Heterogeneous multi-interface ultrafine-grained high-entropy alloy composite coating and preparation method thereof

Abstract

This application provides a heterogeneous multi-interface ultrafine-grained high-entropy alloy composite coating and its preparation method. The preparation method includes: (1) cold spraying heterogeneous multi-interface ultrafine-grained high-entropy alloy composite powder onto the surface of a substrate to prepare an ultrafine-grained high-entropy alloy composite coating; (2) heat-treating the ultrafine-grained high-entropy alloy composite coating under a protective atmosphere to obtain a high-performance heterogeneous multi-interface ultrafine-grained high-entropy alloy composite coating; wherein, the heterogeneous multi-interface ultrafine-grained high-entropy alloy composite powder is a composite powder with a heterogeneous multi-interface structure in which high-entropy alloy / refractory metal heterogeneous phase boundaries and ultrafine grain boundaries coexist. This application constructs an ultrafine-grained composite powder with abundant heterogeneous multi-interfaces, and then uses cold spray solid deposition to completely preserve its fine structure, thereby obtaining a heterogeneous multi-interface ultrafine-grained high-entropy alloy composite coating material with ultra-high strength, good ductility and toughness, and multi-functional service characteristics.

Description

Technical Field

[0001] This application relates to the field of high-entropy alloy coating technology, and in particular to a heterogeneous multi-interface ultrafine-grained high-entropy alloy composite coating and its preparation method. Background Technology

[0002] High-entropy alloys, with their unique design concept of multiple principal elements in equimolar or near-equimolar ratios, break through the limitations of traditional materials based on a single element. By stabilizing simple solid solution phases with high configurational entropy, they exhibit superior properties such as high strength, high hardness, excellent wear and corrosion resistance, and thermal stability. However, the fabrication cost of bulk high-entropy alloys is high, and their size is limited. Furthermore, in most engineering failure cases, material degradation begins at the surface. Therefore, developing high-performance high-entropy alloy coating technology to impart superior intrinsic properties to inexpensive substrate surfaces has become a core strategy for balancing performance and cost.

[0003] Currently, high-energy beam or thermal spraying technologies such as laser cladding, plasma cladding, and supersonic flame spraying are the mainstream methods for preparing high-entropy alloy coatings. These methods all rely on the complete or partial melting of powder followed by rapid solidification, which brings a series of intractable problems: strong convection and diffusion in the molten pool easily cause compositional segregation, inducing harmful intermetallic compounds or topologically close-packed phases, weakening the phase stability of the high-entropy alloy; high heat input leads to substrate dilution rates as high as 10%–30%, causing the coating composition to deviate from the designed ratio; residual tensile stress generated by rapid solidification often induces cracks, and the wide heat-affected zone degrades the substrate properties. More importantly, during the melting-solidification process, constrained by extremely high temperature gradients and cooling rates, the coating microstructure is usually dendritic or equiaxed crystals ranging from micrometers to tens of micrometers, making it difficult to achieve a uniform ultrafine-grained structure throughout the entire process, thus failing to fully realize the potential for fine-grain strengthening. Even if fine microstructures can be obtained locally through process parameter optimization, the high-temperature process inevitably causes grain growth and solute redistribution, causing the coating's microstructure to deviate from the ideal state.

[0004] To overcome the fundamental limitations imposed by high-temperature melting, cold spraying technology offers a novel approach. However, when directly using gas-atomized high-entropy alloy powders for cold spraying, a fatal bottleneck is encountered: high-entropy alloys such as FeCoNiCrAl and FeCoNiCrMn generally possess high hardness and limited room-temperature plasticity. Spherical powders struggle to undergo sufficient plastic rheology under high-speed impact, resulting in weak mechanical bonding between particles, extremely low deposition efficiency, and numerous unbonded interfaces and pores within the coating, with bonding strength far from meeting engineering requirements. Simply increasing the gas preheating temperature to improve particle plasticity may not only induce softening and sintering of the powder within the nozzle but also trigger grain reversion growth, making it impossible to retain the ultrafine grain structure.

[0005] To overcome the challenge of poor depositability in cold spraying of high-hardness powders, pre-treatment with high-energy ball milling has proven to be an effective strategy. However, while vigorous ball milling of a single high-entropy alloy powder can yield ultrafine grains, it often results in severe work hardening, making the powder harder and more brittle. During cold spraying impacts, it is still prone to springback or shattering, failing to bond effectively. The single ultrafine grain strategy faces a performance ceiling.

[0006] The performance of high-entropy alloy coatings in harsh service environments such as high-temperature oxidation and irradiation is a key factor restricting their engineering applications. Under high-temperature oxidation conditions, traditional high-entropy alloy coatings prepared by high-energy beams have coarse microstructures and low interface density. The diffusion of antioxidant elements (such as Al and Cr) to the surface mainly occurs through bulk diffusion, resulting in a limited diffusion rate and making it difficult to quickly form a continuous and dense protective oxide film in the early stages of oxidation. At the same time, residual pores and microcracks in the coating provide short-circuit channels for oxygen diffusion inward, accelerating internal oxidation and oxide film peeling, making it difficult to meet the requirements of harsh operating conditions in terms of high-temperature oxidation resistance. Although existing cold-sprayed high-entropy alloy coatings can avoid oxidation during high-temperature preparation through solid-state deposition, the interparticle bonding interfaces are weak. Numerous unbonded defects at the interfaces become preferential channels for oxidation during high-temperature service, which in turn exacerbates oxidation along the interface and degrades the coating performance.

