alloy

Abstract

To provide an alloy containing boron with a high magnetocaloric effect. 【Solution means】The present invention is an alloy represented by the composition formula of RE(M 1-x A x ) y X z H w where x, y, z, and w satisfy 0.08 ≦ x ≦ 0.13, 12.3 ≦ y ≦ 13.2, 0.005 ≦ z ≦ 0.25, 0 ≦ w ≦ H sat (H sat is the saturation hydrogen amount at room temperature), RE is one or more elements selected from rare earth elements and Zr, with La being essential, M is one or more elements selected from Fe, Co, Mn, Ni, Nb, W, Ta, Cr, Cu, Ag, and Ti, with Fe being essential, A is one or more elements selected from Si, Al, Ga, P, Ge, Sn, and In, with Si being essential, X is one or more elements selected from B, C, and N, with B being essential, and NaZn 13 type crystal structure main phase and a secondary phase containing the RE2Fe 14 X phase, and when the Si concentration in the main phase is Si 1-13 and the Si concentration in the RE2Fe 14 X phase is Si 2-14-1 , then Si 1-13 / Si 2-14-1 ≦ 1.2.

Description

Technical Field

[0001] The present invention relates to an alloy for magnetic refrigeration in which the magnetic transition temperature is controlled while maintaining performance by adding B.

Background Art

[0002] In conventional gas compression / expansion type heat pumps, the use of CFCs, which are ozone-depleting substances, has been prohibited, and currently HFCs are mainly used. However, the problem is that HFCs have a high global warming potential. Although the development of refrigerants with a low global warming potential is being actively carried out, no new refrigerant that satisfies performance, cost, and safety has been put into practical use. Under such circumstances, magnetic refrigeration systems using the magnetocaloric effect without using greenhouse gases have attracted attention.

[0003] Magnetic refrigeration systems utilize the change in magnetic entropy (magnetocaloric effect, ΔS). As materials with a large absolute value of ΔS, there are Mn(As 1-x Sb x )(Patent Document 1) and La(Fe 1-x Si x ) 13 H Z (Patent Document 2), etc. In particular, the former has a very large ΔS of -30 J / kgK and can be an excellent magnetic refrigeration material. However, since As in the components of Mn(As 1-x Sb x ) shows toxicity, it is substantially difficult to apply. La(Fe 1-x Si x ) 13 H Z has a ΔS of ~25 J / kgK, which is large next to Mn(As 1-x Sb x ), and since its constituent elements do not show toxicity and it is not a rare metal, it is the most promising substance.

[0004] These materials are required to operate near room temperature (around -70 to +70°C). However, unlike conventional magnetic refrigeration, which has been used as a means to generate extremely low temperatures that are difficult to achieve with gas refrigeration, there was a problem that the magnetocaloric effect decreased at the above operating temperature because lattice vibrations could not be ignored. With the development of AMR (Active Magnetic Regenerator), which utilizes these lattice vibrations as a heat storage effect, refrigeration and air conditioning systems that utilize the magnetocaloric effect at near room temperature have become a reality.

[0005] When applying magnetic refrigeration materials to AMR systems operating near room temperature, it is necessary to adjust the magnetic phase transition temperature (Tc) to be near room temperature. (La(Fe) 1-x Si x ) 13 H Z In this case, by absorbing hydrogen, the Tc can be raised from approximately -80°C to approximately 60°C with almost no decrease in ΔS. Furthermore, as reported in Non-Patent Literature 1, by adjusting the amount of hydrogen absorbed, the Tc can be controlled within the above temperature range, making it possible to produce a material with a Tc adjusted to near room temperature.

[0006] Furthermore, methods for adjusting Tc include partial substitution of Fe with Mn (Non-Patent Literature 2) or Co (Non-Patent Literature 3). According to this method, adding Mn lowers Tc, while adding Co increases Tc. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] Japanese Patent Publication No. 2003-28532 [Patent Document 2] Japanese Patent Publication No. 2006-89839 [Non-patent literature]

[0008] [Non-Patent Document 1] PHYSICAL REVIEW B 67, 104416 (2003) [Non-Patent Document 2] Journal of Alloys and Compounds 950 (2023) 169883 [Non-Patent Document 3] Journal of Alloys and Compounds 765 (2018) 538-543 [Overview of the project] [Problems that the invention aims to solve]

[0009] Non-patent document 3 shows that Tc can be reduced by adding a small amount of B, suggesting that B addition, like partial substitution of Fe with Mn, Co, etc., is a possible method for adjusting Tc. However, as shown in Non-Patent Document 3, there is a problem in that ΔS decreases along with Tc when B is added. Furthermore, the magnitude of this decrease is greater than the magnitude of the decrease in ΔS per unit of the decrease in Tc when Mn is added, so adjusting Tc by adding B has not been generally practiced until now.

[0010] This invention has been made in view of the above circumstances, and aims to provide an alloy that suppresses the deterioration of performance due to the addition of B. [Means for solving the problem]

[0011] The inventors of the present invention conducted diligent studies to achieve the above objectives and discovered that a B-added alloy having a predetermined composition and in which the elemental concentrations in the microstructure satisfy a specific relationship can suppress the deterioration of properties and become a high-performance alloy, thus completing the present invention.

