Abstract:Double-side ultrasonic shot peening (USSP) was performed on a commercial-purity Zr plate with 2 mm in thickness. The effects of USSP on microstructure evolution and fatigue crack growth (FCG) behavior were investigated. Microstructure evolution was characterized by optical microscopy, laser confocal microscope, electron back-scatter diffraction, transmission electron microscope, and X-ray diffractometer. FCG tests were carried out using compact tension samples, the fracture morphology and crack growth path were analyzed accordingly. The results show that a refined surface gradient structure with compressive residual stress of about 250 μm in depth is formed after USSP treatment. The USSPed samples exhibit higher strength and surface roughness than the as-received samples. Notably, the fatigue crack growth life of USSP-8 min and USSP-12 min samples is increased by 28.1% and 50.9% compared to that of the as-received samples. The USSP treatment helps to improve the resistance to fatigue crack propagation, which in turn reduces the fatigue crack growth rate to a certain extent. The enhancement of the FCG performance can be ascribed to the combined effects of the compressive residual stress and the conspicuous grain refinement. Compressive residual stress enhances the crack closure effect and decreases the effective stress ratio. Meanwhile, grain refinement increases the fraction of grain boundary and decreases the cyclic plastic zone size, which is beneficial for crack growth resistance.

Abstract:Mo-Re alloys have excellent mechanical and processing properties due to their high-temperature resistance, corrosion resistance, and plasticity. To further understand the microstructure and room temperature tensile properties of rolled Mo-14%Re alloy, the microstructure and fracture morphology of the Mo-14%Re alloy were investigated by scanning electron microscopy (SEM) and high-resolution electron backscatter diffraction (EBSD). Channel 5 software was used to analyze the microstructure evolution of rolled Mo-14%Re alloy at different annealing temperatures. With the increase in annealing temperature, the Schmidt factor of the Mo matrix phase and ReO₃ phase decreases gradually. The texture intensity increases rapidly, and the crystal orientation intensity of the polarography increases from 6.51 to 10.18. The initial recrystallization of the rolled Mo-14%Re alloy occurs at 1100 °C, at which the uniform precipitation of the earth-rich ReO₃ phase in the alloy leads to uniform stress distribution during tensile process, the grains of Mo matrix phase and ReO₃ phase show obvious ＜101＞ crystal orientation and ＜111＞ crystal orientation, and the grain boundaries of ReO₃ phase are mainly high-angle grain boundaries, which makes the elongation after fracture reach the maximum of 33.5%. The tensile fracture has the highest number of dimples and the largest size. Besides, the formation, aggregation, growth, and crack propagation of micropores during fracture were studied.

Abstract:The W-Ni alloy specimens were prepared by laser powder bed fusion (LPBF) using 93W-7Ni pre-mixed powder feedstock. The influence of different linear energy densities (LEDs) on relative density, microstructure and microhardness of LPBFed W-Ni alloy specimens. The results show that the defects of the W-Ni alloy specimens are mainly irregular pores with no obvious cracks and the irregular pores can be reduced by increasing the LED. The W-Ni alloy specimens with a maximum relative density of 98.04% can be prepared by using LED of 1.5J/mm. The microstructure of LPBFed W-Ni alloy specimens is mainly composed of W particles and Ni-W matrix phase, accompanied by a large number of fine dendritic/granular W grains. The LPBFed W-Ni specimens have high microhardness with a maximum of 529.83HV0.5, which was not significantly influenced by LED.

Abstract:The Laves phase NbCr2/Nb dual-phase alloy has the potential of being used as a new high-temperature structural material due to its excellent high-temperature mechanical properties. It is known that the flow stress constitutive relationship reveals the hot deformation behavior of an alloy. In this paper, the strain-compensated physical constitutive relationship of Laves phase NbCr2/Nb dual-phase alloy with consideration of the effect of deformation temperature on the Young"s modulus and self-diffusion coefficient of the alloy is explored for the first time based on its isothermal constant strain rate compression experiment data at temperature of 1000-1200 °C and strain rate of 0.001-0.1 s-1. The results show that the correlation coefficient (R) and the average absolute relative error (AARE) of the strain-compensated physical constitutive relationship based on the creep index n=5 are 0.974 and 59.3% respectively, indicating that this physical constitutive model is not accurate for characterizing the flow stress behavior of the alloy. Whereas the R and the AARE of the strain-compensated physical constitutive relationship based on the variable of creep index n are 0.984 and 10.6% respectively, showing that this physical constitutive model can satisfactorily characterize the flow stress behavior of the alloy and the flow stress prediction accuracy of the physical constitutive model is higher than the traditional Arrhenius constitutive model.

Abstract:In order to obtain high quality W/CuCrZr composites, the W/CuCrZr composite plates with dovetail groove structure were fabricated by vacuum melting and casting. The microstructure characteristics and mechanical properties of W/CuCrZr joining interface were systematically analyzed by optical microscopy, scanning electron microscopy coupled with elemtental analysis, hardness tester and other equipment. The results show that the joining interface of W/CuCrZr composite prepared by melting and casting under vacuum conditions of 10-4 Pa and heating temperature of 1100~1200℃ presents flat and straight structure, which is tightly bonded without obvious defects. At the joining interface, the phenomenon of elemental interdiffusion occurred and formed a banded melting diffusion layer with the width of about 6~8μm. The Vickers hardness on the tungsten side of the W/CuCrZr composite plate is improved compared with the base material，while the Vickers hardness on CuCrZr side is lower than that of the base metal.

