Abstract:Dynamic compression tests of Ti6321 titanium alloy were carried out in the temperature range from 193 K to 298 K and strain rate range from 2000 s^-1 to 3000 s^-1 to study the effects of temperature and strain rate on the mechanical properties and deformation behavior of the alloy. The microstructure evolution was observed and analyzed by optical microscope (OM), transmission electron microscope (TEM) and electron backscatter diffraction (EBSD). The results show that with decreasing temperature and increasing strain rate, dynamic yield strength and average flow stress of Ti6321 titanium alloy increase, while the fracture strain decreases obviously. Johnson-Cook constitutive equation is used to predict the mechanical behavior at low temperatures and high strain rates, and the fitting results are in good agreement with the experimental ones. Microstructural study shows that the content of the {112} and {101} extension twins increases significantly as the deformation temperature decreases. The deformation mechanism gradually changes from the auxiliary role of twins to the dominance of twins.

Abstract:Electron beam welding (EBW) was applied to an 8-mm-thick new type Ti-Al-Nb-Zr-Mo titanium alloy seamless tube produced by hot continuous rolling. The microstructure and mechanical properties of welded joint were investigated. Results show that the base metal (BM) consists of primary α, transformed β and Widmanstatten structure. For the EBW joint, the fusion zone (FZ) consists of acicular α′, block α and Widmanstatten structure, and the size of acicular α′ decreases gradually from top to bottom of the FZ. Moreover, only primary α and acicular α′ form in the heat affected zone (HAZ). The average microhardness in welded joint is ranked as follows: FZ＞HAZ＞BM, and the microhardness of the HAZ decreases gradually from the FZ to the BM side. The joint's tensile strength is 893 MPa and the fracture occurs at the base metal. The elongation of tensile specimens can reach 10%. The impact energy of FZ reaches ~80% of that of BM and the bending specimens are bended to 180° without cracks.

Abstract:A heterogeneous microstructure was found in a compressed near-α titanium alloy with a bimodal microstructure. The effect of the local texture on microstructural morphology was analyzed by electron backscattering diffraction techniques. Advanced orientation data processing was performed to study the micro-texture of primary α (α_p) and β. The results show that there is a close relationship between local microstructure heterogeneity and local texture. The deviation angle θ can be used to quantitatively evaluate the orientation relationship (OR) between α_p and the surrounding β grains from Burgers OR. The fractions of the α_p/β boundary with small θ are always higher in the regions where coarse β grains exist than in the regions where the β grain is completely recrystallized. The orientation relationship between α_p and β affects the recrystallization of prior β during deformation; it also exerts effects on the morphology of the transformed α phase by variant selection.

Abstract:High strength and high toughness Ti-alloy with damage tolerance is an important research direction of high strength titanium alloy. This work researched and reviewed the relationship among tensile strength, fracture toughness and impact toughness of 1200 MPa high strength and high toughness Ti-5321 alloy with damage tolerance. Microstructure greatly affects the tensile strength, fracture toughness and impact toughness. Lamella microstructure has good matching among tensile strength, plasticity, fracture toughness and impact toughness. Bimodal microstructure also has good matching among tensile strength, plasticity and fracture toughness, while its impact toughness is low. Based on the microstructure evolution, the changing laws of tensile strength, fracture toughness and impact toughness were analyzed. The future research direction for high strength and high toughness Ti-alloy with damage tolerance was proposed.

Abstract:High strength, low density, and excellent corrosion resistance are the main properties making titanium attractive in a variety of applications. The crystal structures and structural transformations of titanium allotropes, which are of tremendous scientific and technological interest, have attracted a great deal of attention for many years. In addition to hexagonal close packed α-Ti, high temperature phase β-Ti with body-centred cubic structure and ω-Ti with the hexagonal structure, researchers have tried to find other metastable structures which can be maintained under extreme conditions through various methods. During the past decades, the ultrahigh pressure structures γ-Ti and δ-Ti are observed, and the room temperature ω-Ti and fcc-Ti can be obtained by high pressure torsion, laser shock, ultra-thin films, etc. The research progress of crystal structures and structural transformations of titanium were introduced. The structural stability and mechanism of structural transformations on titanium were elaborated.

Abstract:The effect of laser power on microstructure and properties of Ti-6Al-4V-0.25C alloy was studied by laser melting deposition of Ti-6Al-4V-0.25C prealloy powder containing 0.25wt.%C. The results show that the microstructure of Ti-6Al-4V-0.25C alloy is equiaxed grain morphology, and layered α+β structure is formed inside the grains. The average grain size and α lath size increase gradually with the increase of laser power. In addition, with the increase of laser power, the tensile properties of the alloy are obviously improved, especially the ultimate tensile strength and elongation of the alloy prepared at the laser power of 1500 W are 1191 MPa and 8.3%, respectively. On the one hand, the porosity of the alloy decreases with the increase of laser power. On the other hand, Ti-6Al-4V alloy contains trace element C. During the cooling/solidification process, C atoms are solidly dissolved in Ti matrix, resulting in solid solution strengthening.

Abstract:In this paper, Ti-6Al-4V/TiAl3 laminated composites were butt welded by tungsten argon arc welding (TIG). The effects of different welding parameters on the microstructure and mechanical properties of the joint were investigated. The hot rolled Ti-6Al-4V /TiAl3 laminated composites can be reliably connected by TIG welding to avoid the phenomenon of joint embrittlement. The intermetallic compound at the bottom of the plate melts under the influence of heat radiation in the welding process, and the reaction between liquid TiAl3 and Ti generates Ti3Al, TiAl and so on, which causes the depletion zone of Ti atoms around the intermetallic compound and accelerates the diffusion migration of Ti atoms, resulting in the joint profile divided into two parts: The upper part is the weld zone of melting and solidification, and the bottom is the diffusion connection caused by thermal radiation. The overall joint has no obvious defects, and the weld zone is a network of α phase and acicular martensite. The tensile strength of the welded joint is 343MPa, about 90% of the base metal, and the fracture is ductile brittle mixed fracture.