[0007] In terms of radiation resistance, high-entropy alloys theoretically possess a certain potential for self-healing of radiation defects due to severe lattice distortion and short-range chemical effects caused by multiple principal elements. However, for high-entropy alloy coatings dominated by a single solid solution phase, the lack of high-density defect trapping sites within them means that interstitial atoms and vacancies in irradiated Frenkel pairs are prone to long-range migration before diffusion recombination, leading to the aggregation of dislocation loops, voids, or helium bubbles, resulting in radiation swelling and radiation hardening. Although existing research has confirmed that phase boundaries and grain boundaries can act as effective absorption traps for point defects, promoting the recombination and annihilation of interstitial atoms and vacancies, the interface density in traditional high-entropy alloy coatings is far from reaching the critical level that can produce significant radiation resistance.

[0008] Therefore, how to actively construct a high-density, high-stability heterogeneous interface network in the coating, so that it can provide short-circuit diffusion channels for antioxidant elements to improve high-temperature oxidation resistance, and also serve as an effective absorption trap for irradiation point defects to enhance radiation resistance, while maintaining the high strength and high hardness imparted by the ultrafine grain structure, is a problem that urgently needs to be solved in the field of high-entropy alloy coatings. Summary of the Invention

[0009] To overcome the aforementioned deficiencies in the prior art, this application provides a heterogeneous multi-interface ultrafine-grained high-entropy alloy composite coating and its preparation method. This application introduces specific types and proportions of refractory metals (such as niobium, tungsten, tantalum, etc.) into high-entropy alloy powder, and utilizes high-energy ball milling to repeatedly mix, deform, and cold-weld the two in the solid state, constructing a heterogeneous multi-interface ultrafine-grained composite powder with high density, multiple types, and cross-scale interface coexistence. In this powder, a large number of heterogeneous phase boundaries are formed between the ultrafine-grained high-entropy alloy matrix and the dispersed refractory metal nano / micro particles or lamellae. Simultaneously, ultrafine grain boundaries, subgrain boundaries, twin boundaries, and dislocation cellular structure interfaces generated during the ball milling process are densely interwoven. This heterogeneous multi-interface structure is not a simple two-phase mixture, but a complex system with a network-like synergistic effect of internal interfaces, exhibiting significant advantages in multi-dimensional and multi-mechanism coupling during cold spray deposition, coating strengthening, and subsequent heat treatment.

[0010] To achieve the above-mentioned objectives, this application provides the following technical solution: A method for preparing a heterogeneous multi-interface ultrafine-grained high-entropy alloy composite coating includes the following steps: (1) A heterogeneous multi-interface ultrafine-grained high-entropy alloy composite powder was cold-sprayed onto the substrate surface to prepare an ultrafine-grained high-entropy alloy composite coating. (2) The ultrafine-grained high-entropy alloy composite coating is heat-treated under a protective atmosphere to obtain a high-performance heterogeneous multi-interface ultrafine-grained high-entropy alloy composite coating. The heterogeneous multi-interface ultrafine-grained high-entropy alloy composite powder is a composite powder with a heterogeneous multi-interface structure in which high-entropy alloy / refractory metal heterogeneous phase boundaries and ultrafine grain boundaries coexist.

[0011] Preferably, in the method for preparing the heterogeneous multi-interface ultrafine-grained high-entropy alloy composite coating, the preparation step of the heterogeneous multi-interface ultrafine-grained high-entropy alloy composite powder includes: A. Mix high-entropy alloy powder with refractory metal powder to obtain a mixed powder; B. The mixed powder is subjected to high-energy ball milling to obtain heterogeneous multi-interface ultrafine-grained high-entropy alloy composite powder.

[0012] Preferably, in the method for preparing the heterogeneous multi-interface ultrafine-grained high-entropy alloy composite coating, the mass ratio of the refractory metal powder to the high-entropy alloy powder in the mixed powder is 1:(1~10). For example, 1:1, 1:2, 1:3, 1:4, 1:5, 1:6, 1:7, 1:8, 1:9.

[0013] Preferably, in the method for preparing the heterogeneous multi-interface ultrafine-grained high-entropy alloy composite coating, the particle size of the high-entropy alloy powder is 5~50μm; The particle size of the refractory metal powder is 5~10 μm; The particle size of the heterogeneous multi-interface ultrafine-grained high-entropy alloy composite powder is 10~45μm.

