Abstract:The welding heat-affected zone (HAZ) of C-HRA-2 nickel-based alloy under various primary peak temperatures (T_p1=1150, 1250, and 1350 °C) and the secondary peak temperatures (T_p2=850, 950, 1050, 1150, 1250, 1350, and 1450 °C) was obtained by welding thermal simulation. The effect of peak temperature (T_p) and thermal cycling times on the evolution of simulated HAZ microstructure of C-HRA-2 alloy was investigated. The microhardness of simulated HAZs was measured. The HAZ microstructure and carbide were characterized by the optical microscope, scanning electron microscope, and transmission electron microscope. Results show that the fine M₂₃C₆ carbides appear along the grain boundaries in the simulated HAZ with T_p1=1150 °C. For HAZs with T_p1>1250 °C, the γ matrix bonded with M₂₃C₆ carbides appears near the grain boundaries due to component liquefaction. When T_p2 is 1050–1250 °C, the carbides similar to those in HAZ with T_p1=1150 °C can be observed near the grain boundaries due to the difference in the solid solubility of Cr in the matrix obtained at T_p1 and T_p2. In HAZ with T_p2>1250 °C, the melted microstructure similar to that with T_p1=1250 °C can be observed near the grain boundaries. The microhardness fluctuates significantly with increasing the T_p2. The microhardness of specimen with T_p2=1250 °C is slightly higher than that of the base material, because of the grain boundary strengthening effect of the carbides near the grain boundaries.

Abstract:The microstructure evolution and mechanical properties of GH4169 alloy during cold rolling and heat treatment were investigated by scanning electron microscope, electron backscatter diffraction, and transmission electron microscope. Results show that the grains are elongated into fibers with increasing the cold rolling deformation degree, and no δ phase can be observed in the microstructure. After heat treatment, the original deformed grains are replaced by small recrystallized grains, and the grain size is decreased with increasing the cold rolling deformation degree and decreasing the heat temperature. However, the mixed grain structure appears after cold rolling deformation of 50%. When the heat treatment temperature is 950 and 990 °C, the δ phase is precipitated in the matrix. The content of δ phase is increased with increasing the deformation degree and the morphology is changed from short rods into spherical shapes. When the deformation degree is 70%, the ultimate tensile strength (UTS) reaches 1484.27 MPa, which is 1.92 times higher than that of the cold rolled alloy (772.5 MPa). However, the elongation (EL) decreases to 8.93%, and it increases to 46.47% after heat treatment at 990 °C, which is 5.2 times higher than that of the cold-rolled alloy. The optimal combination of mechanical properties (UTS=943.59 MPa, EL=52.31%) can be achieved when the cold rolling deformation degree is 50% and the heat treatment temperature is 990 °C.

Abstract:Powder metallurgy Ni-based superalloy turbine discs serve at high temperatures and high stress levels for a long time, and the comprehensive mechanical properties of the superalloy have stringent requirements, while the surface morphology and microstructure have a significant impact on the performance of the superalloy, which generally requires surface shot peening treatment. Based on this, this work systematically investigates the surface/subsurface microstructure and deformation of the FGH4113A superalloy at different shot peening intensities and explores the quantitative relationship between them. The result indicates that the dislocation pile-up occurs in the subsurface and induces the formation of deformation twins. Meanwhile, the number of deformation twins rises with the increase in shot peening intensity. Furthermore, the dislocations triggered by shot peening induce a large number of low angular grain boundaries in the deformed layer, which results in grain refinement to reinforce the superalloy hardening effect. In addition, with the increase of shot peening intensity, the characteristics of superalloy surface roughness, surface residual compressive stress, hardened layer thickness, and surface microhardness display an increasing trend and exhibit a good linear or power exponential relationship. This finding can provide data to support the regulation of shot peening parameters in the actual production process.

Abstract:Optimisation of the parameters of the selective laser melting process based on the variation of the thermal behaviour of the melt pool through numerical simulation is an effective means of improving the quality of the formed parts. So, a fully parametric finite element analysis model of the temperature field of the selective laser melting process for IN738LC alloy was developed in the APDL language of ANSYS, and the heat source model was calibrated by single melt channel forming experiments. The results show that: with the increase of laser power or the decrease of scanning speed, the linear energy density absorbed by the powder increases, the maximum temperature of the melt pool centre increases, the molten metal volume increases, and the melt channel morphology evolves from irregular intermittent to regular continuous long strip; with the increase of scanning speed or the decrease of laser power, the linear energy density absorbed by the powder decreases, the melt flow capacity decreases, and the melt pool width and The FEM simulations are in good agreement with the experimental results. When the laser power is 270 W and the scanning speed is 1150 mm/s, the single melt channel has a continuous and good shape with few defects.

