A wear-resistant Fe-Cr-Ni-Al medium-entropy alloy and its preparation method

Abstract

This invention provides a wear-resistant Fe-Cr-Ni-Al medium-entropy alloy and its preparation method, wherein the alloy has the general formula Fe 0.5 Cr 0.2 Ni x Al 0.3‑x The value of x ranges from 0.1 to 0.2, and the configuration entropy is from 1.22R to 1.24R. When x is 0.2, the AlNi phase has a cubic block morphology; when x is 0.15, the AlNi phase has a rounded cubic morphology; and when x is 0.1, the AlNi phase has a spherical morphology. By controlling the molar ratio of Ni to Al, a two-phase structure transformation from face-centered cubic AlNi intermetallic compound to body-centered cubic AlNi intermetallic compound can be achieved, with a uniformly dispersed volume fraction of AlNi intermetallic compound of not less than 53% in the matrix. This invention employs a self-propagating high-temperature synthesis process, using Fe2O3 as the sole oxide raw material, combined with high-purity Al, Cr, and Ni elemental powders. The Al powder serves as both a reducing agent for the aluminothermic reaction and a source of alloying elements. The alloy prepared by this invention has a Vickers hardness of 282 HV to 420 HV, a yield strength of 283 MPa to 986 MPa, and excellent wear resistance.

Description

Technical Field

[0001] This invention relates to the field of medium-entropy alloy preparation technology, specifically to a wear-resistant Fe-Cr-Ni-Al medium-entropy alloy and its preparation method. Background Technology

[0002] Medium-entropy alloys are multi-principal element alloys with configurational entropy between 1R and 1.5R. They possess unique microstructures and excellent comprehensive properties, and have broad application prospects in aerospace, machinery manufacturing, energy, and chemical industries. However, the preparation and performance of existing medium-entropy alloys still face many challenges.

[0003] Traditional medium-entropy alloy preparation processes mainly include arc melting and spark plasma sintering. These processes require continuous holding at high temperatures of 1500℃ to 2000℃ for several hours, resulting in high energy consumption, high equipment maintenance costs, and easy occurrence of grain coarsening and internal shrinkage defects, thereby reducing the overall mechanical properties of the alloy.

[0004] The all-oxide aluminothermic reduction process is another method for preparing medium-entropy alloys. This process uses expensive and toxic Cr2O3 and NiO as raw materials, resulting in high raw material costs and requiring a large amount of Al reducing agent. Furthermore, the reaction process is violent and prone to runaway, posing significant environmental and safety risks. In addition, Fe-Cr-Ni-Al alloys prepared using this process generally have a hardness below 282 HV and insufficient wear resistance.

[0005] Conventional face-centered cubic medium-entropy alloys have a room temperature hardness of only 180HV to 250HV, and poor resistance to abrasive cutting and adhesive wear, which cannot meet the wear-resistant requirements of mining machinery, metallurgical equipment, transportation and other fields.

[0006] To this end, a Fe-Cr-Ni-Al medium-entropy alloy with high wear resistance, low cost, low energy consumption, and environmental safety, and its preparation method are proposed. Summary of the Invention

[0007] The purpose of this invention is to overcome the shortcomings of the prior art and provide a wear-resistant Fe-Cr-Ni-Al medium-entropy alloy and its preparation method, thereby solving the technical problems of low hardness, poor wear resistance, high energy consumption, high cost, and high environmental and safety risks in the preparation process of existing medium-entropy alloys.

[0008] The specific technical solution is as follows: A wear-resistant Fe-Cr-Ni-Al medium-entropy alloy was prepared using a self-propagating high-temperature synthesis process. The alloy's general formula is Fe. 0.5 Cr 0.2 Ni x Al 0.3-xThe alloy is a medium-entropy alloy, with x ranging from 0.1 to 0.2 and a configuration entropy of 1.22R to 1.24R. The alloy consists of a matrix phase and a uniformly dispersed AlNi intermetallic compound phase within the matrix, with the AlNi intermetallic compound phase comprising at least 53% by volume. The size of the AlNi intermetallic compound phase ranges from 160 nm to 700 nm. When x is 0.2, the AlNi phase exhibits a cubic morphology; when x is 0.15, it exhibits a rounded cubic morphology; and when x is 0.1, it exhibits a spherical morphology. Through a rational multi-principal component design, the alloy is positioned within the configuration entropy range of medium-entropy alloys, possessing the structural stability characteristic of medium-entropy alloys. The uniformly distributed second phase in the matrix effectively hinders dislocation slip, enhancing the alloy's resistance to deformation and wear, enabling it to maintain good service condition under friction conditions and meet the requirements of various wear-resistant applications. Different sizes and morphologies of the second phase can produce differentiated strengthening effects. The blocky second phase can provide strong load-bearing capacity, the rounded second phase can alleviate stress concentration, and the spherical second phase can play a significant dispersion strengthening role. By controlling the characteristics of the second phase, the optimal match between the strength, toughness and wear resistance of the alloy can be achieved.

[0009] The aforementioned wear-resistant Fe-Cr-Ni-Al medium-entropy alloy exhibits the following characteristics: when x is 0.2, the alloy matrix phase is a face-centered cubic FeCr solid solution; when x ranges from 0.1 to 0.15, the alloy matrix phase is a body-centered cubic FeCr solid solution. By adjusting the relative proportions of the two elements, a controllable transformation of the alloy matrix crystal structure is achieved. The appropriate matrix structure type can be selected based on the different strength and plasticity requirements in practical applications, enabling the alloy to adapt to various working conditions ranging from low load and high plasticity to high load and high strength.

[0010] The aforementioned wear-resistant Fe-Cr-Ni-Al medium-entropy alloy has a Vickers hardness of 282 HV to 420 HV and a 0.2% conditional yield strength of 283 MPa to 986 MPa. The alloy possesses high hardness and yield strength, enabling it to withstand significant external forces without exhibiting obvious plastic deformation. Under complex loads such as impact, extrusion, and friction, it is less prone to permanent deformation and failure, effectively extending the service life of components.