Abstract:In this work, the high-purity tantalum after cold deformation is annealed at different temperatures (850~1050℃). The regularity of microstructure and texture evolution, the dependence of recrystallized nucleation and orientation, and the effect of recrystallized structure on its mechanical behavior were studied after annealing. The results show that the cold-deformed microstructure is the fibrous structure with {100} and {111} orientations, which is dominated by the α-fibre of ()[] component. After annealing, the microstructure of high-purity tantalum is in the recovery stage (850°C), complete recrystallization (950°C) and grain growth stage (1050°C). With increase of annealing temperature, the α-fibre gradually weakened and then the γ-fibre gradually formed, especially the α-fibre is disappeared completely after recrystallization. The yield strength and strain hardening ability decreased with the increase of annealing temperature, and the plasticity was significantly improved, especially the uniform elongation reached 17.85% after recrystallization. When the annealing temperature is increased to 1050°C, the intergranular fracture of the secondary recrystallized grains is prone to occur, resulting in poor mechanical properties.

Abstract:Coating the surface of zirconium alloy is an important way to improve the accident tolerance capability for nuclear fuel cladding after the Fukushima nuclear power plant accident. Transmission electron microscopy (TEM) samples of the irradiated N36 alloy with Nb coating were prepared by focusing ion beam (FIB). Bubble evolution during in-situ heating in the irradiated Nb-coated N36 alloy samples was investigated by in-situ TEM. The results show that the interface has a strong effect on bubble growth during the annealing process. The bubbles near the interface were captured and transported by the interface, which leads to the growth rate of the bubbles near the interface is lower than those away from the interface. The analysis of elements after annealing indicates that both irradiation and heating can increase the diffusion distance of the elements between coating and matrix, the diffusion during irradiation is mainly caused by the thermal spike diffusion mechanism. The diffusion of elements is beneficial to improve the bonding properties of the coating and provide certain corrosion resistance for N36 alloy.

Abstract:Ni-based single-crystal (SC) superalloys were treated by laser shock peening (LSP) and then exposed at 750 and 850 °C for 2 h. The electrochemical corrosion behavior of the as-obtained specimens was investigated in 3.5wt% NaCl solution. The results show an increase in the corrosion resistance of SC alloy treated by LSP; it is related to the compressive residual stresses (CRS) and significantly different dislocation structures in γ/γ′ phases. The non-uniformly distributed dislocations in γ/γ′ phases raise the two-phase misfit. The electrochemical corrosion tests of LSP-treated specimens after heat exposure indicate that CRS and two-phase misfit are the two major factors influencing the corrosion resistance of SC alloys. CRS can enhance the corrosion resistance while the two-phase misfit deteriorates the corrosion resistance of SC alloys. In addition, the improved corrosion resistance of SC superalloys is linked to the formation of Ta₂O₅ and WO₃ oxides.

Abstract:In this paper, series experiments were carried under different fatigue load spectrum for different solution annealing treated GH4720Li alloy. The results show that when the solution temperature is between 1080 °C and 1120 °C, the volume fraction of primary γ′ phase in the alloy is high, and the size of the near spherical tertiary γ′ phase gradually grows, and the grain structure is fine and uniform. The dislocation slip mainly cuts and bypasses the spherical γ′ phase and leaves a small slip band, indicating that the γ′ precipitates can effectively hinder the expansion of the slip band, the alloy has good fatigue performance. When the solution temperature is rise to 1140 °C, the primary γ′ phase dissolves unevenly, inducing the obvious mixed grain size distribution, and the morphology of tertiary γ′ phase gradually transforms into square shape. The size of parallel slip bands increases obviously, and the internal deformation of the material has occurred to a large extent, and the fatigue resistance of the material decreases. When the solution treated temperature is over the γ′ phase transformation point, such as at 1180 °C, the γ′ phase completely dissolves, and resulting in the coarse grain structure.The slip bands cross each other and pass through the grain boundary, which seriously reduces the fatigue resistance of the alloy.

Abstract:In this work, the influence of warm rolling deformation degree on the microstructure evolution and high temperature (760 ℃) mechanical properties of a novel Ni-based superalloy were investigated by EBSD, SEM, TEM and quasi-static high temperature tensile tests. The results show that the reduction of warm rolling can significantly influence the high temperature mechanical properties. The echancement of yield strength, ultimate tensile strength and elongation for high temperature mechanical properties of Ni-based superalloy processed by the warm rolling with the deformation reduction of 10%, compared to that of samples processed by stardard heat treatments, are 230 MPa, 166 MPa, and 4.1%, respectively. Further rolling deformation processing (80%) causes the evident increase (22.5%) of elongation, generating the excellent strength-ductility synergy effect. The results indicate that the increase of strength and ductility can attribute to the transformation of the doformnation mechanism when the tensile test is conducted at 760 ℃. The transition from stacking fault to micro twinning can obtain the high temperature tensile strength-ductility synergy.

