- Ei，ESCI收录期刊
- 中国科学引文数据库(CSCD)核心期刊
- 中文核心期刊
- 文摘与引文数据库(Scopus)
- 剑桥科学文摘(CSA)
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.
AlCoCrFeNi2.1 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 AlCoCrFeNi2.1 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 AlCoCrFeNi2.1 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 AlCoCrFeNi2.1 eutectic high-entropy alloy and puts forward the development direction of material modification of AlCoCrFeNi2.1 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.
As a new material system, the high entropy ceramics have become a hot research topic in the field of materials because of their unique and adjustable properties benefited by the huge component space, unique microstructure and large configuration entropy. The research of the high entropy ceramics is still in the initial stage at present, especially for the accurate composition design theory, preparation of high purity and high conversion powder, new sintering process and other aspects, which need to be further explored. Therefore, the five high entropy effects, new design theory, powder preparation methods, new sintering methods, comprehensive properties and practical applications of high entropy compounds ceramics were sorted and summarized, the composition design of high entropy ceramics (HEC) by the cluster-plus-glue-atom model (CPGA) was analyzed, and the relationship between the components, microstructure, and performance of HEC was explored deeply. The key development direction of future HEC will still be basic theoretical design, especially for the composition and structure of non oxide HEC. At the same time, the breakthroughs in interdisciplinary fields was sought, such as using artificial intelligence machine learning and 3D printing for sample preparation. Finally, the practical applications in structures, thermal barrier and corrosion resistant coatings, machinery, engineering optics, and magnetism were searched, and the strengthening and failure mechanisms were explored and analyzed in-depth under the investigated working environment.
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 TiH1.971, Nb0.696V0.304H and Nb0.498V0.502H2 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 Ea 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-xAlx (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 Al0.3CrFeCoNiMox (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 Al0.3CrFeCoNiMo0.4 and Al0.3CrFeCoNiMo0.6 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 Al0.3CrFeCoNiMox 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 Al0.3CrFeCoNiMox 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.
In order to optimize the hot working window of the novel TiZrAlHf Ti-based medium entropy alloy, the thermal deformation characteristics and microstructural evolution during thermal deformation were investigated by using hot compression simulation experiments and microstructural characterization methods. The results show that the microstructure of TiZrAlHf alloy ingot primarily consists of lamellar α phase and Widmanstatten structure at grain boundaries. The β transformation temperature (Tβ) of TiZr-AlHf alloys is 895 ℃. Within the α/α+β phase region (700-850 ℃) during deformation, an instability zone is identified within the temperature range of 700-750 ℃. The thermal deformation activation energy in the α/α+β phase region is 827.514 kJ/mol, the deformation microstructure predominantly comprised globular α phase, with the softening mechanism involving the globularization of lamellar α phase. When the alloy is deformed in the β phase region (900-1100 ℃) test process range, there is no instability zone in hot processing map, all samples remain intact without any signs of cracking. Consequently, free forging can be employed for roughing and finish forging operations. The hot deformation activation energy is 113.909 kJ/mol, and the deformation microstructure is mainly elongated β grains and acicular martensite α'. The softening mechanism in the region is dynamic recovery. The underlying nature of both deformation softening mechanisms lies in the proliferation of dislocations, slip and the evolution of cellular structures.
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. AlxNbTiV(x=0.5-7) and AlNbTiyV(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 AlxNbTiV 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. AlNbTiyV 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 AlxNbTiV 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 AlNbTiyV 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 587.3HV0.2, 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.
Metal lattice structural materials are widely used in aerospace, automotive industry, and other fields due to their advantages of lightweight, high specific strength, energy absorption, and porosity. High strength and toughness FeCrNi medium entropy alloy (MEA) was taken as the research object, and selective laser melting (SLM) was used to prepare FeCrNi medium entropy alloy lattice structure materials with four simulated lattice structures: BCC, BCCZ, FCC and FCC. The microstructure, mechanical properties, and deformation behavior of these materials were systematically studied.The results indicate that the FeCrNi medium entropy alloy lattice structure prepared by the skip scanning strategy has high node overlap quality, dense interlaced stacking of molten pools, and uniform and fine grains. When the relative density is similar, the specific strength and specific energy absorption values of BCC, FCC, BCCZ, and FCCZ lattice structures increase sequentially.The specific energy absorption of FeCrNi medium entropy alloy material with FCCZ lattice structure reaches 49.8J·g-1, significantly higher than that of Ti6Al4V and 316L stainless steel lattice materials.The finite element simulation analysis shows that the presence of Z-shaped pillars increases the apparent strength and stiffness of the lattice material, and leads to a transition in deformation behavior from bending dominated to tensile dominated, which is the main reason for the strength improvement of the FCCZ lattice structure.
In order to study the effect of Al content on the microstructure properties of FeCoCrNi alloy, AlxCoCrFeNi 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, AlxCoCrFeNi 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 AlxCoCrFeNi 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.
FeCoCrNiAlx (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 FeCoCrNiAl1.0 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 FeCoCrNiAl1.0 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.
AlxCoCrFeNi (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 AlxCoCrFeNi (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 Al0.5CoCrFeNi 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 Al0.6CoCrFeNi alloy due to the increasing fraction of spinodal structure. Therefore, the mechanical properties of heat-treated Al0.6CoCrFeNi alloy are basically unchanged in comparison to that of the as-cast alloy. The as-cast Al0.7CoCrFeNi and Al0.8CoCrFeNi 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 Al0.7CoCrFeNi alloy increases to 14.2%, and the yield strength and tensile strength decrease to 586 MPa and 1092 MPa, respectively.
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