the shallow diffusion depth. The asynchronous surface alloying reduced the wear rate obviously by two orders and the friction coefficient by 50% due to the high surface hardness, thick depth, good thermal oxidization resistance and big surface load-bearing ability.

Abstract:The tensile property and surface composition of U-2%Nb alloy after long storage at different humidity and in underwater environment have been investigated. The results show that the samples stored in 10% humidity environment for 5 years have almost the same tensile property as un-stored samples in the same batch, and are of ductile fracture character. The samples stored at 100% humidity or in underwater environment exhibit a little reduction of tensile strength and remarkable drop of plastic property, and present distinct brittle fracture character. Raman analysis indicates that the primary composition of the surface of the sample in dry environment is UO2, while the sample at 100% humidity or in underwater environment is U3O8 and other UO2+x oxides.

Abstract:Thermal cycling testing to the 8 batches of thermal barrier coating samples for different holding time was carried out by means of cycling heating and cooling apparatus to simulate TBCs service environment. Using a mathematical model of exponential decline to fit thermal cycle experimental data, characterization parameters of static oxidation performance and thermal fatigue performance of thermal barrier coated samples were obtained. The result indicates that static state oxidation performance and thermal fatigue performance of TBCs samples prepared under present experimental technology conditions have different match relation. The estimated value for static state oxidation performance is 677±194 h, and the estimated value for thermal fatigue performance is 6789±1818 times.

Abstract:Compact conversion coatings with much better corrosion resistance for Mg-8.5Li alloy were obtained by immersing in a solution of permanganate. The concentration of potassium permanganate was discussed. The surface morphology of the conversion coatings was observed by scanning electron microscopy (SEM), and the chemical composition was characterized by X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD). The corrosion resistance of Mg-8.5Li alloy and permanganate conversion coatings were investigated by means of potentiodynamic polarization, electrochemical impedance spectroscopy (EIS) and mass loss measurement. The results show that the coatings with cracked morphology are homogeneous and uniform. The corrosion resistance of permanganate conversion coatings is improved greatly compared with that of Mg-8.5Li alloy. When the concentration of permanganate is 4.0 g/L, the corrosion current density is the smallest, capacitance arc is the biggest and corrosion rate reaches minimum and the conversion coating presents the best corrosion resistance behavior.

Abstract:The long persistent phosphors Sr3-xCaxAl2O6:Eu2+, Dy3+ (x=0, 1, 2, 3) were prepared by the high temperature solid state reaction. The structure, photoluminescence, afterglow and thermoluminescence properties were studied. The X-ray diffraction analyses show that all samples have a similar structure, which is cubic structure Sr3-xCaxAl2O6. Results indicate that Sr/Ca ratio has no influence on the phase structure, but luminescent properties change significantly with the Sr/Ca ratio. The initial intensity and attenuating speed of the afterglow are different in different samples. However, all decay curves conform to double exponential decay. Luminescent properties can be adjusted by Sr/Ca ratio. In addition, thermoluminescence of all samples was also recorded. It is found that the initial intensity of afterglow significantly decreased when there were two trap energies in the sample, which may be due to electron transfer between trap energies.

Abstract:The effect of Zr, Mo or Y doping on mechanical and electrical properties of Pt-Ir binary alloys was investigated. The alloys were prepared in a vacuum high frequency melting furnace. X-ray diffraction and metallographic microscopy were employed to detect the microstructures. Electric bridge and eddy current conductive instrument were employed to test the electrical resistivity and the mechanical properties of alloys were tested by AG-X100KN type tensile testing machine. The results show that adding rare metal elements into Pt-Ir system could refine structure effectively, increase the melting point, density, mechanical properties and electrical resistivity of the alloys, but decrease the processing property.

Abstract:The variation rule of color of oxidation layer of TC18 titanium alloy and relationship between color of oxidation layer and corresponded mechanical properties were investigated via oxidative test within the temperature range of 100~1000 °C and mechanical property test. The results show that various colors of oxidation layer can be obtained. Mechanical properties of the alloy remarkably decrease and colors of the oxidation layer gradually turn dark with the increasing of oxidizing temperature. The relationship between color of oxidation layer and corresponded mechanical properties of TC18 titanium alloy was determined. When the oxidation color turns to be light green, the mechanical properties of the alloy significantly decrease which can not satisfy well the standard mechanical properties of TC18 titanium alloy.