[0014] Preferably, in the method for preparing the heterogeneous multi-interface ultrafine-grained high-entropy alloy composite coating, the high-entropy alloy powder includes one or more of FeCoNiCrAl powder, FeCoNiCrMn powder, or FeCoNiCrCu powder. The refractory metal powder includes one or more of the following: niobium powder, tungsten powder, tantalum powder, molybdenum powder, and rhenium powder.

[0015] Preferably, in the method for preparing the heterogeneous multi-interface ultrafine-grained high-entropy alloy composite coating, the process parameters of the high-energy ball milling satisfy at least one of the following conditions: The ball mill speed is 300~500 rpm, for example, 300 rpm, 400 rpm, 500 rpm; The ball milling time is 10~60 hours, for example, 10 hours, 20 hours, 30 hours, 40 hours, 50 hours, and 60 hours. Through repeated cold welding, fracture, and forced mixing during the high-energy ball milling process, high-entropy alloy powder and refractory metal powder undergo mechanical alloying to form an ultrafine-grained composite powder with a heterogeneous multi-interface structure.

[0016] The specific parameters of this application ensure that the particle size and microstructure of the resulting composite powder meet the requirements of cold spray deposition.

[0017] Preferably, in the method for preparing the heterogeneous multi-interface ultrafine-grained high-entropy alloy composite coating, the particle size of the heterogeneous multi-interface ultrafine-grained high-entropy alloy composite powder is 10~45 μm.

[0018] Preferably, in the method for preparing the heterogeneous multi-interface ultrafine-grained high-entropy alloy composite coating, the process parameters of the cold spraying satisfy at least one of the following conditions: The temperature for cold spraying is 700~1000℃, for example, 700℃, 800℃, 900℃, 1000℃; The pressure for cold spraying is 4~6 MPa, for example, it can be 4 MPa, 5 MPa, or 6 MPa; The gases used in cold spraying include nitrogen, helium, or air, with nitrogen being preferred.

[0019] Using cold spraying technology, heterogeneous multi-interface ultrafine-grained composite powder is deposited on the substrate surface via high-speed solid-state impaction. Numerous high-energy interfaces (ultrafine grain boundaries and heterogeneous phase boundaries) in the composite powder effectively induce adiabatic shear instability during impact, significantly improving the plastic deformation capability of the hard high-entropy alloy powder and enabling tight mechanical interlocking and physical contact between particles. The all-solid-state deposition characteristic of cold spraying fully preserves the ultrafine-grained structure and heterogeneous multi-interface structure of the composite powder, keeping the coating grains at the ultrafine grain scale and effectively reducing inter-particle defects.

[0020] In this application, after obtaining the high-entropy alloy composite coating, the coating is subjected to low-temperature heat treatment to obtain an interface-strengthened heterogeneous multi-interface ultrafine-grained high-entropy alloy composite coating.

[0021] The process parameters of the heat treatment satisfy at least one of the following conditions: The heat treatment temperature is 250~450℃, for example, it can be 250℃, 300℃, 350℃, 400℃, or 450℃; The heat treatment holding time is 1 to 5 hours, for example, 1 hour, 2 hours, 3 hours, 4 hours, or 5 hours. The protective atmosphere for the heat treatment is argon or nitrogen.

[0022] Under the specific heat treatment described in this application, the numerous grain boundary and phase boundary short-circuit diffusion channels provided by the heterogeneous multi-interface structure in the coating are selectively activated during low-temperature heat treatment. Atoms undergo short-range diffusion rearrangement along the interfaces, promoting micropore shrinkage and localized metallurgical bonding at the interfaces between cold-sprayed particles, achieving diffusion healing and strengthening of the interparticle interfaces. Simultaneously, the dispersed refractory metal nanoparticles effectively suppress ultrafine grain growth through the Zener pinning effect, ensuring that the coating grain size remains essentially unchanged during heat treatment, thereby significantly improving interfacial bonding strength while maintaining ultrafine grain strengthening.

[0023] on the other hand: This application also provides a heterogeneous multi-interface ultrafine-grained high-entropy alloy composite coating, which is prepared by the preparation method of the heterogeneous multi-interface ultrafine-grained high-entropy alloy composite coating described in any one of the above claims.

[0024] This application utilizes the synergistic effect of cold spraying and low-temperature heat treatment to ensure the complete continuation of the heterogeneous multi-interface structure from the composite powder to the final coating. In high-temperature oxidizing environments, the high-density grain boundaries and heterogeneous phase boundaries in the coating provide rapid channels for the diffusion of antioxidant elements such as Al and Cr to the surface, promoting the rapid formation and self-repair of a continuous, dense protective oxide film, thus endowing the coating with excellent high-temperature oxidation resistance. In irradiation environments, the high-density heterogeneous interfaces act as effective absorption traps for irradiation-induced point defects, promoting the recombination and annihilation of interstitial atoms and vacancies, inhibiting the aggregation and growth of irradiation defects, and significantly improving the coating's radiation resistance. Furthermore, the fine-grain strengthening effect provided by ultrafine grain boundaries and the precipitation strengthening effect provided by refractory metal heterogeneous phase boundaries work synergistically to achieve a simultaneous improvement in both strength and plasticity of the coating.

