Raw material alloys used for magnetic refrigerants and methods for producing these alloys, magnetic refrigerants and methods for producing these materials.

Abstract

The invention relates to a raw material alloy for magnetic refrigerants capable of controlling the amount of hydrogen adsorbed and homogenizing the hydrogen concentration distribution under broader hydrogenation conditions than previously possible, and a method for producing such an alloy, and relates to a magnetic refrigerant with a high ΔS and a controlled phase transition temperature, and a method for producing such a material. The raw material alloy for the magnetic cooling material of the invention is represented by the composition formula La(1-a)Ra(Fe(1-bcd)TMbSicAd)z, containing at least one of the phases (La,R)MSi, (La,R)5M3, (La,R)6M11Si3, and (La,R)2M17 in total amounts of 0.3% by volume or less as a secondary phase containing R, containing α-Fe in amounts of 0.1% by volume or more and 2.2% by volume or less, and containing the remainder as the primary phase (La,R)(Fe,TM,Si,A)13.The magnetic refrigerant material according to this invention is obtained by hydrogenating the raw material alloy used for the magnetic refrigerant material according to the invention.

Description

Raw material alloy for magnetic refrigeration material and its manufacturing method, and magnetic refrigeration material and its manufacturing method

[0001] The present invention relates to a raw material alloy for a magnetic refrigeration material having a controlled transition temperature and a high magnetic entropy change, a method for producing the same, and a magnetic refrigeration material and a method for producing the same.

[0002] Because fluorocarbons are ozone-depleting substances and greenhouse gases, new refrigeration and air-conditioning systems that do not use fluorocarbons are attracting attention for environmental conservation. Although active development of alternative refrigerants to fluorocarbons has been underway, no new refrigerants that are satisfactory in terms of performance, cost, and safety have yet been put into practical use.

[0003] On the other hand, unlike conventional refrigeration and air conditioning systems, magnetic refrigeration systems that utilize the change in entropy (magneto-caloric effect, ΔS) that accompanies an increase in magnetic field have been attracting attention. Materials with a large absolute value of ΔS include Mn(As １－ｘ Sb ｘ ) (Patent Document 1) and La(Fe １－ｘ Si ｘ ) １３ H ｚ (Patent Document 2) and the like. In particular, the former has a very large ΔS of -30 J / kgK, making it an excellent magnetic refrigeration material. However, Mn(As １－ｘ Sb ｘ ) is difficult to apply because of its toxicity. １－ｘ Si ｘ ) １３ H ｚ ΔS is -25 J / kgK and Mn(As １－ｘ Sb ｘ ), and its constituent elements are non-toxic and not rare metals, making it the most promising material. The change in ΔS is also related to the magnetic transition temperature (T ｃ ) and a single material can only operate at a certain temperature, so refrigeration systems that require a wide temperature difference cannot be realized. Therefore, methods such as replacing some of the components with other elements are used to change the operating temperature.

[0004] These substances must operate near room temperature (approximately -70 to +70°C). However, unlike conventional magnetic refrigeration, which has been used as a means of generating extremely low temperatures that are difficult to achieve using gas refrigeration, magnetic refrigeration at the above operating temperatures has the problem of a reduced magnetocaloric effect due to non-negligible lattice vibrations. This problem can be solved by utilizing these lattice vibrations as a heat storage effect. The AMR (Active Magnetic Regenerative) cycle, which utilizes these lattice vibrations as a heat storage effect, has been developed, and refrigeration and air conditioning systems that operate near room temperature using the magnetocaloric effect have become a reality.

[0005] In the AMR cycle, the magnetic refrigeration material is filled with a gap (called the bed section) through which a heat transfer medium such as water can pass. The heat transfer medium can move between the high-temperature and low-temperature ends through the gap. With the heat transfer medium at the low-temperature end, a magnetic field is applied to the bed section using a permanent magnet or other device to reduce the entropy of the magnetic refrigeration material and raise its temperature. The heat transfer medium is then moved from the low-temperature end to the high-temperature end. The heat transfer medium receives heat from the magnetic refrigeration material and moves to the high-temperature end, where it is released using a heat exchanger. The magnetic field from the permanent magnet is then removed, increasing the entropy of the magnetic refrigeration material and lowering its temperature. The heat transfer medium is then moved from the high-temperature end to the low-temperature end. The heat transfer medium is then cooled by the magnetic refrigeration material. The cooled heat transfer medium absorbs heat in the heat exchanger. Repeating this cycle creates a temperature difference between the high-temperature and low-temperature ends, creating a refrigeration cycle.

[0006] In the AMR cycle, the temperature difference that can be generated with a single-composition material is about 2 to 10 K, depending on the material. To generate a large temperature difference required for applications such as refrigerators and air conditioners, different magnetic transition temperatures (T ｃ ) from the high temperature end to the low temperature end. ｃ By filling the materials in order from high to low (cascade filling), and by performing heat exchange between adjacent magnetic refrigeration materials, a large temperature difference can be generated.

[0007] JP 2003-28532 A JP 2006-89839 A

[0008] In order for heat exchange to occur between the cascade-packed magnetic refrigeration materials, the operating temperatures of the adjacent magnetic refrigeration materials must overlap. １－ｘ Si ｘ ) １３ In the case of , the half-width is narrow at 3 to 5 K, so it has been found that controlling the operating temperature (transition temperature) with high precision is preferable for good heat exchange.

