AlCoCrFeNi_2.1 eutectic high entropy alloy has excellent mechanical properties and promising applications in fields such as hydrogen storage and transportation. The surface of the alloy is hydrogenated by electrochemical hydrogenation， and tensile tests are carried out on H-charged and H-free specimens to compare and analyze the fracture morphology characteristics， and the effect of hydrogen-induced precipitated phase evolution on the mechanical properties of the alloy is studied. The results show that compared with the samples without hydrogen charging， the yield strength of the hydrogen charging solution samples with sulfuric acid concentrations of 0.5 mol/L and 1.0 mol/L decreases by 14.60% and 20.22%， respectively， and the tensile strength decreases by 15.50% and 25.15%， respectively. Additionally， the mechanical properties of the alloy further decrease with the increase of the hydrogen ion concentration in the hydrogen-charged solution， and the fracture region near the surface shows more obvious brittle fracture characteristics. The precipitated phase， which undergoes a phase transition after hydrogen charging， remains on the surface of the BCC phase during fracture to form a higher and denser raised structure， and a structure distinct from the two phases is also found at the phase boundary. The evolution of hydrogen-induced nanoprecipitated phases leads to a decrease in the overall mechanical properties of the alloy.

Adding appropriate amounts of Al and Cu atoms to high-entropy alloys （HEAs） can significantly improve mechanical properties of the alloys， but there are few research reports on the corrosion resistance of Al and Cu atoms in HEAs. To reveal the influence of Al and Cu atoms on the corrosion behavior of HEAs， this study focuses on FeCoNi based medium entropy alloys with excellent mechanical properties. FCC single-phase Fe₂₅Co₂₅Ni₂₅Al₁₀Cu₁₅（Al10Cu15） alloy and BCC+FCC dual-phase Fe₂₅Co₂₅Ni₂₅Al₁₅Cu₁₀（Al15Cu10） and Fe₂₅Co₂₅Ni₂₅Al₂₀Cu₅（Al20Cu5） alloys are designed using empirical formulas for high-entropy alloy composition design. XRD analysis shows that the amount of FCC phase decreases and the amount of BCC increases with the increase of Al content， which is consistent with the theoretical calculation. SEM microstructure and EDS analysis show that increasing the amount of Al added and decreasing the amount of Cu added result in a transformation of the grain morphology from dendritic （Al10Cu15， Al15Cu10） to equiaxed （Al20Cu5）， and the composition of the interdendritic also changes significantly. The Al10Cu15 interdendritic microstructure is a Cu-rich FCC phase， the Al15Cu10 interdendritic microstructure is an Al-， Ni- and Cu-rich BCC phase， and the Al20Cu5 grain boundaries microstructure is a Fe- and Co-rich FCC phase. The potentiodynamic polarization（PDP） experiments show that alloys with high Al content have a dual-phase structure and are prone to galvanic corrosion during long-term immersion. The integrity of the passivation film is easily damaged， resulting in poor corrosion resistance of the alloy. The electrochemical impedance spectroscopy （EIS） tests show that the reaction resistance of alloys with higher Al additions decreases significantly with the prolongation of immersion time， which is consistent with the results of PDP analysis. Static immersion experiments at room temperature show that compared with Al10Cu15 alloy， Al15Cu10 and Al20Cu5 alloys are more susceptible to galvanic corrosion under prolonged immersion. It can be concluded that the addition of an excessive amount of Al atoms induced by the second phase significantly deteriorates the corrosion resistance of the material. Ensuring the homogeneity of alloy structure composition is an effective means to improve the corrosion resistance of materials.

Damping alloys can dissipate vibration energy into thermal energy through defective motion with high mechanical properties and functional characteristics， which have a great significance in the development and research of aerospace and military fields. There are differences in microstucture between different alloy systems. The types of defects that play a dominant role in damping are different， and the properties of structureal defect （type， density， and movability） are the key factors affecting the damping performance of alloys. The types and characteristics of damping source for different damping alloys systems were summarized from the perspective of defects （plane defects， line defects， and point defects）. The relationship between damping capacity， mechanical properties， and functional properties （corrosion resistance， casting performance， etc.） was reviewed， the development status of various damping alloys was summarized， and then the development laws and differences of damping alloys were concluded. Finally， the research direction of damping alloys is prospected. The single type of damping source will seriously limit the improvement of the material damping capacity. While the design concepts of composite materials and high-entropy alloys allow for the coexistence of multiple damping sources， which produces the coupling effect of multiple damping mechanisms that can realize the two-dimensional expansion of damping capacity， and improve mechanical properties and functionalities. The design concepts will play a significant guide to enhance comprehensive performance of damping alloys.

The molecular dynamics method was used to simulate the microstructure dynamic evolution， dislocation， and pore motion characteristics of AlCoCrFeNi high-entropy alloy at temperature 300 K and strain rate of 1×10⁹ s^-1， and the failure mechanism was revealed. The simulation results show that the maximum load-bearing， longitudinal modulus， and ductility of the nano-polycrystalline AlCoCrFeNi high-entropy alloy are lower than those of nano-monocrystalline. The strain reduction and peak stress reduction of nano-polycrystalline before yield are 25% and the peak stress reduction is 23.8%. The phase transition， dislocation， hole， and failure mechanism of the two nanocrystallines are different during the stretching process. During the stretching process of nano-monocrystals， the FCC structure is mainly transformed into a non-crystalline structure. The atomic position changes after the phase change， accompanied by a large number of Shorkly dislocations， and moves with the growth direction of the non-crystalline structure. The hole nucleation， growth， penetration， and failure fracture of non-crystalline structure area are mainly amorphous perforation fault. During the stretching process of nano-polycrystalline， the FCC structure mainly transforms to HCP structure and non-crystalline structure， and the atomic position changes after the phase change， accompanied by a large number of 1/6〈112〉 （Shortly） dislocations and a small number of 1/6〈110〉 （Stair-rod） dislocations， 1/3〈100〉 （Hirth） dislocations， and other dislocations continue to be generated and annihilated.The material undergoes certain plastic deformation， with nucleation of pores in the non-crystalline structure area of the grain boundary， growth and expansion along the grain boundary， and penetration through the grain boundary until failure fracture， showing mainly intergranular fracture.

