Abstract:The hot tensile behavior of Ti-22Al-24.5Nb-0.5Mo (at.%) alloy was investigated by the hot tensile tests at the temperature 910-1040°C and the strain rate 0.0001s-1-0.1s-1. The Arrhenius equations were calculated at the three different phase fields and the microstructure evolution mechanisms were studied by microstructure observation. The results show that the activated energies were 759.43kJ/mol, 516.71kJ/mol and 438.59kJ/mol at B2/β+O, α2+B2/β+O and α2+B2/β phase fields, respectively. The microstructure evolution were dominated by dynamic recrystallization of O-phase and dynamic recovery of B2/β phase grains, and the softening mechanism was the globularization of O lamellar grains at B2/β+O phase field, while the softening mechanism was dynamic recrystallization and shear bands of the B2/β-phase grains α2+ B2/β+O.

Abstract:Aluminum is considered as one of the most promising anode materials for the next generation batteries, in this paper, we used conductive Ti₃O₅ shell coating nano-Al powder to prepare the core-shell structure material of Al@Ti₃O₅, and used it as an anode, accompanied by of MCMB as the cathode, to assemble the Al@Ti₃O₅-MCMB Dual-ion battery (DIB). The discharge platform of the Al@Ti₃O₅-MCMB DIB is up to 4.5V, and the discharge capacity can reach 130.6mAhg^_-1, specific energy density 278.8Whkg^_-1 at a current rate of 0.5C (the current rate is based on the theoretical specific capacity of graphite and 1C corresponding to 372 mAhg^_-1). The Al@Ti₃O₅-MCMB DIB shows excellent cyclic stability, and the capacity remains at around 110mAhg^_-1 in the process of circulating 1000 times under the current rate of 5C, with a capacity retention rate of 92.9% after circulation.

Abstract:6061 aluminum alloy, as a kind of heat strengthened aluminum alloy, has good formability, but its plastic flow stress is greatly affected by the final heat treatment parameters, such as heating temperature，holding time and cooling method. Therefore, taking 6061-T6 aluminum alloy cold-rolled sheet as the research object, the plastic deformation behavior of 6061 aluminum alloy under different heat treatment temperatures (500 °C, 530 °C, 560 and 590 °C) were analyzed through uniaxial tensile test, metallographic test and microhardness test. Combined with experimental data and BP, GA-BP and PSO-BP neural networks, the constitutive models of this material under different heat treatment temperature conditions were constructed. The results show that BP, GA-BP and PSO-BP neural network models can better fit the flow behavior of 6061 aluminum alloy under different heat treatment temperature conditions, but PSO-BP neural network model has higher prediction accuracy and performs well in predicting the flow stress of 6061 aluminum alloy , its average absolute error (MAE), average relative error (AARE) and the correlation coefficient (R2) are 1.89, 1.56% and 0.9965, respectively.

Abstract:In order to investigate the effect of crystallographic orientation on the nano-indentation behaviors of single crystal super alloys, the nano-indentation experiments with a Berkovich indenter in an atomic force microscope were carried out on [001], [011] and [111] oriented Nickel based single crystal super alloys. Experimental results showed that the indentation load-depth curve, hardness and elastic modulus were remarkably influenced by crystallographic orientation. It is found that the shape and volume fraction of γ^" strengthening phase is dependent on crystallographic orientation, which will influence the mechanical properties. The nano-indentation experiments performed on three typical crystallographic orientations were simulated by using crystal plasticity theory to investigate the indentation responses and the resolved shear stress induced by indentation, and the simulation results showed a good agreement with the experiment results.

Abstract:The effect of Fe additions on the structure and properties of Al-7Si-0.6Mg alloy by wire arc additive manufacturing (WAAM) was studied and the morphology and distribution of Fe-rich phase in the alloy were observed. The results show that the fine acicular Fe-rich phase in as-deposition alloys is a mixture of metastable Mg-Si phase and π-Fe phase. After heat treatment (T6), Mg₂Si dissolves from Fe-rich phase and forms π-Fe phase. With the increase of Fe additions, the size and quantity of Fe-rich phase in the alloy increase. The change of Fe-content in a small range can have a great effect on the elongation of WAAM alloy (T6), but has no obvious effect on strength. With the additions of Fe increases from 0.11% to 0.18%, the fracture elongation of the alloy decreases by 47.1%.

Abstract:The deformation behavior of ultrafine-grained (UFG) commercially pure (CP) Ti was investigated. The strain rate sensitivity and activation volume were calculated from strain rate jump tests performed at a temperature range of 250-450 °C and strain rate of 1×10-4 - 1 s-1. The results show that flow softening effect in steady state of deformation occurs in UFG CP Ti which is controlled by high-angle grain boundaries and dislocation activity during the deformation process. Strain rate sensitivity of UFG CP Ti is relatively low in value and increases with the rise of temperature. The activation volume of UFG CP Ti is also low in value and invariant with temperature. The values of strain rate sensitivity and activation volume indicate that dislocation-dislocation interactions within the grain interiors take place scarcely and interactions between dislocation and grain boundary can significantly affect plastic deformation of UFG CP Ti.

Abstract:In this paper, 5wt.% Al3Zr/aluminum matrix composites are taken as the research object, plasma welding with Ar gas as ion gas and Al-Ti-B as wire material. The corrosion polarization curve of weld area in 3.5% NaCl solution is measured by electrochemical comprehensive tester. Scanning Electron Microscope (SEM), X Ray Diffraction analyzer (XRD) are used to analyse and characterize the microstructure and phase composition of the composite and its weld.The corrosion behavior and corrosion mechanism of Al3Zr/aluminum matrix composites after plasma welding were studied in 3.5% NaCl solution. The SEM analysis results show that through plasma arc welding, a better weld can be obtained, and the weld microstructure is mainly composed of Al3Ti phase and Al matrix, and the Al3Ti phase is striped and spherical. The electrochemical polarization curves indicate that the corrosion resistance of the materials at the nugget is slightly lower than that of the base metal.The weld of composition corrosion mechanism immersion is that the Al3Ti phase and the matrix phase behave as the anode and cathode of a primary cell.

