Abstract:The formation and expansion of necklace structure in an Al-10Mg alloy have been studied. The alloy was produced by centrifugal casting, which was followed by 673K/24h solid solution treatment and hot uniaxial compression. The different effects of temperature and strain rate on expansion of necklace structure were especially clarified. In this study, bulging is the nucleation type of first layer in necklace structure, and three different types of subboundary were found in the deformation microstructure of Al-10Mg alloy. When temperature increased, microband and recovered subboundary were gradually eliminated, after which strain-induced subboundary nucleation and recrystallized grain coarsening became a main way of necklace expansion. When strain rate decreased, low angle grain boundary was accumulated. Three regions denoted by low misorientation region in interior, new grains in out layer and net structure of subboundary concentration region in middle were observed in non-recrystallized grains. The proportion of recrystallized grain area decreased when strain rate changed from 6.94×10_-1/s to 6.94×10_-2/s, then significantly increased when strain rate changed from 6.94×10_-2/s to 6.94×10_-3/s.

Abstract:2A97 Al-Li alloys with different Li contents have been cast by the near-rapid solidification. After that, perform physical properties analysis by means of tensile and density tests. Simultaneously, use the differential scanning calorimeter (DSC), optical microscope (OM), scanning electron microscope (SEM) and energy dispersive spectrometer (EDS) to explore the microstructure evolution of the Al-Li alloy. The results show that through the near-rapid solidification and a reasonable heat treatment process can effectively reduce the coarse second phase in the 2A97 Al-Li alloy, which is of great interest for obtaining ultra-low-density Al-Li alloys. With the increase of Li content, the Cu element in the alloy is more inclined to capture more Li element to form the Al₂CuLi phase. Accompanied by the relative decrease of Al₂Cu phase and the appearance of the petal-shaped eutectic phase Al₂CuMg. Not only that, the as-cast microstructure of the near-rapid solidified Al-Li alloy transforms from dendritic grains to cellular-like grains, leading to the refinement of the grains. However, with the Li content from 1.5 wt. % to 3.5wt. %, the effect of the heat treatment decreases sharply, resulting in many coarse eutectic phases remaining in the triangular cross boundaries of the alloy and the reduction of alloy mechanical properties.

Abstract:A molecules dynamic simulation model was established to simulate the tension of Al₂Cu with voids under the environment of normal temperature and constant engineering strain rate. The influence of void size, quantity and its distribution on the mechanical properties of Al₂Cu was studied by adopting embedded atomic method. The results show that the presence of void causes the appearance of free surface in the model and stress concentration at the inner edge of void, which greatly reduce the tensile strength and deformation ability of the material. In addition, the plastic and tensile strength of Al₂Cu decrease obviously with the increase of void size. The stress-strain curves corresponding to different number of void are basically overlapped in the elastic deformation stage and both the plasticity and tensile strength decrease for more voids. According to the change of void distribution, it can be find that the smaller the angle between the direction of the connection of the voids and the direction of the tensile, the stronger the plasticity and tensile strength of Al₂Cu

Abstract:Hot compression tests of the Al-9.39Zn-1.92Mg-1.98Cu alloy are carried out in the temperature range from 300 ?C to 460 ?C and the strain rate range from 0.001 s-1 to 1 s-1, and the height reduction degree is 70%. The flow stress is corrected because of the effect of friction. Results show the flow stress decreases with increasing the temperature increasing or decreasing the strain rate. The friction effect is more and more obvious when the temperature is low and the strain rate is high. A revised constitutive equation considering the influence of strain is established based on the Arrhenius-type model. Compared with the experimental and predicted flow stresses, the revised constitutive equation has a higher accuracy. Their correlation coefficient and average absolute relative error is 0.95 and 2.45%, respectively.

Abstract:The extended continuum mixture model with considering the floating grains motion was applied to calculate the macrosegregation of large-size billet of 2024 aluminum alloy during direct-chill (DC) casting. Transport equations of mass, momentum, species and heat were solved simultaneously with the Scheil-Gulliver micro-model. The effects of casting parameters (e.g. billet size, casting speed, casting temperature and intensity of secondary cooling zone) were calculated in nine cases. Influence of the transport mechanisms for macrosegregation formation dependent on casting parameters were discussed in detail. Our study demonstrated that the processing parameters directly impacted the shape and dimension of the sump, thereby affecting the final segregation patterns. The billet size and casting speed played the mostly important roles. A larger billet size usually means a slower cooling rate, a deeper and wider sump, which results in the severer segregation in the billet center. The sump depth dramatically increases with the increase of the casting speed. Therefore, higher casting speed promotes greater macrosegrgation. Nevertheless, the sump depth increases slightly with increasing of casting temperature.

Abstract:The hot-rolled textures in a 5083 aluminum alloy were measured by electron backscattered diffraction technique, and the results show that rolling texture components are developed unequally at different locations, moreover, grain boundary planes are also textured. Grain boundary planes favor the {111} orientation at the center of the specimen, and their population is 50% higher than the random distribution case, whereas grain boundary planes favor the {110} and {112} orientations on the surface of the specimen, and their population is 28% higher than the random distribution case. Moreover, this anisotropic distribution of grain boundary planes occurs at both low and high angle boundaries.

Abstract:During vertical lapped deposition with solidification of an aluminum molten droplet onto an aluminum substrate, the effects of the surface morphology and interior quality of the specimens under different process parameters were studied in this paper. By research of the single metal droplet deposition behavior, the vertical lapped deposition of numerical model was established, and the evolution of morphology and temperature of molten droplets vertical lapped deposition impacting a substrate surface at different time respectively and multiple droplets successively deposition experiments under the different simulation parameters were carried out. In order to confirm the numerical simulations and experimental verification, the comparison between numerical simulations and experiments shows a good agreement, and the optimal parameters are obtained. This investigation is essential to implement effective process control in metal micro-droplet deposition manufacture and it provides technical support and reference for the complex metal parts of molten droplets Vertical lapped deposition process.

