Materials based on binary immiscible metal systems are widely used in aerospace, nuclear fusion engineering, electronic packaging, anti-armor weapons and other fields. However, due to the positive formation heat and the large differences in the properties of the component, the direct alloying of binary immiscible metals and the preparation of the corresponding materials are very difficult. Varieties of methods have been developed for direct alloying of binary immiscible metals at home and abroad, and the thermodynamic and diffusion mechanism of these methods have been studied. In this review, firstly the principle and thermodynamic mechanism of mechanical alloying, physical vapor deposition and ion beam mixing, as well as their applications in binary immiscible metal powder alloys and nano-multilayer films are reviewed. Then the irradiation damage alloying (IDA) and high-temperature structure induced alloying (HTSIA) methods that are proposed and developed by our group are introduced. Besides, the principle, interfacial microstructure, thermodynamic mechanism, diffusion mechanism and application of these two methods were described in detail. Finally, the development trend of the research on alloying of binary immiscible metals is proposed.

Using complex shapes and precise structural parts is becoming a strong trend in modern advanced manufacturing. However, traditional manufacturing technology hardly achieves the complex geometric parts directly. Selective laser melting (SLM) is an advanced manufacturing technology for metallic materials, enables production parts with complex geometry combined with the enhancement of design flexibility. The cooling rate of molten pool can reach 10³~10⁶ K/s during the SLM process. In this case, the solid solubility of the alloying elements in the matrix can be greatly enhanced. Aluminum alloy has been widely used in industry. At present, the strength of SLM-formed aluminum alloys is far lower than that of high-strength aluminum alloys obtained from a traditional process. It is necessary to develop high-strength aluminum alloy composition based on SLM technical characteristics. The present study is devoted to design high-strength AlSiMg1.5 aluminum alloy specifically for SLM using the local structure model based on the liquid-solid structural compatibility of the alloy and the technical characteristics of the liquid quenching in SLM. The effect of the ageing treatment on the microstructure, the hardness, and the compressive properties of the SLM-formed AlSiMg1.5 alloy was systematically studied. Almost completely dense samples were obtained by adjusting the parameters of SLM process. When the ageing temperature was 300 ℃, the super-solid solution Si precipitated and grew in the island-like Al-rich structure, and the reticular Si-rich structure decomposed and spheroidized gradually with the increases of ageing time of SLM-formed AlSiMg1.5 samples. In this case, the hardness and the strength of the samples decreased, but the elongation increased significantly. The microstructures of the SLM-formed AlSiMg1.5 samples did not change obviously when the ageing temperature was 150 ℃. But the hardness and yield strength of the samples significantly increased first and then decreased slightly. The maximum microhardness and compressive yield strength of SLM-formed AlSiMg1.5 samples aged at 150 ℃ were (169±1) HV and (453±4) MPa, respectively, and the elongation of samples exceeds 25%. In this study, a special Al_91.0Si_7.5Mg_1.5 (mass fraction, %) aluminum alloy specifically for SLM with excellent formability and mechanical properties was designed.

