Abstract:The as-cast microstructure, the heat-treated microstructure and the composition characteristics of freckle chains in the third generation single crystal superalloy DD9 were studied by OM, SEM, EBSD and TEM. The results show that freckles are composed of fine disorder-oriented equiaxed grains. They are in the shape of a chain roughly along the direction of crystal growth and only appear on the surface of single crystal castings. The depth and width of freckle chains are 400~800 μm. Freckled area contains a large amount of γ/γ' eutectics. A certain amount of MC carbides and porosity also appear in as-cast freckled area. After heat treatment, large-size γ' phase and granular M₆C phase appear at the equiaxed grain boundary of freckled region. The freckled area contains more Ta and Al, but less Re and W. The composition of the freckled area is similar to the interdendritic composition.

Abstract:DD15 single crystal superalloy with [001], [011] and [111] orientations was cast by seed method in the directional solidified furnace. The creep properties of the alloy with different orientations were investigated at 980 °C/300 MPa. In order to obtain the microstructure evolution after different creep time, the creep after 50 and 100 h and the creep fracture of three kinds of tests were investigated. The alloy microstructure with different orientations were investigated by SEM and TEM. The results show that the alloy with different orientations has obviously various microstructure characteristics on the section perpendicular to the crystal growth direction. The γ′ phase with [001] orientation is regular square, that with [011] orientation is rectangular, and that with [111] orientation is polygon. The creep properties of the alloy exhibit obvious anisotropy at 980 °C/300 MPa. The creep life of the alloy decreases in the sequence of [111], [001] and [011] orientation. The creep strain of the alloy under different conditions decreases in the sequence of [001], [011] and [111] orientation. The common feature of the creep curves is a very short primary creep stage. Compared with creep curves of the [001] and [111] orientation, the creep curve of [011] orientation has a shorter third creep stage. The degree of γ′ coarsening is obviously different for alloy with different orientations after creep. The rafting speed of [001] oriented sample is larger than that of [011] and [111] oriented sample. After creep fracture, the dislocation network of [001] or [111] oriented alloy is denser and better than that of [011] oriented alloy.

Abstract:Tube bundles are the most critical components of steam generators in pressurized water plants. They are the heat exchange interface between primary and secondary circuits, acting as an important safety barrier to prevent the radioactive leakage. Stress corrosion cracking (SCC) initiation behavior of the worn alloy 690 tubes was investigated by slow strain rate tests (SSRT) in the high-temperature alkaline solution. The scanning electron microscope, electron backscatter diffraction and transmission electron microscope were used to analyze the fretting wear and SCC initiation behavior of alloy 690 tubes. Results show that SSRT specimens show typical transgranular SCC characteristics. The number of initiated cracks and their average depth are increased with increase in the wear degree, suggesting a wear-induced SCC initiation. This may have a relationship with the grooves, delamination, micro-cracks and residual strain layer with tens of micrometers in thickness left on the worn surface. Furthermore, a preliminary analysis on the possible procedure of wear-induced SCC initiation and further propagation during SSRT tests was carried out based on slip-dissolution/oxidation mechanism.

Abstract:The preparation quality of Ni-based single crystal alloy (NSCA) with gas film pore structure has become a key factor restricting the application and development of high-performance aero-engine equipment. However, due to the difficulty of quantitatively expressing the microstructure changes during the preparation process, it is difficult to quantitatively evaluate the preparation quality under different processes. In the present study, taking the advantages of ultrasonic guided wave that is sensitive to metal material micro-damage and has high detection efficiency and detection accuracy, excitation frequency (2.05 MHz) and benchmark characteristic parameters (7.58 e^-4/mm) of NSCA are determined, and then the influence mechanism of different preparation quality defects on the nonlinear parameters of guided wave is clarified by theoretical and experimental analysis, which will provide theoretical basis research for the subsequent efficient and controllable preparation of NSCA with gas film pore structure.

Abstract:The paper investigated the influence of heat treatment processes on the γ" phase microstructure of a novel third-generation nickel-based powder superalloy WZ-A3. Differential thermal analysis of different heating and cooling rates, interventional cooling tests, cooling rate tests and aging heat treatment experiments were carried out in order to investigate the dissolution and precipitation behavior of γ" phase as well as its size evolution. The results indicate that: when the WZ-A3 alloy cooled from supersolvus heat treatment, the initial precipitation temperature of γ" phase is between 1148°C~1165°C, the fastest precipitation temperature is between 1028℃~1037℃; the secondary γ" phase nucleation and precipitation temperature range from 885°C to 1008°C, depending on the experimental cooling rate; a slower cooling can further obtain more secondary γ" phase precipitation; the temperature of the supersolvus heat treatment has no significant effect on the size of the γ" phase; the cooling rate after solution heat treatment is inversely proportional to the size of the γ" phase, this relationship can be expressed as a power law function y=1490.74x-0.509; the short-time aging at 800℃ has no obvious influence on the size and morphology of the secondary γ" phase; the coarsening rate of the secondary γ" phase at 800 ° C, 900 ° C and 1000 ° C are 2.153×10-28m3s-1、1.696×10-27m3s-1、and 2.331×10-26m3s-1, respectively; the activation energy of the γ" phase coarsening of the studied alloy is 278 kJ / mol.

Abstract:In this paper, different treatments were used to adjust the “γ′phase+twin” structure of a new Ni-Cr-Co based wrought superalloy, which was low alloying and low stacking fault energy. The contribution of twin boundary to grain refinement, strength improvement and the effect of the “γ′phase+twin” structure on the mechanical properties of the alloy were analyzed. The results show that after solution treatment at 1090 ℃ for 1 h, the γ′precipitates in the microstructure of the forged alloy is basically dissolved, and the content of twins in the structure is as high as 51.65%. The elongation (42.9%) of the solid solution alloy is 63.6% higher than that of the forged alloy (26.8%), and the yield strength is 693 MPa (only 3% lower than that of the forged alloy) σ _tb = 66.98 MPa, and its contribution is basically the same as that of fine grain strengthening (77.4 MPa). The content of twins of the aged alloy treated by 700 ℃ / 8 h / AC is 34.41%, at the same time, a large amount of γ′ phase, which is precipitation strengthening phase, is introduced into the structure, and form the“ γ′phase + twin" composite structure. The hardness, tensile strength, yield strength and elongation of the aged alloy (405 HV, 1042 MPa, 864 MPa, 49.76%) are further improved compared with those in the solid solution state (324.4 HV, 879 MPa, 693 MPa, 42.9%) , and σ _tb=107.94 MPa. In superalloys with low alloying and

Abstract:In this paper, the NiAl-32V pseudo-binary hypoeutectic alloy was prepared by directional solidification technology. The microstructure morphology of the alloy in the steady-state region at different withdrawl rates after high temperature heat treatment was studied, and the variation of its thermal stability and microstructure morphology was analyzed. The results indicates: The primary phase of the alloy has good thermal stability at 900°C(5~100h). The coarsening and spheroidization of NiAl eutectic layers are observed, and the longer the heat treatment time is, the greater the coarsening degree is, and the more obvious the spheroidization is. After high temperature heat treatment at different temperatures(900°C,1000°C,1100°C)for 5 h, the proportion of primary phase area of the alloy also changed slightly. The coarsening and spheroidization of NiAl eutectic lamellae were observed in all samples (withdrawl rates V=6~150μm/s). With the increase of heat treatment temperature, coarsening and spheroidization are more obvious.