Abstract:Super304H austenitic stainless steel has been widely used in superheater and reheater pipes of the ultra-supercritical thermal power unit boilers. During long-term thermal exposure, reheat cracking is prone to occur at the assembly of the pipeline weld joint. This study systematically studied the effect of temperature on the reheat cracking susceptibility of Super304H austenitic stainless steel weld metal by a pre-compressed CT specimen method. The results show that the time required for the weld metal to generate cracks at 650 ℃ is shorter than that of the weld metal at 600 ℃, leading to a higher reheat cracking susceptibility. The main reason for this phenomenon is that the grain boundary strength decays faster with time and the higher stress relaxation rate at 650 ℃, while the influence of intragranular strengthening difference at different temperatures is negligible.

Abstract:The effect of microstructure with high fraction of Σ3_ⁿ boundaries and serrated grain boundaries (SGBs) on high temperature oxidation of Inconel 617 is studied. After deformation then slowing cooling treatment, the fraction of Σ3_ⁿ boundaries can be increased to over 70% also simultaneously changing some of the rest random grain boundaries (RGBs) into SGBs with the average amplitude of 0.83μm and the average wavelength of 15.98μm. The formation of SGB is associated with the precipitation of Mo₆C和Cr₂₃C₆ carbides at RGB. The microstructure with two types of special grain boundaries (GBs) can effectively improve the high temperature oxidation resistance, which is reflected in significantly reducing the thickness of Cr₂O₃ surface oxide layer and the diffusion depth of Al₂O₃ along the GB. This is attributed to that Σ3_ⁿ boundaries, SGBs and unconnected straight RGB network can effectively retard the diffusion of Cr and O elements along the GB.

Abstract:High temperature low-cycle fatigue tests and high temperature tensile tests were designed to study the effects of high temperature low-cycle fatigue damage on mechanical properties of FGH96 powder metallurgy superalloy. The microscopic mechanism of the change of the mechanical properties of FGH96 alloy was analyzed by observing the fractographs. Results show that the yield stress and tensile strength of FGH96 alloy show an upward trend in the early stage of damage due to the effects of dislocation motion; in the later stage of damage, the elasticity modulus and tensile strength of FGH96 alloy are continuously degraded as the internal cracks increase and expand. The change of the mechanical properties of FGH96 alloy shows a clear correlation with the stress level. The microfracture analysis shows that with the increase of the damage degree, the high temperature tensile fracture mode gradually changs from ductile to brittle, and is accelerated by high temperature oxidation.

Abstract:In this study, the "twin + γ′ phase" composite structure was constructed in a novel Ni-based wrought superalloy by means of thermomechanical treatment, and the evolution of twin and γ′ phases was investigated by using EBSD and SEM. Meanwhile, the high temperature mechanical properties of the alloy at 760 ℃ were studied. The results show that the "twin + γ′ phase" composite structure can effectively improve the high temperature mechanical properties of the alloy, and with the increase of the length fraction of the annealing twin, the thickness of the twin lamellar increases, and the high temperature strength of the material decreases; When the rolled alloy (ε=68%) is annealed at 1120 ℃ for 15 min and subjected to two-stage aging treatment (650 ℃/24 h/AC and 760 ℃/16 h/AC), the length fraction of twins in the "twin + γ′ phase" composite structure is 25.38% and the average size of γ′ phase is 32.21 nm. The yield strength of the alloy increased from 775 MPa to 1184 MPa, and the elongation after fracture increased from 3.18% to 18.96%. By constructing the "twin + γ′ phase" composite structure can effectively improve the high-temperature mechanical properties of the alloy, which provides a novel strategy for improving the high-temperature mechanical properties.

Abstract:_{:The changes of microstructure and mechanical properties of GH3230 alloy plate after long-term heat exposure treatment at different temperatures (700-1000 ℃) and different times (1000-2000 h) were studied. The results show that the degree of dendrite segregation of as cast microstructure in the melting zone is significantly reduced after heat exposure treatment, andwith the increase of heat exposure temperature, the reduction effect is more obvious, and the grain structure is gradually formed. The tensile strength and yield strength at room temperature decreased and the elongation increased, which wasmainlycaused by the solubilizing of small granular (CrW)23C6 carbides in the heat affected zone and the coarsening of W6C carbides. With the increase of heat exposure temperature, the protractedrupturetimesignificantly decreases, whilethe endurance plasticity increases. The change of grain size and carbide coarsening are the reasons for fracture of welded plates at the base metal. No harmful phase such as TCP brittleness was found in the welded joint of GH3230 alloy welded plate. The alloy is suitable for long-term use as combustion chamber and blade.}

Abstract:Ni-based single crystal superalloys have been widely applied to turbine blades of aero-engines due to improved mechanical properties at high-temperature environments. There were great progresses on alloy design and sixth-generation Ni-based single crystal superalloys have been developed in the last decades. However, contents of refractory elements such as Re and Ru increase consistently. Additions of refractory elements lead to increase of cost and density of superalloys, which is not beneficial to massive application of alloys. Mo and W are potent solid-solution strengthener with lower cost, and they could serve as main strengthener in single crystal superalloys with low densities and costs. The effects of Mo and W on single crystal superalloys have been widely researched. The present work reviewed research from distribution of elements, microstructure of γ phase and γ′ phase, microstructural stability, creep properties, solidification defects and oxidation and hot corrosion resistance at high temperatures. Finally, we analyzed the current shortcomings of related research and pointed out the potential direction of future research.