Refractory high entropy alloys have excellent high temperature mechanical properties， but the high temperature oxidation resistance has always been one of the limiting factors in their application. Four kinds of refractory high entropy alloys AlNbTaTiZr， AlMoNbTiZr， AlMoNbTaTiZr and AlMo_0.5NbTa_0.5TiZr were designed and prepared by laser additive manufacturing technology. The oxidation mass gain of AlNbTiZr-based refractory high entropy alloys was measured at 900 ℃ and 1000 ℃， and the oxidation layer structure of different samples was studied. The effects of Mo and Ta on the high temperature oxidation resistance of AlNbTiZr-based refractory high entropy alloys were compared and analyzed. The results show that the four kinds of as-deposited high entropy alloys prepared by laser additive manufacturing are BCC＋HCP dual-phase structures. The dendrites are mainly BCC phases with high melting points， and a small amount of HCP phase rich in Al and Zr is distributed among the dendrites. AlNbTaTiZr shows the best oxidation resistance after oxidation at 900 ℃ and 1000 ℃ for a long time， and Ta instead of Mo to some extent improves the oxidation resistance of refractory high entropy alloys.

The morphology and phase stability of precipitated phases are essential for regulating mechanical properties of alloys. The (FeNiCoCr)₉₀Al₅Ti₅ high entropy alloy was prepared by low-speed ball milling and hot-press sintering method, and the effects of high-temperature (1150 ℃) and medium-temperature (850 ℃) aging treatment on the types, morphology, distribution and mechanical properties of precipitated phases in the alloy were investigated. The results show that the compressive strain of the prepared alloy reaches 47%, and the yield strength and ultimate compressive strength are 948 MPa and 1684 MPa, respectively. The high strength is due to the strengthening effect of the L1₂ structure nano-precipitation phases within the crystal. After aging at 850 ℃ for 10 h, the L1₂ precipitated phases grow into equiaxed grains with a size exceeding 10 μm, and some of them transform into a thin lamellar HCP structure η phases, which leads to the decrease of the yield strength and ultimate compressive strength of the alloy. After aging at 1150 ℃ for 2 h, the intracrystalline L1₂ nano-precipitated phases completely redissolve, which leads to a drastic decrease in the yield strength and ultimate compressive strength of the alloy.

The formation mechanism of passivation film and corrosion resistance of (40-x)Zr-30Ti-20Nb-10Al-xTa (x=0, 2, 4, atom fraction/%, the same below, referred to as Tax alloy) high entropy alloy in a 0.3mol/L LiOH solution were investigated by potentiodynamic polarization, electrochemical impedance technique, Mott-Schottky analysis and potentiostatic polarization. The results show that the addition of appropriate amount of Ta (2%) helps to form a compact oxide film, which improves the corrosion resistance, while the excessive amount of Ta (4%) decreases the corrosion resistance due to the increase of oxygen vacancy concentration. The corrosion current density of the Ta2 alloy is 49.66 nA/cm², which is less than the Ta0 and Ta4 alloys of 201.40, 70.16 nA/cm². The concentration of oxygen vacancy point defect in the passivation film of the Ta2 alloy is 9.79×10¹⁸ cm^-3, which is less than 2.13×10¹⁹, 2.05×10¹⁹ cm^-3 in the Ta0 and Ta4 alloys, with the most compact passive film structure. The passivation film of the alloy is a stable n-type composed of ZrO₂, Nb₂O₅, TiO₂, Al₂O₃ and Ta₂O₅. Among them, the oxide content of ZrO₂, Nb₂O₅ and TiO₂ in the oxide film of the Ta2 alloy is the highest, which delays the dissolution rate of the primary oxide film and protects the matrix from further dissolution, with the best corrosion resistance.

A γ′ phase strengthened NiCoCrFeAlTiMoW alloy was prepared in a vacuum arc melting furnace, and X-ray diffractometer (XRD), scanning electron microscope (SEM), energy dispersive spectrometer (EDS) and tensile testing machine were used to investigate the coarsening behavior and the evolution law and mechanism of mechanical properties of the γ′ phase after 200 h long-term aging at 750, 850 ℃ and 950 ℃.The results show that γ′ phase remains spherical during the aging process when the aging time is extended, γ′ phase size gradually increases and the solidification phenomenon occurs at 750, 850 ℃ and 950 ℃. The alloy has a high diffusion activation energy with a value of 357 kJ/mol.This is mainly due to the fact that the matrix is a high entropy solid solution with complex composition, and the diffusion of Al and Ti atoms in the matrix becomes difficult due to the hysteresis diffusion effect. The yield strength of the alloy gradually increases after aging at 750 ℃, the yield strength after aging at 850 ℃ first increases and then decreases, and gradually decreases after aging at 950 ℃. The change in the yield strength of the alloy is caused by the increase in the size of the γ′ phase, which leads to a shift in the precipitation strengthening mechanism of the alloy.

The development of nuclear reactor structural materials with excellent comprehensive performance is the basis of nuclear energy development, and it is one of the difficulties that have long restricted the promotion of nuclear energy. Multiprincipal element alloys(MEAs) have been recognized as candidate materials for advanced reactor structural materials due to their good irradiation resistance and mechanical properties, which has expanded a broad space for the design of new radiation-resistant materials. In recent years, the research on the irradiation damage of multiprincipal element alloys has tried to reveal the influence of some factors and characteristics of multiprincipal element alloys on the formation and evolution of defects in the irradiation process. For example, the type, number and concentration of alloying elements, lattice distortion, chemical short range order, etc. Although some existing research results show that the above factors can improve the resistance of multiprincipal element alloys to irradiation damage, under different irradiation conditions, the influence mechanism of the above factors on the formation and evolution of defects in multiprincipal element alloys is quite different, and it is difficult to draw generalization conclusions. Focusing on the four aspects of irradiation swelling, helium bubble formation, irradiation-induced element segregation and phase transition, irradiation hardening of FCC and BCC systems.The research progress of multiprincipal element alloys in irradiation damage in recent years was reviewed, the mechanism of action of multiprincipal element alloys to improve radiation resistance was summarized.And based on this, the future research directions for multiprincipal element alloys used in nuclear power structures were prospected, including tuning short-range order, high-entropy ceramics, additive manufacturing technology, accelerating development of new materials by integrating high-throughput computing with machine learning, etc. Finally, it is pointed out that new radiation-resistance MEAs must be designed based on the actual environment of material service from the perspective of composition design.