Abstract:The oxidation of α-Mg and Mg₂Ca in Mg-Ca alloy was studied by calculating the adsorption process of O₂ on α-Mg (0001) and Mg₂Ca (0001) based on density functional theory (DFT), and the adsorption process and oxidation mechanism were investigated. Results show that during the adsorption, O₂ has a strong interaction with α-Mg and Mg₂Ca. The interactions are chemisorption due to the excellent E_ad values, but the adsorption structures of Mg₂Ca are not as stable as that of α-Mg. During the oxidation, O₂ reacts with Ca and Mg atoms in α-Mg and Mg₂Ca to form Mg-Ca-O oxide film, hence improving the oxidation resistance of Mg-Ca alloy. Since the adsorption structure of Mg₂Ca is not as stable as that of α-Mg, the oxide film formed by Mg₂Ca shows weaker protective effect on the substrate than that formed by α-Mg.

Abstract:Tension parallel to the radial direction (RDT) and compression along the extrusion direction (EDC) of an extruded AZ31 Mg alloy bar were conducted under a strain rate of 10^-4 s^-1 at room temperature. Twinning behavior was characterized by optical microscopy (OM) and electron backscatter diffraction (EBSD). The results demonstrate that extension twins have an effect on the yield point; the yield point of the alloy under EDC is 139 MPa which is higher than 88 MPa of the alloy under RDT. With increasing strain, strain hardening rates under these two stress states show a trend of fast decline at first, and then the hardening rates under EDC start to increase obviously till fracture while that under RDT keeps almost a constant. The increase in the hardening rate under EDC is related to the formation of extension twins and the twinning texture-induced slip activity. A method to measure the twin volume fraction in grains based on EBSD results was proposed. Under RDT, the volume fraction of extension twin in (0002) grains is about 45% at the strain of 0.04.

Abstract:The effects of adding Yb and Zr elements on the microstructure and mechanical properties of Al7Si0.3Mg alloy and the mechanism of refinement and modification were investigated. The results show that the addition of Yb and Zr elements can significantly refine the α-Al matrix, transforming it from coarse dendritic crystals to fine petal-like crystals with a significant reduction in grain size, and the eutectic silicon metamorphoses from coarse needle-like to short rod-like. The modification mechanism of eutectic silicon is that the adsorption of Yb and Zr at the twin grooves (TPRE) changes the eutectic silicon growth mode and finally changes the eutectic silicon morphology. After heat treatment (T6), a large number of Al₃(Yb, Zr) particles are precipitated to strengthen and refine the grain, and the addition of Yb and Zr can significantly improve the mechanical properties of the alloy. The tensile strength and elongation of the alloy (T6) are 296.3 MPa and 9.2% when the Yb content is 0.3wt% and the Zr content is 0.25wt%, which are 17% and 1.1 times higher than those of the unrefined and unmodified alloy, respectively.

Abstract:The effects of Sr and Y addition on the microstructure and mechanical properties of A356 aluminum alloy were studied by metallographic microscope, scanning electron microscope, transmission electron microscope, energy dispersive spectra and mechanical property tests. The results show that the combined addition of Sr and Y can obtain the best microstructure and mechanical properties compared with the separate addition of Sr or Y. The eutectic Si changes completely from flake-like or acicular-like to fibrous shape, the equivalent grain diameter of α-Al decreases from 42.49 μm to 26.63 μm, the secondary dendrite arms spacing (SDAS) decreases from 22.38 μm to 13.60 μm, the tensile strength increases from 166.1 MPa to 185.3 MPa, the elongation increases from 3.6% to 7.6%, and the fracture mode changes from brittle fracture to ductile-brittle fracture. The refinement mechanism and modification mechanism of Sr and Y were discussed. It is concluded that the main reason for α-Al grain refinement is the rapid heterogeneous nucleation of α-Al based on Al₃Y, and the modification mechanism is impurity-induced twins which grow in the mechanism of twin plane reentrant edge.

Abstract:Keyhole tungsten inert gas (K-TIG) welding is a variant of TIG welding, which can largely improve the weld penetration depth by forming keyholes inside the molten pool during welding. However, K-TIG welding is generally considered unsuitable for aluminum alloys due to their high thermal conductivity. A novel double-pulsed variable polarity TIG (DP-VPTIG) welding process was employed and the stable full penetration keyhole welding of 7 mm-thick AA2219 aluminum alloy was achieved. Keyhole dynamic evolution for DP-VPTIG was investigated based on visual sensing technology. Results indicate that in low-pulsed peak stage of DP-VPTIG process, the keyhole forms under the dominant role of the downward arc pressure against the upward surface tension and hydrostatic pressure acting on the surface of the molten pool, while the keyhole is closed as the upward surface tension and hydrostatic pressure become the dominant role in low-pulsed base stage. The periodic variation of low-frequency pulse in DP-VPTIG process stimulates a periodic keyhole behavior of “opening” and “closing” in the molten pool. The formation of keyhole is beneficial to the increase of weld penetration depth as the arc moves downwards along the keyhole and directly heats the solid metal under the molten pool. The keyhole size decreases with the increase of low-pulsed frequency.

Abstract:The high temperature oxidation behavior of 625 alloy cladding layer with different Si contents was studied by cyclic oxidation method after 144 h oxidation at 700, 800 and 900 °C. The oxide phase was analyzed by XRD. The surface and cross section morphology, elemental composition and oxide film thickness were studied by SEM/EDS. The results show that the oxidation kinetics of the samples at different temperatures keep a parabolic law, and the oxidation mass gain increases gradually with the increase of temperature. The oxidation film of 0wt% Si 625 alloy cladding sample peels off in a large area at 900 °C, while the oxidation film of 3wt% Si alloy cladding sample remains intact. With the increase of Si content at 700 °C, the oxidation particles on the surface of the oxide film decrease in size and become denser, which promotes the formation of Cr₂O₃. At 700 °C, a large area of internal oxidation appears in 0wt% Si sample, there are two strip oxides containing Ni, Cr and Mo in the substrate of 1wt% Si sample, while the inner oxidation of 3wt% Si samples is prevented due to the formation of Si-rich inner oxidation layer. The combined effect of the outer layer of Cr₂O₃ oxide film and the inner layer of SiO₂ not only prevents the infiltration of O anions but also inhibits the diffusion of Fe and other metal ions, thus improving the oxidation resistance of the alloy cladding.