[0025] During high-speed impact in cold spraying, the heterogeneous multi-interface structure significantly improves the plastic deformation and bonding ability of powder particles. Numerous high-energy interfaces act as discontinuities and stress concentration points for plastic deformation, efficiently inducing and accommodating the nucleation and propagation of shear bands. Especially at the heterogeneous phase boundaries between high-entropy alloys and refractory metals, the significant difference in elastic modulus and plastic deformation capabilities between the two phases leads to intense strain incompatibility and stress concentration upon impact, preferentially causing adiabatic shear instability in localized areas. Simultaneously, high-density grain boundaries and subgrain boundaries provide slip and rotation paths for shear band propagation, effectively reducing the macroscopic critical deposition rate of the particles. This allows hard, brittle high-entropy alloy particles, which are normally difficult to deposit, to undergo plastic rheology similar to "interface lubrication" during solid-state impact, forming deep mechanical interlocking and extensive close contact between particles and the matrix, and between particles themselves. Dispersed refractory metal particles can also act as hard compaction bodies and micro-rivets during deformation, embedding and anchoring the collision interface, further strengthening the physical interlocking between particles. Therefore, heterogeneous multi-interface composite powder fundamentally solves the technical defect of poor depositability of single high-entropy alloy powder in cold spraying.

[0026] Secondly, from the perspective of enhancing the mechanical properties of the coating, the heterogeneous multi-interface structure achieves cross-scale synergy of multiple strengthening mechanisms. Ultrafine grain boundaries provide the classic fine-grain strengthening effect, significantly improving the coating's strength and hardness; high-density dislocations and substructure interfaces form dislocation strengthening, enhancing resistance to plastic deformation; and more importantly, the numerous coherent, semi-coherent, or incoherent heterogeneous phase boundaries between the high-entropy alloy matrix and the refractory metal particles strongly impede dislocation movement, producing a precipitation strengthening effect similar to the Orowan bypass or bypass-cutting composite mechanism. Unlike traditional precipitates that may coarsen and dissolve due to heat treatment, these refractory metal phase interfaces, constructed in situ by high-energy ball milling, possess extremely high thermodynamic stability and can continuously exert a hindering effect during stress. More noteworthy is the additional strengthening effect generated by the interaction between heterogeneous interfaces: on the one hand, the intersection of grain boundaries and phase boundaries forms a three-dimensional interface network, making it difficult for slip bands to penetrate over long distances, forcing plastic deformation to be dispersed in multiple micro-regions, thus delaying strain localization and failure; on the other hand, a large number of interfaces act as dislocation traps, dynamically absorbing and storing mobile dislocations, increasing the work hardening rate, and enabling the coating to maintain high strength while possessing better plasticity reserves than single ultrafine-grained materials, alleviating the contradiction of strength-plasticity inversion. The heterogeneous structure with alternating soft and hard phases can also activate toughening mechanisms under load through strain distribution and internal stress transfer, improving the fracture toughness and impact resistance of the coating.

[0027] Furthermore, the heterogeneous multi-interface structure endows the coating with outstanding thermal stability, which is the fundamental guarantee for the successful implementation of subsequent low-temperature heat treatment without sacrificing the strengthening benefits of ultrafine grains. Ultrafine-grained materials, due to their extremely high grain boundary volume fraction, are in a thermodynamically metastable state and possess a strong driving force for grain growth when heated. However, in the heterogeneous multi-interface composite coating, the dispersed nanoscale refractory metal particles exert a strong Zener pinning effect on the grain boundaries. These high-melting-point, low-diffusion-coefficient particles pinning at the grain boundaries significantly increases the energy barrier for grain boundary migration, pushing the significant growth initiation temperature of ultrafine grains to the high-temperature region. Studies have shown that simple nanocrystalline high-entropy alloys may experience significant grain coarsening around 400℃, while the heterogeneous multi-interface structure composed of refractory metal particles effectively compresses the kinetic window for grain growth, providing a broad and safe process window for heat treatment of the coating in the temperature range of 250–450℃. In addition, the high-density phase boundary itself also imposes geometric constraints on the atomic diffusion path, further suppressing the interdiffusion and structural relaxation of matrix elements and maintaining the integrity of the heterogeneous multi-interface structure.

