Soft magnetic high-entropy alloy with high strength, high plasticity and low coercive force and preparation method thereof

Abstract

The invention discloses a high-strength, high-plasticity and low-coercive-force soft magnetic high-entropy alloy and a preparation method thereof. The component expression of the soft magnetic high-entropy alloy is FeaCobNicVdMe according to the atomic ratio, M is one or more than two of solid solution strengthening elements Mn, B, Si, Cr, Mo and W, a is larger than or equal to 41 and smaller than or equal to 62, b is larger than or equal to 25 and smaller than or equal to 30, c is larger than or equal to 13 and smaller than or equal to 21, d is larger than or equal to 0 and smaller than or equal to 3, e is larger than or equal to 0 and smaller than or equal to 5, and a + b + c + d + e = 100. The production process is simple, the mother alloy is firstly prepared into a cast plate through induction / electric arc melting and copper mold casting, and the plate-shaped soft magnetic high-entropy alloy is prepared through high-temperature long-time vacuum heat treatment, multi-pass cold rolling, high-temperature short-time recrystallization heat treatment and air cooling.

Description

Technical Field

[0001] This invention relates to the field of soft magnetic high-entropy alloys, specifically to a high-strength, high-plasticity, low-coercivity soft magnetic high-entropy alloy and its preparation method. Background Technology

[0002] Emerging high-entropy alloys are multi-principal-element solid solution materials that have achieved significant improvements in strength and ductility in numerous reports due to their unique composition and microstructure. However, the strengthening of high-entropy alloys is usually based on the introduction of high-density crystal defects, such as dislocations, grain boundaries, and second phases, all of which pin the movement of magnetic domain walls, resulting in the coercivity of most current high-entropy alloys exceeding 500 A / m, significantly higher than that of common soft magnetic materials. Introducing coherent nanoparticles can improve strength without significantly impairing the alloy's ductility. If the particle size is controlled below the critical size and the specific surface area of ​​the particles is adjusted to reduce internal stress, the pinning resistance of the particles to the magnetic domain walls can be significantly reduced, resulting in soft magnetic high-entropy alloys with low coercivity and high mechanical strength at room temperature. Furthermore, through composition optimization and appropriate heat treatment, nanophases with good thermal stability, such as acicular Widmanstätten structures, can be precipitated, yielding high-entropy alloys that possess both high-temperature mechanical properties and high-temperature soft magnetic properties. Considering the multi-principal-element characteristics of high-entropy alloys, which contain multiple magnetic and non-magnetic elements, the magnetic properties can be controlled within a wide range. Therefore, high-entropy alloys are expected to overcome the performance bottleneck of soft magnetic alloys, which are difficult to obtain high strength and high plasticity, and provide a new platform for the development of new soft magnetic alloys.

[0003] The patent specification with publication number CN116083772A discloses a soft magnetic high-entropy alloy with high-temperature resistance of 900K, including elements such as Fe, Co, Ni, Si, and Al. The atomic percentage of its alloy composition is expressed as Fe. x Co y Ni z Si m Al n The composition is as follows: x = 40%~80%, y = 20%~60%, z = 0~30%, m = 0~20%, n = 0~20%, x+y+z+m+n = 100%; the atomic percentage of other doping elements is p = 0~5%, 0.5≤m / n≤3; the material performance indicators are: room temperature saturation magnetization Ms = 90~150 emu / g, coercivity Hc = 0.1~15 Oe; saturation magnetization Ms = 70~130 emu / g at 900K, coercivity Hc = 0.1~25 Oe.

[0004] The patent specification with publication number CN120082787A discloses a precipitation-strengthened soft magnetic high-entropy alloy with the following elemental composition: Fe: 28 at.%~31 at.%, Co: 28 at.%~31 at.%, Ni: 28 at.%~31 at.%, Ti: 2 at.%~8 at.%, Al: 6 at.%~8 at.%, with the sum of the atomic percentages of each element being 100%. This high-entropy alloy has an L12-type precipitate phase and an FCC matrix. Through composition optimization and heat treatment control, the alloy achieves a certain grain size while controlling the precipitate phase to be within 7~12 nm. It exhibits a yield strength of 618~1089 MPa, a tensile strength of 1068~1569 MPa, an elongation of 17%~31%, a saturation magnetization of 88~120 emu / g, and a coercivity of 1~12 Oe.

