Abstract:With the advancement of nanoindentation technology, more and more data are supporting that the pop-in event is not a homogeneous but a heterogeneous dislocation nucleation process mediated by vacancy-like defects. However, the conclusion is based on the two model-extracted parameters, activation energy and activation volume. There hasn’t been any experiment directly correlating the pop in event with vacancy activities. This work, following our previous nanoindentation study on a FCC high entropy alloy CoCrFeMnNi, aims to verify this correlation with specially-designed nanoindentation experiments. It was found that when the indenter was hold at a subcritical load (in reference to the critical load that triggers instantaneous pop-in) for a period of time, delayed pop-in was observed. Furthermore, the displacement bust size increased with the tip radius up to a few hundred nanometers. These two observations suggested the vacancy was at play because the vacancy can migrate under any applied stress and its number within the indented volume depends on the tip radius.

Abstract:Aiming at the problem of poor formability of titanium alloy sheet, the ultrasonic vibration-assisted forming process was studied, the effects of ultrasonic vibration on the mechanical properties of TA2 titanium alloy sheet and the friction coefficient between the contact surfaces were analyzed. On this basis, the ultrasonic vibration-assisted bulging experiment of specimens with different width-to-length ratios was carried out, and the influence of ultrasonic vibration on the bulging force and limit bulging height of TA2 sheet were analyzed. At the same time, based on the grid strain principle, the forming limit diagram of the TA2 sheet was established by measuring the limit strain of the specimens with different width-to-length ratios. The research results show that choosing appropriate process parameters in ultrasonic vibration-assisted forming can not only improve the formability of TA2 sheet, but also reduce the influence of friction on plastic deformation behavior of sheet, thus effectively increasing the forming limit of TA2.

Abstract:Pulsed electromagnetic coupling treatment equipment was used to strengthen WC-8Co cemented carbide. The mechanical and frictional properties of WC-8Co were studied, and the strengthening mechanism was revealed by analyzing the cutting performance. The cutting behavior of Ti6Al4V in dry turning was analyzed by collecting the cutting force, temperature, and wear signals of the flank surface on the tool in the turning test. Finally, scanning electron microscopy（SEM）and energy-dispersive X-ray spectroscopy（EDS）were used to observe and analyze the WC-8Co cemented carbide. The aim was to obtain the cutting mechanism of WC-8Co cemented carbide for dry turning of Ti6Al4V before and after pulsed electromagnetic coupling processing. The results show that pulsed electromagnetic coupling processing can improve the durability of tools while reducing the temperature of the cutting and the oxidation wear of the flank surface of the tools.

Abstract:In this study, spherical tantalum powder fabricated by radio frequency plasma spheroidization system was used for selective laser melting densification. Through optimizing the processing parameters, the fully dense Ta sample was obtained at the scanning speed of 650 mm/s and the laser power of 240 W. Attributed to the high sphericity, the Ta samples performed better densification behavior and surface quality. Microstructure characterization showed that equiaxed grains and columnar structure were present in the top- and side- views, respectively. The EBSD results revealed a <111> preferred orientation along the building direction. The maximum microhardness and the ultimate tensile strength reached 296.2 Hv and 697 MPa, respectively. A significantly improved ductility with elongation of 28.5% was achieved for the dense sample.

Abstract:The phase, texture, and anisotropy in microstructure and impact toughness of 316L stainless steel were observed and analyzed by means of optical microscope (OM), X-ray diffraction (XRD), scanning electron microscope (SEM), electron back scatter diffraction (EBSD) and metal pendulum tester. Results show that the microstructure and impact toughness of SLM processed 316L stainless steel reveal an obvious anisotropy. The material phase of the samples in the transversal and the vertical direction were equal to γ-Fe phase, and their structure perpendicular to the building direction has a checkerboard morphology. Most of the grains were equiaxed and the grains has been refined (d_mean=9.177 μm), in addition grains in the overlapped area of the molten pool were observed to be finer (below 6 μm), contemporary, the number of grain boundaries with small angle parallel to building direction is large, whereas the morphology parallel to the building direction resembles a fish-scale pattern, most of which comprises columnar grains with a large grain diameter (d_mean= 21.247 μm). Meanwhile, the texture perpendicular to the building direction exhibits a strong fiber texture <110> //rolling direction (RD) (strength of 7.83) and a weak plate texture {112} <110>, whereas the texture parallel to the building direction exhibits a strong fiber texture < 110 >//RD (strength of 12.23). Under a similar density condition, the impact toughness values of transversal direction and vertical direction were 62.8±3.2 and 38.6±4.5, respectively. The toughness of transversal direction was significantly better than the vertical direction and increased by 62.69%. In addition, grain size, size angle grain boundary and texture type has significant effected on impact toughness anisotropy. the grains perpendicular to the building direction were refineed, with an increase the grain boundaries with large angles and an enhancement in the grain toughness, the fiber texture <110> //RD has a low impact toughness resistance, while plate texture {112}<110> has a good impact toughness resistance, the{112}<110> texture perpendicular has low strength and weak {112}<110> texture to the building direction ,therefore, the toughness of transversal direction was preferred.

Abstract:Rotation angle is a key parameter in the processing of three-roller, cold-rolled seamless steel tubes. Using a cold-rolled AZ31 magnesium alloy tube as the research object .Based on the cold-rolling process under different rotation angles, the present paper conducts a comparison and analysis of the effects of different rotation angles on the characteristics of the deformation equivalence effect force, equivalent plastic strain and regularity of the influence of node temperature. Our study shows that increased rotation angles increase the equivalent stress, equivalent plastic strain and node temperature. With the aid of the automaton model and experimental means ,through the experiment and numerical simulation results contrast analysis, the author finds out the grain produced in the process of rolling in the continuous refinement of recrystallization and preliminary organization evolution law. The results reveal that a 50° rotation angle can sufficiently meet technical requirements and provide evidence for the appropriate selection of rotation angles for cold-rolled magnesium alloy tubes.

