A method for hot rolling a layered composite material of TiB2 and CoCrFeNiCu high-entropy alloy.

Abstract

The application relates to the field of metal matrix composite material preparation and hot processing, in particular to a TiB2 and CoCrFeNiCu high-entropy alloy layered composite material package hot rolling preparation method. The scheme is as follows: a high-entropy alloy base blank is prepared through refining; the blank is assembled with pre-prepared TiB2 ceramic powder in a vacuum glove box and is fully sealed and welded to form a sealed composite package blank; after high-temperature pretreatment, multi-pass large reduction hot rolling with a total reduction rate of more than 90% is carried out, and a segmented annealing mechanism of immediately returning to the furnace for heat preservation after each pass is supplemented; and finally, the package is cooled and removed. In the whole project, oxygen is isolated and eliminated, clean interface atoms are driven to deep interdiffusion, and high-strength metallurgical bonding is formed; the processing hardening stress and residual thermal stress are effectively relaxed, the interlayer cracking and ceramic phase crushing are inhibited, and the composite material with dense structure and firm interlayer bonding is obtained.

Description

Technical Field

[0001] This invention relates to the field of metal matrix composite material preparation and hot processing, specifically a method for hot rolling a TiB2 and CoCrFeNiCu high-entropy alloy layered composite material. Background Technology

[0002] Traditional hot rolling processes with added particles suffer from numerous insurmountable technical drawbacks in the preparation of metal-based heterolayered composite materials. Because the metal matrix and the added ceramic reinforcement phase readily react chemically with oxygen in the surrounding environment during high-temperature hot processing, conventional atmospheric pressure rolling or conventional protective rolling cannot achieve long-term oxygen-free interfacial isolation at the microscale. This leads to high-temperature interface oxidation during high-temperature processing. The resulting oxide inclusions severely hinder the close-range lattice contact between matrix atoms and ceramic layer atoms, resulting in only weak mechanical interlocking at the two-phase interface after hot rolling. The low interfacial mechanical bonding strength makes it highly susceptible to interface oxidation and debonding under external shear or cyclic loading. Furthermore, the high-entropy alloy matrix and the ceramic phase exhibit significant differences in thermal expansion coefficients and high-temperature rheological behavior. During continuous large plastic deformation, a large amount of rolling deformation stress rapidly concentrates at the interlayer interface. If this stress cannot be released in time, it can easily induce brittle cracking between layers and lead to disordered fragmentation and severe pulverization of the hard ceramic phase, destroying the macroscopic and microscopic integrity of the layered structure. Therefore, how to control the high-temperature rheological behavior and stress evolution balance during large deformation processes while ensuring the microscopic cleanliness of the interface, and achieve a high-strength continuous bond between the high-hardness ceramic layer and the high-toughness high-entropy alloy layer, is a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0003] The technical problem to be solved by this invention is to overcome the defects that are prone to occur in the traditional hot rolling process of composite materials with added particles, such as high-temperature interface oxidation and debonding, low mechanical bonding strength, interlayer cracking induced by rolling stress concentration and ceramic phase breakage. The invention provides a method for preparing layered high-entropy alloy-based composite materials that can achieve oxygen-free isolation to eliminate oxidation throughout the process, multi-pass gradient rolling to control rheology and large plastic deformation to drive interface metallurgy.

[0004] To achieve the above objectives, the embodiments of this application disclose the following technical solutions:

[0005] This scheme discloses a method for hot rolling a layered composite material of TiB2 and CoCrFeNiCu high-entropy alloy, including the following steps:

[0006] Step S1: Prepare CoCrFeNiCu high-entropy alloy matrix blank;

[0007] Step S2: In a vacuum oxygen-free environment, the CoCrFeNiCu high-entropy alloy matrix blank and TiB2 ceramic powder are assembled inside a 304 stainless steel casing, and a sealed composite casing blank is formed by sealing and continuous welding to isolate it from the external atmosphere.

[0008] Step S3: Perform high-temperature pretreatment on the sealing composite casing blank;

[0009] Step S4: Perform multiple hot rolling passes on the sealed composite cladding billet after high-temperature pretreatment. After each hot rolling pass, the sealed composite cladding billet is reheated in the furnace until the total reduction rate is greater than 90%.

[0010] Step S5: After completing all hot rolling, cool the sealed composite sheath billet to room temperature, remove the 304 stainless steel sheath, and obtain TiB2-reinforced CoCrFeNiCu layered high-entropy alloy matrix composite material.

[0011] Firstly, the starting point of this process chain is the refining and preparation of the matrix blank. The disclosed technology in this step focuses on a highly uniform and surface-clean CoCrFeNiCu high-entropy alloy matrix blank. Its technical role is to lay a high-quality material foundation for subsequent continuous deformation and heterogeneous interface construction. In the process flow, this step inputs the prepared high-entropy alloy raw material, and through melting, purification, and composition control, outputs a standard sample with high uniformity. This sample directly serves as the central assembly unit for the symmetrical sandwich structure in the next step. Based on thermal processing theory, a highly uniform matrix structure helps to reduce micro-rheological inhomogeneities during subsequent large deformation processes, while high-purity surface treatment significantly reduces initial surface impurities and adsorbed gases, thereby reducing the probability of interface inclusions after subsequent encapsulation and providing a quality foundation for the formation of a high-quality interface.

[0012] The next step is inert assembly and fully sealed welding. The disclosed technology in this step involves a hermetically airtight sealed composite cladding blank. Its technical function is to instantly lock the microscopically clean heterogeneous phase interface in an oxygen-free environment, establishing a physical barrier against external oxygen erosion. In the process flow, this step inputs the clean matrix sample from the previous step along with added pre-formed TiB2 ceramic powder. Symmetrical and tight assembly is performed within the inert atmosphere of a vacuum glove box, followed by continuous full-circumference sealed welding. The resulting sealed composite cladding blank is then used for the next step of high-temperature rheological softening. Combining vacuum oxygen control theory, fully sealed welding in an oxygen-free sealed environment ensures that the microscopically clean metal / ceramic heterogeneous interface remains isolated from the external oxygen-rich environment throughout the subsequent high-temperature heating and rolling process. This helps suppress the erosion of the metal matrix and ceramic surface by oxygen and moisture at high temperatures, thus maintaining the atomic-level cleanliness of the interface.

