Abstract:To overcome the shortages of Al composites reinforced with a single primary Si or Mg2Si particles, a new type of gradient composites reinforced with the two particles was investigated through centrifugal casting. The structures and the properties of the composites have the obvious gradient distribution characteristics. The inner zone is the reinforced zone with a high volume fraction of primary Si and Mg2Si particles, whereas the external zone is the unreinforced zone with few or no primary Si and Mg2Si particles. Due to the high volume fraction of the complementary particles, the hardness values of the inner zone are much more than that of the external zone. The assembling mechanism analysis reveals that the massive primary Mg2Si particles are the key factor to form the gradient composites. In the centrifugal field, the relative velocity of the lower density primary Mg2Si particles is higher than that of primary Si particles. The Mg2Si particles will collide and impel primary Si particles to move more quickly towards the inner zone of tubular parts during freezing, resulting in a strong concentration of the primary Si and Mg2Si particles in the inner zone. To obtain the enough primary Mg2Si particles, the amount of Si should not be lower than 19 wt% and that of Mg not lower than 4 wt% in ternary Al-Si-Mg alloys.

Abstract:Electron beam rapid manufacturing (EBRM) is a novel layer-additive manufacturing process which was developed to directly fabricate metal parts from computer aided design (CAD) data. The present study was conducted to evaluate the microstructure and the mechanical properties of Ti-6Al-4V by EBRM. Results show that typical microstructures exhibit large columnar β grains nucleated at the substrate and grew epitaxially along the height direction of deposits through many deposition layers, and alternately light and dark banded textures at layer-layer and bead-bead interfaces have been also found due to complex thermal history during deposition process. As a result, the tensile properties of the as-deposited and the as-annealed deposits exhibit distinct anisotropy. The strength in X and Y directions are similar and markedly higher than that in Z. No significant impact of annealing treatment has been found on room temperature tensile properties. Hot isostatic pressing (HIP) treatment obviously decreases the dispersion of the high cycle fatigue data and improves both ductility and toughness, while at the expense of the tensile strength. The tensile properties of the as-deposited and as-annealed Ti-6Al-4V by EBRM can meet the mechanical property requirements of AMS4999 standard, but can not fully meet the requirements of HB5432 standard.

Abstract:The electron beam (EB) welding process of Ti casting plates was investigated. For achieving the welds with an acceptable quality, the cross-sectional shape, the microstructure and the tensile properties of the electron beam joint of casting TC4 (ZTC4) alloy were studied. The results show that the double-side molding in electron beam welding of ZTC4 can be achieved by adjusting the welding speed and welding current, but it is difficult to achieve double-sided weld shape in welding the thick plates, and its internal quality meets the standard requirement. The microstructure of electron beam weldment of casting TC4 alloy in the base metal is composed of α laths and β phase, the weld consists of acicular martensites, and the heat affected zone (HAZ) consists of thin acicular martensites, α laths and β phase. The tensile strength of ZTC4 EB-joints is higher than that of the base metal, so the tensile strength of ZTC4 EB-weld can be improved by optimizing the composition and the microstructure of base metal. Impact test shows that stress concentration factor has a great effect on absorbed energy.

Abstract:The RE(Nd, Tb)FeCoB magnetic powders were prepared by arc melting, high energy ball milling and a partial oxidation treatment method. A X-ray diffraction device and a vector network analyzer were used to analyze the phase structure and microwave absorbing properties of the powders. The results of B addition to the microwave absorbing performances in the NdFeCo alloy, indicate that Nd2Fe14B phase will precipitate and the relative content of the α-Fe phase increases with the increasing of B in Nd10.53Fe77.84Co11.63 alloy powder. When Nd is replaced by the heavy rare earth Tb in NdFeCoB alloy, the powders consist of α-Fe, Tb2Fe14B, Tb2Fe17 and a small amount of Tb2O3 phases. (Nd10.53Fe77.84Co11.63)97B3 powder has a minimum of absorption peak frequency, which is –9.5 dB at 4.5 GHz. After substituting Tb for Nb in (Nd10.53Fe77.84Co11.63)97B3 alloy the absorption peak frequency increases to 6.3 GHz, but the reflectivity value is reduced to –11 dB.

