Abstract:The anisotropy, which is one of key mechanical properties of Ti-alloy tubes, is usually described in terms of the contractile strain ratio (CSR) macroscopically and dependent on the micro texture evolution. In order to understand the variation of CSR, the texture evolution of Ti-3Al-2.5V titanium alloy tubes is studied by Electron Back-Scattered Diffraction (EBSD). The results show that the basal poles of the α-phase inclined from the radial direction to circumferential direction and stabilized around 45° between these two directions, and the strongly preferred orientation of the β-phase was observed with the increase of axial plastic strain. This change of texture causes the CSR values to decrease rapidly in the initial stage, then decrease slowly until stabilizing in the final stage. The simple model between CSR and texture quantity parameter f is modified by incorporating the texture component in the axial direction. Comparison with experiment shows that the modified model is in better agreement with the experimental values than the simple model.

Abstract:An in-situ synthesized WC/TaC reinforced nickel-based composite coatings have been fabricated on AISI 1045 mild carbon steel substrate by laser cladding of powder mixture of Ni60/WC with Ta2O5 and graphite. The microstructure and hardness distribution of WC/TaC/Ni60 composite coating are investigated utilizing scanning electron microscopy (SEM) and X-ray diffraction (XRD) techniques. It is shown that the microstructure of coating has a metallurgical bonding with substrate and is mainly composed of γ-Ni dendrites, W₂C, M₇C₃ carbides, and dispersed TaC particles. The hardness of WC/TaC/Ni60 composite coating has been enhanced to a value similar to that of HV965, which is 1.3 times higher than Ni60 coating. Measurement results demonstrated that these improvements are attributed to the presence of in-situ synthesized TaC particles, microstructure change and phase variations.

Abstract:The complex-shaped Ti-6Al-4V alloy is widely used in the aerospace engineering and automobile industry. However, because of its high hardness, easy adhesion, large dimension and high precision, it is a great deal of cost of raw materials, and besides, it is difficult to machine unless it uses special cutting tools by the traditional manufacturing methods. In this study, a closed isothermal forging process was adopted for precision forming of the wing. The rational billet shapes were estimated by flow simulation experiment, and then mechanical property, forming ability, process parameters of the Ti-6Al-4V wing were studied by the isothermal forging tests to meet performance targets. The results show that, compared with the titanium wing formed by conventional methods, the wing made by isothermal forging remarkably improved mechanical performances, and material utilization was reaching from 13% to 50%. During the isothermal forging process of Ti-6Al-4V, the flake α grains at 950℃ was transformed to β grains in the matrix; while the progress of transformation diminished when the forging temperature decreased to 900℃.

Abstract:The solubility limit of elements plays a crucial role in alloy designing, as well as in the understanding of kinetic processes in alloys. Using first-principles calculations, we calculated the ground states of Fe-RE compound, and predicted the stable and metastable structures of Fe-Y and Fe-Ce. The results indicate that the stable structures for Fe-Y compounds are Fe₁₂Y.tI26, Fe₁₇Y₂.hP38 and Fe₂Y.cF24, and those for Fe-Ce binary are Fe₁₇Ce₂.hP38, Fe₁₉Ce₅.hR24 and Fe₂Ce.cF24. Based on the statistical-thermodynamic theory of dilute lattice gas, we presented a systematic series of calculations of the solubility limits of RE in α-Fe as a function of temperature. It is found that the solubilities are sorted in the following order: S_La>S_Ce>S_Y, correspond to the trend in the solubility formation enthalpies: H_sol(La)< H_sol(Ce)< H_sol(Y).

Abstract:In this paper, the influence of ball-milling on the structure and hydrogen absorption-desorption behavior of Zr50.7Cu28Al12.3Ni9 metallic glass powders produced by gas atomization were studied. The as-atomized metallic glass powders were ball-milled for 80 h. It is found that the powders remain amorphous state after the ball-milling process. The effects of ball-milling on the hydrogen absorption-desorption behavior of the metallic glass powders were measured with an automatic Sieverts apparatus. After the ball-milling, the hydrogen absorption behavior of the metallic glass powders is improved. In addition, the hydrogen absorption capacity of the ball-milled metallic glass powders increases to 2.66 wt.% (H/M≈1.9) from 0.96 wt.% (H/M≈0.7) of the as-atomized metallic glass powders. However, the hydrogen desorption behavior of the ball-milled metallic glass powders is still poor due to the formation of very stable hydride.

Abstract:We report the microstructural and mechanical analysis of Ti-6Al-4VELI (Extra Low Interstitial) alloy parts fabricated with three diameter distributions of Ti-6Al-4VELI spherical powders by Hot Isostatic Pressing (HIP), which were manufactured via plasma rotating electrode processing (PREP). The powders were canned and pressed at temperatures 940℃ and pressure 120MPa. Alpha-beta mixed phases in the specimens were observed through Optical Microscope (OM), Scanning Electron Microscopy (SEM) and Energy Dispersive Spectroscopy (EDS) methods, respectively. The results show the microstructures of specimens were found to be strongly dependent on the different distributions of powders. The samples formed from fine powders (particle size range from 45μm to 100μm) shows better microstructure properties to those formed from medium powders (particle size range from 100μm to 150μm) and coarse powders (particle size range from 150μm to 250μm). In addition, the billets formed from fine powders exhibited higher tensile strength and ductility than those formed via medium powders and coarse powders. These results were attributed to the initial microstructures of HIP samples, as confirmed by evaluating their fracture features

Abstract:In this study, three kinds of FeCrAl fibers with different pore size were prepared by design, fabrication, sintering and repression. The pore size, resistance and capacity were tested,The results show that the initial resistance and efficiency is reduced, capacity is increased with the increase of pore size. The pulse cleaning of fibers were tested reference VDI3926 standard at different face velocity and cleaning pressure. The result indicates sample 3 with 22μm fiber diameter have the longest cleaning lifespan. The four stages of the standard VDI3926 were completed in the face velocity of 0.06m / s, the dust concentration of 2g/m₃ and cleaning pressure is 3500KPa.The sample increment weighing reached 12.31g, the average efficiency was as high as 98.5% and consumed time 3h after 30 times artificial aging. The fiber with 22μm diameter shows the longest lifespan.

Abstract:The field emission cathode coating of nano-diamond on titanium substrate were prepared by electrophoretic deposition, the hydrogen plasma process was carried out after heat treatment, and then the microstructure , field emission properties and the luminescence performance of the samples were characterized. The results show that the adsorption of H+ and the etching of H+ collectively affect the morphology of diamond coating. Deficient hydrogen treatment can’t reach the requirement and excessive hydrogen treatment can lead to serious etching for the diamond coating, which resulting in worse field emission properties of the coating and luminescence effect. The appropriate hydrogen treatment is helpful to improve the field emission properties and luminescence effect. Finally, the field emission mechanism of nano-diamond coating on titanium substrate was discussed, and the reasons of luminescence effect were explained.

Abstract:Using the substrate with the unique nanometer column arrays, the two dimensional ZnO nanowires network circuit was realized by means of CVD method without catalyst. This work not only removed the catalyst contamination,simplified the process and reduced the cost of Snanowire’s production, but also offered the new technical reference for breaking through the nano electronic devices limit.

Abstract:SnO₂-Al₂O₃ (SAO) binary thin films were prepared on slide glasses substrates by RF magnetron sputtering. The influence of the substrate temperature on the micrographs, crystal structures, electrical and optical properties were analyzed by using the scanning electron microscopy (SEM) images, X-ray diffraction (XRD) patterns, four-probe measuring, UV-IR and photoluminescence (PL) spectra. By increasing substrate temperature, the grain sizes of SAO binary films were enhanced, uniform patterns and large size grains indicate a better surface morphology and crystallinity of SAO films, which were verified by SEM and XRD investigations. All the films have a high average transmittivity of ~80%-90% in visible light region 400-800nm. The calculated band gap was in a range of ~4.11-4.14eV, and the measured sheet resistances of SAO films were in a range of ~7.0 to ~9.4 . By proper choosing sputtering temperature, the band gap can be widened, and the sheet resistances can be reduced. The PL emissions from the films in UV and red bands were also observed. These polycrystalline SAO films can be used in the application of transparent conductive oxide (TCO) films, solar cell windows, sensors, as well as lighter emitters.