Al-Li alloy has been widely applied in the fields of aircraft, aerospace and military applications due to its superior comprehensive properties. Al-Li alloy prepared by traditional casting process will have shrinkage porosities and gas holes defects due to the gas absorption of lithium element. Twin-roll casting (TRC) process combines continuous casting and rolling deformation into one process. The melt subjected to a certain rolling force during cooling and solidifying, compensates for the solidification shrinkage of liquid metal in the roll-casting region, hence solving the problems of porosity and other defects in Al-Li alloy. However, due to the wide solidification range of 2099Al-Li alloy, the central macro-segregation inevitably occurs in the sheets produced by TRC, which seriously deteriorates the mechanical properties of the sheets. How to eliminate segregation in aluminum alloys strips by adjusting the rolling parameters has been studied for decades. But the effect was not obvious and new approaches are required to solve this challenge. Introducing electromagnetic oscillation field in TRC process may be an effective way to solve the central segregation in TRC sheets. In this work, the OM, SEM, EMPA, DSC, conductivity and tensile test are employed to study the microstructure and properties of 2099Al-Li alloy prepared by TRC and electromagnetic TRC, respectively. The Lorentz force generated in the roll-casting region by applying electromagnetic oscillation field during TRC, which can break the dendrite and refine the solidification structure of the alloy. The central segregation band of the TRC sheet basically eliminated, and the segregation degree of Cu, Zn and Mg elements reduced to 2.45, 0.93 and 1.05. The macro-segregation and micro-segregation of sheets were effectively reduced. At the same time, the electromagnetic oscillation field can enhance the mixing ability of solute atoms, reduce the content of non-equilibrium eutectic phase and improve the supersaturated solid solubility of matrix. Compared with TRC sheet, the tensile strength, yield strength and elongation of 2099Al-Li alloy sheet prepared by ETRC increased by 34 MPa, 18 MPa and 2.8% respectively, hence the mechanical properties of the alloy sheet were greatly improved. This research work provides a new idea for the efficient preparation of Al-Li alloy with energy-saving, high-efficiency and green environmental protection.

The material constraint is an important factor affecting the fracture behavior of dissimilar metal welded joint (DMWJ). For accurately design, manufacture and structure integrity assessment, is necessary to clarify the influence of material constraint on the DMWJ. However, there is still a lack of a systematic research on the influence of material constraint on the fracture behavior of the DMWJ in the current nuclear power plants, and how to improve the fracture resistance of the DMWJ by the optimal design of the material constraint should be considered. In this work, a 52M nickel-based alloy DMWJ in nuclear power plants was selected, the initial crack which located in the heat affected zone (HAZ) was manufactured, and the fracture behaviors of the DMWJ under different material constraints of HAZ, fusion zone (FZ) and near interface zone (NIZ) were studied. In addition, the optimal design of the material constraint was investigated. The results show that for the HAZ crack, the J-resistance curves increase monotonously with increasing the strength of HAZ where the crack is located in. And the J-resistance curves increase firstly, then decrease and remain steady with increasing the strength of FZ and NIZ where the crack is nearby. The optimized DMWJs have higher J-resistance curves, and when M_s (HAZ): M_s (FZ):M_s (NIZ)=2:1.4:0.84, the optimized DMWJ has the highest J-resistance curve which is several times of the current J-resistance curve.

Because of having better corrosion resistance properties than crystalline uranium alloys, U-based metallic glasses show strong potential of applications in nuclear fields. U-Co and U-Fe are U-based important base glass systems, from which almost all the reported multi-component U-based amorphous alloys derive. However, which system possessing higher glass forming ability is unclear yet. Therefore, the relationship between the glass formation and the solidification rate is studied on two glassy alloys U_66.7Co_33.3 and U_69.2Fe_30.8 in this work, which are the best glass former in the corresponding system. A series of amorphous samples were prepared by modifying the cooling rate of their melts, and then were measured by using XRD and calorimetric analysis technique. The results show that both alloys were able to nearly amorphize completely at higher cooling rate, and tended to segregate U₆Mn-typed crystalline phase when the cooling rate declined to some extent. In contrast, the U-Fe alloy needs a much lower critical cooling rate to achieve fully amorphous structure, directly demonstrating that U-Fe system possesses stronger glass forming capacity than U-Co. The reason for this conclusion is that the former system is of both thermodynamic and kinetic advantages for glass formation. This result can be applied as the foundation to exploit superior novel multicomponent U-based amorphous alloys.