[0012] Therefore, the present invention provides the following alloys. [1] RE(M 1-x A x ) y X z H wAn alloy represented by the following compositional formula, where x, y, z, and w are 0.08≦x≦0.13, 12.3≦y≦13.2, 0.005≦z≦0.25, and 0≦w≦H, respectively. sat (H sat (where is the amount of saturated hydrogen at room temperature), RE is one or more elements selected from rare earth elements and Zr, and La is required, M is one or more elements selected from Fe, Co, Mn, Ni, Nb, W, Ta, Cr, Cu, Ag and Ti, and Fe is required, A is one or more elements selected from Si, Al, Ga, P, Ge, Sn and In, and Si is required, X is one or more elements selected from B, C and N, and B is required, NaZn 13 Main phase of the crystal structure and RE2Fe 14 The main phase comprises a subphase containing the X phase, and the Si concentration in the main phase is Si 1-13 , RE2Fe 14 The Si concentration in the X phase is Si 2-14-1 When that happens, Si 1-13 / Si 2-14-1 Alloys with a coefficient ≤ 1.2. [2] The amount of B contained in X is z B , the amount of C is z C , the amount of N is z N Let z = z B +z C +z N When z B The alloy described in [1] above, wherein the ratio is 0.005 or greater. [3]z B While keeping the composition the same except for the value of z B Let c0 be the lattice constant when z = 0. B While keeping the composition the same except for the value of z B When the lattice constant is set to >0, c B In that case, c B The alloy described in [2] above, such that c0 ≤ c0. [4] The alloy described in any one of [1] to [3] above, wherein the α-Fe phase content is 6 volume% or less. [5] RE2Fe 14 An alloy according to any one of the above [1] to [4], wherein the volume fraction of the X phase is 0.01% or more and 6% or less. [Effects of the Invention]

[0013] According to the present invention, a B-added alloy with a high magnetocaloric effect can be provided. [Brief explanation of the drawing]

[0014] [Figure 1] Figure 1 is a graph showing the amount of B added and the latent heat of the magnetic phase transition of FP for Comparative Examples 1 and 2 and Examples 1 to 4. [Figure 2] Figure 2 is a graph showing the change in Tc with respect to zB for Comparative Example 1 and Examples 1-4. [Figure 3] Figure 3 is a graph showing the changes in Si concentration in the RE(Fe,Si)13 phase and RE2Fe14X phase when composition 3 is subjected to homogenization treatment at different temperatures for 45 hours. [Figure 4] Figure 4 is a graph showing the dm / dT-T characteristics of Example 5 and Comparative Example 3. [Figure 5] Figure 5 is a graph showing the dm / dT-T characteristics of Example 6 and Comparative Example 4. [Figure 6] Figure 6 is a graph showing the dm / dT-T characteristics of Example 7 and Comparative Example 5. [Figure 7] Figure 7 is a graph showing the progress of splitting when Comparative Example 1 and Examples 1 and 2 were held in a constant temperature bath set to the transition temperature of each sample. [Figure 8] Figure 8 is a graph showing the progress of splitting when Comparative Examples 6-7 and Examples 8-9 were held in a constant temperature bath set to the transition temperature of each sample. [Figure 9] Figure 9 is a graph showing the progress of splitting when Comparative Example 8 and Examples 10-12 were held in a constant temperature bath set to the transition temperature of each sample. [Figure 10] Figure 10 is a graph showing the change in the amount of B added and the lattice constant of the main phase for Comparative Example 1 and Examples 1-4. [Modes for carrying out the invention]

[0015] The alloy of the present invention is RE(M 1-xA x ) y X z H w An alloy represented by the following compositional formula, where x, y, z, and w are 0.08≦x≦0.13, 12.3≦y≦13.2, 0.005≦z≦0.25, and 0≦w≦H, respectively. sat (H sat The alloy of the present invention satisfies the saturation hydrogen content at room temperature. 13 Main phase of the crystal structure and RE2Fe 14 It includes a subphase containing the X phase. Furthermore, the Si concentration in the main phase is Si 1-13 RE2Fe 14 The Si concentration in the X phase is Si 2-14-1 When that happens, Si 1-13 / Si 2-14-1 The value is ≤ 1.2.

[0016] RE is one or more elements selected from rare earth elements and Zr, with La being essential, and may also contain one or more elements selected from Nd, Ce, and Pr. This allows for control of the magnetic phase transition temperature and other parameters.

[0017] When elements other than La are present in RE, homogenization becomes more difficult as the amount of substitution increases. Ce can be contained in up to 40 atomic percent or less of the total RE, Pr in up to 60 atomic percent or less of the total RE, and Nd in up to 40 atomic percent or less of the total RE. This lowers the magnetic phase transition temperature, increases ΔS, and increases hysteresis. The maximum content of RE elements other than La is also affected by the values ​​of x and z; the smaller x and the larger z, the smaller the maximum content. Furthermore, some of the RE in the subphase can be substituted with one or more elements selected from rare earth elements and Zr.