Abstract:The evolution of grain structures, γ" strengthening phases and carbides of FGH113A (WZ-A3) alloy during long-term aging treatment at 760 ℃ and 815 ℃ were studied by means of Optical Microscope (OM), Scanning Electron Microscope (SEM), and Energy Dispersive Spectrometer (EDS) and the effect of long-term aging on the tensile properties of the alloy was analyzed. The results show that the long-term aging at 760℃ and 815℃ has no significant effect on grain size and grain morphology of the alloy. After long-term aging at 760℃, the size and morphology of the γ" strengthening phases have no obvious effect, but after long-term aging at 815℃ for 440h, the γ" phases begin to grow and the morphology changes from quasi-cubic to quasi-spherical. After long-term aging at 760℃ for 2020h, the carbides have changed from dispersed granular particles to aggregated at grain boundaries. After long-term aging at 815℃ for 440h, needle-like carbides begin to precipitate in the grains. After 2020h, granular carbides are enriched at the grain boundaries and form chains, at the same time, the needle-like carbides precipitated in the grains further increased. Under the tensile tests of 704°C and 760°C, the tensile strengths of the alloy during long-term aging treatment 760°C/440h and 760°C/2020h were equivalent, but the yield strengths increased slightly after 2020h; the tensile properties of the alloy show similar discipline at 815 long-term aging. The key reasons for the better tensile strength stability of the alloy were attributed to the stable grain structures and the pinning effect of grain boundary carbides. The new nickel-based powder superalloy FGH113A exhibits excellent stability under long-term aging at 760°C and 815°C.

Abstract:In order to investigate the effect of C content on microstructure and mechanical properties of GH4169 alloy, three kinds of GH4169 alloys were obtained by vacuum induction melting, homogenization heat treatment, forging and solid solution heat treatment. The precipitation behaviors of equilibrium precipitated phases of GH4169 alloy with different C content were investigated by thermodynamic calculation and differential scanning calorimetry. Combined with microstructure observation, X-ray diffraction phase analysis and tensile test at room temperature of alloys with different C content, the effect of C content on the tensile properties at room temperature and strain hardening exponent was analyzed. The results show that the increase of C content can promote the precipitation of MC carbide and M23C6 carbide. The amount of MC carbide enriched with Nb increases in linear with the increase of C content. The increase of C content can inhibit the precipitation of δ phase and has no significant influence on the precipitation of γ′ phase. With the increase of C content, the grain of solid-solution state is refined and the strength at room temperature is improved. The increase of C content will result in the decrease of elongation after fracture, strain hardening exponent and the capacity of uniform plastic deformation. MC carbide and its resulting void are the main factors to cause the fracture of the alloy at room temperature.

Abstract:Ti-6Al-4V titanium alloy plate was welded by a laser beam with self-developed titanium alloy flux-cored wire. The welded joint was solution treated at 920 °C for 1 h and aging treated at 650 °C for 2 h, and its microstructure and properties were compared with those of the as-welded joint. The results show that the heat-treated welded joint is composed of a typical tri-modal microstructure containing α_p phase, α_s phase colony, and α_gb phase, as well as punctate distributed residue β phase. α' martensite microstructure in the as-welded joint is not found in the heat-treated joint, which makes the strength, plasticity, and toughness well balanced and maintained. The strength of the heat-treated welded joint is reduced, while elongation and impact toughness at room temperature are enhanced. The tensile fracture of the heat-treated welded joint is surrounded by massive shear lips. The dimples are deep and uniform, presenting as microvoid coalescence ductile fracture. In the as-welded joint, the proportion of large-angle grain boundaries with misorientation between grains in the weld zone greater than 15° accounts for 83.78%, and in the heat-treated welded joint, the proportion is about 90.21%. Through XRD test, it is discovered that the as-welded weld is mainly composed of α' martensite, with a small amount of extremely weak multi-angle α phase diffraction peak. In the heat-treated weld, the central angle position of α phase diffraction peak is consistent with that of α' martensite in the as-welded weld, with a sharp β phase (110) diffraction peak observed as well.

Abstract:To reduce the risk of β-flecks, the impact of stirring coils' parameters on ingot composition and grain structure was evaluated in TC17 alloys. A model coupling the temperature, electromagnetic, fluid flow, and the solute field was established using MeltFlow vacuum arc remelting (VAR) software. The results show that Cr concentration at the centre increases gradually from the bottom and then increases sharply within 100 mm to the ingot top, showing unlike tendency compared with locations at the edge and 1/2 diameter of the ingot. The increase in either the stirring coil current or reversal time is beneficial to the decrease in Cr content and the width of equiaxed crystal at the ingot centre, due to the accelerated turbulent velocity, which causes additional mixing within the molten pool. From the macromorphology observations of TC17 ingot, at near half of the lower part of the ingot, the location where the disturbance occurs in the direction of columnar crystal growth is corresponding to the position where Cr content increases, both of which have a relationship with stirring coil parameters. The simulation results fit the experimental data well.

Abstract:The enhanced phase Mg₂Si in the magnesium alloy can significantly improve the hardness, wear resistance, especially high temperature creep resistance. But the Mg₂Si phase of the as-cast hyper-eutectic Mg-Si alloy will seriously cut the alloy matrix because of the coarse angular shape of the primary Mg₂Si and complex Chinese script morphology of the eutectic Mg₂Si. In order to improve the properties of Mg-2.5Si-4Zn alloy, the modification experiments of adding Er/Er-Ba were performed and the effects on the alloy microstructure and Mg₂Si phase were investigated by the optical microscopy (OM), scanning electron microscopy (SEM), energy dispersive spectrometry (EDS) and X-ray diffractometer (XRD). The mechanical properties were measured and analyzed by the computer-aided electric-loaded tensile tester. The results show that with the addition of 0.6wt% Er to the Mg-2.5Si-4Zn alloy, the primary Mg₂Si in the microstructure transforms from a coarse dendritic shape into a regular tetragonal block shape, while the eutectic Mg₂Si transforms from a coarse Chinese script type to a more complex short rod shape. When adding 0.8wt% Ba subsequently, the primary Mg₂Si further transforms from a regular tetragonal bulk shape to an irregular fine bulk shape with grooves and holes, and the eutectic Mg₂Si has an obvious refining effect and is diffusely distributed with the dot/short-line shape in the alloy matrix. The best metamorphic effect is obtained by adding 0.6wt% Er and 0.8wt% Ba. The mechanical properties of the Mg-2.5Si-4Zn alloy modified by Er-Ba composite modifier are significantly improved, with the tensile strength σ_b and elongation δ increasing to 168 MPa and 5.04%, respectively.