Abstract:In order to improve the surface strength and heat-insulating capability of Ti-6Al-4V alloy, ZrO2 particles were injected into the Ti-6Al-4V surface melted by laser. In this paper, the melt-injection-interaction process was modeled using CFD method and the simulations were partly verified by experiments. In this model, the moving gauss laser was defined based on the equivalent thermal effect. VOF method is adopted to analyze phase change process and detect the free surface of molten pool. The buoyancy, inertia force and viscous drag were considered when calculating the particle movements. Temperature and velocity fields inside the molten pool were analyzed, and the influences of the convection caused by thermal-fluid coupling on particles injection and distribution were revealed. The results show that the temperature field and flow field in the molten pool are redistributed with the entry of the particles and the fluid flow and the solidification of the molten pool distribute the particles in different positions. The number of ZrO2 particles was counted per 100 μm depth, it’s found that with the increase of laser scanning velocity, particle densest positions became closer to the substrate surface.

Abstract:A series of creep tests of BSTMUF601 superalloy were carried out at different loads and temperatures to investigate creep behaviors at actual service environment. The diameter correction method was proposed to evaluate true stress and strain approximately for addressing the issue that the decrease of sectional area of specimens. And the θ projection creep constitutive model was used for characterizing creep deformation behaviors considering the advantage of reflecting the deformation process under constant true stress conditions. However, the parameters of creep constitutive model cannot be identified accurately by nonlinear multivariate fitting method under constant load conditions. In this paper, these constitutive parameters were calibrated by BP neural network importing temperature, time, stress and strain evaluated from the above correction method as inputs with back-propagation learning algorithm. Consequently, the calibrated constitutive model is determined, the predicted values coincide well with experimental results and the maximum relative error is less than 12%. Moreover, both the apparent creep stress exponent estimated by θ model, experimental results and the TEM patterns indicated the creep deformation mechanism may be dislocation climb, further indicating the BP neural network method is feasible for predicting complex models.

Abstract:The porosity is an important kind of weld defects in deep-penetration laser-arc welds. This paper gives an Experimental study on relationship between molten pool behavior and keyhole-induced porosity in pulsed laser-arc hybrid welding. In this research, the impact effect of laser pulse on the weld pool, and live behavior of the laser keyhole and the porosities in the weld were investigated in detail. Results show that the impact effects from the laser pulse depend on the laser pulse parameters and stronger impact effect helps restrain the porosity formation. The laser keyhole state dominants the welding pool behavior. The keyhole dimension and open-close state directly influences the porosity formation. Extremely high laser pulse power always brings about porosities after welding. Lengthening the laser keyhole opening time and giving the gas enough time to escape will be an effectively way to restrain the porosity.

Abstract:Hydrogen trapping and desorption in a martensitic steel with mixed (Ti,Mo)C precipitates have been investigated by means of Thermal Desorption Spectrometry (TDS) analysis. Results indicated that the spherical (Ti,Mo)C precipitates of 36-60 nm could not absorb hydrogen during electrochemical charging, while the (Ti,Mo)C precipitates of 1-5 nm were effective hydrogen trapping sites. In spite of a relatively low desorption activation energy of 16.4 kJ/mol, which is far lower than that from pure coherent TiC, the hydrogen trapped by the fine (Ti,Mo)C carbides could not desorb during atmospheric exposure.

Abstract:In present work, the wetting behavior of Al-Mg alloys with different Mg amount (3.2, 4.5, 6.5, 8.5, 10, 13, 17 wt.% Mg) on M40 graphite fabrics was investigated by sessile drop method. The effect of Mg amount on the wettability and spreading behavior were discussed. The initial contact angle decreased from 115o in Al-3.2Mg/graphite fabrics to 88.5o in Al-17Mg/graphite fabrics system. The final contact angles decreased from 96.7o in Al-3.2Mg/graphite fabrics to 71o in Al-17Mg/graphite fabrics system. The initial contact angle measured on porous M40 graphite fabrics was lower than reported results on dense carbon plates due to the surface microstructure of M40 fibres. Due to surface tension decrease of Al-Mg alloys, the initial and final contact angles decreased with increasing of Mg amount. According to Dezellus equation, the kinetic constant (k) in spreading behavior was obtained from data fitting of experimental results. Miedema model was introduced in present work to calculate the theoretical k. The experimental or theoretical k changed little with increasing of Mg amount. Moreover, theoretical calculation values of k are very close to the experimental results, which indicate the applicability of Miedema model to the calculation of kinetic constant.

Abstract:In this study, the microstructure evolution and mechanical properties of hypereutectic Al-20Si alloy containing rare earth Yb and Al-5Ti-1B refiner were investigated. The microstructures of the samples were characterized by optical microscopy, scanning electron microscopy, and electron probe microanalysis. Microstructural analysis demonstrated that the primary Si was significantly refined from a coarse polygonal, platelet-like or star-like shape into a fine blocky shape; the eutectic Si structure was modified from a coarse platelet-like/needle-like structure into fine particles or a fibrous structure; and the coarse α-Al dendrites were refined into fine equiaxed dendrites after the addition of 0.5% Yb and 0.3% Al-5Ti-1B complex. However, the primary and eutectic Si phases became coarser when the content of Al-5Ti-1B refiner reached 0.4%. The mechanical properties of the Al-20Si alloy with different modifiers and different modifier concentrations were investigated with the tensile test. The results showed that the ultimate tensile strength and elongation of the prepared sample increased by 83.7% and 92.1%, respectively.

Abstract:The deposited sample of x × y × z (40 mm × 5 mm × 60 mm) Ti-48Al-2Cr-2Nb alloy was successfully fabricated by laser metal deposition. The microstructure, phase composition, grain orientation and fracture morphology of the deposited sample were analyzed by optical microscope (OM), scanning electron microscope (SEM), X-ray diffraction (XRD), transmission electron microscope (TEM) and backscattering diffraction (EBSD). The hardness distribution at different positions of the deposited sample was measured by Vickers hardness tester. The tensile properties of the deposited sample in Z direction were measured by tensile machine. The results show that the well-formed deposited sample is obtained under the optimum process parameters, and no surface cracks are found after penetration detection. The microstructure of the deposited sample is composed of α2+γ lamellar colony and a small amount of bulk γ phase. For as-deposited γ-TiAl alloy, the room-temperature tensile strength along the Z direction is 425 MPa and the elongation is 3.3%. The fracture morphology of tensile specimen is quasi-cleavage fracture.

