La-Fe-Si-based magnetic refrigeration composite material based on FHP technology and preparation method of La-Fe-Si-based magnetic refrigeration composite material

Abstract

The invention discloses a La-Fe-Si-based magnetic refrigeration composite material based on an FHP technology and a preparation method thereof.The preparation method comprises the following steps that a La-Fe-Si-based magnetic refrigeration material with the particle size smaller than or equal to 100 microns is used as main phase particles, 0-5 wt% of pure Fe powder is added to serve as an adhesive, and pre-compaction is conducted after sufficient mixing; the particle size of the Fe powder is less than or equal to 20 microns; and the pre-compacted raw material powder is placed in an FHP rapid hot pressing sintering furnace, the vacuum degree lower than 10 <-3 > Pa is kept, high-temperature rapid hot pressing sintering forming is carried out under the continuous pressure of 10-100 MPa, secondary diffusion heat treatment is carried out in the protective atmosphere after cooling, and the La-Fe-Si-based magnetic refrigeration composite material is prepared. The FH P process is adopted, the high-temperature decomposition phenomenon of the 1: 13 phase is effectively inhibited, the pure Fe powder serves as a reaction type adhesive, the magnetocaloric performance and the mechanical performance of the block are further improved, and the comprehensive performance of the material is comprehensively improved.

Description

Technical Field

[0001] The present invention relates to a La-Fe-Si based magnetic refrigeration composite block material, and in particular to a magnetic refrigeration block material prepared by a high temperature rapid prototyping method, which has high density, good magnetocaloric properties, and low functional phase decomposition, and a preparation method thereof. Background Art

[0002] In the field of room-temperature magnetic refrigeration, La-Fe-Si-based magnetic refrigeration alloys have shown great application potential due to their excellent magnetocaloric properties, green and environmentally friendly characteristics, and low price, combined with their near-room temperature and adjustable operating temperature. They are considered to be one of the most promising room-temperature magnetic refrigeration materials.

[0003] However, the following shortcomings need to be overcome in order to realize the application of La-Fe-Si based magnetic refrigeration alloys: (1) The Curie temperature is low. The Curie temperature of La-Fe-Si based magnetic refrigeration alloys is usually much lower than room temperature, which limits their direct application in the field of room temperature magnetic refrigeration; (2) The phase formation period of the magnetocaloric functional phase is long. In the traditional smelting preparation method, the magnetocaloric functional phase (NaZn 13 Type La(Fe,Si) 13 Phase, referred to as 1:13 phase) is formed by the peritectic reaction of α-Fe phase and rare earth-rich phase, but the peritectic reaction is difficult to proceed fully due to the excessive cooling rate after the alloy is smelted. Subsequently, the cast alloy is usually required to be homogenized and annealed at a high temperature above 1273K for several days or even weeks, which consumes a lot of time and energy, seriously hindering the development of room temperature magnetic refrigeration technology; (3) The mechanical properties need to be improved. The rare earth-rich phase and the 1:13 phase have intrinsic brittleness, which leads to many obstacles in the processing and forming of La-Fe-Si based magnetic refrigeration alloys. This intrinsic brittleness makes the material very easy to crack or even break, and it is difficult to process it into the specific shape required by the refrigeration machine to meet the requirements of the refrigeration machine for the shape of the magnetic refrigeration medium. At present, the preparation of La-Fe-Si based alloy composite blocks with excellent magnetocaloric properties and non-magnetic properties such as mechanical and thermal properties, so that they can be truly processed and applied to production practice, shortening the distance from research and development to practical application of magnetic refrigeration materials, has become a key issue that researchers need to overcome.

[0004] The current improvement methods are as follows: (1) Optimizing the alloy composition. Using Co and Si to replace Fe can regulate the Curie temperature and magnetic entropy change of La-Fe-Si based magnetic refrigeration alloys. At the same time, using Ce, Pr, Nd and other rare earth elements to replace La can also effectively improve the magnetocaloric properties of the alloy; (2) Preparing rare earth-rich non-stoichiometric La-Fe-Si based alloys. The excessive addition of rare earth elements can effectively refine the α-Fe phase in the alloy. It only takes a few hours to achieve the rapid formation of the magnetocaloric functional phase (1:13 phase) in the La-Fe-Si based magnetic refrigeration alloy, which greatly shortens the preparation cycle. The formation of La5Si3 transition phase is also conducive to the growth of 1:13 phase; (3) Using methods such as melt rapid quenching and rapid solidification casting can significantly refine the grains, shorten the diffusion distance between atoms, and improve the uniformity of the structure; (4) Through hot pressing sintering or spark plasma sintering, drawing on powder metallurgy and grain boundary diffusion processes, adding sintering aids, high-density composite blocks can be prepared and their mechanical properties can be effectively improved. However, the addition of sintering aids can trigger a magnetic dilution effect, reducing the magnetocaloric properties of the composite bulk. Furthermore, some sintering aids react with the 1:13 phase during sintering, producing an impurity phase that is detrimental to mechanical properties, which requires subsequent, long-term heat treatment to eliminate.

[0005] At present, the preparation of La-Fe-Si based composite blocks mostly adopts hot pressing sintering (HPS) and spark plasma sintering (SPS) and other technologies. The HPS sintering preparation cycle is too long. Although SPS effectively shortens the preparation cycle, it is very easy to cause the decomposition of the 1:13 type magnetocaloric functional phase due to the heating method of pulse current, thereby deteriorating its magnetocaloric performance. Chinese patent publication number CN111230112A discloses a La-Fe-Si based room temperature magnetic refrigeration composite material based on SPS technology and its preparation method. Although the mechanical properties of the sintered material are already very excellent, the maximum magnetic entropy change of the material is only 2.2 J·kg -1 ·K -1 Therefore, at present, whether it is possible to break through the preparation bottleneck and efficiently obtain La-Fe-Si based magnetic refrigeration fast materials with both large magnetic entropy change and high mechanical properties has become the key to determining whether this material can move towards large-scale application. Summary of the Invention

[0006] In view of the problems that exist in the preparation of La-Fe-Si based magnetic refrigeration materials, such as the long formation time of the magnetocaloric functional phase, the difficulty in eliminating the rare earth-rich impurity phase, and the easy decomposition of the 1:13 phase at high temperature, the present invention is based on the reaction mechanism of "α-Fe phase + 1:1:1 phase → 1:13 phase" and proposes a preparation method based on the fast hot pressing sintering (FHP) process. This method uses micron-sized iron powder as a reactive adhesive, with the help of fast hot pressing sintering technology (FHP), and combines it with secondary diffusion heat treatment, which greatly shortens the preparation cycle of La-Fe-Si based magnetic refrigeration block materials, reduces the rare earth-rich impurity phase, and significantly improves the comprehensive performance of the material.