[0005] Existing technologies require high nickel (Ni > 25 at.%) composition design to form nano-coherent strengthening phases, which leads to insufficient Fe and Co content, resulting in low saturation magnetization of the alloy. M s The Ni content is too low (less than 1.2 T), making it difficult to meet high power requirements. Simply reducing the Ni content to increase... M s This can induce a harmful metastable phase transition from FCC to BCC, forming a high-density phase interface, which in turn pins the magnetic domain walls, leading to coercivity. H c The deterioration of the structure makes it difficult to achieve both high strength and excellent soft magnetic properties.

[0006] Currently widely used non-oriented silicon steels (such as the 35JN series) have insufficient tensile strength (<410 MPa), making it difficult to meet the strength requirements of high-speed motors. While increasing the Si content can improve strength, it leads to a sharp deterioration in plasticity and cold-rolling workability due to the precipitation of ordered phases. Rapid quenching can improve workability to a limited extent, but it cannot solve the problem of thermal stability of ordered phases during long-term service at medium and high temperatures. Other soft magnetic systems, such as iron-cobalt alloys, have inherent brittleness that is difficult to suppress, while amorphous alloys suffer from poor plasticity and low crystallization temperatures. Extensive research has been conducted on the composition and preparation process design of these soft magnetic materials based on traditional single-principal-element alloy frameworks, but the potential for performance improvement is limited. Therefore, there is an urgent need to develop a new type of alloy material that combines high strength, high plasticity, and excellent soft magnetic properties. Summary of the Invention

[0007] To address the aforementioned technical problems and shortcomings in the field, this invention provides a high-strength, high-plasticity, low-coercivity soft magnetic high-entropy alloy and its preparation method, which can overcome the performance defects of existing soft magnetic materials that cannot simultaneously achieve both mechanical and soft magnetic properties.

[0008] This invention provides a novel Fe-Co-Ni multi-principal-element soft magnetic alloy and its preparation method. Through composition design and thermomechanical process optimization (controlling the relaxation evolution path of the microstructure), while reducing the Ni content to increase the saturation magnetization, the variant selection of the metastable phase transformation process (driven by the structural energy state) is effectively controlled, and the formation of large-angle interfaces is suppressed, thereby obtaining low coercivity and ultimately achieving a synergistic improvement in the mechanical properties and soft magnetic properties of the alloy.

[0009] The specific technical solution is as follows: In a first aspect, the present invention provides a high-strength, high-plasticity, low-coercivity soft magnetic high-entropy alloy, with a composition expression of Fe in atomic ratio. a Co b Ni c V d M e M is one or more of the solid solution strengthening elements Mn, B, Si, Cr, Mo, and W, 41≤a≤62, 25≤b≤30, 13≤c≤21, 0≤d≤3, 0≤e≤5, and a+b+c+d+e=100.

[0010] Preferably, in the composition expression of the high-strength, high-plasticity, low-coercivity soft magnetic high-entropy alloy, 43≤a≤49, for example, a=43, 45, or 49, etc.

[0011] Preferably, in the composition expression of the high-strength, high-ductility, low-coercivity soft magnetic high-entropy alloy, 13 ≤ c ≤ 19, for example, c = 13, 17, or 19, etc.