Abstract:In order to detect scale-dependent interfacial evolution of metallic heterostructure during the deposition at room temperature, Ni/Al-typed nanomultilayers were prepared as a function of the periodicity and Ni:Al modulated ratio. Combined with X-ray diffraction, real-time plate curvature measurements by multi-beam optical stress sensor (MOSS) were employed to study the stress buildup so as to speculate interfacial characteristics during the growth process. Experimental results show that, with anisotropic nanocrystalline structure within the sub-layers, the multilayers possess of asymmetrical interfaces, which is a result of dissymmetrical diffusion of Ni to Al lattice near the interface. Specially, for the smallest periodicity with the lowest Ni:Al ratio, above asymmetric intermixing behaviors turns to be aggravated by a promotion effect.

Abstract:In this paper we report recrystallization characterizations, using electron back-scattered diffraction (EBSD) and transmission electron microscope (TEM), of an Al-Zn-Mg-Cu-Zr alloy during multi-pass plain strain compression (PSC) performed to simulate the hot rolling system on Gleeble-l500D thermo-mechanical simulator．The results show that with increase of the deformation, there are mainly two dynamic recrystallization mechanisms responsible for the development of new grain, including continuous dynamic recrystallization (CDRX) and geometry dynamic recrystallization (GDRX). The former is related to original grain boundaries bulging and sub-grain coalescence. The latter can be associated with serious deformation inhomogeneity. Besides, SRX happens during inter-pass time. The particles with a size of more than 1 μm also result in the recrystallization.

Abstract:Finite element method (FEM) was used to investigate the plastic deformation and densification for porous molybdenum in isothermal canned forging. Separate simulations were performed using different sheath materials: 45 steel, 304 stainless steel and GH4169. The simulations demonstrated that the distributions of strain, density and average stress strongly depended on the sheath materials. The distributions of density and strain presented the shape of “U”. The density and strain, increases with increasing of strength for sheath materials at same levels of deformation. The homogeneity of strain and density was best in billet encapsulated with the 304 stainless steel when the deformation extent exceeded 40%. The average stress decreases linearly with increasing of distance from center except for small area near the edges. Among the three materials, the 304 stainless steel was the most suitable materials as sheath during isothermal canned forging of porous molybdenum.

Abstract:The nanotubes with an anatase structure were hydrothermally synthesized using the Fe-doped anatase nanopowder precursors that were annealed in air and reductive atmospheres. The microstructure and physicochemical properties of the nanotubes were comparably investigated. Experimental results show that the reductive pre-annealing yielded more surface-chemisorbed oxygen by introducing lower valance Fe₂₊ and Ti₃₊ ions. The specific surface area, methylene blue adsorption and photoabsorption threshold of the nanotubes were greatly enhanced by the reductive annealing when comparing with annealing in air. 1 mol% Fe doping and the reductive annealing yielded the highest adsorption, photocatalytic efficiency and durability for degradation of MB solution; extreme Fe doping decreased the photocatalytic efficiency. The Fe content of the nanotubes was decreased by the hydrothermal synthesis, especially in the case of annealing in air. Moreover, the action mechanism of the Fe doping and reductive annealing was discussed.

Abstract:CoO/NiO core/shell nanowires (NWs) were synthesized using an efficient two-step approach. The detailed structural analysis through the transmission electron microscopy indicated that the CoO NW core was well enclosed by the NiO nanoflake shell with an unique nanoporous structure. Benefits from these structural advantages, when the obtained CoO/NiO core/shell NW material was used as a supercapacitor electrode, it presented a much enhanced capacitance ( 708 F g-1 at 1 A g-1), better rate capability and excellent cycling performance (>80 % capacitance retention for 1000 cycles) compared with the single component samples. Besides, the synergetic interaction between the CoO NWs and NiO nanoflakes could produces more active sites for redox progresses than single material during the electrochemical reaction, which can provide synergistic effect to the capacitance and electrochemical stability.

Abstract:Cu-TiB₂ composites were prepared by combining in situ reaction and hot-pressing under different temperatures after ball-milling of the mixture powders of Cu, Ti and B. The reaction process of Cu-Ti-B system is discussed in detail. By means of XRD, SEM, EDS and XPS, it was determined that TiB₂ nano-particles generated by in situ reaction in Cu-matrix. According to making the calibration curve of TiB₂ and Cu by XRD, the concrete synthesis rate of TiB₂ in Cu-matrix under different sintering temperature by external standard method was confirmed. The experiments show that under certain temperature range, the higher the temperature is, the higher synthesis rate is, and the best synthesis rate of TiB₂ is 99.27% at 1000℃. Cu-1.5wt%TiB₂ prepared at 1000℃had the best properties, Vickers hardness(HV), electric conductivity(EC), flexure strength(FS), thermal expansivity(TE) and thermal conductivity(TC) at 100℃ were 125.68MPa, 80.1 % IACS, 755.2 MPa, 9.3×10_-6 / K and 260 W/mK, respectively.

Abstract:The time-dependent springback and anelastic behavior of TC4 titanium alloy were investigated as a function of time, prescribed strain and loading strain rate by universal testing machine. In order to infer its basis, the microstructures of samples under different loading conditions were examined by optical microscope(OM) and transmission electron microscope(TEM). The results reveal that the absolute values of time-dependent springback strain(TDSS) accumulated in 10h both presented exponential growth, as the prescribed strain and loading strain rate went up. The OM and TEM results show that the evolutions of “streamline” microstructure, dislocation pile-up, and deformation twin had positive correlation with the change law of TDSS.

Abstract:The lattice constants, elastic properties and electronic density of Ti1-xVxC(x=0,0.1,0.2,0.3,0.4,0.5,0.75,1)were calculated using the first-principles method on the density functional theory, and the calculated results were in good agreement with other’s works. It was found that the lattice constant of Ti1-xVxC got smaller with the content of vanadium decreasing. And Ti0.5V0.5C belonged the best mechanical properties with bulk modulus 282.41GPa, shear modulus 229.01GPa and the ratio of G/B 0.682. It could be found that all of the Ti1-xVxC were conductive, and there were hybridization effect for Ti1-xVxC except VC. It might be the responsible for the change of mechanical properties of Ti1-xVxC.

Abstract:The ω phase transformation of Ti-1300 alloy under 20MPa compressive stress during continuous heating was investigated using high resolution dilatometer DIL 805 A/D. Results show that the ω phase transformation of Ti-1300 alloy could be inhibited by 20MPa compressive stress during continuous heating. The local activation energy of ω phase transformation for Ti-1300 alloy was determined on the basis of Kissinger–Akahira–Sunose(KAS) method. The average activation energy of ω phase transformation is about 73 KJ/mol under 20MPa compressive stress, which is higher comparing with no stress condition (55KJ/mol ). However, the compress stress was able to certain inhibit the ω phase transformation of Ti-1300 alloy during continuous heating. Therefore, owing to the activation energy decresed with increase of transformed volume fraction fω, the inhibiting effect of compressive stress on ω phase transformation of Ti-1300 alloy was gradually weakened.