Abstract:This study provided an effective technique of friction stir processing (FSP) to fabricate the NiTi particle reinforced WE43 magnesium (Mg) matrix composite. The microstructures of FSP specimens were examined by scanning electron microscopy (SEM) coupled with an energy-dispersive X-ray spectroscope (EDS). X-ray diffraction (XRD) was used for phase analysis. The results showed that the composite possessed the shape memory effect. The low processing temperature effectively prevented the interfacial reaction between the NiTi particles and Mg matrix during FSP. Regardless of particle size, the NiTi particles were homogeneously distributed in the Mg matrix. In addition, compared with the Mg matrix, the yield strength, ultimate tensile strength, and elongation of the NiTip/WE43 composite were reduced by 33%, 12%, and 18%, respectively. Both the tensile strength and elongation were decreased with increasing the size of as-received NiTi particles. The failure mechanism of the composite was interface debonding and the fracture of reinforced particles.

Abstract:The influence and mechanism of Ti addition on the crack formation of twin-roll casting plates of 7050 aluminum alloys (TRC-7050) plates were studied with field-emission scanning electron microscopy (FESEM), differential scanning calorimetry (DSC), X-ray diffraction (XRD). The results showed that Ti addition significantly refine the grain sizes of the twin-roll casting plate, change the grain growth modes, improve the fluidity of the alloy, make the cast-rolled structure more dense, eliminate the local stress concentration in the alloy, and inhibit the occurrence of casting cracks. Appropriate amount of Ti addition can reduce the solid-liquid phase interval of the TRC-7050, reduce the temperature gradient of the nucleation solidification front and effectively inhibit the segregation of components, thereby reducing the number of low-melting compounds at the grain boundary and reducing the generation of coarse second phases, and then enhancing the resistance to the thermal cracking of the TRC-7050. 0.2 wt% Ti has the best inhibitory effect on the formation of TRC-7050 cracks. However, excess account of Ti addition will aggregate and form a sheet-like Ti-containing brittle phase, which subsequently will destroy the compactness of the structure and promote the initiation of cracks.

Abstract:The microstructure and macroscopic cracks of five twin-roll cast Al-Zn-Mg-Cu alloys strips with various Zn contents (3.5 wt pct, 5 wt pct, 6.5 wt pct, 8wt pct, and 10 wt pct, marked as Zn3.5, Zn5, Zn6.5, Zn8, and Zn10, respectively) were investigated. The results showed that the macroscopic cracks of strips decreased in numbers as the Zn content decreased from 10 wt pct to 5 wt pct, while this decrease was inhibited as the Zn content continuously decreased from 5 wt pct to 3.5 wt pct. The microstructure sustained a transition from columnar crystals to equiaxed crystals along the surface to the center of the cast strip. The center segregation band of the cast strips became wider and the non-equilibrium coarse eutectic phases increased in amount as the Zn content increased in these Al-Zn-Mg-Cu strips. Unsolidified liquid phases and holes appeared in the microstructures of strips of high Zn content.

Abstract:Carbon/silicon-carbide composites (C/SiC) usually suffer from high-temperature oxidation and ablation. In this study, double-layered SiC/ZrB2-SiC-B4C coatings were fabricated by chemical vapor deposition (CVD) and slurry painting-sintering methods. The naked, single-SiC coated and SiC/ZrB2-SiC-B4C double-layered C/SiC composites were oxidized at 1500 °C and ablated under a heat flux of 4.2 MW/m2. The results indicated that the slurry-painted ZrB2-SiC-B4C coating was dense and intact, which had a surface roughness of ~ 1 μm in Ra and the porosity of ~ 4.2 %. After oxidation at 1500 °C for 30 h, the mass loss rate of SiC/ZrB2-SiC-B4C coated C/SiC composite was ~ 10 %. The oxidation scale on the coating surface is compact without obvious cracking. After ablation for 20 s, the linear and mass ablation rates of SiC/ZrB2-SiC-B4C coating were separately 1.0±0.3 μm/s and 1.1±0.2 mg/s, decreased by 75.0 % and 50.0 % relative to the SiC coating. The formed ZrO2-SiO2 scale provided a protection against the mechanical erosion from the flame.

Abstract:Cu-Cr-Zr alloys are kinds of copper alloys with high strength and high conductivity, which usually apply to the manufacturing of key parts in complex environment such as high temperature and wear resistance. In this paper we studied the microstructure, tensile properties, microhardness, and fracture characteristics of Cu-1.04Cr-0.16Zr alloy at different brazing temperatures (600 ℃―800 ℃) by means of scanning electron microscope, cupping machine, micro-hardness tester, and stereomicroscope. On this basis, the softening mechanism of Cu-1.04Cr-0.16Zr alloy at high temperature was analyzed. The results showed that the ultimate tensile strength (UTS) and microhardness of alloys decreased with the increase of brazing temperature. The UTS , elongation, and microhardness of the samples were about 477.32 MPa, 40.13% and 151.78 HV. When the brazing temperature of Cu-1.04Cr-0.16Zr alloy was 600 ℃, the UTS decreased slightly whereas the microhardness was basically unchanged, and they showed good softening resistance. Partial recrystallization started to occur in the microstructure of Cu-1.04Cr-0.16Zr alloy when the brazing temperature was 650 ℃. Some fine and undistorted equiaxed grains appeared at the boundary of large equiaxed grains, which the grain size was about 2 μm―7 μm. The pinning effect of precipitation on grain boundary began to weaken, the UTS and microhardness decreased significantly. The samples were further softened with the increase of brazing temperature, a lot of annealing twins appeared in the microstructure of Cu-1.04Cr-0.16Zr alloy. Cu-1.04Cr-0.16Zr alloy had necking phenomenon and obvious plastic expansion zones after brazing. The shrinkage of cross section increased gradually with the increase of brazing temperature. The dimples grew along the tensile direction, and Cu-1.04Cr-0.16Zr alloy showed good plasticity. In summary, under the condition of satisfying the properties of the brazed joints, the softening of Cu-Cr-Zr alloys can be avoided by means of brazing filler metals with lower melting temperature.