[0007] The purpose of the present invention can be achieved through the following technical solutions:

[0008] A method for preparing a La-Fe-Si based magnetic refrigeration composite material based on FHP technology comprises the following steps:

[0009] (1) La-Fe-Si based magnetic refrigeration material with a particle size of ≤100 μm is used as the main phase particles, 0-5 wt% pure Fe powder is added as a binder, and the mixture is fully mixed and pre-compacted; the La-Fe-Si based magnetic refrigeration material is (La 1.5-x Ce x )(Fe,Co,Si) 13 alloy, wherein 0≤x≤0.5; the particle size of the Fe powder is ≤20 μm;

[0010] (2) Place the pre-compacted raw material powder in the FHP rapid hot pressing sintering furnace and keep the temperature below 10 -3 Pa vacuum degree, and high-temperature rapid hot pressing sintering at 1123-1323K under a continuous pressure of 10-100MPa. After cooling, secondary diffusion heat treatment is carried out in a protective atmosphere at a heat treatment temperature of 1273-1423K and a heat treatment time of 2-8h to prepare La-Fe-Si based magnetic refrigeration composite materials.

[0011] Preferably, the (La 1.5-x Ce x )(Fe,Co,Si) 13 The alloy is an alloy flake obtained by a rapid solidification flake casting method, wherein 0.1≤x≤0.5.

[0012] Preferably, the (La 1.5-x Ce x )(Fe,Co,Si) 13 The alloy has a content of ≥ 90wt% NaZn 13 Type (La, Ce) 1.5 (Fe,Co,Si) 13phase (1:13 phase), α-Fe phase with content ≤10wt%, (La,Ce)1(Fe,Co)1Si1 phase (1:1:1 phase) and (La,Ce)5(Fe,Co,Si)3 phase (5:3 phase) with La 1.2 Ce 0.3 Fe 11 Co 0.8 Si 1.2 More preferably, the La 1.2 Ce 0.3 Fe 11 Co 0.8 Si 1.2 The alloy casting is obtained by high temperature heat treatment in a protective atmosphere.

[0013] Preferably, the added amount of the Fe powder is 2-4 wt%.

[0014] Preferably, the particle size of the La-Fe-Si based magnetic refrigeration material is 50-100 μm, and the particle size of the Fe powder is 5 μm.

[0015] Preferably, the sintering temperature is 1273±20K, the heat treatment temperature is 1373±20K, and the heat treatment time is 6±1h.

[0016] Preferably, the sintering temperature is 1273±20K, and the heat treatment time is 6±1h.

[0017] Preferably, the sintering temperature rise rate is 100±50K / min, the pressure is 50±10MPa, and the holding time is 1-10min.

[0018] Preferably, the sintering temperature rise rate is 100±50K / min, the pressure is 50±10MPa, and the holding time is 1-10min.

[0019] The rapid hot pressing sintering step is: La 1.2 Ce 0.3 Fe 11 Co 0.8 Si 1.2 The alloy is fully mixed with xwt% pure Fe powder (x=0,2,3,4,5) particles and then loaded into a graphite mold. After pre-compaction, it is placed in a FHP-828 sintering furnace and kept below 10 -3 Pa vacuum, continuously apply 50±10MPa pressure. Rapidly heat the mold to 1173K at a heating rate of 100K / min, then heat it to 1273K at a heating rate of 50K / min. Maintain heat and pressure at this temperature for 1-10 minutes, then cool to room temperature in the furnace to obtain a La-Fe-Si-based composite magnetic refrigeration block.

[0020] The present invention is a preparation method for obtaining a La-Fe-Si based composite magnetic refrigeration block with uniform microstructure, low porosity and high 1:13 phase content in a short period of time. The method is combined with secondary diffusion heat treatment to eliminate the rare earth-rich impurity phase in the block to the greatest extent, further increase the 1:13 phase content, and improve the mechanical properties while maintaining good magnetocaloric properties and refrigeration efficiency of the material.

[0021] The method of the present invention is based on the reaction mechanism of "α-Fe phase + 1:1:1 phase → 1:13 phase" and utilizes a "rapid solidification casting method + FHP technology + secondary diffusion heat treatment" process. Micron-sized iron powder is used as a structural control medium to promote efficient reaction between the various phases, thereby significantly improving the overall performance of the composite material. During the high-temperature FHP process, the Fe powder binder reacts with the rare earth-rich phase to form a metallurgical bond and is squeezed into the pores under continuous pressure, effectively reducing the porosity of the bulk material. The composite bulk material is then subjected to a diffusion heat treatment at 1373K for 6 hours to obtain a La-Fe-Si-based room-temperature magnetic cooling bulk material with high density and excellent magnetocaloric properties. The rapid hot pressing sintering technology described is a molding and preparation technology that utilizes a DC power supply for heating, exhibiting unique technical advantages. Compared with conventional hot pressing sintering technology, the pulsed current heating method used in SPS is prone to overheating of the powder surface. During the preparation of La-Fe-Si-based composite materials, the 1:13 phase has poor high-temperature stability and is easily decomposed in large quantities, deteriorating the magnetocaloric properties of the bulk material. FHP technology, which utilizes DC power for heating, can effectively mitigate the decomposition of the 1:13 phase during sintering, significantly improving its stability during the sintering process. This technology can significantly reduce the risk of decomposition of the 1:13 phase at high temperatures. Furthermore, FHP technology offers the ability to rapidly increase and decrease temperatures, significantly shortening sintering time. The resulting blocks have a uniform microstructure, effectively promoting metallurgical bonding between particles and significantly increasing the density of the blocks. Compared to spark plasma sintering, FHP utilizes a more economical DC power source, yet achieves sintering rates and results comparable to SPS technology, effectively reducing equipment costs and operating expenses.