Abstract:In this paper, the nano-cutting and tensile model of monocrystalline γ-TiAl alloy was established by Large scale molecular dynamics simulations method. The objective is to analyze the effect of different cutting depths on tensile process of workpiece. For one thing, the relationship between lattice transformation and micro-defect evolution is studied in detail. For another, the influences of different cutting depths on stress-strain curve, the nucleation of dislocation and position of fracture surface are discussed. The research results show that amount of lattice transition rises with increases of cutting depth and consistents with micro-defect evolution during nano-cutting. Within a certain range of cutting depth, the yield stress and elastic modulus of workpiece are improved correspondingly. In addition, cutting depths have great influence on the position of dislocation nucleation and fracture surface of workpiece during tensile process. The dislocation of machined workpiece is nucleated at subsurface, while dislocation of unmachined workpiece is nucleated at edge of workpiece. The port position of workpiece is closer to drawing end with cutting depth increases.

Abstract:The mechanical behavior and the fatigue property of Ti films with different thickness were investigated by nanoindentation test. The fatigue property of the films was quantitatively calculated according to the changes of storage stiffness under the nanoscale dynamic mechanical analysis. The results showed that the fatigue life of the films depends on the residual stress remarkably. In situ scanning images showed the thin film was significantly stacked and layered, and long cracks radiated from the center of the indenter perpendicular to the indenter edge. Additionally, there was a sizable pile up around the indentions which demonstrated that a highly localized plastic deformation and stress release occurred in the process of the nanoscale dynamic loading process. The existence of the internal compressive residual stress will offset part of the load stress to improve the fatigue life of films.

Abstract:In the present study, Isothermal compression tests were performed to investigate the hot deformation behavior of TA1/AZ31B multi-layer composites. Flow stress-strain curves were obtained for deformation at temperature from 573K to 723K with the strain rate range from 0.01s-1 to 10s-1, and the height reduction range from 30% to 50%. Effect of the strain on the flow stress, both TA1 and AZ31B had plastic deformation during the compression bonding process. However, all layers deformation of TA1/AZ31B multi-layer composite is not occur at the same time and not uniform. The deformation of AZ31B is larger than that of TA1, and AZ31B occurs dynamic recrystallization during the deformation process. When strain rate is 10s-1, the middle TA1 layer occurs necking and fracture. Based on the flow stress-strain curves, the Arrhenius-type constitutive equation could precisely predict the flow stress behavior of TA1/AZ31B multi-layer composite. Besides, the value of the correlation coefficient was 0.991 when that of average absolute relative error was 3.976%. The processing map at true strain of 0.5 for TA1/AZ31B multi-layer composite was developed using the dynamic materials model (DMM) theory. The processing map of isothermally compressed TA1/AZ31B multi-layer composite exhibited that the optimum parameters were determined at the temperature of 723K and the strain rate of 0.01s-1 with power dissipation’s maximum efficiency of 28%. In the meanwhile, there was one instability domain in the processing map of isothermally compressed TA1/AZ31B multi-layer composite, it is in the deformation temperature range from 573K to 692K and the strain rate range from 0.6s?1 to 10 s?1.

Abstract:The microstructures and mechanical properties of 7B04 aluminum alloy solid solution at 470oC and aged at 100-140 oC without and with electric current were investigated by tensile test, scanning electron microscope (SEM) and transmission electron microscope (TEM). Compared with the traditional T6 treatment (470 oC/30min+120 oC/24h), applying electric current of 500A during solid solution and/or ageing treatment can increase both the tensile strengths and elongation at the age-peak state, due to the significant increase of the precipitation density of Guinier- Preston II (GPII) zones. Applying electric current during solid solution can significantly reduce the time to the peak strength by 12h in the subsequent ageing alloy

Abstract:A new process named equal channel angular extrusion with spherical cavity (ECAE-SC) is proposed based on the idea of breaking through the equal channel during the whole process of traditional ECAP, which combines positive strain with shear strain. On the self-designed ECAE-SC die, the continuous, efficient and compound severe plastic deformation of commercially pure aluminum was realized in a single pass of ECAE-SC at room temperature. Microstructure evolution of commercially pure aluminum during ECAE-SC process was observed and analyzed by optical microscopy (OM), EBSD and TEM. Moreover, microhardness of the processed materials at different deformation regions was tested. The results show that under the severe plastic deformation induced by simple shear, the equiaxed ultrafine grains with average grain size of 400 nm can be obtained by only one pass of ECAE-SC. The deformation mechanism of ECAE-SC at room temperature is dominated by dislocation slip accompanied with incomplete continuous dynamic recrystallization, and the grain refinement process mainly includes the generation of shear bands, the formation of cellular substructures, the appearance of subgrains with low angle boundaries (LABs) and the formation of equiaxed ultrafine grains with large angle boundaries (HABs). After one pass of ECAE-SC, the main texture of commercially pure aluminum is Gauss texture {110} < 001 >, while some {111} < 112 > copper texture exists. The microhardness of the processed materials on the cross section increases significantly, and the average value increases from 28.94 HV to 56.53 HV, with an increase of 95.33%. Meanwhile, a more uniform hardness distribution is obtained.

Abstract:In order to avoid the film were destructed by continuous arc discharge during micro-arc oxidation. This paper used a high-speed camera to capture the discharge phenomenon, combined with the current and voltage wave form of the load to explore the essence of continuous arc discharge. And investigated the destructed area of surface and cross-section morphology and the phase composition relative to the change of normal coating layer. Finally, different duty ratio and frequencies were used to explore the influence of the electrical parameters on the continuous arc discharge phenomenon. The results showed that the surface of the sample exhibits a reciprocating process of arc burning, arc quenching and cooling during micro-arc oxidation. The localized destructed area was characterized by a continuous arc discharge phenomenon. The composition, surface morphology, cross-section morphology and element distribution of the local continuous arc discharge region were very different from that of the normal micro-arc oxidation film layer. And the uniformity, compactness and integrity of the film layer was destroyed, which led to the destruction of the overall uniformity of the film layer, and even caused serious damage to the external size of the sample. The capacitance characteristic of the load caused the arc duration time to be too long while the cooling time of the molten metal oxide was insufficient, the local thermal transmission was insufficient and the heat was concentrated, which was the root cause of the continuous arc destructed. This destruction cannot be repaired after it occurs, so it is possible to avoid the occurrence of continuous arc destruction under different treatment voltages by reasonable matching of frequency and the duty ratio.