Abstract:Gd99.75Fe0.25 alloy prepared by arc melting under purified argon atmosphere and homogenization annealing treatment at 1123 K for 168 h was investigated by X-ray diffraction, physical property measurement system, microhardness tester and electrochemical workstation. The results show that the Gd99.75Fe0.25 alloy still retains hexagonal crystal structure of pure Gd. The Curie temperature of Gd99.75Fe0.25 alloy is 294 K, and the alloy exhibits a second-order magnetic transition from ferromagnetism to paramagnetism. The maximum magnetic entropy changes of Gd99.75Fe0.25 alloy under magnetic field changes of 0~2 T and 0~5 T are 4.99 J·kg-1·K-1 and 9.37 J·kg-1·K-1, respectively, which are larger than that of pure Gd. The micro-hardness (HV0.2) of Gd99.75Fe0.25 alloy is 590 MPa, which is equivalent to that of pure Gd. But the corrosion resistance is improved by doping a small amount of Fe. Large magnetocaloric effect and good application features make the Gd99.75Fe0.25 alloy as a potential magnetic refrigerant at room temperature.

Abstract:Ag replacing Mg can improve the glass-forming ability of Mg75Ni15Gd10, and its preparation size increases from 3 mm up to 7 mm of Mg69Ni15Gd10Ag6. The Ag addition can improve the density of corrosion products in alkali solution, reduce the passivation current density, improve the forming speed and the stability of passive film and enhance the electrochemical reaction charge transfer resistance. The corrosion rate of Mg75Ni15Gd10 in NaCl solution of 0.1 mol/L descended by 62%. After 90 cycles, the capacity retention rate can be enhanced to 75% from 55% of Mg75Ni15Gd10.

Abstract:The effect of rapid hot extrusion on the microstructure and mechanical properties of fine-grained (10~20 μm) 93W-4.9Ni-2.1Fe, fine-grained 93W-4.9Ni-2.1Fe+0.03%Y and traditional coarse-grained (40~45 μm) 93W-4.9Ni-2.1Fe alloy was investigated. The results show that after rapid hot extrusion, the comprehensive mechanical properties of the alloys are significantly enhanced compared with the as-sintered alloys. The initial grain size has a profound effect on the mechanical properties of as-extruded alloys. With the same extrusion processing parameters, the ultimate tensile strength (UTS), elongation and hardness of the as-extruded fine-grained 93W-4.9Ni-2.1Fe+0.03%Y alloy reached 1570 MPa, 6.5% and 45.2 (HRC) respectively. However, the ultimate tensile strength (UTS), elongation and hardness of the as-extruded coarse-grained alloy were 1260 MPa, 5.6% and 39.1. Microstructure observation shows that compared with the traditional coarse-grained alloy, the fibrous degree of the as-extruded fine-grained alloy is much larger under the condition of the same deformation degree. Moreover, the aspect ratio of the tungsten particles in the as-extruded fine-grained 93W-4.9Ni-2.1Fe+0.03%Y alloy achieves 6.8, which is one time larger than that of the as-extruded traditional coarse-grained alloy. TEM shows that after hot extrusion, many subgrains could be observed in fine-grained tungsten phase and numerical dislocations tangled in coarse-grained tungsten phase. In addition, the dislocation density of both kind of matrix is low because of sufficient dynamical recovery-recrystallization.

Abstract:Preparation of protective coatings for uranium with amalgam formed by Zn, Sn and Au reacting with Hg respectively was investigated. The coatings were characterized by scanning electron microscope (SEM) and X-ray energy dispersive spectroscope (EDS). Effects of pretreatment and oxide layer on coatings were also studied. The results show that it is feasible to prepare coatings on uranium surface with amalgam. The thin oxide layer on uranium surface has less effects on the combination between coating and uranium, because the oxide can disperse in the coating during the preparation and fresh uranium was faced to amalgam. 1:1 HNO3 can get rid of the oxide effectively, and better combination between coating and uranium can be obtained. 20~50 μm thickness coatings can be prepared in a single time to Zn and Sn, but to Au, it is necessary to obtain a thick coating repeatedly.

Abstract:The study of dual heat treatment with different parameters has been performed on TA15 titanium alloy, which is a typical near a titanium and widely used in aerospace. The Electronic backscatter diffraction (EBSD) technique has been employed to characterize the microstructure and analyze the crystal orientation distribution of those samples subjected to different heat treatment. The effect of the heat holding time on microstructure morphology and orientation distribution was investigated. The formation and evolution of equiaxed primary ap, lamellar second as and transformed bT during the process of dual heat treatment has been revealed. The crystal orientation relationship between the ap and adjacent as has been analyzed. The results indicate that the holding time of stage I has an obvious influence on the morphology and distribution of ap. The equiaxed ap comes from heat treatment stage I as a result of retained primary ap. The holding time of stage II has a significant effect on the size and morphology of as. The mode of first lengthening and then thickening has been observed during the as coarsening process. A certain degree of match has been found between the crystal orientation of ap and adjacent as.