[0013] The 304 stainless steel sheath specifically comprises a 304 stainless steel nut with an inner diameter of 16.0 mm and a height of 30.0 mm. 304 stainless steel plugs are used to seal the openings at both ends of the 304 stainless steel nut, and argon arc welding is used to continuously weld a full-circumference seal between the 304 stainless steel plugs and the 304 stainless steel nut. The technical function is to utilize the unique inner wall structure of the 304 stainless steel nut to increase the compactness of the ceramic powder filling, and to establish an airtight chemical lock through continuous circumferential welding, ensuring that it can withstand the severe deformation of the sheath caused by the intense triaxial compressive stress during subsequent high-temperature heating and hot rolling, without any sheath rupture or air leakage throughout the entire process.

[0014] The subsequent step is a high-temperature pretreatment process. The disclosed technology in this step involves a sealed composite cladding blank that has undergone thermal activation and rheological softening treatment. Its technical function is to achieve sufficient thermal softening and atomic thermal activation of the cladding and internal core sandwich materials without damaging the oxygen-free seal. In the process flow, this step inputs the sealed composite cladding blank output from the previous step. Through heating and holding at a determined temperature and time, it directly outputs a thermally activated blank with good high-temperature rheological properties, which is then continuously and seamlessly input into the next step for multi-pass deformation processing. Combining solid-state physics and thermal deformation theory, high-temperature pretreatment can enhance the lattice thermal vibration of the internal materials, improve the atomic diffusion capability of the CoCrFeNiCu high-entropy alloy matrix, and significantly reduce the high-temperature rheological resistance of the cladding and matrix materials, thus improving material plasticity. This facilitates more coordinated rheological deformation between the metal and ceramic layers during subsequent rolling processing.

[0015] The next step involves multi-pass hot rolling with large reduction and segmented annealing. This step targets denser rolled pieces with a total reduction exceeding 90%. Its technical function is to provide extremely high-energy mechanical driving force, controlling the microstructure evolution and stress relaxation during large plastic deformation, driving the formation of a dense, strongly bonded heterogeneous structure. In the process flow, this step inputs the thermally activated billet from the previous step, and through a progressive processing of 4-5 passes of hot rolling followed by a segmented annealing mechanism involving immediate reheating and 10-minute holding after each pass, directly outputs a rolled piece with significantly reduced thickness and highly densely bonded heterogeneous layers, which is then input into the final step. Combining the deformation heat treatment mechanism, multi-pass continuous rolling with a large reduction exceeding a certain proportion can induce intense plastic flow at the heterogeneous interface, fostering a continuous high-strain shear band at the metal-ceramic interface. The high-strain shear band refers to the region where local strain is highly concentrated during intense plastic deformation. This is beneficial for significantly reducing the interface diffusion activation energy and promoting deep bidirectional interdiffusion between the five principal atoms of Co, Cr, Fe, Ni, and Cu and Ti and B atoms at a clean interface without oxide barriers, thereby transforming the traditional weak mechanical intercalation into a high-strength metallurgical bond. At the same time, the segmented annealing mechanism of immediately returning to the furnace for heat preservation after each rolling pass can trigger dynamic recovery and dynamic recrystallization within the material. In this scheme, dynamic recrystallization is the evolution process of new grains formed during hot deformation, achieving a dynamic balance between the deformation accumulation energy level and the release of lattice distortion energy. This is beneficial for timely relaxation of the work hardening stress generated during large plastic deformation, regulating the grain refinement of the metal matrix, thereby improving interlayer stress concentration and reducing the risk of interlayer cracking and ceramic phase breakage due to stress deterioration.

[0016] The final step in the entire process chain is the cooling and uncoating step. The disclosed technology in this step involves removing the outer protective shell from the core composite material. Its technical function is to smoothly cool the high-temperature rolled sheet to room temperature, safely release macroscopic residual thermal stress, and completely peel off the sacrificial outer shell, ultimately outputting the target product in a closed loop. In the process flow, this step takes in the large-deformation dense rolled piece output from the previous step, undergoes controlled cooling and uncoating, and exposes the structurally intact final device. Based on the theory of thermal stress evolution, due to the significant difference in thermal expansion coefficients between the TiB2 ceramic phase and the CoCrFeNiCu high-entropy alloy matrix, slow cooling methods such as natural cooling in air provide a buffer time for atomic thermal motion and lattice strain. This allows the microscopic residual thermal stress to undergo timely self-tuning and plastic relaxation through minute grain boundary slip in the matrix, thereby reducing tensile stress concentration at the interface and protecting the newly formed metallurgical bonding transition zone from damage. During the desizing process, the difference in work hardening rate and springback between the outer sheath and the internal high-entropy alloy facilitates the smooth delamination of the residual 304 stainless steel sheath, ensuring the high purity and surface quality of the final layered high-entropy alloy-based composite material.

[0017] This invention organically integrates physical protection, rheological regulation, and interfacial thermodynamic diffusion. Relying on the synergistic process of "oxygen-free isolation throughout the entire process to eliminate oxidation, multi-pass gradient rolling to control rheology, and large plastic deformation to drive interfacial metallurgy," it effectively solves the problems of high-temperature oxidation, debonding, cracking, and ceramic breakage that are prone to occur in traditional processes. By relying on the intense plastic flow induced by a large reduction rate, continuous high-strain shear bands are generated on the clean interface without oxygen barriers, initiating deep bidirectional atomic interdiffusion, thereby transforming weak mechanical interlocking into high-strength metallurgical bonding. Supplemented by a segmented annealing mechanism with immediate post-rolling heat preservation and natural cooling, a dynamic balance between deformation accumulation and stress release is achieved, effectively relaxing thermal and processing stresses. Ultimately, a TiB2-reinforced CoCrFeNiCu layered high-entropy alloy matrix composite material is obtained, characterized by dense microstructure, strong interlayer bonding, and significantly improved comprehensive load-bearing capacity, wear resistance, and corrosion resistance. Attached Figure Description

[0018] Figure 1 The images show electronic and EDS layered images of the interface of the TiB2-reinforced CoCrFeNiCu layered high-entropy alloy matrix composite material prepared in the embodiments of the present invention.