Abstract:In order to study the formation mechanism of explosive welding wave interface, the interface morphology and the welding processes were analyzed by means of explosive welding experiment and numerical simulation. The results show that the plates with lower initial strength are more likely to form periodic wave interface when the welding paremeters are within the weldable window, and the molten material within two wavelength after the collision point still with a high velocity and continues the movement along the interface. However, the plates with higher initial strength and smooth surface are difficult to form wave interface. The results indicate that the formation of the wave interface requires the accumulation of disturbance to trigger the Bahrani enching mechanism. In addition, the molten metal within two wavelength after the collision point will continue to move along the interface and eventually form a stable interface wave eventually.

Abstract:Uranium-niobium (U-Nb) alloys have excellent corrosion resistance and good mechanical properties. They are good candidates for structural materials and functional materials of nuclear engineering. Fabrication of high quality uranium-niobium alloys using direct vacuum induction melting process is of great significance for efficiency promotion. But unsufficient alloying is the main problem of U-Nb alloy fabricated by direct vacuum induction melting process. The dissolution and diffusion of solid Nb in U melt is the key point of direct vacuum induction melting process of U-Nb alloy. So, in this paper, we investigated the dissolution and diffusion of Nb in U melt using experimental method. The actual dissolution rate of Nb in U melt with different temperature was obtained. The dissolution rate of Nb in U melt v and the melt temperature T have a relation of v=0.3651exp(-21150[K]/T)[m/s]. Scanning electron microscope observation shows sheet structure forms at the U/Nb interface during the dissolution process of Nb in U melt. When electromagnetic stirring is used, the dissolution rate of Nb in U melt increases obviously and the morphology of sheet structure at the U/Nb interface changes.

Abstract:Hexagonal martensite α′ gets special metallographical corrosion behavior: the inner microstructure of some grains shows unobvious contrast after corrosion, however, some other grains have obvious corrosion character, namely the inner vimineous α′ array orthogonally. In present work, the mechanism of this corrosion behavior was studied based on OM, AFM and EBSD analyses. It’s found that: there are three groups of orthogonal precipitation directions of α′ when transformed from original β phase, if the metallographical observation surface is parallel or near-parallel to any one of the three groups of orthogonal precipitation directions, then this group of α′ plates must array orthogonally or parallelly. Under this circumstance, α′ plates are perpendicular to the observation surface, thus the α′/α′ interfaces are deep, which leads to deep corrosion depth, and finally deep corrosion characters are shown. For a given grain, the two arrangement modes of α′ plates can exist simultaneously, which appears orthogonal array mode as a whole.

Abstract:In this work, the grain boundary characteristics distribution and texture evolution of GH3625 alloy tubes during short-flow manufacture process (hot extrusion, solution treatment, cold rolling and annealing treatment) were investigated by electron backscatter diffraction (EBSD) and orientation imaging microscopy (OIM) technique. And the cold and hot plastic deformability of alloy tubes via analyzing the Schmid factor and Taylor factor were further studied. The results show that the grain boundary character distribution in the short-flow manufacture process of GH3625 alloy tubes is optimized through annealing twins related to Σ3_ⁿ grain boundaries rather than deformation twins. The Brass texture {110}<112> and fiber texture <111>//RD is generated in the hot extrusion/cold rolling deformation process of the alloy tubes, while the {110}<110> texture and Brass-R texture {111}<112> appear during solution/annealing treatment. GH3625 alloy tubes preferentially plastic deformation in the extrusion direction (RD) during hot extrusion, while plastic deformation occurs in the direction perpendicular to the rolling direction during cold rolling. At the same time, comparing the average Schmid factor value m_s and Taylor factor value M_T of GH3625 alloy tubes during hot extrusion and cold rolling deformation, it is found that the plastic deformability of cold rolling is worse than hot extrusion, and higher deformation work is needed.

Abstract:In this paper, the super-cell model based on SQS methed and first-principles calculation is performed on investigating the influences of Ti concentration and phase structure(hcp and bcc structure )( α and β phase) on phase stability and elastic properties in Zr1-xTix systems.The results show that from the perspective of elastic properties, the structure of Zr-Ti alloy is more stable with the increase of Ti content. The α phase of Zr-Ti alloy generally has higher structural stability than β phase; Zr- Ti alloys generally have ductility. The α phase of Zr-Ti alloy has higher hardness and its hardness and toughness are proportional to the concentration of Ti. From the perspective of electronic structure, the concentration of Ti does not significantly change the DOS of hcp structure and the bcc structure of the Zr-Ti alloy systems.The Fermi level in the DOS distribution of the Zr-Ti alloy system is similar to that of the pure Zr system. Therefore, the content of Ti in the Zr-Ti alloy has little effect on the phase stability of the Zr-Ti alloy.

Abstract:Taking advantage of texture strengthening, the TA18 (Ti-3Al-2.5V) titanium alloy tubing was developed with tensile strength of 860 MPa as well as high formability and a good combination of mechanical properties. While the contractile strain ratio (CSR) of such tubing must be greater than 1.3 to meet the current standard, the upper limit value is not specified. In this paper, a fixture was designed for the hoop tension of tubing with a small diameter, and the mechanical properties in the hoop direction of tubing with different CSR values was tested. The effects of texture on the circumferential strength was analyzed. It was found that the optimal CSR value for the yield strength is 1.75, higher or lower value would lead to a decrease of the strength. Additionally, based on the pole figures and the orientation distribution function (ODF), the essence of the above regulation was well explained from microscopic aspects. Lower circumferential strength of hydraulic tubing will result in poorer fatigue life of hydraulic system in service, hence the upper limit value, not just the lower limit value, of CSR should be controlled. This investigation will be of theoretical significance and application value for the development of safe and reliable aerospace hydraulic systems.