[0011] This invention provides a method for preparing the wear-resistant Fe-Cr-Ni-Al medium-entropy alloy as described above, employing a self-propagating high-temperature synthesis process, including the following steps: Step 1, Raw Material Preparation: An oxide-element composite raw material system is adopted, using Fe2O3 powder as the sole oxide raw material, combined with Al, Cr, and Ni elemental powders, according to the alloy general formula Fe... 0.5 Cr 0.2 Ni x Al0.3-x Weigh each raw material according to the stoichiometric ratio of the chemical reaction; Step 2, Mixing: The weighed raw materials are ball-milled and mixed to obtain a uniform powder; Step 3, pressing and molding: Press the mixed powder into a blank to obtain a green body; Step 4, self-propagating reaction: The billet is placed under a protective atmosphere, and a self-propagating high-temperature synthesis reaction is initiated by instantaneous ignition. The alloy synthesis is completed by relying on the self-exothermic reaction to obtain the reaction product. Step 5, separation and purification: The reaction products are crushed, ground and magnetically separated to remove Al2O3 byproducts and obtain the target alloy.

[0012] The self-propagating high-temperature synthesis process utilizes the heat released by the reaction itself to sustain the synthesis process, eliminating the need for a continuous external high-temperature heat source and significantly reducing production energy consumption. The use of a composite raw material system of oxides and elements simplifies the types of raw materials and reduces production steps. The added separation and purification steps effectively remove reaction byproducts, yielding alloy products with high purity.

[0013] The above-described method for preparing wear-resistant Fe-Cr-Ni-Al medium-entropy alloy includes the following steps: In step one, the purity of Fe2O3, Al, Cr, and Ni powders is not less than 99.9%; Al powder serves simultaneously as a reducing agent in the aluminothermic reaction and as a source of Al element in the alloy. Using high-purity raw materials reduces the adverse effects of impurities on the alloy's microstructure and properties, ensuring the stability and consistency of the alloy's performance. Aluminum powder simultaneously acts as both a reducing agent and an alloying element, eliminating the need for additional reducing agents, further simplifying the raw material system and reducing raw material procurement and processing costs.

[0014] The above-mentioned method for preparing wear-resistant Fe-Cr-Ni-Al medium-entropy alloy includes the following steps: In step two, alumina grinding balls are used for ball milling, with a ball-to-material ratio of 1:1.5 to 1:2.5; the ball milling process follows a cyclic mode of forward rotation for 1 hour, reverse rotation for 1 hour, settling for 1 minute to 3 minutes, and stirring, with a rotation speed of 150 r / min to 190 r / min and a total ball milling time of 5 to 7 hours; after ball milling, a 100-200 mesh sieve is used for ball-to-material separation. Using specific ball milling process parameters ensures that raw material powders of different densities and particle sizes are thoroughly and uniformly mixed, avoiding component segregation. Uniform raw material mixing is a prerequisite for ensuring the smooth progress of subsequent self-propagating reactions and the uniformity of the alloy microstructure, effectively improving the quality stability of the final product.

[0015] The above-described method for preparing wear-resistant Fe-Cr-Ni-Al medium-entropy alloy includes the following step: In step three, the pressing pressure is 50 MPa to 60 MPa, and the holding time is 2 to 4 minutes. Appropriate pressing pressure and holding time allow the powder particles to bond tightly, forming a billet with a certain strength and density. Suitable billet density ensures the stable propagation of the self-propagating reaction wave, allowing the reaction to proceed sustainably, and also prevents the billet from cracking due to thermal expansion during the reaction.

[0016] The above-mentioned method for preparing wear-resistant Fe-Cr-Ni-Al medium-entropy alloy includes the following steps: In step four, the protective atmosphere is argon gas with a pressure of 4 MPa to 5 MPa; the ignition method can be any one of electric arc ignition, laser ignition, or ignition with an igniter; the maximum temperature during the reaction is 2000℃ to 3000℃, and the maximum gas pressure is 8 MPa to 10 MPa. Reaction under inert gas protection prevents alloying elements from reacting with oxygen at high temperatures, ensuring the accuracy of the alloy composition. Multiple ignition methods are available to adapt to different production equipment and scales. A reasonable temperature and pressure range during the reaction ensures that all elements are fully alloyed, forming a uniform solid solution and second-phase structure.

[0017] The above-described method for preparing the wear-resistant Fe-Cr-Ni-Al medium-entropy alloy includes the following step: In step four, the billet is placed in a copper crucible with a thickness of 30 mm to 40 mm, and 1 g to 3 g of igniter is placed on the billet. Then, it is placed in a high-temperature, high-pressure reactor for a self-propagating reaction. Using a copper crucible of suitable thickness allows for rapid dissipation of excess heat generated by the reaction, preventing excessively high reaction temperatures that could lead to grain coarsening. Simultaneously, it can withstand the high pressure generated by the reaction, ensuring the safety of the production process. An appropriate amount of igniter reliably initiates the self-propagating reaction without introducing excessive impurities that could affect the alloy's properties.

[0018] The above-described method for preparing wear-resistant Fe-Cr-Ni-Al medium-entropy alloy includes the following step: Step five, separation and purification, specifically involves: coarsely crushing the reaction product to a particle size of less than 5 mm, then finely grinding it to below 200 mesh, and performing magnetic separation using a magnetic separator with a magnetic field strength of 1200 Gs to 1800 Gs. The collected magnetic product is the target alloy. Through stepwise crushing and grinding, the reaction product can be processed to a suitable particle size, creating conditions for subsequent magnetic separation. Using a suitable magnetic field strength for magnetic separation can efficiently separate the magnetic alloy phase from the non-magnetic byproducts, effectively improving the purity of the product while ensuring alloy recovery rate.