[0018] M is one or more elements selected from the group consisting of Fe, Co, Mn, Ni, Nb, W, Ta, Cr, Cu, Ag, and Ti, with Fe being essential. If M contains elements other than Fe, the magnetic phase transition temperature, full width at half maximum, hysteresis, etc. of the magnetic refrigeration material can be controlled in the same way as above. If M contains Mn, it can be included in a range of 4 atomic percent or less of the total M. By including it within this range, the magnetic phase transition temperature can be lowered. Furthermore, some of the Fe in the subphase can be replaced with one or more elements selected from the group consisting of Co, Mn, Ni, Nb, W, Ta, Cr, Cu, Ag, and Ti.

[0019] A is one or more elements selected from the group consisting of Si, Al, Ga, P, Ge, Sn, and In, with Si being essential. Even if A contains elements other than Si, the magnetic phase transition temperature, full width at half maximum, hysteresis, etc., can be controlled. If A contains Al, it can be substituted for the essential element Si in an amount of 0 to 50 atomic percent. Within this range, the magnetic phase transition temperature can be lowered, and the hysteresis can be further reduced. The larger x is, and the higher the Si concentration in A, the larger the maximum content of RE elements other than La and the maximum content of X can be. Furthermore, some of the Si in the subphase can be replaced with one or more elements selected from the group consisting of Al, Ga, P, Ge, Sn, and In.

[0020] In the above composition, X is one or more elements selected from the group consisting of B, C, and N, with B being essential. X may also contain at least one element of C and N. C and N are inevitably present due to raw material origins or adsorption and reactions during the manufacturing process, but they may be intentionally added within the range of z described later.

[0021] In the above composition, x is between 0.08 and 0.13. If x is less than 0.08, the stability of the main phase decreases, making homogenization difficult, and the formation of heterogeneous phases degrades the properties. As x increases, the stability of the main phase increases, but the first-order phase transition tends to weaken, causing ΔS to decrease. Therefore, if x is greater than 0.13, the performance degradation becomes too great.

[0022] In the above composition, y is between 12.3 and 13.2. By changing y from the symmetric ratio of the main phase (13.0) to produce alloys, the hydrogen storage behavior can be controlled. However, if y is less than 12.3 or greater than 13.2, the proportion of the main phase decreases, resulting in a decrease in properties. For this reason, y is preferably 12.7 or higher. Furthermore, y is preferably 13.1 or lower.

[0023] For the above composition, z is between 0.005 and 0.25. When the amount of hydrogen absorbed by the alloy is less than the saturation hydrogen amount (0 <w<H sat In the case of ), it is known that if the magnetic phase transition temperature is maintained for a long period of time, a phenomenon called split occurs in which the magnetic phase transition occurs at multiple temperatures. If z is less than 0.005 or greater than 0.25, the split progression cannot be effectively suppressed. Also, if z is less than 0.005 or greater than 0.25, reducing the Tc of the alloy may degrade the magnetic performance of the alloy. From this viewpoint, the z of the above composition is preferably 0.04 or higher, preferably 0.13 or lower, and more preferably 0.08 or lower.

[0024] The amount of B contained in the above X is z B , the amount of C is z C , the amount of N is z N Let z = z B +z C +z N When expressed as, z BThe ratio is preferably 0.005 or higher, more preferably 0.01 or higher. Furthermore, it is preferably 0.25 or lower, more preferably 0.05 or lower, and even more preferably 0.01 or lower. Within this range, the alloy is 0 <w<H sat When hydrogen is absorbed within this range, the split progression is more effectively suppressed, and a high-performance material can be obtained that reduces Tc while suppressing performance degradation.

[0025] The alloy of the present invention has the above composition in which w is 0 or more, H sat The alloy is as follows. The effects of the present invention can be obtained regardless of the presence or absence of hydrogen, therefore w=H sat It may contain hydrogen at or below the (saturation point at room temperature). H sat Although it varies depending on the composition, it is generally considered to be around w = 1.4 to 1.7, and a value of around 1.8 can be said to be a sufficient amount of saturated hydrogen. sat H is the amount of saturated hydrogen at room temperature in each alloy composition. In this invention, H is the amount of hydrogen at which Tc does not rise any further when hydrogen is absorbed at a temperature of 30°C and in a hydrogen atmosphere of 0.10 to 0.25 MPa for at least 5 hours. sat Prior to hydrogen storage treatment, an activation treatment is generally performed, for example, by heat treatment at 300-500°C for 1-2 hours in a vacuum or hydrogen atmosphere.

[0026] When hydrogen is stored in the alloy of the present invention, w <H sat In other words, P H (=w / H sat A split occurs when ) is less than 1. H The smaller the value, the faster the split progresses. P of the alloy of the present invention H The P of the alloy of the present invention is preferably 0.95 or less, more preferably 0.90 or less, and more preferably 0.85 or less. H The lower limit of the range is not particularly limited, but the P of the alloy of the present invention His usually 0.01 or more, preferably 0.10 or more, more preferably 0.50 or more, still more preferably 0.55 or more, even more preferably 0.60 or more, and even more preferably 0.65 or more. Note that P H represents the ratio of the occluded hydrogen amount to H sat and is represented by P H = w / H sat Although not particularly limited, when hydrogen is contained in the alloy, the hydrogen amount w can be measured, for example, by an inert fusion conduction method using an oxygen, nitrogen, and hydrogen analyzer ONH836 manufactured by LECO.