Abstract:Based on the Karma thin interface phase-field model which include the solid diffusivity, the effects of interface width and thermal noise on the dendrite growth behavior in undercooled melt of Al-Si alloy were studied by using three-dimensional adaptive meshing method. The simulation results show that with the increase of interface width, the complexity of dendrite morphology decreases, the dendritic tip velocity decreases and the solute concentration at the tip liquid phase decreases. With the increase of thermal noise amplitude, the dendritic tip changes small, the number and asymmetry of secondary dendrites located on both sides of the dendrite increases.

Abstract:The microstructure evolution and recrystallization mechanism of compressed Al-10Mg alloy with and without addition of Sc and Zr have been observed through electron back-scattered diffraction (EBSD) and transmission electron microscope (TEM). Through precipitate of Al₃(Sc,Zr) precipitation, original grain is ferined. Also, flow stress can be increased. In the presence of Al₃(Sc,Zr) precipitation, dislocation motivation is impeded; concentration of dislocation in grain boundary yet, deformation band is decreased and not enough for nucleation of recrystallized grain; accumulation and annihilation of dislocation is affected. Recrystallization grain is formed through rotation of subgrain in Al-10Mg-Sc-Zr alloy. After which, recrystallization mechanism of Al-10Mg alloy was changed from discontinuous dynamic recrystallization (DDRX) into continuous dynamic recrystallization (CDRX).

Abstract:Two kinds of alloys Al-Zn-Mg-Cu and Al-Zn-Mg-Cu-0.15% Er were prepared by steel mould casting. The existence and form of the Er in the as-cast, homogenized, deformed and aged microstructures of the Al-Zn-Mg-Cu alloy were investigated by optical microscopy (OM), scanning electron microscopy (SEM), energy dispersive spectrometer (EDS), differential scanning calorimetry (DSC), transmission electron microscopy(TEM), X-ray diffractometry (XRD). In addition, its effect on the tensile properties of the alloy at room temperature has also been discussed in detail. The results show that trace element Er can refine the as-cast microstructure of Al-Zn-Mg-Cu alloy to a certain extent, but this refinement is limited. Er exists in the alloy mainly in the form of a ternary Al8Cu4Er phase, which forms during the solidification and segregates at the grain boundaries, and often occurs between eutectic networks. Al8Cu4Er has a high melting point and poor plasticity and is therefore easily crushed during the thermal deformation of the alloy. Al8Cu4Er fragments may cause cracks and may also induce recrystallization nucleation, which will eventually have an adverse effect on the comprehensive properties of the alloy.

Abstract:In current research, a novel Al-Mg-Sc-Zr alloy was produced through conventional rolling and annealing process and achieved a high thermal stability, a high ultimate strength (UTS) of 501.7 MPa, a high yield strength (YS) of 320.4 MPa and a high elongation to failure of 21.6%. X-ray diffraction(XRD), electron backscattered diffraction (EBSD) and transmission electron microscope (TEM) were utilized to observe the microstructure of samples. As a result, complex effects of solute Mg atoms and precipitate of Al₃(Sc,Zr) precipitation promoted formation of microstructure with large lattice misfit, sub-grain and dispersive distributed Al₃(Sc,Zr) precipitation. The main mechanisms for observed high strength were found to be due to the solid solution of Mg and precipitate of Al₃(Sc,Zr) precipitation, theoretical strength is in agreement with experimental strength. The presence of bimodal grain structure which was first found in conventional rolling structure and Al₃(Sc,Zr) precipitation provided space for dislocation accumulation, improved the dislocation storage capacity of the alloy, and then directly increases the elongation of the alloy.

Abstract:The wall of ZL205A aluminum alloy were carried out by the wire+arc additive manufacturing technology (WAAM). The microstructure,mechanical properties and so on of ZL205A aluminium alloy wall were investigated by metallographic, SEM, EDS and tensile tests, and compared with that of metal casting alloy. The results show that the thickness of the wall is uniform and the surface is smooth. Meanwhile, the burning rates of B and Cd inStheSdepositSbody are 60% and 50%, respectively. Compared with cast alloys at casting condition, the as-deposited WAAM ZL205A have more uniform grain size, smaller grain size and uniform distribution of precipitated phases in grain and grain boundaries. After heat treatment (T6), θ-phase is completely dissolved into Al matrix, and the re-melted T-phase distributes on the grain boundary. The tensile strength, yield strength and elongation of the wall are 500 Mpa, 450 Mpa and 10%, respectively, which are higher than that of the metal casting alloy, and the mechanical properties of the alloy in transverse and longitudinal directions are the same.

Abstract:The effect of wire arc additive manufacturing process on the structure and properties of aluminum alloy (ZL114A) was studied by means of metallographic microscope, scanning electron microscope and electronic universal test. Compared with the traditional casting method, the structure of as-deposited WAAM ZL114A has smaller dendrite spacing, the distribution of fine Si-phase is uniform, and the chemical composition is controlled effectively. Through T6 heat treatment process, Si-phase is fully spheroidized and the second phase is dispersed on the matrix of alpha-Al. Meanwhile, the mechanical properties are significantly improved. The tensile strength, yield strength and elongation are 360MPa, 315 MPa and 7.5%, respectively. Especially, the elongation is 2.1 times than that of sand casting sample, and the tensile fracture is characterized by ductile fracture. The defects of ZL114A(WAAM) are mainly pores less than 30 μm. After heat treatment, the number of pores decreases and the size increases.