Abstract:Al2O3 ceramic and TiAl alloy were brazed with AgCuTi filler and the interfacial structure with the change of brazing parameters as well as the forming mechanism of the joint were studied. Results show that the typical interfacial microstructure of the brazed joints was: Al2O3/Ti3(Cu,Al)3O/Ag(s.s)+Cu(s.s)+AlCu2Ti/AlCuTi/TiAl. During the brazing, Ti and Al would dissolve from the TiAl substrate and make a major impact on the microstructure and mechanical properties of the brazed joints. With the increase of brazing temperature and time, the thickness of Ti3(Cu,Al)3O reaction layer increased and the blocky AlCu2Ti compounds aggregated and grew up gradually, which influced collectively the mechanical properties of the jont. The average shear strength reached a maximum of 94 MPa with the joint brazed with 880 ℃/10 min. The crack primarily propagated at Al2O3 substrate and partially along the reaction layer.

Abstract:The α-Ti and C fiber composite material samples was produced through pressure-less sintering in argon atmosphere with different process parameters such as sintering temperature and carbon fiber morphology, using Ti powder and carbon fiber as raw materials. During the sintering, TiC was generated from the reactions of Ti atom and C atom between Ti and carbon fiber with the trend of the carbon fiber oriented TiC fiber formation, which was proved by the scanning electron microscopic analysis, micro-component analysis and XRD analysis. The influence of process parameters on TiC formation and its micro- -morphology was observed by additional analysis of microstructure and micro-hardness. The results showed that, with the increase of sintering temperature, the morphology of TiC, formed at the interface of Ti matrix and carbon fiber, changed dramatically from a dense fibrous shape to the fibrous shape composed of remarkable transformation particles during the sintering. However, dispersible granular TiC was produce by the addition of carbon fiber powder.

Abstract:In present paper, the fracture toughness and fracture behavior of Ti17 titanium alloy with basket-weave microstructure are studied. The results show that fracture toughness is attributed to two major contributions, namely the crack path tortuosity (extrinsic part) and plastic deformation work along the crack path (intrinsic part). Good plasticity and tortuous crack propagation path are both favorable to improve the fracture toughness of Ti17 alloy. Moreover, based on the power theory, a fracture toughness prediction model is built., which prediction error is within 6%. In addition, by analyzing the prediction results of this model, it can be found that the contribution of plasticity work to the fracture toughness of Ti17 alloy is the major part, which occupies over 80%. The contribution of crack propagation tortuosity to the fracture toughness of Ti17 alloy, however, is the minor part, which is within 20%.

Abstract:Using stir casting method, fly ash cenosphere/AZ91D composites were fabricated by adding fly ash cenospheres into magnesium alloy melt, and the microstructure uniformity, phase composition, mechanical properties and damping properties of the composites were studied. The results showed that the fly ash cenospheres distributed uniformly in the matrix, without segregation phenomenon. In the preparation process of the composites, the cenospheres reacted with the magnesium alloy melt and were filled in by the melt. Mg₂Si and MgO phases formed in the reaction. Compared with the matrix alloy, the mechanical properties and damping properties of the composites are obviously improved. The cleavage fracture occurs when the composites fail, indicating that the fracture is brittle fracture. The walls of the cenospheres are torn in the process of fracture. The damping mechanisms of the composites are mainly dislocation damping and interface damping.

Abstract:The flow behavior of the Mg-Zn-Zr-Y alloy was investigated by hot compressive test using Gleeble thermal simulator in the temperature range of 573~723K and strain rate range of 0.001~1s_-1. The results show that the flow stress is significantly affected by both deformation temperature and strain rate. The flow behavior were characterized by the SsaturationSnonlinearity and positiveSskewness occur simultaneously, and the flow stress increases with either decreasing deformation temperature or increasing strain rate. The average activation energy(Q=152.307 KJ.mol_-1), and stressSexponent(n=5.521)for the hot deformation have been determinded to be using the Arrhenius-type and Zener-Holloman equations. A nonlinear flow model and its constitutive equation have been established and employed for studying the deformation behavior. Meanwhile,ScalculationSresults of constitutive equations were comparedSwith experimentalSresults; the level of data match depends on temperature and strain rate. TheSsaturationSnonlinearity of flow behavior in the alloy was satisfactorily described, theStheoretical calculating valuesSmatchSwellSwithSthe experimentalSSvalues. Furthermore, the calculation values of flow stress will be bigger than its experimental values with the positiveSskewness of flow behavior , and as the peak strain of calculationSresults ahead. Research show this constitutive equations effectively depict the flow behaviors of hot compression deformation, however, it is more specifically suited to high deformation temperature(＞623K) and low strain rate(＜0.01 s _-1).

Abstract:In this work, effects of the Sn additions (3 wt.%, 6 wt.%, 9 wt.%)on thermal conductivities of the as-cast, as-homogenized and as-aged Mg-Sn binary alloys were investigated. The results showed that thermal conductivities of the both as-cast and as-homogenized Mg-Sn alloys decreased with content of Sn addition, and corresponding thermal conductivity of the as-homogenized Mg-10Sn decreased as 52.6W/m.K. Compared with as-homogenized sample, thermal conductivity of the as-cast alloy with the same solute content was lower. Thermal conductivity of the Mg-Sn alloy increased with aging treatment, and thermal conductivities of the as-aged Mg-3Sn, Mg-6Sn and Mg-10Sn alloys saturated as 125W/m.K, 120W/m.K and 110W/m.K respectively. Purification of the Mg matrix contributed to the thermal conductivity increment, and atomic size, electron configuration and the charge of the Sn element determined the thermal conductivity of the Mg-Sn alloy.

Abstract:Stress relaxation behaviour of GH4145 alloy at 566 oC was investigated. The results showed that the alloy has good resistance to stress relaxation. During the stress relaxation test, although the average grain size of the alloy obviously increases, the coarsening rate of secondary γ′ phase is very slow. The increase of the volume fraction of cuboidal secondary γ′ particles with larger size and the precipitation of spherical tertiary γ′ particles with smaller size make the hardness of the alloy increase.

Abstract:Microstructure and mechanical property of 2099 alloy under different pre-stretch degree have been studied by micro-hardening test, mechanical test and TEM observation. The results show that with the increase of pre-stretch the aging process is accelerated greatly and the mechanical properties are improved obviously. Precipitation phases become more fine and dispersed in matrix, some coarse phases in grain boundaries tend to discontinuous and point chain. The main aging strengthen phases of 2099 alloy experience a transformation from T1, δ′ and θ′ three phases coexistence to T1 phase, which indicated that pre-stretch have important effect on the size, type and distribution of precipitation, which can promote T1 phase precipitation in the expense of δ′ and θ′ phases consumption during the aging process.

Abstract:When the rolling temperature was 350℃, the angular velocity of the roller was about 3.14rad/s and the wall thickness reduction rate was 20%, 30% and 40% respectively, the coupled thermo-mechanical numerical simulation of the AZ31B magnesium alloy tube with the size of 50mmX7mmX1000mm in continual mandrel rolling process was carried. Then, the research on the damage stress and the distribution of temperature field of the simulation was conducted on the condition that the magnesium alloy tube was at the same rolling temperature but differ in reduction rate.The results show that: when the rolling temperature is same, the maximum damage value of the AZ31B magnesium alloy tube and the heat generated by the plastic deformation is increased with the increase of the wall thickness reduction ratio. With the location of the maximum damage value appears in the roller gap. And, because of the large heat exchange between the roller and the tube, the temperature of the roller gap is higher than the top of the roller, and the temperature difference is increased with the increase of the Wall thickness reduction ratio.So, when in the same rolling condition, the damage of magnesium alloy tube in Longitudinal rolling is smaller than the magnesium alloy sheet.