Abstract:Abstract: In this paper, we investigated the physical characteristics, solidification microstructure, and inter element distribution of Ni-based superalloy powders, which prepared by electrode induction melting gas atomization (EIGA) process. Some factors on metal droplet size during primary atomization were also deeply analyzed. The cooling rate of different size powders were calculated through convective heat transfer principle. It is found that the EIGA powders are mainly spherical, the Hall flow rate is 13.4s/50g, and the D90 is 121.5μm. The microstructure of powders on surface and internal changes from microcrystals to cell crystals and dendrites increasing with the powder size. At the same time, the smoothness of powders decreases as the gap increases on the surface. The relationship between cooling rate and particle size is |〖dT〗_d/dt|=〖8.98*10〗^(-5)/d^2 , when the atomization gas pressure is 4MPa. There is slightly segregation in crystal axis and intercrystal of powders. The content of Ni, Al, Co, and C in crystal is higher than intergranular, while the content of Ti, Mo, Cr, and Nb in intergranular is much higher.

Abstract:The research object were additive manufacturing GH3625 metal powders,the two-dimensional microstructure of the powders were observed by scanning electron microscopy(SEM), the three-dimensional structure of the powders were characterized by micro-CT,and the geometric parameters such as particle size, volume and sphericity of the powders were quantitatively analyzed. All the pores inside the hollow powders were successfully extracted by three-dimensional(3D) segmentation, and the 3D printed powder quality was characterized by volume porosity, probability of hollow powder, sphericity and other parameters.Finally, the influence of the pore diameter in the hollow powder on the sphericity of powders were investigated. The experimental results show that micro-CT is an ideal tool to characterize the quality of metal powders of additive manufacturing, a total of 20576 GH3625 powder particles were detected by CT, the average particle diameter of the powder is 28.16 μm, the number of hollow powder particles is 1440,the number of internal pores is 1515, and a few powder particles have multiple pores,it is found that the sphericity of the hollow powder particles decreases with the increase of the internal pore diameter of the hollow powders.

Abstract:In this paper, a low-pressure cold spray technique was used to prepare copper-zinc coated samples on 45# steel substrate and 45# steel plus chrome-plated substrate. Corrosion performance of coatings and coatings with chrome plating by static soaking and copper accelerated acetate spray corrosion test (CASS). The microstructure and elements of the coating and chrome plating before and after corrosion were characterized by SEM and XPS. The results show that the corrosion resistance of copper-zinc coating is better than that of copper-zinc coating plus chrome plating during static corrosion. In the CASS experiment, with the increase of zinc content in the original powder, the corrosion resistance of the coating sample and the coating plus chrome plating sample is improve. When the copper-zinc ratio is 6:4, The corrosion resistance of the corresponding coating sample, the coating plus chrome layer sample and the pure chrome layer reaches the sixth grade. Copper and zinc coatings are corroded in the corrosive liquid due to electrochemical corrosion and chlorination. The corrosion products are mainly Zn(OH)2, Cu2O and CuCl2. In the process of corrosion of copper-zinc coating and chrome-plated layer, the corrosion of zinc can play a role in slowing the corrosion of chrome plating. The effect of this mitigation together with the copper film deposited on the chrome layer protects the chrome layer and enhances its corrosion resistance.

Abstract:A laser deposition repair experiments were carried out on DZ125 casting substrate. The microstructure, hardness and friction and wear properties of laser deposition were studied. The results show that the morphology of the deposition area from bottom to top is as follows:Planar crystals with a width of about 8μm and columnar crystals with close arrangement along the deposition direction are grown. The dendrites in the middle of the sedimentary zone and the chaotic equiaxed crystals at the top. The size of γ "phase at the boundary of the deposit zone is larger than that of the layer, and the size of the γ" phase at the grain boundary is larger than that of the crystal, the phenomenon of the distribution of the eutectic and the mc carbides along the grain boundary is obvious, Different morphologies of MC carbides were found in the deposited area.Most of the MC carbides in the middle and lower parts of the deposit area are short rod-like MC carbides, and the top of the deposit areas are mostly small blocks and octahedral MC carbides.The microhardness of the deposited area is about 455～475 HV0.3, which is higher than that of the substrate 410～420HV0.3.The wear resistance of the deposition area is superior to that of the matrix, and the wear mechanism is mainly abrasive wear .

Abstract:Precipitation behavior of α-phase and its influence on mechanical properties has been systematically investigated in Ti-6Cr-5Mo-5V-4Al metastable β-Ti alloy by comparing the double aging and the single aging. The microstructural characterization shows that the quenched sample consists of equiaxed β-grains. After the following low-temperature pre-aging, dense clusters composed of numerous α nano-laths evenly distribute inside β-grain interiors, while there are precipitate free zones (PFZ) around β grain boundaries. This precipitation feature between β-grain interiors and their grain boundaries is inherited into the later high-temperature aged samples. It can be seen that fine equiaxed α precipitates homogeneously distribute in β-grain interiors but the α-phase exhibits a coarse plate shape adjacent to β-grain boundaries. On the contrary, the α-plates distributes much more evenly in the single-aged microstructure although the plates have larger dimensions. Tensile testing shows that the ultimate tensile strength can be tuned up to ~1630 MPa but accompanied by the degradation of ductility (~2%). The ultra-strength originates from the significant precipitation-strengthening effect as a result of the precipitation of α-particles at the submicron- and nano-scales, and the lost ductility can be attributed to the premature intergranular fracture caused by deformation localization along β-grain boundaries.

Abstract:The CuMn - based filler was used to brazing TZM and Kovar alloys.By means of DTA, helium mass spectrometer, laser confocal microscope, SEM and EDS,the melting point and wettability of TZM and Kovar alloys were tested and the gas tightness, microstructure, interfacial structure composition of the welds were also tested. The results show that: At 965 ℃, the wetting Angle of Cu-Mn base solder on TZM and Kovar alloy sample is 30.77 ° and 12.30 ° respectively. When the largest induced current is 430A, the solder spread out evenly on weld and the weld areas were without crack, without defects such as bubbles. The leakage rate test of welding are better thanS6×10^-11 Pa.m3/s. The middle area of the weld is CuMn metallurgical solidification organization, solder with TZM reaction interface area is relatively narrowd and with Kovar alloy interface reaction area is wider. Mn and Cu in the filler metal and Fe in Kovar alloy are more likely to diffuse and migrate to each other to form the metallurgical fusion reaction.