Abstract:In this study,the B₄C particles reinforced aluminium matrix composite tube with different deformation was first fabricated by spark plasma sintering (SPS) and followed by asynchronous offset spinning. It was found that the B₄C particles distributed change from net to relatively homogeneously in the aluminium matrix with the spun deformation increase. The interface between B₄C and aluminium was formatted metallurgical bonding due to the discharge was happened lead to the local high temperature existed during SPS processing and the interface was mainly consisted of AlB₂ and Al₃BC phase. With the deformation increasing, the aluminium grain and B₄C size was decrease. But, large size of B₄C particles fracture was decrease the fine-grain and particles strengthening function for the tensile strengthening.

Abstract:A kind of triazole Schiff base was synthesized: 3-pyridine-4-amino-1,2,4-triazole-5-thione. The inhibition effects of Schiff base and Ce(NO₃)₃ complex on corrosion of 1060 pure aluminum in 3.5% NaCl have been studied by potentiodynamic polarization, electrochemical impedance spectroscopy and scanning electron microscopy with energy dispersive spectrometer. The results show that Schiff base can effectively inhibit the corrosion of pure aluminum in NaCl solution at 293 K. When concentration of Schiff base is 0.4 g.L_-1, the inhibition efficiency is up to the highest, 76.0%. Schiff base is a mixed inhibitor, the adsorption of Schiff base on the 1060 pure aluminum surface was well fit by the Langmuir isotherm model, and there are both physisorption and chemisorption. Schiff base can inhibit the corrosion of pure aluminum and possesses a good synergistic effect with Ce(NO₃)₃, the corrosion inhibition efficiency of 0.2 g.L_-1 Schiff base and 0.03 g.L_-1 Ce(NO₃)₃ is up to 88.2%.

Abstract:Indirect extrusion of 7A99 ultrahigh-strength aluminium alloy was heat treated by T6 peak aging treatment and peak cold-heat cycle aging treatment of -180℃ (T6-DCT). XRD, TEM, HRTEM and 3DAP were applied to study the influences of T6-DCT treatment on the strength and toughness properties, precipitation behavior. The result shows that The lattice constant of Al matrix increases from 0.40551 nm to 0.40626 nm after T6-DCT, which plays a solid solution strengthening role. A large number of η phase generate in the grains, and the η phases at the grain boundaries are discontinuous, meanwhile the precipitation free zone is formed at the grain boundaries, which reduces the tensile strength. After T6-DCT treatment, the segreation degree of Zn and Mg increases, the precipitation ratio and distribution uniformity of precipitated phases decrease. The avearge equivalent radius of the precipitated phases changes from 1.2 nm to 1.14 nm after T6-DCT treatment, the density of the precipitated phases decrease from 4.53×10₂₄/m₃ to 3.87×10₂₄/m₃, which weaken the precipitation-strengthening. The strength and toughness improve significantly after T6-DCT treatment, which shows that the strength is slightly reduced and the toughness is improved remarkably.

Abstract:The effect of precipitation microstructure change on the stress corrosion behavior of AA2024 aluminum alloy was investigated by constant load stress corrosion tests, scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The results show that the T3 alloy is much more sensitive to stress corrosion than the T8 alloy. The corrosion process and precipitation microstructure change of T3 and T8 alloys were investigated by in-situ corrosion observations operated by high-angle annular dark-field scanning TEM (HAADF-STEM), which intuitively demonstrate the different corrosion morphologies: the corrosion morphology of T3 alloy is intergranular corrosion and that of T8 alloy is a combination of intergranular corrosion and grain attack. Because of the change in precipitation microstructure and corrosion mechanism, the alloys with different ageing conditions possess different stress corrosion susceptibility.

Abstract:The microstructure and mechanical properties of 5A06 aluminium alloy laser welded joint with thickness of 30 mm were investigated in this paper. The experimental results show that an amount of pore defects were found in weld seam zone, and the welded defects were mainly located at the grain boundary. The proportion of the welded defects with size less than 100 μm was beyond 50%. The microstructure in weld seam zone was mainly composed of dendritic grians, and several dendritic grians were located in a single grains. The misorientation between the dendritic grians was less than 5o, and the contrast between the dendritic grians was caused by element Mg microsegregation. The obvious interface was observed between the weld seam zone and heat-affected zone, and the contents of low angle boundary in heat-affected zone were higher than that of weld seam zone. Meanwhile, the grain morphology and size in heat-affected zone were different from the weld seam zone. Microhardness measurement shows that the definitive fluctuation of microhardness values in weld seam zone was observed, and the microhardness values of weld seam zone were beyond that of the microhardness values of matrx.

Abstract:The mechanical properties and microsctructures of the 6156 Al alloy subjected to a thermomechanical treatment consisting of under-ageing at 180 ℃ for 1 h, cold-rolling at room temperature with the thickness reductions of 50~80% and re-ageing at 100 ℃ for 48 h were investigated by optical microscopy, tensile test, X-ray diffraction, scanning electron microscopy and transmission electron microscopy. The tensile test indicates that the alloy can achieve high strength and relatively good ductility simultaneously and the ultimate strength, yield strength and elongation to failure are 515~564 MPa, 472~551 MPa and 5.7~11.1%, respectively. The microsctrucural observations show that the high strength results from the combination of deformation and precipitation strengthening and increases with increasing the thickness reductions. The improved ductility is attributed to both the decreased dislocation density and increased precipitation strengthening. The fractographies of the alloy consist of intergranular and dimple-induced transgranular fracture and the dimples have shallow depths and increased number with increasing the thickness reductions.