[0028] Besides thermal stability, heterogeneous multi-interface structures play an irreplaceable role as short-circuit diffusion channels in the process of strengthening interfacial bonding during low-temperature heat treatment. In cold-sprayed coatings, although close mechanical contact has been formed between particles, the interface is essentially still dominated by physical interlocking and local micro-region bonding, with countless atomic-scale unbonded regions, lattice mismatches, and micropores. In conventional annealing, the volume diffusion path of atoms is long, and achieving sufficient interfacial healing often requires high temperatures and long durations, which inevitably leads to grain growth. Heterogeneous multi-interface structures provide a high-speed diffusion network along grain boundaries, phase boundaries, and dislocation channels. At low temperatures of 250–450°C, although bulk diffusion is almost frozen, grain boundary diffusion and interfacial diffusion still have significant mobility. Atoms can undergo short-range rearrangement along these short-circuit diffusion channels, promoting micropore shrinkage, atomic step reconstruction, and the formation of local atomic-level metallurgical bonds at the particle interface. This process is like spot-stitching the interface at the nanoscale, effectively eliminating defects, transforming physical contact into metallurgical bonding, and significantly improving the cohesive strength and interfacial bonding strength of the coating. Because the heat treatment temperature is strictly controlled below the critical temperature for significant grain growth, and thanks to the pinning effect of refractory particles on grain boundaries, this diffusion healing process is almost unaffected by grain size coarsening or loss of heterogeneous interface density. In other words, low-temperature heat treatment selectively activates rapid diffusion at heterogeneous interfaces, achieving the ideal post-treatment effect of "strengthening only the interface without damaging the microstructure." This allows the coating to maintain ultrafine grain reinforcement while significantly improving the ductility, toughness, and bonding strength resulting from interfacial metallurgical strengthening.

[0029] The proposed method for preparing heterogeneous multi-interface ultrafine-grained high-entropy alloy composite coatings involves mechanically alloying high-entropy alloy powder with a specific proportion of refractory metal powder to construct an ultrafine-grained composite powder with abundant heterogeneous multi-interfaces. Cold spray solid-state deposition is used to fully preserve its fine structure, and low-temperature heat treatment is employed to achieve selective diffusion strengthening of the heterogeneous interfaces. This process, encompassing powder interface design and coating interface strengthening, overcomes the technical limitations of cold spray deposition of high-hardness high-entropy alloys and the difficulty in strengthening the bonding of ultrafine-grained coatings. The resulting coating exhibits excellent high-temperature oxidation resistance and radiation resistance, along with ultra-high strength, good ductility and toughness, and multifunctional service characteristics, making it a next-generation coating material.

[0030] Compared with the prior art, this application has the following beneficial effects: (1) The high-density ultrafine grain boundaries and heterogeneous phase boundaries in the high heterogeneous multi-interface ultrafine grain high-entropy alloy composite coating form an efficient atomic diffusion channel. Compared with conventional coarse grain coatings, it can accelerate the migration rate of anti-oxidation elements such as Al and Cr to the surface, and form a continuous, dense, low-defect protective oxide film in a short time, effectively extending the service life of the coating in high-temperature oxidation environment.

[0031] (2) Vacancy, interstitial atoms and other point defects generated by high-energy irradiation can be efficiently captured by a large number of heterogeneous interfaces in the coating, promoting rapid recombination and annihilation of defects, inhibiting the formation of voids and dislocation loops, and making helium bubbles in a fine and diffuse state, effectively inhibiting their coarsening and aggregation, thereby greatly reducing irradiation damage.

[0032] (3) On the one hand, the ultrafine grain boundaries bring about a fine grain strengthening effect, improving the overall strength and hardness of the coating; on the other hand, the heterogeneous phase boundary formed by the high-entropy alloy and the refractory metal hinders dislocation slip and plays a role in second-phase strengthening. The coupling effect of multiple strengthening mechanisms, and the network interface structure can disperse plastic deformation and alleviate stress concentration, effectively alleviating the problem of strong plasticity inversion that is common in ultrafine grain materials, so that the coating has both high structural strength and good plasticity and toughness; in addition, the interface pinning effect inhibits grain growth, ensuring the structural stability of the coating at high temperature and making it more mechanically adaptable. Attached Figure Description

[0033] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of this application. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0034] Figure 1 The image shows the surface morphology of the heterogeneous multi-interface FeCoNiCrAl-Nb high-entropy alloy composite powder in Example 1.

[0035] Figure 2 The image shows the cross-sectional SEM microstructure of the cold-sprayed FeCoNiCrAl-Nb high-entropy alloy composite coating from Example 1. Figure 3 This is a TEM microstructure image of the cross-section of the cold-sprayed FeCoNiCrAl-Nb high-entropy alloy composite coating in Example 1.

[0036] Figure 4 The image shows the grain distribution EBSD of the cold-sprayed FeCoNiCrAl-Nb high-entropy alloy composite coating in Example 1.

[0037] Figure 5 The image shows the cross-sectional SEM microstructure of the heterogeneous multi-interface FeCoNiCrAl-Nb high-entropy alloy composite coating after heat treatment in Example 1.

[0038] Figure 6 This is an EBSD (grain distribution diagram) of the heterogeneous multi-interface FeCoNiCrAl-Nb high-entropy alloy composite coating after heat treatment in Example 1. Detailed Implementation

[0039] The technical solutions provided in this application will be described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of this application.

[0040] Unless otherwise specified, the raw materials used in the embodiments of this application are all purchased commercially and used directly without any special treatment.

[0041] Unless otherwise specified, the analytical methods in the embodiments all adopt conventional instrument or equipment settings and conventional analytical methods.