Abstract:In order to improve the utilization rate of explosive energy and reduce the amount of welding charge, self-constrained structure explosive was proposed to carry out explosive welding. A T2 copper plate and a Q345 steel plate were used as base layer and flyer layer, respectively, and T2/Q345 explosive welding window was obtained through theoretical calculation. An experimental study on explosive welding of T2 copper and Q345 steel was carried out with double-layer honeycomb structure explosive as self-constrained welding energy. The bonding properties of the clad plate were studied by mechanical property testing and microstructure observation. The results show that compared with single-layer explosive with detonation velocity of 2505 and 3512 m·s^-1, the charge of double-layer honeycomb structure explosive used in T2/Q345 explosive welding can be saved by 54.4% and 31.4%, respectively. The bonding interface of the clad plate transforms from straight to wavy as the propagation distance increases. The tensile shear strength of the clad plate is 237.0 MPa, meeting the requirements of bonding strength of T2/Q345 clad plate. Explosion hardening occurs near the bonding interface. The T2/Q345 clad plate obtained by explosive welding with double-layer honeycomb structure explosive has good bonding property.

Abstract:The optimized manufacturing route of selective laser melting (SLM) for Ti6Al4V alloy was simulated by Simufact Additive software through orthogonal experiment. The results show that laser power 200 W, scanning speed 1200 mm/s, spot diameter 0.1 mm and powder thickness 0.03 mm are the optimal processing parameters. Samples with different pore structures were fabricated by SLM according to the optimized parameters, and scanning electron microscopy images show that the porous structures processed by this process have better fidelity. The compressive strength and elastic modulus of solid and different pore structures were compared and analyzed through compression experiments. It is concluded that the composite structure as the structural model of the implant can better meet the requirement for mechanical properties of the implant.

Abstract:Porous material is a new type of lightweight structure-functional material with high damping performance, low density, light weight, and other characteristics, making it useful in many applications. Mg97Zn1Y2 with long-period stacking ordered phase (LPSO phase) as a matrix, MgCO₃ as foaming agent and SiC as tackifier was used to prepare magnesium-based porous materials by melt-foaming method. The mechanical properties and damping properties of the porous Mg97Zn1Y2 were studied by OM, SEM, XRD and DMA technology. Results show that the porous Mg97Zn1Y2 composites are mainly composed of magnesium matrix (α-Mg), LPSO phase and SiC phase. When the strain amplitude is small, the damping value of porous Mg97Zn1Y2 composites is obviously better than that of Mg97Zn1Y2 alloy, and the damping properties are improved as porosity is increased. However, increased porosity decreases the compression properties of porous Mg97Zn1Y2 composites. In addition to the dislocation damping, interface damping, and grain boundary damping of the Mg97Zn1Y2 alloy, “gas phase” damping is found to affect the damping properties of the porous Mg97Zn1Y2 composites jointly.

Abstract:Microstructure of gold wires with different mechanical characteristics was characterized by electron backscattering diffractometer. The loop profile, the heat affected zone and bonding point morphology were observed by scanning electron microscopy and optical microscopy, and the pulling force and ball shear force were measured by push-pull tester. Finally, the influence of mechanical characteristics of gold wires on the ball bonding quality was analyzed. The results show that there is obvious difference in microstructure along the radial direction. The core of the gold wire in semi-hard state 1 and 2 retains fibrous structure, and the edge grains are fine equiaxed grains. The length of the heat affected zone (HAZ) formed after forming the ball is short, the structure of the ball neck has obvious step, and the loop height after bonding is small compared with the soft state. The soft gold wire shows coarser equiaxed crystal, lower pulling force, and is prone to ball slip. The gold wire in semi-hard 2 state has strong bonding force to the pad, high pulling force and excellent overall bonding quality, which is the most suitable for the ball bonding process.

Abstract:A novel method of spray coating deposition (SCD) was proposed to deposit TbF₃ powder solution uniformly onto the surface of Nd-Fe-B magnets, and then the Tb element was introduced into the magnets through the grain boundary diffusion process (GBDP). Nd-Fe-B magnets with thickness up to 5 mm were treated with this method (SCD+GBDP). The effects of mass gain ratio (w) of TbF₃ coatings, diffusion time and the diffusion temperature on the microstructure and magnetic properties of the sintered magnets were investigated. The samples were diffused at 940 °C for 10 h and then annealed at 480 °C for 5 h. Results show that when the TbF₃ mass gain ratio increases from 0% to 0.8%, the coercivity of the magnets increases from 1201 to 1930 kA/m and the remanence is only decreased by 0.01 T. With increasing the mass gain ratio of TbF₃, the coercivity of the magnets increases firstly and then decreases obviously. SEM results show that the (Nd, Tb)₂Fe₁₄B core-shell phases can be formed by Tb which replaces the Nd in the boundary region among Nd₂Fe₁₄B grains. The improved decoupling effect by the continuous grain boundary phase and the higher magnetocrystalline anisotropy of the core-shell phase plays a positive role in the coercivity enhancement. The distribution and concentration of core-shell phase have a close influence on the coercivity. When the TbF₃ mass gain ratio is more than 2.4%, the grain boundary diffusion is obviously enhanced in the region close to the magnet surface. The SEM image of the element shows that the more Tb enters the inside of the grain, the higher the Tb concentration in the core than in the shell. Furthermore, the formation of a large amount of Nd-F/Nd-O-F phase causes the grain boundary phase not being as continuous as that of the sample with w=0.8%, which may be the main reason for the decrease in coercivity.

Abstract:The isothermal phase diagram of SiO₂-CaO-Al₂O₃ slag system was calculated by FactSage6.4. By fixing the agent MgO content at 8wt% and controlling Al₂O₃ content lower than 35wt%, a reasonable liquidus temperature and mineralogical phase of the glass slag were obtained. The effects of temperature, binary basicity w_CaO/w_SiO2 and Al₂O₃ content on viscosity of the feasible SiO₂-CaO-Al₂O₃-MgO slag were investigated by the rotating spindle method and simulating calculation. Results show that with increasing the temperature, the slag viscosity decreases, Al₂O₃ content increases from 15wt% to 35wt% and binary basicity w_CaO/w_SiO2 increases from 0.3 to 1.0 according to the univariate investigation. It is known from the smelting experiment using iron as collector that the recovery rate of palladium increases with increasing the mass fraction of waste catalyst in material system, and it increases first and then decreases with continuously increasing the basicity and temperature. With the waste Pd/Al₂O₃ catalyst used in this study and using the optimized slag ingredients of about 30wt% Al₂O₃, 8wt% MgO and binary basicity w_CaO/w_SiO2=0.5, the recovery rate of palladium reaches 99% and the residual palladium in glass tailing is less than 4.50 g/t.