Abstract:ZnO nanosheet thin films were obtained by the ultrasonic spray pyrolysis technique (USP) on tourmaline and glass substrates at different deposition temperature. Structural studies suggested that ZnO crystals were polycrystalline with hexagonal wurtzite structure. The intensity of the characteristic Raman peak, and the (002) preferential orientation, the degree of crystallinity, the grain size achieved by the XRD results were significantly increased with the elevation of the substrate temperature. SEM images showed that the ZnO nanoplates laminated in parallel to the substrate and assembled to the flower-like column morphology, ZnO nano crystals had larger lamellae sizes and wider crystalline columns at higher temperature. UV-Vis measurement confirmed the maximum absorption peak of the ZnO films on the tourmalines had more red shifts and stronger intensities than that on the glass substrates, and relatively greater wavelength shifts under higher substrate temperature were also observed.

Abstract:Through rolling assisted biaxially textured substrate route, X-ray diffraction and electron backscatter diffraction technique were used to research systematically the laws of orientation and texture formation in Ni-W alloy substrates with 5at.%, 7at.% and 9.3at.% of W contents during cold rolling deformation and recrystallizing heat-treatment processes. It finds that, during cold rolling deformation process, the increments of S and Copper orientation fractions present a downward trend, while that in Brass orientation fraction shows a rising trend with the increase of W content. Therefore, the alloy substrates with lower and higher W contents will gain Copper and Brass types rolling texture, respectively. During recrystallizion heat-treatment process, the cube nuclei in lower W content alloy substrates will initiate early and grow quickly, and then it will obtain cube texture easily by annexing other orientations. However, cube-oriented grains will nucleate and grow together with other orientation grains in higher W content alloy substrates. It will obtain random orientations finally because the growth rate of cube grains is slower than others.

Abstract:The microscopic damage and fracture mechanism of an aluminum matrix composite, TiB2 particle reinforced 2024-T4 alloy synthesized through a mixed salt reaction, was investigated via in situ tension test monitored by scanning electron microscopy (SEM). The material fracture behavior can be separated into three stages, i.e. the nucleation, accumulation and coalescence of micro-cracks. The primary micro-cracks firstly initiate in by-product particles, micron-sized TiB2 particles and TiB2 particle clusters. With the increasing load, more micro-cracks appear in the region of TiB2 particle segregation band. Finally, the macro-cracks are formed as the consequence of the coalescence of micro-cracks through the Al matrix of particle sparse region in between, leading to the instant fracture of the material. Based on the analysis of the unit cell finite element model, the effect of particle segregation action on the initiation of micro-cracks in the Al matrix within particle segregation band was studied. The numerical results showed that the particle segregation enhances the maximum equivalent plastic strain and stress triaxiality in the Al matrix, which will facilitate the growth and coalescence of micro voids and results in the nucleation of premature micro-cracks, just as those observed in the tests.

Abstract:The generation mechanism of arc erosion is a key problem in the research of electric contact materials. Arc erosion characteristics of AgWC30 electrical contact material are investigated under direct current 25A and voltage in 20V, 25V, 30V, 35V respectively. The images of breaking arc light are obtained by a high-speed camera to deduce the forming regularity of arc evolution. The arc formation processes in different voltages are similar and go through three stages, including forming stage, steady burning and discharge quenching stage. On the other hand, the bullet-shaped convex, pore, crack and starchiness coagulum structure are observed on erosion surface of contacts under scanning electron microscopy (SEM). The bullet-shaped convex is formed in the break off of liquid bridge and is formed by the WC skeleton and Ag cladding. The results indicate that the liquid bridges occur allowing with the arc discharges and is promoted under the action of the arc heat flow.

Abstract:Co₆W₆C is a ternary compound that is often found in the preparation process of WC-Co cemented carbides. Its content and phase transition have significant effect on the performance of cemented carbides. However, there are limited investigations on the thermodynamic parameters, thermal stability and phase transition characteristics of this compound in the literature. In the present work, W, Co and carbon black powders were used as raw materials to prepare the single phase Co₆W₆C compound. By optimizing the preparation parameters, i.e. with the carbon black addition of 1.06wt.% and the reaction temperature kept at 1000°C for 1h in the vacuum condition, pure compound of Co₆W₆C was made. Subsequently, by a series of experimental measurements, the thermodynamic parameters of Co₆W₆C were obtained, based on which thermodynamic calculations were performed. The thermodynamic properties such as the standard molar entropy ( ),standard molar enthalpy of formation ( ), isobaric heat capacity (C_p), enthalpy ( ), entropy ( ) and Gibbs free energy (G) were obtained as a function of temperature.

Abstract:Because of the differences in the mechanical properties of the welded joint district, the deformation law and forming characteristics of aluminum alloy Tailor Welded Blanks (TWB) joint is quite different compared to traditional sheet metal forming. This kind of mechanical properties mismatch often leads to the forming property of aluminum alloy TWB lower than the base metal, which greatly limits the popularization and application of aluminum alloy TWB in automobile manufacturing industry. Based on the 2024-O aluminum alloy TWB of Friction Stir Welding, through the tests combined with the finite element method, study the influence law and influence mechanism of mechanical properties mismatch on the formability of aluminum alloy TWB. Microstructure and hardness test of aluminum alloy FSW joint were carried out. According to the distribution of the hardness of welded joint, the FSW joint can be divided into Thermal Mechanical Affect Zone (TMAZ), Heat Affect Zone (HAZ) and Base Metal (BM). Finite element simulation of uniaxial tensile test was carried out base on the finite element model of FSW joint. Using the finite element model, the influence of mechanical properties mismatch of WNZ, TMAZ, and HAZ on tensile property of joint is studied. The results show that the stress is lowest on minimum yield stress area, and corresponding increased on larger yield stress region. The stress will mutate if there is mismatch ratio difference. In the views of the strain energy, the results are contributed by the nonuniform property of deformation and the constraint in the FSW joint, furthermore which leads to the variation of yield strength, location of yield, tensile strength and elongation with the diversity of mechanical properties mismatch.

Abstract:The phase structure and element distribution of surface of ZrCo alloys with Ti modification were investigated by EDS and XRD. Effect and mechanism of Ti modification on hydrogenation behavior of ZrCo alloys with poisoned by CO was investigated via TOF-SIMS and TPD. The results showed that the hydrogenation period of ZrCo and Zr0.8Ti0.2Co alloys are less than 2 minutes and 4 minutes under the pure hydrogen atmosphere, and the capacity of hydrogenation could reach 1.8wt% and 1.9wt%, respectively, whereas the capacity of hydrogenation of ZrCo and Zr0.8Ti0.2Co just obtained 0.91wt% and 0.48wt% within 2500 minutes in the presence of CO contaminant gas, which meant the hydriding kinetics of ZrCo decreased with Ti modification. And performance of posioned sample could revert with treatment of vaccuming at 773K for 0.5h

Abstract:The time-temperature-transformation(TTT) curves and CCT curves of four Al-Zn-Mg-Cu alloys were completed in the Al-based database of software JMatPro7.0 with the first principles. To conclude, for 7055 alloy with the highest gross amount of main alloying elements and highest Cu element content, TTT and CCT curves were at the top left. For 7085 alloy with the lowest Cu element content and highest Zn/Mg ratio, TTT and CCT curves were at the bottom right, thus the incubation of equilibrium phase precipitation was the longest, start precipitation temperature and the nose temperature were the lowest, and therefore the quench sensitivity was the lowest. For 7075 alloy with the lowest Zn/Mg ratio and the incoherent E (Al₁₈Cr₂Mg₃) phase within grains, the quench sensitivity was the highest. The results show that compared with the conductivity of as-quenched and hardness as-aged at 960℃/s, the conductivity difference and hardness drop rates for 7075,7055,7050,7085 four alloys cooled at 1.8℃/s were decreased and the hardness drop rates were 35.5%, 19%, 13.8% and 9.5% respectively. The lattice constant and the size and area fraction of the quench-induced phases for the four alloys cooled at 1.8℃/s reduced, and thus the quench sensitivity decreased.