[0027] The alloy of the present invention preferably has a Tc that is 2 K or lower compared to Tc when w = H while keeping the composition other than the value of w the same. Thereby, an alloy with suppressed split can be obtained while sufficiently reducing Tc. From such a viewpoint, the alloy of the present invention preferably has a Tc that is 5 K or lower, more preferably 10 K or lower, and even more preferably 20 K or lower compared to Tc when w = H while keeping the composition other than the value of w the same. sat From such a viewpoint, the alloy of the present invention preferably has a Tc that is 5 K or lower, more preferably 10 K or lower, and even more preferably 20 K or lower compared to Tc when w = H while keeping the composition other than the value of w the same. sat is more preferably 10 K or lower, still more preferably 2 K or lower compared to Tc when w = H while keeping the composition other than the value of w the same.

[0028] The alloy of the present invention sets the lattice constant when z B = 0 while keeping the composition other than the value of z the same as c0, and sets the lattice constant when z B > 0 while keeping the composition other than the value of z the same as c B When this is done, it is preferable that c B ≤ c0. Thereby, a magnetic refrigeration material with suppressed split and high characteristics can be obtained. From such a viewpoint, when the lattice constant at the time when the lattice constant takes the minimum value is c B , it is more preferable that c B ≤ c min ≤ c0. min ≤ c B ≤ c0 is more preferable.

[0029] Generally, it is generally speculated that when light elements such as B, C, and N enter the interstitial sites in a solid solution form, the crystal lattice is expanded and the lattice constant increases monotonically. However, when a small amount of B is added and the addition amount is increased, the lattice constant once decreases, takes a minimum value at a certain point, then reverses and begins to increase. At the same time, Tc also once decreases to the minimum value and then increases. The reason for this is not necessarily clear. In the case of adding a small amount of B, the lattice constant decreases because B replaces, for example, the Fe site in the form of substitutional solid solution. On the other hand, when B is added beyond a certain amount, substitutional solid solution becomes difficult, and B begins to dissolve in the interstitial sites in the form of interstitial solid solution, resulting in an increase in the lattice constant.

[0030] Under the above assumptions, when evaluating the stability of the main phase hydride in the paramagnetic state and ferromagnetic state for three cases: no B solid solution, B substitutional solid solution, and B interstitial solid solution, in the case of substitutional solid solution, the difference in the stability between paramagnetism and ferromagnetism becomes smaller in the entire hydrogen content region, showing a tendency that splitting is more suppressed. In the case of interstitial solid solution, in the low hydrogen concentration region such as below H sat / 2, the difference in the stability between paramagnetism and ferromagnetism is small, showing a tendency that splitting is suppressed. Therefore, it is considered that splitting is suppressed in the region where B is added and the lattice tends to contract, and further in the region where the lattice tends to expand. However, although increasing the addition amount of B can suppress the progress of splitting, if it is increased too much, the amount of formation of the second phase increases and the properties deteriorate. Therefore, it is preferable that the lattice constant when B is added is about below the lattice constant when z B =0.

[0031] The alloy of the present invention includes a main phase having a NaZn 13 type crystal structure and a secondary phase containing a RE2Fe 14 X phase. For example, by adding B as the X element, a RE2Fe 14 X phase can be formed in the alloy as the secondary phase. The alloy of the present invention is RE2Fe 14It is preferable that the alloy contains 0.01% or more of the X phase. This allows for more effective suppression of splitting. Furthermore, the alloy of the present invention is RE2Fe 14 It is preferable that the X phase be present in a volume percentage of 6% or less. This helps to suppress the deterioration of properties due to a decrease in the proportion of the main phase. The method for measuring the volume fraction is not particularly limited, but the volume fraction can be calculated by, for example, using a JSM-IT300LV (manufactured by JEOL Corporation), binarizing the SEM image obtained using the difference in contrast due to composition, calculating the area of ​​each phase, and considering the area fraction as the volume fraction. RE2Fe 14 The reason why the X phase can suppress the progression of the split is not entirely clear, but it can be thought of as follows: When the sample is hydrogenated, not only the main phase but also RE2Fe 14 The X phase can also form hydrides, but when the sample is held directly above Tc where the split is progressing, ferromagnetic and paramagnetic phases RE(Fe,Si) with different hydride stabilities are formed. 13 In addition, there is a third RE2Fe with a different hydride stability. 14 It is presumed that the presence of the hydride in phase X causes the third phase to act as a hydrogen buffer, making it difficult for differences in hydrogen concentration to occur between the ferromagnetic and paramagnetic phases.

[0032] In the field of permanent magnets, RE2Fe 14 It is known that the B phase can have some of its B sites replaced with carbon. In the present invention, carbon, whether due to impurities or intentionally added, is also found in RE2Fe 14 It is thought that the B site of the B phase is being replaced. Therefore, it is inevitably included as an impurity, but even if C is intentionally added as X, RE2Fe 14 It is presumed that the formation of (B,C) is promoted, enhancing the split-suppressing effect.