Abstract:In this paper, the microstructure evolution of the Mg-Al-Zn-Nd alloys were characterized by XRD, SEM and TEM, and the strengthening behavior of the rare earth phases in the alloys was studied. Results show that the microstructure consists of the α-Mg, Mg17Al12, Al2Nd and Al11Nd3 phases in the experimental alloys. Meanwhile, as the content of Nd element increasing, the size and the number of the Mg17Al12 phase gradually decrease, however, the number of the dispersed Al2Nd and Al11Nd3 phases increase. Moreover, the shape of the Al11Nd3 phase changes from needle-like to the rod-like with the Nd increasing, and the semi-coherent interface between Al11Nd3 phase and matrix Mg exists strong binding ability. Furthermore, the strengthening behavior of the rare-earth-containing phases includes the following aspects: (1) During tension, the increase of stress concentration around the rare-earth-containing phases may induce the formation of twin around the matrix Mg, which can coordinate the increase of some external strain energy. (2) Compared with Mg17Al12 phase, the hard rare-earth-containing phases with good binding ability initiate micro-cracks hardly, therefore, the dispersed rare-earth-containing phases play an important role of pinning dislocation movement. (3) The increasing number of the rare-earth-containing phases results in the decreasing number of the micro-cracks sources, where the micro-cracks sources initiated at the interface between matrix and eutectic structure (M/E), as well as the island-like Mg17Al12 phase. Finally, the mechanical properties of the Mg17Al12, the Al2Nd and the Al11Nd3 phases were calculated and briefly discussed.

Abstract:More and more applications have been made to realize lightweight design of aerospace parts by additive manufacturing to form complex lattice structures. However, the lattice structure design and its performance evaluation are still lacking. In this study, the diamond structure was used as the matrix, and the specimens with different geometric parameters were designed for forming with TC4 titanium alloy, aiming at lattice density and structure form. Compression tests were carried out on the formed specimens to study the differences of compressive properties between specimens of different sizes. The results show that the stress of the diamond lattice structure specimens will concentrate at the joint position and cause fracture after being loaded. Increasing cell density can alleviate the phenomenon of stress concentration, increase specific strength, reduce cell size and add shell can make the stress uniform and improve the stability. Small cell size specimens are more sensitive to metallurgical defects such as spheroidization and pore, resulting in a decrease in strength.

Abstract:Tantalum powder was prepared by RF plasma process from irregular sodium reduced tantalum powder, and spherical, pore-free powder with lower oxygen content was obtained. The effects of feeding rate, carrier gas flowing rate and pressure of reactor chamber on spheroidization efficiency and powder properties were studied. The selective laser melting process of spherical tantalum powder was also explored. The results showed that tantalum powder after plasma processing possess smooth surface , high internal density, high purity and low oxygen content, and the spheroidization ratio was almost 100%.The particle size distribution became narrow after spheroidizing. Spheroidization efficiency decreased with the increasing of feeding rate, while increased firstly and then decreased with the increasing of carrier gas flowing rate. Meanwhile, lower negative pressure in reactor chamber was more favorable to obtain powder with high spheroidization efficiency. With the increasing of spheroidization efficiency, the powder flow ability, apparent density and tap density were significantly improved. The processing parameters, the feeding rate, carrier gas flowing rate and reactor pressure were optimized at 30g/min, 5.0 slpm, and 12.0 psi, respectively. Compared to the raw materials, the spherical tantalum powder hall velocity reached 5.98s/50g, the apparent density increased from 3.503g/cm3 to 9.436g/cm3 and the tap density also improved from 5.344g/cm3 to 10.433g/cm3. It was interesting to find that the oxygen content is decreased from 0.076% to 0.0481% after the plasma process. Finally, spherical tantalum powder was proved to be compatible with selective laser melting process. The SLM parts with high dense (≥99.5%) were obtained and the tensile, the yield strength and the elongation were 693MPa, 616MPa, and 28.5%, respectively.

Abstract:Based on the ductile-brittle composite principle of biomaterials , Al foils, Ti foils and Ti2AlNb foils were stacked in a certain order in this work, and Al-Ti-Ti2AlNb laminated composites were prepared by vacuum hot pressing sintering. The microstructure was analyzed by means of SEM and XRD, and the flexural and compressive properties were also analyzed. It is found that the laminated composites were composed of Ti, a series of TiAl compounds and Ti2AlNb combined with obvious hierarchical structure and clear interface. The flexural strength and compressive strength are 1231±71 MPa and 1341±63 MPa, respectively, which have significant advantages over similar materials. The analysis shows that the existence of laminated structures plays an important role in optimizing the mechanical properties. Compared with the conventional binary TiAl layered materials, the existence of Ti2AlNb layers significantly improves the mechanical properties.

Abstract:High temperature oxidation resistant coatings were prepared by nitriding and siliconizing the surface of Mo-W alloys with different tungsten content by in-situ reaction method. The influence of W content on the morphology and microstructure of coating was analyzed by Scanning Electron Microscope and X ray diffraction. The oxidation resistance properties were also evaluated. In addition, the mechanism of anti-oxidant was researched. The results indicate that the amount of silicon seepage on the coating surface decreases as W content in Mo-W alloy increasing, which reveals that the increase of W content can slow down the outward diffusion of Si element effectively. Furthermore, the high temperature oxidation experiment at 1600℃ proves that the Mo-30%W surface coating has the best oxidation resistance, and the oxidation resistance time is up to 327 h. As a result, the increase of tungsten content improves the oxidation resistance of the coating to a certain extent.

Abstract:Ni-Fe-Co-P-CeO₂ composite coating was prepared by spray electrodeposition technique. The surface morphology, Cross section morphology, microstructure and composition of the composite coating were tested by SEM, XRD, EDS, etc. At the same time, the hardness, wear resistance and corrosion resistance of the composite coating were characterized. The performance of the nano-rare particles CeO₂ on the coating performance was investigated and analyzed. Impact. The results show that the multi-component composite coating is amorphous. With the increase of CeO₂ particle concentration in the plating solution, the microhardness, wear resistance and corrosion resistance of the composite coating are firstly enhanced and then weakened. When the CeO₂ particle concentration is 1g/L, the surface of the composite coating is uniform and dense, and its microhardness reaches the maximum value (598.21HV), and has the best wear resistance and corrosion resistance.