Abstract:Based on the thermodynamic conversion mechanism and energy transition principle, the three-dimensional (3D) grain growth process of AZ31 magnesium alloy was simulated by using the improved cellular automata (CA) model of Metropolis algorithm, and the grain size and grain growth kinetics were analyzed statistically. The simulation results showed that CA model with the improved transformation rules was closer to the normal growth process of the actual 3D grain. In the simulation process, the total free energy of the system decreased, and the grain size presented normal distribution at different times. The ratio of grain diameter to average grain diameter (R/Rm) of 1.0 was the largest in grain distribution, which satisfied the minimum energy criterion of grain evolution. The analysis of grain growth kinetics showed that the 3D grain growth process follows the relationship between average grain size and time during grain evolution, and the grain growth index was 0.47941, which was much closed to the theoretical value of 0.5. The grain size variation of AZ31 magnesium alloy during heat preservation was studied by experiments, which further verified the reliability and accuracy of the 3D cellular automata model established in this paper.

Abstract:A theoretical model of calculating activation energy by ignition temperature of metal particles is proposed. The critical condition of ignition temperature is that the heat generation rate of combustion reaction and the heat loss rate to the surrounding reach a heat balance. The heat loss rate is controlled by Knudsen number. The heat generation rate of aluminum particle combustion is calculated using the simplest Arrhenius-type model. The heat generation rate of zirconium particle combustion is calculated by diffusion model. And the activation energy corresponding to the ignition temperature of metal particle is obtained by iterative calculation. The results show that the activation energy of aluminum particles and zirconium particles increases with the increase of particle size, which is linear with the logarithm of particle size. In the larger size range of nanometer to micron, a single theoretical model is not enough to describe the size effect of activation energy of metal particles. The polynomial model based on data fitting is more universal.

Abstract:A comprehensive understanding on interaction among grains, boundaries, strain and dislocations are beneficial for microstructure optimization and properties enhancement. A two-mode phase field crystal (PFC) method is employed to focus on hexagonal to square phases transformation. Hexagonal phases with a misorientation of 6° and tilt angle of 0 °, 15°, 30°, and 45° are checked. The hexagonal grains grow up, coalesce and form coherent grain boundaries with dislocation sets in two orientations. Square phases nucleate on these dislocation sets and their orientations are determined by these dislocation sets. These square grains of each case have two variants, which the misorientations are 30°, 30°, 10°, and 5° when tilt angles are 0 °, 15°, 30°, and 45°. Square grains of different orientation grow and ripen in different pace, the grains that locate on preferential orientation will dominate. Dislocation sets are generated to relieve strain concentration that rises from grain growth with coherent boundaries.

Abstract:FH40 experimental steel with different Ce content was prepared by vacuum induction furnace. The rolling microstructure of the steel was observed by OM, SEM, TEM and EDS, and its tensile properties and fracture morphology were tested and analyzed. The influence mechanism of Ce on the rolling microstructure and tensile properties of FH40 steel was studied.The results show that with the increase of Ce content from 0 to 0.058%, the rolling microstructure of the steel was refined. The rolling microstructure changed from polygonal ferrite to fine equiaxed ferrite, with the formation of granular bainite. The composite inclusion sof Ce-O-S+TiN and Ce-O-S were produced in the steel containing 0.0273%Ce and 0.058%Ce, with four and five pieces of IAF induced, respectively.The yield strength and tensile strength of the experimental steel containing 0.058%Ce are 31MPa and 33MPa higher than that of the experimental steel without Ce respectively.The experimental steels showed dislocation strengthening and second phase strengthening. The precipitates in the experimental steel without Ce was mainly the composite phase of Nb-Ti. Nb-Ti-Ce was the main composite phase in the experimental steel containing 0.058%Ce, and being more dispersive and fine with higher dislocation density. The fracture morphology is more uniform. The dimple became larger and deeper, which makes it more difficult to fracture under the action of shear stress, thus improving the tensile strength of steel.

Abstract:Cu/Al bimetals were fabricated by diffusion welding (DFW) at welding temperatures ranging between 683 and 803 K, welding time between 20 and 80 min, and a welding pressure of 15 MPa. The scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) results of the Cu/Al interface showed that the width of interface layer gradually increased with increasing welding temperature and prolonged welding time. Following welding at 803 K for 80 min, intermetallic compounds (IMCs) of Al4Cu9, Al3Cu4, AlCu, and Al2Cu occurred at the Cu/Al interface from the copper side to the aluminum side. The IMCs occurred in the sequence of Al2Cu, AlCu, Al3Cu4, and Al4Cu9 . Shear test of Cu/Al bimetal showed brittle facture, and the interfacial strength increased with lower amount of IMCs. A maximum shear strength of the Cu/Al bimetal of 63.8 MPa was obtained following DFW at a welding temperature of 723 K for 20 min.

Abstract:Base on the Gleeble-3500 thermo mechanical simulator, the real stress-strain data of C71500 cupronickel alloy in isothermal compression test were obtained in the temperature range (1073-1273k) and strain rate range (0.01-10s-1). Johnson-Cook, modified Johnson-Cook, modified Zerilli-Armstrong, Arrhenius-type, Fields-Backofen-Zhang and Zhou-Guan models were used to regress the constitutive equation of high temperature flow stress. The applicability of the six models were evaluated by comparing the accuracy, correlation coefficient (R), root mean square error (RMSE), average absolute relative error (AARE), the number of uncertaintyl and the time consuming for calculation of these parameters. According to the fitting results of parameters and time consumption, the Zhou-Guan model is the best for predicting the deformation resistance of C71500 alloy at different strain rates and temperatures. The results provide a theoretical basis for the capability selection and verification of C71500 alloy and other similar copper alloys which are not easily deformed by cold working.

Abstract:The effects of yttrium (Y) addition on microstructures and properties of the as-cast Ti-6Al-4V alloys were studied. The microstructure and mechanical properties were characterized by optical microscopy (OM), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and tensile testing. Ti-6Al-4V alloy showed typical Widmanstatten structure. With Y addition, Y2O3 particles formed and primarily distributed along the prior-β grain boundaries, and it induced the formation of special paralleled α/β lamellas on either side of the prior-β grain boundaries, that was the influence of Y2O3 particles on the Ti matrix. While it exhibited alternate α/β lamellas inside the grains of Ti-6Al-4V-0.3Y alloys. Comparing with Ti-6Al-4V, the Y addition improved the strength slightly, both the paralleled α/β lamellas and Y2O3 caused the transformation from cleavage fracture to intergranular fracture and the significant decrease of elongation. Therefore, the variation of the microstructure of Ti matrix caused by Y2O3 also played an important role in the ductility of the alloys.