Abstract:The spheroidization behavior of α laths in TiB-TC25G alloy during hot working at 950 oC was investigated. The globularization process is controlled by continuous dynamic recrystallization. It can be seen that a large number of subgrain boundaries generated inside the α phases, and the continuous orientation accumulation of the α phase occurs. Coinciding with the globularization process of α phase, the Burgers orientation relationship between equiaxed α grains and neighboring β grains has been destroyed and results in a weakened texture. As a joint result of β recrystallization behavior and pencil glide, The density of β phase texture increased at first and then decreased with the increase of deformation.

Abstract:For the design of pore structure of titanium alloy implants, most of the current researches were on positive Poisson"s ratio pore structures, while few of them were concerned with the design of negative Poisson "s ratio pore structures. Some samples of titanium alloy negative Poisson "s ratio pore structure implants with different deformation mechanisms and porosities were fabricated by selective laser melting(SLM), and microscopic material characterization was performed, and manufacturability evaluation was completed. Through the test of mechanical properties, the related mechanical data were obtained, which reveal the influence of mechanical properties such as strength and elastic modulus on cellular structure types and structural parameters through compression tests, and evaluates the matching degree of different structures with mechanical properties of human bone. The results show that: each structure has high manufacturability, and the forming quality is related to the structural characteristics and porosity; The mechanical performance of negative Poisson"s ratio structure highly depends on the structure design and porosity; The designed negative Poisson"s ratio structure can reduce the elastic modulus of solid metal to a range close to that of human bones by changing the diameter of the struts, which is expected to further achieve a wide-span regulation of the mechanical properties of the implant by adjusting the structural parameters.

Abstract:Additive manufacturing technology is a rapid prototyping technology that has developed rapidly in recent years. It is widely used due to its many advantages, such as short manufacturing cycle, low cost, and the ability to manufacture complex parts. This article introduces the classification of additive manufacturing and the characteristics of the metallurgical structure. The special super-normal metallurgical process of the additive manufacturing process leads to the existence of (1) significant coarse columnar crystals in the metallurgical structure of titanium alloys, and with the change of manufacturing methods, the size of the columnar crystals occurs Change; (2) There is an uneven distribution of the structure, including the uneven distribution of phase and grain size. Focusing on the metallurgical structure of additive manufacturing, the method to improve the metallurgical structure is systematically explained, including changing process parameters, external field assistance, such as magnetic field, ultrasonic field, online rolling plastic deformation, adding nucleating agent to refine grains, etc. The systematic elaboration of the thesis will provide a reference for the improvement of additive manufacturing organization in the future.

Abstract:The mechanical anisotropy of high temperature titanium alloy Ti65 plate under the conditions of original state, aging state and high temperature state was studied by unidirectional tension. Optical microscopy (OM), electron backscattering diffraction (EBSD) and scanning electron microscopy (SEM) were used to observe the microstructure of each state. The results show that original Ti65 sheet has highest strength in RD and lowest strength in the 45° direction, which is due to the elongated α phase and strong crystallography texture: (0001) ∥RD-TD plane and <10-10>∥RD. After aging at 790℃, Ti65 sheet has highest strength in TD because of the coarsing of α phase and weakening of fiber structure. At 790℃, the thermal tensile strength decreases greatly, and anisotropy changes obviously. The TD strength is remarkably higher than other two directions, primarily because the critical resolved shear stress of each slip system in α phase decreases greatly with the increase of temperature and the decline of different slip systems is different. In addition, there is stronger recovery and recrystallization at high temperature. The fracture mechanism of Ti65 at room temperature is ductile, and the fracture mechanism at 790℃ is interconnected by dispersed micropores.

Abstract:The effects of Ba-Nd composite modification on the microstructure and mechanical properties of Mg-3Si-4Zn cast alloy were investigated. The microstructure was characterized by OM, SEM, EDS and XRD. The mechanical properties were tested by hardness test. The best modification effect was achieved when a single denaturant Ba of 1.2wt% was added to the Mg-3Si-4Zn alloy. Results show that the formed phase BaMg₂Si₂ can act as a heterogeneous nucleation core for the primary Mg₂Si, refining the primary Mg₂Si. Ba-Nd composite modification is achieved by adding the modifier Nd to the Mg-3Si-4Zn-1.2Ba alloy. By the calculation of the Gibbs free energy using the Miedema model and a linear fit, it is found that the growth rate of primary Mg₂Si is suppressed and the primary Mg₂Si phase in the microstructure becomes smaller because more stable compounds like NdSi, NdSi₂, Ba₂Si, and BaSi₂ can be formed by Nd and/or Ba atoms with Si atoms, preventing Si atoms from binding to Mg atoms at the initial stage of solidification. The best Ba-Nd composite modification effect is achieved when the Nd content is 2.0wt%, i.e. the primary Mg₂Si changes from a dendritic shape with an average area of about 600 μm² to a nearly square-shape with an average side length of about 5 μm and the eutectic Mg₂Si changes from complex and coarse Chinese-script shape with an average area of about 444 μm² to simpler shape with a mean area of about 89 μm². The hardness of the alloy is increased from 575.75 MPa to 612.11 MPa, increased by 6.31%.

Abstract:Magnesium-strontium series alloys are one of the most prospective biodegradable metal materials, which perform well in biocompatibility because strontium has the function of promoting osteogenesis and regeneration. But the shortcomings of magnesium alloys such as inadequate strength and rapid degradation rate still exist. In the present study, an appropriate amount of human nutrient element zinc was added into Mg-2Sr alloy. Since the solid solution effect of zinc in the alloy can refine the grains, the strength and plasticity of Mg-2Sr alloy are improved. Results show that the Mg-2Sr-2Zn alloy has better corrosion resistance during the degradation processing. The corrosion protection layer is relatively dense, which hinders the penetration of chlorine ions in the simulated body fluid during the soaking process.

Abstract:Refractory metal carbides have been widely proven to be an effective strategy to enhance the oxidation resistance of ceramic matrix composites. The modification effect of ZrC-HfC-TaC system on cyclic oxidation and ablation behavior has rarely been explored. Herein, ZrC-HfC-TaC modified C/SiC composites were fabricated by polymer infiltration and pyrolysis and chemical vapor deposition processes. The mechanical strength, chemical composition and microstructure after cyclic static oxidation test under 1600 °C/5 h were investigated, and the corresponding oxidation mechanism was proposed according to the characterization results. The cyclic oxyacetylene torch tests under 1700 °C/4000 s were also employed to verify the effectiveness of ZrC-HfC-TaC modification on C/SiC composites. Results suggest that ZrC-HfC-TaC modified C/SiC composites possess outstanding cyclic oxidation and ablation behavior.