[0022] Compared with the prior art, the present invention has the following advantages:

[0023] 1) This invention utilizes rare earth-rich, non-stoichiometric La-Ce-Fe-Co-Si alloy flakes, combined with a rapid-setting casting process, to rapidly form a high 1:13 phase, exceeding 90% by weight. Compared to conventional preparation methods, the precise control of the rare earth-rich composition and the synergistic effect of the rapid-setting process significantly shorten the alloy's phase formation cycle and significantly improve material production efficiency.

[0024] 2) The present invention utilizes a rapid hot pressing sintering process, which uses a DC power supply as a heating source and has the characteristics of uniform heating and rapid temperature rise. Compared with the SPS process, it avoids the overheating of the powder surface caused by the pulse current, and prevents the 1:13 phase from decomposing due to overheating and reducing the material performance; compared with the HPS process, it shortens the sintering time and effectively reduces the unstable decomposition of the 1:13 phase in a long-term high-temperature environment. This enables the FHP process to maintain the magnetocaloric properties of the material to the greatest extent while obtaining high-density La-Fe-Si magnetic refrigeration blocks. In addition, due to the use of a DC power supply, the equipment cost and operating expenses of the FHP process are much lower than those of the SPS process that relies on expensive pulse power supplies, which greatly reduces the preparation cost of the composite blocks and is more in line with the needs of large-scale actual production.

[0025] 3) The present invention is based on the reaction mechanism of "α-Fe phase + 1:1:1 phase → 1:13 phase" and introduces micron-sized Fe powder as a reactive adhesive. During the high-temperature FHP process, driven by pressure, the fine Fe powder particles can effectively fill the pores inside the block material, significantly reduce the porosity, hinder the expansion of cracks, and improve the mechanical properties of the block material. After secondary diffusion heat treatment, the evenly distributed Fe powder adhesive will react with the brittle rare earth-rich phase remaining in the main phase particles to further generate a 1:13 phase. This process not only improves the mechanical properties of the block material, but also enhances the magnetocaloric properties of the block material due to the increase in the 1:13 phase content, achieving a comprehensive improvement in the comprehensive performance of the material. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 The La in Examples 1 to 5 was sintered at 1273K by FHP and then heat treated at 1373K for 6h. 1.2 Ce 0.3 Fe 11 Co 0.8 Si 1.2 / xwt%Fe(x=0,2,3,4,5) magnetic refrigeration composite block XRD pattern.

[0027] Figure 2 The La in Examples 1 to 5 was sintered at 1273K by FHP and then heat treated at 1373K for 6h. 1.2 Ce 0.3 Fe 11 Co 0.8 Si 1.2 / xwt%Fe(x=0,2,3,4,5) magnetic refrigeration composite block determined by refined XRD pattern.

[0028] Figure 3a 、 Figure 3b 、 Figure 3c 、 Figure 3d and Figure 3eThe La content of Example 1 (0 wt% Fe powder addition), Example 2 (2 wt% Fe powder addition), Example 3 (3 wt% Fe powder addition), Example 4 (4 wt% Fe powder addition) and Example 5 (5 wt% Fe powder addition) is respectively 1.2 Ce 0.3 Fe 11 Co 0.8 Si 1.2 Backscattered electron image of / xwt%Fe(x=0,2,3,4,5) magnetic refrigeration composite block.

[0029] Figure 4 The La in Examples 1 to 5 was sintered at 1273K by FHP and then heat treated at 1373K for 6h. 1.2 Ce 0.3 Fe 11 Co 0.8 Si 1.2 / xwt%Fe(x=0,2,3,4,5) magnetic refrigeration composite block density and porosity.

[0030] Figure 5 The La in Examples 1 to 5 was sintered at 1273K by FHP and then heat treated at 1373K for 6h. 1.2 Ce 0.3 Fe 11 Co 0.8 Si 1.2 M–T curves and dM / dT–T curves of / xwt%Fe(x=0,2,3,4,5) magnetic refrigeration composite blocks.

[0031] Figure 6 The La in Examples 1 to 5 was sintered at 1273K by FHP and then heat treated at 1373K for 6h. 1.2 Ce 0.3 Fe 11 Co 0.8 Si 1.2 Magnetic entropy change-temperature relationship curve of / xwt%Fe (x=0, 2, 3, 4, 5) magnetic refrigeration composite block.

[0032] Figure 7 The La in Examples 1 to 5 was sintered at 1273K by FHP and then heat treated at 1373K for 6h. 1.2 Ce 0.3 Fe 11 Co 0.8 Si 1.2 Stress-strain curves of / xwt%Fe(x=0,2,3,4,5) magnetic refrigeration composite blocks. DETAILED DESCRIPTION

[0033] The present invention will be further described in detail below with reference to the embodiments.

[0034] Example 1

[0035] A La-Fe-Si based magnetic refrigeration block material, the preparation method of which is as follows:

[0036] Step 1: Press La 1.2 Ce 0.3 Fe 11 Co 0.8 Si 1.2 The nominal composition of the alloy is made of pure La (≥99.5wt.%), Ce (≥99.5wt.%), Fe (≥99.95wt.%), Co (≥99.5wt.%), and Si (≥99.95wt.%) blocks, of which the balance of La and Ce is 5wt% to make up for the volatile mass loss during the smelting process. La is obtained by the rapid solidification casting method. 1.2 Ce 0.3 Fe 11 Co 0.8 Si 1.2 alloy castings;

[0037] Step 2: The cast sheet obtained in step 1 was sealed in a protective atmosphere and heat treated at 1373K for 6 hours to obtain a well-formed La 1.2 Ce 0.3 Fe 11 Co 0.8 Si 1.2 castings;

[0038] Step 3: La obtained in step 2 1.2 Ce 0.3 Fe 11 Co 0.8 Si 1.2 The cast sheet was mechanically ground and then sieved to obtain main phase particles with a particle size of 50-100 μm;

[0039] Step 4: Weigh 9g of La with a particle size of 50-100μm obtained in step 3 1.2 Ce 0.3 Fe 11 Co 0.8 Si 1.2 alloy powder;

[0040] Step 5: Pour the powder weighed in step 4 into a Φ16mm mold and pre-compact it;

[0041] Step 6: Place the mold containing the pre-compacted powder from step 5 into an FHP-828 sintering furnace. Heat the mold with a direct current while applying an axial pressure of 50 MPa. Rapidly heat the mold to 1223 K at a heating rate of 100 K / min, then rapidly heat the mold to 1273 K at a heating rate of 50 K / min. Hold the mold for 5 minutes, then stop heating. Cool the mold as it cools down, then remove it from the mold.