Abstract:Microstructure evolution and fracture morphology during high cycle fatigue in AZ31 magnesium alloy were investigated by fatigue test at different loading frequencies (3 and 30 Hz) and stress amplitudes (90, 95, 100, 105, 110 MPa). Electron back-scattered diffraction (EBSD) analysis results show that the number of residual twins in the matrix increases with the increase in loading stress, and the residual twins mainly exist in the form of {102} tensile twins. Gradual grain refinement is observed with increasing stress amplitude, which is due to the grain refinement induced by the evolution of tensile twinning during fatigue deformation. The significant weakening of the texture strength with increasing stress amplitude is related to the recrystallization mechanism after fatigue deformation. Through the scanning electron microscope (SEM) analysis of the fatigue fracture, it is found that the fatigue crack initiation (FCI) occurs in twin layer, the area of the fatigue crack growth (FCG) in the specimen gradually decreases with the increase in stress, and obvious fatigue striations (FS) are observed in FCG. The final fracture (FF) is rough surface, and there are mainly tear ridges and dimples. The dimple is observed in the final fracture, and the size and number of dimples decrease with the increase in stress.

Abstract:Ni-Cr alloy cladding layers with Cr contents of 10wt%, 20wt%, and 40wt% were prepared by laser melting technique and their high temperature oxidation characteristics at 900 °C and hot corrosion characteristics in Na₂SO₄+25wt% K₂SO₄ mixed salt at 600 °C were investigated. The results show that the Cr content plays a key role in the high temperature characteristics of cladding layers. Increasing the Cr content is more effective in improving the resistance of cladding layers to sulfate-induced hot corrosion than in improving the resistance to cyclic high-temperature oxidation. Cr40 provides the best resistance to high-temperature oxidation and hot corrosion. The oxidation products of Cr10 are dominated by NiO, which is extremely easy to shed and the internal oxidation is serious. Although a single Cr₂O₃ layer can be formed on the Cr40 surface, cracking within the Cr-rich oxides caused by thermal and growth stresses renders the resistance of Cr40 to cyclic high-temperature oxidation only slightly better than that of Cr20. Suffering from hot corrosion, the surface of Cr10 presents lamellar NiO and Ni₃S₂ stacked distribution of corrosion products, and Ni sulfide is also generated in the inner corrosion zone. The Cr₂O₃ layer on Cr20 surface is destroyed, and internal corrosion is severe, generating CrS. A dense protective Cr₂O₃ layer is generated on Cr40 surface, efficiently preventing further corrosion.

Abstract:The alloy ingots with nominal compositions of (Nd_1-xCe_x)_2.4Fe₁₄B (x=0, 0.2, 0.4, 0.6, 0.8, 1.0) were prepared by induction melting and then melt-spun to form nanocrystalline ribbons. Phase composition, magnetic properties and microstructure were investigated. XRD results show that all melt-spun ribbons exhibit the tetragonal structure (Nd,Ce)₂Fe₁₄B phase. When Ce substitution content is more than x=0.6, CeFe₂ phase appears and CeFe₂ content increases with the increase in Ce substitution content. Remanence, remanence ratio (M_r/M_s) and lattice constant decrease while increasing Ce substitution content. A coercivity of 1.31×10⁶ A/m and the maximum energy product of 103 kJ/m³ for (Nd_0.8Ce_0.2)_2.4Fe₁₄B melt-spun ribbon are achieved. The coercivity mechanism and intergrain exchange coupling were studied. The positive δM value was observed in every sample, confirming the existence of exchange coupling interaction. The δM maximum value reaches 0.76 at the Ce substitution content x=0.2, indicating that the intergranular exchange coupling effect is the strongest, which is consistent with the varying remanence ratio. SEM observation reveals that increasing Ce substitution deteriorates the columnar crystal structure of ribbons.

Abstract:The effect of addition of RE and Ti on the microstructure and corrosion resistance of Zn-2.5Al-3Mg alloy were investigated by XRD, SEM, TEM and XPS. Results reveal that the microstructure of the Zn-2.5Al-3Mg alloy is composed of Zn-rich phase, binary eutectic (Zn-MgZn₂/Mg₂Zn₁₁) and ternary eutectic (Zn/Al/Mg₂Zn₁₁). New phases of (Ce_1?xLa_x)Zn₁₁ and Al₂Ti appear with the addition of RE and Ti elements. Electrochemical impedance spectroscopy indicates that the corrosion resistance of Zn-2.5Al-3Mg-0.1RE-0.2Ti alloy can be significantly improved compared to that of Zn-2.5Al-3Mg alloy. XPS analysis results show that the addition of RE element promotes the formation of Zn₅(CO₃)₂(OH)₆ and MgAl₂O₄ in the corrosion products, while the simultaneous addition of RE and Ti elements promotes the formation of corrosion products Zn₅(CO₃)₂(OH)₆, ZnAl₂O₄ and MgAl₂O₄, and inhibits the formation of loose porous ZnO. Zn₅(CO₃)₂(OH)₆, ZnAl₂O₄ and MgAl₂O₄ attach well to the surface of the sample, which provides a dense protective layer for the alloys, thus improving the corrosion resistance of Zn-2.5Al-3Mg alloy.