Abstract:Diamond/Cu composites have advantages of low density, high thermal conductivity and tailorable coefficient of thermal expansion (CTE), and possess a good thermal matching performance with new generation chips. Therefore, it has a widespread application prospect in electronic packaging with high heat flux density and other fields. However, due to the poor wettability between diamond and Cu as well as high interfacial thermal resistance, bringing about the conductivity of composite is even lower than copper, which restricts its application. The interface of composite is modified to transform their mechanical and physical bonding state into a chemical and metallurgical bonding by pre-metallization, pre-alloying copper matrix and optimization of composite processing so as to improve wettability at home and abroad nowadays. In this paper, surface modification, interface theory related to thermal conducting model and research development in finite element simulation are reviewed. The difficulties of fabricated process, thermal conducting models, and key direction of future development are discussed. The effects of parameters such as diamond content and particle size on microstructure and thermal conducting performance are summarized.

Abstract:The forming of ordering structure in NiCrAlFe precision alloy is a vital factor for the electrical properties. Using the first-principles pseudopotential plane-wave method, the lattice constants, binding energies and density of states of an NiCrAlFe precision resistance alloy were calculated based on the disordering solid solution and L12-type ordering structures. The microstructure of the alloy was analyzed by high-resolution transmission electron microscope (HRTEM), also, the electrical resistance of the alloy was measured after solid-solution and aging treatment. From the binding energy point of view, the ordered structure is more stable than the disordered solid solution. The calculation results of density of states show that in the ordered structure, Ni, Cr, Al and Fe atoms bond with each other more strongly than they do in the disordered solid solution, and thus the stability of the alloy is improved. In fact, ordering structure with L12-type was revealed by HRTEM in the as-aged alloy, and its lattice parameter is close to the calculated result. According to the comparison of density of states at the Fermi level of different structures, the electrical conductivity of the alloy will decrease due to the formation of L12 ordered structure from the disordered solid solution, which is consistent with the experimental results.

Abstract:In this paper, we study a new model for predicting the reacted fraction of hydriding in La(Fe,Si)₁₃ compounds. This model is simple and practical, which offers the reacted fraction of hydrogen absorption as a function of time and temperature explicitly. The basic principle and reaction mechanism of hydrogen absorption of alloy materials are briefly introduced. Besides, the “characteristic absorption time” as a new concept has been introduced, which directly reflects the hydrogen absorption rate of the alloy, and the smaller the characteristic reaction time, the faster the hydrogen absorption rate. Application of the Chou model, quantitatively exploring the hydrogen-absorbing reaction characteristics of La_0.7Pr_0.3Fe_11.5Si_1.5 and La_0.7Pr_0.3Fe_11.5Si_1.5C_0.2 alloys. At the same time, the change of temperature will also affect the hydrogen absorption characteristics of the alloys, the relationship between the reacted fraction of hydrogen and the temperature is obtained by the model equation, indicating that the higher the temperature, the smaller the characteristic reaction time, the faster the hydrogen absorption rate of the alloys.

Abstract:In the Mg-Y base rare earth alloy system, study on the diffusion growth of intermetallic compounds is important due to its close interrelation with property. Based on the experimental data of the formation and growth of intermetallic compounds ε-Mg₂₄Y₅ and δ-Mg₂Y in the Mg-Y diffuison couples, the interdiffusion coefficients of each phase in the Mg-Y binary alloy system depending on components and temperatures was calculated by numerical inverse method. The results show that the diffusion coefficient of ε-Mg₂₄Y₅ is 4 times higher that of δ-Mg₂Y. Moreover, the annealing induced element diffusion distribution, diffusion flux and growth thickness of IMC layer with time and temperature can be quantitatively simulated.

Abstract:Ultrasonic vibrations with ultrasonic powers of 0 W, 600 W, 1000 W and 1400 W were applied during laser melting deposition of 316L stainless steel. The effects of ultrasonic powers on the grain morphologies and sizes, the microstructure formation mechanism and grain growth characteristics of 316L stainless steel were studied. The results show that the application of ultrasonic vibrations can break the directional epitaxial growth of large sized columnar grains, resulting in a refinement of microstructure, and increases of cumulative misorientation and dislocation densitie along the long axis of grains. By promoting the convections in the melt pool, and thus reducing the temperature gradient along the depostion direction, the application of ultrasonic vibrations accelerate the transitions of growth directions for columnar grains. The application of ultrasonic vibrations also help to increase the cooling rate during solidification, resulting in refinements of both columnar grains and the interior columnar dendrites.

Abstract:By use of first-principles calculations based on density-functional theory, the stability of low-index surfaces of Al3V intermetallic were analyzed, then the adsorption of oxygen on Al3V surface and the effects of alloying elements were studied with the most stable surface. The results show that Al-terminated (110) surface is the most stable. The adsorption of oxygen at brige sites of the surface are preferable, and the adsorption of oxygen are more and more stable as the coverage increases. It can be inferred from DOS analysis and the distance between O and other atoms that at the initial stages the oxidation of Al atoms and internal-oxidation of V atoms occurred, that means the protecting Al2O3 scale can be formed after oxidation. Ti and Cr atoms prefer to substitue V atoms in 2nd layer, the substitution of the atoms can both improve the adsorption stability of oxygen on the surface, while the mechanisms are different. The interactions between Ti and O atoms are strong, so the interactions between Al and O atoms are weakened after Ti substitution, that means Ti and Al can both be oxidized to form mixed oxides. On the other hand, the interactions between Al and O atoms are slightly enhanced after Cr substitution, so the oxidation of Al atoms are improved, that means the protective Al2O3 scale can be formed.

Abstract:The constitutive equation and the secondary recrystallization maps, which reflect the flow stress characteristics and microstructure-deformation relationship of the material respectively, are the key data for the TC18 titanium alloy during the hot deformation. The hot compression deformation was taken on a Gleeble-3800 with the conditions that the deformation temperatures were 790℃~900℃, the strain rates were 0.01s-1~10s-1 and the strains were 0.1~0.5. By fitting the 6th polynomials of ε and α, n, Q, lnA in the Arrhenius formula respectively, TC18 titanium alloy’s constitutive equation of hot compression was established，the predicted values of flow stress of the hot compression are in a good agreement with the measured values; the secondary recrystallization maps of each strain rate were drawn by observing the microstructure and measuring α grains’ sizes.