[0042] Step 7: Cut the block obtained in step 6 by wire cutting, seal the tube under protective atmosphere, and then heat treat at 1373K for 6 hours.

[0043] After the above seven steps, a Φ16mm×6mm magnetic refrigeration block is obtained, which is recorded as FHP+1373K / 6hLa 1.2 Ce 0.3 Fe 11 Co 0.8 Si 1.2 Block material.

[0044] FHP+1373K / 6h La in Example 1 1.2 Ce 0.3 Fe 11 Co 0.8 Si 1.2 The XRD pattern of magnetic refrigeration block can be found in Figure 1 .

[0045] FHP+1373K / 6h La in Example 1 1.2 Ce 0.3 Fe 11 Co 0.8 Si 1.2 The phase content of magnetic refrigeration blocks can be found in Figure 2 During the high-temperature rapid hot-pressing sintering process, the temperature inevitably passes through the 1:13 phase decomposition range, resulting in slight decomposition of the 1:13 phase. Diffusion heat treatment converts the decomposed area back into the 1:13 phase. Since no binder is added, the α-Fe phase in the block hardly reacts with the rare earth-rich phase. The 1:13 phase content (92.09wt%) decreases by only 1.66wt% compared to the master alloy ingot (93.75wt%) heat-treated at 1373K for 6h.

[0046] Figure 3a FHP+1373K / 6h La in Example 1 1.2 Ce 0.3 Fe 11 Co 0.8 Si 1.2Backscattered electron image of a magnetic refrigeration block. During high-temperature rapid hot pressing, the α-Fe phase, under sustained pressure, forms long strips within the block. Diffusion heat treatment transforms the decomposed regions back into a 1:13 phase. Because no binder is added, the α-Fe phase within the block barely reacts with the rare-earth-rich phase. The Fe element in the 1:13 phase diffuses into the α-Fe phase, causing it to grow. After high-temperature rapid hot pressing and diffusion heat treatment, the block forms a uniform, dense structure.

[0047] FHP+1373K / 6h La in Example 1 1.2 Ce 0.3 Fe 11 Co 0.8 Si 1.2 The density and porosity of magnetic refrigeration blocks can be found in Figure 4 .

[0048] FHP+1373K / 6h La in Example 1 1.2 Ce 0.3 Fe 11 Co 0.8 Si 1.2 MT curve of magnetic refrigeration block, the inset is the dM / dT-T curve, the Curie temperature of the sample is 268K.

[0049] FHP+1373K / 6h La in Example 1 1.2 Ce 0.3 Fe 11 Co 0.8 Si 1.2 The relationship between the magnetic entropy change of magnetic refrigeration block and temperature is shown in Figure 6 The maximum magnetic entropy change of the sample under a 2T magnetic field is 6.65 J·kg -1 ·K -1 , the maximum cooling capacity is calculated to be 130.00 J·kg -1 The maximum magnetic entropy change is better than that of LaFe prepared by hot pressing sintering combined with secondary diffusion heat treatment in the literature [1]. 11.8 Si 1.2 / 5wt%Y 64 Co 36 Block (~4.94 J·kg -1 ·K -1 ) and LaFe prepared by hot pressing sintering combined with secondary diffusion heat treatment in the literature [2] 11.8 Si 1.2 / 10wt%Ce 40 Co 60 Block (~3.50J·kg -1 ·K -1 ).

[0050] La treated with FHP+1373K / 6h in Example 1 1.2 Ce 0.3 Fe 11 Co 0.8 Si 1.2 The stress-strain curve of magnetic refrigeration block can be found in Figure 7 The maximum compressive strength of the sample is about 422MPa. It is better than the LaFe prepared by hot pressing sintering combined with secondary diffusion heat treatment in the literature [1]. 11.8 Si 1.2 / 5wt%Y 64 Co 36 Bulk material (~192MPa) and LaFe prepared by hot pressing sintering combined with secondary diffusion heat treatment in reference [2] 11.8 Si 1.2 / 10wt%Ce 40 Co 60 Block material (~296MPa).

[0051] Example 2

[0052] A La-Fe-Si based magnetic refrigeration block material, the preparation method of which is as follows:

[0053] Step 1: Press La 1.2 Ce 0.3 Fe 11 Co 0.8 Si 1.2 The nominal composition of the alloy is made of pure La (≥99.5wt.%), Ce (≥99.5wt.%), Fe (≥99.95wt.%), Co (≥99.5wt.%), and Si (≥99.95wt.%) blocks, of which the balance of La and Ce is 5wt% to make up for the volatile mass loss during the smelting process. La is obtained by the rapid solidification casting method. 1.2 Ce 0.3 Fe 11 Co 0.8 Si 1.2 alloy castings;

[0054] Step 2: The cast sheet obtained in step 1 was sealed in a protective atmosphere and heat treated at 1373K for 6 hours to obtain a well-formed La 1.2 Ce 0.3 Fe 11 Co 0.8 Si 1.2 castings;

[0055] Step 3: La obtained in step 2 1.2 Ce 0.3 Fe 11 Co 0.8 Si1.2 The cast sheet was mechanically ground and then sieved to obtain main phase particles with a particle size of 50-100 μm;

[0056] Step 4: Weigh 0.82g of La with a particle size of 50-100μm obtained in step 3 1.2 Ce 0.3 Fe 11 Co 0.8 Si 1.2 Alloy powder: weigh 0.18g of pure iron powder with a particle size of 5μm.