High entropy alloys (HEAs) were first reported in the early 2000s. High mixing entropy of the HEAs makes it present good thermal stability. Meanwhile, the large lattice distortion in the HEAs leads to significant solution strengthening. Additionally, cluster structures are formed within grains due to the large negative enthalpy. Consequently, the movement of dislocation is effectively hindered, and the strength of the HEAs is remarkably improved. Given to these unique characteristics, the HEAs is expected to have excellent physical and chemical properties at low and high temperatures. As a result, the HEAs have become a hot area with lots of published research papers. Based on existing physical and mechanical properties of the HEAs with BCC and FCC structure, relation among electron concentration, lattice constant, atomic mismatch, mixing enthalpy, hardness, elasticity modulus and normalized hardness were analyzed to develop a formula calculating elasticity modulus and hardness of the HEAs. On this basis, the composition design method of the HEAs with BCC and FCC structures is established by considering density, ductility and working environment. Finally, it is pointed out that the persistent strength of HEAs, the uniformity of composition and properties of large-sized ingots, and the preparation of large-sized alloy ingots are key issues that need to be addressed in the engineering application of HEAs.

Due to excellent comprehensive properties such as high strength, high hardness, and excellent high-temperature oxidation resistance, the refractory high-entropy alloys have broad application prospects and research value in the fields of aerospace and nuclear energy. However, the refractory high-entropy alloys have very complex composition features, making it difficult to perform alloy design. It seriously restricts the development of high-performance refractory high-entropy alloys. In recent years, the machine learning technique has been gradually applied to various high-performance alloys with efficient and accurate modeling and prediction capability. In this review, there was a comprehensive summary of research achievements on machine learning-driven design of refractory high-entropy alloys. A detailed review on the applications and progress of machine learning technique in different aspects was given, including alloy phase structure design, mechanical property prediction, strengthening mechanism analysis and acceleration of atomic simulations. Finally, the currently existing problems in this direction were summarized. The prospect about promoting the design of high-performance refractory high-entropy alloys was presented, including development of high-quality database for refractory high-entropy alloys, establishment of quantitative relation of "composition-process-structure-property" and achievement of multi-objective optimization of high-performance refractory high-entropy alloys.

The high entropy alloy overturns the traditional design idea that one or two elements are the main elements, and its design concept of multi-element and high mixing entropy endows it with excellent properties such as high strength, high toughness, corrosion resistance, high temperature resistance and oxidation resistance, etc., making high entropy alloy being a research hotspot in the field of new high-performance structural materials. The research and development of high entropy alloys will inevitably lead to engineering application, where hot working is an important way to further control the microstructure and properties. As a result, the hot deformation behavior which characterizes the hot working properties has become a new research emphasis and hotspot. Based on the research status of hot deformation, the high entropy alloys were classified according to phase structure firstly, and the constitutive relation of hot deformation and prediction model of flow stress were introduced. Then, microstructure evolution of high entropy alloys with FCC, FCC+BCC and BCC structures during hot deformation was analyzed. On this basis, deformation mechanism and recrystallization mechanism during hot deformation were summarized. Finally, the challenges faced by hot deformation of high entropy alloys in the future are emphasized, and some suggestions for research trends in the future are put forward as follows: establishing constitutive relation based on physical properties of high entropy alloys, constructing recrystallization model based on structural characteristics of high entropy alloy, strengthening systematic study of hot deformation behavior under different preparation conditions and complex loads, and breaking through the key preparation process of high entropy alloy.

High-entropy alloys exhibit excellent properties such as high strength and toughness, good wear resistance, superb corrosion resistance and superior high-temperature oxidation resistance, which have good potential applications in terms of energy chemical industry, aerospace and national defense. The mechanical behavior of high-entropy alloys under the condition of dynamic loading is different from that under the quasi-static loading, presenting higher strength, more twins and adiabatic shear bands and so on. And different phase structures have a significant impact on the dynamic properties and deformation mechanism of high-entropy alloys. Moreover, the high-entropy alloys have a certain research value in the field of energetic structural materials due to their good energy release characteristics under the condition of dynamic loading. Usually, the stability of dynamic experiment is unacceptable and the test is also difficult to achieve. In contrast, the dynamic mechanical properties of high-entropy alloys can be well predicted based on the constitutive models with experimental verification. As above-mentioned analysis, the dynamic mechanical behavior of high-entropy alloys with different phase structures, energy release characteristics and constitutive models were reviewed. Meanwhile, the comprehensive properties and their constitutive models as well as the simulation calculations were prospected. Finally, it is pointed out that the dynamic mechanical properties of high-entropy alloys can be improved by adjusting the type and proportion of elements, phase structure and concentration distribution. At the same time, the influence mechanism of temperature and strain rate on the dynamic mechanical behavior of high-entropy alloy needs further study. The model calculation also needs to play a greater role in revealing its deformation mechanism and predicting its performance at high strain rate.

AlCoCrFeNi_2.1 eutectic high-entropy alloy is characterized by a fine, homogeneous, and regular lamellar structure, as well as good organizational structure and mechanical properties with both strength and plasticity over a wide range of temperature (70-1000 K) and compositional deviation, thus making it the most widely studied eutectic high-entropy alloy at present. In this paper, regarding the additive manufacturing of AlCoCrFeNi_2.1 eutectic high-entropy alloy, the influence of different processes and process parameters on the microstructure and mechanical properties of the alloy was reviewed, and the phase distribution, microstructure, and strengthening mechanism of AlCoCrFeNi_2.1 eutectic high-entropy alloy prepared by the selective laser melting technology were highlighted. Finally, it points out the differences and deficiencies in phase formation mechanism and organization evolution process of the current additive manufacturing AlCoCrFeNi_2.1 eutectic high-entropy alloy and puts forward the development direction of material modification of AlCoCrFeNi_2.1 eutectic high-entropy alloy as the substrate of the material modification and the new technology of additive manufacturing high-entropy alloy, which will provide ideas for the promotion of the industrialized application of the alloy.