[0019] Figure 2 for Figure 1 Energy dispersive X-ray spectral scanning image of iron in the region;

[0020] Figure 3 for Figure 1 Energy-dispersive X-ray spectral scanning image of cobalt element in the region;

[0021] Figure 4 for Figure 1 Energy-dispersive X-ray spectral scanning image of chromium in the region;

[0022] Figure 5 for Figure 1 Energy dispersive X-ray spectral scanning image of nickel in the region;

[0023] Figure 6 for Figure 1 Energy dispersive X-ray spectral scanning image of copper in the region;

[0024] Figure 7 for Figure 1 Energy dispersive X-ray spectral scanning image of titanium in the region;

[0025] Figure 8 for Figure 1 Energy-dispersive X-ray spectral scanning image of boron in the region;

[0026] Figure 9 for Figure 1Energy dispersive X-ray spectral scanning image of oxygen in the region. Detailed Implementation

[0027] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. In the following description, numerous specific details are set forth to provide a comprehensive understanding of the present invention. The present invention may be practiced without some or all of these specific details. In other instances, well-known processes have not been described in detail to avoid unnecessarily obscuring the present invention.

[0028] When used in conjunction with the terms "comprising," "method comprising," or similar language in this specification and appended claims, the singular forms "a," "some," and "the" include plural references unless the context clearly indicates otherwise. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0029] CoCrFeNiCu high-entropy alloy matrix billet refers to the CoCrFeNiCu high-entropy alloy prefabricated metal matrix used in the subsequent composite rolling process. It is formed by melting and processing multi-principal alloy materials of Co, Cr, Fe, Ni and Cu, and is used to provide the main body for metal plastic deformation in the subsequent hot rolling process.

[0030] The sealed composite sleeve blank is a rigid unit assembly formed by assembling a stainless steel nut outer sleeve, a stainless steel plug, TiB2 ceramic powder, and a CoCrFeNiCu high-entropy alloy matrix blank according to a specific spatial structure in a vacuum oxygen-free environment, and then sealing it through continuous welding around the entire circumference. This assembly is completely isolated from the external atmosphere.

[0031] The symmetrical sandwich composite structure refers to a three-layer alternating spatial arrangement of "ceramic-metal-ceramic" in which a CoCrFeNiCu high-entropy alloy matrix blank is symmetrically filled with pre-made TiB2 ceramic powder of equal thickness and mass on both sides of the cavity inside a 304 stainless steel sheath.

[0032] Example

[0033] This embodiment describes a hot rolling method for preparing TiB2 and CoCrFeNiCu high-entropy alloy layered composite materials. Targeting defects such as oxidation debonding and cracking, this process utilizes a "vacuum billet preparation, oxygen-free encapsulation, high-temperature preheating, large reduction multi-pass hot rolling, and immediate heat preservation" flow. By employing a reduction rate exceeding 90% to drive intense plastic flow and inter-atomic interdiffusion at the interface, continuous, defect-free, high-strength metallurgical bonding is achieved.

[0034] Step S1: Prepare CoCrFeNiCu high-entropy alloy matrix blank;

[0035] This step aims to prepare a five-element high-entropy alloy matrix with precise chemical composition, highly uniform macroscopic and microscopic structure, standard geometric dimensions, and no surface oxidation contaminants. This provides a high-quality metal base material for subsequent composite assembly and large deformation hot rolling. Without the control of compositional uniformity and surface quality purification in this step, the matrix is ​​prone to cracking due to localized stress concentration caused by segregation during subsequent hot rolling. Furthermore, a rough or contaminated surface will be directly inherited to the composite interface, compromising its cleanliness.

[0036] CoCrFeNiCu high-entropy alloys are typical multi-principal-element solid solution alloys. Due to the differences in melting points and densities among the elements, conventional melting easily leads to grain boundary segregation and heterogeneous crystallization. This method employs high-energy arc melting under high vacuum, combined with a specific number of tumbling melting processes, along with pre-processing precision mechanical polishing and ultrasonic cleaning, overcoming the limitations of traditional melting methods that are prone to slag inclusions and segregation. This design ensures that the rheological resistance of the matrix is ​​completely consistent at the microscale, representing a creative prerequisite for achieving large deformation rolling without cracking.

[0037] The core technologies involved in this step include the "CoCrFeNiCu high-entropy alloy button ingot" and the "standard cylindrical sample". The former is a non-equilibrium crystal assembly formed by in-situ quenching and solidification of metal raw materials in a water-cooled copper crucible after being melted by a high-energy electric arc; the latter is a precision cylinder with a specific aspect ratio (diameter 15.5 mm, height 4 mm) obtained by stress-free machining of the button ingot using wire electrical discharge machining, which is the geometric core of the subsequent composite sandwich structure.

[0038] In this embodiment, 100g of high-purity Co, Cr, Fe, Ni, and Cu metal raw materials were first accurately weighed according to their atomic ratio. Then, each metal raw material was mechanically polished using 1200-grit sandpaper to remove the dark oxide scale that had formed on its surface due to long-term storage, revealing a bright metallic luster. Next, the polished raw materials were placed in a beaker containing anhydrous ethanol and continuously cleaned in an ultrasonic cleaner for 15 minutes to remove residual metal dust and oil. After cleaning, they were thoroughly dried in a drying oven at 60°C. Then, the processed metal raw materials were layered sequentially inside a water-cooled copper crucible of a vacuum arc melting furnace in order of decreasing melting point (i.e., Cr, Fe, Co, Ni, Cu). After closing the furnace chamber, a molecular pump was started to perform a vacuum operation until the vacuum level inside the furnace reached 4 × 10⁻³ Pa. Subsequently, high-purity argon gas with a purity greater than 99.999% was introduced into the furnace cavity to one standard atmosphere, igniting the plasma arc and adjusting the current to rapidly raise the furnace temperature to 2500℃, ensuring complete melting of all metal raw materials. To eliminate internal component segregation, the molten alloy was repeatedly turned over four times while in the melting state using the operating handle. After melting, the arc was closed, and the alloy ingot was rapidly cooled to room temperature in the furnace before demolding, yielding a CoCrFeNiCu high-entropy alloy button ingot free of surface porosity and macroscopic defects. Finally, a wire EDM machine was used to precisely and stress-free cut the button ingot along its thickness direction, machining it into a standard cylindrical sample with a diameter of 15.5 mm and a height of 4 mm, which was then used as the CoCrFeNiCu high-entropy alloy matrix blank for later use.