The anisotropy of elasticity of single crystal superalloy is essential to understand its mechanical behavior, e.g. calculating the vibration frequency of turbine blade and avoiding resonance during operation. However, it's difficult to calculate the stiffness constants of single crystal superalloy by theory methods. In this work, one simple experimental method is employed to determine the stiffness constants. The slabs of a first generation single crystal superalloy in two orientations 〈001〉〈100〉 and 〈011〉〈110〉 are employed to measure the Young's modulus and shear modulus of this alloy. The Young's modulus and shear modulus of the first specimen and the shear modulus of the second specimen are measured by resonance method from room temperature to 1100 ℃. The three stiffness constants C₁₁, C₁₂ and C₄₄ of this superalloy are calculated from the measured moduli. The Young's modulus and shear modulus in any orientation can be calculated based on the stiffness constants. Further, the 3D distribution map of Young's modulus and maximum and minimum of shear modulus related to primary orientation can be drawn, so the distribution feature of modulus in 3D space can be acquired conveniently. When the primary orientations are along 〈001〉 and 〈111〉, the shear modulus in plane is isotropy with secondary orientation. When the primary orientation is along 〈011〉, the shear modulus demonstrates significant anisotropy with secondary orientation, the shear modulus reaches minimum with secondary orientation 〈110〉, while the maximum is obtained in secondary orientation 〈100〉.

Hot-dip galvanizing is the most economical way to improve the corrosion resistance of advanced high strength automobile steel. With the high trend of developing of automobile steel towards light-weight and high-strength, the contents of Si, Mn, Al alloy elements in steel increase accordingly. These alloy elements would be selectively oxidized during hot-dip galvanizing process, which affect in turn the wettability of steel surface and form different interface microstructures. However, its effect on the mechanical behavior of steel has never been known as clear as desired. Base on this point, the thermodynamics of the surface oxide and its effect on the interface microstructure of three high-strength automobile steels were studied after the same hot-dip galvanizing treatment as well as their tensile fracture behavior under different deformation conditions was in situ analyzed. Combined with the microstructure analysis and thermodynamic calculation, it can be concluded that different compositions of steel would produce different kinds of oxide on its surface. When Mn₂SiO₄ and SiO₂ were formed as thermodynamic stable phases, it was difficult to form a continuous Fe₂Al₅Zn_0.4 inhibition layer at the interface, zinc liquid could penetrate into the iron substrate and then form the brittle phase ζ-FeZn₁₃, where the crack was easily to be obtained and expanded to the substrate, resulting in the decrease of mechanical properties. When MnO and Mn₂SiO₄ with a small amount were formed as thermodynamic stable phase, the Fe₂Al₅Zn_0.4 inhibition layer can be obtained. Under the tensile stress, this crack generated at the interface and extended to the zinc layer. So, the fracture of the experimental steel was mainly resulted from the failure of substrate. When MnO and FeO were formed as metastable phase, Fe, as formed by aluminothermic reduction during hot-dip galvanizing, would reacted with zinc liquid to form Γ-Fe₁₁Zn₄₀ phase in the zinc layer. The crack generated under the tensile stress and expanded in the zinc layer. Since the unreduced MnO layer at the interface exhibited a higher bonding strength with substrate, tensile fracture of the experimental steel was caused by the failure of substrate.