TiVNbTa refractory high-entropy alloy was prepared by vacuum electromagnetic levitation melting technology.The hydrogen absorption and desorption properties of the alloy were tested by multi-channel hydrogen storage tester, the hydrogen absorption-desorption behavior and corresponding kinetic mechanisms were investigated.The results show that BCC single-phase structure in the alloy is transformed into three new phases including TiH_1.971, Nb_0.696V_0.304H and Nb_0.498V_0.502H₂ after the hydrogen absorption process. The hydrides in the hydrogenated high-entropy alloy decompose at 519, 593 K and 640 K, respectively and change to BCC phase again after hydrogen desorption process.Therefore, the hydrogenation reaction is reversible.The alloy exhibits high hydrogenation (dehydrogenation) rates at 423-723 K. The kinetics of hydrogen absorption and desorption can be described by Johnson-Mehl-Avrami (JMA) model and second-order rate model, respectively. The apparent activation energies E_a of hydrogen absorption and desorption are -21.87 J/mol and 8.67 J/mol, respectively.

The refractory high entropy alloys (HEAs) based on refractory elements are developed for potential applications in high temperature areas, since these alloys always have melting temperature higher than 1800 ℃, high temperature structural stability and high resistance to heat softening. However, large density induced lower specific strength and room temperature brittleness hinder their application.In this study, the light-weight non-equimolar (Ti₃₅Zr₄₀Nb₂₅)_100-xAl_x (x=0, 5, 10, 15, 20) HEAs were designed and fabricated, then the effect of Al content on the phases, microstructure and mechanical properties were investigated. X-ray diffraction results indicate that the phase changes from the disorder BCC to ordered B2 of other alloys with the increase of Al content. Five alloys have similar phase morphology. Lots of long and slender dendrites grow along the cooling direction at the edge of the ingots, while equiaxed dendrites form at the center of the samples. Energy dispersive X-ray analysis imply the enrichment of Nb in dendritic regions, while Al and Zr segregate in the interdendritic regions.This can be attributed to the highest melting temperature of Nb and stronger bonding between Al and Zr. Room temperature tests reveal that the increase of Al content leads to the increase of both the yield stress and compression stress, but has less influence on the room temperature ductility, the fracture strain of all alloys exceeds 50%.

In order to improve the mechanical properties and corrosion resistance of Al-Cr-Fe-Co-Ni system high-entropy alloys (HEAs), the effects of Mo on the microstructure, mechanical properties and corrosion behavior of the Al_0.3CrFeCoNiMo_x (x=0.2, 0.4, 0.6, 0.8, molar ratio, the same below) HEAs were studied. The results show that the microstructures of the HEAs evolve from the FCC phase (x=0.2) to the FCC+σ phases (x=0.4-0.8) with the increase of Mo content. The compressive yield strength and hardness of the HEAs are enhanced from 304 MPa and 214HV (x=0.2) to 1192 MPa and 513HV (x=0.8), respectively, while the plastic strain decreases from > 50% to 5.2%, mainly due to the solution strengthening and the increase in σ phase of the alloys.Among the present alloys system, the Al_0.3CrFeCoNiMo_0.4 and Al_0.3CrFeCoNiMo_0.6 alloys show relatively high yield strength (571-776 MPa) combined with good plasticity (plastic strain of 10.3%-23.8%).In 3.5%(mass fraction) NaCl solution, the Al_0.3CrFeCoNiMo_x HEAs are spontaneously passivated and exhibited low corrosion rates of 3.6×10^－4-5.9×10^－4 mm/a, and the addition of Mo effectively suppresses pitting corrosion. The corrosion resistance of the Al_0.3CrFeCoNiMo_x HEAs could be improved with the increase of Mo content, which is related to the increment in the electrochemical impedance and the thicknesses of the passive films on the alloys. Appropriate addition of Mo to the Al-Cr-Fe-Co-Ni system HEAs can lead to a combination of good mechanical properties and corrosion resistance.

The lightweight high entropy alloys have shown great application value in the lightweight structural materials. Laser melting and laser additive manufacturing technology provide new ideas for the development of high entropy alloys due to their extreme metallurgical conditions. Al_xNbTiV(x=0.5-7) and AlNbTi_yV(y=1-7) button samples were prepared by laser melting technology, and their phase structure, microstructure and hardness were systematically studied. The results show that the Al content has a significant effect on the phase structure and microstructure of the alloy. When the Al content is low (x ≤ 2), the Al_xNbTiV alloy is composed of BCC single-phase solid solution. When the Al content is high (2 ≤ x ≤ 7), intermetallic compounds appear in the alloy. With the increase of Al content, the BCC and TiAl phases change into TiAl₃ and NbAl₃ phases. Ti content in a certain range (y ≤ 7) will not affect the phase structure of the alloy. AlNbTi_yV alloys are composed of BCC single-phase solid solution. The content of Al and Ti has a great influence on the hardness of the alloy. When the Al_xNbTiV alloy is composed of BCC single phase, the hardness of the alloy increases with the increase of Al content, and the appearance of intermetallic compounds makes the hardness of the alloy no longer change with the change of Al content. The hardness of AlNbTi_yV alloy decreases with the increase of Ti content.

In order to obtain high quality AZ31B/stainless steel resistance spot welded joints, the FeCoNiCrMn high entropy alloy was used as the interlayer. The reaction-diffusion behavior of the transition zone and the base material on both sides was analyzed, and the joint performance and the welding process were investigated. The results show that the transition zone consists of FeCoNiCrMn particles which successfully connects two base materials of AZ31B and stainless steel. The interface near AZ31B is mainly Fe₄Al₁₃ intermetallic compounds generated by the reaction around the particles; while the boundary of stainless steel is mainly composed of (Fe, Ni) solid solution and Fe₄Al₁₃ intermetallic compounds. The tensile shear load F shows a tendency that increases first and then decreases with the increase of welding current I, welding force P, and the prolongation of welding time t. The tensile shear load of the added high entropy alloy magnesium/steel spot welded joints are above 3.2 kN in the test process range of 18.2-22.5 kA, 15-35 cycle, and 2.0-10.6 kN, and the maximum tensile shear load is 5.605 kN, which is 397% higher than that of Mg/steel spot welded joints without high entropy alloy. A large number of (Fe, Ni) solid solution are formed in the high entropy alloy transition layer, which reduces the generation of Fe₄Al₁₃ brittle intermetallic compounds and effectively improves the mechanical properties of the joint.