[0039] Ultrasonic chemical cleaning utilizes cavitation to remove micron-sized impurities from metal surfaces. During the smelting stage, raw materials are stacked in descending order of melting point, with high-melting-point metals (Cr, Fe) positioned in the high-temperature core of the electric arc, and low-melting-point metals (Cu) located below, close to the water-cooled copper crucible. This effectively prevents the violent volatilization of low-melting-point elements at high temperatures while ensuring the complete dissolution of high-melting-point elements. The high temperature of 2500℃, combined with the intense electromagnetic stirring of the electric arc and subsequent repeated turning, provides extremely high thermal convection driving force, causing the five principal atoms to achieve complete random and disordered mixing in the liquid state, eliminating crystal segregation.

[0040] Under the repeated tumbling of the liquid alloy and the high-speed nucleation and quenching effect of the water-cooled copper crucible, the alloy liquid solidifies rapidly, effectively suppressing long-range controlled diffusion and resulting in extremely rapid solid solution crystallization. The final CoCrFeNiCu high-entropy alloy button ingot exhibits a typical equiaxed face-centered cubic (FCC) single-phase solid solution microstructure, with no low-melting-point eutectic phase enrichment at the grain boundaries and a near-atomic-level uniform distribution of multiple components within the grains, greatly improving the plastic rheological uniformity of the matrix material.

[0041] The final output of this step is a standard cylindrical sample with a diameter of 15.5 mm, a height of 4 mm, and a high surface finish. Its geometric outer diameter forms a tiny 0.5 mm single-sided gap with the inner diameter (16.0 mm) of the 304 stainless steel sheath in the next step. This precise dimensional matching ensures smooth filling and tight encapsulation of TiB2 ceramic powder in step S2, while avoiding non-uniform rheology caused by excessive gaps in the early stages of hot rolling, thus forming a tight closed loop in the process flow.

[0042] Step S2: Assemble and seal the blank in a vacuum oxygen-free environment to form a sealed composite casing.

[0043] This step involves assembling in a vacuum oxygen-free environment and continuous welding and sealing to create clean interface conditions before hot rolling, providing an interface basis for forming a high-quality metallurgical bond during the subsequent hot rolling process.

[0044] The task of this step is to create a sealed space that effectively prevents the entry of oxygen and moisture, locking the loose pre-formed TiB2 ceramic powder and the CoCrFeNiCu high-entropy alloy matrix blank within a symmetrical sandwich geometry. If the material is not encapsulated in a high-purity inert atmosphere and continuously welded around its circumference before hot rolling, oxygen in the air will instantly penetrate the gaps during the subsequent rolling process at temperatures as high as 1200°C. This will cause severe oxidation of the metal matrix and sintering deterioration of the ceramic surface, filling the interface with brittle oxide inclusions.

[0045] Traditional sheathing rolling is mostly assembled in an atmospheric environment. Due to the microscopic porosity, TiB2 ceramic powder and metal surfaces inevitably adsorb trace amounts of water vapor and oxygen molecules. This solution creatively selects a 304 stainless steel nut with a specific size match as the outer sheath, and completes the entire process from powder filling to plug sealing within a high-purity argon vacuum glove box. Subsequently, continuous argon arc welding is used for fusion sealing. This "full-process glove box assembly + continuous fusion welding" design upgrades the traditional simple physical wrapping to an airtight chemical lock, cutting off the kinetic pathway of interfacial oxidation.

[0046] The key technologies involved in this step include "304 stainless steel sheath (304 stainless steel nut)," "symmetrical sandwich composite structure," and "sealing composite sheath blank." The 304 stainless steel nut, due to its internal thread or special internal wall structure, can increase the compactness of the powder filling; the symmetrical sandwich composite structure refers to a three-layer strictly spatially symmetrical body of "TiB2 ceramic powder—high-entropy alloy—TiB2 ceramic powder"; and the sealing composite sheath blank is the airtight physical unit after welding and sealing.

[0047] In this embodiment, the standard columnar sample prepared in step S1, the pre-prepared dry TiB2 ceramic powder, a 304 stainless steel nut with an inner diameter of 16.0 mm and a height of 30.0 mm, and a matching 304 stainless steel plug are placed into a vacuum glove box. By continuously evacuating and filling with high-purity argon, the oxygen and moisture content inside the glove box are strictly controlled to be below 1 ppm. During assembly, firstly, a 304 stainless steel plug is screwed into or pressed into the bottom opening of the 304 stainless steel nut. Then, an equal amount of pre-prepared TiB2 ceramic powder is weighed, and one portion is evenly filled into the lower cavity inside the stainless steel nut, and then compacted and flattened using a special tool. Finally, the standard columnar sample is horizontally and centered on the central surface of the lower layer of TiB2 ceramic powder. Next, another equal amount of pre-made TiB2 ceramic powder was filled into the cavity above the standard cylindrical sample and compacted again using tooling, thus constructing a strictly axially symmetrical sandwich composite structure of "TiB2 ceramic powder - CoCrFeNiCu high-entropy alloy matrix blank - TiB2 ceramic powder" inside the casing. After assembly, another 304 stainless steel plug was pressed into the top opening of the stainless steel nut. Finally, on the welding workbench built into the glove box, the argon arc welding gun was started, and 360° continuous welding was performed along the annular joint connecting the two ends of the 304 stainless steel plug and the 304 stainless steel nut, ensuring that the weld was continuous, flat, and free of any pores, ultimately forming a sealed composite casing blank completely isolated from the external atmosphere.