[0009] However, La(Fe １－ｘ Si ｘ ) １３ The operating temperature of varies depending on the composition of the material as well as on manufacturing conditions such as alloy homogenization conditions and hydrogenation conditions during manufacturing, and ΔS is similarly significantly affected by the manufacturing conditions (for example, the hydrogen concentration distribution within the material). Therefore, it has been difficult to precisely control the transition temperature and achieve a high ΔS value on a manufacturing scale of kg or more, rather than in a research-based experiment on a few grams scale.

[0010] The hydrogenation heat treatment is particularly problematic. It is generally known that the degree of hydrogen absorption changes depending on the pretreatment (activation treatment) conditions. Furthermore, the temperature and time of the hydrogenation heat treatment, the atmosphere during cooling, and the cooling rate can affect the degree of hydrogen absorption. １－ｘ Si ｘ ) １３ Because the amount of hydrogen absorbed by the material and the hydrogen concentration distribution within the material change, it is not easy to control the amount of hydrogen absorbed (control of the transition temperature) and homogenize the hydrogen concentration distribution (high ΔS) on a manufacturing scale.

[0011] The present invention has been made in view of the above circumstances, and aims to provide a raw material alloy for a magnetic refrigeration material, a method for manufacturing the same, and a magnetic refrigeration material and a method for manufacturing the same, which are capable of precisely controlling the transition temperature in response to changes in hydrogenation conditions and achieving a high ΔS.

[0012] As a result of extensive research into achieving the above object, the inventors have discovered that by adjusting the composition of a raw material alloy to a predetermined range and then performing a homogenization treatment on the resulting raw material alloy so that the amount of precipitated subphase containing a rare earth element and α-Fe is in a predetermined ratio, it is possible to control the amount of hydrogen absorption over a wide range of hydrogenation conditions, thereby adjusting the transition temperature, and by homogenizing the hydrogen concentration distribution, achieving a high ΔS value, and have completed the present invention.

[0013] Therefore, the present invention provides the following raw alloy for a magnetic refrigeration material and a method for producing the same, as well as a magnetic refrigeration material and a method for producing the same. （１－ａ） R ａ (Fe （１－ｂ－ｃ－ｄ） TM ｂ Si ｃ A ｄ ) ｚ (R is one or more rare earth elements selected from Ce, Pr, and Nd; TM is one or more elements selected from Co, Mn, Ni, Nb, W, Ta, Cr, Cu, and Ag; A is one or more elements selected from Al, Ga, P, Ge, Sn, and In, and satisfy the following conditions: 0≦a≦0.5, 0≦b≦0.03, 0.09≦c≦0.14, 0≦d≦0.05, 13.0≦z≦13.4), and the (La, R)MSi phase, (La, R) ５ M ３ Phase, (La, R) ６ M １１ Si ３ phase, and (La, R) ２ M １７ The alloy contains at least one of the following subphases (wherein M is one or more elements selected from Fe and TM) in a total amount of 0.3 vol% or less as a subphase containing R, and contains 0.1 vol% to 2.2 vol% of the α-Fe phase, with the balance being (La, R)(Fe, TM, Si, A). １３ 2. A raw material alloy for a magnetic refrigeration material according to 1, containing a La phase as a main phase. 3. A raw material alloy for a magnetic refrigeration material according to 1, wherein the average circular approximation diameter of the α-Fe phase is 6 μm or less. （１－ａ） R ａ (Fe （１－ｂ－ｃ－ｄ） TM ｂ Si ｃ A ｄ ) ｚ3. The method for producing a raw alloy for a magnetic refrigeration material according to 1 or 2, wherein an alloy represented by the following composition formula is heat-treated in a vacuum atmosphere or an inert gas atmosphere at 1000 to 1300°C for 10 to 100 hours: (R is one or more rare earth elements selected from Ce, Pr, and Nd; TM is one or more elements selected from Co, Mn, Ni, Nb, W, Ta, Cr, Cu, and Ag; A is one or more elements selected from Al, Ga, P, Ge, Sn, and In, and the following conditions are satisfied: 0≦a≦0.5, 0≦b≦0.03, 0.09≦c≦0.14, 0≦d≦0.05, 13.0≦z≦13.4). （１－ａ） R ａ (Fe （１－ｂ－ｃ－ｄ） TM ｂ Si ｃ A ｄ ) ｚ H ｅ (R is one or more rare earth elements selected from Ce, Pr, and Nd; TM is one or more elements selected from Co, Mn, Ni, Nb, W, Ta, Cr, Cu, and Ag; A is one or more elements selected from Al, Ga, P, Ge, Sn, and In, and satisfy the following conditions: 0≦a≦0.5, 0≦b≦0.03, 0.09≦c≦0.14, 0≦d≦0.05, 0<e≦1.5, 13.0≦z≦13.4), and the (La,R)MSi phase, (La,R) ５ M ３ Phase, (La, R) ６ M １１ Si ３ Phase, (La, R) ２ M １７ phase and at least one of their hydride phases (M is one or more elements selected from Fe and TM) in a total amount of 0.3 vol% or less as subphases containing R, and α-Fe phase in an amount of 0.1 vol% to 2.2 vol%, with the balance being (La, R)(Fe, TM, Si, A). １３ H ｅ 5. A magnetic refrigeration material containing the α-Fe phase as a main phase. 6. The magnetic refrigeration material according to 4, wherein the average circular approximation diameter of the α-Fe phase is 6 μm or less. （１－ａ） R ａ (Fe （１－ｂ－ｃ－ｄ） TM ｂ Si ｃ A ｄ ) ｚ(R is one or more rare earth elements selected from Ce, Pr, and Nd; TM is one or more elements selected from Co, Mn, Ni, Nb, W, Ta, Cr, Cu, and Ag; A is one or more elements selected from Al, Ga, P, Ge, Sn, and In, and satisfy the following conditions: 0≦a≦0.5, 0≦b≦0.03, 0.09≦c≦0.14, 0≦d≦0.05, 13.0≦z≦13.4), and the (La, R)MSi phase, (La, R) ５ M ３ Phase, (La, R) ６ M １１ Si ３ phase, and (La, R) ２ M １７ The alloy contains at least one of the following subphases (wherein M is one or more elements selected from Fe and TM) in a total amount of 0.3 vol% or less as a subphase containing R, and contains 0.1 vol% to 2.2 vol% of the α-Fe phase, with the balance being (La, R)(Fe, TM, Si, A). １３ 6. The method for producing a magnetic refrigeration material according to 4 or 5, wherein the alloy containing the phase as a main phase is subjected to a hydrogenation heat treatment at a cooling rate of 0.1° C. / min to 50° C. / min.