Machine learning(ML) assisted high-entropy alloys(HEA) design is dedicated to solving the problem of long period and high cost of designing by traditional trial and error experimental methods. The classic AlCoCrCuFeNi HEA was taken as the research object. The phase structure prediction model and hardness prediction model were established respectively. The support vector machine(SVM) models have the best training performance in both tasks. The best phase classification accuracy is 0.944, and the root mean square error(RMSE) of the hardness regression model is 56.065HV. The two ML models are further connected in series. Based on the upper and lower limits of the data set, the high-throughput prediction and selection of phases and hardness of AlCoCrCuFeNi HEA are carried out simultaneously, thus realizing the efficient composition design of the new alloy. The experimental results show that the five new alloys are in accord with the predicted results, and the RMSE is 12.58HV. It shows that the ML models can predict the phase and hardness of HEA efficiently and accurately.

CoCrFeNi-(Nb, Ta) high-entropy alloys (HEAs) were prepared by a vacuum arc melting process, and the synergistic effect of Nb and Ta concentrations on the microstructure evolution and mechanical properties was investigated in detail. Nb and Ta concentrations in the HEAs affect the microstructure compositions, eutectic phase lamella spacings, Laves phase size topographies, phase volume fractions and compositions. The alloy with an equal atomic ratio of Nb/Ta show an eutectic microstructure of the face centered cubic (FCC) crystal matrix and Laves phase, while those with non-equal atomic ratio of Nb/Ta exhibit the microstructure of the eutectic (FCC+Laves) phase and primary Laves phase. The volume fraction and grain size of the primary Laves phase monotonically increase with the increase of Nb/Ta atomic ratio. The compressive yield strength of HEAs is monotonously improved with the volume fraction of Laves phase, whereas the ultimate strength is hardly affected by the microstructure composition. Compression plasticity is negatively correlated with the volume fraction, type, and size distribution of Laves phase. The strengthening mechanism of CoCrFeNi-(Nb, Ta) HEAs was analyzed with theoretical calculation, and the relationship between the microstructure composition and the alloy strengths was established. The results indicate that the fine-grain strengthening and second phase strengthening of Laves phase are the main factors for the improvement of yield strength.

To further promote the industrial application of medium/high entropy intermetallics, a bulk of FeCoNi₂Al medium entropy intermetallic ingot with 16 kg as the research object was prepared in this study. Microstructure and mechanical properties of the as-cast alloy were studied and analyzed in detail. Moreover, characteristic structural components were obtained via investment casting route, by which the forming performance of the alloy was evaluated. Results show that the FeCoNi₂Al medium entropy intermetallic ingot has good composition uniformity. The as-cast alloy is composed of B2 primary phase with dendritic morphology and interdendritic L1₂+B2 phase eutectic structure with lamellar morphology. The tensile strength of the as-cast alloy is 1115 MPa at room temperature, and the elongation is 4.6%. At 650 ℃, the tensile strength of the as-cast alloy is 434 MPa, and the elongation can reach 14.6%. Melt fluidity of the FeCoNi₂Al medium entropy intermetallic is lower than that of TC4 alloy but better than that of TiAl-4822 alloy. When the thickness of the characteristic structural component is 2 mm, the plate casting is incompletely filled and a mass of shrinkage porosity is formed within the casting. Moreover, the cessation mechanism of flow for the molten alloy is due to the accumulation of solid particles at the tip of flow. Results of this research will lay a certain technical foundation for the casting process optimization and industrial application of medium/high entropy intermetallics.

AlCrNiFeTi high-entropy alloy (HEA) with a diameter of 7 mm was prepared as electrode by vacuum arc melting method, and AlCrNiFeTi high-entropy alloy coating was successfully prepared on the surface of 304 stainless steel by using electric spark deposition technology. The microstructure and friction and wear properties of the coatings were studied by XRD, OM, EDS, SEM, microhardness tester and friction and wear tester. The results show that both the AlCrNiFeTi electrode and the coating are dominated by BCC1 and BCC2 simple solid solutions, and the microstructure of the electrode is typical of dendrites. The coating is formed by stacking and spreading of deposition points, and the surface is uniform and dense as orange peel, convex and concave, unfolding for sputtering pattern, and there is no macroscopic defects in the coating cross-section structure, and the thickness is about 59.67 μm.The maximal microhardness of AlCrNiFeTi coating is 587.3HV_0.2, which is about 2.45 times higher than that of the base material. As the load increases, the wear mechanism of the coating changes from oxidized wear and slight abrasive wear to abrasive and adhesive wear. When the friction load is 5 N, the wear rate is 1.213×10^-3 mm³/(N·m), and the friction coefficient is only 0.446. The wear rate of the coating decreases by about 28.3% compared with that of the substrate.

A new MnCuNiFeZn high entropy damping alloy was prepared. The microstructure, damping properties and phase transition characteristics of the alloy were studied by X-ray diffractometer, scanning electron microscopy, transmission electron microscopy, dynamic thermomechanical analyzer (DMA) and thermal dilatometer. The results show that the MnCuNiFeZn alloy is a single parent phase with uniform grain size and high fault density under solid solution and different aging processes. It is found that the magnetic transformation of the alloy occurs at room temperature with the extension of aging time, but the internal friction value at room temperature is very low. However, the internal friction value of MnCuNiFeZn alloy increases sharply in the high-temperature domain above 673 K due to the phase transformation.