Abstract:Design and fabrication of various gold micro- and nanostructures is a promising way to amplify surface enhanced Raman scattering (SERS) signals. Gold porous nanoplates were produced by simple heating aqueous solutions of HAuCl₄ and polyethylene glycol (PEG). The reaction was carried out in a one-pot, by one-step process at mild temperature, and PEG was used as capping agent and reducing agent in this cost-effective and environmentally benign fabrication strategy. Results show that the gold porous plates are about several micrometers in size and can be modified by experimental parameters such as growth time, PEG concentration, and gold ion concentration. The EDS measurements confirm the metallic nature of the cleaned gold porous nanoplates with no organic contaminants on the surface. The gold porous nanoplate substrate offers an excellent SERS-effect and exhibits a good reproducibility in SERS detection. Importantly, the as prepared gold porous plate substrates can be used for rapid and highly sensitive determination of organic pesticides such as thiram and phorate.

Abstract:In order to establish a constitutive equation which can reasonably describe the Ti/Ni/Ti laminated composites process, the hot deformation behavior of Ti/Ni/Ti laminated composite during the bonding process was studied on Gleeble-3500 thermo-mechanical simulator at the temperature of 550~850 °C, strain rate of 0.001~1 s^-1, and deformation of 65%. Four constitutive models, including modified Johnson-Cook (MJC) model, train compensated Arrhenius (SCA) model, multivariate nonlinear regression (DMNR) model, and modified Inoue Sin (MIS) model were used to predict the elevated temperature flow behavior of laminated composite. A comparative research on the experimental values and the predicted values of the four models was conducted. Besides, the accuracy of the average absolute relative error (AARE), correlation coefficient (R) and the relative error was compared to confirm the reasonability of these four models. Results show that the MJC, DMNR and MIS model are not suitable for the description of flow behavior of Ti/Ni/Ti laminated composites, while the predicted values of SCA model agree well with the experimental values except under some deformation conditions.

Abstract:First-principles calculations with supercell (SC) method and virtual crystal approximation (VCA) method were preformed to study the formation energy, mixing energy, lattice constant, volume, elastic constants, melting points, elastic modulus, vickers hardness, fracture toughness and density of states of (Ti/Zr)1-x(Ta/Nb)xB2 (0≤x≤1) solid solutions. The formation energy results show that the structural stability of the diboride solid solution of (Ti/Zr)1-x(Ta/Nb)xB2 decreases with the increase of the concentration of doped atoms. The volume of Ti1-x(Ta/Nb)xB2 increases with the increase of the concentration of doped atoms, because the atomic radii of Ta and Nb are larger than Ti. While the volume of Zr1-x(Ta/Nb)xB2 becomes smaller, since the atomic radius of Ta and Nb is smaller than that of Zr. Moreover, the diboride solid solution of (Ti/Zr)1-x(Ta/Nb)xB2 are mechanically stable and brittle materials. In particular, Ta and Nb dopants can significantly improve the brittleness, bulk modulus and fracture toughness of the solid solution (Ti/Zr)1-x(Ta/Nb)xB2, and reduce their vickers hardness.

Abstract:The anomalous flow behavior of Ni3Alat high temperature is closely related to the cross-slip of super-partial dislocations. Using a first-principles calculation, an impact of Re-effect on dislocation slip mediated creeps in the Ni3Al is investigated. The analysis of energy factors associated with the formation enthalpy of point defects reveals Re prefers to occupy Al sites, and the Re-Re pair prefers to occupy Al-Al sites in γ′-Ni3Al phase. By calculating the generalized stacking fault energies for and systems in Ni3Al, it is found that the Re occupying Al sites can promote the cross-slip of screw dislocations. A longitudinal arrangement of and defects should be able to effectively impede the nucleation and movement of dislocations compared with their horizontal layout. As their interaction is characterized and assessed by a correlation energy function between and point defects, a weak correlation is demonstrated to be favorable for the improvement of the anomalous flow of γ′ phases at high temperature. Re atoms preferentially occupy Al sites for the improvement of yield strengths of Ni3Al can be attributed to a weak repulsive interaction between and defects.

Abstract:Doping the third element is an important method to promote ordering transition of FePt and reduce the ordering transition temperature. However, it is a great challenge to explore the mechanism of the third element promoting FePt ordering and clarify the role of the third element in FePt ordering transition. Therefore, this work has investigated the effects of Bi element on the lattice constant, formation energy, differential charge density, saturation magnetization and ordering transition temperature of FePt with the first principle density functional theory. The results show that the substitution formation energy of Bi atom replacing Fe atom is lower than that of Pt atom. Bi atom is easier to replace Fe atom. The substitution formation energy of Bi atoms replacing near neighbors is lower than that of far neighbors. Bi atoms tend to aggregate in the lattice. Fe atoms are the main source of magnetism of FePt system. Bi atoms have little effect on the electronic structure and magnetism of FePt. The ordering transition temperature of FePt can obviously be reduced after doping Bi element. In the case of double doping, the lowest ordering transition temperature of FePt system is 623.32 K. The vacancy mechanism plays a leading role in the ordering transition. Bi element reduces the vacancy formation energy of FePt, increases the vacancy concentration of Fe and Pt atoms in the system, and promotes the diffusion and migration of Fe and Pt atoms, so as to promote the ordering transition of FePt.

Abstract:The mechanical properties of metals are closely related to the microstructure. As the most common solidified microstructure, dendrite has a great influence on the microstructure, and the change of temperature has a significant influence on the microstructure. Domestic and foreign scholar have carried out a lot of studies on the relationship between dendrite growth state and the properties of alloys, however, the study of microstructure growth in uniform temperature field usually ignores the effect of temperature on dendrite growth, which has certain limitations. Therefore, an improved cellular automata model was used to study the effect of temperature variation on dendrite growth in a non-uniform temperature field. The dendrite morphology, dendrite tip growth rate and solute distribution in melt were compared and analyzed under non-uniform temperature field and uniform temperature field. The results show that the dendrite morphology and solute distribution in melt are significantly changed with the change of temperature during the growth process of single dendrite. When the initial undercooling degree is 10K in the undercooled melt, the dendritic arm length of the solidification terminal reaches 1030μm at a cooling rate of 10K/s, which is increased by 49.3% compared with the dendritic arm length of uniform temperature field under the same conditions. When the cooling rate reaches 30K/s, the length of dendrite arm reaches 1460μm, which increases by 111.6%. As the cooling rate increases, the concentration of solid solute in the dendrite increases, but the solute fluctuated at the solid-liquid interface, which results in the non-conservation of solute concentration at the solid-liquid interface and irregular distribution, and more lateral dendrite arms appear. For the growth of multi-dendrite, the solid fraction of the alloy reaches 45% at the cooling rate of 10K/s, which is 15.9% higher than that at isothermal condition. When the cooling rate is up to 30K/s, the solidification area of the alloy accounts for 65%, an increase of 35.9% compared with that in the isothermal state. At the same time, several dendrite arms and the coarsening of dendrite arms are observed in the model domain.