[0048] The extremely low oxygen-water environment (below 1 ppm) inside the glove box fundamentally eliminates the chemical adsorption of active powder onto the alloy surface. Continuous argon arc welding is employed throughout the circumference, utilizing localized high temperatures to melt and solidify the plug and nut base metal, forming a seamless, metal-bonded closed ring. This high-strength welded joint can withstand the high pressure generated by the thermal expansion of residual gas during subsequent high-temperature heating, as well as the severe deformation of the sheath caused by intense triaxial compressive stress during hot rolling, ensuring that the sheath does not rupture or leak throughout the entire process.

[0049] During the room-temperature, oxygen-free mechanical assembly process in this step, the micron-sized TiB2 ceramic powder undergoes spatial rearrangement under mechanical compaction, reducing the porosity between particles and causing the powder to adhere tightly to the upper and lower end faces of the CoCrFeNiCu high-entropy alloy matrix blank. At this point, the two-phase interface is in a purely microscopic contact state. Although the atoms on both sides of the interface are not bonded, the surface is in an extremely clean atomic contact state free from oxide scale and moisture contamination.

[0050] The sealed composite sleeve blank with an initial total height of 30mm output in this step can directly withstand the long-term baking at 1200℃ in step S3 without internal oxidation or deterioration due to the inert gas lock-in and high compaction stacking, and smoothly enter the hot processing stage.

[0051] Step S3: Perform high-temperature pretreatment on the sealing composite casing blank.

[0052] The task of this step is to achieve a fully deformable and softened state for each phase inside the sealed composite cladding blank through external high heat conduction, and to pre-impart sufficiently high thermal activation energy to the interface atoms. If this high-temperature pretreatment is omitted and hot rolling is carried out directly, the outer 304 stainless steel cladding and the inner CoCrFeNiCu high-entropy alloy will cause severe rolling cracks due to excessively high yield strength and insufficient plasticity. At the same time, the loose TiB2 ceramic powder will not be able to achieve initial smooth thermal densification with the matrix.

[0053] Traditional direct hot rolling is prone to uneven deformation due to excessive differences in the deformation resistance of different phases. This design incorporates a pretreatment at 1200℃ for up to 2 hours. This parameter is chosen based on the high-temperature rheological properties of metallic solid solutions: 1200℃ is the ideal temperature for both 304 stainless steel and CoCrFeNiCu high-entropy alloys to undergo sufficient rheological softening without overheating. Rheological softening refers to the state in which the material's deformation resistance decreases under high-temperature conditions. Maintaining this temperature for 2 hours ensures uniform heat penetration from the surface to the core of the rigid cladding, which is crucial for ensuring the smooth progress of subsequent large-reduction rolling.

[0054] The process object involved in this step is "sealed composite casing blank after high-temperature pretreatment". It refers to a thermally activated entity in which the outer stainless steel casing, the inner CoCrFeNiCu high-entropy alloy matrix blank, and TiB2 ceramic powder reach a thermal equilibrium rheological state while maintaining macroscopic sealing after a long period of high-temperature heat conduction.

[0055] In this embodiment, the sealed composite sheath blank, welded in step S2 and passing the airtightness inspection, is smoothly fed into the center of a muffle furnace cavity preheated to 1200°C and already at a constant temperature using high-temperature crucible tongs. The furnace door is closed, and the temperature control program is activated. The blank is held at 1200°C for 2 hours, allowing the high-temperature radiant heat flow within the furnace cavity to be evenly conducted through the 304 stainless steel sheath to the CoCrFeNiCu high-entropy alloy matrix blank and TiB2 ceramic powder inside. After the holding period, the blank is ready for the next rolling pass.

[0056] In a high-temperature environment of 1200℃, the lattice thermal vibrations within the solid solution of 304 stainless steel and CoCrFeNiCu high-entropy alloy intensify, significantly increasing atomic kinetic energy. Prolonged high-temperature heat penetration completely eliminates existing work hardening or internal stresses within the material, resulting in a substantial decrease in the metal's yield strength, a reduction in rheological resistance to extremely low levels, and a maximization of plastic deformation capacity. Simultaneously, the thermal activation energy of metal atoms and ceramic surface atoms at the interface is released, creating an excellent thermodynamic background for deformation-driven heterogeneous atomic contact and diffusion.

[0057] Within 2 hours of high-temperature pretreatment, the outer 304 stainless steel cladding underwent complete austenitization, resulting in a more uniform grain distribution. The inner CoCrFeNiCu high-entropy alloy solid solution experienced significant recovery, reducing the dislocation density within the matrix grains to extremely low levels and completely eliminating the localized micro-distortions caused by the original cutting. Under thermal expansion, the CoCrFeNiCu high-entropy alloy matrix blank and the surrounding tightly stacked TiB2 ceramic powder were further compressed, and the interfacial contact pores began to close microscopically under thermal stress.

[0058] The high-temperature heat-through and fully rheologically softened sealed composite cladding blank output in this step has excellent impact resistance and large plastic deformation capacity at 1200℃, which can perfectly match the drastic deformation mechanical requirements of the single-pass large reduction in step S4, ensuring perfect engagement of the process chain in the high-temperature rheological section.

[0059] This step focuses on disclosing the specific combination of high-temperature pretreatment parameters of 1200℃ and 2h and their control effect on the overall thermal softening of the billet, which fundamentally supports claim 7.

[0060] Step S4: Perform multi-pass hot rolling on the sealed composite sheath blank after high-temperature pretreatment.

[0061] This step is the core deformation stage in the entire hot rolling process. Its task is to drive the metal matrix to undergo intense plastic flow through continuous high-energy rolling mechanical force, completely compacting and embedding the granular TiB2 ceramic powder into the matrix surface, ultimately achieving atomic-level bonding at the two-phase interface. Without the multi-pass rolling in this step or with insufficient total reduction, the material will not be able to eliminate internal porosity, and the two-phase interface will only remain in a state of microscopic contact or fragile mechanical interlocking.