Abstract:Ni-base metal-intermetallic laminate (MIL) composites were obtained from in-situ combustion reaction between the Ni and Al foils by a plasma activated sintering (PAS). Microstructural observation reveals that the laminates consist of alternate residual Ni layers and reacted layers which can be further divided into multiple layers of Ni-aluminides. The compositional gradient series of these intermetallic phases change in a stepwise fashion from Al-rich phases to Ni-rich phases with the increasing of the treatment temperature. Accordingly, the tensile strength of the composite increases steadily with the increase of temperature. The composites fabricated at 1473 K have the highest tensile strength and elongation. The fractographies of the tensile samples indicate that the failure of the composites treated at lower temperatures (1073 K and 1173 K) result from the interaction between the transversal cracks in the intermetallic layers and the shear bands in the Ni layers. When the treatment temperature increases, a transition from multiple cracking to a single cracking of the intermetallic layers can be observed.

Abstract:The Ni-base alloy composite coatings synergistically reinforced by WC and CeO2 particles were prepared on the surface of 7005 aluminum alloy by the plasma spray technique. The microstructures and the tribological properties of the composite coatings were researched. The results show that with the addition of CeO2 particles, the microstructure of the composite coating is refined; meanwhile, the WC reinforcing particles change from round to irregular polygon and their decarburization are alleviated. The friction coefficients and the wear losses of the composite coatings are lower than those of the WC/Ni-base alloy composite coatings and the Ni-base alloy coatings at different PV values. When the PV values are smaller than 3.36 N·m/s, the maximum contact stress of the composite coating is lower than its elastic limit contact stress, the wear mechanisms of which are mainly micro-cutting wear and fatigue wear. As the PV values are bigger than 3.36 N·m/s, the maximum contact stress exceeds the elastic limit contact stress of the composite coating and the contact temperature sharply increases to 648 °C, obvious plastic deformation and desquamation traces appear on the worn surface and the wear mechanisms turn into multi-plastic deformation wear, abrasive wear and adhesive wear accompanied with oxidative wear.

Abstract:The aim of this work is to investigate the influence of NaOH pretreatment time on the phases and morphologies of Ti6Al4V substrates and hydroxyapatite (HA) coatings. Ti6Al4V substrates were pretreated with a sodium hydroxide (NaOH) solution for different amounts of time (12, 24, 36, 48, and 60 h). After NaOH pretreatment, a three-dimensional porous network of sodium titanate gel was observed on the Ti6Al4V surface. Subsequently, HA deposition was achieved using the hydrothermal-electrochemical methods, while the electrolyte solution containing NaCl, K2HPO4·3H2O, and CaCl2, was maintained at 120 °C and applied by a constant current density of 1.25 mA/cm2 for 120 min. The results indicate that the growth pattern and micromorphology of the HA coating are all influenced by different pretreatment time. After pretreating Ti6Al4V substrates with NaOH for 12 h, needle-like structures are primarily formed on the HA coating, and some dandelion-like morphologies are presented. During 48 h NaOH solution pretreatment, the dandelion-like structures increase with the increase of time. However, the amount of the dandelion-shaped HA drops slightly, when pretreatment time is longer than 48 h. The orientation index of the (002) plane of HA reaches the minimum when Ti6Al4V substrates are pretreated for 48 h, whereas the crystallinity is the highest for this pretreatment time.

Abstract:The influence of Al content on the microstructure of FeNiCrAl/NiAl composite prepared by thermite reaction was studied. The results show that the NiAl intermetallic compound and the FeNiCrAl present different microstructures morphologies with increasing of Al content. When the Al content is low, NiAl phase exists as particulate inside the grains, and as lath structure in the grain boundary. With the increase of Al content, the intertexture structure first appearing near the grain boundary extends into the grains. Finally a consistent intertexture structure is formed. However, with the further increase of Al content, the size of intertexture structure decreases and even disappears inside the grains. The reason of these microstructure morphology changes was discussed.