Abstract:An experimental research of a commercial hot rolled 7055-T7951 aluminum alloy thick plate on composition, microstructure details, uniaxial tensile properties at room temperature, and texture feature was carried out. Especially, a quantitative analysis for texture feature as well as their influences on the mechanical anisotropy was investigated carefully. The results show that there are little undissolved alloy compounds existed in the microstructure of this plate, possibly due to a low level of magnesium. The precipitations in grains mainly consist of η＇and η phases, which indicates a slight overaged status for the material. The uniaxial tensile properties along the 0°and the 90°to the rolling direction of the plate are almost equal and both superior to that along the 45°to the rolling direction. In addition, the strength indicators in central layer of the plate are all superior to corresponding parts in surface layer, and the tensile mechanical property anisotropy in central layer is more intense than that in surface layer. The texture near the center of the plate mainly consist of rolling type of Brass and S. While, the texture R with recrystallization type is dominant near the surface. The mean yield strengths along different in-plane directions through the thickness were studied and compared based on the Schmid’s law. The relationship between texture characterization and the nonuniformity of mechanical behavior was discussed finally.

Abstract:Using carbon, silicon carbide and silicon as raw material, the composite raw material powder was prepared by pretreatment process and C/Si 80/20at% target via hot pressing. The target material was then sputtered on different substrates. The micromorphology was analyzed by SEM; the resistivity was measured by four probes; the crystal structure was examined by XRD combined with Raman spectroscopy. The results yielded are: (1) Uniformly distributed C / Si powder of Si elements was obtained after consistent ball milling for 48 hours. While the powder is vacuum heat treated at 1900 ℃, liquid silicon and solid carbon generate equiaxed 3C-SiC through inter-diffusion. (2) Whenβ-SiC powders with different size were vacuum heat-treated at 1900 ℃, there was a significant disparity between neck growth rate and crystal structure transformation. Under high temperature, the nano-β-SiC powder had higher vapor pressure and its neck growth rate was relatively faster. Subsequently, pure 3C-SiC microparticles with higher sphericity were acquired after evaporation-coagulation and recrystallization. (3) Using C / Si / SiC 70/10/10 at% powder as raw materials and through ball milling /high-temperature vacuum heat treatment as pretreatment methods, C / Si 80/20 at% target was hot-pressed. The results show that: In comparison with the C / SiC 60/20 at% binary component system, the target prepared by the ternary component pretreatment powder has better uniformity, the average resistivity is 3.9×10-3 ohm · cm and the range is 0.59, the density is 2.34g / cm3, the degree of graphitization is 0.17, the graphite crystals have good integrity. (4) C / Si 80 / 20at% target was magnetron sputtered on glass, silicon wafer and ceramic substrate to deposit diamond-like thin films. The results exhibited that the film on the Si substrate had a longitudinal growth mode and the film particles were less than 20nm; The film layer on glass had a layered growth mode and were tightly bonded; The film on the ceramic substrate, composed of micron-sized particles that were similar to the microstructure of the ceramic matrix.

Abstract:With the increase of the number of automobiles and its widespread use, the modern automobile industry has put forward higher requirements for the mechanical properties of materials. In this paper, quasi-static and dynamic compression tests of B610 steel used in a truck frame have been carried out at different temperatures. It is found that the temperature softening effect of B610 steel is the most obvious in the high temperature region (400℃-600℃) under quasi-static loadings, and the strain rate hardening effect is the most obvious in the low temperature region (-80℃-25℃) under dynamic loadings. The Johnson-Cook constitutive model of B610 steel considering temperature and strain rate is obtained by fitting the test data. The numerical simulation of front collision of B610 steel truck frame is carried out. It is found that the internal energy conversion calculated by Johnson-Cook model is 92.8%, while that of linear elasticity is only 21.4%, and the peak value of equivalent stress is also reduced by 47%. This fully explains the importance of considering the temperature softened effect and strain rate strengthening effect of materials in the study of vehicle passive safety.

Abstract:As one of the methods of severe plastic deformation, accumulative roll bonding (ARB) is a technique that can refine the grains to sub-μm level, and it is also the only method that can greatly improve the comprehensive performance of TA15 sheet while ensuring cost. By studying the influence of the initial structure, ARB rolling trajectory and rolling reversion on the spheroidization degree of the lamellar structure, the effect of ARB process on the spheroidization of TA15 sheet can be obtained. The results show: When the initial lamellar thickness is small and the difference of thickness between grain boundary and intragranular lamellae is small, the lamellar spheroidization is more thorough. The pass deformation of ARB process is too large, the temperature of the TA15 sheet will rise significantly, leading to the uneven spheroidization of the grain boundary and the matrix of TA15. That the pass deformation is too small leads to the incomplete spheroidization of the sheet, and affect the equiaxation effect of the matrix of TA15. With the increase of reversing passes in ARB forming process, uniformity of the sheet is increasing, the grain size and range of the sheet are further reduced, and the room temperature tensile properties are significantly improved.

Abstract:In this study, catalytic electrode prepared via a simple one-step hydrothermal method to load La-doped NiCo on a copper sheet. XRD, FESEM, cyclic voltammetry and other tests were used to study the influence of the molar ratio of NiCo salt and the amount of La doped on the microstructure of the sample and the electrocatalytic oxidation performance of methanol. The results show that the introduction of Co increases the particle size, and the performance get better when the molar ratio of Ni2 +/Co2 + in the solution is 8: 2. The doping of La affect the morphology of the particles. As the doping amount of La increases, the peak current density can increase and then decrease. The sample doped with 10-4 mol/L La obtained superior performance; the peak current density reached 50.36 mA/cm2. After 2000 cycles, it retained nearly 100% of the initial current density. It has good stability and can be used with direct methanol fuel cell (DMFC).