[0019] The above-mentioned method for preparing wear-resistant Fe-Cr-Ni-Al medium-entropy alloys, wherein: when preparing Fe 0.5 Cr 0.2 Ni 0.2 Al0.1 When alloying, the reaction equation is: ; When preparing Fe 0.5 Cr 0.2 Ni 0.15 Al 0.15 When alloying, the reaction equation is: ; When preparing Fe 0.5 Cr 0.2 Ni 0.1 Al 0.2 When alloying, the reaction equation is: .

[0020] The clearly defined chemical reaction equations in this scheme provide a basis for the accurate weighing of raw materials during the production process. This allows for strict control of the addition ratio of each element, ensuring that the final alloy composition is completely consistent with the designed composition. It also avoids fluctuations in alloy performance due to compositional deviations, thus ensuring the stability and repeatability of product quality.

[0021] The present invention has the following beneficial effects: 1. This invention achieves a controllable transformation of the alloy's phase structure by optimizing the alloy composition and controlling the molar ratio of Ni to Al. A high volume fraction of AlNi intermetallic compound phase is uniformly dispersed in the matrix, resulting in a Vickers hardness of 282 HV to 420 HV and a yield strength of 283 MPa to 986 MPa, far exceeding traditional medium-entropy alloys. Simultaneously, the alloy can form a dense Cr2O3 oxide protective film in situ during friction, significantly improving wear resistance. Under loads of 15 N to 25 N, the wear rate is no higher than 8 × 10⁻⁶. -4 mm 3 / N·m.

[0022] 2. This invention employs an oxide-element composite raw material system, completely eliminating the need for expensive Cr2O3 and NiO raw materials, significantly reducing the amount of Al reducing agent used, and substantially lowering the overall cost of raw materials per batch. Simultaneously, the process is simplified, requiring only one type of oxide raw material, greatly reducing mixing difficulty, shortening ball milling time, and significantly improving production efficiency.

[0023] 3. This invention does not use toxic heavy metal oxides such as Cr2O3 and NiO, but only conventional Fe2O3 oxide, significantly reducing dust pollution and harmful emissions, thus meeting environmental protection requirements. The reaction process is stable and splash-free, with no risk of overheating or explosion, greatly reducing safety requirements and potential accidents during production.

[0024] 4. This invention employs a self-propagating high-temperature synthesis process, requiring only an externally supplied instantaneous ignition energy, eliminating the need for continuous high-temperature heating and significantly reducing production energy consumption. The self-exothermic reaction can rapidly raise the local temperature to 2000℃ to 3000℃, fully meeting the thermodynamic conditions required for alloying and uniform element solution, enabling the one-step synthesis of the target alloy. Attached Figure Description

[0025] Figure 1 For Fe 0.5 Cr 0.2 Ni x Al 0.3-x X-ray diffraction patterns of alloys (x=0.1, 0.15, 0.2); Figure 2 For Fe 0.5 Cr 0.2 Ni x Al 0.3-x Scanning electron microscopy characterization and EDS distribution of alloys (x=0.1, 0.15, 0.2); Figure 3 For Fe 0.5 Cr 0.2 Ni x Al 0.3-x Transmission electron microscopy morphology and corresponding EDS distribution of alloys (x=0.15, 0.2); Figure 4 For Fe 0.5 Cr 0.2 Ni x Al 0.3-x True stress-true strain curves for room temperature compression of alloys (x=0.1, 0.15, 0.2); Figure 5 For Fe 0.5 Cr 0.2 Ni x Al 0.3-x Vickers hardness charts for alloys with x = 0.1, 0.15, and 0.2; Figure 6 For Fe 0.5 Cr 0.2 Ni x Al 0.3-x Friction coefficient curves of alloys (x=0.1, 0.15, 0.2) under a 15N load; Figure 7 For Fe 0.5 Cr 0.2 Ni x Al 0.3-x Friction coefficient curves of alloys (x=0.1, 0.15, 0.2) under a 20N load; Figure 8For Fe 0.5 Cr 0.2 Ni x Al 0.3-x Friction coefficient curves of alloys (x=0.1, 0.15, 0.2) under a 25N load; Figure 9 Fe under a load of 25N 0.5 Cr 0.2 Ni x Al 0.3-x (x=0.1, 0.15, 0.2) Wear surface morphology and EDS analysis results of alloys; Figure 10 Fe under a load of 25N 0.5 Cr 0.2 Ni x Al 0.3-x 3D views of wear marks on alloys at x=0.1, 0.15, 0.2; Figure 11 For Fe 0.5 Cr 0.2 Ni x Al 0.3-x Wear rate diagram of alloys under different test forces (x=0.1, 0.15, 0.2). Detailed Implementation

[0026] The technical solution of the present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0027] The accompanying drawings are for illustrative purposes only and are schematic diagrams, not actual images. They should not be construed as limiting the scope of this application. To better illustrate the embodiments of the present invention, some parts in the drawings may be omitted, enlarged, or reduced, and do not represent the actual dimensions of the product. It is understandable to those skilled in the art that some well-known structures and their descriptions may be omitted in the drawings.

[0028] In the accompanying drawings of the embodiments of the present invention, the same or similar reference numerals correspond to the same or similar components. In the description of the present invention, it should be understood that if terms such as "upper," "lower," "left," "right," "inner," and "outer" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, they are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, the terms used to describe positional relationships in the drawings are only for illustrative purposes and should not be construed as limiting the present application. For those skilled in the art, the specific meaning of the above terms can be understood according to the specific circumstances.