[0014] According to the present invention, it is possible to provide a raw material alloy for a magnetic refrigeration material that can control the amount of hydrogen absorption and homogenize the hydrogen concentration distribution over a wider range of hydrogenation conditions than conventional methods, a method for manufacturing the same, and a magnetic refrigeration material that has a high ΔS and a controlled transition temperature, and a method for manufacturing the same.

[0015] 1 is a microstructure photograph of the alloy for magnetic refrigeration materials obtained in Comparative Example 1. 2 is a microstructure photograph of the alloy for magnetic refrigeration materials obtained in Example 3. 3 are measurement results of the mT characteristics of the alloys for magnetic refrigeration materials obtained in Examples 1 to 3 and Comparative Examples 1 to 4. 4 are measurement results of the mT characteristics of the magnetic refrigeration materials obtained in Examples 1 to 3 and Comparative Examples 1 to 4. 5 are a microstructure photograph of the alloy for magnetic refrigeration materials obtained in Comparative Example 5. 6 are a microstructure photograph of the alloy for magnetic refrigeration materials obtained in Example 4. 7 are a microstructure photograph of the alloy for magnetic refrigeration materials obtained in Example 5. 8 are measurement results of the mT characteristics of the magnetic refrigeration materials obtained in Examples 4 to 5 and Comparative Example 5. 9 are measurement results of the mT characteristics of the alloys for magnetic refrigeration materials obtained in Examples 4 to 5 and Comparative Example 5.

[0016] The raw material alloy for magnetic refrigeration material of the present invention is La （１－ａ） R ａ (Fe （１－ｂ－ｃ－ｄ） TM ｂ Si ｃ A ｄ ) ｚ (R is one or more rare earth elements selected from Ce, Pr, and Nd; TM is one or more elements selected from Co, Mn, Ni, Nb, W, Ta, Cr, Cu, and Ag; A is one or more elements selected from Al, Ga, P, Ge, Sn, and In, and satisfy the following conditions: 0≦a≦0.5, 0≦b≦0.03, 0.09≦c≦0.14, 0≦d≦0.05, 13.0≦z≦13.4), and the (La, R)MSi phase, (La, R) ５ M ３ Phase, (La, R) ６ M １１ Si ３ phase, and (La, R) ２ M １７ The alloy contains at least one of the following subphases (wherein M is one or more elements selected from Fe and TM) in a total amount of 0.3 vol% or less as a subphase containing R, and contains 0.1 vol% to 2.2 vol% of the α-Fe phase, with the balance being (La, R)(Fe, TM, Si, A). １３ The raw material alloy for magnetic refrigeration contains the phase as the main phase.

[0017] In the above composition formula, R is one or more rare earth elements selected from Ce, Pr, and Nd, and a is 0 to 0.5, preferably 0.2 to 0.4. A method of changing ΔS and the transition temperature by substituting a portion of La with other rare earth elements is known, and particularly high properties can be obtained by substituting a portion of La with one or more rare earth elements selected from Ce, Pr, and Nd, so it is desirable to substitute an appropriate amount depending on the required magnetic properties. However, if the substitution ratio is large, RM may occur when a homogenization treatment is performed to obtain a raw material alloy for a magnetic refrigeration material. １３ The substitution ratio is 0.5 or less because a different phase other than the Fe phase is stably formed, causing deterioration of magnetic properties including a decrease in ΔS.

[0018] In the above composition formula, TM is one or more elements selected from Co, Mn, Ni, Nb, W, Ta, Cr, Cu, and Ag, and b is 0 or more and 0.03 or less, preferably 0.005 or more and 0.025 or less. The transition temperature of the magnetic refrigeration material obtained by subjecting the raw alloy for the magnetic refrigeration material to the hydrogenation heat treatment described later is controlled by controlling the amount of hydrogen storage or the amount of TM added. However, since it is difficult to control the transition temperature of about 1 to 3°C required for AMR by controlling the amount of hydrogen storage alone, the TM element is added to control it. However, if b exceeds 0.03, TM becomes a cause of RM after homogenization treatment. １３ phases are less likely to form.