Abstract:In this paper, a layered double hydroxide film layer MgAl-LDHs-NO3 was synthesized by hydrothermal method. Tungstate anions (WO42-) and Cysteine(Cys) anions were intercalated into the LDHs interlayer by virtue of the anion exchange reaction to acquire MgAl-LDHs-WO4 and MgAl-LDHs-Cys films. X-ray diffraction (XRD), scanning electron microscope (SEM), Energy spectrometer (EDS), and electrochemical impedance test (EIS) were performed to study the morphology, structure, corrosion resistance and self-healing performance. The results showed that the corrosion resistance were in the sequence of LDHs-WO4＞LDHs-Cys＞LDHs-NO3.All of three film were of effectively self-healing ability. Electrochemical results showed that the films induced to the scratch treatment have better corrosion resistance after immersed in 3.5 wt.% NaCl solution for 8 days, and then showed a downward trend. .Compared to MgAl-LDHs, LDHs-WO4 and LDHs-Cys, contained corrosion inhibiting anions, were displayed the better self-healing ability, due to the film layer could not only capture Cl-, but also release corrosion-inhibiting anions.

Abstract:The as-cast Mg-6Al-2Ca-2Sm alloys were heat treated by solid solution and solid solution + aging treatment to obtain samples with different initial microstructure, and then hot extrusion was performed on samples with different initial microstructures. Effect of different initial microstructure on the microstructure and mechanical properties of hot-extruded Mg-6Al-2Ca-2Sm alloy was carried out by analyzing and testing. The results show that the Mg-6Al-2Ca-2Sm alloy undergoes obvious partial recrystallization after hot extrusion, and the grain is significantly refined; solid solution or solid solution + aging treatment can improve the distribution of metallic phases, and the precipitated phase distribution after hot extrusion is more uniform. The heat treatment before extrusion can improve the room temperature and high temperature mechanical properties of the hot extruded Mg-6Al-2Ca-2Sm alloy, and the solid solution + aging hot extruded alloy has the highest tensile strength and elongation.

Abstract:Evolution of the primary phase of spray forming 7055 aluminum alloy during pre-heattreatment before deformation was studied by SEM, TEM and XRD test. The primary phases of as-sprayed 7055 alloy are AlZnMgCu phase and Al7Cu2Fe phase. The AlZnMgCu phases are fine in the grain while the ones on the grain boundary are coarsed. The grain boundary phases formed as a symbiotic microstructure including AlZnMgCu and Al7Cu2Fe phase. When the treat temperature below 400℃, the dissolution of primary phase is less due to the low diffusion coefficient. However, the Zn content has an apparently decline in both intragranular phase and grain boundary phase. When the temperature increases to 450℃，the fine primary phase is completely dissolved, while the coarsened phases on grain boundary transformed to an ellipsoid-like Al2CuMg phase. When treated at 470℃, inner phase has the same dissolved behaviour but the transformation of grain boundary phase to Al2CuMg is avoided. The results show that the evolution of primary phase depends on the second pre-heattreatment temperature.

Abstract:Multi-walled carbon nanotubes (MWCNTs) were purified by concentrated nitric acid and sulfuric acid. MWCNTs/Zn0.96Co0.04O composite nanofibers were prepared through electrospinning and calcination technique. The crystalline phase and micromorphology of the samples were examined by TGA, XRD, FT-IR, SEM and TEM. Microwave absorption properties and infrared emissivity of MWCNTs/Zn0.96Co0.04O composite nanofibers were determined with a vector network analyzer and a IR-2 infrared emissivity analyzer respectively. The results showed that the average diameter of MWCNTs/Zn0.96Co0.04O composite nanofibers were about 160nm. The lowest infrared emissivity of MWCNTs/Zn0.96Co0.04O composite nanofibers was 0.61, at which the mass fraction of MWCNTs was 6%. The matching thickness of MWCNTs/Zn0.96Co0.04O composite nanofibers was 1.5mm, at which the microwave absorption properties were fine: The minimum reflection could reach -26.4 dB at 13.8 GHz, and the frequency band with reflectivity less than -10 dB was 11.8～15.8 GHz. It is possible that MWCNTs/Zn0.96Co0.04O composite nanofibers were used as a novel and promising infrared/radar compatible stealth material.

Abstract:The effects of Gd content on the microstructure, mechanical properties and corrosion resistance of as-cast Mg-0.5Zr-1.8Zn-xGd bio-magnesium alloy were studied at high melting temperature (780±5 ℃). The results show that the grain size of the alloy decreases with the increase of Gd content at the range of 0-2.5wt%. The alloy without Gd is mainly composed of α-Mg and a small amount of dispersed micron Zr particles, while the alloy containing Gd is mainly composed of α-Mg and different morphologies of (Mg, Zn)₃Gd phase. The mechanical properties of the alloy increase at first and then decrease with the increase of Gd content. When the Gd content is 1.5wt%, the alloy has better mechanical properties. At the same time, the corrosion resistance increases at first and then decreases with the increase of Gd content. The uniformly distributed and fine reticulated second phase at 1.5wt% Gd content makes it better corrosion resistance. In the immersion test for 120 h, the static corrosion rate is 0.801±0.04 mm/a, and the corrosion morphology is relative uniform.

Abstract:The high-temperature self-lubricating CoCrNi-(3.0 wt.%, 5.0 wt.%, 7.0 wt.%) MoS2 coatings were prepared on the surface of GH4169 alloy by using a powder metallurgy technology (P/M). The high-temperature tribological properties of coatings sliding against Si3N4 ceramic ball were investigated by using a ball-on-disk high-temperature tribo-meter. The effect of testing temperature, sliding speed and applied load on the tribological properties of coatings was systematically studied from 20 °C to 800 °C. The phase and microstructure of the coatings were analyzed by X-ray diffractometer and scanning electron microscope, and the bonding strength of coating and substracte was tested through the thermal shock test. The results showed that the MoS2 formed Mo2S3 and CrxSy phases with other metal elements. The coatings had a good interface structure with the substrate. The coatings consisted of γ(fcc), ε(hcp), CrxNiy and solid lubricating phases (Mo2S3, CrxSy). At low temperature, the friction coefficient of coatings gradually decreased with the increase of MoS2. At high temperature, the coatings had an excellent high-temperature tribological properties. It was ascribed to the synergistic effect of chromate, oxide and sulfide on the worn surface. The wear rate of the coatings was below 5.5×10-5 mm3N-1m-1 over a wide temperature range, and the wear resistance of the coatings was 4~17 times higher than that of the substrate from 20 °C to 600 °C. The CoCrNi matrix coating with 5.0 wt.% MoS2 showed the best high-temperature tribological properties.