[0012] Preferably, in the high-strength, high-plasticity, low-coercivity soft magnetic high-entropy alloy, the composition expression contains 0... <d≤3。

[0013] Preferably, in the high-strength, high-plasticity, low-coercivity soft magnetic high-entropy alloy, the composition expression contains 0... <e≤5。

[0014] In some preferred embodiments, the high-strength, high-ductility, low-coercivity soft magnetic high-entropy alloy has a composition expression of Fe in atomic ratio. 43 Co 30 Ni 19 V3Mn5, Fe 45 Co 30 Ni 17 V3Mn5 or Fe 49 Co 30 Ni 13 V3Mn5, further preferably Fe 45 Co 30 Ni 17V3Mn5 is a two-phase structure of FCC and BCC, and its metallographic structure shows a two-phase morphology of FCC matrix and BCC laths.

[0015] In some preferred embodiments, the high-strength, high-plasticity, low-coercivity soft magnetic high-entropy alloy is a sheet material.

[0016] In a second aspect, the present invention provides a method for preparing the high-strength, high-ductility, low-coercivity soft magnetic high-entropy alloy described in the first aspect, comprising the steps of: S1: Prepare raw materials of pure Fe, pure Co, pure Ni, and optional pure V and pure M according to the composition formula; S2: In step S1, the raw materials are placed in an induction melting furnace, a vacuum is drawn, and the alloy is melted under an argon atmosphere. Each alloy ingot is repeatedly melted multiple times and cast into a copper mold to form a uniform master alloy casting plate. S3: Perform a long-term high-temperature vacuum homogenization heat treatment at 1200℃ on the cast plate in step S2 to eliminate component segregation during casting and obtain a homogenized alloy plate with stable phase structure. S4: For the multi-pass cold rolling of the homogenized alloy sheet in step S3, the final rolling ratio must reach more than 85% to obtain a cold-rolled sheet with a thickness of no more than 0.8 mm. S5: The cold-rolled sheet from step S4 is subjected to a short-time vacuum recrystallization heat treatment at 1200℃ to form a recrystallized sheet with uniform grain size distribution. The sheet is then cooled at room temperature to complete the spontaneous metastable phase transformation process within the alloy, resulting in the high-strength, high-plasticity, low-coercivity soft magnetic high-entropy alloy.

[0017] Preferably, in step S3, the vacuum degree is 3.0 × 10⁻⁶. -4 Pa.

[0018] Preferably, in step S3, the high-temperature vacuum long-term homogenization heat treatment time is 18 h.

[0019] Preferably, in step S5, the high-temperature short-time vacuum recrystallization heat treatment time is 0.5 h.

[0020] This invention provides a soft magnetic high-entropy alloy sheet with low coercivity, low loss, and strong toughness. The production process is simple. The master alloy is first prepared into a cast plate by induction / arc melting and copper mold casting. The plate is then prepared by high-temperature long-term vacuum heat treatment, multi-pass cold rolling, high-temperature short-time recrystallization heat treatment and air cooling.

[0021] The cast plates of this invention are prepared by melting and casting, allowing for easy control of the content of each component. The content of impurity elements such as O, S, and P is low, resulting in good compositional uniformity and improving the stability of industrial production batches. The components of this invention exhibit excellent cold-rolling performance, maintaining edge-free operation at room temperature and a rolling ratio of over 85%, eliminating the need for intermediate stress-relieving tempering and significantly simplifying the production process while saving production costs. After high-temperature, short-time recrystallization heat treatment, the resulting plates achieve strength and toughness surpassing other existing soft magnetic high-entropy alloys, extremely low coercivity, and excellent practicality for production.

[0022] The atomic percentages of Fe and Co are related to the saturation magnetization. Alloy compositions with high Fe and Co content contribute to achieving high saturation magnetization. In the soft magnetic high-entropy alloy, the atomic percentages of Fe and Co are 41 ≤ a ≤ 62 and 25 ≤ b ≤ 30. By controlling the Fe and Co content, the saturation magnetization of the alloy can be increased, resulting in excellent soft magnetic properties.