Abstract:The relationship between microstructure characteristics and fatigue properties of Ti-6Al-2Sn-4Zr-2Mo-0.1Si (Ti6242s) alloy was investigated. According to the microstructure quantitative analysis results, the solution treatments at different temperatures have an obvious effect on the proportion and morphology of primary α-phase. The changes in microstructure characteristics slightly influence the tensile property and low-cycle fatigue property of Ti6242s alloy at room temperature, whereas the dwell fatigue life and the fatigue sensitivity index are sensitive to these changes. Additionally, it is verified that the relatively strong stress concentration and inhomogeneous micro-area plastic deformation occur in the Ti6242s alloy under dwell fatigue load. Moreover, the characteristics of small plane regions and the surrounding quasi-cleavage regions in the Ti6242s alloy under dwell fatigue load at room temperature are formed through the analysis of fatigue failure fracture morphologies. The related experiment results are in good agreement with the stress-strain distribution characterizations of microstructures of equiaxed primary α-phase and the surrounding soft phase/grain. Accordingly, the relatively low inhomogeneous micro-area plastic deformation in the alloy with equiaxed primary α-phase of low volume fraction is beneficial to reduce the probability of crack initiation and can delay crack propagation, thus improving the dwell fatigue property.

Abstract:The effects of Er addition on the microstructure and mechanical properties of ZL201A aluminum alloy were studied via metallographic microscope, scanning electron microscope, transmission electron microscope, energy dispersive spectrometer, and mechanical property tests. Results show that the Er addition can refine the α-Al matrix from columnar grains into fine equiaxed grains. Additionally, the θ phase (Al₂Cu) is transformed from fine network structure into the dispersed fine particle structure. When the Er content reaches 0.4wt%, the grain refinement effect reaches the maximum state and the mechanical properties of the alloy are optimal. The average grain size of α-Al matrix is 19 μm; the tensile strength and the elongation are 298.14 MPa and 6.56%, respectively. The fracture mode also changes from brittle fracture to ductile-brittle fracture, which is beneficial to the practical application of aluminum alloys. When Er content exceeds 0.4wt%, the grain size increases and the mechanical properties of alloy decrease.

Abstract:The magnetocaloric effect and phase transition properties of La_0.75Ce_0.25Fe_11.5-xAl_0.2Si_1.3Sn_x (x=0, 0.05, 0.1, 0.2, wt%) alloys were investigated. X-ray diffraction results show that with increasing the Sn doping content, the content of 1:13 main phase is decreased, and the content of α-Fe and LaFeSi phases is increased. By combining the density functional theory with experimental results, it is found that increasing the Sn doping content can increase the lattice constant and enhance the exchange interactions between adjacent atoms, thereby increasing the Curie temperature. When the magnetic field is 2 T, the maximum magnetic entropy change in the system is 13.59 J·kg^-1·K^-1 and its relative cooling power is 154 J/kg, showing great potential as magnetic refrigeration material. Based on the Banerjee criterion and the field dependence index n of isothermal entropy change, it is concluded that when the Sn doping content is 0.05wt%, the first-order phase transition changes to the second-order phase transition of the alloy. The phase transition behavior of the alloy is very sensitive to the Sn content, and multi-stage series refrigeration can be achieved by adjusting the doping content.

Abstract:To investigate the effect of Si content on the high-temperature corrosion resistance of Ni-Cr-Mo alloy cladding layers, four cladding layers with different Si contents were prepared by laser melting technique. The corrosion resistance of the four cladding layers was tested by the mass loss method in a simulated waste-to-energy corrosive environment at different temperatures. Through the analysis about the characteristics of corrosion products of four cladding layers generated at 600 and 650 °C, it is found that the Si addition is beneficial to the stability of the Cr-rich oxide in the corrosion products. The adhesion of Cr-rich oxide to the substrate can also be enhanced through the pinning effect, thus effectively improving the corrosion resistance of cladding layer. However, excess Si addition has the negative effect. When the temperature is above 600 °C, the cladding layer with 3wt% Si shows the optimal corrosion resistance. This phenomenon is attributed to the formation of SiO₂ protective layer in the corrosion layer, which improves the corrosion resistance of cladding layer with 3wt% Si. Because of the small Si addition amount and the severe Si segregation, the effective SiO₂ protective layer cannot be formed in the cladding layers with 1wt% and 5wt% Si, respectively.

Abstract:To investigate the corrosion characteristics and anti-fouling properties of Cu-Mn cladding layers with different Mn contents, the laser cladding technique was used to prepare Cu-Mn cladding layers with homogeneous composition and low dilution rate. Electrochemical tests, salt spray corrosion experiments, corrosion morphology observations, and copper ion release tests were conducted to investigate the corrosion characteristics of Cu-Mn cladding layers with different Mn contents in 3.5wt% NaCl solution. The effect of Mn on corrosion products and copper ion release rate was particularly studied. Results show that the corrosion resistance of cladding layers is decreased with increasing the Mn content during the electrochemical tests. In the salt spray corrosion experiments, the corrosion degree of the Cu-Mn cladding layer is deepened with increasing the Mn content, and the average mass loss is increased. The corrosion morphology of cladding layers after electrolytic corrosion was observed. Compared with those of Cu-Mn cladding layer with low Mn content, the corrosion products generated from Cu-Mn cladding layer with high Mn content have more sparse structure, the number of crack holes is larger, and the corrosion products are easier to peel off. In the copper ion release test, all cladding layers can inhibit the growth of sea creatures. The higher the Mn content, the greater the copper ion release rate, presenting great application potential in anti-fouling materials.