[0042] Example 1 This embodiment provides a method for preparing a heterogeneous multi-interface ultrafine-grained high-entropy alloy composite coating, the specific steps of which are as follows: (1) FeCoNiCrAl high-entropy alloy powder with a particle size of 5-50 μm (D50=28 μm) and niobium elemental powder with a particle size of ≤10 μm are mixed at a mass ratio of 4:1 to obtain a mixed powder, wherein the niobium elemental powder accounts for 20% of the mass of the mixed powder; (2) The mixed powder was ball-milled at 300 rpm for 40 h to refine the grain size of the high-entropy alloy matrix to the ultrafine grain size. At the same time, niobium was dispersed in the matrix in the form of nano / micro particles or sheets, forming a heterogeneous multi-interface structure with the coexistence of high-entropy alloy / refractory metal heterogeneous phase boundary and ultrafine grain boundary, thus obtaining heterogeneous multi-interface high-entropy alloy composite powder. (3) Using zirconium plate as substrate, the heterogeneous multi-interface high-entropy alloy composite powder obtained in step (2) is used as spraying powder. The composite powder is cold-sprayed onto the substrate to obtain an ultrafine-grained high-entropy alloy composite coating. The cold spraying temperature is 900℃, the spraying pressure is 5 MPa, and the spraying gas is nitrogen. (4) Under argon protection, the coating obtained in step (3) is heat-treated at 400℃ for 2 h to obtain an interface-strengthened heterogeneous multi-interface ultrafine-grained high-entropy alloy composite coating.

[0043] Example 2 This embodiment provides a method for preparing a heterogeneous multi-interface ultrafine-grained high-entropy alloy composite coating, the specific steps of which are as follows: (1) FeCoNiCrAl high-entropy alloy powder with a particle size of 5-50 μm (D50=28 μm) and tungsten elemental powder with a particle size of ≤10 μm are mixed at a mass ratio of 9:1 to obtain a mixed powder, wherein the tungsten elemental powder accounts for 10% of the mass of the mixed powder; (2) The mixed powder was ball-milled at 350 rpm for 50 h to refine the grain size of the high-entropy alloy matrix to the ultrafine grain size. At the same time, tungsten was dispersed in the matrix in the form of nano / micro particles or lamellae, forming a heterogeneous multi-interface structure with the coexistence of high-entropy alloy / refractory metal heterogeneous phase boundary and ultrafine grain boundary, thus obtaining heterogeneous multi-interface high-entropy alloy composite powder. (3) Using zirconium plate as substrate, and using the heterogeneous multi-interface high-entropy alloy composite powder obtained in step (2) as spraying powder, the composite powder is cold-sprayed onto the substrate to obtain an ultrafine-grained high-entropy alloy composite coating; wherein the cold spraying temperature is 800℃, the spraying pressure is 5 MPa, and the spraying gas is nitrogen. (4) Under argon protection, the coating obtained in step (3) is heat-treated at 350°C for 3 h to obtain an interface-strengthened heterogeneous multi-interface ultrafine-grained high-entropy alloy composite coating.

[0044] Example 3 This embodiment provides a method for preparing a heterogeneous multi-interface ultrafine-grained high-entropy alloy composite coating, the specific steps of which are as follows: (1) FeCoNiCrMn high-entropy alloy powder with a particle size of 5-50 μm (D50=22 μm) and tungsten elemental powder with a particle size of ≤20 μm are mixed at a mass ratio of 5:1 to obtain a mixed powder, wherein the tungsten elemental powder accounts for about 16.7% of the mass of the mixed powder; (2) The mixed powder was ball-milled at 400 rpm for 50 h to refine the grain size of the high-entropy alloy matrix to the ultrafine grain size. At the same time, tungsten was dispersed in the matrix in the form of nano / micro particles or sheets, forming a heterogeneous multi-interface structure with the coexistence of high-entropy alloy / refractory metal heterogeneous phase boundary and ultrafine grain boundary, thus obtaining heterogeneous multi-interface high-entropy alloy composite powder. (3) Using zirconium plate as substrate, and using the heterogeneous multi-interface high-entropy alloy composite powder obtained in step (2) as spraying powder, the composite powder is cold-sprayed onto the substrate to obtain an ultrafine-grained high-entropy alloy composite coating; wherein the cold spraying temperature is 750℃, the spraying pressure is 5.5 MPa, and the spraying gas is nitrogen. (4) Under argon protection, the coating obtained in step (3) is heat-treated at 300°C for 4 h to obtain an interface-strengthened heterogeneous multi-interface ultrafine-grained high-entropy alloy composite coating.

[0045] Comparative Example 1 This comparative example provides a method for preparing a high-entropy alloy coating, which differs from Example 1 only in that: in step (1), no refractory metal powder is added, and only FeCoNiCrAl high-entropy alloy powder is used for high-energy ball milling and subsequent cold spray deposition. The specific steps are as follows: (1) FeCoNiCrAl high-entropy alloy powder with a particle size of 5-50 μm (D50=28 μm) was ball-milled at 300 rpm for 20 h to obtain high-entropy alloy powder; (2) Using zirconium plate as substrate, and high entropy alloy powder obtained in step (1) as spraying powder, the powder is cold sprayed on the substrate to obtain high entropy alloy coating; wherein the cold spraying temperature is 750℃, the spraying pressure is 5 MPa, and the spraying gas is nitrogen. (3) Under argon protection, the coating obtained in step (2) is heat-treated at 350°C for 2 h to obtain a high-entropy alloy coating.