Abstract:In order to investigate the properties of rubidium tungsten bronze and cesium tungsten bronze nanopowders with different shapes and their film, rubidium and cesium tungsten bronze nanopowders were prepared by hydrothermal reaction and a subsequent heat-treatment. Tungsten bronze transparent insulation film was prepared by spin coating method on a piece of glass. The synthesized powders were characterized by X-ray diffraction, scanning electron microscopy and transmission electron microscopy, and the photothermal properties of the powders were studied. The near infrared shielding performance and heat insulation performance of tungsten bronze films were analyzed by UV-Vis NIR spectroscopy. The results show that the tungsten bronze nanopowders after heat treatment have excellent photothermal properties and have a promising application prospect in cancer photothermal therapy. Compared with the film made by rod-shaped powers, the film made by laminar rubidium and cesium-tungsten bronze powders have higher near-infrared shielding performance of 95% and 98.8%, respectively. Compared with blank glass, the indoor temperature using glass with laminar rubidium and cesium tungsten bronze films decreased by 9.4℃ and 8.5℃ respectively. In summary, sheet rubidium and cesium tungsten bronze have excellent near-infrared shielding performance, and have great application prospects in the fields of energy saving and photothermal therapy.

Abstract:In order to solve the problems of elemental segregation, limited properties and high cost in the preparation of high difference of multi-alloys melting point, a new process of accumulative roll bonding (ARB)-diffusion alloying (DA) has been developed. The properties of the ARB-DA Cu-21Ni-5Sn alloy were characterized by SEM, EDS, TEM, XRD and the universal testing machine. The effects and mechanisms of the ARB and step diffusion heat treatment processes on the compositional homogeneity of the Cu-21Ni-5Sn alloy were investigated, and the effects and mechanisms of the subsequent aging regime on the properties of the Cu-21Ni-5Sn alloy were revealed. The results show that Cu-21Ni-5Sn alloy with less than 5% elemental error and homogeneous composition was prepared by ARB 7 passes + 650 ℃/5 h + 1000 ℃/8 h step vacuum diffusion heat treatment process. The Cu-21Ni-5Sn alloy was aged at 470 ℃ for 60 min under 40% pre-cooling deformation for 60 min to fully spinodal decomposition. Dense DO22 and L12 ordered solid solution with matrix with α-Cu matrix was(-1-1-1 )Cu//(-2-20)DO22, (-200)Cu//(-310)L12. The alloy reached tensile strength of 925 MPa, a modulus of elasticity of 135.4 GPa, and an alloy conductivity of 6.23% IACS.

Abstract:Based on SYSWELD simulation software, a computational method combining the thermal elastic plastic finite element method(FEM) and the inherent strain method FEM is used to study the influence of the welding process on welding defor-mation of the thin-walled GH3536 tail nozzle assembly. Firstly, the plate docking process test and thermal elastic plastic FEM calculation are carried out to check the welding heat source model, and the average inherent strain value of the joint and the modified thermal expansion coefficient of the material under different welding processes are obtained. Secondly, the finite element model of full-size three-dimensional tail nozzle welding is established. Based on the elastic FEM of the inher-ent strain theory, the influence of welding process parameters and welding constraints on the welding deformation of the tail nozzle assembly was calculated by using the thermal expansion coefficient of the material obtained by plate docking. The results show that when the welding current is 40 A, the minimum inherent strain value of the thin-walled GH3536 plate butt welding joint is 0.00660 mm, and the deformation of the nozzle after welding is also the smallest, which is the recommended optimal welding process. When the weld, air inlet and exhaust port are clamped at the same time, the deformation of the nozzle is the smallest after welding, and the overall deformation is 1.39 mm.

Abstract:TiB2-TiC-Co composite powders were successfully synthesized from a Co-Ti-B4C system by self-propagating high-temperature synthesis (SHS), and TiB2-TiC-Co cermet coatings were produced on a Q235 steel substrate by atmospheric plasma spraying (APS). Phase composition and microstructure of the SHS products and APS coatings were investigated, and bonding strength and wear resistance of the coatings were examined. The results show that the phase of Co-Ti-B4C SHS products mainly consists of strong TiB2 and TiC diffraction peaks in addition to the diffraction peaks of a small amount of remained NaCl additive. Both TiB2 and TiC ceramic particles are fine. With the increase of Co content, the disk-like splats increase on the surface of TiB2-TiC-Co coating, and the surface becomes smooth gradually. The thickness of the coatings are uniform, and the densification is improved. The bonding strength and sliding wear resistance present the trend of first increasing and then decreasing. The bonding strength and sliding wear resistance of the coating reaches optimum value with 10 wt.% Co content. The wear mechanism of the coating is mainly adhesive wear and lamellar peeling wear.

Abstract:Chalcogenide perovskites are an emerging class of functional semiconductor materials with unique electronic structures and optoelectronic properties. In this paper, chalcogenide perovskite BaZrS₃ nanostructures were prepared by a sol-gel method combined with chemical vapor reaction. And BaZr_1-xFe_xS₃ magnetic semiconductor was obtained by doping method. The structure, optical and magnetic properties were studied. The results show that the oxide perovskite BaZrO₃ can still exhibit a perovskite structure after vulcanization, that is, replacing O element with S element. And the sulfide treatment can reduce the band gap width of the sample. At the same time, 3d transition metal elements with localized magnetic moment, such as Fe, are used for cation doping of perovskite B site. The band gap width of the samples can also be systematically regulated by controlling the doping amount of Fe. In particular, the BaZr_99.7Fe_0.03S₃ and BaZr_99.5Fe_0.05S₃ exhibit room temperature ferromagnetism.