Abstract:The microstructure evolution and properties of continuous columnar-grained (CCG) polycrystalline copper during intense drawing deformation at room temperature were investigated by optical microscope, scanning electron microscope, Vickers microhardness tester, and universal tensile testing machine. The stored energy was calculated according to the structural parameters of dislocation cells in different textures based on high-resolution electron backscattered diffraction. Results show that CCG microstructure is gradually thinned into fibrous tissue. The as-cast CCG polycrystalline copper has tensile strength of 168 MPa, elongation of 52%, and conductivity of 103%IACS. After the drawing deformation of 99% at room temperature, the tensile strength of CCG polycrystalline copper increases to 455 MPa. However, the elongation reduces to 3%, and the conductivity decreases 96.8%IACS. Both the transverse and longitudinal sections of CCG polycrystalline copper have <001> original preferred orientation. A large number of fiber textures of <111> orientation and a small number of fiber textures of <001> orientation are formed with increasing the drawing deformation amount. Cube texture of the transverse section gradually decreases, and S texture and Copper texture gradually increase. Meanwhile, the Cube texture and Goss texture of longitudinal section are gradually transformed into Brass texture, Copper texture, and S texture. The kernel average misorientation (KAM) value at grain boundaries and in the deformation bands is large. Additionally, with increasing the deformation amount, KAM value is gradually increased and the stress is more concentrated. Under the same deformation conditions, the transverse section has higher stored energy than the longitudinal section does, and <001> orientation fiber texture has lower stored energy than <111> orientation fiber texture does. After the strong plastic deformation, CCG polycrystalline copper still has a large number of deformation textures with “soft” <001> orientation, which is an important reason for its low work hardening rate and excellent cold deformation ability.

Abstract:The deformation microstructure and texture evolution of single crystal copper after cryogenic equal channel angular pressing (Cryo-ECAP) process were characterized by optical microscope, scanning electron microscope, X-ray diffractometer, and electron backscatter diffraction. The mechanical properties and conductivity properties were analyzed. The microstructure transition mechanism and its effects on the mechanical properties and conductivity properties were discussed. Results show that the directional shear bands formed in the early stage of Cryo-ECAP process seriously affect the microstructure transformation during the subsequent deformation. With increasing the strain, a high-density dislocation pile-up is formed in the shear bands during deformation by route A, and the proportion of characteristic grain boundaries is increased. The dislocations in the shear bands during deformation by route B_C present strong interactions, and the orientation of shear bands is dispersed after the deformation by route C. After 6 passes of deformation, the strong {111}<112> texture forms in the microstructure of single crystal copper, the strength increases from 126.0 MPa to 400.2 MPa, and the conductivity remains of above 98%IACS. After Cryo-ECAP, the directional shear bands form in the texture and the high-density dislocations are produced. The entanglement of dislocations effectively prevents the dislocation slip, and therefore the grains maintain the characteristics of single crystal.

Abstract:First-principles simulations were conducted to investigate the micromechanics, thermodynamic, and electrical characteristics of L1₂-Al₃Zr/Al alloy. The computional results show that the interface with bulk-like atomic organization possesses excellent adhesion and the highest interface strength. During the machining process, the interface system preferentially fails at the Al side. According to the non-relaxation tensile test results, the L1₂-Al₃Zr(001)/Al(001) interface system has the highest tensile stress (16.78 GPa). However, after the relaxation tensile test, the L1₂-Al₃Zr(110)/Al(110) interface system has the highest tensile stress (10.18 GPa). Additionally, covalent and metallic bonds are generated between the atoms at interface based on the differential charge density and electronic localized function. The formants of interfacial atom orbitals show that the Al and Zr interface atoms have s-p-d or s-p hybridized orbitals.

Abstract:To improve the microstructure compactness and wear resistance of the micro-arc oxidation (MAO) coating on the surface of TC21 alloy, a laser remelting modification was performed on the surface of the MAO coating. The microstructure, composition, phase composition, hardness, friction, and wear properties of the remelted coating were characterized. The results show that the laser remelted coating consists of three layers: outer layer, inner layer, and heat-affected layer, of which the outer and inner layer is mainly composed of Al2TiO5, rutile-TiO2 and α-Al2O3, and the heat affected layer is mainly composed of α-Ti and the transformed β phases. The hardness of the remelted MAO coating increases significantly. The friction coefficient of the remelted coating is lower than MAO coating and TC21 substrate in the wear test. The wear mechanism of remelted coating is adhesive wear, accompanied by slight abrasive wear. Laser remelting MAO coating significantly improved the friction and wear properties of TC21 titanium alloy.