Abstract:AM60 magnesium alloys reinforced with titanium particles (Ti_p) were prepared by semi-solid stirring assisted ultrasonic vibration at different stirring speeds. The microstructure results show that the grain size increases after adding Ti particles. The Al₈Mn₅ phase is precipitated at the interface of Ti particles, and the interface structure between Ti particles and Mg matrix is a coherent interface. The tensile test results show that the strength of Ti_P/AM60 composites is higher than that of the AM60 matrix. With increasing the stirring speed from 300 r/min to 900 r/min, the UTS and elongation both increase first and then decrease. The UTS and elongation of Ti_P/AM60 composites reach the maximum of 183 MPa and 14.3%, respectively, when the stirring speed is 600 r/min. The UTS is increased by 15% and elongation is increased by 51% compared with those of the AM60 matrix alloy.

Abstract:Using Ni-Ti duplex foils as joining materials, Ti₃Al alloy was bonded to Ti₂AlNb alloy by transient liquid phase (TLP) diffusion bonding at 990 °C under low bonding pressure (0.1 MPa). The effects of bonding time on the microstructure and mechanical properties of Ti₃Al/Ti₂AlNb joint were analyzed, as well as the interfacial evolution and forming mechanism of the TLP joint were studied. Results show that the Ti₃Al/Ti₂AlNb alloy joints with typical interface structure of Ti₃Al | Al_0.5Nb_0.5Ti₃ | residual Ni | NiTi | NiTi₂ | residual Ti | Al_0.5Nb_0.5Ti₃ | Ti₂AlNb can be formed. In addition, with the extension of bonding time, the shear strength of the joint first increases and then decreases, and the maximum shear strength, up to 167±12 MPa, of the Ti₃Al/Ti₂AlNb alloy joint can be achieved when the bonding time reaches 60 min. The joint fracture, characterized by brittle fracture, mainly occurs at the NiTi₂ layer adjacent to the Ti₂AlNb/Ti interlayer and extends to the Ti interlayer.

Abstract:Molten chloride salt is a candidate heat transfer medium (HTM) for the next generation high temperature concentrating solar power (CSP). A corrosion product MgO will be formed on metal surface in the molten chloride containing MgCl₂. Based on the corrosion behavior comparison of a carbon steel and three kinds of Fe-Cr-Ni alloys in solid (345 °C) and molten state NaCl-MgCl₂ (445 and 545 °C), the effects of MgO on corrosion resistance of the four kinds of samples were discussed. Results show that in solid eutectic NaCl-MgCl₂ at 345 °C, the MgO layer is dense and complete on the carbon steel surface, which can protect the specimen from corrosion. In the molten salt, a dense MgO layer is also formed on the four kinds of sample surface, but the molten salt penetrates the MgO/matrix interface along cracks of the oxide layer due to the peeling off of MgO layer under thermal stress, which cannot protect specimen from corrosion. The corrosion mechanism is the chemical-electrochemistry reactions.

Abstract:The laser-welded 2A97-T3 aluminum-lithium (Al-Li) alloy joints were sampled from upper horizontal surface, transverse section, longitudinal section, and lower horizontal surface to develop the comprehensive and spatial understandings for microstructure and microtexture evolution. Various characterization methods in terms of electron backscattered diffraction such as orientation imaging microscopy, pole figure, inverse pole figure, misorientation angles distribution, orientation distribution function, and numerical simulation were used. The results show obvious differences in the grain morphology, orientation, and microtexture in different areas of the joint, due to the nonequilibrium characteristic of cold rolling and laser beam welding. The laser beam can induce the formation and growth of dynamic recrystallization and sub-structure grains in the heat affected zone. Moreover, the original microtexture characteristics of the base metal is weakened and thus eliminated in both the heat affected zone and the weld zone.

Abstract:The formation and evolution of the Al₈Cu₄Er phase and its influence on the corrosion resistance of Al-Zn-Mg-Er-Sc-Zr alloys were studied by changing the element content of Cu. The results show that with the increase in Cu content, the grains of the alloy are significantly refined, but at the same time, different types of residual phases in the solid-solution-state of the alloy increase. There is a companion relationship between the Al₈Cu₄Er phase and the Al-Fe phase, and they achieve phase transformation through the interaction between Cu and Fe. It can be expressed as the relationship: . The intergranular corrosion of alloys with different compositions shows pitting characteristics closely related to the residual phase. Although the Al-Fe phase containing Cu and Er has a smaller corrosion pit size, the network distribution characteristics increase the corrosion depth, while the Al₈Cu₄Er with better corrosion resistance has a serious decline in the counterpart of the alloy due to its tendency to coarsen and interactive relationship with the Al-Fe phase.

Abstract:The stress corrosion cracking (SCC) and its susceptibility (I_SCC) of commercial Zr702 applied for spent nuclear fuel reprocessing industry was investigated in boiling nitric acid. Stress-strain curves of Zr702 in boiling nitric acid with strain rate of 10^-5 s^-1 were obtained using independent designed slow strain rate tension (SSRT) system. Microscopic characterizations as well as numerical analysis were carried out to quantify the SCC behavior of Zr702. Results reveal that the I_SCC of Zr702 obviously increases from 5% to 26.67% with the increase in HNO₃ concentration. The sharp decline in the mechanical properties of commercial Zr702 in boiling HNO₃ solutions is attributed to cleavage fracture on surfaces of specimen, and the depth of the cleavage cracks increases with the growing HNO₃ concentration. Finally, a model and an equation to predict the SCC behavior of commercial Zr702 in boiling HNO₃ solutions was proposed. The quantitative relationship among HNO₃ concentration, I_SCC, fracture stress (σ_SCC) and cleavage crack depth (d_cc) can be described and predicted using a high-order regression equation.

Abstract:Nickel as a trace element was added into zirconium alloy (Zr-4) and then alloy sheet samples were prepared. The microstructure, corrosion property, and hydrogen content of the Zr-4 alloy were studied. Results show that the steam corrosion resistance at 400 °C can be greatly improved by adding nickel from 0.001wt% (the content in the sponge zirconium) to 0.005wt%, and there is no obvious effect on hydrogen absorption property. Trace nickel addition increases the content of the second phase particles in the form of Zr(Fe, Ni)₂ obviously, and promotes the aggregation of silicon around second phase particles, which can prevent or delay the oxidation of fine particles. In addition, zirconium tubes (Φ63.5 mm×10.92 mm) with the same alloy component also exhibit excellent nodular corrosion resistance and uniform corrosion resistance.