[0046] Effect Example Figure 1 The image shows the SEM morphology of the heterogeneous multi-interface FeCoNiCrAl-Nb high-entropy alloy composite powder obtained in Example 1. It can be seen that the average particle size of the composite powder after high-energy ball milling is approximately 24 μm, and the microstructure is an approximately equiaxed ellipsoid with a uniform particle size distribution, meeting the requirements of cold spraying for powder flowability and deposition characteristics.

[0047] Figure 2 The image shows the cross-sectional microstructure of the sprayed FeCoNiCrAl-Nb high-entropy alloy composite coating in Example 1. It can be seen that the particles in the high-entropy alloy composite coating are tightly bonded, and no obvious polygonal pores were observed, indicating that the interparticle interface bonding quality is good.

[0048] Figure 3 Transmission electron microscopy (TEM) images of a typical region of the sprayed FeCoNiCrAl-Nb composite coating reveal its fine microstructure. Bright-field images show that the high-entropy alloy matrix grain size has been refined to the ultrafine grain scale, with slightly elongated grains, clear grain boundaries, and extremely high density. A clear heterogeneous phase interface is formed between the niobium particles and the high-entropy alloy matrix.

[0049] Figure 4 The image shows the grain size distribution (EBSD) of the sprayed FeCoNiCrAl-Nb composite coating. Statistical results indicate that the coating grain size exhibits a unimodal distribution, with an average grain size of approximately 0.746 μm, and over 90% of the grains being smaller than 2 μm. This result quantitatively confirms that the cold spraying process completely preserves the fine-grained structure of the composite powder. Such a high grain boundary density provides the coating with significant potential for fine-grain strengthening and also provides ample short-circuit diffusion channels for interfacial diffusion during subsequent heat treatment.

[0050] Figure 5The image shows the cross-sectional microstructure of the heterogeneous multi-interface FeCoNiCrAl-Nb high-entropy alloy composite coating of Example 1 after heat treatment at 400℃ for 2 h. It can be seen that after heat treatment, the high-entropy alloy base coating eliminates some of the inter-particle interfaces in the high-entropy alloy composite coating through atomic diffusion, and the inter-particle interface bonding quality is further strengthened.

[0051] Figure 6 This is an EBSD (Extended Entropy Size Distribution) map of the FeCoNiCrAl-Nb high-entropy alloy composite coating after heat treatment in Example 1. Figure 4 In comparison, the average grain size increased slightly from approximately 0.746 μm to approximately 0.845 μm, with extremely limited grain growth. This fully demonstrates that the dispersed niobium nanoparticles effectively exert the Zener pinning effect on grain boundaries, successfully suppressing grain coarsening at a heat treatment temperature of 400 ℃. Figure 5 The results confirm that the low-temperature heat treatment process achieves the goal of "strengthening interfacial bonding without sacrificing fine grain structure", and verifies the excellent thermal stability of the coating imparted by the heterogeneous multi-interface structure of this application.

[0052] In Example 1, the coating bond strength was tested using ASTM C633 standard and found to be 78 MPa. The coating hardness was measured to be 8.5 GPa using nanoindentation. The coating was then peeled from the substrate using wire EDM and fabricated into I-beam micro-tensile specimens for testing. The tensile strength was measured to be 1.22 GPa, and the elongation was 3.6%, significantly higher than the comparative example (1.4%), indicating improved plasticity. After oxidizing the coating in air at 800℃ for 100 h, the oxidation weight gain was only 0.84 mg / cm³. 2 Furthermore, the oxide film is dense and continuous, exhibiting excellent high-temperature oxidation resistance. In terms of resistance to He ion implantation, after irradiation with 3 MeV He ions at room temperature to 10 dpa, the coating irradiation hardening rate is only 13%, and the microstructure remains stable, demonstrating good tolerance to He implantation damage.

[0053] Example 2, tested according to ASTM C633 standard, showed a coating bond strength of 74 MPa. The coating hardness, measured by nanoindentation (Berkovich indenter, maximum load 10 mN), was 8.1 GPa. Micro-tensile specimens were prepared and tested using the same method as in Example 1, yielding a tensile strength of 1.15 GPa and an elongation of 3.9%, showing a significant improvement in plasticity compared to the comparative example. The weight gain after oxidation at 800℃ for 100 h was 0.92 mg / cm³. 2 The oxide film is dense and continuous. After irradiation with 3 MeV He ions at room temperature to 10 dpa, the hardness increased by 15%, demonstrating good resistance to He ion implantation hardening.