Abstract:Super GH4738 superalloy has been chosen as a candidate alloy used for oversized turbine disc in gas turbine field. Thermo-Calc and JMatPro softwares were used to optimize composition of alloy combined with experiments. The effects of elements C, Al, Ti and Cr on phase precipitation and mechanical properties were calculated. Based on the calculated results, Several GH4738 superalloys with different contents of Al, Ti were melted and examined by tensile strength properties at room temperature and the final elements of super GH4738 superalloy were determined and its phases analysis were carried out. The results showed that increasing of C content can promote an increase of carbides( M₂₃C₆ and MC) and solution temperature, but it has almost no effect on the changes of γ￠ phase amount. Elements Al, Ti can significantly increase solution temperature and its amount for γ￠ phase and improve strength of GH4738 alloy. Solution temperature γ￠ phase would increase with increasing of element Cr, while almost no influence on precipitating γ￠ phase. The influence degree on solution temperature and amounts γ￠ phase for element were Al>Ti>Cr. The design principles of GH4738 super alloy was to reduce the C content, and improve Al, Ti content to the upper limit in the range of the alloy. The amount of super GH4738 alloy was about 24.0%, its lattice constant a₀=0.357-0.359 nm, its composition (Ni_0.9236Co_0.0415Fe_0.0025Cr_0.0322)₃ (Cr_0.0972Al_0.3585Ti_0.5059Mo_0.0366Cr_0.0018). The results would provide a guideline and design idea for large higher strength GH4738 superalloy turbine disk.

Abstract:Al and Y modified aluminide coatings were prepared by pack cementation process at 1000℃ for 2 h. The microstructure and constituent phases of the co-deposition coatings were studied, the formative mechanism and erosion behavior of the coating were also analysed. The results show that the coating prepared by co-depositing Al-Ce-Y at 1000℃ for 2 h have a multiple layer structure: an outer layer composed of NiAl and a little Al3Ni2 , a middle layer composed of Al3Ni2 and a Al-rich inter-diffusion zone. Y and Ce mainly existed in the outer layer, which plays the role of reducing the grain size and promoting permeation. The solid particle erosion resistance of DZ125 alloy with Al-Ce-Y coating was significantly increased at the small impact angle, and then the erosion rate of Al-Ce-Y coatings increased with the increasing of impact angles, and the erosion mechanism shift from plough and cutting damage to brittle fracture and fatigue failure. The erosion rate of Al-Ce-Y coating is higher than that of DZ125 matrix when the impact angle at 90°.

Abstract:There’s no dispute that the control of interaction between cell and implant which includes drug delivery system and biosensor is a long-purchased goal. Recently, scientists are looking forward to exploring new materials in restricting cell adhesion and activity. In this essay, titanate tanowire was formed on the surface of titanium disks by hydrothermal route and the interaction between titanate tanowire and MG63 osteoblasts(including cell adhesion, proliferation and differentiation)was investigated. It’s shown that fewer cells were adhered on the smooth titanium disks rather than the nanowire one. Only a few cells were fixed on the tanowire surface which showed an irregular long spindle shape observed by SEM. Immunofluoresense also illustrated an irregular cell shape without forming a cell structure, the proliferation was restricted at the same time. Meanwhile, alkaline phosphatase and RUNX2 activity test shared the same results. It can be well concluded that cell adhesion and activity was seriously restricted titanate nanowire surface, such results can be applied on the further studies of drug delivery system and biosensor.

Abstract:High entropy alloy is a novelty structural and functional materials. For the excellent interfacial wettability between HEAs and Al alloy, the interfaces of HEAs-Al is well-bonded. In this paper, the Al_0.25Cu_0.75FeNiCo particles were used as the reinforcement to improve the strength and ductility of aluminum alloy. The effects of HEAs content on microstructure and mechanical properties of the composites were investigated. Microstructure observation showed that the HEAs particles were distributed uniformly in the composites. With the reinforcement content increasing, particles clustering were found in local region. Results showed that the modulus and hardness of the composites increase with increasing of reinforcement content. While the tensile strength and elongation of the composites increase firstly then drop with increasing of reinforcement content. At a reinforcement content of 5%, the maximum tensile strength and elongation of the composites is 437.6 MPa and 11.42%, which were 20.54% and 36.6% higher than those of the aluminum alloy matrix. The excellent comprehensive mechanical properties is due to the well-bonded interfaces of HEAs-Al.

Abstract:In order to examine the crack growth behavior of GH2036 supealloy subjected to low cycle fatigue (LCF) loading, crack growth experiments on GH2036 superalloy plates under different ratios at 550 °C were performed and the crack opening stress intensity factor of GH2036 superalloy were measured using Digital Image Correlation (DIC) technique. It was shown that no crack closure is observed at 550 °C when the stress ratio is greater than 0.7. Meanshile, crack closure model in GH2036 superalloy was established in terms of the residual crack tip opening displacement and stress ratio. In addition, SEM analysis of fracture analysis showed that with the increase of stress raio, the fracture mode at the crack growth region changes from transgranular to intergranular. Finally, crack growth life of GH2036 superalloy under LCF loading was predicted using the established crack closure model in GH2036 superalloy plates. Low life scatter factor through model validation indicated satisfactory results of the predicted crack growth life model.

Abstract:TiC cermet and GH3128 nickel-based superalloy was brazed using AgCuNiLi filler alloy. The results show that the interfacial microstructure of the joint brazed at 840°C for 10min is TiC cermet/(Cu,Ni)/Ag(s.s)+Cu(s.s)/(Cu,Ni)/GH3128. With the increase of temperature and holding time, the (Cu,Ni) solid solution at the TiC cermet side thickens and grows in the form of dendrite crystal; besides, the eutectic microstructure in the brazing alloy decreases. The analysis on the interfacial microstructure shows that the addition of Li in the alloy promotes the forming of the (Cu,Ni) solid solution. However, the continuing growth of the (Cu,Ni) solid solution is controlled by diffusion of the Cu element in the brazing alloy. Shear strength of the joint increases gradually and then decreases slowly with the increase of the brazing temperature. The highest shear strength of 204MPa was obtained when the specimens were brazed at 880°C for 10min.

Abstract:The impacts of different mass fraction TiC (0%, 5%, 10 /%, 15%) on the microstructure and properties of titanium-based composite material by microwave sintering were studied.The results show that the TiC/TC4 composite material is only consist of TiC and matrix ɑ-Ti + β-Ti. The relative density, microhardness and compressive strength of the TiC/TC4 composite increase with the increasing of TiC content at room temperature, which reaching 98.01%, 661 HV, 1789MPa respectively, the relative density of the composite increases about 2% to 6% compared to the vacuum sintering with the referred literatures, and the compressive strength increases about 5% to 15% compared to the cast titanium matrix composites prepared by melting-casting process. Beside, the wear resistance of TiC/TC4 composite also enhances with the addition of TiC content which the friction coefficient is between 0.25 to 0.30.Therefore its wear mechanism changes from the abrasive wear and adhesive wear into a slight delamination.

Abstract:The microstructures and mechanical properties of electron beam weldment BT25Y after 700℃/2h AC (AT) and 940℃/2h AC+600℃/8h AC (SAT) were investigated. The results indicated that the fusion zone microstructure of non heat treatment (NHT) specimen is mainly composed of α′ martensite phase and which show high microhardness and strengthen in comparison to base metal zone (BZ). For the specimens after AT, the α′ martensite in FZ transformed to fine α phase which shows similar microhardness regular pattern in comparison to NHT specimen. The fracture generated in BZ because of lower hardness and strengthens of BZ in comparison to FZ. Under this condition the specimen shows bad high temperature lasting strength. For the specimens after SAT, the α′ martensite in FZ transformed to α phase with rather big size and there is continuous or interrupted big size α precipitation bands along the original β grain boundaries. These precipitation bands in FZ lead to the brittle fracture of welded specimen and the fracture generated in FZ. Under this condition the specimen shows better high temperature lasting strength.