[0029] In the description of this invention, unless otherwise explicitly specified and limited, the term "connection" or similar designation indicating a connection between components should be interpreted broadly. For example, it can refer to a fixed connection, a detachable connection, or an integral part; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium; it can refer to the internal communication between two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0030] The wear-resistant Fe-Cr-Ni-Al medium-entropy alloy provided by this invention has the general formula Fe 0.5 Cr 0.2 Ni x Al 0.3-x , where x ranges from 0.1 to 0.2. >1.5R is a high-entropy alloy. =(1-1.5R) is a medium-entropy alloy. <R represents a low-entropy alloy, and R is the gas constant; the entropy is calculated according to the configuration entropy formula. The calculation yielded Fe 0.5 Cr 0.2 Ni 0.2 Al 0.1 The configurational entropy is 1.22R, Fe 0.5 Cr 0.2 Ni 0.15 Al 0.15 The configurational entropy is 1.24R, Fe 0.5 Cr 0.2 Ni 0.1 Al 0.2 The configuration entropy is 1.22R, which is within the configuration entropy range of medium-entropy alloys.

[0031] like Figure 1 As shown, XRD (X-ray Diffraction) phase analysis results indicate that the prepared Fe... 0.5 Cr 0.2 Ni x Al 0.3-x The series of alloys consist of two phases: face-centered cubic with AlNi intermetallic compounds and body-centered cubic with AlNi intermetallic compounds. Their phase composition is significantly modulated by the molar ratio of Ni to Al. When the Al content is 0.1%, the corresponding alloy is Fe. 0.5 Cr 0.2 Ni 0.2 Al 0.1The material consists of a face-centered cubic FeCr solid solution and an AlNi phase. When the Al content is increased to 0.15 and 0.2%, the phases transform into a body-centered cubic FeCr solid solution and an AlNi phase. At 2θ values ​​of approximately 44.7°, 64.4°, and 81.7°, the diffraction peaks of AlNi and the body-centered cubic phase completely coincide, and all experimental diffraction peaks precisely match those on standard PDF cards 065-0431, 071-4649, and 065-7775.

[0032] like Figure 2 and Figure 3 As shown, all three alloy compositions exhibit a uniformly dispersed blocky phase in their microstructure. Combined with EDS (Energy Dispersive X-ray Spectroscopy) elemental analysis and XRD phase characterization data, it can be confirmed that this blocky phase is an AlNi intermetallic compound phase, distributed in a dispersed, embedded manner within the FeCr matrix. Using ImageJ software to estimate the volume fraction of each phase, the volume fraction of the uniformly dispersed AlNi phase in all three alloys exceeds 53%. Comparison of the microstructures of the three alloys reveals that Fe... 0.5 Cr 0.2 Ni 0.2 Al 0.1 The size of the AlNi phase is approximately 400 nm, exhibiting a cubic morphology. 0.5 Cr 0.2 Ni 0.15 Al 0.15 The AlNi phase in the alloy is approximately 700 nm in size and exhibits a rounded cubic morphology; Fe 0.5 Cr 0.2 Ni 0.1 Al 0.2 The AlNi phase in the alloy has a size of approximately 160 nm and exhibits a spherical morphology.

[0033] like Figure 4 As shown, the true stress-true strain curves under room temperature compression indicate that Fe 0.5 Cr 0.2 Ni 0.2 Al 0.1 The alloy exhibits the lowest 0.2% yield strength, with a measured value of approximately 283 MPa. This is primarily due to the alloy's phase composition: face-centered cubic (FCC) with AlNi phase. The FCC phase possesses superior plastic deformation capacity and is more prone to plastic deformation under compressive loads. In contrast, Fe... 0.5 Cr 0.2 Ni 0.15 Al 0.15 with Fe 0.5 Cr 0.2 Ni 0.1 Al0.2 The 0.2% yield strength of the alloys was significantly improved, reaching 781 MPa and 986 MPa, respectively. The main reason for the strength improvement is that both are body-centered cubic systems with a coexistence of AlNi phases. Compared with the face-centered cubic phase, the atomic arrangement of the body-centered cubic phase gives it a higher resistance to dislocation movement.

[0034] like Figure 5 As shown, the Vickers hardness test results indicate that when the molar ratio of Ni to Al is 1:2, the corresponding alloy is Fe. 0.5 Cr 0.2 Ni 0.1 Al 0.2 The Vickers hardness reaches its maximum value, approximately 420 HV; when the molar ratio of Ni to Al is 1:1, the corresponding alloy is Fe. 0.5 Cr 0.2 Ni 0.15 Al 0.15 The Vickers hardness is approximately 387 HV; when the molar ratio of Ni to Al is 2:1, the corresponding alloy is Fe. 0.5 Cr 0.2 Ni 0.2 Al 0.1 Its Vickers hardness is approximately 282 HV. This is mainly due to Fe. 0.5 Cr 0.2 Ni 0.1 Al 0.2 The fine spherical second phase in the alloy greatly hinders dislocation slip through strong dispersion strengthening.

[0035] like Figure 6-8 As shown, the friction coefficients of the three alloys exhibit different variation patterns under different loads. Under a load of 15 N, Fe... 0.5 Cr 0.2 Ni 0.2 Al 0.1 The coefficient of friction of the alloy initially increases, then decreases slightly after 550 s, and finally stabilizes at around 0.7; Fe 0.5 Cr 0.2 Ni 0.15 Al 0.15 The friction coefficient of the alloy fluctuates significantly; Fe 0.5 Cr 0.2 Ni 0.1 Al 0.2 The friction coefficient of the alloy fluctuates significantly before 900 s, then rises to around 0.61 between 900 and 1000 s and tends to stabilize. Under a load of 20 N, Fe... 0.5 Cr 0.2 Ni 0.2 Al 0.1 with Fe 0.5 Cr0.2 Ni 0.1 Al 0.2 The coefficient of friction of the alloy stabilized at around 0.72 after 300 s. 0.5 Cr 0.2 Ni 0.15 Al 0.15 The friction coefficients of the alloys still exhibit a sawtooth-like fluctuation. Under a load of 25 N, the friction coefficients of all three alloys decrease significantly, with Fe... 0.5 Cr 0.2 Ni 0.2 Al 0.1 with Fe 0.5 Cr 0.2 Ni 0.1 Al 0.2 The coefficient of friction of the alloy increases before 200 s, then stabilizes at around 0.43; Fe 0.5 Cr 0.2 Ni 0.15 Al 0.15 The alloy exhibited sawtooth-like fluctuations again after 1000 s.