Multi-pass processing is commonly used in hot working of steels. Dynamic recrystallization (DRX) occurs during hot deformation, while post-dynamic softening takes place during the inter-pass times and post-deformation annealing. Three different mechanisms are believed to be responsible for the post-dynamic softening stage. These are static recovery (SRV), static recrystallization (SRX), and post-dynamic recrystallization (P-DRX). Each of these mechanisms can change the microstructure of austenite (i.e. grain size and distribution). As a result, the post-dynamic softening behavior of austenite may play an important role in the microstructures and the final mechanical properties of the steel product. In this work, a Ni-30%Fe model alloy is used to study softening of austenite in post-deformation annealing after the hot deformation at 900 °C and strain rate 0.001 s^-1. The microstructures in the annealed samples are carefully analyzed by EBSD in conjunction with TEM. The results show that P-DRX and sub-structural restoration are believed to be responsible for softening of the material after hot deformations. The P-DRX generally consumes deformed structures by the growth of the preformed nuclei of dynamic recrystallization. The sub-structural restoration in austenite usually takes place through the dislocation climb, leading to sub-boundary disintegrations and dislocation annihilations. When the sample is deformed to the peak strain, the deformation microstructure is composed of both recrystallized grains and deformed matrix. The large gradient of stored energy between the recrystallized grains and deformed matrix effectively promotes the strain-induced migration of the large-angle grain boundaries, which makes the P-DRX become the predominated post-dynamic softening mechanism during the post-deformation annealing. Meanwhile, the sub-boundaries within the deformed matrix gradually disintegrate through the restoration mechanism, which also contributes to the post-dynamic softening of austenite. On the other hand, the dislocation annihilation can result in a reduction of the stored energy within the deformation matrix, which inhibits the further migration of grain boundaries. In contrast, when the sample is deformed to the steady-state stage of the dynamic recrystallization, a fully recrystallized microstructure is obtained. The sub-structural restoration process of the fully recrystallized microstructure is much faster than that in the deformed matrix during the post-deformation annealing. It makes the sub-structural restoration become the predominated post-dynamic softening mechanism of this alloy in the steady-state condition. Furthermore, the disintegration of large numbers of sub-boundaries leads to an increase of the dislocation density in local region around the grain boundaries, which facilitates local migration of the high-angle grain boundaries and accelerates the softening of the material.

It is unavoidable for coated steel bars to be scratched during transportation and construction, which will lead to the damage of coating and exposure of steel matrix. Consequently, the corrosion resistance of coated steel bars after damage will directly affect the durability of structures. The corrosion evolution behavior of damaged epoxy coated steel bars under the coupling action of chloride ion and carbonization was studied by comparing with bare steel bars and perfectly coated steel bars. On the basis of characterizing the composition and structural characteristics of epoxy coating, the corrosion morphology and product composition at the damage site of the coating were analyzed by CLSM and Raman spectroscopy, and the corrosion process was monitored by corrosion potential and electrochemical impedance spectroscopy to reveal the dynamic of corrosion evolution. The results show that the epoxy coating without damage has a good protective effect on steel matrix, and no corrosion occurs during long-term immersion in all six solutions including the chloride ions and carbonization corrosive environments. The corrosion activation or passivation behavior of damaged coated steel bars is consistent with that of uncoated bare bars, which is obviously affected by chloride ion and carbonization. Passivation occurs in the system without Cl^- and with pH of 12.6 or 9.8. Activation dissolution occurs in the chloride-free system with pH of 9.2, and in the system of different pH values with 0.6 mol/L NaCl. In the active systems, the corrosion rate increases with time. In the chloride-free system, the corrosion products after long-term corrosion are mainly α-FeOOH, while in the chloride-containing system with different pH, the corrosion products contain not only α-FeOOH, but also β-FeOOH and a small amount of Fe₃O₄. Under the coupling action of chloride ion and carbonization, the corrosion of damaged coated steel bars occurs only in the damaged site, and the corrosion extends towards to the depth of the matrix, which will not cause the peeling of coatings in other sites.

The corrosion of steel rebar in concrete will be induced once the passive film is destroyed by chlorides or carbonation. Several techniques have been employed to reduce the corrosion so far. Among them, adding inhibitors is effective one because of its advantages, such as high efficiency and easy handling. 1-hydroxyethylidene-1,1-diphosphonic acid (HEDP), a typical organic phosphonic acid, is a low toxic corrosion inhibitor for steel and iron in neutral aerobic environment. This compound was first used as scale inhibitor in water treatment industry, such as cooling water circulation system. The molecule of HEDP has two phosphate groups, making it a powerful chelating ability with metallic ions. However, most of the current studies of HEDP focus on neutral or near-neutral systems, and there are few reports on the corrosion inhibition of steel reinforcement in alkaline environment. Therefore, it is not clear whether HEDP can play the role of corrosion inhibitor by protecting the passive film and resist foreign corrosive Cl^-. In this work, the inhibition effect of HEDP towards 20SiMn steel was investigated in simulated concrete pore solution contaminated by Cl^- (Sat.Ca(OH)₂+1 mol/L NaCl) by electrochemical methods (corrosion potential, potentiodynamic polarization curves, EIS and Mott-Schottcky curves) and surface analysis techniques (SEM, XPS). The results showed that HEDP was a mixed inhibitor and its inhibition efficiency increased first and then decreased with the increase of concentration, the optimal concentration is 1.441×10^-4 mol/L . At the optimal concentration, HEDP could obviously enlarge the passive region, prolong the passive period of 20SiMn steel from 6 h to 9 h , and improve the charge-transfer resistance significantly with the inhibition efficiency around 46.45%~59.78%. When pitting corrosion occurs, HEDP could hinder its development with the inhibition efficiency over 93%. The inhibition mechanism was the preferential adsorption of HEDP over Cl^- by forming a complete adsorption film outside the passive film of the steel.