Abstract:The nanocrystalline Ti films were deposited by the method of physical vapor deposition in high pulse electric field, the grain size of which was obtained by a sharp increase in the peak current to investigate the effects of the films growth mode and mechanical properties. The results show that the larger peak current could obtained the small grain size but cannot change the crystal surface preferential growth of Ti (100) crystal in the films. However, the film surface morphology showed the increase of the particle aggregation size and greatly reduce of the particle clearance while the peak current increased, the whole structure is showing a spherical close growth. The shape of the cross section of the film growth morphology is gradually changed from the fiber to columnar shape, and it can effectively reduce the film defects and increase the density with the increase of peak current. The hardness and modulus of the films increased firstly and then decreased with the increase of the peak current, the highest value appeared between 30A-45A of the peak current.

Abstract:Thermal oxidation (TO) process was employed to treat TC4 alloy. Corrosive wear behavior of the TO treated TC4 alloy in simulated oilfield medium was investigated. The results showed that the obtained TO layer was mainly composed of rutile TiO2 phase. The TO layer presented higher surface hardness and lower mass loss values and specific wear rate. TO treatment had significantly improve the resistance to corrosive wear of TC4 alloy.

Abstract:In order to explore a new rapid prototyping technique using TC4 alloying sheet as molding material, the laminated forming samples were prepared with self-made Ti-based rapidly solidified brazing ribbons by means of high frequency induction brazing technology. The tensile strength and interfacial microstructure of the brazed joints were examined and analyzed. The results shows that the tensile strength of the amorphous forming sample is higher than TC4, while the crystalline one is lower than TC4, both of the brazed joints consist of (Ti,Zr)2(Cu,Ni)+(Ti,Zr)ss eutectic, Zr-rich solid solution of a-Ti. The tensile fracture shows that the fractures in the joints is brittle with herringbone.

Abstract:Ti-36Nb-2Ta-3Zr-xO (x=0, 0.1, 0.3, 0.5, wt.%) alloys were prepared by non-consumable arc-melting, and the effects of oxygen contents on microstructure, mechanical properties and damping behaviors of Ti-36Nb-2Ta-3Zr-xO were researched by X-ray diffraction (XRD), universal testing machine and Dynamic Mechanical Analyzer (DMA). The results show that the α″ phase transformation is suppressed by addition of oxygen. The damping behavior of the alloys is the typical Snoek-type relaxation and all Ti-36Nb-2Ta-3Zr-xO alloys show good damping capacities at high temperature. With the increase of oxygen content, the peak capacity of damping increases while the temperature change of the damping peak is not obvious. When the oscillating frequency is 1.0 Hz, the peak capacity of damping increases from 0.0283 (x=0) to 0.0355 (x=0.5), and the damping peak temperature is roughly 230℃.

Abstract:In order to obtain the optimal heat treatment condition of explosive-welded zirconium-titanium-steel clad plate, the effects of holding temperature, holding time and rate of temperature on bonding strength and residual stress of clad plate were studied by orthogonal test method. The investigation results show that the clad plate can obtain the best combination of bonding strength and residual stress under holding temperature of 540℃, holding time of 1h and rate of temperature of 60℃/h. If the holding temperature is too higher or the holding time is too longer, the bonding strength of explosive-welded zirconium-titanium-steel clad plate will decrease. Besides, the microhardness, the microstructures and the fracture morphology of bonding interface were measured and observed under the optimal heat treatment condition. The analysis shows that the fine grain zone is formed near the bonding interface and its microhardness is higher. The fracture appearance of bonding test is a mixture of ductile and cleavage fracture.

Abstract:The Cr₃₊ doped LiNi_0.5Mn_1.5O₄ cathode materials were successfully synthesized by solid-state method and the effect of doping amount into cathode material on its physical and electrochemical properties was studied. With the structure and morphology of cathode material characterized by X-ray diffraction and SEM, the results showed that the sample exhibited a pure spinel crystal structure. The effect of different Cr₃₊ doping amounts on the properties of LiCr_xNi_0.5-0.5xMn_1.5-1.5xO₄(x=0, 0.05, 0.1, 0.15, 0.2)cathode materials was discussed. The results of galvanostatic charge-discharge, CV and EIS test suggested that electrochemical properties of LiCr_0.1Ni_0.45Mn_1.45O₄ is the best when the Cr₃₊ doping amount is 0.1. At discharge rates of 0.1, 0.5, 1, 2, and 5C with the first specific capacities of 131.54, 126.84, 121.28,116.49 and 96.82mAh g_-1 respectively. At 1C rate after 50 cycles, its specific discharge capacity retention rate is 96.5%.

Abstract:20%SiCp/2009Al composites fabricated by powder metallurgy (PM) method were processed by isothermal forging in this paper, and the effects of different deformation on microstructure and mechanical properties were studied by optical microscopy, SEM, tensile and fracture toughness testing. The results show that, with the total strain increasing, distribution of SiC particles is better, the intensity and plasticity are significantly improved. The crack propagation paths of fracture toughness were observed by SEM, and the main crack occurred in the aluminum matrix where SiC particles agglomerated. The fracture mode of the composites combines mainly with toughness fracture of matrix and particle brittle fracture.

Abstract:Ni-Al (molar ratio is 1:1) energetic structural material (ESM) was prepared by cold-pressing and sintering with Ni and Al elemental powders. The effect of sintering temperature on the interface diffusion, mechanical properties ,initial reaction temperature and energy density of Ni-Al energetic structural materials was investigated. The results demonstrate that the increasing sintering temperatures result in increase in the rate of diffusion, boundary adhesion strengthSand mechanical properties of Ni-Al ESM while the decrease in energy density. The ESM with excellent combination of both energy density and mechanical properties can be obtained by sintering Ni-Al green body at 550 ℃, of which the tensile and compressive strengths are 66.0 MPa and 294.6 MPa, respectively, the energy density is 436.1 J/g .

Abstract:Abstract: Laser cladding Ni-based WC composite coating was fabricated on the surface of Q235 steel by using 6kW fiber laser. By using scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and micro-hardness tester, we investigated the morphology, composition, and micro-hardness of composite coating in different laser power. The results show that WC particles partially dissolve and react with other elements to form eutectics, which exist in the shape of block, strip and grain. The cladding height, penetration and dilution of laser cladding coating increased gradually with the increase of laser power. Moreover, the average hardness of the coating increased first and then decreased with the increase of laser power. When the laser power was 2500W, cladding coating could get the highest hardness, which could reach 5 times of the matrix hardness.

Abstract:The SiC/ZrSiO4-SiO2 composite coatings were prepared on carbon/carbon(C/C) composites by combining pack cementation and slurry painting method to improve the oxidation resistance and decrease the infrared emissivity. The phase compositions and microstructures of the as-prepared coatings were characterized by XRD, SEM and EDS. The oxidation resistance of the SiC/ZrSiO4-SiO2 coatings were evaluated in dynamic air (air flow rate: 0.6 L/min) at 1400℃ and 1500℃, respectively. The infrared emissivity of the SiC/ZrSiO4-SiO2 coatings coated C/C samples were also investigated at 90℃ and 500℃, respectively. The results show that the composite coatings which are composed of SiC inner coating with loose structure and ZrSiO4-SiO2 outer coating with mosaic structure exhibit excellent oxidation resistance and can protect C/C matrix from oxidation for long time. The mass loss rates of the SiC/ZrSiO4-SiO2 coatings coated samples are only 0.124% and 0.03% in dynamic air at 1400℃ and 1500℃ after 55h oxidation, respectively. The infrared emissivity of C/C composites can be decreased by coated SiC/ZrSiO4-SiO2 composite coatings, and the infrared emissivity descends with the temperature increasing. The average infrared emissivity of the coated C/C samples in 3~5μm and 8~14μm at 90℃ are 0.55 and 0.66, respectively. And the average infrared emissivity in 3~5μm and 8~14μm at 500℃ are 0.48 and 0.62, respectively. From the anti-oxidation and infrared emissivity property point of view, the C/C composites coated SiC/ZrSiO4-SiO2 coatings may be one of the most promising candidates as high-temperature structural materials applied in the field of aeronautics and astronautics.