[0036] like Figure 9 and Figure 10 As shown, the wear surface morphology and 3D view under a 25N load indicate that Fe 0.5 Cr 0.2 Ni 0.2 Al 0.1 The surface of the wear track is relatively smooth, with visible furrows parallel to the sliding direction. The wear debris is fine and evenly distributed, and the wear mechanism is mainly adhesive wear; Fe 0.5 Cr 0.2 Ni 0.15 Al 0.15 The surface contains a large amount of agglomerated wear debris, and the furrows are shallow, uniform, and regularly undulating, indicating more pronounced abrasive wear characteristics. 0.5 Cr 0.2 Ni 0.1 Al 0.2 The wear track morphology of the alloy is mainly continuous furrows, with clear layered spalling marks visible in some areas. The wear process is dominated by both spalling wear and abrasive wear. EDS surface distribution and energy dispersive spectroscopy analysis show that Fe, Cr, and O elements are enriched in the wear track area, confirming that oxidation reactions occurred during the wear process to generate Fe2O3 and Cr2O3.

[0037] like Figure 11 As shown, the wear rate test results under different loads indicate that as the applied load increases from 15N to 25N, Fe... 0.5 Cr 0.2 Ni 0.2 Al 0.1 The wear rate of the alloy is significantly reduced, from approximately 8 × 10⁻⁶.-4 mm 3 / N·m decreased to approximately 4.3×10 -4 mm 3 / N·m;Fe 0.5 Cr 0.2 Ni 0.1 Al 0.2 The wear of the alloy initially increases and then stabilizes, remaining at approximately 4 × 10⁻⁶ under both 20 N and 25 N loads. -4 mm 3 / N·m; while Fe 0.5 Cr 0.2 Ni 0.15 Al 0.15 The alloy consistently exhibits the lowest wear rate, and the change is gradual with increasing load, demonstrating optimal wear resistance.

[0038] Fe 0.5 Cr 0.2 Ni 0.15 Al 0.15 The optimal composition of this series of alloys is achieved through the synergistic effect of multiple factors, resulting in superior wear resistance. The high-volume-fraction AlNi second phase exhibits a rounded cubic morphology with an approximately continuous gradation, exhibiting tight bonding with the matrix, mutual support between particles, and appropriate phase spacing. Simultaneously, the dense Cr2O3-rich oxide film formed in situ during wear inhibits Fe oxidation, effectively resisting abrasive cutting and material spalling. Although the large particle size and relatively large phase spacing of this second phase limit the dispersion strengthening and fine-grain strengthening effects, leading to lower alloy hardness and yield strength, its smooth morphology significantly alleviates stress concentration. The continuous gradation constructs a stable load-bearing structure, and combined with the alloy's good toughness, it effectively inhibits crack initiation and brittle spalling, preventing cutting-type wear and ultimately achieving excellent tribological performance.

[0039] And Fe 0.5 Cr 0.2 Ni 0.2 Al 0.1 The second phase in the matrix has a cubic block morphology with distinct edges and corners, and its hardness is typically much higher than that of the matrix. During cyclic friction, its sharp edges act like micro-cutting blades, plowing the matrix surface and forming grooves. Simultaneously, the stress concentration effect at the edges is significant, and cyclic friction loads create high-stress regions at the interface between the second phase and the matrix, easily inducing microcrack initiation, which then propagates along the phase boundary or within the matrix, leading to increased wear rate.

[0040] Fe 0.5 Cr 0.2 Ni 0.1 Al 0.2The alloy's plastic deformation capacity is significantly reduced. Under the cyclic shear stress caused by frictional contact, its surface is unable to dissipate energy through plastic deformation, making it highly susceptible to microcrack initiation. Once formed, these cracks propagate rapidly and interconnect, leading to material failure in the form of brittle spalling and blocky detachment, resulting in a substantial increase in wear. Although the spherical second phase can alleviate stress concentration, its limited interfacial bonding area with the matrix means that fine particles are easily pulled out or peeled off from the matrix under the alternating stress of reciprocating friction. These detached hard particles form three-body abrasive grains between the friction pairs, cutting and plowing the matrix, triggering a self-wearing effect, and further increasing the material's wear rate. In addition, these high-hardness, low-plasticity materials are highly sensitive to micro-defects, scratches, and localized stress concentrations. Even minor contact unevenness during friction can trigger localized stress overload, promoting the initiation and propagation of microcracks. The material itself lacks sufficient plasticity to passivate these cracks, ultimately exhibiting a hard but not wear-resistant frictional wear characteristic.

[0041] Performance testing conditions: 1. Vickers hardness test: A Vickers hardness tester was used with a load of 1 kg and a holding time of 15 s. Five points were tested on each sample and the average value was taken.

[0042] 2. Room temperature compression test: A universal testing machine was used, the sample size was 3mm×6mm, and the loading rate was 0.5mm / min.

[0043] 3. Friction and wear test: A ball-disc friction and wear tester was used. The friction pair consisted of GCr15 steel balls with a diameter of 6 mm. The sliding speed was 0.2 m / s, the sliding stroke was 5 mm, and the test time was 1800 s.