Abstract:In this paper, ultracoarse grained cemented carbide was prepared by in-situ fine grain dissolution-precipitation method with WC, WO₃, Co and C as raw materials. The effects of different WO₃ content on the microstructure and mechanical properties of the alloy were analyzed. The results show that the WO₃ and C could undergo in-situ reduction-carbonization reaction to form fine WC with high activity. In the liquid phase sintering, fine WC dissolution-precipitation could promote the coarse WC grains growth, reducing the micro defects and growth steps, flattening the boundary of WC grains, which could make the morphology of coarse WC grains tend to a fully developed triangular prism. The ultracoarse WC grains with high flattening degree effectively increased the proportion of WC (0 0 0 1) axial plane, improved the hardness, hindered the crack propagation, and strengthened the alloy. So, the alloy with 4.20wt% WO₃ added had the maximum hardness (1085kg/mm2) and transverse rupture strength (2692MPa).

Abstract:In this paper, ZL101-xCr (x=0, 0.1, 0.2, 0.3, 0.5, 0.8wt.%) aluminum alloys were prepared by vacuum electromagnetic induction melting furnace. Using OM, XRD, SEM, EDS and TEM, the microstructures of the experimental alloys with different Cr contents were characterized, and their mechanical properties were tested. The results show that the main phases of the experimental alloy include primary α-Al, (α-Al+Si) eutectic, Al₁₃Cr₄Si_4, α-Al₁₂(Cr, Fe)₃Si₂, and Fe-rich phases (β-Al₅FeSi and π-AlSiMgFe). The microstructure of the experimental alloys after adding trace element Cr is refined. With the increase of Cr content, the α-Al dendrites tend to be equiaxed, the eutectic structure area becomes narrow, and the Fe-rich phase and eutectic Si size become smaller. Al₁₃Cr₄Si₄ and α-Al₁₂(Cr, Fe)₃Si₂ phases are formed in the alloy eutectic structure. Adding Cr element can improve the undercooling degree of the alloy, which has a positive effect on refining the alloy structure. When the Cr content is 0.3%, the microstructure refinement and modification effect and mechanical properties of the cast alloy are the best, and the tensile strength and elongation are 182.88Mpa and 3.38%, respectively

Abstract:Grain boundary character distribution (GBCD) of the hot isostatic pressed (HIPed) beryllium was systematically analyzed by Electron backscatter diffraction (EBSD), and the pressureless sintered beryllium was prepared for making a comparison. It is discovered that some grains of the HIPed beryllium has very dense low angle grain boundaries (LAGBs) of 2°-5° and a large number of fine-grains within grain interiors. The size of fine-grains is mostly in the range of hundreds of nanometers. Conversely, the pressureless sintered beryllium has few LAGBs and no fine-grains. The results show that the beryllium which has very high stacking fault energy not only takes place dynamic recovery (DRV) during HIPing, but also enables access to dynamic recrystallization (DRX). It is very unique that the dynamic recrystallization behavior of the metal beryllium during HIPing. A large number of recrystallized grains are densely formed within grains interior at the same time, but they have a specific orientation relationship with the beryllium matrix. The specific disorientations are 29°<2 0>/<0001>, 59°<2 0>, 74°<2 0> or 78°<2 11>/<10 0>, and 88°<2 0>/<10 0>, respectively. The disorientations can be divided into two categories according to their characteristic. One is that its disorientation axis is the slip direction of beryllium, and the other is the low Σ value coincidence site lattice (CSL) grain boundaries of beryllium, in which 59°<2 0> and 74°<2 0> disorientations are both. The highly efficient recovery and recrystallization of beryllium powder sintered body during HIPing to acquire more optimized dislocation configurations is the prerequisites for the HIPed beryllium to achieve high ductility. Increasing the hot isostatic pressing temperature is able to effectively promote the dynamic recovery and recrystallization of beryllium powder sintered body during HIPing, and thus the ductility of the HIPed beryllium is improved.

Abstract:LaB6-C/C preform containing 9.73% wt.% LaB6 was prepared by slurry impregnation combined with resin infiltration pyrolysis, and then LaB6 modified C/C-ZrC-SiC composites were obtained by reactive melt impregnation (RMI). The microstructure and ablative behavior of the composites were studied, and the mechanism of LaB6 on the ablation properties of the composites were investigated. The results show that, after oxyacetylene ablation at the heat flux of 2380 kw/m2 for 120 s, the mass ablation rate and linear ablation rate of LaB6 modified C/C-ZrC-SiC composites are 1.05×10-3 g/s and 2.17×10-3 mm/s, which are 74.8 % and 61.9 % lower than those of unmodified C/C-ZrC-SiC composites, respectively. During ablation, LaB6 is oxidized to La2O3 and B2O3. The solid solution and chemical reaction between La2O3 and ZrO2, coupled with the effect of liquid B2O3 to promote mass transfer in solid phase reaction, make the surface of the material form a large area of continuous and stable ZrO2-La2Zr2O7-La0.1Zr0.9O1.95 molten protective layer, which is the main reason for the excellent ablation performance of the material.