Abstract:The microstructure of an Al-Ti-C-Ce alloy was studied by XRD,SEM,and EDS. This mother alloy consisted of α(Al),(AlTi),(TiC),and (Ti2Al20Ce) phases,and there was a second phase of a composite structure in the alloy.The TiC phase was the primary crystal nucleus,and the (TiAl) phase was segregated on the surface of TiC phase to form a TiC-(TiAl) composite crystal nucleus. Al formed a fine TiC-(TiAl)-α(Al) primary composite crystal nucleus by a peritectic reaction.The primary composite crystal nucleus with higher energy and larger cluster size was taken as the core,and other composite crystal nuclei were segregated on its surface to form a secondary composite crystal nucleus.Next,the secondary composite crystal nucleus formed the tertiary composite crystal nucleus,and so on,to form the titanium-enriched area of composite particles.

Abstract:Semi-solid isothermal heat treatment microstructural evolution of die casting Al-5Mg-2Si-Mn alloy with different injecting pressure was studied. The average α-Al grain size of as-cast die casting experimental alloys was smaller than that of gravity casting, and it decreased while microstructure distortion energy increased with the increase of the injecting pressure. It was found that semi-solid microstructural evolution process of die-casting alloy was similar with, but faster than that of gravity casting. The results from regression analysis show that the relationship between the average α-Al grain diameter and the isothermal holding time fits the formula r ?^3=Kt+〖r ?_0〗^3, and the coarsening rate (K) is decreased with the increase of the injecting pressure. For the fixed injecting pressure, the average α-Al grain size of the experimental alloy increased while the K reduced with the increase of the isothermal holding temperature. For the fixed isothermal holding time, the solid fraction and α-Al grain coarsening rate of die-casting alloy were lower than those of gravity. The appropriate semi-solid isothermal heat treatment parameters of the die casting experimental alloy were determined to be 620 ℃ for 20 min.

Abstract:High pressure torsion (HPT) experiment followed with heat treatment were carried out on as-received Al-Zn-Mg-Cu-Zr alloy at 400 ℃ under the pressure of 1 GPa. Optical microscope, electrochemical workstation and slow strain rate tensile machine were used for microstructure observation, electrochemical corrosion and stress corrosion resistance test for the as-received and HPT processed samples respectively. The results show that HPT processing can improve the tensile strength and stress corrosion resistance by modifying the size and distribution of grains and second phases. The second phases agglomerated at the grain boundary corrode continuously, which leads to obvious intergranular corrosion and weak stress corrosion resistance of the as-received alloy. After 0.5 turn of HPT processing, the fragmentation and content reduction of second phase lead to the decrease of corrosion sensitivity, at the same time, the planar slip reduces and homogeneous slip mode increases due to grain refinement, which synthetically results in a significant improvement of the stress corrosion resistance. The HPT processed sample with 2 turns has finer grains with uniform distribution, which leads to the further increases of homogeneous slip mode compared with 0.5 turn, but under the interaction of intense pitting and stress concentration, the resistance to stress corrosion slightly decreases.

Abstract:Based on electromagnetic flanging process of aluminum alloy sheet metal, numerical simulation was conducted to investigate the distribution characteristics of the electromagnetic force and the influence of geometry parameters on the electromagnetic force distribution, and then the influence of the electromagnetic force distribution on the forming quality of workpieces was revealed. The results show that in the process of electromagnetic flanging of aluminum alloy sheet metal, the marginal accumulation effect of the electromagnetic force was produced due to the existence of the precast hole. The aperture of the sheet metal and the inner diameter of the forming coil can affect the distribution of electromagnetic force by changing the ratio of the projection area to the coil area. With the decrease of the ratio of the projection area to the coil area, the marginal accumulation effect of the electromagnetic force becomes more prominent, and the electromagnetic force density of the hole edge increases. Materials in the corner area flow more significantly under the circumstance of the uniform electromagnetic force distribution, meanwhile higher forming height and smaller edge reduction rate can be obtained after forming, which means more uniform thickness distribution of the deformation area and better forming quality of workpiece.

Abstract:In this work, sintered NdFeB permanent magnet (NdFeB) was firstly soldered with DP1180 steel using Zn-5Sn-2Cu-1.5Bi (ZSCB) solder. Soldering was performed in an inert atmosphere control high-frequency induction furnace, and then the microstructure, magnetic properties and shear strength were investigated by optical microscope, scanning electronic microscopy, energy dispersive X-ray analysis, NIM-2000H magnetic tester and mechanical testing machine. Results showed that the interface between NdFeB / ZSCB solder formed metallurgical bonding with Nd-Fe-Zn and Fe-Zn. FeZn13 and Fe3Zn10 phases formed in steel side of the joints. Besides, the soldering temperature had slight influence on the magnetic properties of NdFeB. Finally, compared with adhesive bonding in traditional method, the shear strength of the soldering joints were dramatically improved by 35.38%, from 32.50 MPa to 44.00 MPa. The shear strength was high enough to cause failure in NdFeB side of the joints. Fracture of the joints was caused by large difference thermal expansion coefficient between NdFeB and ZSCB solder as a result of high stress at the reaction layer closing to NdFeB.

Abstract:The wide compositional space of multi-component Zr-based metallic glass gives rise to a huge challenge for the discovery of the Zr-based alloys with excellent glass-forming ability. Moreover, most of the bulk-sized Zr-based metallic glasses contain either the toxic element Be or precious metals. Thus, economical approaches using to search multi-component bulk-sized Zr-based metallic glass free of poisonous and noble elements are extremely necessary. Here, a new Zr₅₀Ti₅Cu₂₇Ni₁₀Al₈ metallic glass, with a critical diameter of 10 mm, was explored after only a few experimental trials through the method of proportional mixing of the binary eutectics and slightly partial replacing of element. The thermal stability and the hardness of this metallic glass were also respectively investigated by in-situ high-temperature X-ray diffraction and nanoindentation experiments.