Abstract:To investigate the microstructure evolution during high-temperature deformation of the duplex high entropy alloys (HEAs), compression tests were performed at temperatures from 900 °C to 1050 °C with different strain rates. Four typical flow curves were selected and the corresponding microstructures were analyzed to investigate the dynamic recrystallization (DRX) and texture evolution of the duplex HEAs. The results show that the flow curves are totally different for samples deformed at the strain rate of 0.1 and 0.01 s^-1. The difference of mechanical flow curves is correlated with the DRX and texture evolution process. Two-component textures combining the <110> and <100> components are obtained after compression at 1050 °C and 0.1 s^-1. It is attributed to the dominance of diffusion-controlled solute drag at high temperature. Moreover, the effect of bcc phase relies on interphase boundary and strain heterogeneity around these particles, since no phase transformation occurs and most of the strain is accommodated by fcc phase.

Abstract:Silver brazing flux, composed of K₂B₄O₇, H₃BO₃, KF and/or KHF₂, was used to remove the oxide film on the surface of 304 stainless steel. The oxide film removal mechanism was studied. The results show that K₂B₄O₇ and KF cannot remove the oxide film on the surface of 304 stainless steel at 700 °C. Under the synergistic action of any two components, only the mixture of K₂B₄O₇ and H₃BO₃ cannot melt at 700 °C. The calculation results of the reaction equilibrium constant (K^θ) and Gibbs free energy (△G_m^θ) show that the main reason for removing oxide film is that F in the brazing flux can replace O in the oxide in the process. XRD results show that the peak pattern at 2θ=18° is changed, indicating that the mechanism of removing oxide film is different when KF is replaced by KHF₂ in silver brazing flux. No. 3 brazing flux with both KF and KHF₂ can effectively remove the oxide film on the surface of the 304 stainless steel plate at 540 °C. The reaction product has the characteristics of amorphous structure.

Abstract:The isothermal transformation kinetics of U-2Nb alloy was investigated. Based on metallographic quantitative measurements, the general kinetics was presented with the time-temperature-transformation (TTT) diagram. Results show that considerable discrepancies are identified in comparison with previous work on similar alloys. The differences are mainly attributed to two different transformation mechanisms, namely the monotectoid and the discontinuous precipitation reactions, which are operated at higher (550~647 °C) and lower (450~550 °C) temperatures, respectively. In addition, the growth rate of the acicular α precipitate in its lengthening direction, which proceeds through monotectoid reaction, was discussed. Modeling of the lengthening rate was carried out with the Zener-Hillert model supposing a diffusion-controlled mechanism.

Abstract:ProCAST software was used to simulate the casting of fine grain blisk by thermal controlled. Traditional Udimet720Li deformed superalloy was used as the casting material of blisk to simulate the solidification process, porosity distribution, stress distribution and grain growth of blisk. The solidification behavior and microstructure characteristics of the high γ" superalloy used in fine grain blisk casting were studied. The solidification of the blisk begins at the blade tip and ends at the center of riser. The porosity of the main area of the blisk is 1.5%~3%. In the solidification process, due to the shrinkage and segregation, some areas will form relatively large porosity areas. A safety threshold of 13 (K·Sec)0.5/cm was established to evaluate the feasibility of casting process parameters. The maximum shear stress, effective plastic strain and hot crack index at each position of the blisk are 0, but the effective stress is more than 1200 MPa in the blade tip and edge corner area. The average grain diameter of the blisk is 0.88 mm, which meets the requirement of thermal control method. However, thermal control method is not easy to control the uniformity of grain size, so it should be combined with kinetic method to improve the uniformity of grain size.

Abstract:The absorptive characters of O2 on Fe31MnC(001) surface at three different sits (top, bridge and hollow) and effect of C on the magnetic properties of Fe31Mn has been investigated by using the generalized gradient approximation (GGA) based on density functional theory (DFT). The results indicate that O2 tend to be vertically over the four-coordination vacancy hollow site. For Oxygen atom adsorption, it has a larger adsorption energy when oxygen atoms occupy the adjacent four-coordination vacancy hollow site. Among several possible adsorption configurations considered, oxygen at bridge site on Fe31MnC(001) surface is 3.8 eV, which is the most favorable adsorption site. Meanwhile, Carbon atom not only increase the magnetization hybridization of matrix, but also inhibit antiferromagnetic interaction of the adjacent Fe and Mn atoms.

Abstract:Ag bonding wires are widely applied to the field of microelectronic packaging because of their good electrical properties. However, pure Ag wires possess the disadvantages of low strength and high temperature failure, and can not be used in high power devices. Therefore, we try to design an equal atomic AgAuPd medium entropy alloy as new bonding material to replace pure Ag wires. In this work, based on the SQS model, the crystal structure of AgAuPd medium entropy alloy is established. The elastic properties (elastic constants, elastic modulus, shear modulus), thermodynamic properties and electronic structure of AgAuPd medium entropy alloy under different pressures are calculated by first principle. It can be predicted that AgAuPd medium entropy alloy has good structural stability, good plasticity, high temperature stability and good conductivity with increasing of pressure. AgAuPd medium entropy alloy has great potential to become a bonding material. Through using the first principle to calculate the mechanical, thermodynamic and electrical properties of AgAuPd medium entropy alloy under different pressure, it has certain theoretical significance for the development of new Ag base bonding wires.

Abstract:Materials are the bottleneck of the fusion reactor application. According to the requirements of low activation materials and reducing cost, Fe, Cr and V elements are selected to design a single-phase medium entropy alloy with non-equal atomic ratio of Fe36.41Cr28.06V35.53 based on minimizing Gibbs free energy. The alloys were synthesized by vacuum melting method followed by hot-rolling and heat treatments. It is found that Fe36.41Cr28.06V35.53 alloy are single-phase bcc solid solution in different treatment states. No any phase transformation is detected, it reveals that the phase structure of the alloy is quite stable, which is in good agreement with the design results. The hardness of the Fe36.41Cr28.06V35.53 alloy is higher than that of the traditional heat-resistant alloys, and the compressive plasticity of the alloys in different treatment states is more than 50%, which achieves a good match of strength and plasticity. Due to the interaction between segregation elements and dislocations, the compressive stress-strain curve of the alloy exhibits serrated flow behavior during the compression deformation process. The microstructures of the Fe36.41Cr28.06V35.53 alloy were characterized in details, and the mechanism of the excellent properties for the alloy was also explained.