Abstract:The mechanical properties and corrosion resistance of a novel Al-Zn-Mg-Er-Zr alloy under different aging processes were systematically studied. The microstructure of the alloy was analyzed by using EBSD、XRD, SEM , TEM to understand the relationship between the best comprehensive properties of the alloy and its microstructure mode. It is found that the excellent two-stage aging process is 90℃/12h+145℃/18h. The related mechanical properties including ultimate tensile strength (UTS) and elongation were 388 MPa and 14.0%. The susceptibility to exfoliation corrosion is PB. At the same time, the main strengthening phase（G.P zone and η′ phase）of the alloy are numerous precipitated in matrix, the η phase at the grain boundary is discontiguous distribution.

Abstract:The aluminum / magnesium dissimilar metal composite structure has great application value in the field of structural lightweighting. In this paper, a novel friction stir spot welding - brazing (FSSW-B) technology was used for lap spot welding of aluminum / magnesium dissimilar metals. At the same time, it was compared with friction stir spot brazing (FSSB) technology to study the effect of the existence of the stirring pin in the welding tool on the microstructure and Mechanical properties of the joint. The middle layer of the interface of FSSW-B joint is divided into two parts: the upper interface is mainly composed of MgZn2, and the lower interface is mainly composed of Mg7Zn3; the FSSB joint is mainly composed of MgZn2 phase. The fracture mode of the joint is mainly interface peeling fracture, and the eyebrow-shaped fracture mode appears due to the existence of the stirring pin. The existence of the stirring stir improves the tensile shear resistance and fatigue performance of the joint. The maximum tensile shear force of the FSSW-B joint is 7600 N, and the fatigue limit is 3366.6 N; The contribution rate of stirring to tensile shear performance is 53.5%, and the contribution rate to fatigue performance is 11.4%; The existence of stirring pin in FSSW-B increases the dispersion of joint fatigue properties.

Abstract:Deep eutectic solvents (DESs) are a new class of ionic liquid (IL) analogues that show a wide electrochemical window and the unique physicochemical properties, and with promising for applications in electrodeposition. Herein, a choline chloride-urea based DES was proposed as a medium for electrodeposition of three rare-earth metals (yttrium, samarium and terbium). All three metals were successfully deposited in the DES by cyclic voltammetry and potentiostatic methods. The results indicate that the electrodepositions of yttrium, samarium and terbium in the DES are diffusion controlled processes, and the diffusion coefficient (D_o) of yttrium, samarium and terbium is 7.3744×10^_-13 1.1032×10^_-12 and 9.2936×10^_-13 cm^₂/s, respectively. The deposits of three rare-earth metals with two-dimension nanonetwork structure were obtained by cyclic voltammetry and potentiostatic methods. This study provides a new approach into electrodeposition and extract and purify of rare-earth metals.

Abstract:Ti-6Al-4V(wt.%)/Ti-43Al-3V-2Cr(at.%) composite plates with no interfacial defects were successfully prepared by a high-reduction hot-rolling method. Microstructure and mechanical properties were studied. The experimental results show that no obvious defects in the interfacial region are observed, and the Kirkendall phenomenon is successfully avoided. The interface thickness of the composite plate is about 230 μm, according to different phase compositions, the interface is divided into two regions, one of which is near the interface of Ti6Al4V alloy and is mainly composed of α/α2 + β/B2 phase; Interface 2 is near the interface of TiAl alloy, and mainly consists of α/α2 + β/B2 + γ phase. The interface region structure is due to the diffusion of Ti element in Ti6Al4V alloy to TiAl alloy layer and the diffusion of Al and Cr elements from TiAl layer to Ti6Al4V alloy layer. The Vickers hardness and three-point flexural strength of the composite panels were tested with different loading methods. The experimental results show that the interface 1 has the highest microhardness, and the composite plate exhibits the best bending resistance when the surface of the transverse specimen is loaded, and the bending strength reaches 1150.82 MPa. The mechanical properties were analyzed and discussed in detail in combination with the microstructure characteristics.

Abstract:In order to improve the irradiation damage resistance and irradiation hardening resistance of the welds of China Low Activation Martensitic steel (CLAM), the CLAM steel welds before and after heat treatment exposed to He+ with energy of 70-KeV to a dose of 1×1017 ions/cm2 at room temperature were analyzed by atomic force microscopy (AFM), scanning electron microscopy (SEM), grazing incident X-ray diffraction (GIXRD), tensile and nano-indentation techniques. The results show that micro defects such as voids are produced in different weld metals after ion irradiation, and the mechanical properties are reduced in varying degrees. After heat treatment, the weld of CLAM steel has the characteristics of smaller grain structure and higher grain boundary density, which hinders the mutual aggregation of micro defects. The defects formed in the weld are more evenly distributed and smaller in size. The weld always has better mechanical properties before and after irradiation. It is a feasible idea and method to refine weld grain through heat treatment process and improve the ability of weld to resist irradiation damage and irradiation hardening.