Abstract:The effect of hydrogen on 120o<111> twin boundaries in γ phase of an as-cast and as-forged Ti–46Al–2V–1Cr–0.3Ni alloy was investigated by means of annealing treatment in hydrogen atmosphere, and the microstructure was observed by an optical microscopy, a scanning electron microscopy, an electron back scattered diffraction technique, a transmission electron microscopy and a X-ray diffraction apparatus. The results showed that hydrogen could promote γ-phase static recrystallization of the as-cast and as-forged alloy, and the extent of static recrystallization increased with increasing hydrogen content. Many static recrystallization grains possessed 120o<111> twin boundaries. The relationship between the fraction of 120o<111> twin boundaries and hydrogen content was given. Hydrogen-weakened γ-phase elastic anisotropy increased 120o<111> twin boundaries.

Abstract:In this paper, the effect of V elememt addition on the properties of a (Ni56Mn25Ga19)100-xVx (x = 0, 1, 3) (at.%) high-temperature shape memory alloys was investigated by optical microscopy, X-ray diffraction, scanning electron microscopy, transmission electron microscopy and compression test. The results show that the microstructure and some properties of our alloys are very different from that of the reported Ni56Mn25Ga19-xVx alloy due to the V substitution method difference. Single phase of non-modulated martensite with tetragonal structure is observed for the undoped alloy, and dual-phase structure which is consisted of tetragonal martensite and bamboo leaf shaped γ phase is present for x=1 and 3. With increasing V content, the amount of γ phase increases, while the size and shape of γ phase keep unchanged. V addition enhances the mechanical properties and shape memory effect. The reversible strain of 6.7% is obtained in the (Ni56Mn25Ga19)99V1 alloy under pre-strain of 10% after heating.

Abstract:The microstructure evolution and coarsening behaviors of disordered γ phase in the inverse Co-19.7Ti alloy have been investigated by experiment and phase-field method. Both the experimental and simulated results show that the morphologies of γ particles evolved from near-circular shape to plate-like shape as the aging time increases. The coarsening kinetics for the mean particle size obeys the cube law r₃ = kt, and it can be obtained as: . There exist two distinct stages of the mean particle sizes increase versus aging time, the growth rate is dramatically larger in stage I and has a relatively slower increase in stage II. The summit value of precipitate size distributions become larger and the breadth of the distributions decrease from 700_oC to 750_oC, the simulated results reproduce well the experimental results.

Abstract:The inherent relationship between the microstructure parameters and anti-impact strength is established by micromechanical strength and dynamic destruction criterion of eutectic composite ceramic. Firstly, in line with the microstructure characteristic of eutectic composite ceramic, the effective stress field of composite ceramic is computed by the interaction direct derivative estimate and sufficiently simplified calculation method. Secondly, according to equivalent inclusion method and Griffith micro-crack propagation theory, the micromechanical strength of eutectic ceramic composite is predicted. Thirdly, the dynamic destruction criterion of the comminuted zone is built by the unified pressure shear criterion. Finally, on account of the dynamic destruction criterion which is associative with microstructure, the calculated mode of anti-impact strength is obtained. The influence of microstructure parameters on anti-impact strength is quantitatively analyzed. Results show that decrease in interface defect size among eutectic grains and increase in eutectic grain stiffness will increase anti-impact strength.

Abstract:A series of Graphene-ZnGa2O4composites (G-ZnGa2O4) were synthesized by hydrothermal method. The prepared materials were characterized by means of XRD, SEM, TEM, Raman and XPS, respectively. The gas sensing properties of G-ZnGa2O4 composites were investigated. The results indicated that the graphene content has a great influence on the response and the gas sensing selectivity, the optimal composition of G-ZnGa2O4 gas sensing material was 0.1%G- ZnGa2O4. The sensor based on 0.1% G-ZnGa2O4 exhibited high response to 1000 ppm formaldehyde when operated at 203oC and the response reached 32.2; the detection limit for formaldehyde was as low as 1ppm; the gas sensing selectivity to formaldehyde was also good, the ratio of S1000 ppm formaldehyde and S1000 ppm acetone reached 26.8. The response time and recovery time for 1000 ppm formaldehyde were 11 s and 5 s, the response time and recovery time for 1 ppm formaldehyde were 6 s and 5 s, respectively.

Abstract:The microstructural evolution of different generations of ?′ precipitates during various heat treatment processes of a nickel base superalloy has been investigated. After solutionizing in the single ? phase field, continuous cooling, interrupted cooling and isothermal annealing tests were performed and characterization of the precipitates was carried out by scanning electron microscopy. It is found that a monomodal size distribution of the secondary ?′ precipitates can be achieved at a very high cooling rate in the continuous cooling process. With the decrease of the cooling rate, the secondary ?′ precipitates grow gradually and gather together to form a flowery morphology. When the secondary supersaturation is developed in the vicinity of the secondary ?′ precipitates during isothermal annealing, the water-quenched tertiary ?′ precipitates are produced and result in a bimodal size distribution of ?′ precipitates with the larger secondary precipitates. Furthermore, the effects of the secondary ?′ particle growth on the hot deformation are also discussed.

Abstract:Embedded material shell was prepared using wax grid with 8? mesh. The effects of micro-alloy elements B, Y, Mn and Er on the mold filling capacity of Ti-46Al-8Nb melt were studied. The results showed that the fluidity and mold filling property of Ti-46Al-8Nb melt was improved to some extent by B, Y, Mn and Er addition. Especially, 0.5Y and 1Mn addition had significant improvement on the mold filling capacity of the alloy, which increased the filling rate by 54.5% and 48.5% respectively. The effect of 0.1Er, 0.5B and 1B addition on the mold filling capacity of the alloy was not so remarkable, with the filling rate increasing by 3.0%, 4.5% and 5.3% respectively.