Abstract:Based on the diffusion Karma phase field model with thin interface limit, the dendrite growth behavior of pure Ni undercooled melt was simulated under different temperature coupling strength. Results show that as the thermal coupling strength decreases, the impact of the temperature field on the phase field weakens, the solid-liquid interface disturbance increases, and secondary dendrites develop gradually from the main branch. Meanwhile, the dimensionless growth velocity of dendrite tip increases, while the dimensionless dendrite tip radius decreases. Furthermore, at the initial solidification stage, the transient growth velocity of dendrite tip is greater than the theoretical stable growth velocity; with the growth process going on, the growth velocity of dendrite tip gradually decreases until it equals to the theoretical stable value. Therefore, the computational results by the phase-field method are in good agreement with that by the microsolvability theory.

Abstract:Highly ordered Co antidot arrays with different pore diameters (1.0，2.1，3.0，4.1, 5 μm) and the same thickness were prepared via sputtering Co into the gaps of PS colloidal crystal templates with different sputtering time. The structure and magnetic properties of Co antidot arrays were characterized by SEM, AFM, XRD and VSM. It is found that the coercivity and remanence ratio of Co antidot arrays are up to 253.18×10-4 T and 0.85, respectively, and they are 3.4 and 2.3 times larger than those of Co films, respectively. Moreover, with the increase of the pore diameter, the coercivity and the remanence ratio decrease gradually. The results of theoretical analysis indicate that the excellent magnetic characteristics come from the shape anisotropies induced by the structure itself, and the change of the shape anisotropies caused by pore diameter and pore spacing results in the change of the magnetic properties.

Abstract:Structural stabilities, elastic properties and electronic structures of Mg17Al12, Al2Y and Al2Ca phases have been determined by Castep and Dmol program based on the density functional theory. The calculated heats of formation and cohesive energies show that Al2Y has the strongest alloying ability as well as the highest structural stability. The calculations of thermodynamic properties display that the Gibbs free energy of Al2Y is always the smallest and it has the highest stability within 298~573 K. The next is Al2Ca, and the last one is Mg17Al12. Y and Ca addition to the Mg-Al alloys can improve the heat resistance. The calculated elastic constants reveal that Mg17Al12, Al2Y and Al2Ca are all brittle, and among the three phases Mg17Al12 is a phase with the best plasticity. The results of elastic constant calculation predict that Al2Y has the highest melting temperature and the best structural stability. The calculations of the density of states (DOS) and Mulliken electronic populations indicate that the highest structural stability of Al2Y attributes to more covalent bonds below Fermi level compared with those of Mg17Al12 and Al2Ca phases.

Abstract:The effect of microstructures obtained by different heat treatments on the stress rupture properties of Ti-24Al-15Nb-1.5Mo/TC11 dual-alloy with electron beam welds has been evaluated. The results indicate that after double heat treatment, the microstructures of the weld and the heat affected zone of Ti-24Al-15Nb-1.5Mo alloy consist of large quantities of strip α and α2 phases which are parallel arranged and vertical to the direction of stress, and there are also intermittent grain boundaries α and α2 phases. All these make microcracks connect and extend fast, reducing the rupture life of specimens. However, under the same deformation condition, the welding seam after gradient heat treatment consist of plenty of fine strip and equiaxed α, α2 phases and a few large size α, α2 phases. Under the long time load, mcirocracks consume more energy or spend more time in order to go round or go through the large size grains. The long time load at high temperature has little impact on the microhardness.

Abstract:The Pr-Zr complex oxides were prepared by coprecipitation and the effects of the synthesis conditions on the formation of perfect solid solution were investigated. The catalytic performance of methane partial oxidation supported on the prepared samples was also studied. The Pr-Zr perfect solid solution could be synthesized under the conditions of precipitation temperature 20 oC, precipitation pH 12 and calcination temperature 800 oC through Pr(NO3)3·6H2O and Zr(NO3)4. The formation of solid solution could improve oxidative activity of the Pr-Zr due to the high oxygen mobility.