Abstract:In this paper, the regulation of oxygen content on the surface of tantalum foil was studied by mechanical polishing and chemical polishing. The results show that it is difficult to obtain relatively clean tantalum surface by mechanical polishing, and tantalum film with low oxygen content can be obtained by argon ion sputtering. Chemical polishing can obtain a relatively clean tantalum surface. The Pd/Ta composite membrane was prepared by electroless plating on the surface of tantalum foil after chemical polishing. In the experiment, by controlling the electroless plating time, a complete and uniform palladium membrane without holes was obtained on the surface of tantalum foil, and the thickness of the palladium film is about 2.8μm.

Abstract:The direct friction weldability of TiAl alloy and 42CrMo is poor, so the friction welding process of TiAl and GH3039/K418/N80A/N6 dissimilar materials was studied by introducing superalloy GH3039, K418, N80A and N6 as intermediate materials. The hardness, microstructure, composition and mechanical properties of welded joint were analyzed by hardometer, scanning electron microscope and universal tester. Studies had shown that complex intermetallic compound layers were formed at the weld interface of TiAl alloy and dissimilar materials; Additionally, the friction weldabilities of TiAl with GH3039 and N80A are better than that with K418 and N6; GH3039 is selected as the intermediate material to improve the friction weldability of TiAl alloy and 42CrMo dissimilar material based on a) the linear expansion coefficient that varies with temperature, b) the tensile strength of the welded joints with TiAl, and c) the friction weldability with structural steel 42CrMo. By introducing the intermediate material, the integral rotors of TiAl turbine + 42CrMo shaft are obtained, which represents a practical application of TiAl alloy in the field of the turbocharger.

Abstract:The hot rolled plates of TC4 titanium alloys were welded by friction stir welding. The wear of tool of DZ22 superalloy stirring head characterization was carried out by weight loss measurement, 3D photographic technique and microscopic observations during friction stir welding of TC4 titanium alloy. This experiment has been studied Influence of welding distance tool wear in friction stir welding of TC4 alloy. The results indicate that severe tool wear deformation occurred after welding 180mm. The wear of tool is positively correlated with welding distance. The length of tool pin was shortened by 0.24mm and the wear rate was 0.97%. The depth of tool shoulder was shortened by 0.4mm and the wear rate was 1.73%. The weight of tool was reduced by 0.15g and the wear rate was 0.74%. In the process of friction stir welding of TC4, high temperature and high pressure are the main reasons for the wear of tool.Tool wear types are mechanical wear and tear、abrasive wear、adhesion wear and oxidative wear. The wear of tool is usually the result of the interaction of these wear. The wear of tool will pollute the FSW joints and form defects, thus affecting the performance of the FSW joints.

Abstract:The variations of the heat storage and heat transfer properties such as heat capacity, thermal conductivity, and thermal stability of Platinum electrode for oxygen sensor with temperature, time and grain radius are studied by using the theory and method of solid-state physics, and the effect of anharmonic vibration of atoms on the heat storage and heat transfer properties and the thermal stability is discussed. The results show that the heat capacity of Pt electrode first increases with emperature, then tends to be constant, and decreases with grain radius and time. The thermal storage stability coefficient of the electrode material increases sharply at first and then decreases rapidly with temperature, and finally tends to be constant. When the temperature is about 60K, the thermal storage stability is the worst. The thermal conductivity of Pt electrode material decreases sharply at first and then tends to be constant with temperature, increases with grain radius, and decreases with time. The contribution of the surface layer to thermal conductivity decreases sharply at first and then tends to zero with temperature. The anharmonic effect of the electrode material reduces the heat capacity, while increases the thermal storage stability coefficient and thermal conductivity. The results obtained in this paper are basically consistent with that in other literatures, and the conclusions can provide theoretical guidance for the stability of solid electrolyte oxygen sensors.

Abstract:The growth process of Cd0.9Mn0.1Te crystal by vertical Bridgman method (VBM) was simulated in detail by Fluent software. A two-dimensional finite volume numerical model was established to discuss the heat transfer, flow and growth interface of the melt in the crucible. The effects of three different temperature gradient conditions (5 K / cm, 10 K / cm and 15 K / cm) on the solid-liquid interface were analyzed. The results show that under the model calculation conditions, with the increase of temperature gradient, the trend of interface concave to liquid region increases in the middle growth period, which can better suppress convection. With the crystal growth, the melt ratio will continue to decrease, the melt flow rate near the growth interface increases gradually, and the flow velocity fluctuation increases gradually. The experimental conditions were improved according to the simulation results, and CdMnTe crystals with good quality were finally grown.