Abstract:The grain boundaries as a fast diffusion path for solutes play an important role in multi-component diffusion-controlled phase transformations. In order to study the phase transformations in consideration of the grain boundary diffusion, the diffusion along grain boundary is incorporated in the quantitative phase field model coupled with the Kim-Kim-Suzuki (KKS). An integration method was used to calculate the equivalent grain boundary diffusion in the phase field method. The thermodynamic and mobility data was obtained from Thermo-Calc and DICTRA software respectively. The effect of the number of grain boundaries, the spatial distribution and size distribution (PSD) of α phase on the α phase dissolution was researched in the paper. The results show that grain boundaries are a faster element diffusive path. The number of grain boundaries is larger, the kinetics of α phase dissolution is faster. Namely, the kinetics of α phase dissolution is fastest when phase located at triple junctions; However, the dissolution kinetics is little difference when α phase is on the grain boundary and distribute uniformly in the matrix. Compared to the phase dissolution rate in two-dimensional condition, the effect of the grain boundary diffusion on dissolution kinetics is more obvious in three-dimensional condition. When phase transformation is dominated by bulk diffusion of solute, the spatial distribution of α phase is a main factor affecting the α phase dissolution. But when phase transformation is dominated by grain boundary diffusion of solute, the effects of other size distributions on the dissolution of alpha phase are not obvious except for uniform PSD.

Abstract:An important goal of materials genome initiative program is to build the calculation model and establish the database of physical properties of the materials, aiming to shorten the development period of the materials, reduce the cost of research and development in material and accelerate the production of new material. Although the existing model has been available for the calculation of pure component"s thermal expansion coefficient, a proper model to deal with metal solid solution"s thermal expansion coefficient is still lacking. Here, based on the calculation of phase diagram method (CALPHAD method), a model of the thermal expansion coefficient of solid solution containing ferromagnetic-paramagnetic transition is constructed by modifying the traditional heat capacity model and adding extra magnetic item. The experimental data of Ni-Fe binary system were used to assess the model parameters by Levenberg-Marquardt method. The interaction parameters in the temperature range of 300~1200K were obtained after assessment. Using assessed parameters, the thermal expansion coefficient of Ni-Fe binary alloy were calculated. Results indicated the sharp peak around Curie’s temperature precisely. The height of the peak gradually decreased as increasing Fe’s content and the shape of the thermal expansion curve changed from a peak into a valley, which were in agreement with the experimental data. This model can precisely predict the thermal expansion coefficient of any Ni-Fe binary alloy when Fe’s content is less than 50wt.%. This work provided a general calculation model for the thermal expansion coefficient in metal solid solution, and obtained the basic CALPHAD database of thermal expansion coefficient for Ni-Fe binary system, which can provide theoretical guidance for the design of low-expansion superalloy and also pave the way to establish the physical properties database of multi-element metal solid solution in the future.

Abstract:By improving Brust method, we synthesize 1-hexanthiol modified gold-silver alloy nanoparticles with an atomic composition of Ag_0.66Au_0.33. By using the alloy nanoparticles as “building block”, we successfully assemble one-dimensional waveguided alloy photonic crystals through a solution processible method. Under the same conditions, the sensitivity of the biosensor built with the waveguided alloy photonic crystals is 2.5 times that of the similar structure made of pure gold. Gold-silver alloy nanoparticles assembled waveguided metallic photonic crystals exhibits potential application in biosensors due to its low-cost fabrication process and simple testing methods.

Abstract:AgSnO₂NiO electrical contacts with different NiO contents were prepared by internal oxidation method. Electrical contact experiments were conducted on the JF04C contact material testing machine. The contact resistance, anti-weldability and material transfer properties of materials were studied. The sample surface morphology changes were analyzed by scanning electron microscopy (SEM). The results show that the addition of NiO is beneficial to reduce and stabilize the contact resistance. When the voltage is not higher than 18 V, the contact resistance gradually decreases with the increase of test times and finally tends to be stable. When the voltage reaches 25 V, the contact resistance of materials will increases, and the increased degree of the contact resistance is different. Both the welding power and the arcing energy of the material will increase with the voltage increases. The increase of the NiO content does not significantly reduce the melting, but it played a important role in reducing the arc energy. The electrical contact process is anodic transfer. The total mass loss of materials decreases with the increase of NiO contact. The surface of the cathode is obviously accompanied by a layer of solidified molten metal. The material transfer is mainly carried out by a fused-bridge mode with a convex peak. The surface exhibits a paste-like peak topography.

Abstract:The Type and Precipitation Mechanism of Carbide in Co-Cr-W-Ni Alloy have significant influence on the mechanical properties of alloy.Therefore, the precipitation type, distribution characteristics and precipitation mechanism of carbides after aging of Co-Cr-W-Ni alloy were studied in this work. The ageing samples were observed by XRD, scanning electron microscopy and transmission electron microscopy. The experimental results show that the types of carbides are M₇C₃, M₆C and M₂₃C₆. M₂₃C₆ carbide preferentially precipitates at grain and twin boundaries with a cube-cube orientation relationship with the matrix. The M₇C₃ carbide decomposed gradually with the M₆C carbide precipitating in situ is an important mechanism of carbide precipitation.