Abstract:Microstructural characteristics of TiAl-3Ta-x(Cr,W) alloy have been investigated in various annealing conditions, including cooling rates, heating temperatures and holding time by optics microscope (OM), X-ray diffraction (XRD) and transmission electron microscopy (TEM). The results show that the α2+γ grains grow with longer heat treatment time while the fault and the dislocation are found in the full lamellar microstructure. The massive γ precipitate in the microstructure by oil quenching and the full lamellar microstructure occurs by furnace cooling. Besides, the grain size of full lamellar is the smallest in the microstructure at the heat treatment temperature from Tα to Tα+20 oC, which is caused by weak β stable element Ta.

Abstract:The ZrB2-SiC ceramics were joined to themselves using Ag-Cu eutectic/Ti lamination as interlayer. The SEM and EDS analyses demonstrate that ZrB2 could react with Ti in brazing alloy to form an in situ TiB whisker array with preferred orientation. The typical microstructure of the joint is ZS/TiB(Ag(s,s))/TiCu(AgCu4Zr)/Ag(s,s)/TiCu(AgCu4Zr)/TiB(Ag(s,s))/ZS. The microstructural evolution at various brazing temperatures was investigated. It is revealed that the ZrB2 decomposing temperature is 860 oC and TiB formation temperature is 880 oC. The maximum shear strength of 134 MPa is obtained when joining at 900 oC for 10 min. The high strength mainly benefits from stress accommodation by TiB and gradient transition from the ceramic to the seam center.

Abstract:The effect of the elastic energy on the morphology and orientation of g ′ particles and the coalescence behavior of multi-particle were studied based on the three-dimensional phase-field method, and the influence of precipitate volume fraction on the number, average size and size distribution of g ′ particles were also studied. The results show that the g ′ particle is cubic under elastic energy, aligned along the <100> elastic soft directions. The effect of the elastic energy on the coalescence behavior of multi-particle mainly depends on the elastic interaction which is related to the particles' distribution, size and the distance of domain boundary. With the increase of precipitate volume fraction, the number of g ′ particles first increases to the maximum and then reduces; meanwhile the average size increases gradually.

Abstract:Low cyclic fatigue (LCF) properties of three kinds of high temperature alloys (Inconel-718, Incoloy-825 and Incoloy-800H) as candidate materials for supercritical water cooled reactor (SCWR) were investigated at 650 oC and room temperature (RT) under a strain amplitude of ±0.5%, and fracture morphology of all the samples was observed by scanning electron microscope (SEM). The results show that the fatigue property of 718 is the best at both temperatures. The temperature has few effects on the area of hysteresis and elastic deformation for each alloy. The area of hysteresis for 718 is much lower than that of 825 and 800H, while the elastic deformation of 718 is as twice as that of other alloys, which is beneficial for improving the fatigue life. The 718 alloy shows a cyclic softening behavior in the testing; however, 825 and 800H coincide with the hardening-saturation mode; in addition, their cyclic hardening behavior is more obvious at 650 oC. SEM observation finds that the fatigue striation width after LCF testing at 650 oC is no more than 1 μm for 718, but up to 2.28 μm and 2~20 μm for 825 and 800H, respectively, which further demonstrates that 718 has the best fatigue property at 650 oC.

Abstract:Constitutive analysis for hot working of Aermet100 steel was carried out using experimental stress-strain data from isothermal hot compression tests, in a wide range of temperatures (1073~1473 K), strains (0.05~0.9) and strain rates (0.01~50 s-1). A constitutive equation based on orthogonal experiment has been established considering the independent effects of strain, strain rate and temperature. With consideration of the effects of the deformation temperatures and the stain rates on microstructures and properties of Aermet100 steel, processing maps were established based on the dynamic material model (DMM). And the instability zones of flow behavior could also be recognized by the maps. The hot deformation characteristics of Aermet100 steel in different zones were also analyzed.

Abstract:The interdiffusion behavior of W coating with Mo alloy at 1600 ℃ was studied, the monocrystal samples remained monocrystal feature without after long time (maximum of 5000 h) annealed, and grain boundary of polycrystal W was perpendicular to the surface of Mo. As the result of line scan of SEM: the diffusion depth of W in Mo was larger than that of Mo in W. The interdiffusion coefficient D of monocrystal Mo-W system was calculated with EPMA datas by the method of Den Broeder, and as the result: D was 10-15~10-16 cm2/s at 1600 ℃, lnD was linear relationship inverse of concentration of W, and the slope was –1.82.