[0044] Example 1 Preparation of Fe 0.5 Cr 0.2 Ni 0.2 Al 0.1 Alloying, the specific steps are as follows: 1. Raw material preparation: according to the reaction equation The following measurements were taken: 798.50g of Fe2O3 powder with a purity of 99.9%, 323.76g of Al powder, 208.00g of Cr powder, and 234.76g of Ni powder were weighed.

[0045] 2. Mixing Process: Divide the weighed raw material into 6 equal portions and place each portion in a ball mill jar. Use alumina grinding balls with a ball-to-material ratio of 1:2. The ball milling process follows a cycle of 1 hour forward rotation, 1 hour reverse rotation, 2 minutes settling, and stirring, at a speed of 170 rpm. Complete 3 cycles, for a total milling time of approximately 6 hours. After milling, separate the ball particles using a 150-mesh sieve to obtain a uniformly mixed powder.

[0046] 3. Press molding: The mixed powder is pressed into a blank using a 50mm diameter mold, and a pressure of 55MPa is applied and held for 3 minutes to prepare the blank.

[0047] 4. Self-propagating reaction: The pressed preform is placed in a 35mm thick copper crucible, and 2g of igniter is placed on the preform. The crucible is then placed into a high-temperature, high-pressure reactor. Argon gas at 4.5MPa is introduced into the reactor as a protective atmosphere, and a self-propagating high-temperature synthesis reaction is initiated by instantaneous ignition. The highest temperature during the reaction is approximately 2430℃, and the highest pressure is approximately 8.5MPa. After the reaction is complete, the mixture is allowed to cool naturally to room temperature to obtain the reaction product.

[0048] 5. Separation and purification: The reaction product is coarsely crushed to a particle size of less than 5 mm using a jaw crusher, then finely ground to below 200 mesh using a planetary ball mill. Magnetic separation is then performed using a magnetic separator with a magnetic field strength of 1500 Gs. The collected magnetic product is pure Fe. 0.5 Cr 0.2 Ni 0.2 Al 0.1 alloy.

[0049] The alloy was tested and found to have a Vickers hardness of 282 HV, a 0.2% conditional yield strength of 283 MPa, and a wear rate of approximately 4.3 × 10⁻⁶ MPa under a 25 N load. -4 mm 3 / N·m.

[0050] Example 2 Preparation of Fe 0.5 Cr 0.2 Ni 0.15 Al 0.15 Alloying, the specific steps are as follows: 1. Raw material preparation: according to the reaction equation The following quantities were weighed according to the measurement ratio: 800.00g of Fe2O3 powder with a purity of 99.9%, 351.00g of Al powder, 208.00g of Cr powder, and 177.00g of Ni powder.

[0051] 2. Mixing process: Same as in Example 1.

[0052] 3. Compression molding: Same as in Example 1.

[0053] 4. Self-propagating reaction: The pressed preform is placed in a 35mm thick copper crucible, and 2g of igniter is placed on the preform. The crucible is then placed into a high-temperature, high-pressure reactor. Argon gas at 4.5MPa is introduced into the reactor as a protective atmosphere, and a self-propagating high-temperature synthesis reaction is initiated by instantaneous ignition. The highest temperature during the reaction is approximately 2830℃, and the highest pressure is approximately 9.3MPa. After the reaction is complete, the mixture is allowed to cool naturally to room temperature to obtain the reaction product.

[0054] 5. Separation and purification: Same as in Example 1.

[0055] Tests showed that the alloy has a Vickers hardness of 387 HV, a 0.2% conditional yield strength of 781 MPa, and a wear rate of less than 1 × 10⁻⁶ MPa under loads ranging from 15 N to 25 N. -4 mm 3 / N·m, with the best wear resistance.

[0056] Example 3 Preparation of Fe 0.5 Cr 0.2 Ni 0.1 Al 0.2 Alloying, the specific steps are as follows: 1. Raw material preparation: according to the reaction equation The following measurements were taken: 798.45g of Fe2O3 powder with a purity of 99.9%, 377.72g of Al powder, 208.00g of Cr powder, and 117.38g of Ni powder were weighed.

[0057] 2. Mixing process: Same as in Example 1.

[0058] 3. Compression molding: Same as in Example 1.

[0059] 4. Self-propagating reaction: The pressed green body is placed in a 35mm thick copper crucible, and 2g of igniter is placed on the green body. The crucible is then placed into a high-temperature, high-pressure reactor. Argon gas at 4.5MPa is introduced into the reactor as a protective atmosphere, and a self-propagating high-temperature synthesis reaction is initiated by instantaneous ignition. The highest temperature during the reaction is approximately 2950℃, and the highest pressure is approximately 9.5MPa. After the reaction is complete, the mixture is allowed to cool naturally to room temperature to obtain the reaction product.

[0060] 5. Separation and purification: Same as in Example 1.

[0061] Tests showed that the alloy has a Vickers hardness of 420 HV, a 0.2% conditional yield strength of 986 MPa, and a wear rate of approximately 4 × 10⁻⁶ MPa under loads of 20 N and 25 N. -4 mm 3 / N·m.

[0062] Table 1 Comparison of Raw Material Costs with Existing Technologies (Based on the Preparation of 20 mol of the Target Alloy)

[0063] Table 2 Comparison of Energy Consumption in Production with Existing Technologies

[0064] In summary, the working principle of this invention is detailed as follows: The working principle of this invention combines precise control of composition, structure, and performance with an innovative design of a self-propagating high-temperature synthesis process to solve common industry problems such as poor wear resistance, high energy consumption, high cost, and significant environmental risks associated with traditional medium-entropy alloys. The overall working principle can be divided into two parts: alloy composition design and performance control principle, and self-propagating high-temperature synthesis preparation principle. These two parts work synergistically and are indispensable.