Abstract:In order to investigate the heterogeneous-interface characteristics between LaS/CeS and γ-Fe, the edge-to-edge matching (E2EM) model was employed to calculate the atomic matching mismatch between LaS/CeS and γ-Fe from the crystallographic point view. On the basis of the crystallographic calculations, the first-principle calculation based on the density functional theory was performed to calculate the interfacial bonding characteristics and the interface energy between LaS/CeS and γ-Fe on the atomic scale. The crystallographic calculations indicated that the minimum of the interatomic spacing misfit between LaS/CeS and γ-Fe along the matching direction was 10.63%/10.52%, and the minimum of interplanar spacing mismatch is 2.04%/3.32%, respectively. The rough orientation relationships (ORs) were predicted as follows: LaS∥γ-Fe &LaS∥γ-Fe and LaS∥γ-Fe &LaS∥γ-Fe; CeS∥γ-Fe &CeS∥γ-Fe and CeS∥γ-Fe &CeS∥γ-Fe. Based on the predicted ORs, six interface models with different atomic terminations were constructed using the coherent interface approximation. The first-principles calculations showed that the adhesion work of the interface between LaS/CeS and γ-Fe with the lowest interatomic mismatch was 4.78J·m-2/3.65J·m-2，which indicated the larger bonding strength of the interface between LaS/CeS and γ-Fe with the lower interatomic mismatch. The interface bond was dominated by the metal bond. The calculations of interface energy between LaS/CeS and γ-Fe indicated that the smaller the interatomic mismatch was, the lower the interface energy was obtained. The interface energy between LaS/CeS and γ-Fe with the lowest interatomic mismatch was -0.58J·m-2/-3.43J·m-2. The first-principles calculations can provide the theoretical foundations from the energetics point view for the crystallographic matching between LaS/CeS and γ-Fe. current method.

Abstract:For industrially produced C-Mn cryogenic steel, the effects of rare earth Ce additions of 0、6 ug/g、9 ug/g and13 ug/g on the strength and low-temperature toughness of the steel was investigated. Through the tensile experiment and impact experiment, combined with the scanning electron microscope, the fracture morphology-inclusions of the samples with different Ce contents were analyzed and observed. The research results indicated that with the increase of Ce content, the yield strength and tensile strength of C-Mn cryogenic steel increase slowly, while the elongation shows a tendency to increase and then decrease, that is, when the Ce content is 9 ug/g, the strong-plasticity of the product is the best. When the amount of Ce added is 9 ug/g, it obtains the best low temperature toughness, which is mainly attributed to the addition of an appropriate amount of Ce, which effectively modifies the morphology of inclusions, forms fine cotaining Ce inclusions, and enhance fracture resistance in low temperature environment. Moreover, this paper also compares the low temperature toughness at -40℃ of the same specification steel strips with the addition of 9 ug/g (±1 ug/g) Ce and 0 Ce. It is concluded that the impact energy of the steel strip containing 9 ug/g Ce is about 10J higher than that of 0 Ce.

Abstract:In order to study the effect of CeO2 addition on the structure and performance of Ni-Mo-P electroless plating coatings, Ni-Mo-P coatings and Ni-Mo-P/CeO2 composite coatings on the surface of GH4169 nickel-based superalloy were prepared by electroless composite plating technology. The influence of the heat treatment at 400 ℃ on the structure and properties of the coatings was also investigated. The microstructure, element composition, and phase structure of the coatings were analyzed by SEM, EDS and XRD respectively. The mechanical and tribological properties of the coatings was analyzed by microhardness tester, nanoindenter, ball-disk friction and wear tester, and three-dimensional surface profiler.The results show that the Ni-Mo-P coatings exhibits a typical spherical structure with nano and amorphous mixed crystalline structure.The crystallinity of the coatings was only 16%. The addition of CeO2 particles in the Ni-Mo-P/CeO2 composite coatings induces the voids in coatings and promotes the coarseness in morphology. The crystallinity of the mixed crystalline structure increases to 51%. The heat treatment has positive effect on the structure of the coatings, such as promoting the precipitation of Ni3P nano phase, increasing the crystallinity, eliminating the voids and promoting the density. Addition of CeO2 reduces the hardness of the coating. However, heat treatment can improve the hardness of the coatings significantly. The hardness of the Ni-Mo-P coatings increases from 645 HV in the plating state to 1378 HV in the heat treatment state, and the hardness of the Ni-Mo-P/CeO2 composite coatings increases from 546 HV in the plating state to 1141 HV in the heat treatment state. The wear resistance of the coatings is improved obviously after heat treatment. The addition of CeO2 particles to the coatings could enhance the toughness of the coatings, inhibit the occurrence of cracks during the wear process, thus the Ni-Mo-P/CeO2 composite coating have the best wear resistance.

Abstract:The surface of GH3535 superalloy was shot peened with shot peening pressures of 0.3MPa, 0.45MPa and 0.6MPa respectively. The optical profiler and scanning electron microscope (SEM) were used to observe the surface profile morphology of the alloy and the structure of the strengthening layer. Through metallographic microscope (OM), Vickers hardness tester, X-ray stress analyzer, the surface grain size, surface microhardness, surface residual stress distribution and X-ray diffraction peak half-height width are analyzed. The high-cycle fatigue experiment was carried out at room temperature, and the morphological characteristics of the fracture were observed and analyzed by means of scanning electron microscope (SEM). The results show that the grain refinement layer, hardened layer and residual compressive stress layer are formed on the surface of GH3535 alloy after shot peening. And the thickness of the grain refinement layer, the thickness of the hardened layer and the thickness of the residual compressive stress layer produced on the surface of the alloy all increase with the increase of the shot peening pressure.The shot peening pressure is in the range of 0.3MPa to 0.6MPa, and the fatigue life is more sensitive to the impact of shot peening pressure, and the fatigue life increases with the increase of shot peening pressure.When the shot peening pressure is 0.6MPa, the effect of shot peening is the best, and the fatigue life is increased by 471.1%.The increase in fatigue life of GH3535 alloy after shot peening benefited from the improvement of the alloy surface condition.