[0033] As described above, although the reason why the inclusion of X suppresses the progression of splitting is not entirely clear, it is presumed that two factors contribute. The first is the reduction of the difference in stability between the paramagnetic and ferromagnetic phase hydrides due to the solid solution of B in the main phase. The second is the formation of RE2Fe by adding X. 14The X phase acts as a hydrogen buffer, making it difficult for the hydrogen concentration to differ between the ferromagnetic and paramagnetic phases of the main system. It is presumed that these combined effects suppress the progression of the split.

[0034] In the alloy of the present invention, the Si concentration in the main phase is Si 1-13 RE2Fe 14 The Si concentration in X is Si 2-14-1 When that happens, Si 1-13 / Si 2-14-1 The result is ≤ 1.2. Si 1-13 / Si 2-14-1 If the ratio is >1.2, lowering Tc by adding B may result in poor magnetic properties. Subphase is RE2Fe 14 If the X phase is present, changing the homogenization temperature (temperature, time, etc.) will produce RE(Fe,Si). 13 Phase and RE2Fe 14 The amount of Si in the X phase changes, which is due to the change in the constituent phases as the homogenization conditions change, RE2Fe 14 RE(Fe,Si) from phase X 13 This is presumed to be due to the movement of Si into the phase. The main phase is RE(Fe,Si) 13 It is known that as the Si concentration increases, the magnetic phase transition approaches a second-order transition from a first-order transition, causing ΔS and dm / dT to decrease. However, within the above range, B is added to RE2Fe 14 Even in environments where an X phase is formed and the Si concentration changes due to homogenization conditions, it is believed that a material with high magnetic properties can be obtained by suppressing the increase in Si concentration in the main phase. While not particularly limited, the Si concentration in each phase can be measured, for example, by point analysis using EDS with JSM-IT300LV (manufactured by JEOL Corporation).

[0035] In the alloy of the present invention, the α-Fe content is preferably 6% by volume or less, and more preferably 4% by volume or less. By controlling homogenization to fall within this range, a high-performance alloy can be obtained.

[0036] The evaluation of split progression involves changing the hydrogen concentration to H sat For alloys controlled to a certain temperature, the Tc of the alloy is held above the alloy's Tc for a sufficiently long period of time. Measurements used to detect the magnetic phase transition of magnetic refrigerants, such as DSC-T properties by DSC measurement and dm / dT-T properties by VSM measurement, can be evaluated by the temperature difference between each separated magnetic phase transition temperature. A smaller temperature difference indicates a smaller difference in hydrogen concentration in each region and suppressed splitting. The magnetic phase transition temperature is determined by fitting the vicinity of the peak value in each measurement with a quadratic function and using the temperature at which the maximum value is obtained.

[0037] To evaluate the split progression, it is necessary to maintain the state directly above Tc where paramagnetism and ferromagnetism coexist, but RE(Fe,Si) 13 The magnetic phase transition of a phase is fundamentally a first-order phase transition and therefore exhibits temperature hysteresis. The temperature (Tc) changes when the temperature is lowered (a transformation from paramagnetic to ferromagnetic, called the PF transformation) and when the temperature is raised (a transformation from ferromagnetic to paramagnetic, called the FP transformation). It is necessary to pay attention to the direction of the transition when determining the holding temperature. For example, a constant temperature bath is used to control the temperature of a sample. If the sample's Tc is lower than room temperature, when lowering the temperature by placing it in the constant temperature bath from room temperature, a transformation from paramagnetic to ferromagnetic occurs, so it is necessary to hold the sample just above the Tc of the PF transformation. If the Tc is too far away, splitting is less likely to occur, making it difficult to determine how the peaks separate. Furthermore, since there are usually differences between the temperature of measuring devices such as DSC measuring instruments and the temperature of the constant temperature bath, it is necessary to maintain the temperature while taking into account the differences between each device.

[0038] Regarding retention time, depending on the sample composition and hydrogen content, split progression may not be observed for several months, so it is necessary to use a sufficiently long retention period. Since split progression tends to accelerate as the hydrogen content decreases, it is also possible to accelerate and evaluate the split using samples with reduced hydrogen content.

[0039] It is preferable that the magnetic phase transition temperature difference between the magnetic phase transition temperature (Tc) of the alloy of the present invention and the magnetic phase transition temperature obtained when the alloy of the present invention is subjected to hydrogen absorption treatment at 300°C and 0.10 MPaH2 until it reaches a saturated hydrogen amount, held at the magnetic phase transition temperature for 300 hours to allow splitting to proceed is 3.0 K or less. Alloys within this range have sufficiently suppressed splitting and can be said to be suitable for use as magnetic refrigeration materials. From this viewpoint, the above magnetic phase transition temperature difference is more preferably 2.8 K or less, even more preferably 2.0 K or less, and even more preferably 1.5 K or less.

[0040] To quantify the split progression, the saturated hydrogen amount H sat Ratio of absorbed hydrogen to (w / H sat ) to P H Let t be the time when the temperature between peaks is separated by more than a certain temperature, and plot P on the x-axis. H log 10 Plot (t). While 2K is often used as the threshold for the temperature difference between peaks that determines t, it is not limited to 2K and can be set to any value, as long as it is consistent within the test being evaluated. In this case, P H vs log 10 (t) can be approximated by a straight line, and a small slope a and a large intercept b indicate that the split is less likely to progress. This method can also be used for predicting lifespan through accelerated split testing.