Abstract:In this paper, sponge titanium and electrolytic titanium are used as raw materials for melting TC4 titanium alloy. The smelted ingot is subjected to hot rolling and solution aging treatment. The microstructure and properties of TC4 titanium alloy sheet rolled from ingots of different raw materials after different solid solution aging treatments were studied. The results show that the α → β transition of sponge titanium TC4 and electrolytic titanium TC4 titanium alloys is an endothermic process. When the sponge titanium TC4 titanium alloy is solid-solved at a temperature exceeding the transformation point temperature, its structure is Weiss-structure, and the other structures under the solid-solution aging condition are all bimorphic. After solid solution aging treatment, the tensile strength of sponge titanium TC4 increased first and then decreased with the increase of the solution temperature, and the elongation continued to decrease. The tensile strength of electrolytic titanium TC4 increases with increasing solution temperature, while the elongation continues to decrease. Both of them obtained the best comprehensive mechanical properties after solid solution holding at 890℃ for 30min and 550℃ for 3h. Compared with sponge titanium TC4, the electrolytic titanium TC4 has a more significant increase in strength and hardness after solid solution aging treatment.

Abstract:In this study, a lead-free composite solder was synthesized by adding SnO2 nanoparticles in Sn0.6Cu solder by ultrasonic-assisted method. Effects of the SnO2 nanoparticles on the microstructure, melting property, and the interfacial reaction products of Cu/Sn0.6Cu-XSnO2/Cu brazing joints were investigated. The thickness and grain size of intermetallic compound layer were measured. The results showed that 1.0wt.% SnO2 inhibited the growth of β-Sn in the brazing filler metal and refined the grain size. The melting point of the SnO2-containing solder is substantially the same as that of the SnO2-free solder, but the melting range is significantly reduced. In addition, The application of ultrasonic waves during the solders melting process can refine the grains, the melting point and liquidus temperature of the solder are also lower than the conventional melting solder. the IMC layer at the interface of the solder joint with SnO2 solder is thinner and the grain size is smaller. The main reason is that SnO2 nanoparticles are adsorbed to the crystal plane of the interfacial intermetallic compound, which hinders the interdiffusion between the copper plate and the solder matrix, resulting in a lower driving force for the formation of IMC, thus hindering the growth of interface compound.

Abstract:In this paper, an amorphous carbon-coated mixed-crystal TiO2 nanoring array (C@TNTs) with good electrochemical properties was prepared by combining the hydrothermal carbonization method and anodizing method. Scanning electron microscopy (SEM), Raman spectroscopy (Raman), X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and electrochemical methods were used to characterize and analyze respectively the unmodified TNTs sample and the C@TNTs samples that obtained at annealing temperatures of 550 °C, 650 °C and 750 °C. The results show that the hydrothermal carbonization method can uniformly coat an amorphous carbon layer with a thickness of about 3.4 to 6.5 nm on the TiO2 nanotube array, but it will not affect its morphology and structure. The specific discharge capacities of C@TNTs-550, C@TNTs-650 and C@TNTs-750 are 2.83 mF·cm-2, 6.52 mF·cm-2and 1.48 mF·cm-2, which are 27, 62 and 14 times higher than the unmodified TNTs, respectively. What’s more, the introduction of a certain rutile phase in TiO2 nanotube array is conducive to the improve its electrochemical performance.

Abstract:Due to the characteristics of rapid melting and solidification in the process of preparing Inconel 738 alloy by selective laser melting (SLM), there is residual stress in alloy, so alloy cannot be directly used. Stress relief annealing is required. The evolution of residual stress, precipitation behavior, microstructure and properties in the alloy was mainly studied after annealing at different temperatures (700~900 ℃) for 24 h. The results show that the microstructure evolution mechanism is recovery，dislocation migration and rearrangement and grain boundary style changes were occured，a bimodal distribution of spherical γ "phase (50~250 nm) and short rod-shaped γ" phase (240~440 nm) are formed，the grain boundary carbides change from point to continuous and the type of carbides changed from MC to M23C6; After annealing at 800 ℃, the residual stress decreased from 380.94 MPa (AS-SLMed) to -66.7 MPa, and the residual stress was eliminated; With the annealing temperature increased, the microhardness and tensile strength first increased and then decreases, and the elongation decreases first and then increases. The alloy has the highest microhardness and tensile strength (581.2 HV, 1330 MPa) which are 1.42 times and 1.41 times of the properties of casting (410 HV, 945 MPa) after annealing at 800 ℃.

Abstract:In this paper, a digital Patternless freezing casting method is proposed. It is a new technology that pure water is used as the binder for sand mold casting, sand particles premixed with a proper amount of moisture are frozen at low temperature to form a frozen sand blank, and then the frozen sand mold cutting is carried out based on the principle of material reduction manufacturing and forming. In this paper, the evolution law of micro-morphology of the water film coating sand particles is revealed, which freezes into ice crystal bonding bridge after low-temperature phase transformation. It is found that the strength of frozen sand mold is produced by the interfacial bonding between ice crystal particles and sand particles, and the tensile strength of sand mold increases significantly with the decrease of freezing temperature. In addition, the rapid solidification forming mechanism of A356 aluminum alloy in the frozen sand mold was systematically studied, including the as-cast microstructure, composition distribution and mechanical behavior of the frozen sand mold Casting. The results show that with the increase of solidification rate, the secondary dendrite arm spacing (SDAS) of primary α-Al phase in the microstructure is significantly reduced, the grain size is significantly refined, and the solubility of Si element in the matrix is increased. Tensile strength, plastic value and microhardness value of the test piece are significantly increased, and the dimensional accuracy of the metal component can reach CT8 grade.

Abstract:In this paper, GNPs/Al composites were fabricated by friction stir processing(FSP) used pure aluminum as the matrix materials. The microstructure (including the matrix, reinforcement and interface) and mechanical properties were investigated, and the reinforcing mechanism of the composites was analyzed. The results showed that the matrix was?obviously refined, and many high angle grain boundaries were generated. The GNPs tended to be exfoliated and broken resulting in large amounts of GNPs edges during FSP. The Al-C atomic-sacle diffusion is easy owing to C atoms activity at the GNPs edges, as a result the interface transitions were formed between the GNPs edges and Al matrix. The yield strength and ultimate tensile strength of 1.8 vol% GNPs/Al composites were 72MPa and 147MPa. Compared to that of unreinforced Al, they increased by 89.5% and 79.3%, respectively. One by one, interface load transfer, Orowan and grain refinement were the principal reinforcing mechanism according to the theoretical calculation，and the calculated and experimental yield strength of the composites increase with the graphene content, concurrently, the deviations between the experimental and calculated strengths also slightly increased. However, the interface load transfer can not be well achieved owing to GNPs disorder distribution in the composites, therefore there is still a gap between the actual yield strength and theoretical calculation.