Abstract:TIG welding experiment of Zr-702 zirconium plate was carried out with 99.999% high purity Ar as shielding gas. The Zr-702 welding joint was studied at 250%, 15%(ω) by static isothermal weight loss method. Influences of soaking time in sulphuric acid medium on its corrosion performance and explore its corrosion mechanism. The results show that the corrosion rate of welded joint is higher than that of base metal in the same temperature and concentration and different soaking time in sulfuric acid medium. When soaking time is 2 days, both welded joint and base metal have good corrosion resistance. The corrosion rate of welded joint and base metal increases significantly when the soaking time increases to 180 days, and the corrosion rate of welded joint and base metal is greatly affected by the soaking time. According to the characterization and analysis of composition, structure and properties of 180-day soaked samples, a large amount of zirconium hydride was precipitated in weld zone and heat-affected zone of weld joint, and the amount of zirconium hydride in base metal or base metal zone was relatively small. The corrosion of Zr-702 base metal in sulphuric acid medium is the combination of uniform corrosion and hydrogen corrosion. Potential difference exists in weld joint due to obvious structural gradient in each zone. Therefore, its corrosion is the local corrosion combined by galvanic corrosion and hydrogen brittleness.

Abstract:In order to obtain reliable Cu/Al dissimilar joints, current assisted Cu/Al high-power ultrasonic welding was proposed. The effects of current on the temperature rise, plastic flow, intermetallic compound (IMC) growth, and mechanical properties of the joints in Cu/Al ultrasonic welding were investigated. The results show that the obtained hybrid welded joint is well bonded, the tensile-shear force of the hybrid welding joint is 3030 N, and the fracture mode of the hybrid welding joint is ductile-brittle composite fracture. At the same welding time of 0.2 s, with the increase of the current, the peak temperature of the Cu/Al interface increases, and the metal plastic flow and diffusion at the interface also increase. This indicates that the assisted current can significantly enhance the interfacial metallurgy; compared with the single ultrasonic welding at welding time of 0.4 s, the assisted current can meet the welding formation requirements of interface temperature and material plastic deformation, but reduce the thickness of the interface IMC layer. This is the primary reason for the enhanced Cu/Al joint by assisted current. The results provide guidance for optimizing the strength of Cu/Al current assisted ultrasonic welded joints.

Abstract:In-situ TiC-TiB₂/Al-12Si composites were fabricated by ultrasonic assisted laser deposition using Ti、B₄C and Al-12Si powders as precursor materials at different proportions. The phase constitution, microstructure, frictional wear behavior of the composites were analyzed using X-ray diffraction (XRD), energy dispersive spectrum (EDS), optical microscope (OM), scanning electron microscope (SEM), friction and wear testing machine and 3D profile measurement. The results show that the α-Al phase is refined with the increasing of Ti+B₄C, rod-like TiB₂ synthesized in-situ can act as the heterogeneous nucleation core of α-Al phase. The TiC synthesized in-situ is a polygonal shape of 150nm. The wear resistance of in-situ TiC-TiB₂/Al-12Si composites is improved. The wear mechanism of Al-12Si alloy without Ti+B₄C addition is adhesive wear, and the wear mechanism of TiC-TiB₂/Al-12Si composites changes from adhesive wear to abrasive wear when the addition of Ti+B₄C is 8wt.%. When the addition of Ti+B₄C is 10wt.%, the wear mechanism of TiC-TiB₂/Al-12Si composites is adhesive wear.

Abstract:To investigate the effect of γ′ morphology and secondary phase on the plastic deformation behavior of co-8.8al-9.8w alloy were prepared,Mo was added to prepare the alloy with different morphology of γ′ phase and secondary phase. The microstructure and room temperature compression behavior of the alloy were studied by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results showed that the compressive strength and plastic deformation ability of the two alloys are almost the same, but the hardness of the 0Mo alloy with cubic γ′ phase is significantly higher than that of the 2Mo alloy with spherical γ′ phase; The fracture mechanism of 0Mo alloy during compression is cleavage fracture, but 2Mo alloy is quasi-cleavage fracture; The spherical γ′ phase rafted under the action of stress, and segregated along the deformation direction, however the morphology and distribution of the cubic γ′ phase did not change significantly; The W-rich secondary phase distributed in the 2Mo alloy will hinder the movement of dislocations.

Abstract:As a new degradable metal material for medical implantation, magnesium alloy has great development potential in medical fields such as bone transplantation and vascular support. However, selective dissolution and accidental hydrogen accumulation are still the key factors affecting the clinical application of magnesium alloys. In this study, optical microscopy (OM), X-ray diffraction (XRD), scanning electron microscopy (SEM), static immersion and potentiodynamic electrochemical test were used to explore the influence mechanism of microstructure and film structure changes induced by the change of rolling shape variable on the degradation performance of hot-rolled magnesium alloy in physiological environment. The results show that the degradation product layers of magnesium alloys with different rolling shape variables are mainly composed of Mg(OH)2, MgCO3, CaHPO4 and HA. With the increase of rolling shape variable, the microstructure of Mg-Zn-Sr-Zr-Mn alloy becomes uniform gradually, and the degradation rate decreases from 1.03 mm?y-1 to 0.24 mm?y-1. This is because with the increase of rolling shape variable, the matrix grain is significantly refined, resulting in more grain boundaries, hindering the expansion of corrosion cracks, and acting as a barrier in the corrosion process of corrosive medium. In addition, with the increase of rolling shape variable, the second phase in the alloy is broken and dispersed, which reduces the density and intensity of galvanic corrosion in the alloy, promotes the uniform occurrence of corrosion and reduces the pitting pit. Finally, hot rolling can improve the defects of the corrosion film, provide more nucleation points for the oxide film on the surface of the alloy, and reduce the cracking of the oxide film. The compactness and stability of the oxide film are greatly improved with the increase of rolling shape variable, and further slow down the infiltration of corrosion ions.