Abstract:In this paper, the copper indium gallium aluminum selenium Cu (InGaAl) Se₂(hereinafter referred to as CIGAS) nanometer powders were prepared by the solvent thermal, and the copper indium gallium aluminum selenium CIGAS film was prepared by directly using the nanometer powders as the evaporation materials. And then the amorphous film was placed in homemade sealing flange with high purity selenium powder to selenide and anneal under vacuum, and conform to the stoichiometric ratio of selenium CIGAS copper indium gallium aluminum selenium film. The structure and composition of CIGAS thin films were determined by X-ray diffraction (XRD), Raman spectroscopy (Raman), scanning electron microscopy (STM) and energy spectrum (ED). The elliptic parameters Ψ(λ) and Δ (λ) of copper indium gallium aluminum selenium CIGAS film were measured using elliptic polarization spectral measurement technique, and then the thin film optical parameters such as refractive index n (λ), extinction coefficient k (λ), absorption coefficient and the film’s light energy gap Eg were obtained , and it was found that the doping of Al significantly increases the light energy ga Eg, and the related physical questions were analyzed too.

Abstract:Three U720Li ingots with different B contents were produced by vacuum induction melting and afterwards they were fully homogenized. The effect of B on the isothermal oxidation behavior of as-homogenized U720Li alloy at 1100 ℃ was investigated by a discontinuous increasing weight method. After the homogenization treatment, extremely serious B depletion from the alloy matrix was found by ICP-AES, indicating that B could diffuse rapidly towards the oxide scale during high temperature air exposure (above 1100 ℃). The B addition decreased the oxidation rate and reduced the volume fraction of pores and the thickness of γ′ depleted layer. The scales formed on both low B and high B alloys consist of three layers, loose outer layer composed of (Ni/Co)O, TiO2 and complex spinel, compact intermediate layer is mainly Cr2O3 and discrete internal oxides are Al2O3+TiO2. It is deemed that B improves the oxidation resistance mainly by promoting the formation of a more continuous and protective Cr2O3 intermediate layer.

Abstract:Zirconium alloys are important structural materials used as nuclear fuel cladding in nuclear reactors. Investigation on the initial oxidation behavior of zirconium alloys in low vacuum environment is helpful to understand the oxidation mechanism of zirconium alloys. Zr-0.75Sn-0.35Fe-0.15Cr(mass fraction, %), Zr-0.75Sn-0.35Fe-0.15Cr-0.15Nb and Zr-1.5Sn-0.35Fe-0.15Cr alloys were made into large-grain samples, and then TEM thin samples were prepared by electrolytic double-spraying. By studying the oxidation of TEM large-grain samples in a vacuum tube furnace with a vacuum of 3 Pa at 280℃ and 290℃, the effect of Sn and Nb on the initial oxidation behavior of zirconium alloys were investigated, and the nucleation and growth of ZrO2 grains on the surface of the alloys was also observed. The results showed that the addition of Nb or the increase of Sn content promoted the nucleation and growth process of ZrO2 grains formed on Zr-0.75Sn-0.35Fe-0.15Cr alloy in low vacuum environment at 280 ℃ and 290 ℃ oxidation. When oxidizing at 280 °C/30 min under low vacuum conditions, the addition of Nb content promoted the increase of ZrO2 grain size, while the increase of Sn content made the ZrO2 grain change from spherical to short rod. With the increase of oxidation temperature (290 °C/30 min), the ZrO2 grains on the surface of the Zr-0.75Sn-0.35Fe-0.15Cr and Zr-1.5Sn-0.35Fe-0.15Cr alloy grew up, while the ZrO2 grains on the Zr-0.75Sn-0.35Fe-0.15Cr-0.15Nb alloy had a faster nucleation rate.

Abstract:In this paper, an Al film was deposited on the surface of sintered NdFeB magnets by electrophoretic deposition(EPD). It was found that different EPD voltages and times have a great influence on the deposition of Al films. It also investigated the effects of different grain boundary diffusion processes on the microstructure and magnetic properties of the magnet. The results show that the best EPD process is 90 V/30 s. At this time, the combination of the film and the magnet is well, and the thickness is even and moderate. When the grain boundary diffusion process is 500 °C / 1h, the magnet obtains the best comprehensive magnetic properties, and its coercivity, remanence and maximum magnetic energy product are 953 kA/m, 1.41 T and 342 kJ/m3, respectively, which is increased by 30.2%. 0.7% and 11.4%. Through microstructure and composition analysis, it is found that after the grain boundary is diffused, a more flat and smooth rare earth-rich phase thin layer is formed between the crystals, which helps to reduce the demagnetizing field and enhance the magnetic isolation effect, and finally leads to the improvement of coercive force.

Abstract:The CoCrAlY coating was deposited on the surface of the nickel-based superalloy by Air plasma spraying (APS). And on this basis, electron beam vacuum deposition (EBVD) method was used to deposit aluminum film on the coating surface in order to increase the Al content. The above two coatings were reinforced by laser peening (LP) technique. X-ray diffraction (XRD) and scanning election microscope (SEM) were used to compare the phase structure, morphology and composition of the CoCrAlY coating before and after LP treatment. The results of microstructural analysis showed that the surface roughness of APS-CoCrAlY coating was decreased, and the microstructure became more compact after LP treatment. The surface Al content of CoCrAlY coating deposited with Al film after LP impact was increased significantly, and the content of β-CoAl phase was increased. The grain size was refined concurrently. The results of high-temperature oxidation test at 1050 °C showed that the oxide film formed on the surface of LP treated coating became smoother and denser than that of the original one, and the thickness of the oxide film was significantly thinner. In addition, the aluminized CoCrAlY coating after LP treatment achieved optimal performance of high-temperature oxidation resistance.