Abstract:Sn is one of the main interconnect materials for transient liquid phase bonding of 3D packaging chip stacking.The results show that Ti nanoparticles can improve the wetting spreading area of Sn paste on the surface of copper substrate and significantly increase the tensile force and shear force of Sn solder joint, but excessive Ti nanoparticles would deteriorate the mechanical properties of solder joint. Based on the content optimization of Ti nanoparticles, it is confirmed that the optimal addition amount of Ti nanoparticles is about 0.1wt.%. Analysis of Cu/Sn/Cu and Cu/Sn-0.1 Ti/Cu 3D packaging samples reveales that the thickness of Cu/Sn-0.1 Ti/Cu solder joint intermetallic compound is significantly lower than that of Cu/Sn/Cu, confirming that 0.1wt.% could significantly reduce the growth rate of intermetallic compound. Based on the finite element simulation, it is found that 0.1wt.%Ti can significantly reduce the stress-strain of solder joint in 3D packaging and improve the reliability of 3D interconnect joint.

Abstract:Using La₂O₃ powder, Al powder, CuO powder as raw materials and pure copper as matrix, in-situ synthesis technology and near melting point casting method were used to prepare particle-reinforced Cu matrix composites.The effect of La₂O₃ on the microstructure and properties of Cu matrix composites prepared by Al-CuO system was studied. The results show that the addition of La₂O₃ can obtain nano-Al₂O₃ particles, which are dispersed in the Cu matrix, and the prepared material structure is more fine and uniform, and its electrical conductivity and wear performance are significantly improved. When added 0.6% wtLa₂O₃, the electrical conductivity of the composite reached 90.2% IACS, and the amount of wear reached a minimum. Compared with the absence of La₂O₃, the electrical conductivity increased by 10.1%,and the wear decreased by 36.6%.

Abstract:The simulation defects in the Nickel - Based Single Crystal DD407 alloy were repaired by BNi5 brazer . The microstructures, precipitates and element distribution of the repaired joint were observed and analyzed by optical microscope (OM), scanning electron microscopy (SEM) and micro XRD test techniques. The results show that simulation defects can be locally repaired by adopting paste BNi5 alloy. A reaction interface with elemental gradient and white Cr6Ni16Si7 particles was formed between the repaired zone and the base metal. The amount of the Cr6Ni16Si7 particles and the width of the interface were increased as the increasing of the holding time. When the holding time is 120min, the interfacial width reached the maximum value which is approximately 224μm. Only adopted the BNi5 alloy as the filler material is the main reason responsible for the interfacial width increasing as the holding time. Further analysis of the content and the type of the filler material was needed to obtain a completely repaired defects in shape and size. Moreover, further extend the diffusion time was also needed to achieve a uniform TLP microstructure which is a foundation for TLP repair processing of nickel-based single crystal alloys.

Abstract:The high temperature superconductor (HTS) tape is generally working in the environment of liquid nitrogen under high pressure, liquid nitrogen maySpermeated into the interior of the tape resulting from the high pressure. The material would be damaged by the vaporized liquid nitrogen, when the HTS tape recovers from low temperature to room temperature. The HTS tapes with different manufacturing technologies are soaked in high pressure liquid nitrogen and rewarmed, the changes of properties and protective measures are studied in this paper.

Abstract:Cadmium (Cd), boron (B) and some rare elements possess a large thermal neutron absorption cross section, which has a wide application prospect in the field of nuclear shielding neutron absorption. This paper summarizes the types of neutron-absorbing materials currently used for wet storage of spent fuel in nuclear power plants and discusses the advantages and disadvantages of these materials. The research progress of B4C/Al neutron absorption material, and presents different preparation methods and their merits and demerits. Besides, connecting methods of neutron absorption material are introduced, especially the advantages of friction stir welding and diffusion welding in fabricating metal matrix composites with high particle contents. Composition and structure design of neutron absorption materials are analyzed, and future nuclear shielding neutron absorption material is prospected.

Abstract:High-entropy alloys have attracted extensive attention due to its new design concept and excellent performance. As a kind of high-entropy alloy, refractory high-entropy alloys are mainly composed of BCC crystal structure, which has the characteristics of high strength and high hardness as well as the high temperature softening resistance. In this paper, the preparation method, Phase structure, microstructure, mechanical properties and application fields of refractory high entropy alloy were described, and its directions of future research are also discussed.

Abstract:The research progress on the refrigeration performance of Ni-Mn-Ti based all-d-metal Heusler alloy was reviewed. The crystal structure and atomic occupancy of this alloy series were introduced. The crystal structure is L2₁ or B2 ordered structure, in which Ti atom with the least valence electrons takes the place of the original mainSgroupSelements. The treatment technology and doped elements have a certain effect on the martensitic transformation temperature and Curie temperature. The martensitic transformation temperature can be adjusted to near the room temperature by these means to achieve the purpose of practical application. The refrigeration methods and principles of Ti-Mn-Ti based all-d-metal Heusler alloy were emphatically analyzed, and the development of the refrigeration properties of Ti-Mn-Ti based Heusler alloy in the future was prospected.

Abstract:As an important part of polymer derived ceramics, polysiloxane derived silicon oxycarbide (SiOC) ceramics have been paid much attention due to the high performance-to-cost ratio. The research on fiber reinforced SiOC composites was a milestone to promote the development of polysiloxane derived SiOC ceramics. The fiber reinforced SiOC composites have made great progress for many years and show wide application prospect. In this paper, the current status of fiber reinforced polysiloxane derived SiOC composites was reviewed from the viewpoint of different fiber reinforcement. And then, the development proposals and key problems needed to be solved were offered for the high-temperature structural applications and function expansion.