Abstract:Ti-44Al-3Ta-0.3(Cr,W) (at%) bars were prepared by the hot canned extrusion. The as-extruded (AE)and heat-treatment structure（HT）microstructure, the tensile properties and fracture morphology of the bars were investigated by SEM、XRD、TEM . The results show that the yield strength of the two kinds of microstructure decreases with the increase of the tensile temperature, and the peak stress value increases with the increase of the temperature from room temperature to 600℃. The ultimate strain value of the extrusion microstructure is slightly higher than that of the heat treatment. The brittle-toughness transition (BDT) temperature of the alloy is around 800℃. The room temperature fracture of the extruded microstructure is mainly controlled by the mixed fracture modes of inter-lamellar and tans-lamellar fracture, and there are secondary cracks on the fracture surface. The tensile temperature has affected the size, the lamellar thickness, twin and phase transformation in the two kinds of the microstructure.

Abstract:CNTs@SiC Coaxial Core-shell composite absorber was prepared by chemical vapor deposition (CVD) with monatomic silicon and functionalized multi-walled carbon nanotubes (CNTs). The one-dimensional tubular core-shell structure of CNTs@SiC is conducive to the improvement of dielectric properties and the adjustment of impedance matching performance, and effectively improves the initial oxidation temperature of CNTs. The mass ratio of Si to CNTs is a key parameter affecting electromagnetic properties of the composite. When m (Si): m (CNTs) = 1:1.5, the composite has the best absorbing performance. The effective bandwidth reaches 4.8GHz when the thickness is 1.7mm. When m (Si): m (CNTs) = 1:2, the material has the best absorbing effect in X band, with effective bandwidth up to 3GHz. The CNTs@SiC composite absorber not only has excellent absorbing effect at normal temperature, but also is expected at high temperature due to its unique one-dimensional cored-shell structure.

Abstract:The mechanical behavior and microstructure evolution of TA32 titanium alloy during superplastic deformation were investigated by uniaxial tensile tests at different temperatures (880~940 ℃) and initial strain rates (5×10-4~1×10-2 s-1). The modified Johnson-Cook constitutive model and BP neural network constitutive model were established. The results indicate that the flow stress and elongation of TA32 titanium alloy are sensitive to temperature and strain rate. The strain rate sensitivity exponent decreases with the increase of strain and increases with the increase of temperature. Increase of temperature and deformation degree promotes the α to β phase transformation and the grain growth of the two phases. Decrease of strain rate moderately increases the grain size of the two phases. The morphology of β phase grains changes significantly with the change of deformation conditions, while α phase grains remains equiaxed. The superplastic fracture mode of TA32 titanium alloy is microporous aggregation fracture caused by the growth and coalesce of cavities. The prediction accuracy of BP neural network constitutive model is higher than modified Johnson-Cook constitutive model under large scale deformation condition.

Abstract:Since the commercial application of rare earth magnesium alloys is increasing gradually, there are considerable advantages to prepare lower cost and higher performance magnesium alloys with a high abundance rare earth (RE) elements. However, the addition of RE elements completely changes the alloying order of the matrix magnesium alloy. Therefore, further study the strengthening mechanism of Ce element on magnesium alloy is required. In this work, thermodynamic stability of the may exist Mg-Ce, Al-Ce and Mg-Al phases were analyzed based on first-principles calculations, and the results were examined through SEM, XRD, EDS and other experimental methods. Moreover, the compositions and precipitation sequence of the key RE phases were deduced as consequence. Then, whether the preferentially precipitated second phase can be the nucleating core of primary α-Mg was discussed based on the mismatch theory, and the modification mechanism of Ce on magnesium alloy was revealed as result. On the other hand, the complex alloying problem in multi-component magnesium alloy system was simplified with the aid of electronegativity theory, which was associated with the alloying reactions at different temperature stages based on Al-Ce, Mg-Al binary phase diagrams and Al-Ce-Mn ternary phase diagrams. Accordingly, the strengthening mechanism of the Ce addition on magnesium alloys was clarified with the temperature as a dimension. The results of this work showed that large numbers of needle-like Al11Ce3 phase or rod-like Al10Ce2Mn7 phases would form preferentially and distribute along the grain boundaries or through grains after the adding of Ce element. However, the preferentially precipitated Al11Ce3 and Al10Ce2Mn7 phases cannot be the nucleating core of primary α-Mg which means the grain refinement mechanism was that the second phase at grain boundary prevents the growth of magnesium grain. Besides, the tensile test results showed that the formation of an Al-Ce phase and Mg-Al phase reinforced hybrid structure is beneficial to improve the ambient temperature and high-temperature mechanical properties of magnesium alloys, which could achieve by adjusting the amount of Ce element added.

Abstract:There is an urgent demand in aerospace applications to develop titanium alloy materials with high specific strength, high-temperature resistance, and wear resistance. Hence, the TC4 titanium alloy composite material was developed through fabrication by laser cladding deposition (LCD) technology, and the effect of boron (B) content on its microstructure and mechanical properties was studied. The results show that the B element can significantly reduce the grain size of the TC4 titanium alloy as fabricated by LCD. The increment of B content exhibits grain size reduction from 1294 μm to 28.6 μm with 1% wt B content, which gradually weakens the columnar grain. The TiB acicular becomes precipitate at the β grain boundary as the B content increases. Consequently, the TC4 composite material"s hardness increases from 313.23 HV to 359.24 HV and tensile strength from 848 MPa to 1119.5 MPa. The research in this paper provides theoretical support for the application of additive manufacturing of high-performance platform-based alloy components with complex structures in the aerospace field.