Abstract:Compressing bonding tests between pure titanium TA2 and 304L austenitic stainless steel have been carried out with the heating temperature 800, 850, 900, 950 °C by a thermal simulation machine. And then hot-rolling bonding test has been performed with the best heating temperature derived from the thermal simulation test results. The microstructure of the interfaces has been analyzed by optical and scanning electron microscopy (SEM). The interdiffusion of the elements and the reaction products at the interfaces have been evaluated by electron probe microanalysis (EPMA) and X-ray diffraction technique. And the shear strengths have been tested by a universal testing machine. Results show that the diffusion zone is dominated by σ-phase, σ′-phase, FeTi, NiTi and CrTi4. With a rise in the heating temperature the shear strength of the interface drops owing to an increase in the width of reaction products. The thermal simulation test sample heated at 850 °C gets the highest shear strength of about 147.5 MPa. And shear strength of the hot-rolling bonding plate heated at 850 °C is as high as 215 MPa.

Abstract:The La0.67Mg0.33Ni3 alloys were prepared by magnetic field assisted sintering synthesis (MASS). The hydriding/dehydriding properties and phase structure of the as-prepared materials were investigated through X-ray diffraction (XRD), identical volume method (PCT) and Differential Scanning Calorimetry (DSC). The results show that all the La-Mg-Ni alloys have the major phase of PuNi3 type (La, Mg)Ni3. After hydriding/dehydriding cycles, the phase structure is changed to La2Ni7, MgNi2 and LaNi3 with the lattice expansion. The measurement of PCT curves at room temperature indicates that the sample prepared under 1 T magnetic field has the minimum hydriding/dehydriding hysteresis (0.480), and the maximal dehydriding capacity (1.307wt%). DSC measurement indicates that the sample has two overlapping endothermic peaks which respectively corresponded to the hydrogen desorption of (La, Mg)Ni3 and LaNi5 hydride.

Abstract:TiC-doped 12-filament MgB2 wires was prepared by PIT method and enhanced by Cu/Nb composite cores. The precursor powder was treated in two steps. The effects of different temperatures on the phase composition, microstructure and superconductivity of the MgB2 wires were studied. Results show that two-step powders can increase the C substitution level effectively, and meanwhile the grain size of MgB2 reaches submicrometer level in the cores. MgB2 grains have good bonding property. The Jc can reach 3×104 A/cm2 when the wires are prepared at 4.2 K, 5 T.

Abstract:Nb-16Si-22Ti-2Al-2Hf-2Cr bulk alloys have been prepared by powder metallurgy. The effects of milling time (5, 10, 20 h) of powder mixtures and hot-pressing temperatures (1500, 1600 °C) on the microstructure and room-temperature mechanical properties of the bulk alloys were investigated. It is revealed that the hot-pressed alloys are mainly composed of 3 phases including Nb solid solution (NbSS), Ti solid solution (TiSS) and Nb5Si3 silicides. With prolonging the milling time, the volume fractions of Nb5Si3 and TiSS phases increase, but that of NbSS phases decreases. The improvement in room-temperature hardness of bulk alloys is achieved with milling time and hot-pressing temperature increasing, and the bulk alloy milled for 20 h and hot-pressed at 1600 °C has the highest hardness of 11500 MPa. Moreover, the fracture toughness of the alloys hot-pressed at 1500 °C and 1600 °C both decreased with milling time prolonging. The bulk alloy milled for 5 h and hot-pressed at 1500 °C has the highest fracture toughness of 10.14 MPa·m1/2.

Abstract:A new processing technique was proposed called High Power Pulsed Magnetron Sputtering-Plasma Ion Implantation & Deposition (HPPMS-PIID) based on High Power Pulsed Magnetron Sputtering (HPPMS) and Plasma-Based Ion Implantation & Deposition (PBII&D) processing. In this paper, CrN films were prepared by this technique and the surface morphologies, structure, composition and properties were studied compared with those of the CrN films fabricated by conventional HPPMS biased by DC–100 V and no bias. Once high voltage is applied, the film shows a smooth surface, very dense packed grains, and a discontinuous columnar structure. A highest intensity of CrN(200) preferential orientation and best adhesion were obtained by HPPMS-PIID due to the highly energetic ion implantation and bombardment. Compared with that of conventional HPPMS, high deposition rate was achieved in HPPMS-PIID since most ions were attracted into the sheath induced by negative high-voltage pulse, and consequently were deposited on the substrate.