[0065] I. Principles of Alloy Composition Design and Performance Control (I) Entropy Stabilization Principle of Medium-Entropy Alloy Configuration This invention achieves a stable configurational entropy of the alloy between 1.22R and 1.24R by precisely controlling the molar ratio of Fe, Cr, Ni, and Al, placing it within the category of standard medium-entropy alloys. The unique high mixing entropy effect of medium-entropy alloys significantly reduces the Gibbs free energy of the system, suppressing excessive precipitation and phase separation of intermetallic compounds. This allows the alloy to maintain a stable two-phase structure at high temperatures and during service, avoiding performance fluctuations caused by aging precipitation or microstructure evolution in traditional alloys. Simultaneously, the uniform solid solution of multiple principal elements generates a lattice distortion effect, providing a basis for solid solution strengthening of the alloy.

[0066] (II) The principle of Ni / Al molar ratio regulating phase structure transformation The phase composition and microstructure of the alloy are entirely determined by the molar ratio of Ni to Al. The atomic radius of Al atoms is significantly larger than that of Fe, Cr, and Ni atoms. As the Al content increases, the lattice distortion energy of the alloy continuously increases, and the stability of the face-centered cubic structure gradually decreases. When the Al content reaches 0.15% or higher, the system undergoes a structural transformation from face-centered cubic to body-centered cubic. The face-centered cubic matrix exhibits excellent plastic deformation capacity, while the body-centered cubic matrix possesses higher strength and hardness. By adjusting the Ni / Al molar ratio, the alloy can be continuously controlled from high plasticity to high strength to meet the performance requirements of different working conditions.

[0067] (III) Synergistic Principle of High Volume Fraction AlNi Phase Dispersion Strengthening and Wear Resistance Regardless of changes in the matrix structure, the alloy always maintains a uniformly dispersed AlNi intermetallic compound phase with a volume fraction of not less than 53%. The AlNi phase itself possesses extremely high hardness and strength, effectively hindering dislocation slip and movement, resulting in a significant dispersion strengthening effect, and greatly improving the overall hardness and yield strength of the alloy.

[0068] Meanwhile, the morphology and size of the AlNi phase directly determine the wear resistance of the alloy: The cubic AlNi phase has sharp edges and corners, which can generate micro-cutting action during friction. At the same time, stress concentration can easily occur at the edges and corners, inducing cracks and leading to increased wear rate. Although the spherical AlNi phase can alleviate stress concentration, its bonding area with the matrix is ​​limited, making it easy to be pulled out and form three-body abrasive grains, which can lead to self-wearing effects. The rounded cubic AlNi phase combines high load-bearing capacity with low stress concentration. The interparticles support each other to form a stable load-bearing structure. Combined with the alloy's good toughness, it can effectively suppress crack initiation and brittle spalling, achieving optimal wear resistance.

[0069] (iv) The principle of friction reduction and wear resistance of in-situ Cr element oxide protective film During friction and wear, the constant chromium content in the alloy reacts with oxygen in the air to form a dense and thermochemically stable oxide film in situ on the wear surface. This oxide film effectively isolates the friction pair from the alloy matrix, inhibits further oxidation of Fe, reduces the coefficient of friction, alleviates abrasive and adhesive wear, and further improves the alloy's wear resistance and service life.

[0070] II. Principle of Self-propagating High-Temperature Synthesis (I) Reaction principle of oxide-element composite raw material system This invention creatively employs a composite raw material system using Fe2O3 as the sole oxide raw material, combined with Cr, Ni elemental powders, and Al powder. The Al powder simultaneously serves as a reducing agent in the aluminothermic reaction and a source of Al element for alloying. A vigorous aluminothermic reaction occurs between Fe2O3 and Al, releasing a large amount of heat sufficient to rapidly raise the local temperature of the reaction system to 2000°C to 3000°C, fully meeting the thermodynamic conditions required for the melting, diffusion, and alloying of each element.

[0071] Compared with traditional all-oxide raw material systems, this system completely eliminates the high-priced and toxic Cr2O3 and NiO, which not only significantly reduces the cost of raw materials and the amount of Al reducing agent, but also reduces the heat release of multiple reduction reactions, making the entire reaction process more stable and controllable, avoiding the risk of reaction splashing and explosion, and eliminating heavy metal dust pollution at the source.

[0072] (ii) The principle of self-propagating reaction and self-sustaining propagation The self-propagating high-temperature synthesis reaction relies on the heat released by the reaction itself to sustain the reaction, without the need for continuous external heating. When the billet is instantaneously ignited, aluminothermic reaction occurs first in a local area, releasing heat. This heat is rapidly transferred to adjacent unreacted raw materials, causing them to reach the reaction temperature and react. This forms a continuous reaction wave that propagates rapidly from the ignition end to the other end of the billet until the entire billet is completely reacted.

[0073] To ensure the stable propagation of the reaction wave, this invention optimizes the ball milling mixing process and pressing parameters to achieve uniform mixing of raw material powders and a suitable green body density. Uniform raw material mixing ensures the uniformity of the reaction, avoiding localized component segregation and incomplete reaction; suitable green body density ensures effective heat transfer and provides sufficient escape channels for reactant gases, preventing cracking of the green body during the reaction.

[0074] (III) Principle of Inert Atmosphere Protection and Product Control The reaction is carried out under a high-pressure argon protective atmosphere. Argon, as an inert gas, effectively prevents the alloying elements from reacting with oxygen, nitrogen, etc., at high temperatures, ensuring the accuracy and purity of the alloy composition. Simultaneously, the high-pressure argon atmosphere suppresses the volatilization of reaction products, improving the alloy yield. The Al2O3 byproduct generated during the reaction exhibits a significant magnetic difference from the target alloy. Subsequent crushing, grinding, and magnetic separation processes efficiently remove the non-magnetic Al2O3 phase, yielding a high-purity Fe-Cr-Ni-Al medium-entropy alloy product.