Abstract:To improve the Y-Gd-Hf-O pressed cathode thermionic emission ability, Sc2O3 doped different molar ration of Y2O3/HfO2 pressed cathodes are prepared. The cathode with ratio of 5/2 demonstrates the best emission ability of 2.79 A/cm2 at 1500℃. The cathode has worked stably over 1320 h at 1500 ℃ with the load of 1 A/cm2 during the lifetime test, and the emission decrease to 86% of the initial one under 10 W, 696 h continuous bombardment at the same temperature, reflecting a good anti-electron bombardment ability. XPS depth profile results show the main active substances in work are concentrated in the depth range of 50 nm from the surface. After cathode being activated, the SEM and EDS results show the active materials diameter increase to an extent, and the surface n-type semiconductor contents increase with the Y2O3, which is favorable for enhancing the conductivity, improving thermionic emission, and lowering the work function.

Abstract:In this work, the advanced Cu-Fe-(C) alloys with dual-phase structure was prepared by combining a vacuum melting and rapid solidification. The microstructure evolution and deformation behaviors of Cu–Fe–(C) alloys in the different conditions were studied systematically by optical microscopy (OM), transmission electron microscopy (TEM) and mechanical properties test. The results show that, the addition of C element is beneficial to avoid the grain boundary segregation of the Cu-3wt%Fe alloy in the as-cast state, reduce the size of the fine γ-Fe phases and increase the number density in the matrix, so that the alloy has a lower yield strength and higher elongation; although most of the γ-Fe phases can be transformed into α-Fe phases after cold rolling at low temperature, resulting in the significant increased yield strength above 520MPa, yet, the addition of C can reduce the transformation rate of γ-Fe→α-Fe in the alloy during the cold rolling, and causing the higher elongation in this state; additionally, if the cold rolled alloys are aged at different temperatures for 1h, the hardness of the alloys decreases with increasing temperature, corresponding to the recovery and recrystallization; however, compared with 1# alloy, much more fine precipitates and remained dislocations can be found in the 2# alloy after aging at 400℃ for 1h, an finally resulting in the higher strengths and elongation. In addition, based on the TEM characterization on the precipitates in the alloys and the calculated strengthening contribution of them, the different strengthening mechanisms have been deeply discussed in this paper.

Abstract:Aiming at the remanufacturing difficulties of U71Mn track surface wear, low surface wear resistance and easy porosity defects caused by laser remanufacturing, the technology and method of preparing FeCrNiB coating on track surface by pulse laser cladding were proposed and verified. The results show that the top of the cladding layer is mainly distributed with fine and dense equiaaxial crystals, and there are more dendrites in the middle of the cladding layer. The dendrite grains have primary and secondary crystal arms, and the lower part of the cladding layer presents a cellular crystal structure, which is roughly perpendicular to the interface.The existence of Cr₇C₃ hard phase and nano-sized granular and flake pearlite structure in the cladding layer makes the cladding layer have high hardness and wear resistance, and the average hardness of the cladding layer increases from 310 HV_0.2 to 750HV_0.2.Under the same friction and wear conditions, the wear resistance of the cladding layer increases by 5 times.The tensile strength of butt sample is slightly less than that of matrix, but it can still meet the requirements of rail.

Abstract:In order to study the friction behavior of hard surface coatings under different media, the coatings were prepared by HVOF with WC-12Co, WC-10Co4Cr and Cr3C2-25NiCr materials as raw materials. The properties of the coatings were analyzed by micro-hardness tester, wear tester, scanning electron microscope and so on. The results showed that the porosity of the coating was closely related to the content of the binder phase. In air, WC-10Co4Cr had the highest hardness and the lowest friction coefficient, while Cr3C2-25NiCr had the lowest hardness and the highest friction coefficient. In the environment of 1mol/L HCl, the best corrosion resistance of NiCr binder made the friction coefficient of Cr3C2-25NiCr coating stable, and the poor corrosion resistance of pure Co and CoCr made the friction coefficient of WC-10Co4Cr and WC-12Co coatings with high and low fluctuations. In the friction process under 1mol/L NaOH environment, the corrosion of hard phase could reduce the hardness and increase the friction coefficient.

Abstract:In this paper, different CDPF samples were prepared on the CDPF catalyst by doping with 10, 20 and 30 g/L of different concentrations of La2O3additives. Using XRD, XPS, H2-TPR and other characterization methods and activity evaluation techniques, the relationship between the physicochemical characteristics and catalytic activity of the CDPF carrier surface catalyst doped with different concentrations of La2O3was studied. The results show that as the La2O3 doping concentration increases, the crystallinity of the sample first increases and then decreases; the Pt atomic concentration on the surface of the sample first decreases and then increases; the oxidation activity of the sample to CO shows a downward trend; The characteristic temperature T10 and T50 of the samples for C3H8 both increased first and then decreased, and then increased again; the T10 of the samples for NO2generation rate showed an increasing tendency.

Abstract:In order to investigate the performance of MnCo₂O₄ spinel coating as a metal linker surface coating for solid oxide fuel cells, pure precursor powder was prepared by sol-gel method, and then dense MnCo₂O₄ spinel coating was prepared by electrophoretic deposition method. The four-probe method was used to measure the surface specific resistance of MnCo₂O₄ spinel coatings before and after oxidation at 800°C for 200 h. The bond strength of the coatings was tested at different interface roughnesses using the pull-out method and verified using finite element simulations. The results show that the MnCo₂O₄ spinel coating has a homogeneous structure and good densities. Compared to the AISI430 stainless steel substrate, oxidation at 800°C in air for 200h increases the oxidation resistance by nearly three times. And the specific resistance at the medium temperature surface is less than the limit value specified for SOFC metal connectors. In addition, the surface roughness of the substrate can effectively increase the mechanical bite between the coating and the substrate, but at the same time it can also lead to stress concentration and defects, which reduce the bond strength.