Abstract:The microstructure and electrochemical property of nano-silicon alloy anode material are studied in this paper. The research shows that the outline of the nano-silicon particle is basically circular, and two copper-rich phases with different silicon contents are detected in the particle, and both phases with nanostructure are observed in its surface layer. The nano-silicon alloy negative electrode material needs to be used in a certain proportion with graphite, binder and conductive agent, and the stirring process also has an important influence on its electrochemical performance. The first-cycle coulombic efficiency of the material is improved to about 90%, and the specific capacity is still higher than 500 mAh/g after 100 cycles. The battery manufacturing process is similar to the graphite negative electrode, so it is easy to be applyed.

Abstract:Electrolytic copper foils with different thicknesses were prepared by adjusting the electrodeposition time and controlling the parameters of other electrolytic processes. Using SEM, XRD, EBSD, and Universal testing machine to research the effects of surface morphology, texture, size effect and fracture mechanism on the tensile properties of electrolytic copper foil with different thicknesses. The results show that with the progress of electrodeposition, the grain size of the surface increases, and the orientation of the crystal plane {220} becomes stronger. When the copper foil thickness is less than 18 μm, the tensile strength and elongation of the ultra-thin copper foils increase with the thickness of the copper foil due to the size effect.However, when the thickness of the copper foil is more than 18 μm, as the thickness of the copper foil increases, the grain size becomes larger and the degree of crystal plane orientation becomes higher, which reduces the tensile strength of the copper foil. Key words: Electrolytic copper foil; texture; mechanical properties; size effect

Abstract:This work aims at identifying, by coupled X-Ray diffraction, scanning and transmission electron microscopy (XRD, SEM and TEM) observations, the microstructural evolution mechanisms occuring when an atomized Ti-47Al-2Cr-2Nb-0.2W powder is densified by spark plasma sintering (SPS). For this purpose, interruptions of the SPS cycle have been performed to follow the evolution of the microstricture step by step. During heating-up, the microstructure undergoes successive transformations. At begaining temperature of 1100℃ the α phase transforms into γ and residual B2. The γ phase formed is supersaturated in W. At temperature above 1200℃, TEM observations show that the repartition of the plastic dedormation is correlated to the dendritic microstructure, and the deformation induced α₂ →γ phase transformation and the twins.

Abstract:In order to find the influence of duplex aging on microstructure and mechanical properties of TC29 titanium alloy accompanied with primary α phase, different heat treatments and analysis methods including OM, SEM, and TEM were adopted. Results show that after treated by α+β two-phase solution and aging secondary α precipitates in TC29 titanium alloy are sub-micron level. After 895℃ solution and single aging, secondary α precipitates are mainly 100~300 nm in length. After 895℃ solution and duplex aging, "α clusters" are observed in β transformed microstructure and secondary α precipitates in them are thin slat-shaped. Compared with single aging, duplex aging results in an equal or lower microhardness. During the pre-aging treatment, a large amount of ω phases precipitate in β matrix, and the local element distribution gradually becomes inconsistent due to the diffusion near the primary α/β phase interface, where the “α cluster” is locally formed during the subsequent aging process.

Abstract:By comparing the microstructures,static mechanical properties and microhardness of laser deposition TC4 alloy in the as-deposited and heat-treated states, the approaches to perfect the microstructure of laser deposition TC4 alloy are explored. Results show that after the as-deposited sample undergoes 970℃ heat treatment, the grain boundary α is thoroughly broken which is continuous initially; with the extension of solution time, globular α phases are more and bigger, and their laths are in full growth and increase dramatically; two hours later, when the sample undergoes aging treatment, its structure turns to be constituted by equiaxed α, basketweave α and transformed β phase, which results in the optimized textural parameters. Compared with as-deposited and annealed samples, the plasticity of the solution aging sample is enhanced significantly and the strength is decreased slightly, and their integrated mechanical properties improved remarkably. Its equiaxed structure performs coordinating function and its basketweave structure can reduce the dislocation pile-up to improve the plasticity. The microhardness is gradually increased in laser deposition TC4 alloy in the as-deposited, annealing, solution aging and solid-solution. But when the solution temperature rises to the transformation point, the microstructure of the sample rearranges after crystallizing, leading to marked decline in microhardness.

Abstract:The Ti–6Al–4V alloy were thermo-forged in α+β two phase region,and then recrystallized in three different temperatures. The results show that the initial microstructure were fully transformed into fine equiaxed α and lamellar α+β,the fine equiaxed α and lamellar α+βwere gradually coarsening as increasing recrystallization temperature,the relative frequency of recrystallization grain were also increased,low angle boundary shows a converse trend. The total elongation and area reduction reach up to 19.9% and 42.5%,the mechanical properties gradually decreased as the elevate temperature which were attribute to coarse and inhomogeneous grain.

Abstract:The effect of strain path (unidirectional rolling and cross rolling) on microstructure and texture in deformed and recrystallized state was investigated by electron backscatter diffraction (EBSD) and X-ray diffraction (XRD). The results show that the lamellar structure is dominant in both of samples with two rolling mode, but the stored energy in the unidirectional rolled (UDR) sample is higher than that in the cross rolled (CR) sample. The deformation texture is significantly affected by the strain path. The UDR sample is characterized by the typical “copper type” rolling texture, while the CR counterpart is mainly composed of Brass (Bs) and ND-rotated Brass (BsND) texture components. In addition, the minor cube and rotated cube were found in both of deformed samples. When the two samples were simultaneously annealed at different temperatures for 1h, the different recrystallization textures were obtained. The cube texture was prevailed in the UDR sample, while the weakened fiber texture was dominant for the CR sample. In addition, the abnormal grain growth was observed in the UDR sample annealed at 800℃ for 1h, which was attributed to the formation of clustered grains with a preferred cube orientation leading to the inhomogeneous microtexture, while the cross rolling mode suppressed the occurrence of abnormal grain growth during annealing.