In view of the excellent corrosion resistance and high temperature strength of TiVNbTa refractory high entropy alloy, and the potential application prospect of the TiVNbTa RHEA/Inconel 600 joining component, the diffusion bonding properties were studied. Diffusion joining of the two materials under conditions ranging from 850 ℃ to 1150 ℃ were carried out, the joints achieved at 850~1000 ℃ were submitted for microstructure examining, and the joints joined at all temperatures were used for shearing test. The results indicate that except for the joints obtained at 850 ℃, which only contain a lot of Ni-rich interface layers, all other joints have a multi-layer interface structure of "Inconel 600/Ni-based diffusion layer/Cr-rich layer/Ti-rich layer/Ni-rich layer/TiVNbTaNi (Fe, Cr) diffusion layer/TiVNbTa RHEA". The Ni-rich layer is a Ni₂Ti type intermetallic compound with rhombohedral crystal structure, and the Cr-rich layer is a Cr₂X type intermetallic compound with hexagonal crystal structure. The joint achieved at 950 ℃ has the highest shear strength, which is 357 MPa. The fracture mainly occurs in the weak interfacial area of Ni₂Ti in the joint, and the crack propagates through the multi-layer interface. The analysis of the joints formation mechanism shows that during the diffusion joining process, Ti, V, Nb, and Ta atoms diffuse from the RHEA side to the Inconel 600 side, while Ni, Fe, and Cr atoms diffuse from the Inconel 600 side to the RHEA side. The diffusion of Ti and Ni atoms is intense. The segregation of Cr and Ni elements occurs under the driving source of interfacial chemical reactions. The diffusion of Nb and Ta atoms is hindered by the formation of Ni₂Ti type interfacial layers, resulting in delamination.

In order to study the effect of Al content on the microstructure properties of FeCoCrNi alloy, Al_xCoCrFeNi high-entropy alloy (0≤x≤0.9) was prepared by multi-channel laser cladding. The phase composition, microstructure, chemical composition and hardness of the alloy were test by X-ray diffractometry, metallography microscope, scanning electron microscope, electron probe and microhardness tester. The results show that with the increase of Al content, Al_xCoCrFeNi high-entropy alloy changes from single FCC phase (x≤0.35) to FCC+BCC biphase structure (0.35 < x < 0.85), and finally to BCC structure (x≥0.85). The microstructure of the high entropy alloy consists of epitaxial columnar dendrites and uniform equiaxed dendrites. When Al content reaches to x=0.5, characteristic structure of spinodal decomposition with alternating light and dark contrast starts to appear between the dendrites, which consists of disordered phase A2 and ordered phase B2.The microhardness test results show that the microhardness of Al_xCoCrFeNi alloys almost increases with the increasing Al content and a total of 146% improvement has been achieved when the Al content increases from x=0 to x=0.9. It should be noted that cracks begin to appear in the alloy when the Al content increases to a certain value (x≥0.6).The size and density of cracks increase with the increase of Al content.There are two main reasons. Firstly, the hot-cracking increases since the solidification range widen and their viscosity values near the solidification temperatures increase with the increasing Al content.Besides, cold cracking also increases as the brittle BCC and σ phases increase with the increasing Al content.

FeCoCrNiAl_x (x=0, 0.5, 1.0, mole ratio, the same below) coatings were prepared on the surface of TC4 titanium alloy by electric explosion spraying technology. The effects of Al content on the phase structure, surface morphology, microhardness and wear resistance of high-entropy alloy coatings were studied by means of XRD, SEM, EDS, microhardness tester and friction and wear test. The results show that the grain size of the coatings is nano-scale, and simple FCC, BCC and FCC+BCC solid solutions are formed. With the increase of Al element, the phase structure is gradually changed from FCC phase to BCC phase. The surface of the coatings is smooth and dense, without obvious cracks, and the elements are evenly distributed on the surface of the coatings, and no obvious segregation of elements is found. The scratch test shows that the average critical load for the failure of the FeCoCrNiAl_1.0 coatings is 37.2 N. The coating is metallurgically bonded to the substrate. The hardness and wear resistance of the coatings are positively correlated with the Al content. When x is 1.0, the average microhardness reaches the maximum value of 531.8HV, which is about 1.62 times that of the substrate. The FeCoCrNiAl_1.0 coatings have the smallest amount of wear, and the wear resistance is about 3.9 times that of the substrate. The wear mechanism is mainly abrasive wear.

In order to solve the protection problem of metal parts surface, the mixed metal coating was prepared on 45^# steel by cold spraying, and then synthesized into FeCrAlCu, FeCrAlCuNi, FeCrAlCuCo, FeCrAlCuNiCo HEA coating by induction remelting technology.The effect of the addition of Ni and Co on the phase composition, microstructure, hardness and wear resistance of the FeCrAlCu series HEA coating were investigated by XRD, SEM, EDS, TEM, microhardness tester and abrasive wear tester, etc. The results show that the coating of FeCrAlCu series HEA is composed of FCC+BCC phase, and the addition of Ni element can promote the formation of FCC phase, and the addition of Co element can promote the formation of B2 phase(AlCo).The microstructure of FeCrAlCu HEA coating is dendrite. With the addition of Ni and Co, the dendrite number in the coating increases and coarsenes obviously. When Ni and Co are added at the same time, the friction property of FeCrAlCuNiCo HEA coating is the best. The hardness of the coating is 565.5HV, the friction coefficient is 0.349, and the wear rate is 3.97×10^-5 mm³·N^-1·m^-1.

Al_xCoCrFeNi (0.5≤x≤0.8) high-entropy alloys were prepared by arc-melting method and the effect of 1100 ℃ heat treatment on the microstructure and mechanical properties of the alloys was investigated. The results show that the as-cast Al_xCoCrFeNi (0.5≤x≤0.8) high-entropy alloys present FCC dendrite (x=0.5 and 0.6), "eutectic-like" structure (x=0.7) and BCC/B2 dendrite (x=0.8) morphologies successively as Al content increases. Correspondingly, the yield strength and tensile strength of the alloys increase from 291 MPa and 733 MPa (x=0.5) to 1004 MPa and 1423 MPa (x=0.7), respectively, and the elongation decreases from 39.7% (x=0.5) to 6.8% (x=0.7). After heat treatment at 1100 ℃, a large number of rod-like B2 phases are precipitated from the FCC dendrite region, which can improve the strength of heat-treated alloys, while the BCC/B2 spinodal structure transforms into FCC and B2 dual-phase structure, which can enhance the plasticity of heat-treated alloys. Therefore, the yield strength and tensile strength of heat-treated Al_0.5CoCrFeNi alloy with FCC dendrite morphology increase to 370 MPa and 866 MPa, respectively, and the elongation decreases to 30.1%. However, both phase transition behaviors have great influence on the microstructure and property of Al_0.6CoCrFeNi alloy due to the increasing fraction of spinodal structure. Therefore, the mechanical properties of heat-treated Al_0.6CoCrFeNi alloy are basically unchanged in comparison to that of the as-cast alloy. The as-cast Al_0.7CoCrFeNi and Al_0.8CoCrFeNi alloys contain higher fractions of spinodal structure, while the heat-treated alloys present typical FCC and B2 dual-phase structure, resulting in an increase of plasticity but a decrease of strength. Correspondingly, the elongation of heat-treated Al_0.7CoCrFeNi alloy increases to 14.2%, and the yield strength and tensile strength decrease to 586 MPa and 1092 MPa, respectively.