Abstract:Fe-based biodegradable metals having good biocompatibility and excellent mechanical property exhibit great promise for applications in orthopedic implants, while the slow degradation rate is a major bottleneck. In this study, the surface of the porous Fe-30Mn scaffold was dealloyed by electrochemical technology. When using hydrochloric acid and sodium chloride as medium solution in dealloying treatment, micro-nano porous network and sheet-like structures were formed on the surface of the scaffolds, respectively. The contact angle and surface roughness tests showed that the two micro-nano structure significantly improved the hydrophilicity of the Fe-30Mn scaffold and enhanced its roughness. The Fe-30Mn with micro-nano porous network exhibited higher roughness and hydrophlicity than the Fe-30Mn with sheet-like structures. The static immersion method and electrochemical corrosion test were used to evaluate the degradation rate of the before and after alloyingthe scaffolds. The results showed that the construction of surface micro-nano structure could accelerate the degradation of the scaffold. The in vitro cell culture using MC3T3-E1 cells showed that all porous Fe-30Mn scaffolds had good cytocompatibility. The above results confirmed that the Fe-30Mn scaffold had a suitable degradation rate and good biocompatibility after electrochemical dealloying treatment, suggesting its great clinical application prospect in the fields of bone repair.

Abstract:316L austenitic stainless steel samples were prepared by warm compacting and vacuum sintering powder metallurgy method. Effects of sintering temperature on microstructure, phase and mechanical performances such as hardness and tensile strength was investigated. And corrosion weight loss curve, anodic polarization curve, Nyquist diagram and Mott-Schottky curve were studied to investigate the immersion corrosion behaviors of the sintered 316L austenitic stainless steel in 3.5 wt. % NaCl solution. Tensile fracture，immersion corrosion morphology and passivation film composition and elemental valence was analyzed by SEM (Quanta 450 FEG), laser scanning confocal microscopy (LSM 800) and XPS (AXIS Supra) respectively. Results shown that the highest sintering density (7.203 g?cm-3),elongation(65.46%), mechanical tensile strength (420.368 MPa) and hardness (63.1 HRB) are achieved after the samples were warm compacting at 115 ℃ and vacuum sintering at 1290 ℃, and presented high toughness with the tensile fracture morphologies of ductile rupture, deep and numerous dimples. In addition, the lowest corrosion current density (5.07×10-5 A?cm-2), the carrier density (7.23×1019 cm-3), the highest charge transfer resistance (8111 Ω?cm-2) and passivation film resistance (14780 Ω?cm-2) among the sintered samples after 600 h immersion in 3.5 wt. % NaCl exhibited very good corrosion resistance.

Abstract:In view of the requirement of nuclear power plant for the integration of structure and function of neutron shielding materials, the influence of Gd content on thermal neutron shielding performance and microstructure of 06Cr19Ni10 stainless steel was studied. Based on Thermal neutron shielding calculation and simulation analysis, Gd-06Cr19Ni10 melting and rolling tests with different Gd contents were carried out. The results from OM and SEM show that the addition of Gd can refine the grain size of 06Cr19Ni10 stainless steel, but it is easy to form the brittle Ni-Gd second phase. With the increase of Gd content, the area percentage of Ni-Gd second phase also increases obviously, which makes the plasticity of 06Cr19Ni10 stainless steel decrease, the rolling property is obviously reduced. Combined with Thermal neutron shielding calculation and rolling test results, it is considered that Gd-06Cr19Ni10 can obtain relatively balanced thermal neutron shielding performance and rolling performance when Gd content is about 1.7 wt.%.

Abstract:The aluminum-lithium (Al-Li) alloys, which are characterized with lower density, higher specific strength and better corrosion resistance as compared with conventional aluminum alloys, had been widely applied in the fields of aviation, aerospace and navigation. A1-Li alloys exceptional properties are attributed to the addition of Li into the Al matrix. However, A1-Li alloys have problems such as poor formability, large rebound, and anisotropy at room temperature, which severely limit their applications. While the formability of Al-Li alloys could be effectively improved by heating. Schlors had made a lot of research on the hot forming process of Al Li alloys. This paper firstly, introduced the development of Al Li alloys and the research process on thermal formability of Al?Li Alloys based on experiments, instablity criterion and damage theory; aiming at obtained the macro and micro deformation mechanism and damage evolution law of Al Li alloys at high temperature. Additionally, thermal forming and ageing hardening of the Al-Li alloys would be integrated together to approach the target of shape forming and properties improvement of the parts. Finally, the development direction of thermal formability of Al?Li Alloys for aeronautic industry was prospected. This paper can provide a theoretical guidance for the application of the Al-Li alloys thermal forming process.

Abstract:Magnesium alloy and aluminum alloy (Mg alloy and Al alloy) have excellent properties and play an increasingly important role in modern industry. It is of great significance to realize the reliable welding of Mg/Al dissimilar metals for the development of lightweight. However, there are some urgent problems to be solved in the welding of Mg/Al dissimilar metals, such as the easy oxidation of Mg alloy and Al alloy, the formation of pores and the continuous distribution of intermetallic compounds (IMCs), which significantly affect the joint performance. This paper analyzed the weldability of Mg/Al dissimilar metals, reviewed the research progress of Mg/Al dissimilar metal welding, expounded the improvement and elimination of Mg-Al IMCs, and put forward the prospect of Mg/Al dissimilar metal welding.

Abstract:Silver films / coatings is a kind of new material with great potential in the field of high and new technology, and has been extensively used in modern industry in recent years.SThe silver thin films/coatings prepared by magnetron sputtering have excellent adhesion. The microstructure and properties adjustment of silver thin films/coatings can be achieved by selecting appropriate deposition parameters.SIn this paper, the main preparation methods of silver thin films/coatings deposited by magnetron sputtering are summarized the research progress of silver thin films/coatings in its main application fields is reviewed, and the future development of silver thin films is prospected.

Abstract:The traditional T6 heat treatment of ZL114A alloy is difficult to meet the increasing performance requirements of aerospace field. Therefore, a new low-to-high two-stage solution heat treatment process was designed in this paper, and the effects of single-stage solution treatment and two-stage solution treatment on the microstructure and mechanical performance of subsequent aged alloys were compared. The results show that the two-stage solution treatment increases the Mg concentration from 0.43 wt.% up to 0.54 wt.%, significantly improves the number density of Mg2Si aging precipitates, and promotes the intractable long strips π-Fe (FeMg3Si6Al8) phase which is difficult to eliminate in the single-stage solution treatment, into spherical β-Fe (FeSiAl5). At the same time, eutectic silicon particles with higher spheroidization were obtained. As a result, the mechanical properties of ZL114A alloy have been significantly improved: the ultimate tensile strength is 347MPa, the yield strength is 287MPa, and the elongation is 7.7%.