Abstract:The force of fluid particles in the filling process of horizontal centrifugal casting was analyzed, and the precipitation separation time of different kinds of inclusions and optimal pouring temperature were deduced according to the movement law of inclusions. The movement trajectory of inclusions in the filling process of horizontal centrifugal casting was established using ProCAST software, and the numerical simulation and process optimization of the movement trajectory and final residence position of inclusions in centrifugal casting pipes under different rotating speeds were carried out. Under the condition of these process parameters, the actual casting experiment of centrifugal cast pipe was carried out, and the inclusion distribution information was obtained by optical microscope (OM) and scanning electron microscope (SEM-EDS). The microscopic analysis results of inclusions in actual castings were consistent with the data simulation, which verified the effectiveness of the prediction and simulation results. The results showed that the smaller the specific gravity of inclusions and the larger the particle size, the shorter the separation time. It was found that 5 μm SiO2 inclusions were most likely to be thrown out of the liquid metal under the action of centrifugal force and finally stay on the inner surface of the cast pipe. The optimal pouring temperature for L605 centrifugal cast pipe was 1580 ℃, and the optimal centrifugal speed was 2800r/min.

Abstract:A fully coupled thermo-mechanical numerical model is developed for the butt friction stir welding (FSW) of 5A06 aluminum alloy and AZ31B magnesium alloy based on the coupled Eulerian-Lagrangian (CEL) method, and the temperature field and material mixing flow characteristics during FSW process are studied by numerical simulation and experimental tests. The temperature cycle curves, the weld surface morphology and the mixed distribution of dissimilar materials on the cross section obtained by numerical simulation are in good agreement with the experimental results. On this basis, the particle tracking method is used to analyze the mixing flow behavior of dissimilar materials. The results show that the high temperature zone is located in the region below the tool shoulder, and the temperature on the retreating side (Mg side) is lower and its gradient is larger. The fusion line of dissimilar materials on the top surface is inclined to the advancing side (Al side). The material near the pin flows significantly and most of the materials deposit evenly on the advancing and retreating sides behind the pin. The mixing flow of the materials on the advancing and retreating sides in the horizontal and vertical directions finally forms the zig-zag interface characteristics of the two materials.

Abstract:Transient liquid phase (TLP) diffusion bonding of TC4 titanium alloy was realized using an electrodeposited Ni/Cu layer as interlayer. The effects of Cu interlayer thickness on interfacial microstructure and mechanical property of TC4 joint were studied by scanning electron microscopy, energy disperse spectroscopy and X-ray diffractometer, and the reaction mechanism was clarified by Ti-Cu and Ti-Ni binary phase diagram. The results show that the typical interfacial microstructure of the joint is TC4/α-Ti+Ti2(Cu, Ni)/TC4, and Ni element exists in the form of solid solution. With the increase of the thickness of electrodeposited Cu layer, the width of diffusion layer and welding seam increased, and the voids in the center of the joint disappeared. Continuous Ti2(Cu, Ni) intermetallic layer appeared in the reaction layer and its width increased gradually. The tensile strength of the joint increased first and then decreased, reaching the maximum value of 500 MPa when the thickness of Cu layer was 15 μm. Fracture analysis showed that all of the bonded joints fractured at the welding seams in the form of cleavage modes.

Abstract:Bayan Obo rare earth tailings contain Fe, Ce and other active elements conducive to catalytic denitration. As a natural mineral, it is environment-friendly and low-cost. It is a natural raw material for denitration catalyst, but the temperature window of rare earth tailings catalyst is narrow (350-450℃). In order to broaden the temperature window of rare earth tailings catalysts, a series of Ce-M (Nb, Co) modified rare earth tailings catalysts were prepared by hydrothermal method. Exploring the effect of element ratio and element type on denitrification performance. In particular, the experimental materials are Bayan Obo rare earth tailings, cerium nitrate, niobium oxalate and cobalt nitrate. The mixed solution of Bayan Obo rare earth tailings and cerium nitrate is made, poured into the reactor, and then placed in the muffle furnace, hydrothermal at 120℃ for 12h. After washing with water and drying at 80 ℃, the Ce modified rare earth tailings catalyst was prepared. The preparation methods of other modified rare earth tailings catalysts are the same. The modified rare earth tailings were characterized and analyzed by BET, XRD, XPS, H2-TPR and NH3-TPD. Finally, the NH3-SCR mechanism of Ce-Co modified rare earth tailings was explored by in situ DRIFTS technology. The steady-state reaction is carried out at 350℃ and the transient reaction is carried out at 50-400℃, which can analyze the existing forms of adsorbed NH3 and NOx species in the catalytic process and their changes with temperature. Therefore, the NH3-SCR reaction mechanism of Ce co modified rare earth tailings catalyst is analyzed. The results show that the maximum denitration efficiency of Ce-Nb (2:1) modified rare earth tailings is 85% at 300-400℃, and the denitration efficiency of Ce-Co (2:1) modified rare earth tailings can reach 90% at 250-400℃. The addition of Nb and Co improved the dispersion of CeCO3F on the catalyst surface and exposed more active adsorption sites. At the same time, the interaction between elements promotes the transfer of electrons. The existence of Nb5+ hinders the reduction of Ce4+, regulates the redox performance, and makes the Ce-Nb modified rare earth tailings have excellent N2 selectivity. The addition of Co improves the redox capacity of the catalyst and increases Co3+. Further, the adsorption strength of Br?nsted acid site is improved. NH4+ and Co3+-NH2 can react with NO first, form intermediate products such as NH3HNO and NH2NO. The surface of the catalyst follows both E-R mechanism and L-H mechanism, and E-R mechanism is dominant.