Abstract:The hexagonal phase with close packed structure has a obvious anisotropic characteristic, and the primary α phase content in TA19 titanium alloy bar at room temperature is as high as 70%. Therefore, the α texture has a significant effect on the mechanical properties of TA19 titanium alloy bar, and effective texture prediction can greatly reduce the production cost and improve the production efficiency, and it can also help to determine the mechanism of texture formation. In this paper, the multi-scale coupling method of macroscopic finite element model and mesoscopic visco-plastic self consistent model was used to simulate the forging process of large TA19 titanium alloy bar under close to the actual process conditions, and the β→α phase transition process was considered. At first, the simulated β deformation textures of the center, R/2 and edge of the bar above the phase transition temperature were obtained. And then, according to the Burgers orientation relationship, the laws of variant selection of different positions of bar during cooling were obtained by analyzing the β texture characteristics of different positions, and the α transformation textures were obtained. Finally, combining with the α texture characteristics at the center, R/2 and edge of the bar after transformation, the orientation evolution of α grains with different initial orientation was analyzed when different slip systems started, and α deformation textures were obtained. By comparing the final simulation results with the actual forging results, it was found that they are in good agreement. It illustrated that the model had good reliability in predicting the deformation and transformation textures of titanium alloy bars during forging, which had great significance for controlling and adjusting the texture of titanium alloy bars during forging.

Abstract:60NiTi alloys were fabricated by spark plasma sintering (SPS) at 1000 ℃. The effects of the sintering pressure on the microstructure, microhardness and tribological properties of 60NiTi alloys were also investigated. The phase structures and microstructures of 60NiTi alloys were analyzed by X-ray diffractometer (XRD) and scanning electron microscopy (SEM). The microhardness and tribological properties of 60NiTi alloys at different sintering pressure were evaluated by microhardness tester and ball-on-disk wear tester. The wear volumes were calculated by three-dimensional white light profilometer. The wear morphologies of 60NiTi alloys were analyzed by SEM with energy disperse spectroscopy (EDS) and three-dimensional white light profilometer. The experimental results showed that the microstructures of 60NiTi alloy prepared by SPS was uniform and the NiTi phase and Ni3Ti phase were presented in the microstructures. The microhardness of 60NiTi alloys were increased with the increase of the sintering pressure. The microhardness of 60NiTi alloys has the biggest value of 534 HV0.2kg at the sintering pressure of 50MPa. The wear rate and wear scar depth of 60NiTi alloys decreased as the sintering pressure increased. However, when the sintering pressure reached to 50MPa, the wear rate and wear scar depth of 60NiTi alloys are the smallest, which are 0.76×10-6 mm3/N?m and 15 μm, respectively. The wear mechanisms of 60NiTi alloys were abrasive wear and adhesive wear through the wear surfaces analysed by SEM and EDS.

Abstract:The effect of rolling at room temperature on the microstructure evolution and mechanical properties of TiNi alloy was investigated by optical microscopy (OM), X-ray diffraction (XRD), differential scanning calorimetry (DSC) and transmission electron microcopy (TEM) technique. The results indicate that the B2 austenite phase to B19" martensite phase transformation has occurred in the TiNi alloy; when the deformation is intensified, the non-uniform deformation of microstructure increases, and nanocrystalline and amorphous phases appear. Cold-rolling TiNi alloy exhibits only the elastic deformation and plastic deformation stages of the austenite and martensite phases during the stretching process, and the stress-induced martensite phase-transformation disappears, showing a continuous yielding process. The TiNi alloy have different deformation mechanism at different deformation mechanism: when the strain is 0<ε≤0.3, the main deformation mechanism of the alloy is dislocation slip; When the strain ε>0.3, the deformation mechanism is the combination of twinning and dislocation slip.

Abstract:With as-prepared SnO2 and Bi2Sn2O7 as reinforcing phase powder and chemical silver powder as matrix phase, series of Bi2Sn2O7 modified Ag/SnO2 electrical contacts were prepared by high energy ball milling assisted sintering process. The effects of Bi2Sn2O7 content, milling time and sintering parameters on the microstructure and physical properties of Ag/SnO2-Bi2Sn2O7 electrical contacts were investigated. The results show that with milling time ranged from 1h up to 12h, the morphologies of Ag/SnO2-(6 wt.%) Bi2Sn2O7 composite powder changed from granular to flake structure. The resistivity of Ag/SnO2-(6 wt.%) Bi2Sn2O7 electrical contact increased gradually but the density decreased. The increase of sintering temperature and the increase of Bi2Sn2O7 doping content could benifit for reducing the resistivity of Ag/SnO2-Bi2Sn2O7 contacts. With the Bi2Sn2O7 doping content of 12 wt.% and the sintering temperature at 900℃, the resistivity of Ag /(12 wt.%) Bi2Sn2O7 reaches the optimal value of 2.24 μ Ω·cm. According to the initial arc ablation testing after 50 cycles, compared with pure Ag/SnO2, the ablation area of the modified Ag/SnO2-Bi2Sn2O7 samples did not rapidly expand to the whole surface, and when the Bi2Sn2O7 content was 6 wt.%, the ablation area of Ag/SnO2-(6 wt.%) Bi2Sn2O7 sample is the smallest. While, with the Bi2Sn2O7 content of 12 wt.%, the Ag /(12 wt.%) Bi2Sn2O7 sample appeared obvious splash phenomenon, which may be due to its lower hardness of 82.38HV0.3.

Abstract:The preparation of highly efficient and stable non-precious metal catalysts is essential for the development of electrocatalytic water-splitting to produce high-purity hydrogen. In this work, NiMo/TNAs nanohierarchical arrays were constructed by simple anodic oxidation and electrodeposition route, The research of its hybrid cocatalyst is envisioned to bestow more active sites with appropriate crystal engineering and modi?ed electronic properties for enhancing catalytic performance. NiMo alloy is firmly coated on the unique curved and ordered interface of TiO₂ nanotube arrays (TNAs) by electrodeposition, When the deposition current and the concentration of Mo ions in the electrolyte change, the state and catalytic ability of NiMo in TNAs also change,the study proved that the samples prepared by depositing 1 min under the parameters of deposition current density of 15 mA.cm^_-2 and Mo ion concentration of 4g.L^_-1 show higher HER catalytic performance. The electrode exhibits the relatively small onset overpotential of 55 mV and presents an overpotential of 110 mV and 227 mV at 10 mA.cm^_-2 and 100mA.cm^_-2 HER current density, also remained an excellent stability with no performance degradation after scanning for 15h at a constant potential. NiMo alloy particles deposited on the curved sidewalls with uniform distribution of TNAs is demonstrated to be an effective method to prepare the cheap and efficient electrocatalyst.

Abstract:As a novel composite ceramic, B4C/Al has been widely used in the lightweight protective armour due to its excellent physical properties such as high hardness, high fracture toughness, and low density. In order to obtain the mechanical properties of B4C/Al composites under dynamic loading, the waveforms under different impact speeds and the fracture morphology with the split Hopkinson pressure bar (SHPB) testing and electron microscope scanning (SEM) has been performed, as well as the stress-strain curve characteristics and failure modes of the materials under different strain rates. Furthermore, the influence of Al content on the dynamic compressive strength of the material has analyzed. The results can provide reference for the design and application of B4C / Al composites.