High entropy alloys have been proposed in 2004, which are expected to be widely used in aerospace, petrochemical and other fields due to their excellent properties compared with the traditional alloys, and have become a hot spot in current metal material research. It has become one of the methods to improve the comprehensive properties of high entropy alloys by introducing suitable reinforcement phase into the high entropy alloy matrix, and to form high entropy alloy matrix composites (HEAMCs). In this review, according to the current research status in HEAMCs at home and abroad in the past few years, the reinforcement phase selection, preparation method, phase structure, microstructure and strengthening mechanism of HEAMCs were systematically introduced, and the evolution of properties of HEAMCs were summarized, including strength and plasticity, hardness, wear resistance and corrosion resistance. Finally, the challenges to HEAMCs were discussed and future research directions in HEAMCs were suggested.The wettability between the reinforcement phase and the matrix seriously affects the preparation and performance of large-scale composites, and finding an efficient and simple method to prepare large-scale composites is a problem that needs to be solved in high-entropy alloy matrix composites; reinforcing particles will lead to a decrease in plasticity, and the balance between strength and plasticity of metal matrix composites also needs to be studied.

With the current-assisted bonding technology, the rapid brazing of SiC ceramics was realized at 1125℃ with CoFeCrNiCuTi₂ high-entropy alloy as the bonding layer material, which improves the bonding efficiency and ensures the full diffusion of elements. The influence of brazing temperature on the microstructure and mechanical properties of the bonding interface was studied. The results show that the obtained brazed joint has no obvious defects and the weld microstructure is mainly composed of high-entropy FCC, TiC phase and Cr₂₃C₆ phase. The formation of TiC reaction layer with dense interface inhibits the decomposition of high-entropy alloy and the formation of intermetallic compounds to a certain extent, and relieves the thermal stress between interface matrix SiC and high-entropy alloy filler. At the same time, due to the delayed diffusion effect of high-entropy alloy filler, the filler in the center of weld still keeps the FCC structure of high-entropy alloy. The mechanical test shows that the strength of brazed joint decreases at first and then increases. When the joining temperature is 1125℃, the maximum bending strength of SiC joint is 37 MPa, which is higher than that of ordinary Ni-based filler by about 21.3 MPa.

Thermal barrier coating (TBC) materials are an important method to provide thermal protection and prolong service life for aero-engines and gas turbines. In recent years, various kinds of high-entropy (HE) rare earth oxides have emerged in the exploration of novel thermal barrier coating materials, in order to obtain thermal, mechanical, high temperature phase stability, sintering corrosion resistance and other properties better than single principal rare earth oxides through HE effect on the thermodynamics and kinetics of hysteresis diffusion effect, the structure of the lattice distortion effect and "cocktail" effect on the performance. The thermal, mechanical and other performances of HE rare-earth zirconates, cerates, hafnates, phosphates, tantalates, niobates, etc. were summarized and analyzed in comparison with the performance of the corresponding single phases to investigate the various factors affecting the performance. Finally, it was pointed out that in the future, it may be possible to combine experiments with first-principles calculations to select high-entropy ceramic thermal barrier coating materials with superior comprehensive performance; at the same time, extending high-entropy to complex components or medium-entropy ceramic thermal barrier coating materials is also an important development direction.

Fe₄₀Cr₂₅Ni₂₅Al₅Ti₅ (atom fraction/%) medium entropy alloys (MEAs) were prepared by a vacuum arc-melting furnace with a water-cooled copper mold, and the microstructure, mechanical properties and strengthening deformation mechanism of the alloy in solid solution and annealed states were studied by scanning electron microscopy (SEM), energy spectrometry(EDS), X-ray diffractometer (XRD), transmission electron microscopy(TEM) and tensile testing machine.The results show that the Fe₄₀Cr₂₅Ni₂₅Al₅Ti₅ medium entropy alloy has FCC+BCC1+BCC2 triple-phase organization of solid solution state, with yield strength of 520 MPa, fracture strength of 852 MPa and elongation of 13%. After annealing at 600 ℃ for 2 h, the phase composition of the alloy has no change, the size of granular BCC2 phase increases, and the volume fraction of FCC zone and BCC zone has no change significantly. The yield strength is 668 MPa, the fracture strength is 1029 MPa, and the elongation is reduced to 9%. The strength of Fe₄₀Cr₂₅Ni₂₅Al₅Ti₅ alloy originates from the synergistic effect of coherent strengthening, solid solution strengthening and phase boundary strengthening. Dislocation slips are the main deformation mechanism of alloy.

The high temperature oxidation behavior of NbMoTaWV refractory high entropy alloy(RHEA) prepared by arc melting was studied by static oxidation experiment, XRD and FSEM. The results reveal that the NbMoTaWV RHEA is not protective due to severe cracks in the oxide layer at 1000 ℃ and 1200 ℃. The mass gain follows a linear oxidation law. Molten oxides formed at 1400 ℃, which release the growth stress of the oxide layer and fill the holes left by the volatilization of Mo and V oxides.In the oxidation process of NbMoTaWV, oxygen diffuses into the matrix and first oxidizes with Nb and Ta in the diffusion layer to generate needle-rod like oxidation products, and then oxidizes with other alloy elements. In the subsequent oxidation process, the oxides of W are dissolved in Nb and Ta oxides, while the granular mixed oxides of Mo and V volatilize at high temperatures.