[0019] The Si content c in the above composition formula is 0.09 or more and 0.14 or less, and preferably 0.095 or more and 0.11 or less. The smaller c is, the larger the amount of magnetization change due to phase transition. However, if c is less than 0.09, the RM １３ The phase becomes unstable, making it difficult to obtain a raw alloy for magnetic refrigeration material by homogenization. On the other hand, if c is greater than 0.14, the phase transition approaches a second-order phase transition, resulting in a decrease in ΔS of the raw alloy for magnetic refrigeration material obtained after homogenization. If c is 0.095 or greater, an alloy in which 95% or more of the phase is the main phase can be easily obtained by general homogenization, for example, treatment at 1100°C for 50 hours. On the other hand, since ΔS increases as c becomes smaller, it is preferable that c be 0.11 or less. ΔS is the jump in entropy (S) that appears at the phase transition temperature.

[0020] In the above composition formula, A is one or more elements selected from Al, Ga, P, Ge, Sn, and In, and d is 0 to 0.05, preferably 0.03 or less. Since these substitution elements A are substitution elements for Si, if the addition ratio exceeds 0.05, RM １３ Since the phase transition approaches a second-order phase transition, ΔS decreases significantly.

[0021] In the above composition formula, z is 13.0 or more and 13.4 or less, and preferably 13.0 or more and 13.2 or less. As will be described later, in order to appropriately control the hydrogen storage capacity and hydrogen concentration distribution in the present invention, the (La, R)MSi phase and the (La, R)５ M ３ Phase, (La, R) ６ M １１ Si ３ Phase, (La, R) ２ M １７ Since the volume fraction of the RM phase and its hydride phase (where M is one or more elements selected from Fe and TM) must be equal to or less than a certain value, z must be 13.0 or more. Also, if z exceeds 13.4, the RM responsible for the magnetocaloric effect may not be fully utilized. １３ H ｘ Since the amount of phase is reduced, the volumetric output of the magnetic refrigeration material is reduced.

[0022] Note that Fe is the balance of TM, Si, and A. In addition to the elements described above, the inclusion of unavoidable impurities such as oxygen, nitrogen, and carbon is permitted, but the content thereof is preferably as low as possible.

[0023] The raw alloy for magnetic refrigeration material of the present invention is NaZn １３ (La, R) (Fe, TM, Si, A) type crystal structure １３ The volume ratio of the main phase is the remainder of the subphases described below.

[0024] The raw alloy for a magnetic refrigeration material of the present invention contains the (La, R)MSi phase and the (La, R) ５ M ３ Phase, (La, R) ６ M １１ Si ３ phase, and (La, R) ２ M １７ The magnetic refrigeration material contains at least one of the subphases, the total amount of which is 0.3 vol% or less. Here, M is one or more elements selected from Fe and TM. If the subphases are contained in an amount exceeding this amount, microcracks will occur originating from the subphases during the hydrogenation heat treatment described below, causing the magnetic refrigeration material to be crushed. This increases the hydrogen absorption and desorption capabilities of the magnetic refrigeration material, making it more likely to absorb hydrogen in a hydrogen atmosphere and more likely to desorb hydrogen in a non-hydrogen atmosphere during the cooling process during the hydrogenation heat treatment. This makes it difficult to appropriately control hydrogen absorption and hydrogen concentration distribution during the hydrogenation heat treatment.

[0025] The volume ratio of the α-Fe phase is 0.1% or more and 2.2% or less. The α-Fe phase does not occlude hydrogen and has high toughness, so it is thought to suppress microcracks caused by the subphase containing R described above. For this reason, it is preferable to include the α-Fe phase in the magnetic refrigeration material. However, if the volume ratio of the α-Fe phase exceeds 2.2%, the amount of the main phase responsible for the magnetocaloric effect decreases, which is not appropriate because it reduces the volumetric output of the obtained magnetic refrigeration material.

[0026] The average circular diameter of the α-Fe phase is 6 μm or less. The average circular diameter is obtained by binarizing 20 SEM photographs, taking advantage of the contrast difference due to the composition, calculating the number and area of ​​the α-Fe phase, and then calculating the average diameter assuming the α-Fe phase is circular. The α-Fe phase contributes to improving the toughness of the material, but to do so, it must be appropriately dispersed within the raw alloy for the magnetic refrigeration material. If the average circular diameter of the α-Fe phase exceeds 6 μm, the α-Fe phase will not be appropriately dispersed, resulting in poor toughness of the material. This will cause microcracks to occur within the magnetic refrigeration material, making it difficult to appropriately control the hydrogen storage capacity and hydrogen concentration distribution during hydrogenation heat treatment. The lower limit of the range of the average circular diameter of the α-Fe phase is not particularly limited, but is, for example, 0.1 μm.

[0027] The composition analysis and volume fraction calculation of the main phase, subphase, and α-Fe described above can be performed using an SEM. Specifically, 20 photographs taken with the SEM are binarized using the contrast difference due to the composition, and the area of ​​each phase is calculated for each photograph. The area fraction of each phase is then calculated for each photograph, and the average value of the area fractions of each phase for the 20 photographs is taken as the volume fraction of each phase.

[0028] As will be described later, a magnetic refrigeration material can be obtained by hydrogenating the magnetic refrigeration material alloy of the present invention. However, if there is no need to increase the magnetic transition temperature, the magnetic refrigeration material alloy of the present invention can be used as is for the desired application.