Abstract:With the development of industries such as mining and urban infrastructure construction, higher requirements have been put forward for the wear resistance of mining WC-Co mining tools. It is a feasible new idea to enhance the wear resistance of WC-Co mining tools by adding diamonds. In the process of sintering the diamond-WC-Co composites, the cobalt phase acts as a catalyst to accelerate the conversion of diamond to graphite. In order to study the influence of Co on the degree of graphitization of diamond in composites, spark plasma sintering (SPS) was used to prepare diamond-WC-Co composites, the degree of diamond graphitization in composites was analyzed, and the grinding wheel method was used to study the wear performance and wear mechanism of the composites. The research indicates that diamond in the diamond-WC-Co composites can play a toughening effect; Increasing Co content will promote the densification process of the composites while reducing the hardness of the composites; As the Co content increases, the wear resistance of the composites becomes worse. During the experiment, the WC-Co matrix was first removed by abrasion, and then the diamond was worn. Diamond will enhance the wear resistance of the composites.

Abstract:In this paper, the linear friction welding of TC21 titanium alloy was investigated. The microstructure evolution of each region of the joint was analyzed by OM and SEM. The microhardness and tensile properties of the joint were tested. The results showed that a sound weld joint can be obtained using LFW. The joint was obviously divided into base metal zone(BM), thermo-mechanically affected zone(TMAZ) and weld zone(WZ); during the welding process, phase transformation and dynamic recrystallization took place in WZ, forming fine recrystallized grains, lath α precipitated at grain boundary, acicular martensite α phase precipitated inside grain,and a few residual α phase reminded at room temperature. Away from the weld center,the degree of recrystallization gradually decreased and the proportion of a phase gradually increased,the grain size gradually increased from the weld center to the end of flash. Due to the different of flash formation phase and cooling rate after welding. The microhardness of TC21 titanium alloy linear friction welded joint is arched,and the maximum value of microhardness in weld center is 460HV. The tensile test results indicated that the strength of the joint is equivalent to that of the base metal.

Abstract:The effects of 0.5~1.0 at.% W contents on the solidification microstructure and element distribution behavior in the βo,α2,γ phases of Ti-42Al-5Mn alloy (at.%, the same below) with low cost and good hotworkability were systematically studied. The results show that the refractory metal W in different positions of the alloy ingots prepared by one-step vacuum induction melting with CaO crucible is evenly distributed, and the O content is controlled in the range of 556 ~ 560 ppm. The solidification microstructure can be refined by W addition, and the lamellar structure size and content are generally decreased with the increase of W content. By analyzing the distribution behavior of alloying elements in different phases, it is found that the enrichment order of Al in different phases is as follows: γ＞α2＞βo, while those of Ti, Mn and W are all: βo＞α2＞γ. W addition cannot change the distribution behavior of Ti and Al, but will change the distribution behavior of Mn to a certain extent. The partitioning coefficients of W in α2 and βo phases are generally increased linearly with its content rised, and they meet kWα2/γ=1.4026CW(at.%)+0.4313, kWβo/γ=1.3290CW(at.%)+1.8745,respectively. In Ti-42Al-5Mn alloy, the enrichment tendency of W in βo phase is about 5.6 times that of Mn, and the enrichment tendency in phase α2 is about 7.5 times that of Mn.

Abstract:In this study, precipitates in COST-FB2 steel equilibrium conditions were calculated using Thermal-Calc thermodynamic software. The microstructure, M23C6 carbides, and Laves phase evolution of COST-FB2 steel for the rotors of the supercritical power station at 620 ℃ under different aging times were studied by scanning and transmission electron microscope; and chemical phase analysis. The effects of the microstructure and precipitates on the properties of the steel were also analiyzed. The results showed that the room temperature strength and plasticity of COST-FB2 steel changed minimally after aging, whereas the strength and plasticity at high temperature fluctuated. The impact property and hardness decreased greatly after 1 000 h of aging, but with the further extension of time decreased slightly. The martensitic lath structure of COST-FB2 steel was stable during 0-10 000 h of aging, the dislocation density and small-angle boundaries decreased, and the average particle size of M23C6 carbides increased. The Laves phase began to precipitate at 2 000 h of aging, and increased in size from 2 000 h to 10 000 h. After 10 000 h, the average diameter was approximately 410 nm, and the coarsening rate of the Laves phase was much greater than that of the M23C6 carbides. After aging for 2 000-6 000 h, the number of Laves phase in the unit area increased continuously, but after 6 000 h, the number begans to decrease; after 8 000 h, it tended to be in equilibrium. The rotor forgings of domestic COST-FB2 steel exhibited a stable microstructure and properties after aging at 620 ℃ for 10 000 h.

Abstract:The forming process of wire and arc additive manufacturing (WAAM) based on the cold metal transfer (CMT) is studied. By monitoring the arc shape, current signal and molten pool shape, the characteristics of droplet and the stress of molten pool metal in different stages of arc are studied. Based on the investigation on the force of the molten pool metal in the forming process of the suspensed structure, the propeller was manufactured and the microstructure and properties were also analyzed. The results show that the rapid prototyping of suspension structure and good mechanical properties can be obtained by precise control of Ibase and Ibase/Ipeak during the CMT process. Under the conditions of this study, the form of short-circuit transfer is the main metal transfer during CMT additive of titanium alloy, and there is no droplet transfer in the peak stage. When Ibase/Ipeak is less than or equal to 0.2, the cantilever structure with large inclination can be obtained by reducing the base current, and the maximum inclination angle of Ti6321 propeller manufactured by CMT process is 53.26°. The Ti6321 alloy fabricated by the optimized overlapping parameters has dense internal structure and no coarse columnar crystals penetrating multiple layers are found in the part. The mechanical properties of the AM parts are the same as the standard of forging, and the anisotropy between horizontal and vertical is not obvious.

Abstract:The microstructure and mechanical properties of 2195 Al-Li alloy under different aging regimes were analyed by hardness test, tensile test and transmission electron microscopy. The results show that the results show that the peak aging system of single stage aging is 160℃ × 56h and 190℃ × 16h. Its peak tensile strength is 565MPa and 541MPa, and its elongation is 6.3% and 7.1%, respectively. The tensile strength and elongation of the alloy aged at 190℃ × 4h + 160℃ × 32h are 588MPa and 13.5%. Both of them are much better than single - stage aging alloys. The elonged T₁ phase and compact region in the double stage aging alloy matrix play an important role in improving the strength. In addition, the narrow precipitation free zone along grain boundary and the cell structure inside grains are the main factors for the performance enhancement of plasticity. The double stage aging system of 190℃ × 4h + 160℃ × 32h can obtain better comprehensive mechanical properties than that of single stage aging.