[0062] Single-pass hot rolling with ultra-large reduction can easily lead to cladding cracking, while continuous multi-pass rolling without heat preservation can cause a sudden drop in billet temperature during the roll exit process, accumulating huge work hardening stress and inducing severe interlayer tearing and disordered fragmentation of ceramic particles. This solution creatively designs a gradient stress-relieving rolling system of "4-5 passes of hot rolling + immediate reheating in the furnace for 10 minutes after each pass + total reduction rate greater than 90%". This process of alternating deformation and tempering utilizes large reduction to build high-energy shear bands to drive diffusion, and uses reheating in the furnace to remove residual work hardening, perfectly resolving the classic contradiction between "deformation densification" and "stress cracking" in layered composite materials.

[0063] The core technical concepts involved in this step include "multi-pass hot rolling", "reheat heat treatment", and "total reduction rate greater than 90%". Multi-pass hot rolling refers to progressive processing in which the total deformation is distributed in 4 to 5 deformation ranges; reheat heat treatment refers to short-term stress relief heat treatment implemented between passes; and a total reduction rate greater than 90% refers to the proportion of macroscopic deformation reduction of the final thickness of the rolled piece relative to the initial height (30 mm).

[0064] In this embodiment, the 1200℃ muffle furnace door is quickly opened, and the sealed composite cladding billet, which is red-hot at 1200℃, is removed using crucible tongs. Within 3 seconds, it is fed into the gap between the rolls of a twin-roll hot rolling mill for the first pass of hot rolling. After the first pass is closed, the thickness of the rolled piece is significantly reduced. At this point, no further continuous rolling is performed; instead, the rolled piece is immediately returned to the muffle furnace at 1200℃ and held for 10 minutes. After the holding period, the rolled piece is removed and quickly subjected to the second pass of hot rolling, with the reduction per pass increasing gradually. After rolling, it is immediately returned to the muffle furnace again and held for 10 minutes. This cycle is repeated for a total of 5 passes of hot rolling, with the above-mentioned return-to-furnace holding operation performed after each pass. The initial total height of the sealing composite sleeve blank is 30mm. Under five consecutive progressive rolling passes, its thickness decreases with each pass. Finally, the thickness of the entire rolled piece is strictly controlled at 2.8mm. According to calculations, the actual total reduction rate reaches 90.7%, successfully completing the large plastic deformation stage.

[0065] A total reduction rate exceeding 90% macroscopically generates extremely strong normal extrusion and tangential shear forces. Under intense pressure, the rheologically softened CoCrFeNiCu high-entropy alloy matrix undergoes superplastic-like fluid motion, forcibly squeezing into the tiny micropores between TiB2 ceramic powder particles. Under the influence of severe shear forces, a continuous, high-strain shear band forms at the two-phase interface. This shear band accumulates extremely high density of mechanical and distortion energy, causing severe lattice distortion at the interface and significantly reducing the atomic diffusion activation energy. This allows for forced bidirectional deep rheological interdiffusion between Co, Cr, Fe, Ni, and Cu atoms on the metal side and Ti and B atoms on the ceramic side, without reaching the melting point, forming a wide elemental gradient transition region. The elemental gradient transition region refers to the transition area formed by the continuous change in elemental concentration on both sides of the interface.

[0066] During each hot rolling pass, high-density dislocation pile-up and lattice distortion occur within the high-entropy alloy grains, resulting in intense grain elongation. The subsequent 1200℃, 10-minute furnace hold triggers timely dynamic recovery and recrystallization. Newly formed, distortion-free recrystallized grains rapidly nucleate and grow, causing large-scale annihilation of accumulated dislocations and releasing residual stress. Simultaneously, the granular TiB2 ceramic powder undergoes mechanical rearrangement and densification sintering under high pressure, becoming tightly embedded at the leading edge of the recrystallized high-entropy alloy. Through five repeated cycles of alternating "deformation grain elongation—re-recrystallization refinement," the matrix structure transforms into extremely fine equiaxed grains, and a stable atomic-level metallic / covalent hybrid metallurgical interface is formed at the interface, without any cracks or micropores.

[0067] The final output of this step is a dense composite sheet rolled product with a total reduction rate of greater than 90% and a thickness of less than 3mm, in which densification and interfacial element diffusion have been completed. At this point, the material is still encased in the deformed 304 stainless steel sheath and is ready to be input into step S5 for final cooling, temperature control, and sheath removal.

[0068] Step S5: After completing all hot rolling, cool the sealed composite sheath blank to room temperature and remove the sheath.

[0069] The task of this step is to safely cool the high-temperature rolled sheet to room temperature and completely peel off the sacrificial outer 304 stainless steel cladding, ultimately exposing the TiB2-reinforced CoCrFeNiCu layered high-entropy alloy matrix composite material with a complete and continuous layered structure. Without proper control of the cooling rate in this step, or if the cladding is improperly removed, the material is prone to interlayer delamination during cooling due to severe residual thermal stress, or damage to the core composite sheet during mechanical cladding removal.

[0070] The coefficient of thermal expansion (CTE) between the TiB2 ceramic phase and the CoCrFeNiCu high-entropy alloy matrix differs significantly. Common water quenching or rapid air cooling induces extremely high instantaneous tensile stress at the interface, leading to brittle cracking of the newly formed metallurgical bond layer. This approach employs natural air cooling, providing a buffer time for atomic thermal motion and lattice strain, ensuring a gradual release of stress and constituting a creative conclusion to the entire long-lifespan material preparation process.

[0071] This step involves the "TiB2-reinforced CoCrFeNiCu layered high-entropy alloy matrix composite". This is a novel layered metal matrix composite material, characterized by alternating parallel arrangements of high-hardness TiB2 ceramic layers and high-toughness CoCrFeNiCu high-entropy alloy layers, with a seamless element diffusion metallurgical bonding state at the interface between the two phases.

[0072] In this embodiment, after the fifth hot rolling pass and the final heat treatment pass are completed, the 2.8mm thick red-hot rolled piece is removed from the muffle furnace and placed stably on the refractory bricks of an air cooling platform without any forced cooling medium, allowing it to cool naturally to room temperature in still air. Subsequently, the weld edge is cut along the deformed 304 stainless steel cladding edge using a combination of mechanical milling and manual tapping. Due to the difference in work hardening rate and springback between the 304 stainless steel and the internal high-entropy alloy after rolling, the remaining outer stainless steel shell is successfully delaminated. Finally, all the outer 304 stainless steel cladding is removed, exposing the TiB2-reinforced CoCrFeNiCu layered high-entropy alloy matrix composite material with a continuous and intact internal structure and a smooth surface.