[0057] Step 5: Mix the two powders weighed in step 4 for 20 minutes using a mixer, put the mixed powder into a Φ16mm mold, and pre-compact it;

[0058] Step 6: Place the mold containing the pre-compacted powder from step 5 into an FHP-828 sintering furnace. Heat the mold with a direct current while applying an axial pressure of 50 MPa. Rapidly heat the mold to 1223 K at a heating rate of 100 K / min, then rapidly heat the mold to 1273 K at a heating rate of 50 K / min. Hold the mold for 5 minutes, then stop heating. Cool the mold as it cools down, then remove it from the mold.

[0059] Step 7: Cut the block obtained in step 6 by wire cutting, seal the tube under protective atmosphere, and then heat treat at 1373K for 6 hours.

[0060] After the above seven steps, a Φ16mm×6mm magnetic refrigeration block is obtained, which is recorded as FHP+1373K / 6hLa 1.2 Ce 0.3 Fe 11 Co 0.8 Si 1.2 / 2wt%Fe bulk.

[0061] La treated with FHP+1373K / 6h in Example 2 1.2 Ce 0.3 Fe 11 Co 0.8 Si 1.2 / 2wt%Fe magnetic refrigeration block XRD pattern see Figure 1 .

[0062] La treated with FHP+1373K / 6h in Example 2 1.2 Ce 0.3 Fe 11 Co 0.8 Si 1.2 / 2wt%Fe magnetic refrigeration bulk phase content see Figure 2. During the high-temperature rapid hot pressing sintering process, the temperature inevitably passes through the 1:13 phase decomposition range, resulting in slight decomposition of the 1:13 phase. Diffusion heat treatment causes the decomposition area to be converted back into the 1:13 phase, and the Fe powder binder reacts with the residual rare earth-rich phase in the main phase particles to form a 1:13 phase. However, due to the low content of the binder, the content of the generated 1:13 phase is lower than the decomposition amount. However, the decrease in the content of the 1:13 phase in the block material (0.21wt%) is significantly lower than the decrease in Example 1 (1.66wt%).

[0063] Figure 3b La treated with FHP+1373K / 6h in Example 2 1.2 Ce 0.3 Fe 11 Co 0.8 Si 1.2 Backscattered electron image of a 2wt% Fe magnetic refrigeration block. During high-temperature rapid hot pressing sintering, the α-Fe phase is distributed in the block as elongated strips under the action of continuous pressure. Diffusion heat treatment transforms the decomposed regions back into a 1:13 phase. The residual rare earth-rich phase in the main phase particles reacts with the Fe powder binder to form a metallurgical bond. However, due to the low amount of Fe powder binder added, a significant amount of rare earth-rich phase remains in the block. After high-temperature rapid hot pressing sintering and diffusion heat treatment, the block forms a uniform and dense structure.

[0064] La treated with FHP+1373K / 6h in Example 2 1.2 Ce 0.3 Fe 11 Co 0.8 Si 1.2 / Density and porosity of 2wt%Fe magnetic refrigeration block refer to Figure 4 .

[0065] La treated with FHP+1373K / 6h in Example 2 1.2 Ce 0.3 Fe 11 Co 0.8 Si 1.2 MT curve of / 2wt%Fe magnetic refrigeration block, the inset is the dM / dT-T curve, the Curie temperature of the sample is about 267K.

[0066] La treated with FHP+1373K / 6h in Example 2 1.2 Ce 0.3 Fe 11 Co 0.8 Si 1.2 The relationship between the magnetic entropy change of / 2wt%Fe magnetic refrigeration block and temperature is shown in Figure 6 The maximum magnetic entropy change of the sample under a 2T magnetic field is 5.96 J·kg -1·K -1 , the maximum cooling capacity is calculated to be 131.72 J·kg -1 .

[0067] La treated with FHP+1373K / 6h in Example 2 1.2 Ce 0.3 Fe 11 Co 0.8 Si 1.2 The stress-strain curve of / 2wt%Fe magnetic refrigeration block is shown in Figure 7 The maximum compressive strength of the sample is about 470MPa.

[0068] Example 3

[0069] Step 1: Press La 1.2 Ce 0.3 Fe 11 Co 0.8 Si 1.2 The nominal composition of the alloy is made of pure La (≥99.5wt.%), Ce (≥99.5wt.%), Fe (≥99.95wt.%), Co (≥99.5wt.%), and Si (≥99.95wt.%) blocks, of which the balance of La and Ce is 5wt% to make up for the volatile mass loss during the smelting process. La is obtained by the rapid solidification casting method. 1.2 Ce 0.3 Fe 11 Co 0.8 Si 1.2 alloy castings;

[0070] Step 2: The cast sheet obtained in step 1 was sealed in a protective atmosphere and heat treated at 1373K for 6 hours to obtain a well-formed La 1.2 Ce 0.3 Fe 11 Co 0.8 Si 1.2 castings;

[0071] Step 3: La obtained in step 2 1.2 Ce 0.3 Fe 11 Co 0.8 Si 1.2 The cast sheet was mechanically ground and then sieved to obtain main phase particles with a particle size of 50-100 μm;

[0072] Step 4: Weigh 0.73g of La with a particle size of 50-100μm obtained in step 3 1.2 Ce 0.3 Fe 11 Co 0.8 Si 1.2Alloy powder: weigh 0.27g of pure iron powder with a particle size of 5μm.

[0073] Step 5: Mix the two powders weighed in step 4 using a mixer for 20 minutes, put the mixed powder into a Φ16mm mold, and pre-compact it;

[0074] Step 6: Place the mold containing the pre-compacted powder from step 5 into an FHP-828 sintering furnace. Heat the mold with a direct current while applying an axial pressure of 50 MPa. Rapidly heat the mold to 1223 K at a heating rate of 100 K / min, then rapidly heat the mold to 1273 K at a heating rate of 50 K / min. Hold the mold for 5 minutes, then stop heating. Cool the mold as it cools down, then remove it from the mold.

[0075] Step 7: Cut the block obtained in step 6 by wire cutting, seal the tube under protective atmosphere, and then heat treat at 1373K for 6 hours.

[0076] After the above seven steps, a Φ16mm×6mm magnetic refrigeration block is obtained, which is recorded as FHP+1373K / 6hLa 1.2 Ce 0.3 Fe 11 Co 0.8 Si 1.2 / 3wt%Fe bulk.