Abstract:As the "heart" of the Arcjet, cathode is responsible for heating the gaseous propellant to produce propulsion. Due to the long service cycle and frequent ignition times of satellite, high requirements are put forward for the service life and erosion resistance of cathode materials. Based on W-La-Ce-Y and W-La-Y-Zr electrodes, W-La-Ce-Y-Re and W-La-Y-Zr-Re electrode materials were prepared by hydrogen reduction-median frequencySsintering. By simulating the actual working condition of the Arcjet, the arcing test was carried out at 250A current, the erosion resistance of each electrode material was studied, and the morphology of the electrode tip after arcing was observed. The results show that the rhenium electrode has less burning loss quality, better tip morphology stability, and better burning loss resistance after 2 hours of arc burning. Under SEM, it was observed that the rhenium inhibited the growth of dendrites and weakened the recrystallization degree of tungsten matrix grains. The grain orientation on the surface of rhenium electrode was more conducive to the migration of rare earth oxides; Under the metallographic microscope, it was observed that the grains at the tip of the rhenium electrode are finer, and rhenium plays a role in refining the recrystallized grains. The cathode voltage drop of rhenium electrode is lower at different currents. The addition of rhenium improves the electron emission performance of electrode materials.

Abstract:A conduction-cooled and no-insulation high temperature superconducting (HTS) dipole magnet with a 1.5T center magnetic field has been developed. It consists of a room temperature iron, HTS double pancake coils and a cryostat. The poles of iron utilize the cylindrical structure and the distance between two poles is 120mm. Each coil has 176 turns and the nominal operating current is 286A. The cold mass of coil is cooled by using a GM cryocooler and the operating temperature is below 20K. This paper describes the HTS dipole magnet design and the carrying-current capacity of YBCO tape and reports the charging and discharging test research of the no-insulation coil with and without iron core. The charging delay time constant is acquired by the experiment and the test result shows that the center magnetic field meets design requirement at the operating current of 286A.

Abstract:Due to the perfect processing property and sufficient mechanical performance, Ag based filler metal is one of the main jointing materials for brazing. The effect of rare earth Pr on the microstructure and properties of BAg30 filler metal was investigated. The results show that rare earth Pr can increase the melting temperature with ~3℃, improve the wetting spreading area of filler metal on the surface of steel substrate and obviously increase the shear strength of brazed joint, but excessive rare earth Pr would decrease the wettability and shear strength. Based on the content optimization analyze of rare earth Pr, it is found that the optimal addition amount of rare earth Pr is about 0.12%. With the observation of SEM pictures, it is indicated that the addition of rare earth Pr (≤0.12%) can refine the microstructure of filler metal, when the content of Pr is more than 0.12%, the microstructure will be coarsening obviously. The elements mapping demonstrates the uniform distribution of elements and the precipitation of PrCu₆ phase.

Abstract:As one type of continuous ceramic fiber reinforced ceramic matrix composites that emerged in the 1990s, alumina/alumina composites (Al2O3/Al2O3) have become a major category of ceramic matrix composites alongside C/SiC, SiC/SiC, etc. Compared with non-oxide ceramic matrix composites, Al2O3/Al2O3 possess unique advantages such as long-term oxidation resistance, high-temperature corrosion resistance and low cost etc, and display broad application prospects in the field of military and civilian thermal structural materials such as aircraft engines and gas turbines. This paper focuses on the research process of porous matrix Al2O3/Al2O3 (P-Al2O3/Al2O3), especially the engineering applications in recent years, and has reference significance for the future development of Al2O3/Al2O3 system in domestic. Finally, the key problems and the future development proposals of P-Al2O3/Al2O3 are summarized.

Abstract:Tantalum is a refractory metal and have broad application prospects in high temperature technology, electronic technology, corrosion resistance engineering, atomic energy and medical industries, which is due to their excellent properties, such as excellent corrosion resistance, biological characterization and dielectric properties. Additive manufacturing technology can realize the integral forming of tantalum parts with complex shapes and high utilization, and the obtained parts can be individual customization. In this paper, the principle and research states of spherical tantalum powder for additive manufacturing were introduced. The research states of microstructures and properties in tantalum and porous tantalum components were summarized and analyzed. Some current problems existed in additive manufacturing of tantalum were analyzed, and the future development of this technology was put forward.

Abstract:TiAl based alloy is one of the most competitive materials for nickel-base superalloys for aeroengines due to its low density, high elastic modulus and high specific strength performance. In this paper, the research progress of high temperature oxidation resistant coatings on TiAl alloy is summarized based on Diffusion infiltration, Laser cladding, Double glow plasma Infiltration, Atmospheric plasma spraying, Physical vapor deposition and other preparation technologies. In addition, the research direction of realizing TiAl alloy application in advanced engine is put forward according to the high requirement of materials for continuous improvement of aero-engine performance.

Abstract:In-situ TiC-TiB2/Al-12Si hybrid aluminum matrix composites were fabricated by laser deposition. The microstructures and corrosion properties of in-situ TiC-TiB2/Al-12Si hybrid aluminum matrix composites were analysized by XRD、OM、SEM、TEM and electrochemical test. The results show that the in-situ TiC particles with fine and uniform polygons and the TiB2 particles with rod-like can act as the heterogeneous nucleation core of α-Al phase to refine grains. With the increasing of in-situ TiC-TiB2 particles, the corrosion potential shifts positively, the corrosion current density decreases significantly, and the impedance modulus and phase angle increases gradually, indicating that the in-situ TiC-TiB2/Al-12Si hybrid aluminum matrix composites has better corrosion resistance.

Abstract:To improve the stability and tritium permeation resistance of the AlN single-layer coating, a Ti-AlN system coating is proposed. Ti/AlN/Ti/AlN multiple coatings with a total thickness of about 500 nm were prepared on the substrate surfaces of 316L stainless steel by magnetron sputtering. The coated samples were heat-treated under different conditions, and the microstructure and phase composition before and after heat treatment were analyzed by SEM, XRD, and AES. The deuterium permeation experiment was then conducted for all the samples. The results show that only some amount of Al3Ti products are formed at the Ti-AlN interface for all the coated samples heated at 700 ℃ or 760 ℃ for 4 h. Among all the coated samples, the coated sample with a heating temperature of 700 ℃ and heating rate of 1.5 ℃/min exhibits the best deuterium resistance performance, and its PRF (Permeation Reduction Factor) value at 600 ℃ is 536. When the heating temperature is increased to 760 ℃ or the heating rate increased to 2.5 ℃/min, the cracking of the coating will be aggravated, which lowers the deuterium permeation resistance. On the other hand, with the decrease of the penetration temperature, the PRF values of all the coated samples also decreased sharply, indicating that the deuterium gas penetration process had an obvious failure effect on the coating structure, the mechanism of which needs to be further studied.