[0073] Natural cooling in air falls into the category of slow cooling. As the temperature slowly decreases from 1200℃ to room temperature, the matrix metal lattice and the ceramic lattice undergo simultaneous thermal contraction. Due to the microscopic thermal stress caused by the mismatch in thermal expansion coefficients, under slow cooling rates, the residual trace amounts of high-temperature creep and grain boundary slip in the CoCrFeNiCu high-entropy alloy matrix billet can be promptly self-tuned and plastically relaxed. This significantly reduces the concentration of residual tensile stress at the interface, protecting the metallurgical bonding transition zone from damage.

[0074] During natural cooling, no more drastic phase transformations occur within the material, and the fine-grained solid solution structure formed in step S4 and the TiB2 ceramic sintered structure are perfectly locked in at room temperature. Co, Cr, Fe, Ni, Cu, Ti, and B atoms at the interface cease long-range diffusion and solidify into stable compositional gradient grain boundary transition zones within a few micrometers on both sides of the interface. The two phases maintain a continuous bond at the interface, without any obvious cracks or porosity defects.

[0075] To visually confirm the microscopic layered structure evolution morphology of the final product after uncoating and the element interdiffusion characteristics at the heterogeneous phase interface, this embodiment uses an energy-dispersive X-ray spectral scanning analysis (EDSMapping) system to perform microscopic characterization of the sample interface region.

[0076] Depend on Figure 1 It can be seen that the high-entropy alloy matrix layer and the TiB2 ceramic reinforcement layer are arranged in parallel and alternately, with a straight, continuous, and macroscopically seamless interlayer interface. No microscopic delamination, warping, or thermal stress cracking defects were found at the interface between the two phases, proving that the high-reduction rolling combined with natural cooling successfully achieved densification of the heterogeneous configuration. Further analysis of the interfacial atomic behavior using characteristic element distribution images reveals the following:

[0077] See Figure 7The corresponding Ti Kα1 spectrum shows that titanium is highly enriched and strictly confined within the ceramic layer space, confirming that the dispersed TiB2 ceramic powder completed high-density rearrangement and in-situ densification sintering under mechanical extrusion with a total reduction rate exceeding 90%. Combined with... Figures 2 to 6 As can be seen from the corresponding elemental surface scan diagrams, the main elements of high-entropy alloys, such as Fe, Co, Cr, Ni, and Cu, are uniformly distributed within the metal matrix layer. No obvious long-range macroscopic segregation of each element is observed, indicating that the high-entropy alloy matrix maintains good compositional homogeneity.

[0078] Crucially, see Figure 9 The corresponding OKα1 spectrum shows extremely low oxygen element characteristic counts across the entire surface scan region spanning the metal / ceramic interface, and the absence of oxide-enriched bright bands commonly found in conventional hot-rolled composite materials at the two-phase interface directly confirms the existence of the "clean interface" constructed by the oxygen-free encapsulation process in step S2 of this invention at the microstructural level, eliminating the hard and brittle oxide inclusion layer that hinders diffusion. Under the clean premise of oxygen-free barrier, the high-energy shear band generated by the large plastic deformation in step S4 greatly reduces the diffusion activation energy of heteroatoms, promotes a certain degree of interdiffusion of elements on both sides of the interface, and forms a continuous element transition region, thereby achieving high-strength metallurgical bonding. Figures 2 to 9 The corresponding elemental surface scans show that Ti and B elements are mainly distributed in the ceramic reinforcement layer, while Fe, Co, Cr, Cu, and Ni elements are mainly distributed in the high-entropy alloy matrix layer. Oxygen elements are not significantly enriched in the interface region. The distribution boundaries of each element are clear and the interface is continuous, indicating that the TiB2-reinforced CoCrFeNiCu layered high-entropy alloy matrix composite material prepared in this invention has a good layered structure and a clean interface.

[0079] This step, as the endpoint of the entire process chain, directly outputs the final device without any outer casing or packaging, ready for subsequent machining or testing under extreme wear and corrosion conditions. The process data flow is perfectly closed at this point.

[0080] The hot rolling preparation method of TiB2 and CoCrFeNiCu high-entropy alloy layered composite material of the present invention achieves excellent technical effects that are not simply the linear superposition of the effects of each step, but the inevitable result of the highly synergistic effect of the entire process chain at the level of "space oxygen control, thermal flow control, and deformation phase control".

[0081] First, the vacuum glove box inert assembly and full-circumferential weld joint in step S2, together with the high-purity surface treatment in step S1, form an anti-oxidation synergy. This eliminates the corrosion of metal and ceramic surfaces by oxygen and moisture in the air at high temperatures, ensuring the two-phase interface remains atomically clean before entering the rolling mill. This clean interface state paves the way for the close-range atomic contact at the interface induced by a total reduction rate exceeding 90% in subsequent step S4, eliminating the brittle oxide inclusion layer that hinders diffusion in traditional rolling and ensuring the purity of the interfacial rheology.

[0082] Secondly, the high-temperature, long-duration pretreatment in step S3 softens the cladding and internal interlayers, creating a sophisticated stress-rheological synergy with the multi-pass gradient hot rolling and the immediate 10-minute reheating after each single pass in step S4. The 1200℃ high-temperature pretreatment endows the material with extremely high initial rheological plasticity; while in the multi-pass rolling, the dislocation accumulation and high-energy states of lattice distortion generated by single-pass deformation immediately trigger dynamic recrystallization during the subsequent 10-minute short reheating. This cyclical process of "deformation accumulation energy level - thermal activation recrystallization release hardening" achieves dynamic and continuous relaxation of work hardening stress. It not only suppresses interlayer tearing, void deterioration, and cladding cracking that are prone to occur in layered materials under ultra-large deformation (>90%), but also induces extreme grain refinement of the matrix, achieving high-density uniform deformation.