Abstract:The VB group (Nb, V, Ta) refractory metals have higher hydrogen permeability and lower price than commercial Pd, so they have become a new generation of preferred hydrogen separation membrane materials to replace palladium. In order to prepare high flux hydrogen separation alloy film on a large scale, the ingot alloy was first cold rolled to obtain large size flat film, and then the flux efficiency of alloy film was improved by annealing treatment to improve permeability. In this paper, the research progress of cold rolling formability, rolling and subsequent annealing microstructure evolution and hydrogen permeability of alloys are reviewed, the composition effect of cold rolling film formation is analyzed, and the relationship between microstructure and permeability of cast, cold rolling and annealing alloys is described. The problems of developing high flux hydrogen separation alloy membranes by rolling subsequent annealing to improve the microstructure were discussed. Finally, the prospect of cold rolling and subsequent annealing to realize the large-scale production of low thickness and high permeability hydrogen separation alloy membranes at low cost was prospected.

Abstract:In recent years, the problem of bacterial resistance has become increasingly serious, which poses a great threat to human health. Faced with the decline in the effectiveness of traditional antibacterial drugs, the development of a new antibacterial material has become a frontier research topic. Metal-organic frameworks (MOFs) are porous coordination polymers composed of metal ions and organic ligands, which is considered a promising antibacterial material. In recent years, researchers have prepared MOFs and their composite materials with different structures, which have been widely used in various antibacterial fields. In this paper, based on the action mode and antibacterial mechanism of MOFs materials, the application of MOFs materials and their coatings in biological antibacterial field was reviewed. Meanwhile, the development trend of this field has been forecasted.

Abstract:Binary transition metal borides have an important application prospect in aerospace field because of their high melting point, high hardness and high thermal conductivity, but their intrinsic brittleness and poor oxidation resistance seriously restrict their high temperature application in extreme environment. MAB phase is a new ternary transition metal boride obtained by introducing IIIA and IVA atoms into binary boride cells, which shows many excellent properties like ceramics and metals. In all the MAB phases, MoAlB has become the research focus due to its excellent fracture toughness, oxidation resistance, damage tolerance and machinability. Thus, the preparation methods and some basic properties of the MoAlB powder, bulk and coating, including physicochemical properties, mechanical properties, friction and high temperature oxidation resistance, were summarized in this paper. Additionally, the modification method and mechanism of MoAlB materials were discussed in order to clarify the key problems and possible solutions in the preparation and application of MoAlB materials, and the potential application fields of MoAlB materials were also presented.

Abstract:Taking the WC-Co-Ti3SiC2 cemented carbide dropped with 3.0wt.% Ti3SiC2 as the case, the effect of sintering temperatures (1350~1470 oC) on the microstructure, density and mechanical properties of WC-Co-Ti3SiC2 cemented carbide were investigated. The results show that as sintering temperatures increase, the fractions of decomposed Ti3SiC2 as well as volume fractions of (W,Ti)C and WSi2 phases in as-received WC-Co-Ti3SiC2 cemented carbides gradually increase. Meanwhile, the increase of sintering temperature results in the increase of the WC mean grain size. The hardness of WC-Co-Ti3SiC2 cemented carbides increases and then decreases with the increase of sintering temperature, while the fracture toughness decreases gradually. When the sintering temperature is 1410 oC, the density of WC-Co-Ti3SiC2 is optimum, and the porosity is 0.47 %. Meanwhile, the 1410 oC is optimum sintering temperature for the mechanical properties of WC-Co-Ti3SiC2 cemented carbides. The hardness and fracture toughness are 2076.36 kgf/mm2 and 10.15 MPa·m1/2, respectively. The enhancement in hardness is attributed to the increase in density of cemented carbides, while the reduction in fracture toughness result from the increase in the content of brittle phases (W,Ti)C and WSi2 in the cemented carbide.

Abstract:Porous NiTi alloy was prepared by the gel injection method using titanium powder and atomized nickel powder as the original powder and hydroxyethyl methacrylate (HEMA)-1,6-hexanediol diacrylate (HDDA) as the gel system. The effects of initiator, catalyst, curing temperature and solid volume fraction on the curing process were investigated. The results showed that the curing time decreased with the increase of initiator and catalyst addition, and the best amount of catalyst N,N-dimethylaniline (DMA) was 1.5 wt.%, and the amount of initiator tert-butyl peroxybenzoate (TBPB) was 2 wt.%; The curing reaction was accelerated with the increase of curing temperature and solid phase volume fraction; Based on the DSC test results, the apparent activation energy of the curing reaction of the HEMA-HDDA-TBPB-DMA gel system was obtained as 61.52 kJ/mol, and the reaction order was 0.91. Porous NiTi alloy with porosity of 32.68%, compressive strength of 331 MPa and three-dimensional connected two-stage pore structure was prepared using 50 vol.% Ni Ti slurry under the optimal curing process conditions.