[0023] The atomic percentage of Ni is related to the phase structure stability of the alloy. Within the aforementioned range of Fe and Co atomic percentages, the Ni content has a decisive influence on the formation of single-phase FCC, single-phase BCC, or two-phase structures. Single-phase FCC structures exhibit low strength, high plasticity, low coercivity, and low saturation magnetization, while single-phase BCC structures exhibit high strength, low plasticity, high coercivity, and high saturation magnetization. The two phase structures show an inverse relationship in terms of performance parameters. Therefore, controlling the Ni content can ensure that the target alloy recrystallizes in a metastable state between the single-phase FCC and single-phase BCC phase regions, achieving a balance of properties between the two structures: high strength-toughness synergy, low coercivity, and high saturation magnetization.

[0024] The addition of V not only increases the resistivity of the alloy (helping to reduce eddy current losses), enhances the stability of the BCC phase, and contributes a significant solid solution strengthening effect, but its key role lies in significantly increasing the critical temperature for the precipitation of ordered phases (such as the B2 phase) from Fe-Co based solid solutions. This effect significantly broadens the temperature window for the alloy system's heat treatment process, effectively preventing the precipitation of brittle ordered phases, thereby preventing their deterioration on the alloy's toughness and soft magnetic properties (such as coercivity).

[0025] By microalloying small amounts of one or more of the solid solution strengthening elements Mn, B, Si, Cr, Mo, and W, a high-entropy alloy composition system of five elements or more is formed. Utilizing the high-entropy effect to broaden the marginal solubility range of disordered solid solutions, the solid solution concentration of these elements is increased. Under the condition of avoiding phase separation, a significant solid solution strengthening effect is obtained. Simultaneously, the significant lattice distortion is beneficial to improving the resistivity of the alloy and mitigating eddy current losses. Attached Figure Description

[0026] Figure 1 X-ray diffraction patterns (a) of the soft magnetic high-entropy alloys in Examples 1-3 and metallographic photograph (b) of Example 1 are shown.

[0027] Figure 2 The figures show the quasi-static room temperature tensile stress-strain curves of the soft magnetic high-entropy alloys in Examples 1-3.

[0028] Figure 3 The figures show the magnetometer curves of the vibrating sample of the soft magnetic high-entropy alloys in Examples 1-3. In the figures: (a) the hysteresis loop measured by the vibrating sample magnetometer (VSM) reflects the saturation magnetization of each alloy; (b) a magnified view of the hysteresis loop measured by the static hysteresis loop tester reflects the coercivity level of each alloy.

[0029] Figure 4 The figures show a performance comparison between the soft magnetic high-entropy alloys in Examples 1-3 and other soft magnetic component systems. In the figures: (a) comparison of saturation magnetization vs. coercivity, and (b) comparison of strength and toughness vs. coercivity. Detailed Implementation

[0030] The present invention will be further described below with reference to the accompanying drawings and specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Operating methods not specifically specified in the following embodiments are generally performed under conventional conditions or as recommended by the manufacturer.

[0031] Example 1: In this embodiment, the atomic ratio composition of the alloy is expressed as: Fe 45 Co 30 Ni 17 The preparation and heat treatment methods and steps of V3Mn5 soft magnetic high-entropy alloy are as follows: S1: Pure Fe, pure Co, pure Ni, pure V and pure Mn are used. Each element is weighed according to the atomic ratio composition expression to prepare the raw materials. The purity of the raw materials is above 99.9 wt.%.

[0032] S2: The raw materials from step S1 are placed in an induction melting furnace, and a vacuum is drawn to a value less than 1.0 × 10⁻⁶. -3 Pa, then melt the alloy in an argon atmosphere with a purity of 99.99%, each alloy ingot is repeatedly melted 5 times, and then cast into a copper mold to form a uniform master alloy casting plate.

[0033] S3: Vacuum seal the cast plate from step S2 (vacuum degree 3.0 × 10⁻⁶). -4The homogenization heat treatment, which involves holding the alloy at 1200℃ for 18 hours (Pa), eliminates compositional segregation during casting, resulting in a homogenized alloy plate with a stable phase structure. The plate is then air-cooled to room temperature.

[0034] S4: For the multi-pass cold rolling of the homogenized alloy sheet in step S3, the final rolling ratio needs to reach more than 85% to obtain a cold-rolled sheet with a thickness of 0.6 mm.