The quasicrystal (QC)-abrasive wear produces a flattened surface compared with traditional abrasives when used to polish metals, opening up new application fields for QC in particle form, but the influence range and extent of QC-abrasive on metal surface are not clear. In this work, the single particle grinding model was used for finite element simulation to qualitatively characterize the effect of QC-abrasive on the subsurface of stainless steel, which was ground by diamond, Al₂O₃ and QC single particle abrasive, respectively. The effects of three kinds of abrasives on the equivalent stress and strain of stainless steel surface were compared. Combined with the measurement of the gradient hardness of stainless steel subsurface, the Mott-Schottky plots and potentiodynamic polarization curve were given, analyzing the corrosion resistance mechanism of passivation film formed on the surface of stainless steel pretreated with QC-abrasive. The results show that the equivalent plastic strain of the stainless steel surface is the highest, up to 73%, when it is ground by QC single particle abrasive repeatedly for six times, which is consistent with the smearing coefficient measured in the experiment. The smearing-dominating on the surface of stainless steel treated with QC-abrasive is strengthened with time increased, but diamond and Al₂O₃ abrasives are improved cutting-dominating with time increased. At the same time, a large number of plastic deformation areas accumulated a higher stress, longitudinal sub-surface of stainless steel treated by QC-abrasive show a higher gradient distribution of equivalent stress. The simulation results are consistent with the changes of hardness of stainless steel at different depths measured in the experiment. The hardness of QC-abrasive treated stainless steel maintains the highest value at 200, 400 and 1800 nm to the surface, respectively. It is manifested as the gradient law of gradual decrease from the surface layer to the interior of the matrix. The Mott-Schottky plots with the minimum carrier concentration prove a large amount of plasticity accumulated on the subsurface of stainless steel treated via QC-abrasive, providing the preferred channel for the passivation element to bond with oxygen when the passivation film is formed on the surface. It can promote the formation of a complete passivation film on surface. The minimum passivation current density with 0.73×10^-6 A/cm² of potentiodynamic polarization curve indicates that QC-abrasive pretreated the surface of stainless steel is easier to be passivated. It is also less likely to be punctured to form pitting corrosion due to the relatively high breakdown potential.

The oxygen adsorption behavior of V(110) surfaces and the alloying effects of Al, Ti, Cr are calculated using first-principles method. Then the surface phase diagrams for oxygen adsorption on binary V alloy surfaces are constructed combining with thermodynamics formalism. The microscopic mechanisms for oxidation of V alloy surfaces are analyzed. The calculated results of surface energies indicate that Al and Ti are preferable to be segregated on V(110) surfaces, while Cr is not. The oxygen adsorption behavior indicates that Al and Ti are favored to be oxidized on V(110) surfaces, while Cr is not. In this work, the microscopic oxidation mechanisms of V alloy surfaces have been successfully used to explain the experimental results of oxidation behavior. Moreover, the selective oxidation behavior of V-Al alloys has been predicted, and it would provide guidance for the fabrication of oxide tritium permeation barrier.