Abstract:Abstract: Plasma Rotating Electrode Process (PREP) is one of the most important methods of manufacturing superalloy powder in China. The quality of powder is highly concerned in the field of Powder Metallurgy(PM). One kind of abnormal particles in nickel-based superalloy powder by PREP was observed, classified, and analyzed statistically in this paper. Research has shown that the abnormal particles which consist of powder and adhering sublimation, slag, ceramic and organic impurities exist in the superalloy powders. The formation of abnormal particles has a close relationship with the purity of master alloys, properties of inclusions as well as powder atomization parameters. The ability of removing abnormal particles by screening and electrostatic separation was associated with the size, shape and chemical composition, physical properties(density, permittivity）of adhering inclusions. Compared with the screening process, the number of abnormal particles in 1kg powder sample reduce by 63% after electrostatic separation process. In 50-150μm finished powders, the abnormal particles adhering slag account for 36% in residual inclusions, the particles adhering ceramic -4%, the particles adhering organic-11%.

Abstract:The effects of single-step, two-step and three-step homogenization treatments on the microstructures of 5052-Er Al alloy were studied by optical microscopy, scanning electron microscopy and transmission electron microscopy. The results showed that after 560℃/30h high temperature homogenization treatment, most of the non-equilibrium eutectic phases existed in the as-cast alloy dissolved, with the remaining phases being Fe-rich phases like Al₃Fe and Al-Fe-Er. The second step treatment performing at lower temperature was found to be beneficial to the spherization and refinement of the Fe-rich phases. The results also showed that homogenization treatment regimes had an obvious effect on the precipitation behavior of the fine precipitates. During the slow cooling process from 560℃/30h isothermally holding to room temperature, there were a large amount of rod β’(Al₃Mg₂) and spherical Al₃(Er, Zr) and Al₃Zr phases precipitating out of the matrix. The total volume fraction of the precipitates, 7.4%, was the highest among the four regimes conducted in this experiment. However, these precipitates distributed unevenly and their sizes differed greatly with each other. The second step treatment favored the formation of fine and homogenously distributed precipitates of Al₃(Er, Zr) and Al₃Zr. When the second step treatment was carried out at 150℃, the quantity density of the precipitates was the highest (20.3um_-1) with the finest particle size(average radius being 14nm). Three-step homogenization treatment could obtain a higher quantity density while maintaining a comparable particle size with that in two-step treatment.

Abstract:Rare earth doped calcium phosphate ceramic composite coating was prepared on the surface of titanium alloy by using laser cladding technology. The interface, phases, micromorphology and iron release of the coating were respectively measured by a series of experimental methods including Optical microscope, X-Ray Diffraction, Scanning Electronica Microscope, Inductively Coupled Plasma Mass Spectrometry. The results are shown that calcium phosphate ceramic composite coating is obtained on the titanium surface by laser cladding, and the coating is rich in hydroxylapatite and tricalcium phosphate. The Ca-P coating consist of three parts which are substrate, alloyed layer and ceramic layer. And its interface is bonding excellent. As the weight lost, the coating can be degraded by physiological saline. And it is found that a new apatite-like phase is formed on the surface of the coating which soaked in physiological saline for three weeks. With the degradation of the coating, Ca₂₊ iron and La₃₊ iron release to physiological saline. The concentration of Ca₂₊ is wavelike rise with time in the range from 15 PPM ～ 40 PPM. But the concentration of La₃₊ is fluctuation decreased with time in the range from 0.15 PPB ～ 0.45 PPB.

Abstract:CrMoN coatings were deposited with different Mo content on 4Cr13 stainless steel by multi-arc ion plating (MAIP). The binding force, hardness and corrosion resistance properties of CrMoN coatings were respectively investigated by adhesion scratch tester, hardness instrument, and electrochemical measuring instrument. The corrosion solution concentration were in 3.5% NaCl solution, 1 mol?L-1 NaOH solution and 1 mol?L-1 H2SO4 solution. Influence of different Mo content on corrosion resitance of CrMoN coatings was investigated. The result indicate that: NaCl-type fcc-phased (Cr, Mo)N were observed; when the Mo content achieved to 31.08%, diffraction peak of Mo2N was observed in the direction of (200), the coatings are always composed of three phases CrN, (Cr,Mo)N and Mo2N. When the Mo content achieve to 7.09%, the biggest binding force and micro-hardness are respectively 57 N, 2962.3 HV; When the Mo content achieve to 14.26%, the corrosion resistance of CrMoN coatings is the best in 1 mol?L-1 NaOH solution and 1 mol?L-1 H2SO4 solution; When the Mo content achieve to 5.15%, the corrosion resistance of CrMoN coatings is the best in 3.5% NaCl solution; Corrosion mechanism of coatings is mainly pitting corrosion, and crevice and galvanic corrosion occue.

Abstract:Cryogenic treatment was conducted by immersion of the melt-spun Fe₄₀Ni₃₈B₁₉Mo₃ amorphous alloy in liquid nitrogen for different times. The structures of the specimens after cryogenic treatments with different times were characterized by X-ray diffraction. The changes of coercive forces due to cryogenic treatment were investigated by B-H hysteresis loop tracer. The XRD results show that the atomic configuration of amorphous alloy becomes more disorderly due to cryogenic treatment. With the increase of the cryogenic treatment time, the free volume of amorphous alloy tends to decrease. Furthermore, the coercive force shows a non-monotonic change with the cryogenic treatment time. The coercive force after cryogenic treatment of 2 h is slightly larger than the melt-spun state, and longer time treatment results in decrease of coercive force. The coercive force is the comprehensive results of changes of chemical short-range orders and the free volume.

Abstract:The commercial twin-roll cast AZ31 magnesium alloy sheet is used in this paper. Multi-pass asymmetry rolling (ASR) is conducted on the sheet by small diameter rollers ASR at temperatures of 150℃, 200℃, 300℃, respectively, and the effect of ASR on the microstructure, texture, mechanical properties of rolled magnesium alloy sheet is investigated. The experimental results indicate that the mechanism of grain refinement is totally different at various temperatures: the grains are segmented into sub-grains by twins at 150℃, meanwhile, the dynamic recrystallization (DRX) is main grain refinement mechanism at 200℃ and 250℃, respectively. The texture evolution of the symmetry rolling (SR) and ASR sheet are analyzed, which predicts that the texture intensity of ASR sheet increases with rolling temperature elevated, but they are obviously lower than texture intensity of SR sheet.

Abstract:Biological Mg-x(2~8) wt%Zn alloys were fabricated from pure magnesium and zinc powders using high-energy ball milling and spark plasma sintering method. The microstructure, mechanical properties and corrosion performance of the biological Mg-Zn alloys were investigated. The results reveal that the sintered samples have a compact and homogenous internal structure. The mechanical properties, i.e. hardness and compression strength increased with increasing Zn content, and reached the maximum (69.0 Hv_0.1 and 379.5 MPa) at the 6wt% of Zn. The corrosion potential increased with increasing Zn content, while representing opposite tendency in current density tested in the SBF, and achieved the maximum and minimum respectively at the 6wt% of Zn. Moreover the corrosion mode in SBF transformed from severly crevice corrosion and pitting corrosion into particle spalling, finally presening a internal corrosion of particles and light pitting corrosion with the Zn content increased.