Abstract:Superconducting materials are always severely restricted in practical engineering applications due to the degradation of superconductivity under external mechanical loads. Based on the damage theory of fragile fiber reinforced metal matrix composites and the Weibull distribution function, a degradation model to describe the mechanical deformation influence of the Bi-based superconducting multi-filamentary composite tape on its critical current under axial load was proposed. The critical currents of superconducting tape with the axial strain in the processes of axial loading and unloading were analyzed. The degradation of the critical current of superconducting tape under the conditions of different initial damages and pre-strains was predicted theoretically. It is shown that the theoretical model we developed can predict well the degradation of critical current of the Bi-based superconducting multi-filamentary composite tape with axial strain. The results are in good agreement with the experimental data. The present investigation will be helpful for superconducting composites in applications.

Abstract:Segregation defect of ZL205A alloy casting during practical production process was researched. The microstructure of the segregation, the compositions and the microhardness of the segregation phase, and the effect of segregation defect on the mechanical properties of the casting were studied. The results reveal that the chemical compositions of the segregation phase are Al3Ti, Al3V and Al3Zr, and the microstructure is in the form of rectangle or petal shape. The segregation defect has an obvious effect on the tensile strength and the elongation. But the microhardness of the segregation phase is higher than that of the matrix. Hot treatment can not eliminate the segregation. Actually the massive segregation belongs to the microsegregation. It is caused by downward movement of Al3Ti, Al3V and Al3Zr of heterogeneous nucleation particle to agglomerate during solidification. And the coarse massive structures in the ingot casting have certain morphological heredity in its formation.

Abstract:A series of thickness of oxygen-enriched α layer were obtained after TC6 titanium alloy were treated with different thermal exposure processing (thermal exposure temperature, holding time). Their relationship network model was built by BP artificial neural network. The results show that the built model can be used for the prediction of the thickness of oxygen-enriched α layer of TC6 titanium alloy under different thermal exposure treatments. Meanwhile, the model can also serve as a guide for the heat treatment of TC6 titanium alloy if the thickness is given.

Abstract:Ti-35Nb-7Zr-5Ta alloys were fabricated by spark plasma sintering (SPS) technology. The effects of different sintering temperatures on the relative density, microstructure and mechanical properties of the alloys were studied. The results show that the alloys are mainly composed of the mixed matrix which contains β-Ti phase, Ti-Nb-Ta-Zr solid solution phase, as well as some unmelted Nb and Ta metal particles in the sintering temperature range from 950 to 1150 oC. In addition, the alloys have a higher relative density and a higher compressive strength. With the increasing of the sintering temperatures, the mixed matrix bonds further with each other and its size increases. Meanwhile, the size and the amount of the unmelted Nb and Ta metal particles decrease. And the relative density and the compressive strength of the alloys are increased. The prepared alloys exhibit a low compressive elastic modulus in the range of 50~57 GPa, and they reveal an excellent mechanical compatibility. The results also show that the effect of sintering temperatures on compressive elastic modulus is very little.

Abstract:The different doping methods of La-TZM alloy plate were studied by observing and comparing the fracture and structure. The effect of La2O3 and La(NO3)3 on tensile properties and elongation of TZM alloy was discussed. The results show that the tensile strength of La2O3-TZM alloy plate is 1057 MPa and the elongation is 8.2%, while the tensile strength of La(NO3)3-TZM alloy is 1202 MPa, and the elongation is 7.0%. La(NO3)3 doped TZM alloy plate has finer second phase, and it makes the strength even higher, but lower the elongation.

Abstract:By means of powder electrical explosion spraying of continuously carrying powder with pressure-sensitive adhesive, WC coating was prepared. The effects of initial voltage and the cross-sectional area of jet chamber on the forming of coating were analyzed. The result shows that in the distance of 3~7 mm, hybrid coating is formed which consists of a surface for liquid spraying coating and a bottom for vapor deposition coating. When raising the initial voltage within minor cross-sectional area of jet chamber, the temperature and the velocity of the blast area can be increased to raise vapor share. It is thought that vapor deposition coating is formed preferentially and combined with substrate densely. Residual droplets spurt is lagged, and liquid spraying coating is formed which covers the vapor deposition coating.