Abstract:In this paper, Ni-plated ZrO2 reinforced alloy was prepared by thermal decomposition and reduction method, and Ni-plated ZrO2 reinforced Sn1.0Ag0.5Cu composite filler metal was prepared by powder metallurgy method. The surface metallization of ZrO2 nanoparticles and its effect on the microstructure, material properties and brazing joints of Sn1.0Ag0.5Cu composite filler metal were studied. The results showed that the particle size and agglomeration of ZrO2 decreased after mechanical pretreatment. The Ni-plated ZrO2 enhanced phase was successfully prepared by thermal decomposition and reduction method. The Ni particles were uniformly attached to the surface of ZrO2 with a spacing of 8-11 nm, and the interface between ZrO2(02) and Ni(11) showed a semi-coherent relationship. The melting point and resistivity of Ni/ZrO2-Sn1.0Ag0.5Cu composites were not significantly affected by adding a proper amount of nickel-plated ZrO2, but the wettability and tensile strength were improved. The tensile strength and shear strength of brazed joint of Ni/ZrO2-Sn1.0Ag0.5Cu composite filler metal reach the peak when the adding amount of ZrO2 reinforcing phase is 0.7 wt.%, which are increased by 43.3% and 40% compared with the matrix material. With the addition of Ni/ZrO2 reinforcing phase, the fracture position of the brazing joint of the composite filler metal moves from the interfacial IMC layer to the side near the brazing seam in the transition zone, and the fracture mechanism gradually changes from the mixed tough-brittle fracture to the ductile fracture dominated by dimple.

Abstract:Subsphaeroidal MoS2 anode powder material with good electrochemical performance for lithium-ion batteries (LIBs) were synthesized by enhanced hydro-thermal process (EHP) in relatively short reaction time. The ammonium molybdate, thiourea and polyvinyl pyrrolidone (PVP) were used as molybdenum source, sulfur source and soft mold surfactant, respectively. The crystal structure, morphology, element component and valencies of the as-prepared samples were characterized by XRD, SEM, FESEM, TEM, HRTEM and XPS. Galvanostatic charge-discharge, cyclic voltammetry and electrochemical impedance spectroscopy test was utilized to evaluate the electrochemical performance of the batteries assembled by the as prepared powder. The experimental results showed that the as-prepared powder was subsphaeroidal MoS2 particles with an average grain size of about 150nm. After annealing at 500℃ for 2h, there is no significant change in morphology. As anodes for LIBs, subsphaeroidal MoS2 without annealing delivered an relatively high initial discharge capacity of 874.7 mAh/g at a current density of 500 mA/g, which decays in the following cycles. The capacity retention rate after 100 cycles was only 53.3%. As a contrast, electrochemical properties were enhanced for the counterparts after annealing, which exhibited an ultimate (100 cycles) discharge capacity of 571.3 mAh/g and a capacity retention rate of 83.2%. The coulomb efficiency of samples without annealing for the first cycle was only 68.88% and elevated afterwards to reach 100% at the 47th cycle while it is 100% for the annealed specimens in the initial stage and without decay in the following cycles, which indicating an improvement of charge-discharge efficiency. The performance of the annealed specimens enhanced due to the following reasons. The residual molybdenum oxide in the material sublimates during annealing, and lead to some voids appear inside the material, which increase the contact area between the active substance and the electrolyte. Furthmore, the heating treatment improves the crystallinity of the specimens, which can stabilize the crystal structure of MoS2, and inhibit the volume expansion in the discharge/charge process.

Abstract:A new Be-50 wt. %Al alloys were prepared by spherical beryllium powder. The Be phase keeps near spherical shape in the billet prepared by hot isostatic pressing ,and the proportion of Be phase with shape factor greater than 0.5 exceeds 77%. At room temperature, the alloy has good rigidity and the elastic modulus is 171GPa. The uniaxial compression experiment was carried out on the Gleeble tester to study the hot deformation ability of Be-50Al alloy at the temperature range from 250℃ to 550℃, and the strain rate 0.01s-1.The results show that the peak stress is significantly lower than that of traditional beryllium aluminum alloy. The strain hardening index of Be-50Al alloy is very stable at the temperature of 300℃ ~ 350 ℃, and it has good uniform plastic deformation ability. The deformation mechanism of compressed Be-50Al at various temperatures is mainly dominated by the plastic deformation of aluminum phase well coordinated by the beryllium phase. The tensile fracture surfaces at ambient temperature show cleavage fracture of beryllium particles, ductile fracture of aluminum and the interfacial debonding between beryllium phase and aluminum phase. Differently, the compression fracture at high temperature is caused by tearing of aluminum phase.

Abstract:The texture formation of TB6 titanium alloy under different forging processes was investigated by simulation, and compared with tantalum and copper. Firstly, the difference of temperature, equivalent stress and equivalent strain in different parts of TB6 titanium alloy during square drawing was analyzed by finite element method, after that, VPSC (visco-plastic self-consistent model) was used to simulate the texture evolution of different materials in forging process and make a comparative analysis. The results show that the central textures of BCC β phase in titanium alloy and Ta are not uniform with the edges, and the FCC copper textures have little fluctuation. The multi-side drawing is beneficial to weaken the {110} strong texture which is parallel to the axial direction during square drawing, and the compression texture can be retained in the drawing process.