[0077] La treated with FHP+1373K / 6h in Example 3 1.2 Ce 0.3 Fe 11 Co 0.8 Si 1.2 / 3wt%Fe magnetic refrigeration block XRD pattern see Figure 1 .

[0078] La treated with FHP+1373K / 6h in Example 3 1.2 Ce 0.3 Fe 11 Co 0.8 Si 1.2 / 3wt%Fe magnetic refrigeration block phase content see Figure 2 . During the high-temperature rapid hot pressing sintering process, the temperature inevitably passes through the 1:13 phase decomposition range, resulting in slight decomposition of the 1:13 phase. Diffusion heat treatment causes the decomposition area to be converted back into the 1:13 phase. The Fe powder binder reacts with the residual rare earth-rich phase in the main phase particles to form a 1:13 phase. The content of the generated 1:13 phase is higher than the decomposition amount, resulting in an increase of 2.07wt% in the 1:13 phase content (93.01wt%) in the bulk material compared to the theoretical 1:13 phase content (90.94wt%) of the pre-sintered powder after mixing with 3wt% Fe powder binder.

[0079] Figure 3c La treated with FHP+1373K / 6h in Example 3 1.2 Ce 0.3 Fe 11 Co 0.8 Si 1.2 Backscattered electron image of a 3wt% Fe magnetic refrigeration block. During high-temperature rapid hot pressing sintering, the α-Fe phase is distributed in the bulk as elongated strips under the action of sustained pressure. Diffusion heat treatment transforms the decomposed regions back into a 1:13 phase. The residual rare earth-rich phase in the main phase particles reacts with the Fe powder binder to form a metallurgical bond, and the Fe powder binder fully reacts with the residual rare earth-rich phase in the block. After high-temperature rapid hot pressing sintering and diffusion heat treatment, the block forms a uniform and dense structure.

[0080] La treated with FHP+1373K / 6h in Example 3 1.2 Ce 0.3 Fe 11 Co 0.8 Si 1.2 / 3wt%Fe magnetic refrigeration block density and porosity refer to Figure 4 .

[0081] La treated with FHP+1373K / 6h in Example 3 1.2 Ce 0.3 Fe 11 Co 0.8 Si 1.2 MT curve of / 3wt%Fe magnetic refrigeration block, the inset is the dM / dT-T curve, the Curie temperature of the sample is about 266K.

[0082] La treated with FHP+1373K / 6h in Example 3 1.2 Ce 0.3 Fe 11 Co 0.8 Si 1.2 / 3wt%Fe magnetic refrigeration block magnetic entropy change versus temperature curve see Figure 6 The maximum magnetic entropy change of the sample under a 2T magnetic field is 6.20 J·kg -1 ·K -1 , the maximum cooling capacity is calculated to be 137.64 J·kg -1 .

[0083] La treated with FHP+1373K / 6h in Example 3 1.2 Ce 0.3 Fe 11 Co 0.8 Si 1.2 / 3wt%Fe magnetic refrigeration block stress-strain curve see Figure 7 The maximum compressive strength of the sample is about 404MPa.

[0084] Example 4

[0085] Step 1: Press La 1.2 Ce 0.3 Fe 11 Co 0.8 Si 1.2 The nominal composition of the alloy is made of pure La (≥99.5wt.%), Ce (≥99.5wt.%), Fe (≥99.95wt.%), Co (≥99.5wt.%), and Si (≥99.95wt.%) blocks, of which the balance of La and Ce is 5wt% to make up for the volatile mass loss during the smelting process. La is obtained by the rapid solidification casting method. 1.2 Ce 0.3 Fe 11 Co 0.8 Si 1.2 alloy castings;

[0086] Step 2: The cast sheet obtained in step 1 was sealed in a protective atmosphere and heat treated at 1373K for 6 hours to obtain a well-formed La 1.2 Ce 0.3 Fe 11 Co 0.8 Si 1.2 castings;

[0087] Step 3: La obtained in step 2 1.2 Ce 0.3 Fe 11 Co 0.8 Si 1.2 The cast sheet was mechanically ground and then sieved to obtain main phase particles with a particle size of 50-100 μm;

[0088] Step 4: Weigh 8.64g of La with a particle size of 50-100μm obtained in step 3 1.2 Ce 0.3 Fe 11 Co 0.8 Si 1.2 Alloy powder: weigh 0.36g of pure iron powder with a particle size of 5μm.

[0089] Step 5: Mix the two powders weighed in step 4 using a mixer for 20 minutes, put the mixed powder into a Φ16mm mold, and pre-compact it;

[0090] Step 6: Place the mold containing the pre-compacted powder from step 5 into an FHP-828 sintering furnace. Heat the mold with a direct current while applying an axial pressure of 50 MPa. Rapidly heat the mold to 1223 K at a heating rate of 100 K / min, then rapidly heat the mold to 1273 K at a heating rate of 50 K / min. Hold the mold for 5 minutes, then stop heating. Cool the mold as it cools down, then remove it from the mold.

[0091] Step 7: Cut the block obtained in step 6 by wire cutting, seal the tube under protective atmosphere, and then heat treat at 1373K for 6 hours.

[0092] After the above seven steps, a Φ16mm×6mm magnetic refrigeration block is obtained, which is recorded as FHP+1373K / 6hLa 1.2 Ce 0.3 Fe 11 Co 0.8 Si 1.2 / 4wt%Fe bulk.

[0093] La treated with FHP+1373K / 6h in Example 4 1.2 Ce 0.3 Fe 11 Co 0.8 Si 1.2 / 4wt%Fe magnetic refrigeration block XRD pattern see Figure 1 .

[0094] La treated with FHP+1373K / 6h in Example 4 1.2 Ce 0.3 Fe 11 Co 0.8 Si 1.2 / 4wt%Fe magnetic refrigeration bulk phase content see Figure 2 . During the high-temperature rapid hot pressing sintering process, since the temperature inevitably passes through the 1:13 phase decomposition range, the 1:13 phase undergoes slight decomposition. In addition, a large amount of Fe powder binder tends to agglomerate to form large pieces of binder particles, which seize the Co and Si elements of the 1:13 phase, causing the 1:13 phase to become unstable and decompose. However, during the diffusion heat treatment process, the decomposition area is converted back into the 1:13 phase, and the Fe powder binder further reacts with the residual rare earth-rich phase in the main phase particles to form a larger amount of 1:13 phase. The amount of 1:13 phase generated is higher than the amount of decomposition, which increases the 1:13 phase content in the block material (91.86wt%) by 1.86wt% compared to the theoretical 1:13 phase content (90.00wt%) of the pre-sintered powder after mixing with 4wt% Fe powder binder, but is slightly lower than the increase in Example 3 (2.07wt%).