Abstract:Effect of different heat treatment processes on the microstructure and mechanical properties of TIG welded Hastelloy X welded joints was studied by SEM and EDS. The results showed that the central area of the weld was mainly composed of fine equiaxed grains, and the fusion zone was dominated by dendrites. The secondary phase was not precipitated in the weld joints heat treated at 1050°C, and a large number of secondary phases were precipitated in the grains at the grain boundary at 1100°C. The secondary phase at 1150°C were partly re-dissolved. The tensile strength of joint reaches up to 773.49 MPa after heat treatment at 1150°C. The joint treated at 1100°C was intergranular fractures, the rest were ductile fractures.

Abstract:TC4 titanium alloy was brazed to 30CrMnSiNi2A ultra-high strength steel by Ti-37.5Zr-15Cu-10Ni and Ag-Cu28 brazing filler metals respectively. Microstructure and mechanical property of both brazed joints were analyzed comparatively. Results show that Ag-Cu28 brazed interface is composed of Ag(s,s) and intermetallic compounds in Ti-Cu system. Ag-Cu28 brazed joint has relatively high shear strength due to the exisitence of Ag based solid solution and the shear fracture shows the characteristics of ductile fracture. Ti-37.5Zr-15Cu-10Ni brazed interface consists of Ti-Zr solid solution and solidified brazing filler metals, which lead to the low hear strength of brazed joint. The shear fracture of Ti-37.5Zr-15Cu-10Ni brazed joint shows the characteristics of brittle fracture. Compared with Ti-based brazing filler metal, Ag-based brazing filler metal is suitable for brazing TC4 titanium / 30CrMnSiNi2A ultra-high strength steel dissimilar materials. Sound brazed joints with the shear strength of 125.52MPa can be attained at the brazing temperature of 830℃ with the bolding time of 15 min by Ag-Cu28 brazing filler metals.

Abstract:Ti3SiC2 ceramic and TC4 alloy were successfully joined by a contact-reactive brazing technique using Ti/Ni/Ti interlayers. The results showed that the typical interfacial microstructure of the TC4/Ti3SiC2 joint obtained at 1000 °C for 10 min was TC4/α-Ti + β-Ti + Ti2Ni/Ti2Ni + Ti3AlC + Ti5Si3Cx + TiC/Ti3SiC2. The width of the brazing seam increased and the content of Ti2Ni phase decreased with increased brazing temperature and brazing time. Large amount of Ti2Ni phase distributed in the joint brazed at 980 °C. The joint brazed at 1000 °C for 10 min was well bonded, and the maximum shear strength, 82 MPa, was obtained in corresponding joint and the fracture occurred mainly in the Ti3SiC2 substrate. When the brazing temperature was further elevated, a large number of voids appeared at the interface between the TC4 alloy and the brazing layer, and the shear strength dramatically decreased. Moreover, the formation mechanism of the brazed joints is discussed.

Abstract:In order to study the microstructure and fatigue properties of laser deposited TC4/TC11 gradient materials, directly transited and gradiently transited TC4/TC11 composite materials were prepared by laser deposition manufacturing technology. The microstructures of composite materials by different transition were observed, the fatigue properties of these two composite materials under stresses of 550 MPa and 800 MPa were tested, and fatigue fractures were analyzed. The results show that the interface of the microstructure of the gradient material with 3 transition layers is not obvious, and microstructures of TC4 and TC11 are integrated more tightly in the transition zone than that of the directly transition composite materials. The fatigue life of the gradient material with 3 transition layers under either stress is higher than that of the direct transition, which is relatively increased by 129.3% under low stress and 81.8% under high stress. The direct transition composite material cracks along the bunch of α-sheet during crack propagation, with a large sliding surface and a low fatigue life. The cracks of gradient material with 3 transition layers grow along a single α-sheet, the slip plane is small, and the crack propagation path is more tortuous, which improves the fatigue life.

Abstract:The pores existed commonly in the thermal sprayed coatings. The pore morphology, size and distribution took great effects on the performance of coatings. Therefore, it is very important to characterize pore structures of thermal sprayed coatings. In this work, the characterization means of thermal sprayed coatings’ pore structure were comprehensively reviewed. The often-used image analysis means of pore structure characterization included optical microscope, scanning electrical microscope and transmission electron microscope. Besides these, there were infiltration compression method, gas adsorption and desorption, contact measurement of atomic force probe, 3D ray scanning imaging including X-ray and neutron ray, ultrasonic imaging analysis, and so. The advantage and disadvantage of all kinds of pore characterization means were discussed. The application scopes of each mean were analyzed. The future characterization technology of thermal sprayed pore structure was prospected.

Abstract:Lamellar structure is the most important microstructure in TiAl alloy. We summarize the research progress of coarsening of lamellar structure in TiAl alloy so far, introduce the two types of the lamellar coarsening: continuous and discontinuous coarsening in TiAl lamellar structure, analyse thermodynamic driving force source, including chemical volume free energy, interface energy, elastic strain energy and grain boundary energy of lamellar coarsening, describe the dynamic characteristic of lamellar coarsening and discuss the influence factor of lamellar coarsening, incuding temperature, time, condition of microstructure, alloy elements and so on. On this basis, we astudy the lamellar coarsening of Ti-4822 alloy, describe and analyse its continuous and discontinuous coarsening of lamellar structure at elevated temperature and its change with temperature and time. We conclude that two coarsening types compete obviously at 1160 ℃. Discontinuous coarsening dominates at about eutectoid temperature while continuous coarsening dominates at higher temperature (above 1200 ℃) and discontinuous coarsening is suppressed.