[0075] III. The Synergistic Effect of Component Design and Preparation Process The composition design and preparation process of this invention are a highly matched and synergistic whole. The rapid cooling characteristics of self-propagating high-temperature synthesis are conducive to the formation of fine and uniform AlNi phase, avoiding the grain coarsening and second-phase segregation problems caused by slow cooling in traditional smelting processes. Furthermore, the composition design of this invention fully utilizes the thermodynamic characteristics of the self-propagating reaction. By controlling the Ni / Al molar ratio, the heat release of the reaction is kept within an appropriate range, ensuring that the reaction can proceed sustainably while avoiding grain growth and performance degradation caused by excessively high reaction temperatures.

[0076] The synergistic effect of the two ultimately achieves a synergistic improvement in the alloy's strength, toughness, and wear resistance, while significantly reducing preparation costs and energy consumption, improving production efficiency and environmental safety, thus giving the technical solution of this invention significant industrial application value.

[0077] The above are merely preferred embodiments of the present invention and are not intended to limit the implementation methods and protection scope of the present invention. Those skilled in the art should recognize that any equivalent substitutions and obvious changes made based on the description and illustrations of the present invention should be included within the protection scope of the present invention.

Claims

1. A wear-resistant Fe-Cr-Ni-Al medium-entropy alloy, characterized in that, Prepared using a self-propagating high-temperature synthesis process, the alloy has the general formula Fe. 0.5 Cr 0.2 Ni x Al 0.3-x The value of x ranges from 0.1 to 0.2, and the configuration entropy is from 1.22R to 1.24R, which belongs to the medium entropy alloy. The alloy is composed of a matrix phase and an AlNi intermetallic compound phase uniformly dispersed in the matrix, and the volume fraction of the AlNi intermetallic compound phase is not less than 53%. The size range of the AlNi intermetallic compound phase is 160 nm to 700 nm; when x is 0.2, the AlNi phase has a cubic morphology; when x is 0.15, the AlNi phase has a rounded cubic morphology; and when x is 0.1, the AlNi phase has a spherical morphology.

2. The wear-resistant Fe-Cr-Ni-Al medium-entropy alloy according to claim 1, characterized in that, When x is 0.2, the alloy matrix phase is a face-centered cubic FeCr solid solution; when x is between 0.1 and 0.15, the alloy matrix phase is a body-centered cubic FeCr solid solution.

3. The wear-resistant Fe-Cr-Ni-Al medium-entropy alloy according to claim 1, characterized in that, The alloy has a Vickers hardness of 282 HV to 420 HV and a 0.2% conditional yield strength of 283 MPa to 986 MPa.

4. A method for preparing a wear-resistant Fe-Cr-Ni-Al medium-entropy alloy as described in any one of claims 1 to 3, characterized in that, The process employs a self-propagating high-temperature synthesis technique, including the following steps: Step 1, Raw Material Preparation: An oxide-element composite raw material system is adopted, using Fe2O3 powder as the sole oxide raw material, combined with Al, Cr, and Ni elemental powders, according to the alloy general formula Fe... 0.5 Cr 0.2 Ni x Al 0.3-x Weigh each raw material according to the stoichiometric ratio of the chemical reaction; Step 2, Mixing: The weighed raw materials are ball-milled and mixed to obtain a uniform powder; Step 3, pressing and molding: Press the mixed powder into a blank to obtain a green body; Step 4, self-propagating reaction: The billet is placed under a protective atmosphere, and a self-propagating high-temperature synthesis reaction is initiated by instantaneous ignition. The alloy synthesis is completed by relying on the self-exothermic reaction to obtain the reaction product. Step 5, separation and purification: The reaction products are crushed, ground and magnetically separated to remove Al2O3 byproducts and obtain the target alloy.

5. The method for preparing the wear-resistant Fe-Cr-Ni-Al medium-entropy alloy according to claim 4, characterized in that, In step one, the purity of Fe2O3, Al, Cr, and Ni powders is not less than 99.9%; Al powder serves as both a reducing agent for the aluminothermic reaction and a source of Al element in the alloy.

6. The method for preparing the wear-resistant Fe-Cr-Ni-Al medium-entropy alloy according to claim 4, characterized in that, In step two, alumina grinding balls are used for ball milling, with a ball-to-material ratio of 1:1.5 to 1:2.

5. The ball milling process is a cycle mode of forward rotation for 1 hour, reverse rotation for 1 hour, standing for 1 minute to 3 minutes, and stirring. The rotation speed is 150 r / min to 190 r / min, and the total ball milling time is 5 hours to 7 hours. After ball milling, a 100-mesh to 200-mesh sieve is used for ball-to-material separation.

7. The method for preparing the wear-resistant Fe-Cr-Ni-Al medium-entropy alloy according to claim 4, characterized in that, In step four, the protective atmosphere is argon, and the argon pressure is 4 MPa to 5 MPa; the ignition method is any one of electric arc ignition, laser ignition, or ignition by an igniter; the maximum temperature during the reaction is 2000℃ to 3000℃, and the maximum gas pressure is 8 MPa to 10 MPa.

8. The method for preparing the wear-resistant Fe-Cr-Ni-Al medium-entropy alloy according to claim 4, characterized in that, In step four, the billet is placed in a copper crucible with a thickness of 30mm to 40mm, and 1g to 3g of igniter is placed on the billet. Then it is sent into a high-temperature and high-pressure reactor for a self-propagating reaction.

9. The method for preparing the wear-resistant Fe-Cr-Ni-Al medium-entropy alloy according to claim 4, characterized in that, When preparing Fe 0.5 Cr 0.2 Ni 0.2 Al 0.1 When alloying, the reaction equation is: ； When preparing Fe 0.5 Cr 0.2 Ni 0.15 Al 0.15 When alloying, the reaction equation is: ； When preparing Fe 0.5 Cr 0.2 Ni 0.1 Al 0.2 When alloying, the reaction equation is: 。

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