[0095] Figure 3dLa treated with FHP+1373K / 6h in Example 4 1.2 Ce 0.3 Fe 11 Co 0.8 Si 1.2 Backscattered electron image of a 4wt% Fe magnetic refrigeration block. During high-temperature rapid hot pressing sintering, the α-Fe phase is distributed in elongated strips within the block under the action of sustained pressure. Diffusion heat treatment transforms the decomposed regions back into a 1:13 phase. The residual rare earth-rich phase within the main phase particles reacts with the Fe powder binder to form a metallurgical bond, and the Fe powder binder fully reacts with the residual rare earth-rich phase within the block. After high-temperature rapid hot pressing sintering and diffusion heat treatment, the block forms a uniform and dense structure.

[0096] La treated with FHP+1373K / 6h in Example 4 1.2 Ce 0.3 Fe 11 Co 0.8 Si 1.2 / Density and porosity of 4wt%Fe magnetic refrigeration block refer to Figure 4 .

[0097] La treated with FHP+1373K / 6h in Example 4 1.2 Ce 0.3 Fe 11 Co 0.8 Si 1.2 MT curve of / 4wt%Fe magnetic refrigeration block, the inset is the dM / dT-T curve, the Curie temperature of the sample is about 265K.

[0098] La treated with FHP+1373K / 6h in Example 4 1.2 Ce 0.3 Fe 11 Co 0.8 Si 1.2 / 4wt%Fe magnetic refrigeration block magnetic entropy change versus temperature curve see Figure 6 The maximum magnetic entropy change of the sample under a 2T magnetic field is 6.04 J·kg -1 ·K -1 , the maximum cooling capacity is calculated to be 127.44 J·kg -1 Compared with the maximum magnetic entropy change of the parent alloy (8.05J·kg -1 ·K -1 ) and cooling capacity (132.80 J·kg -1 ).

[0099] La treated with FHP+1373K / 6h in Example 4 1.2 Ce 0.3 Fe11 Co 0.8 Si 1.2 / 4wt%Fe magnetic refrigeration block stress-strain curve see Figure 7 The maximum compressive strength of the sample is about 470MPa.

[0100] Example 5

[0101] Step 1: Press La 1.2 Ce 0.3 Fe 11 Co 0.8 Si 1.2 The nominal composition of the alloy is made of pure La (≥99.5wt.%), Ce (≥99.5wt.%), Fe (≥99.95wt.%), Co (≥99.5wt.%), and Si (≥99.95wt.%) blocks, of which the balance of La and Ce is 5wt% to make up for the volatile mass loss during the smelting process. La is obtained by the rapid solidification casting method. 1.2 Ce 0.3 Fe 11 Co 0.8 Si 1.2 alloy castings;

[0102] Step 2: The cast sheet obtained in step 1 was sealed in a protective atmosphere and heat treated at 1373K for 6 hours to obtain a well-formed La 1.2 Ce 0.3 Fe 11 Co 0.8 Si 1.2 castings;

[0103] Step 3: La obtained in step 2 1.2 Ce 0.3 Fe 11 Co 0.8 Si 1.2 The cast sheet was mechanically ground and then sieved to obtain main phase particles with a particle size of 50-100 μm;

[0104] Step 4: Weigh 8.55g of La with a particle size of 50-100μm obtained in step 3 1.2 Ce 0.3 Fe 11 Co 0.8 Si 1.2 Alloy powder: weigh 0.45g of pure iron powder with a particle size of 5μm.

[0105] Step 5: Mix the two powders weighed in step 4 using a mixer for 20 minutes, put the mixed powder into a Φ16mm mold, and pre-compact it;

[0106] Step 6: Place the mold containing the pre-compacted powder from step 5 into an FHP-828 sintering furnace. Heat the mold with a direct current while applying an axial pressure of 50 MPa. Rapidly heat the mold to 1223 K at a heating rate of 100 K / min, then rapidly heat the mold to 1273 K at a heating rate of 50 K / min. Hold the mold for 5 minutes, then stop heating. Cool the mold as it cools down, then remove it from the mold.

[0107] Step 7: Cut the block obtained in step 6 by wire cutting, seal the tube under protective atmosphere, and then heat treat at 1373K for 6 hours.

[0108] After the above seven steps, a Φ16mm×6mm magnetic refrigeration block is obtained, which is recorded as FHP+1373K / 6hLa 1.2 Ce 0.3 Fe 11 Co 0.8 Si 1.2 / 5wt%Fe bulk.

[0109] La treated with FHP+1373K / 6h in Example 5 1.2 Ce 0.3 Fe 11 Co 0.8 Si 1.2 / 5wt%Fe magnetic refrigeration block XRD pattern see Figure 1 .

[0110] La treated with FHP+1373K / 6h in Example 5 1.2 Ce 0.3 Fe 11 Co 0.8 Si 1.2 / 5wt%Fe magnetic refrigeration block phase content see Figure 2 . During the high-temperature rapid hot pressing sintering process, since the temperature inevitably passes through the 1:13 phase decomposition range, the 1:13 phase undergoes slight decomposition. In addition, a large amount of Fe powder binder tends to agglomerate to form large pieces of binder particles, which seize the Co and Si elements of the 1:13 phase, causing the 1:13 phase to become unstable and decompose. However, during the diffusion heat treatment process, the decomposed area is reconverted into the 1:13 phase, and the Fe powder binder further reacts with the residual rare earth-rich phase in the main phase particles to form a larger amount of 1:13 phase. The amount of 1:13 phase generated is higher than the amount of decomposition. The 1:13 phase content in the block material is higher than the theoretical 1:13 phase content (89.06wt%) of the pre-sintered powder after mixing with 5wt% Fe powder binder, but slightly lower than Example 4. The 1:13 phase content (91.33 wt%) in the bulk material is increased by 2.27 wt% compared to the theoretical 1:13 phase content (89.06 wt%) of the pre-sintered powder after mixing with 5 wt% Fe powder binder, which is higher than the increase in Examples 3 and 4.