Abstract:Mg/Ti dissimilar metals were welded by ultrasonic welding. The effects of different welding energy on the interfacial peak temperature, interfacial morphology, interfacial atom diffusion degree and mechanical properties of the joint were investigated. It is shown that the overall interface of Mg/Ti is relatively straight during the welding process, the local interface has small fluctuations, no cracks, lack of fusion and other defects are found, and no obvious reaction layer is observed. The interfacial peak temperature ,the thickness of the atomic diffusion layer , the connection zone and mechanical properties of the joint increase with the increase of welding energy. When the energy reaches 2000J, the magnesium side base material shows welding cracks. The joint fracture mode is divided into interface fracture and button fracture. The fracture location occurs at the magnesium side diffusion layer area and the magnesium side non-diffusion layer area. Scanning electron microscopy and X-ray diffractometry analysis showed that there was no obvious intermetallic formation in the Mg/Ti interface region.

Abstract:This paper presents results from a research initiative aimed at the γ′ precipitation behavior in superalloy FGH97 during continuous cooling from supersolvus temperature by Gleeble-3800 and heat treatment simulator furnace at cooling rates of 15~240 °C/min. The influence of cooling rates on γ′ size, paticle morphology and tensile strength is investigated. During cooling from supersolvus temperature γ′ nucleation and growth, even coarsening, simultaneously occur. However, ageing treatment seems to exert little influence on γ′ evolution. At the cooling rate of 15 °C/min a large number of secondary γ′ split and form square paticles with ~0.38 μm. Meanwhile, there are lots of small tertiary spherical γ′ around secondary γ′. As the cooling rate decreasing to 60 °C/min the size of secondary γ′ decreases to ~ 0.22 μm and the precipitation of tertiary γ′ is completely inhibited. The tensile strength tends to increase after an initial decrease with a decline of cooling rates, due to the combined influence of γ′ volume fraction, particle size and γ/γ′ mismatch.

Abstract:Metal melt deposition involves thermo-physical processes such as the formation, morphological evolution, flow and solidification of metal melts. According to the discontinuous characteristics of liquid metal flow, a metal melt deposition device was designed and developed. By studying the development process of metal melt deposition experimental platform and software control system, the key parameters (pulse pressure, melt temperature, substrate temperature, etc.) in the process of metal melt fluid deposition are controlled and monitored. The results show that the monitoring and control of the key parameters (scanning speed, melt temperature, substrate temperature, etc.) in the process of metal melt deposition is realized by this experimental device, which provides the necessary experimental software and hardware basis for the further study of melt deposition forming technology.

Abstract:Nickel plating on the surface of magnesium alloy is widely used in the anti-corrosion of magnesium alloy workpiece, but blistering and peeling from nickel plating will seriously affect service life of the workpiece. In this paper, effects of the different substrate surfaces on nickel plating properties of ZK60 magnesium alloy were studied. The results showed that the surface scratch and corrosive pitting significantly reduced the coating quality and caused blistering and peeling from nickel plating. The surface scratch of the substrate was retained under the nickel plating layer, which made the coating thinner, and caused stress concentration in the coating, and increased the probability of coating cracking. Differences in electrochemical properties between impurities in pitting pits and magnesium substrate led to thinning of the coating and weakened the adhesion of the coating. Therefore, good substrate surface finish and no substrate surface corrosive pitting are the guarantee of high quality nickel plating of magnesium alloy workpiece.

Abstract:Objective: To optimize the anodized film on the magnesium surface and explore its effect on the structure,corrosion resistance and biocompatibility through anodizing and annealing treatments.Methods: Pure magnesium was anodized with different voltage parameters (5V, 10V, 20V, 40V), and then annealed at high temperature. The surface and cross-section morphology of the coatings formed were analyzed by scanning electron microscopy.Three-dimensional structure and roughness were analyzed by atomic force microscope. The corrosion behavior of each group of samples was evaluated by electrochemical polarization experiments and in vitro immersion test.The proliferation activity of mouse osteoblasts MC3T3-E1 was evaluated by the CCK-8 method. Results: The increase of the voltage can make the surface coating become porous from the lamellar shape, and then continue to increase voltage，the layer become smooth and uniform. The annealing treatment maintained the basic morphological characteristics, the coating thickness increased and the roughness decreased.The corrosion resistance of the unannealed coating does not increase due to the existence of micropores and the instability of magnesium hydroxide. The dense magnesium oxide crystalline coating formed by the annealing has a certain protective effect. The 40V post-oxidation annealing group has relatively good corrosion resistance and has no obvious inhibitory effect on cell proliferation.Conclusion: Voltage affects the structure of anodized coating. Annealing can further stabilize the coating and improve its corrosion resistance.The 40V post-oxidation annealing group has a better corrosion resistance and biocompatibility .

Abstract:Using metal Al as substrate and titanium fiber as reactive source，an Al3Ti/Al composite was fabricated by applying induction heating，and the inductive magnetic field generate by the coil was used to promote the in-situ reaction rate of aluminum and titanium.The reaction temperature was preliminarily judged by differential thermal analysis (DTC) to be about 800 degrees, and the obtained samples were characterized by X-ray diffraction(XRD),scanning electron microscopy(SEM) and wear testers.The results show that when the alternating current frequency is 7KHz, the current is 8A, and the time is 5min.,the titanium fiber react with Al completely，and the dispersed distribution of Al3Ti particles are in-situ synthesized, and the average size of the particles reach 3μm; Under the condition of 10N load and air as medium, the friction coefficient decreases first and then increases with the increase of alternating current frequency. The friction coefficient at the frequency of 7KHz is the lowest value of 0.2, the wear amount is the least, and the wear resistance is optimal.

Abstract:The Pd-Ag alloy membrane has been commercially used as a metal membrane for separating high-purity H2, but the material cost of the Pd-Ag alloy membrane is high, and its large-scale application is limited. The single-phase V-based alloy membranes have higher hydrogen permeability and mechanical strength and lower cost than the Pd-Ag alloy membrane, and the hydrogen embrittlement resistance is greatly improved compared with the pure V, and the plasticity and hydrogen permeability are also higher than that of multi-phase V-based alloy membranes, thus become one of the potential materials to replace the Pd-Ag alloy membrane. In this paper, the research progress of single-phase V-based alloy membranes for hydrogen separation is reviewed, including the types of single-phase V-based alloy membranes and hydrogen permeability, the influence of microstructure on hydrogen permeability, and the failure mechanism of alloy membranes, etc.. The future development trend of single-phase V-based alloy membranes for hydrogen separation is also prospected.