[0029] The magnetic refrigeration material of the present invention can be obtained by subjecting the above-mentioned raw alloy for the magnetic refrigeration material to the hydrogenation heat treatment described below. （１－ａ） R ａ (Fe （１－ｂ－ｃ－ｄ） TM ｂ Si ｃ A ｄ ) ｚ H ｅ (R is one or more rare earth elements selected from Ce, Pr, and Nd; TM is one or more elements selected from Co, Mn, Ni, Nb, W, Ta, Cr, Cu, and Ag; A is one or more elements selected from Al, Ga, P, Ge, Sn, and In, and satisfy the following conditions: 0≦a≦0.5, 0≦b≦0.03, 0.09≦c≦0.14, 0≦d≦0.05, 0<e≦1.5, 13.0≦z≦13.4), and the (La,R)MSi phase, (La,R) ５ M ３ Phase, (La, R) ６ M １１ Si ３ Phase, (La, R) ２ M １７ phase and at least one of their hydride phases (M is one or more elements selected from Fe and TM) in a total amount of 0.3 vol% or less as subphases containing R, and α-Fe phase in an amount of 0.1 vol% to 2.2 vol%, with the balance being (La, R)(Fe, TM, Si, A). １３ H ｅ The magnetic refrigeration material contains the phase as the main phase.

[0030] The magnetic refrigeration material of the present invention is used in a hydrogenated state in order to raise the transition temperature. When hydrogenated, the magnetic refrigeration material as a whole can theoretically occlude up to 3.0 atomic % of hydrogen, but under atmospheric pressure, it can usually occlude approximately 1.5 atomic % or less of hydrogen. When using the magnetic refrigeration material at room temperature, it is generally used in a hydrogenated state in order to raise the transition temperature.

[0031] In the above composition formula, e is greater than 0 and is equal to or less than 1.5. As mentioned above, it is necessary to change e together with b depending on the transition temperature required for the magnetic refrigeration material. However, if e exceeds 1.5, the RM１３ H Ｘ This is not practical because the phase becomes unstable and hydrogen is released from the material over time.

[0032] The amount of hydrogen contained in the magnetic refrigeration material can be determined by the following method. The hydrogen concentration contained in the magnetic refrigeration material of the present invention is approximately 1000 to 2000 ppm, but it is generally difficult to measure a difference in hydrogen concentration of several tens of ppm for a material with a hydrogen concentration of several thousand ppm. Therefore, the amount of hydrogen can be estimated by the following method and used as the amount of hydrogen in the magnetic refrigeration material. Specifically, an alloy with the same composition and homogenization conditions is subjected to an activation treatment in which heat is treated in a vacuum, after which hydrogen is introduced and subjected to a hydrogenation heat treatment under specified heat treatment conditions. After that, the alloy is cooled to room temperature while maintaining the hydrogen atmosphere to prepare a comparison sample. This sample is considered to have a saturated hydrogen content at room temperature, and its hydrogen equivalent is set to 1.5. The transition temperatures T ｐｅａｋ The change in T ｐ＿ｍａｘ is measured by the method described below, and then the transition temperature T ｐｅａｋ After measuring, T ｐ＿ｍａｘ The hydrogen equivalent can be estimated from the ratio of

[0033] The above-mentioned T ｐｅａｋ The mT characteristic of the sample is measured using, for example, the VSM unit of a small refrigerant-free physical property measuring device (manufactured by Quantum Design Co., Ltd., product name "VersaLab"), and the transition temperature is determined by temperature differentiation of the mT characteristic to determine the dm / dT-T characteristic, and the temperature at which the peak is obtained is called T. ｐｅａｋ It can be calculated as:

[0034] Next, a raw material alloy for a magnetic refrigeration material and a method for manufacturing the magnetic refrigeration material of the present invention will be described. The raw material alloy for a magnetic refrigeration material and a method for manufacturing the magnetic refrigeration material of the present invention are used to manufacture the above-mentioned magnetic refrigeration material, and include a melting step in which raw materials are melted to obtain a raw material alloy containing La, Fe, and Si, a homogenization step in which the obtained raw material alloy is heat-treated to obtain a raw material alloy for a magnetic refrigeration material with a predetermined structure, and a hydrogenation heat treatment step in which hydrogen is absorbed into the alloy as needed to raise the magnetic transition temperature.

[0035] In the melting process, the metals or alloys that will be used as raw materials for each element are weighed so as to obtain the composition of the raw material alloy for magnetic refrigeration material of the present invention described above. The raw materials are heated to 1500°C by high-frequency melting in an Ar atmosphere, for example, and melted. The alloy is then obtained by cooling as rapidly as possible at a cooling rate of 300 to 1000°C / sec. Although there are no particular limitations on the casting of this alloy, strip casting or liquid quenching can be applied. Strip casting allows for rapid cooling, making it easy to obtain a fine and favorable structure. Liquid quenching allows for even faster cooling, making it easy to obtain an even finer and favorable structure. In this way, a raw material alloy having the desired composition can be obtained.