To obtain Al-Co-Cr-Fe-Ni high entropy alloys (HEAs) with high strength and high ductility, Al_1.2Co_xCrFeNi(x=1, 1.6, 2.2, 2.8) HEAs were successfully prepared by arc melting method and its microstructure and mechanical properties were systematically studied. The results show that in Al_1.2Co_xCrFeNi alloy, Co element can induce the transformation from BCC to FCC phase. With the increase of the atomic ratio of Co from 1 to 2.8, the volume fraction of FCC phase increases from 0% to 59%, and the volume fraction of BCC phase decreases from 100% to 41%. The results of compression experiment show that the addition of Co plays an important role in improving the plasticity of Al_1.2Co_xCrFeNi high entropy alloys but has no obvious effect on the strength of the high entropy alloys. With the increase of Co content, the fracture strain of Al_1.2Co_xCrFeNi HEAs increases from 16.9% to 30%. The ultimate compressive strength decreases from 2128 MPa to 1913 MPa, and the maximum compressive strength is 2361 MPa, and the average hardness decreases from 513.7HV to 323.4HV. The increase of Co content decreases the atomic size difference of the alloys, which weakens the lattice distortion effect and solid solution strengthening effect caused by the large atomic radius of Al element. At the same time, the increase of Co content also increases the valence electron concentration (VEC) of the alloys. The changes of the above two parameters are the main factors for the increase of FCC phase volume fraction in the alloy. The increase of the volume fraction of FCC phase is the main reason for the improvement of the plasticity of the alloy.

High-entropy alloys have attracted great attention in various fields due to their high-entropy effect, severe lattice distortion, slow diffusion and special and excellent material performance due to the combination of various alloying elements in equal or near-equal molar proportions. Its high strength and hardness, fatigue resistance, excellent corrosion resistance, radiation resistance, near-zero thermal expansion coefficient, catalytic response, thermoelectric response and photoelectric conversion make high-entropy alloys have potential applications in many aspects. High-throughput computation and machine learning technology have rapidly become powerful tools to explore the huge composition space of high-entropy alloys and comprehensively predict material properties. The basic concepts of high-throughput computing and machine learning were introduced in this paper as well as the advantages of first-principles calculation, thermodynamic/kinetic calculation and machine learning in the research of high-entropy alloys. The application research status of high-entropy alloy composition screening, phase and microstructure calculations and performance prediction were summarized. In the final part, the existing problems, and the solutions and future prospects of this field were summarized, including developing tools for first-principles calculations and machine learning of high-entropy alloys, building high-quality databases for high-entropy alloys and integrating high-throughput computing with machine learning to globally optimize the mechanical property and service performance of high-entropy alloys.

AlFeNiCrCoTi_0.5 high entropy alloy powder was prepared by mechanical alloying, and (AlFeNiCrCoTi_0.5)_p/6061Al composites were prepared by cold isostatic pressing combined with equal-channel angular pressing. The alloying behavior between elemental metals and effects of milling time on powder morphology of high entropy alloy were investigated. The microstructure and properties of (AlFeNiCrCoTi_0.5)_p/6061Al composites with different volume fractions were analyzed. The results show that the alloying time of AlFeNiCrCoTi_0.5 metal powder increases with the increase of melting point of the elements. The higher the melting point of the elements, the earlier the alloying. AlFeNiCrCoTi_0.5 metal powder is fully alloyed and forms a FCC+BCC two-phase solid solution structure after 70 h ball milling time. A transition layer of element infiltration of elements is formed between Al matrix and the reinforcement. With the increase of the volume fraction of reinforcement, the agglomeration of reinforcement is intensified, the tensile strength increases and the plasticity decreases. When the volume fraction is 10%, the composites have good comprehensive properties. Compared with 6061 aluminum matrix, the tensile strength increases by 21.8% and the elongation decreases by 7.4%. For the composites after T6 treatment, the tensile strength and the elongation are 284.05 MPa and 11.51%, respectively.

High-entropy alloy coatings show great potential for improving the wear resistance of the stainless steel substrate. To investigate the effects of Cu/Si doping on the microstructure and high temperature tribological properties of FeCoCrNi high-entropy alloy coating, FeCoCrNiCu_x and FeCoCrNiSi_x series of high-entropy alloy coatings were prepared on the 304 stainless steel by laser cladding.The microstructure and phase distribution of the coatings were characterized by XRD, SEM and EDS, and the high temperature tribological properties of the coatings were tested by a high temperature friction and wear tester. The results show that both FeCoCrNiCu_x and FeCoCrNiSi_x high entropy alloy coatings form a single FCC-type solid solution with good metallurgical bonding to the substrate under suitable laser cladding parameters.The addition of Cu reduces the surface hardness of FeCoCrNi coatings, but improves the metallurgical bonding due to the increase of thermal conductivity of the coating; the addition of Si promotes grain refinement and improves the surface hardness of the coating. At 600 ℃, the addition of Cu/Si elements significantly improves the tribological properties of the coating, with the coefficients of friction of 0.24 and 0.19 for FeCoCrNiCu and FeCoCrNiSi coatings, respectively, and the wear rates are 1.58×10^-4 mm³·N^-1·m^-1 and 6.77×10^-5 mm³·N^-1·m^-1, respectively, which are 56.1% and 81.9% lower than FeCoCrNi coating.The main wear mechanisms of FeCoCrNiCu coating are oxidation wear, fatigue wear and slightly abrasive wear, while FeCoCrNiSi coating is oxidation wear.

FeCoNiAlCr_x(x=0, 0.2, 0.4, 0.6, 0.8, atomic ratio) high-entropy alloy ingots were prepared by vacuum arc melting method, and the effect of Cr content on the microstructure and mechanical properties of the alloy was investigated. The phase structure, microstructure and the composition of the alloy were analyzed and characterized by X-ray diffractometer (XRD), scanning electron microscope (SEM) and energy dispersive spectrometer (EDS).The compression properties of the alloy were tested by universal testing machine. The results show that with the increase of Cr content, the microstructure of the alloy changes from a single-phase BCC structure to a BCC+FCC mixed structure; the microstructure of the alloy gradually changes from an equiaxed structure to a dendrite structure, and the grain size of the alloy is obviously refined. The five alloys prepared in this experiment have relatively good mechanical properties, and the compressive strength of the alloy increases greatly with the increase of Cr content. When x=0, the compressive strength and plastic strain of the alloy are the lowest, which are 1500 MPa and 13.56%, respectively; when x=0.8, the compressive strength and plastic strain of the alloy reach the maximum, which are 2460 MPa and 30.09%, respectively; the compressive strength of the alloy increases by 64%. It indicates that Cr addition plays an important role in the microstructure refinement, the improvement of compressive strength and ductility of FeCoNiAlCr_x high-entropy alloys.