[0035] S5: The cold-rolled sheet from step S4 is subjected to high-temperature short-time vacuum recrystallization heat treatment (held at 1200℃ for 0.5h) to form a recrystallized sheet with uniform grain size distribution. The sheet is then cooled at room temperature to complete the spontaneous metastable phase transformation process inside the alloy, resulting in a soft magnetic high-entropy alloy sheet with high strength, high plasticity, and low coercivity.

[0036] Example 2: In this embodiment, the atomic ratio composition of the alloy is expressed as: Fe 43 Co 30 Ni 19 The preparation and heat treatment methods and steps of V3Mn5 alloy are the same as steps S1-S5 in Example 1.

[0037] Example 3: In this embodiment, the atomic ratio composition of the alloy is expressed as: Fe 49 Co 30 Ni 13 The preparation and heat treatment methods and steps of V3Mn5 alloy are the same as steps S1-S5 in Example 1.

[0038] The soft magnetic high-entropy alloys in Examples 1-3 were subjected to the following tests: The soft magnetic high-entropy alloy sheet obtained in step S5 was subjected to electrical discharge cutting, followed by stepwise sanding and polishing. X-ray diffraction (XRD) was used to analyze the microstructure of the sample surface; the XRD pattern is shown below. Figure 1 As shown in (a), Example 1 is a biphase structure of FCC and BCC, while Examples 2 and 3 are single-phase face-centered cubic (FCC) and single-phase body-centered cubic (BCC) structures, respectively. Figure 1 As shown in (b), after etching with an etchant, the metallographic structure of Example 1 exhibits a dual-phase morphology of FCC matrix and BCC laths.

[0039] The mechanical properties of the soft magnetic high-entropy alloy prepared in step S5 were analyzed using a universal testing machine. The stress-strain curves obtained are shown below. Figure 2 As shown.

[0040] The magnetic properties of the soft magnetic high-entropy alloy after heat treatment in step S5 were analyzed using a vibrating sample magnetometer (VSM) and a static hysteresis loop apparatus, respectively. The obtained hysteresis loops are shown below. Figure 3 As shown. By Figure 3 (a) The VSM images show that Examples 1-3 exhibit typical ferromagnetic properties. Figure 3 (b) The curves show that Examples 1 and 2 have good soft magnetic properties, while Example 3 has poor soft magnetic properties.

[0041] Table 1 shows the yield strength of the soft magnetic high-entropy alloys in Examples 1-3 ( σ y ),tensile strength( σ u ), plasticity ( δ ), saturation magnetization ( M s ), coercivity ( H c ) and resistivity ( ρ ).

[0042] Table 1

[0043] The comparative examples 1-3 in Table 1 are explained as follows: Comparative Example 1: In Example 1 of the patent specification with publication number CN120082787A, the design incorporates five elements: Fe, Co, Ni, Ti, and Al. It has an FCC matrix and an L12 reinforcing phase, with the L12 reinforcing phase dispersed within the FCC. The manufacturing process requires hot forging and hot rolling, along with a two-step heat treatment process, making the production steps complex. Its coercivity is 2.3 Oe, which is relatively high and not conducive to reducing losses.

[0044] Comparative Example 2: In Example 1 of the patent specification with publication number CN119287240A, the alloy composition is designed as Fe-Co-Ni-Al-Ti-Mo, which is a single-phase face-centered structure. The preparation process requires hot rolling, and its coercivity is relatively high at 1.26 Oe, which is not conducive to reducing losses.

[0045] Comparative Example 3: In Example 1 of the patent specification with publication number CN117701974A, the alloy composition is designed as Fe-Co-Ni-Al-Si, which is a single-phase body-centered structure. Among its performance indicators, it has a high hardness of 464.5 HV, but it is brittle, which is not conducive to forming and processing and long-term use under alternating load conditions.