[0036] In the homogenization process, the raw alloy obtained in the melting process is subjected to heat treatment to homogenize the structure. This homogenization process is not particularly limited, as it depends on the alloy structure and composition. For example, it can be performed in a vacuum or inert gas atmosphere at a temperature ranging from 1100°C to 1300°C. In particular, as described above, when a portion of the La is substituted with a rare earth element, the optimal heat treatment temperature for the homogenization process changes. For example, when a portion of the La is substituted with Ce, the temperature tends to vary by approximately −10 to −20°C compared to the unsubstituted case, and when substituted with Pr or Nd, the temperature tends to vary by approximately +10 to +30°C. In addition, the temperature also varies by several tens of degrees depending on the amount of Si and the type and amount of element substituting a portion of the Fe element. For example, when the Si content is low, the decomposition temperature decreases, and the optimal heat treatment temperature tends to decrease. Therefore, the optimal heat treatment temperature is not limited to the above range. The optimum heat treatment temperature is the temperature at which the magnetocaloric effect is maximized, i.e., the peak value of the dm / dT-T characteristic is maximized, and can be experimentally confirmed taking the above factors into consideration. The homogenization treatment time can be appropriately adjusted depending on the state of the alloy obtained in the melting step, and can be performed for example in the range of 1 hour to 100 hours, and more preferably in the range of 25 hours to 75 hours. Within this range, the amount of subphase containing rare earth elements (R), especially R, can be controlled. ５ A ３The amount of the α-Fe phase and the amount of α-Fe can be controlled within optimal ranges. Furthermore, the homogenization treatment is preferably performed in an Ar atmosphere to prevent deviation from the initial composition due to evaporation of specific elements from the raw alloy. The raw alloy for magnetic refrigeration materials of the present invention can be obtained by this homogenization treatment process.

[0037] In the hydrogenation heat treatment step, the magnetic transition temperature of the resulting magnetic refrigeration material alloy is increased by absorbing hydrogen into the magnetic refrigeration material alloy in a hydrogen atmosphere, thereby obtaining the magnetic refrigeration material of the present invention. While specific conditions are not particularly limited, the hydrogen atmosphere can be, for example, 0.1 to 0.25 MPa. Furthermore, the hydrogenation temperature can be, for example, 200°C or higher and 500°C or lower. This range allows the hydrogen saturation concentration at the treatment temperature to be reached in a relatively short time. The hydrogenation treatment time can be, for example, 1 hour to 200 hours, and more preferably 3 hours to 10 hours. After hydrogen introduction, the alloy is cooled to room temperature. By cooling at a rate of 50°C / min or lower in an inert, non-hydrogen atmosphere, such as a hydrogen atmosphere or an Ar atmosphere, the hydrogen absorption amount and hydrogen concentration distribution can be controlled. Specifically, cooling at a rate of 0.1°C / min to 50°C / min after the hydrogenation heat treatment is preferred. It is known that the faster the cooling rate after hydrogenation, the more accurately the amount of hydrogen absorption can be controlled, but in consideration of productivity, the cooling rate must be 50°C / min or less. If the cooling rate is slower than 0.1°C / min, hydrogen absorption or release during cooling may become significant.

[0038] EXAMPLES The present invention will be explained in more detail below with reference to examples and comparative examples, but the present invention is not limited to these examples.

[0039] [Examples 1 to 3, Comparative Examples 1 to 4] La metal, Ce metal, Mn metal, Si metal, and electrolytic iron were weighed to obtain a predetermined composition, and the materials were melted in an Ar gas atmosphere in a high-frequency melting furnace by heating to 1500°C. The materials were then strip-cast to produce alloy ribbons with an average thickness of approximately 300 μm by cooling at a rate of 300 to 1000°C / sec. The compositions of the obtained raw alloys for magnetic refrigeration materials are shown in Table 1. The alloy compositions were analyzed using a high-resolution ICP optical emission spectrometer (manufactured by Hitachi High-Tech Corporation, product name "SPS3500DD").

[0040]

[0041] The alloys of Examples 1 to 3 and Comparative Examples 1 to 4 were homogenized in an Ar atmosphere at the optimal homogenization conditions of 1115°C for 50 hours to obtain alloys for magnetic refrigeration materials. The volume ratios of the subphases and α-Fe contained in the alloys for magnetic refrigeration materials, as well as the main phase composition and subphase composition, were then analyzed using a scanning electron microscope (SEM) (manufactured by JEOL Corporation, product name "JSM-IT300LV"). The volume ratios were obtained by performing image analysis on 20 captured SEM images. The main phase and subphase compositions were analyzed using EDS. The subphase amounts, α-Fe phase amounts, and average circular approximation diameters of the α-Fe phase for each alloy are shown in Table 2. Example structural photographs are shown in Figure 1 for Comparative Example 1 and Figure 2 for Example 3.

[0042]

[0043] The resulting alloy for magnetic refrigeration was subjected to the following hydrogenation heat treatment. First, activation treatment was performed in a vacuum at 500°C for 2 hours. After hydrogen was introduced at 0.15 MPa, hydrogen was introduced and hydrogenation heat treatment was performed at 200°C for 24 hours. After hydrogenation heat treatment, the alloy was cooled to room temperature at a cooling rate of 0.1°C / min while maintaining the hydrogen atmosphere, yielding a magnetic refrigeration material. The composition after hydrogenation is shown in Table 3. The hydrogen content in the alloy was determined using the following method. The hydrogen concentration of this material was approximately 1000-2000 ppm. However, since it is difficult to measure a difference in hydrogen concentration of tens of ppm compared to a material with a hydrogen concentration of several thousand ppm, the hydrogen content was estimated using the following method. First, as a comparison sample, an alloy with the same composition and homogenization conditions was activated in a vacuum at 500°C for 2 hours, then hydrogen was introduced at 0.15 MPa, hydrogenation heat treatment was performed at 500°C for 2 hours, and then cooled to room temperature over 60 hours while maintaining the hydrogen atmosphere. This sample was considered to have a saturated hydrogen content at room temperature, and the hydrogen equivalent was set to 1.5. The transition temperature T ｐｅａｋ The change in T ｐ＿ｍａｘ The transition temperature T ｐｅａｋ After measuring, T ｐ＿ｍａｘ The hydrogen equivalent was estimated from the ratio of

[0044] The mT characteristics of the obtained magnetic refrigeration material were then measured using the VSM unit of a small cryogen-free physical property measuring device (manufactured by Quantum Design Co., Ltd., product name "VersaLab"). The transition temperature was determined by temperature differentiation of the mT characteristics to determine the dm / dT-T characteristics, and the temperature at which the dm / dT-T characteristics peaked was designated as T. ｐｅａｋ The results of the mT characteristic measurements are shown in FIG.