Abstract:Copper coated tungsten composite powders were prepared by an electroless plating method. The electroless plating of copper on tungsten powders with an irregular shape and a spherical shape was studied. The spherical shape of tungsten powder was made by a radio frequency plasma process. For the particles of irregular and angular shape, there is no obvious edge after plating and their surface becomes rough. But for spherical particles with surface defects, they become surface-round and the spherical degree has no obvious change because copper is deposited uniformly on the particle surface in the electroless plating process. Thus, the surface quality of tungsten powder is improved and the surface defect is eliminated. After annealing in hydrogen at 600 oC, the surface of copper coated tungsten becomes smooth, and the pores in the coated layer are decreased obviously. Finally, a compact layer of copper is coated on the surface of tungsten powder to form a W-Cu composite powder.

Abstract:The Ti-Si-C nanocomposite film was deposited in gas mixtures of Ar and CH4 by middle frequency unbalanced magnetron sputtering Ti80Si20 composite targets. The microstructure of the film was investigated by X-ray diffraction, Raman spectrum and X-ray photoelectron spectroscopy. The results show that the film exhibits nc-TiC/a-C:Si:H nanocomposite structure with about 10 nm nanocrystallites TiC embedded in hydrocarbon (a-C:Si:H) matrix. The results of XPS analysis strongly depend on Ar+ sputter-etching. The C and O content on the film surface distinctly decreases, while the Ti and Si content gradually increase with the increasing of Ar+ sputter-etching time. It is found that Ar+ sputter-etching results in the graphitization of the amorphous carbon phase in the nanocomposite film. In other words, the sp3C-C(H)/sp2C-C ratio decreases with the increasing of Ar+ sputter-etching time. In addition, the C-Ti*/C-Ti and C-(Ti+Ti*)/C-C ratios obviously increase.

Abstract:Chemical conversion treatment on as-cast Zr-Al alloy was studied. After degreasing, pickling and chemical conversion treatment, a zinc chemical conversion film was fabricated on the surface of Zr-Al alloy. The microstructure and the phase composition of Zr-Al alloy and the chemical conversion film were observed using SEM and XRD, respectively. The results show that as-cast Zr-Al alloy is composed of α-Zr and Zr2Al, where α-Zr is substrate and Zr2Al spreads along grain boundaries discontinuously. A Zn3(PO4)2·H2O and ZnZr(PO4)2·2H2O chemical conversion film is formed by treatment in the chemical conversion solution successfully. The film consists of small crystal particles densely. It is uniform, compact and has no obvious defects. The forming mechanism of zinc chemical conversion film on Zr-Al alloy was discussed.

Abstract:The uniform heat treatment of direct chill continuous casting Al-Si/Al-Mn clad slab was investigated with different temperatures and time, and the microstructure, hardness and solute distribution of the uniform heat treated samples was studied. The results show that the coarse net-work compounds of Al-Si alloy change into spot and short-bar compounds, the Mn element distribution is more uniform, and the interface of Al-Si/Al-Mn clad slab is clearer because of element solution. The hardness of Al-Si alloy is reduced after the treatment, but the hardness of Al-Mn alloy is not sensitive to temperatures and time of the uniform heat treatment. The elemental EPMA mappings show that the distribution of solute elements are more uniform, and elements are diffused on the interface of Al-Si/Al-Mn clad slab, especially Mg element becomes not obvious on the interface after uniform heat treatment. It can be concluded that the best Al-Si/Al-Mn clad slab is obtained when the uniform heat treating temperature is 480 oC and the time is 15 h.

Abstract:Anodizing has become an important anticorrosive surface treatment technique of magnesium alloy, but the mechanism of anodic film formed on magnesium alloy is not understood fully. Several aspects were summarized up about the formation dynamics process of anodic film, including formation process, microstructure, composition, diffusion behavior of elements, the influence of alloy phase on formation of the film and the physical model. Finally, several important research problems of anodic film on Mg alloy were listed. It will benefit mastering the formation mechanism, improving the anodizing technology and enlarging the practical application.