[0083] Ultimately, based on the premise of a clean and uncontaminated interface, the large-scale deformation in step S4, which induces continuous high-strain shear bands at the interface, provides a massive amount of lattice distortion energy. Combined with high-temperature thermal activation at 1200℃, this significantly reduces the cross-boundary diffusion activation energy of heterogeneous atoms on both sides of the interface. This promotes deep bidirectional interdiffusion between the five principal atoms of Co, Cr, Fe, Ni, and Cu and Ti and B atoms in a very short time, constructing a continuous, smooth, and macroscopically boundaryless elemental gradient transition region at the two-phase interface. Furthermore, the natural cooling in step S5 gently relaxes the CTE mismatch thermal stress, perfectly preserving this high-strength interfacial atomic-level metallurgical bond at room temperature. The entire process chain is interconnected, ultimately resulting in the stable preparation of a TiB2-reinforced CoCrFeNiCu layered high-entropy alloy matrix composite material with an extremely dense microstructure, complete elimination of oxide inclusions, strong two-phase metallurgical bonding, and a qualitative leap in comprehensive load-bearing, wear resistance, and corrosion resistance.

[0084] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them; although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications can still be made to the specific implementation methods of the present invention or equivalent substitutions can be made to some technical features without departing from the spirit of the technical solutions of the present invention, and all such modifications should be covered within the scope of the technical solutions claimed in the present invention.

Claims

1. A method for hot rolling a layered composite material of TiB2 and CoCrFeNiCu high-entropy alloy, characterized in that, Includes the following steps: Step S1: Prepare CoCrFeNiCu high-entropy alloy matrix blank; Step S2: In a vacuum oxygen-free environment, the CoCrFeNiCu high-entropy alloy matrix blank and TiB2 ceramic powder are assembled inside a 304 stainless steel casing, and a sealed composite casing blank is formed by sealing and continuous welding to isolate it from the external atmosphere. Step S3: Perform high-temperature pretreatment on the sealing composite casing blank; Step S4: Perform multiple hot rolling passes on the sealed composite cladding billet after high-temperature pretreatment. After each hot rolling pass, the sealed composite cladding billet is reheated in the furnace until the total reduction rate is greater than 90%. Step S5: After completing all hot rolling, cool the sealed composite sheath billet to room temperature, remove the 304 stainless steel sheath, and obtain TiB2-reinforced CoCrFeNiCu layered high-entropy alloy matrix composite material.

2. The method for preparing TiB2 and CoCrFeNiCu high-entropy alloy layered composite material by hot rolling according to claim 1, characterized in that, In step S1, high-purity Co, Cr, Fe, Ni, and Cu metal raw materials are weighed according to equiatomic ratio; after removing the oxide scale from the surface of each metal raw material, they are ultrasonically cleaned with anhydrous ethanol and dried; the treated metal raw materials are placed in a vacuum arc melting furnace for melting, and after cooling, CoCrFeNiCu high-entropy alloy button ingots are obtained; the CoCrFeNiCu high-entropy alloy button ingots are processed into standard columnar samples by wire electrical discharge machining as CoCrFeNiCu high-entropy alloy matrix blanks.

3. The method for preparing TiB2 and CoCrFeNiCu high-entropy alloy layered composite material by hot rolling according to claim 2, characterized in that, The melting process of the vacuum arc melting furnace includes: placing the various metal raw materials in a water-cooled copper crucible in order of their melting points from high to low, drawing a vacuum until the vacuum degree inside the furnace reaches below 5×10⁻³Pa, introducing high-purity argon gas, igniting the electric arc to completely melt the various metal raw materials, and repeatedly turning the molten alloy melt over and over 3 to 5 times, and then cooling it to room temperature with the furnace.

4. The method for preparing TiB2 and CoCrFeNiCu high-entropy alloy layered composite material by hot rolling according to claim 2, characterized in that, The standard cylindrical specimen has a diameter of 15.5 mm and a height of 4 mm.

5. The method for preparing TiB2 and CoCrFeNiCu high-entropy alloy layered composite material by hot rolling according to claim 1, characterized in that, In step S2, the vacuum oxygen-free environment is the high-purity argon environment inside the vacuum glove box; TiB2 ceramic powder is filled into the upper and lower sides of the 304 stainless steel sheath, and CoCrFeNiCu high-entropy alloy matrix blank is placed between the two layers of TiB2 ceramic powder to form a symmetrical sandwich composite structure of TiB2 ceramic powder-CoCrFeNiCu high-entropy alloy matrix blank-TiB2 ceramic powder.

6. The method for preparing TiB2 and CoCrFeNiCu high-entropy alloy layered composite material by hot rolling according to claim 5, characterized in that, The 304 stainless steel sheath consists of a 304 stainless steel nut with an inner diameter of 16.0 mm and a height of 30.0 mm. 304 stainless steel plugs are used to seal the openings at both ends of the 304 stainless steel nut, and argon arc welding is used to continuously weld and seal the 304 stainless steel plugs and the 304 stainless steel nut around the entire circumference.

7. The method for preparing TiB2 and CoCrFeNiCu high-entropy alloy layered composite material by hot rolling according to claim 1, characterized in that, In step S3, the sealing composite casing blank is kept at 1200℃ for 2 hours to complete the high-temperature pretreatment.

8. The method for preparing TiB2 and CoCrFeNiCu high-entropy alloy layered composite material by hot rolling according to claim 7, characterized in that, In step S4, the multi-pass hot rolling includes 4 to 5 passes. After each pass is completed, the sealed composite cladding billet is immediately returned to the furnace for 10 minutes of heat preservation before proceeding to the next pass.

9. The method for preparing TiB2 and CoCrFeNiCu high-entropy alloy layered composite material by hot rolling according to claim 8, characterized in that, The initial total height of the sealing composite sheath blank is 30mm, and the final overall thickness is less than 3mm after multiple hot rolling passes.

10. The method for preparing TiB2 and CoCrFeNiCu high-entropy alloy layered composite material by hot rolling according to claim 9, characterized in that, In step S5, after the sealing composite sleeve blank is cooled to room temperature by natural cooling, the 304 stainless steel sleeve is removed.

Images