[0045]

[0046]

[0047] In Comparative Examples 1 and 2, the transition temperature is high at around 306 K, and the amount of hydrogen absorption cannot be controlled appropriately. This is thought to be because the amount of subphases is large, which causes frequent microcracks, and the magnetic refrigeration material is pulverized, causing hydrogen absorption during cooling. Comparative Example 3 has a transition temperature of 294 K, but as shown in Figure 3, it has multiple transition points with multiple stages. This is because the hydrogen concentration distribution within the material is uneven, and it is difficult to obtain RM with multiple hydrogen concentrations. １３ H ｘ This is due to the presence of the α-Fe phase. This is thought to be because the amount of subphases caused microcracks to occur in parts of the alloy, which was crushed into various particle sizes and absorbed hydrogen unevenly. In addition, in Comparative Example 4, the transition temperature was well controlled, but the dm / dT was low. This is because the amount of α-Fe phase in the material was large, which was the reason for the RM １３ H ｘ This is thought to be because the total amount of phases decreased, resulting in a decrease in the total amount of magnetocaloric effect. In Examples 1 to 3, the transition temperature was about 291 K and dm / dT was 0.02 or more, which was favorable, and it can be judged that the control of the hydrogen absorption amount and the homogenization of the hydrogen concentration distribution were performed well.

[0048] Separately from the above, the obtained alloy for magnetic refrigeration material was subjected to the following hydrogenation heat treatment. First, activation treatment was performed in a vacuum at 500°C for 2 hours, and then 0.15 MPa of hydrogen was introduced and hydrogenation heat treatment was performed at 200°C for 24 hours. After the hydrogenation heat treatment, the hydrogen was evacuated and the alloy was cooled to room temperature in a non-hydrogen atmosphere (Ar atmosphere) at a cooling rate of 50°C / min. The composition at this time is shown in Table 5. The mT characteristics of the obtained magnetic refrigeration material were then evaluated using the same method. The results of this mT characteristic measurement are shown in Figure 4 and Table 6.

[0049]

[0050]

[0051] In Comparative Examples 1 and 2, the transition temperature of the mT curve is unclear and the maximum value of dm / dT is low. This is thought to be due to the non-uniform distribution of hydrogen concentration within the material, but the cause is the RM due to the crushing of the alloy caused by the generation of microcracks during hydrogenation. １３ H ｘThis is thought to be because the reactivity of the phase was improved, resulting in increased hydrogen release in a non-hydrogen atmosphere. Examples 1 to 3 and Comparative Examples 3 and 4 gave good results.

[0052] [Examples 4 and 5, Comparative Example 5] La metal, Ce metal, Si metal, and electrolytic iron were weighed to obtain a predetermined composition, and the materials were melted in an Ar gas atmosphere in a high-frequency melting furnace by heating to 1500°C. The materials were then cooled at a rate of 300 to 1000°C / sec by strip casting to produce alloy ribbons with an average thickness of about 300 μm. The composition of the resulting raw alloy for magnetic refrigeration material was as follows: ０．７ Ce ０．３ ) (Fe ０．８９５ Si ０．１０５ ) １３．０ The composition of the alloy was analyzed using a high-resolution ICP optical emission spectrometer (manufactured by Hitachi High-Tech Corporation, product name "SPS3500DD").

[0053] The resulting magnetic refrigeration material alloys were subjected to homogenization treatment in an Ar atmosphere at 1130°C, 1140°C, and 1150°C for 50 hours, respectively, to obtain magnetic refrigeration material alloys. The subphase and α-Fe volume ratios, main phase composition, and subphase composition contained in the magnetic refrigeration material alloys were then analyzed using a scanning electron microscope (SEM) (manufactured by JEOL Corporation, product name "JSM-IT300LV"). The volume ratios were obtained by performing image analysis on 20 captured SEM images. The main phase and subphase composition were analyzed using EDS. The subphase amount, α-Fe phase amount, and average circular approximate diameter of the α-Fe phase for each alloy are shown in Table 7. Example microstructure photographs are shown in Figure 5 for Comparative Example 5, Figure 6 for Example 4, and Figure 7 for Example 5.

[0054]

[0055] The obtained alloy for magnetic refrigeration material was subjected to the following hydrogenation heat treatment. First, activation treatment was performed in a vacuum at 500°C for 2 hours, and then hydrogen of 0.15 MPa was introduced and hydrogenation treatment was performed at 250°C for 24 hours. After the hydrogenation heat treatment, the hydrogen was evacuated and then cooled to room temperature in a non-hydrogen atmosphere (Ar atmosphere) at a cooling rate of 50°C / min. The composition obtained at this time was (La ０．７ Ce ０．３ ) (Fe０．８９５ Si ０．１０５ ) １３．０ H １．２３ The mT characteristics of the obtained magnetic refrigeration material were then evaluated using the same method. The results of the mT characteristic measurements are shown in Figure 8 and Table 8. For reference, the results of the mT measurements of the alloy before hydrogenation are shown in Figure 9.