[0041] In the linear approximation above, z B Let a0 be the slope and b0 be the intercept when z is 0. B When the value is 0.005 or greater, the slope is a B , the intercept is b B When a0 > a B Or, b0 B When this occurs, splits are suppressed, allowing the AMR system to maintain performance for a longer period of time.

[0042] Next, the method for producing the magnetic refrigeration alloy of the present invention will be described. ​The present invention provides a method for producing an alloy, comprising: a melting step of dissolving raw materials to obtain a raw material alloy containing RE, M, A, and X; a homogenization step of performing heat treatment on the obtained raw material alloy to obtain a predetermined structure; and a hydrogenation step of performing hydrogen storage in the alloy.

[0043] In the melting process, the raw materials metals or alloys of each element are weighed to obtain the alloy composition of the present invention described above. The raw materials are heated to 1600°C and melted by, for example, high-frequency induction melting in an Ar atmosphere, and the alloy is obtained by cooling as rapidly as possible at a cooling rate of 500°C / sec or more. There are no particular limitations on the casting of this alloy, but methods such as strip casting, liquid quenching, and atomization can be applied. With the strip casting method, cooling can be performed quickly, making it easier to obtain a fine and good microstructure. Using the liquid quenching method allows for even faster cooling, making it easier to obtain an even finer and better microstructure.

[0044] In the homogenization process, the alloy obtained in the melting process is heat-treated to create a homogeneous RE(Fe,Si) alloy. 13A heat treatment is performed to form the phase. This homogenization treatment is not particularly limited as it depends on the alloy structure and composition, but can be performed in a temperature range of, for example, 1000°C to 1300°C. In particular, as mentioned above, when rare earth elements other than La are included as RE, the optimal heat treatment temperature range for the homogenization treatment becomes narrower. For example, compared to the case with La alone, the temperature tends to fluctuate by about +10 to +20°C when Ce is included, and by about +10 to +50°C when Pr and Nd are included. In addition, the temperature can fluctuate by several tens of degrees depending on the amount of element A and the type of element M and its substitution amount. For example, when the amount of Si as element A is small, the decomposition temperature decreases, so the optimal heat treatment temperature tends to decrease. Therefore, the optimal heat treatment conditions are not limited to the above range, but are the state in which the amount of Fe deposition is minimized or the latent heat obtained from DSC is maximized, and can be experimentally confirmed considering the above factors. Furthermore, the homogenization time can be appropriately adjusted depending on the state of the alloy obtained in the melting process, and can be carried out in a range of, for example, 1 hour to 200 hours, with a range of 25 hours to 75 hours being more preferable. Within this range, a sufficiently homogenized alloy can be obtained while maintaining mass productivity. In addition, it is preferable to carry out the homogenization treatment in an Ar atmosphere in order to suppress compositional deviations caused by the evaporation of specific elements from the raw alloy.

[0045] In the hydrogenation process, to increase the magnetic phase transition temperature of the obtained magnetic refrigeration material, hydrogen can be absorbed into the magnetic refrigeration material under a hydrogen atmosphere to obtain a hydride. While there are no particular restrictions on specific conditions, before hydrogenation, it is common to perform an activation treatment, such as heating in a vacuum or hydrogen atmosphere at 300-500°C for 1-2 hours, to promote hydrogen absorption. For the hydrogen atmosphere in the hydrogenation treatment, conditions of 0.1-0.35 MPa can be used, for example. The temperature during hydrogenation can be, for example, between 100°C and 500°C. Within this range, the hydrogen saturation concentration can be reached in a relatively short time. The hydrogenation treatment time can be, for example, between 1 hour and 1000 hours, but considering mass productivity and the attainment of hydrogen saturation concentration, a time of 3 hours to 30 hours is more preferable. [Examples]

[0046] The present invention will be described more specifically below with reference to examples, but the present invention is not limited to these examples.

[0047] La metal, Ce metal, Mn metal, Si metal, electrolytic iron, and metal B were weighed to achieve the desired composition. These were then heated to 1500°C in an Ar gas atmosphere in a high-frequency induction melting furnace to melt them, and then cooled at a rate of 300-1000°C / sec by strip casting to produce alloy strips with an average film thickness of approximately 300 μm. The obtained alloys were heat-treated under an Ar atmosphere for 45 hours, with the homogenization temperature varied between 1000°C and 1250°C. The composition of the prepared samples and the optimal homogenization temperature are shown in Table 1. Furthermore, the Si concentration in the main phase of the samples homogenized at the optimal homogenization temperature was determined. 1-13 RE2Fe 14 The Si concentration in the X phase is Si 2-14-1 When Si is considered 1-13 / Si 2-14-1 The values ​​are shown in Table 2. The alloy composition was analyzed using SPS3500DD (Hitachi High-Tech Corporation). The optimal homogenization temperature was determined by performing DSC (NETZSCH, DSC3500Sirius) measurements after the hydrogenation treatment described later, and the temperature at which the latent heat was greatest was considered the optimal homogenization condition. In addition, the Si concentration in each phase was measured by point analysis using EDS with JSM-IT300LV (JEOL Corporation).