Abstract:In order to develop new high-strength cast aluminum alloys, AlZn6Ni4Mg2Cu casting aluminum alloys based on Al-Ni eutectic system were prepared in sand casting process, permanent-mold casting process and squeeze casting process. The influence of Ni element, casting process and heat treatment on the microstructure and mechanical properties were studied. The result indicated, 4% (mass percent) of Ni formed a large number of eutectic structure (a-Al + Al3Ni) in the aluminum alloy, which improved their casting properties and mechanical properties, and had a role of eutectic strengthening. Heat treatment resulted in globalization of Al3Ni phases and aging precipitation of MgZn2 phases, which improved their strength. Compared with sand casting and permanent-mold casting, the grains and Al3Ni phases in squeeze casting process were finest, the mechanical propertis were best, the tensile strength of 586MPa, the elongation percent of 3.5%. The conclusion is that strengthening mechanism of AlZn6Ni4Mg2Cu casting aluminum alloy is aging strengthening of η(MgZn2) phases and dispersion strengthening of Al3Ni phases, mechanical properties reach the best value after squeeze casting and T6 heat treatment.

Abstract:This thesis researching on the influence of Fe-25Cr-12Co fabricated by directional solidification under different drawing speed, the microstructure and magnetic performance of alloy with heat treatment under high magnetic field. The microstructure was characterized by Metallurgical Microscopy and Transmission Electron Microscopy(TEM). The results showed that the increasement of drawing speed of directional solidification is benefit to decrease the precipitation of σ phase, but a drawing speed too high is harmful to the directional regular arrangement of microstructure.Applying magnetic field on annealing treatment is benefit to the formation of long-rod-shaped α₁ particles, and has influence on the remanence and coercivity of alloys.Applying magnetic field has a better effection on improving the magnetic performance than 0T magnetic in parallel direction , but worse effection than 0T magnetic field in perpendiculare direction.

Abstract:To improve the photocatalytic activities of TiO₂, SnO₂@TiO₂ core-shell structure was synthesized. SnO₂ nanowires were prepared by chemical vapor deposition (CVD) based on the VLS growth mechanism, and then TiO₂ was deposited on the surface of SnO₂ nanowires by Atomic Layer Deposition (ALD) using tetraisopropyltitanate as the metal precursor. The results showed that titanium dioxide possesses the rutile structure in SnO₂@TiO₂ core-shell structure and the anatase structure appears by the effect of the intercalation of Al₂O₃. To examine the photocatalytic activity for degradation of methyl orange solution under ultraviolet light, the thickness and crystal structureof TiO₂ in the core-shell structure were studied

Abstract:Dispersion strengthened tungsten with tantalun carbide was prepared by Spark Plasma Sintering (SPS).High heat flux tests were performed with the electron beam device EMS-60 (60 kW Electron-beam Material-test Scenario) at Southwestern Institute of Physics.The polished tungsten surfaces were exposed to single shot disruption-like and repetitive ELM-like thermal shock loads at various absorbed energy densities.The thermal shock-induced damages were analysed by scanning electron microscope and the microstructure was observed by transmission electron microscope . The result show that no crack were detected on the tungsten surface when sample exposed to single shot thermal shock with absorbed energy density at 740MW/m₂, crack appeared when sample exposed to repetitive thermal shock with absorbed power density at 550MW/m₂. SEM and TEM images show that TaC particles disperse in tungsten grains interior including both intragranular and intergranular. This strategy including strengthening phase boundaries through coherent structure, strengthening grain boundaries through semi-coherent structure which leads to the excellent strengthen of W-TaC alloy plate.

Abstract:SiC_f/Ni-Cr-Al precursor wire has been obtained by deposition of (Al+Al₂O₃) diffusion barrier layers and Ni-Cr-Al alloy coating on the surface of SiC fiber via magnetron sputtering. The morphology, composition and the phase of coatings were studied, and the influence of the coatings on the mechanical property of SiC fiber was investigated. The precursor wires were treated in vacuum at 850℃ and 900℃ for 150 hours. The results show that (Al+Al₂O₃) coating is uniform and dense, the Al₂O₃ coating is in the form of amorphous,and the composition of Ni-Cr-Al alloy coating is close to that of Ni alloy target. The (Al+Al₂O₃) layer and Ni-Cr-Al layer combine well with SiC fiber and have extremely slight negative effect on the tensile strength. After heat treatment in vacuum, the Ni-Cr-Al alloy coating remains intact, and Al₂O₃ coating effectively blocks the element diffusion and restricts the reaction between SiC fiber and Ni-Cr-Al alloy, which can ensure the preparation of high performance of SiC_f/Ni-Cr-Al composites.

Abstract:As compared with traditional Ni based single crystal (SC) superalloy, the composition characteristic of Mo-rich Ni3Al based SC superalloy is high Al and Mo contents, which indicated that this alloy has the advantage of low density. This work summarized the solidification characteristics of this alloy. Al was found to significantly increase the average liquid diffusion coefficient during solidification, and the liquid diffusion coefficients of Ni3Al based SC superalloys were one to two order of magnitude higher than those of Ni based SC superalloys, reached 10-8 m2/s magnitude. Meanwhile, high Al and Mo contents in experimental alloy led to the solidification of interdendritic primary γ'' phase and Mo-rich phase at the last stage of solidification, which was significantly different from the typical interdendritic precipitation of Ni based SC superalloy (γ/γ'' eutectic and γ'' phase). Moreover, the influence of high Al and Mo contents on solidification characteristic temperatures was little. Mo had the strongest tendency to segregate to interdendritic residual liquid phase during solidification of Mo-rich Ni3Al based SC superalloy, and this microsegregation behavior can decrease the tendency of freckle formation. The investigation of solidification behavior of this Mo-rich Ni3Al based SC superalloy will be beneficial for the preparation technique and industrial application for this newly developed SC superalloy.

Abstract:As is known, phases, defects, residual stress, deposition efficiency and mechanical properties of plasma sprayed coatings depend dramatically on the fabrication parameters and substrate pretreatment state. In other words, slight changes might lead to distinguished differences between coatings. Therefore, it is of great importance to perform researches on the formation process of plasma sprayed coatings microscopically. Basically, plasma sprayed coatings are constituted of enormous molten or semi-molten droplet, which are heated and accelerated by plasma torch. Hence, the flattening and solidification behavior of single droplet after impacting on the substrate are the most elementary process of the formation of coatings. The factors influencing the flattening and solidification behavior can be divided into two categories, namely, droplet properties: velocity, temperature, size, material properties, molten status, etc.; substrate status: roughness, preheated temperature, surface chemistry status, deposition of adsorbates and condensates, wetting properties and interfacial thermal contact resistance between droplet and substrate, etc.. With different droplet properties and substrate conditions, the droplets might spread into five different types, i.e., disk-like, fragmented, finger-like, flower-like and bubble-like. Each type represents specific deposition mechanism and quality. Therefore, series of parameters can be used to quantificationally characterize the morphologies of splats, such as perimeter, area, volume, depth, circularity, eccentricity, solidity, flattening degree and so on.

Abstract:The disadvantages of TiAl alloys such as narrow hot-working window ( forging, hot extrusion, rolling, etc. ), poor high temperature deformability and brittleness at room temperature limit its applications in actual projects. The research state of effects of alloying additions on hot deformation processing and superplasticity of TiAl based alloys was reviewed. The effects of alloying additions on hot deformation processing of TiAl alloys were discussed from the aspects of the crystal structure of TiAl alloys, the fraction of β phase, microstructures, activation energy respectively. The principles and the developing trend that alloying method improves hot deformability of TiAl based alloys was finally proposed.