[0056]

[0057] The mT curves before hydrogenation were almost the same, but the dm / dT after hydrogenation was higher in Example 4 than in Comparative Example 5. This is thought to be because the amounts of the subphase and the α-Fe phase were controlled within appropriate ranges, suppressing crushing due to microcracks and achieving a uniform hydrogen concentration distribution. In Example 5, the amounts of the subphase and the α-Fe phase satisfied the specified ranges, but the average circular approximation diameter of the α-Fe phase was 15.3 μm, which was large, making it impossible to achieve appropriate dispersion of the α-Fe phase. As a result, the hydrogen concentration distribution became non-uniform, and the dm / dT was lower than in Example 4.

Claims

1. La （１－ａ） R ａ (Fe （１－ｂ－ｃ－ｄ） T.M. ｂ S ｃ A ｄ ) ｚ (R is one or more rare earth elements selected from Ce, Pr, and Nd; TM is one or more elements selected from Co, Mn, Ni, Nb, W, Ta, Cr, Cu, and Ag; A is one or more elements selected from Al, Ga, P, Ge, Sn, and In, and satisfies 0≦a≦0.5, 0≦b≦0.03, 0.09≦c≦0.14, 0≦d≦0.05, and 13.0≦z≦13.4), and is represented by the composition formula of (La,R)MSi phase, (La,R) ５ M ３ Phase, (La, R) ６ M １１ S ３ phase, and (La, R) ２ M １７ At least one of the phases (wherein M is one or more elements selected from Fe and TM) is contained as a subphase containing R in a total amount of 0.3 vol% or less, the α-Fe phase is contained in an amount of 0.1 vol% to 2.2 vol%, and the balance is (La, R)(Fe, TM, Si, A). １３ A raw material alloy for magnetic refrigeration containing the phase as the main phase.

2. A raw alloy for a magnetic refrigeration material according to claim 1, wherein the average circular approximation diameter of the α-Fe phase is 6 μm or less.

3. La （１－ａ） R ａ (Fe （１－ｂ－ｃ－ｄ） T.M. ｂ S ｃ A ｄ ) ｚ 3. A method for producing a raw alloy for a magnetic refrigeration material according to claim 1 or 2, comprising heat treating an alloy represented by a composition formula of: (R is one or more rare earth elements selected from Ce, Pr, and Nd; TM is one or more elements selected from Co, Mn, Ni, Nb, W, Ta, Cr, Cu, and Ag; and A is one or more elements selected from Al, Ga, P, Ge, Sn, and In, and satisfying 0≦a≦0.5, 0≦b≦0.03, 0.09≦c≦0.14, 0≦d≦0.05, and 13.0≦z≦13.4) at 1000 to 1300° C. for 10 to 100 hours in a vacuum atmosphere or an inert gas atmosphere.

4. La （１－ａ） R ａ (Fe （１－ｂ－ｃ－ｄ） T.M. ｂ S ｃ A ｄ ) ｚ H ｅ (R is one or more rare earth elements selected from Ce, Pr, and Nd; TM is one or more elements selected from Co, Mn, Ni, Nb, W, Ta, Cr, Cu, and Ag; A is one or more elements selected from Al, Ga, P, Ge, Sn, and In, and satisfies 0≦a≦0.5, 0≦b≦0.03, 0.09≦c≦0.14, 0≦d≦0.05, 0<e≦1.5, and 13.0≦z≦13.4), and is represented by the composition formula of (La,R)MSi phase, (La,R) ５ M ３ Phase, (La, R) ６ M １１ S ３ Phase, (La, R) ２ M １７ phase, and at least one of the hydride phases thereof (M is one or more elements selected from Fe and TM) in a total amount of 0.3 vol% or less as a subphase containing R, α-Fe phase in an amount of 0.1 vol% to 2.2 vol%, and the balance being (La, R)(Fe, TM, Si, A). １３ H ｅ A magnetic refrigeration material containing the phase as a main phase.

5. The magnetic refrigeration material according to claim 4, wherein the average circular approximation diameter of the α-Fe phase is 6 μm or less.

6. La （１－ａ） R ａ (Fe （１－ｂ－ｃ－ｄ） T.M. ｂ S ｃ A ｄ ) ｚ (R is one or more rare earth elements selected from Ce, Pr, and Nd; TM is one or more elements selected from Co, Mn, Ni, Nb, W, Ta, Cr, Cu, and Ag; A is one or more elements selected from Al, Ga, P, Ge, Sn, and In, and satisfies 0≦a≦0.5, 0≦b≦0.03, 0.09≦c≦0.14, 0≦d≦0.05, and 13.0≦z≦13.4), and is represented by the composition formula of (La,R)MSi phase, (La,R) ５ M ３ Phase, (La, R) ６ M １１ S ３ phase, and (La, R) ２ M １７ At least one of the phases (wherein M is one or more elements selected from Fe and TM) is contained as a subphase containing R in a total amount of 0.3 vol% or less, the α-Fe phase is contained in an amount of 0.1 vol% to 2.2 vol%, and the balance is (La, R)(Fe, TM, Si, A). １３ 6. The method for producing a magnetic refrigeration material according to claim 4, wherein the alloy containing the phase as a main phase is subjected to a hydrogenation heat treatment at a cooling rate of 0.1° C. / min to 50° C. / min.