Abstract:Tantalum element was used to improve wear resistance of laser clad NiCrBSi coating (Ni60) heat treated at 900 °C. Microstructure, microhardness and wear resistance of the pure NiCrBSi and Ta reinforced NiCrBSi coatings were investigated. The coatings were analyzed by scanning electron microscope (SEM) with energy energy-dispersive spectrometer (EDS). The phase constitution was identified using X-ray diffraction (XRD) experiments. Dry sliding wear tests were carried out on a pin-on-disc tribometer to study wear behavior. The results show M7C3 and M23C6 carbides were decomposed after 900 °C heat treatment, which resulted in the decrease in the microhardness of the coatings. However, after the heat treatment, the Ta reinforced NiCrBSi composite coating had higher microhardness and wear resistance compared to pure NiCrBSi coating since in situ TaC particles in the composite coating were not decomposed due to its high thermal stability.

Abstract:The uniformly dispersed silver nanopowders were prepared by even precipitation combined with thermal decomposition. The formation mechanism of silver nanopowder was investigated. The effects of pH value, calcination temperature and time on the size and morphology of the silver nanopowder were studied. The structure, composition, size and morphology of silver nanopowder were characterized by X-ray diffraction and scanning electron microscope. Results show that when the pH value is 7, calcinations temperature is 300 ℃ and the time 2 h, the obtained silver powders with an average size of 50 nm have excellent dispersion and uniform size. The method used for silver nanopowder production in this study has many advantages: the raw materials are easy to get and cheaper, the side-products in the production is recoverable with water, and the recovery can be used as a fertilizer in agriculture. Therefore, the processes can meet the requirements of clean-production of silver nanopowders.

Abstract:Gr.3 titanium tubes with two kinds of different oxygen content was designed, the thick-walled Gr.3 titanium tubes deforming cones were intercepted in accordance with determinate rule, then the micro-hardness on cross sections were tested, and the distribution curve of HV in the whole rolling duration was drawn. Comparing the microstructure at different positions of tubes rolled, the relation of HV variation and rolling process were investigated. Results show that the difference of HV on cross sections is large when the deformation rate is below 10%~20%, which is much more obvious in the case of lower oxygen content. The higher oxygen content is, the larger tendency of non-homogeneous of HV in radial direction of tubes becomes. As a result, the deformation rate should be greater than 35% and the entering amount should be small in the rolling process of thick-walled tubes; furthermore, the groove curve keeping smooth is beneficial to improve the quality of tubes.

Abstract:Lithium hydride (LiH) is one important thermo nuclear materials and its equation of state (EOS) date is of importance in inertial confinement fusion. In this paper, LiH film was produced by vacuum hot pressing technology. Process parameters were given below: vacuum was less than 5.0×10-4 Pa, the temperature was 450 °C, calefactive velocity 10 °C /min and the pressure from 4000 N/cm2 to 25000 N/cm2. The results indicate that thickness of LiH film is less than 100 μm, surface root mean square roughness less than 100 nm and thickness uniformity more than 98%. And the main component of film is LiH from XRD. LiH film has prefer-oriented, crystal-fined characteristic and internal stress.

Abstract:Antisite defects are the intrinsic defects for intermetallic compounds, affecting the materials’ mechanical, physical and chemical properties, and serving as a decisive structural factor to the properties under certain condition. Firstly, the theories for antisite defect study are reviewed, in which the physical and chemical aspects of antisite defect are generally studied by first principle and molecule dynamic methods based on quantum physics, while the temporal-evolution aspects linking to the microstructures are studied using microscopic phase field method based on Ginzburg-Landau equation. Secondly, the graphical demonstration of the antisite defect-diffusion mechanism relation explains the contribution as well as the potential harm of antisite defect to intermetallic structural materials. Finally, the authors summarize the research progress of antisite defect study on L12 and B2 structure as well as the site preference study of dopants, and conclude the deficit about antisite study.

Abstract:Iridium is the most promising material due to its high melting point and good chemical inertness, which is one of the most potential high-temperature oxidation-resistant materials for refractory metals above 1800 oC in aerospace filed. In this paper, the impendence and necessity of the iridium coating on refractory metals were introduced. The properties of iridium were presented in detail. The deposition methods and applications of the iridium coating from American, Japan, Europe and China were reviewed. Further, the advantages of double glow plasma technology and microstructure of the iridium coating produced by double glow plasma on refractory metals were highlighted in this study.