[0048] [Table 1] [Table 2]

[0049] The subsequent hydrogenation treatment involved activation in a vacuum at 500°C, followed by hydrogen absorption in a 0.10 MPa hydrogen atmosphere at 250-300°C for 1-200 hours, and then rapid cooling. 13 The main phase of the type crystal structure has less hydrogen storage capacity at higher temperatures, so hydrogenation storage at 50°C or higher, preferably 100°C or higher, is required to achieve a saturated hydrogen content (H sat The following materials are produced. The method for adjusting the amount of hydrogen is not limited to temperature; it can also be controlled by controlling the hydrogen partial pressure and time.

[0050] Subsequent split experiments were conducted using ESPEC constant temperature baths (SH-642, LU-114) to measure the T of the alloy. c The samples were kept at a temperature, removed after a certain period of time, and their mT characteristics were measured using a VersaLab VSM unit (manufactured by QuantumDesign Inc.). The evaluation was performed by calculating the temperature difference between peaks from the peak values ​​of the dm / dT-T curve.

[0051] [Comparative Examples 1 and 2, Examples 1-4] The alloys obtained by homogenizing compositions 1 to 6 at the optimal homogenization temperature for 45 hours, followed by hydrogen storage at 300°C for 15 hours at 0.10 MPaH2, are Comparative Example 1, Examples 1 to 4, and Comparative Example 2, respectively.

[0052] P of the alloys in Examples 1-4 and Comparative Examples 1-2 H , and the Si concentration in the main phase is Si 1-13 RE2Fe 14 The Si concentration in the X phase is Si 2-14-1 When Si is considered 1-13 / Si 2-14-1 The values ​​are shown in Table 3. [Table 3]

[0053] Figure 1 shows the amount of B added and the latent heat of the magnetic phase transition of FP for Comparative Examples 1 and 2, and Examples 1 to 4. B As z increases, the latent heat decreases, BIn the case of =0.3 (Comparative Example 2), the latent heat is less than half.

[0054] Figure 2 shows the z of Comparative Example 1 and Examples 1-4. B This shows the change in Tc relative to Si. 1-13 / Si 2-14-1 By adjusting the value to the range where it is ≤1.2, it is possible to adjust Tc while maintaining the high performance of the magnetic refrigeration material. In particular, in Example 1, it was possible to reduce Tc by approximately 5K while maintaining the latent heat.

[0055] Table 4 shows the α-Fe and RE2Fe of Comparative Examples 1 and 2, and Examples 1-4. 14 This shows the volume fraction of X. Increasing the amount of B added results in α-Fe and RE2Fe. 14 The proportion of the main phase decreases as the amount of X formed increases. The decrease in latent heat shown in Figure 1 is presumed to be due to the decrease in the proportion of the main phase. Therefore, in order to obtain a high-performance magnetic refrigeration material, α-Fe is preferably 6 volume% or less, more preferably 4 volume% or less, and RE2Fe 14 It is preferable that X is 6% by volume or less, and more preferably 5% by volume or less.

[0056] [Table 4]

[0057] [Examples 5-7, Comparative Examples 3-5] RE(Fe,Si) when homogenization treatment was performed on composition 3 at different temperatures for 45 hours. 13 Si concentration of the phase (Si 1-13 ) and RE2Fe 14 Si concentration in phase X (Si 2-14-1 The change in RE(Fe,Si) is shown in Figure 3. When the homogenization temperature is 1140°C or higher, RE(Fe,Si) 13 The Si concentration in the phase increases, RE2Fe 14 The Si concentration in the X phase is decreasing.

[0058] Example 5 and Comparative Example 3 are alloys obtained by homogenizing composition 3 at 1130°C and 1150°C for 45 hours, respectively. Figure 4 shows the dm / dT-T properties of Example 5 and Comparative Example 3. Si1-13 / Si 2-14-1 It can be seen that alloys with a ratio of ≤1.2 exhibit high properties.

[0059] [Example 6, Comparative Example 4] For Example 5 and Comparative Example 3, alloys subjected to hydrogen storage at 300°C for 15 hours at 0.10 MPaH2 were designated as Example 6 and Comparative Example 4, respectively. P of the alloys in Example 6 and Comparative Example 4 H The values ​​are shown in Table 5. Figure 5 shows the dm / dT-T characteristics of Example 6 and Comparative Example 4. Therefore, Si 1-13 / Si 2-14-1 By adjusting the value to the range where ≤1.2, it is possible to obtain a magnetic refrigeration material with high performance even when controlling the amount of hydrogen absorbed and stored.

[0060] [Example 7, Comparative Example 5] For Example 5 and Comparative Example 3, alloys subjected to hydrogen storage at 80°C for 408 hours in an atmosphere of 0.10 MPaH2 were designated as Example 7 and Comparative Example 5, respectively. P of the alloys in Example 7 and Comparative Example 5 H The values ​​are shown in Table 5. Figure 6 shows the dm / dT-T characteristics of Example 7 and Comparative Example 5. Therefore, Si 1-13 / Si 2-14-1 By adjusting the value to the range where ≤1.2, a magnetic refrigeration material with high performance can be obtained even when hydrogen is absorbed to a saturation point.