[0111] Figure 3e is La sintered by FHP at 1273K in Example 5 1.2 Ce 0.3 Fe 11 Co 0.8 Si 1.2 Backscattered electron image of a magnetic refrigeration block. During high-temperature rapid hot pressing sintering, the α-Fe phase is distributed in elongated strips within the block under the action of continuous pressure. Diffusion heat treatment transforms the decomposed regions back into a 1:13 phase. The residual rare earth-rich phase within the main phase particles reacts with the Fe powder binder to form a metallurgical bond, and the Fe powder binder fully reacts with the residual rare earth-rich phase within the block. After high-temperature rapid hot pressing sintering and diffusion heat treatment, the block forms a uniform and dense structure.

[0112] La treated with FHP+1373K / 6h in Example 5 1.2 Ce 0.3 Fe 11 Co 0.8 Si 1.2 / Density and porosity of 5wt%Fe magnetic refrigeration block refer to Figure 4 .

[0113] La treated with FHP+1373K / 6h in Example 5 1.2 Ce 0.3 Fe 11 Co 0.8 Si 1.2 MT curve of / 5wt%Fe magnetic refrigeration block, the inset is the dM / dT-T curve, the Curie temperature of the sample is about 265K.

[0114] La treated with FHP+1373K / 6h in Example 5 1.2 Ce 0.3 Fe 11 Co 0.8 Si 1.2 / 5wt%Fe magnetic refrigeration block magnetic entropy change versus temperature curve see Figure 6 The maximum magnetic entropy change of the sample under a 2T magnetic field is 4.78 J·kg -1 ·K -1 , the maximum cooling capacity is calculated to be 130.49 J·kg -1 Since the amount of binder added is higher than that in Examples 1 to 4, the magnetocaloric performance of the La-Fe-Si based bulk material prepared in this example is more seriously diluted, and the maximum magnetic entropy change (8.05 J·kg -1 ·K -1 ) and cooling capacity (132.80 J·kg -1), its maximum magnetic entropy change decreased by 40.62%, but the cooling capacity only decreased by 1.74%.

[0115] La treated with FHP+1373K / 6h in Example 5 1.2 Ce 0.3 Fe 11 Co 0.8 Si 1.2 / 5wt%Fe magnetic refrigeration block stress-strain curve see Figure 7 Since the sample contains a large amount of dispersed high-strength and tough α-Fe phase, the compressive strength of the sample is increased to 486 MPa. The compressive strength of this embodiment is higher than that of Examples 1 to 4.

[0116] [1]GPLi,XCZhong,X.Huang,CLliu,JHHuang,KWLong,HYYu,Z.

[0117] W.Liu,RVRamanujan.Microstructure, magnetocaloric and mechanicalproperties

[0118] of LaFe 11.8 Si 1.2 / Y 64 Co 36 composites prepared by hot pressing and difusionannealing.Journal of Materials Research,2023,38:3720-3729.

[0119] [2]XCZhong, 13 -based composites by Ce-Co grainboundary diffusion. Journal of Materials Science,2020,55:5908-5919.

Claims

1. A method for preparing a La-Fe-Si based magnetic refrigeration composite material based on FHP technology, characterized in that: The steps include: (1) La-Fe-Si based magnetic refrigeration material with a particle size of ≤100 μm is used as the main phase particles, 0-5 wt% pure Fe powder is added as a binder, and the mixture is fully mixed and pre-compacted; the La-Fe-Si based magnetic refrigeration material is (La 1.5-x Ce x )(Fe,Co,Si) 13 alloy, wherein 0≤x≤0.5; the particle size of the Fe powder is ≤20 μm; (2) Place the pre-compacted raw material powder in the FHP rapid hot pressing sintering furnace and keep the temperature below 10 -3 Pa vacuum degree, and high-temperature rapid hot pressing sintering at 1123-1323K under a continuous pressure of 10-100MPa. After cooling, secondary diffusion heat treatment is carried out in a protective atmosphere at a heat treatment temperature of 1273-1423K and a heat treatment time of 2-8h to prepare La-Fe-Si based magnetic refrigeration composite materials.

2. The preparation method according to claim 1, characterized in that The (La 1.5-x Ce x )(Fe,Co,Si) 13 The alloy is an alloy flake obtained by a rapid solidification flake casting method, wherein 0.1≤x≤0.

5.

3. The preparation method according to claim 2, characterized in that The (La 1.5-x Ce x )(Fe,Co,Si) 13 The alloy has a content of ≥ 90wt% NaZn 13 Type (La, Ce) 1.5 (Fe,Co,Si) 13 phase, α-Fe phase with content ≤10wt%, (La,Ce)1(Fe,Co)1Si1 phase and (La,Ce)5(Fe,Co,Si)3 phase of La 1.2 Ce 0.3 Fe 11 Co 0.8 Si 1.2 Alloy castings.

4. The preparation method according to claim 1, 2 or 3, characterized in that: The added amount of the Fe powder is 2-4 wt%.

5. The preparation method according to claim 4, characterized in that The particle size of the La-Fe-Si based magnetic refrigeration material is 50-100 μm, and the particle size of the Fe powder is 5 μm.

6. The preparation method according to claim 1, 2 or 3, characterized in that: The sintering temperature is 1273±20K, the heat treatment temperature is 1373±20K, and the heat treatment time is 6±1h.

7. The preparation method according to claim 4, characterized in that The sintering temperature is 1273±20K, and the heat treatment time is 6±1h.

8. The preparation method according to claim 6, characterized in that The sintering temperature rise rate is 100±50K / min, the pressure is 50±10MPa, and the holding time is 1-10min.

9. The preparation method according to claim 7, characterized in that The sintering temperature rise rate is 100±50K / min, the pressure is 50±10MPa, and the holding time is 1-10min.

10. La-Fe-Si based magnetic refrigeration composite material prepared by the method according to any one of claims 1 to 9.

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