[0054] Example 3, tested according to ASTM C633 standard, showed a coating bond strength of 70 MPa. The coating hardness, measured by nanoindentation (Berkovich indenter, maximum load 10 mN), was 7.8 GPa. Micro-tensile specimens were prepared and tested using the same method as in Example 1, yielding a tensile strength of 1.08 GPa and an elongation of 4.2%, demonstrating significant improvement in plasticity. The weight gain after oxidation at 800℃ for 100 h was 1.05 mg / cm³. 2 The oxide film is dense and continuous. After irradiation with 3 MeV He ions at room temperature to 10 dpa, the hardness increased by 18%, demonstrating good resistance to He ion implantation hardening.

[0055] Comparative Example 1, tested according to ASTM C633 standard, showed a coating bond strength of only 31 MPa, a coating hardness of 6.0 GPa, a tensile strength of 0.78 GPa, and an elongation of 1.4%. The weight gain after oxidation at 800℃ for 100 h was as high as 2.35 mg / cm³. 2 The oxide film was severely peeled off. After being irradiated with 3 MeV He ions at room temperature to 10 dpa, the hardness increased by 37%, and obvious irradiation voids appeared in the microstructure.

[0056] A comparison of the performance of Comparative Example 1 with Examples 1-3 shows that Comparative Example 1 lacks a heterogeneous multi-interface structure constructed from refractory metals, resulting in weak interfacial bonding, insufficient strength, low plasticity, and significantly deteriorated high-temperature oxidation resistance and resistance to He ion implantation damage.

[0057] The comparison results between Comparative Document 1 and Example 1 fully demonstrate that introducing a refractory metal phase to form a heterogeneous multi-interface structure is the key to achieving excellent overall performance of the coating.

[0058] The above description is only a preferred embodiment of this application. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of this application, and these improvements and modifications should also be considered within the scope of protection of this application.

Claims

1. A method for preparing a heterogeneous multi-interface ultrafine-grained high-entropy alloy composite coating, characterized in that, Includes the following steps: (1) A heterogeneous multi-interface ultrafine-grained high-entropy alloy composite powder was cold-sprayed onto the substrate surface to prepare an ultrafine-grained high-entropy alloy composite coating. (2) The ultrafine-grained high-entropy alloy composite coating is heat-treated under a protective atmosphere to obtain a heterogeneous multi-interface ultrafine-grained high-entropy alloy composite coating. The heterogeneous multi-interface ultrafine-grained high-entropy alloy composite powder is a composite powder with a heterogeneous multi-interface structure in which high-entropy alloy / refractory metal heterogeneous phase boundaries and ultrafine grain boundaries coexist.

2. The method of claim 1, wherein the method further comprises: The preparation steps of the heterogeneous multi-interface ultrafine-grained high-entropy alloy composite powder include: A. Mix high-entropy alloy powder with refractory metal powder to obtain a mixed powder; B. The mixed powder is subjected to high-energy ball milling to obtain heterogeneous multi-interface ultrafine-grained high-entropy alloy composite powder. 3.The method of claim 2, wherein the method further comprises: performing a heat treatment on the prepared coating layer. The mass ratio of the refractory metal powder to the high-entropy alloy powder in the mixed powder is 1:(1~10). 4.The method of claim 2, wherein the method further comprises: The particle size of the high-entropy alloy powder is 5~50μm; The particle size of the refractory metal powder is 5~10 μm; The particle size of the heterogeneous multi-interface ultrafine-grained high-entropy alloy-based composite powder is 10~45μm.

5. The method for preparing a heterogeneous multi-interface ultrafine-grained high-entropy alloy composite coating according to claim 2, characterized in that, The high-entropy alloy powder includes one or more of FeCoNiCrAl powder, FeCoNiCrMn powder, or FeCoNiCrCu powder; The refractory metal powder includes one or more of the following: niobium powder, tungsten powder, tantalum powder, molybdenum powder, and rhenium powder.

6. The method of claim 2, wherein the method further comprises: The process parameters of the high-energy ball mill satisfy at least one of the following conditions: The ball mill speed is 300~500 rpm; The ball milling time is 10~60 h.

7. The method of claim 1, wherein the method further comprises: The particle size of the heterogeneous multi-interface ultrafine-grained high-entropy alloy-based composite powder is 10~45 μm. 8.The method of claim 1, wherein the method further comprises: depositing a first layer of the high-entropy alloy on the substrate; and depositing a second layer of the high-entropy alloy on the first layer of the high-entropy alloy. The process parameters for the cold spraying meet at least one of the following conditions: The temperature for cold spraying is 700~1000℃; The pressure for cold spraying is 4~6 MPa; The gases used in cold spraying include nitrogen, helium, or air.

9. The method for preparing a heterogeneous multi-interface ultrafine-grained high-entropy alloy composite coating according to claim 1, characterized in that, The heat treatment process parameters satisfy at least one of the following conditions: The heat treatment temperature is 250~450℃. The heat treatment holding time is 1~5 hours. The protective atmosphere for the heat treatment is argon or nitrogen.

10. A heterogeneous multi-interface ultrafine-grained high-entropy alloy composite coating, characterized in that, It is prepared by the method for preparing heterogeneous multi-interface ultrafine-grained high-entropy alloy composite coating according to any one of claims 1 to 9.

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