[0046] In summary: 1. This invention enables the formation of a dual-phase alloy (BCC+FCC) by adjusting the Fe and Ni elements to a certain ratio in the FeCoNiVMn system. Based on the inverted property characteristics of the FCC and BCC phases, the dual-phase alloy can achieve a good balance between mechanical and soft magnetic properties.

[0047] 2. With the specific composition in Example 1, the lowest coercivity level in the current high-entropy soft magnetic alloy system was achieved, while the mechanical properties showed excellent strength and toughness.

[0048] 3. The heat treatment and cold rolling processes are simple and low-cost, making them practical for production.

[0049] Furthermore, it should be understood that after reading the above description of the present invention, those skilled in the art can make various alterations or modifications to the present invention, and these equivalent forms also fall within the scope defined by the appended claims.

Claims

1. A high-strength, high-ductility, low-coercivity soft magnetic high-entropy alloy, characterized in that, The atomic ratio composition expression is Fe a Co b Ni c V d M e M is one or more of the solid solution strengthening elements Mn, B, Si, Cr, Mo, and W, 41≤a≤62, 25≤b≤30, 13≤c≤21, 0≤d≤3, 0≤e≤5, and a+b+c+d+e=100.

2. The high-strength, high-ductility, low-coercivity soft magnetic high-entropy alloy according to claim 1, characterized in that, 43≤a≤49。 3. The high-strength, high-ductility, low-coercivity soft magnetic high-entropy alloy according to claim 1, characterized in that, 13≤c≤19。 4. The high-strength, high-ductility, low-coercivity soft magnetic high-entropy alloy according to claim 1, characterized in that, 0<d≤3。 5. The high-strength, high-ductility, low-coercivity soft magnetic high-entropy alloy according to claim 1, characterized in that, 0<e≤5。 6. The high-strength, high-ductility, low-coercivity soft magnetic high-entropy alloy according to claim 1, characterized in that, The high-strength, high-plasticity, low-coercivity soft magnetic high-entropy alloy has the following composition expression based on atomic ratio: Fe 43 Co 30 Ni 19 V3Mn5, Fe 45 Co 30 Ni 17 V3Mn5 or Fe 49 Co 30 Ni 13 V3Mn5.

7. The high-strength, high-ductility, low-coercivity soft magnetic high-entropy alloy according to claim 1, characterized in that, The high-strength, high-plasticity, low-coercivity soft magnetic high-entropy alloy is a sheet material.

8. The method for preparing a high-strength, high-ductility, low-coercivity soft magnetic high-entropy alloy according to any one of claims 1 to 7, characterized in that, Including the following steps: S1: Prepare raw materials of pure Fe, pure Co, pure Ni, and optionally pure V and pure M according to the composition formula; S2: In step S1, the raw materials are placed in an induction melting furnace, a vacuum is drawn, and the alloy is melted under an argon atmosphere. Each alloy ingot is repeatedly melted multiple times and cast into a copper mold to form a uniform master alloy casting plate. S3: Perform a long-term high-temperature vacuum homogenization heat treatment at 1200℃ on the cast plate in step S2 to eliminate component segregation during casting and obtain a homogenized alloy plate with stable phase structure. S4: For the multi-pass cold rolling of the homogenized alloy sheet in step S3, the final rolling ratio must reach more than 85% to obtain a cold-rolled sheet with a thickness of no more than 0.8 mm. S5: The cold-rolled sheet from step S4 is subjected to a short-time vacuum recrystallization heat treatment at 1200℃ to form a recrystallized sheet with uniform grain size distribution. The sheet is then cooled at room temperature to complete the spontaneous metastable phase transformation process within the alloy, resulting in the high-strength, high-plasticity, low-coercivity soft magnetic high-entropy alloy.

9. The preparation method according to claim 8, characterized in that, In step S3, the vacuum degree is 3.0 × 10⁻⁶. -4 Pa, the high-temperature vacuum long-term homogenization heat treatment time is 18 h.

10. The preparation method according to claim 8, characterized in that, In step S5, the high-temperature short-time vacuum recrystallization heat treatment lasts for 0.5 h.

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