Abstract:Oxygen-free and easy to process AlN/BN refractory composite ceramics were prepared by pressure-free sintering at 1850 ℃ for 4 h with a new type of refractory material AlN as the matrix, adding different contents of high-activity h-BN and sintering assistant Y2O3. The microstructure of the composite ceramics was analyzed, and the wetting behavior and interfacial reaction between the composite ceramic and TiAl melt were studied. The results show that the addition of BN particles can effectively fill the gap of AlN particles and promote the sintering densification of composite ceramics. When adding 5 wt% BN particles, the density of the composite ceramics reaches the highest: 89.24%. The microstructure of the composite ceramics is composed of AlN, BN and yttrium aluminate Y4Al2O9, which is mainly distributed at the interface of AlN particles. The interfacial wettability between the composite ceramics and the TiAl melt is reduced by addition of BN particles. The interfacial wettability angle of the composite ceramic containing 5 wt% BN and the TiAl melt is about 136°, indicating that the composite ceramics and TiAl melt are poorly wetted and the composite ceramics exhibit good chemical inertia. The interfacial reaction experiments show that the composite ceramics have good corrosion resistance to TiAl melt. The interface between the composite ceramics and TiAl melt is smooth and clear, the thickness of the interfacial layer is only 9.5 μm, and no obvious element diffusion occurs. It indicates that AlN/BN composite ceramics are a potential refractory for titanium alloy melting.

Abstract:The effect of different annealing processes on microstructure of 29Cr-4Mo super ferritic stainless steel seamless tube after cold rolling was investigated. The results show that the main inclusions in 29Cr-4Mo super ferritic stainless steel are Cr2O3·MnO·Al2O3. After annealing at 900 ℃for 30 min, the grain boundaries especially on triple junctions and near the inclusions firstly formed a small amount of σ phase. The average area fraction of σ phase increases with time prolonging while decrease with the temperature raising. There is no σ phase precipitating after holding for 50 min at 1000 ℃ and not founding χ phase during 900 ℃ to 1050 ℃. The empirical formula of ferrite recrystallization grain growth under classical Sellars model is established. The formula can accurately predict the average grain size in the whole annealing process by comparing the calculated value and the experimental value.

Abstract:Lithium-sulfur batteries have gotten to be a hot inquire about subject due to their tall hypothetical particular capacity (1675 mAh g_^-1) and energy density (2600 Wh kg_{-1). Focal points such as plenteous sulfur assets, non-toxicity and natural invitingness moreover make lithium-sulfur batteries one of the foremost promising vitality capacity frameworks. In any case, the destitute electrical conductivity of sulfur, the "transporting" of polysulfide between anodes and the contrast in thickness between sulfur and its diminishment items are still issues that restrain its application. Related studies have appeared that move metal selenides have great electrical conductivity. Based on their polar characteristics, move metal selenides can quicken the energy of redox responses, smother carry impacts, and make strides the electrochemical execution of lithium-sulfur batteries. This paper mainly reviews the applications of move metal selenides in lithium-sulfur battery cathode materials and stomachs, and presents an viewpoint on long run investigate course and advancement drift of move metal selenides in lithium-sulfur battery applications.}

Abstract:Degradable metals are decomposed into powders in an aqueous environment after completing the set function. With the progress of unconventional oil and gas field exploitation technology, the potential applications of degradable metals include but are not limited to fracturing balls, bridge plugs, ball seats, etc. Taking degradable aluminum alloy as an example, this paper summarizes the meaning of degradable, the degradation principle of aluminum, and the advantages of degradable aluminum in oil and gas field exploitation equipment. The mechanical properties, degradation properties, environmental compatibility and other requirements of downhole tools are summarized. The degradable aluminum alloy systems are introduced, such as Al-Ga-In-X, Al-Ga-Sn-X, andAl-Ga-In-Sn-X(X is Mg, Cu, Zn, Ti and other elements), etc. The factors affecting degradation performance such as temperature, medium and manufacturial technology are summarized. The application cases of degradable metals in oil and gas field exploitation equipment are introduced. The issues of industry-university-research-application cooperation and commercial standards that need to be solved at present are put forward, and the development direction in the future is forecasted.

Abstract:High-entropy alloys (HEA) are a research hotspot in the field of materials and engineering sciences. Unlike traditional alloys, HEA is composed of many main elements. Thus, the number of HEA components may greatly exceed that of traditional alloys. HEA has excellent properties (e.g., high hardness, oxidation resistance, corrosion resistance, high-temperature resistance and wear resistance) due to its unique composition of "near/equimolar ratio." The combination of additive manufacturing (AM) and HEA can produce metal parts with high strength, high plasticity, and highly complex geometry. This paper discusses the currently widely used selective electron beam melting (SEBM), selective laser melting (SLM), laser cladding (LC), and plasma cladding (PC) technology. The first two are used to prepare bulk HEA. The last two are used to prepare the coated HEA. The HEA prepared by SEBM has good ductility and is not easy to crack. The HEA prepared by SLM has high forming accuracy, strength, and surface finish. The HEA cladding layer prepared by LC has a very low dilution degree and a dense structure. The HEA cladding layer prepared by PC has almost no pores and no cracks. This paper systematically summarizes the technical characteristics of four different AM methods, as well as the advantages of the prepared HEA compared with traditional casting techniques in terms of microstructural characteristics, mechanics and corrosion resistance, and introduces its intrinsic mechanism in detail. This paper provides theoretical ideas for the development of cutting-edge technologies for preparing high-entropy alloys by AM.

Abstract:An eco-friendly and high corrosion-resistant lithium carbonate coating was firstly fabricated on LAZ141 by low temperature plasma. To investigate effect of Li content on structure and properties of as-prepared coating, SEM, EDS, EIS and hydrogen evolution test were adopted for characterization and analysis. The results showed that the content of lithium carbonate in coatings were determined by Li content in alloys. A protective layer with a high ratio of Li₂CO₃ can be formed in the coating when the Li content in alloy reaches the value of 10 wt.%. Hydrogen evolution and EIS results in 0.6 M NaCl solution indicate that the protective layer can improve the resistance of coating over two order of magnitude and reduce the hydrogen evolution rate of substrate at least by 3 times.