[0061] [Table 5]

[0062] [Examples 1 and 2, Comparative Example 1] Figure 7 shows the progression of splitting when Comparative Example 1, Examples 1 and 2 were held in a constant temperature bath set to the transition temperature of each sample. The vertical axis represents the temperature difference between each transition temperature at the time of splitting, and the horizontal axis represents the holding time. It can be seen that as the amount of B added increases, it takes longer for the temperature difference between peaks to widen, and the progression of splitting is suppressed.

[0063] [Comparative Examples 6-7, Examples 8-9] Compositions 1 and 3 were homogenized under optimal homogenization conditions, and then hydrogenated at 275°C for 148 hours at 0.10 MPaH2 to obtain a hydrogenated alloy. Comparative Example 6 is the result of the above treatment on composition 1, and Example 8 is the result of the above treatment on composition 3. Compositions 1 and 3 were homogenized under optimal homogenization conditions, and then hydrogenated at 250°C for 166 hours at 0.10 MPaH2 to obtain a hydrogenated alloy. Comparative Example 7 is the result of the above treatment on composition 1, and Example 9 is the result of the above treatment on composition 3. P of the alloys in Examples 8 and 9 and Comparative Examples 6 and 7 H The values ​​are shown in Table 6.

[0064] [Table 6]

[0065] Figure 8 shows the progress of splitting when Comparative Examples 6-7 and Examples 8-9 were held in a constant temperature bath set to the transition temperature of each sample. The vertical axis represents the temperature difference between each transition temperature at the time of splitting, and the horizontal axis represents the holding time. H In the sample with a high amount of B added, it takes longer for the temperature difference between peaks to widen, indicating that the progression of splitting is suppressed. From this, it can be concluded that, regardless of the hydrogen concentration, if B is an alloy with a predetermined concentration, the splitting will be suppressed.

[0066] [Examples 10-12, Comparative Example 8] Compositions 7 to 10 were homogenized under optimal homogenization conditions, and then hydrogenated at 275°C for 148 hours at 0.10 MPaH2 to obtain hydrogenated alloys. Comparative Example 8 is obtained by performing the above treatment on composition 7, and Examples 10 to 12 are obtained by performing the above treatment on compositions 8 to 10. P of the alloys in Examples 10-12 and Comparative Example 8 H The values ​​are shown in Table 7.

[0067] [Table 7]

[0068] Figure 9 shows the progress of splitting when Comparative Example 8 and Examples 10-12 were held in a constant temperature bath set to the transition temperature of each sample. The vertical axis represents the temperature difference between each transition temperature at the time of splitting, and the horizontal axis represents the holding time. H In the sample with a high amount of B added, it takes longer for the temperature difference between peaks to widen, indicating that the progression of splitting is suppressed.

[0069] Figure 10 shows the change in the amount of B added and the lattice constant of the main phase for Comparative Example 1 and Examples 1-4. B As the value increased, the lattice constant initially decreased, then reversed and increased. This is thought to reflect the difference in the solid solution form of B, as mentioned above.

Claims

1. RE(M １－ｘ A ｘ ) ｙ X ｚ H ｗ An alloy represented by the compositional formula, where x, y, z, and w respectively satisfy 0.08 ≤ x ≤ 0.13, 12.3 ≤ y ≤ 13.2, 0.005 ≤ z ≤ 0.25, and 0 ≤ w ≤ H ｓａｔ (H ｓａｔ is the saturated hydrogen content at room temperature), RE is one or more elements selected from rare earth elements and Zr, with La being essential, M is one or more elements selected from Fe, Co, Mn, Ni, Nb, W, Ta, Cr, Cu, Ag, and Ti, with Fe being essential, A is one or more elements selected from Si, Al, Ga, P, Ge, Sn, and In, with Si being essential, X is one or more elements selected from B, C, and N, with B being essential, and NaZn １３ type crystal structure as the main phase and RE ２ Fe １４ X phase as the secondary phase, and when the Si concentration in the main phase is Si １－１３ and the Si concentration in the RE ２ Fe １４ X phase is Si ２－１４－１ , an alloy where Si １－１３ / Si ２－１４－１ ≤ 1.2.​

2. The amount of B contained in X is z Ｂ , the amount of C is z Ｃ , the amount of N is z Ｎ Let z = z Ｂ +z Ｃ +z Ｎ When z Ｂ The alloy according to claim 1, wherein the ratio is 0.005 or more.

3. z Ｂ While keeping the composition the same except for the value of z Ｂ When c is set to = 0, the lattice constant is c. ０ to, z Ｂ While keeping the composition the same except for the value of z Ｂ When the lattice constant is set to >0, c Ｂ In that case, c Ｂ ≤ c ０ The alloy according to claim 2.

4. The alloy according to claim 1, wherein the α-Fe phase content is 6 volume percent or less.

5. The aforementioned RE ２ Fe １４ The alloy according to claim 1, wherein the volume fraction of phase X is 0.01% or more and 6% or less.

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