Alloy

Abstract

The present invention is an alloy represented by a composition formula of RE(M1-xAx)yXzHw, wherein: x, y, z, and w satisfy 0.08 ≤ x ≤ 0.13, 12.3 ≤ y ≤ 13.2, 0.005 ≤ z ≤ 0.25, and 0 ≤ w ≤ Hsat (Hsat is a saturated hydrogen amount at room temperature), respectively; RE is at least one element selected from rare earth elements and Zr, and must include La; M is at least one element selected from Fe, Co, Mn, Ni, Nb, W, Ta, Cr, Cu, Ag, and Ti, and must include Fe; A is at least one element selected from Si, Al, Ga, P, Ge, Sn, and In, and must include Si; X is at least one element selected from B, C, and N, and must include B; and the alloy includes a main phase having a NaZn13-type crystal structure and a sub-phase including a RE2Fe14X phase, and when a Si concentration in the main phase is Si1-13 and a Si concentration in the RE2Fe14X phase is Si2-14-1, Si1-13 / Si2-14-1 ≤ 1.2 is satisfied. With the present invention, it is possible to provide a B-added alloy having a high magnetocaloric effect.

Description

Alloy

[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.

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

[0003] A magnetic refrigeration system utilizes the change in magnetic entropy (magnetocaloric effect, ΔS). As materials with a large absolute value of ΔS, there are Mn(As １３ , Ｚ Sb ｘ )(Patent Document 1) and La(Fe １－ｘ Si ｘ )(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 )(Patent Document 2) is the most promising substance because ΔS is ~25 J / kgK, which is large after Mn(As １－ｘ Sb ｘ ), and its constituent elements do not show toxicity and are not rare metals.

[0004] ​​​​​​​​These materials are required to operate at or 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 with gas refrigeration, there was a problem that the magnetocaloric effect decreased at the above operating temperatures 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 or 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 Document 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 partially substituting Fe with Mn (Non-Patent Document 2) or Co (Non-Patent Document 3). According to this method, adding Mn lowers Tc, and adding Co increases Tc.

[0007] Japanese Patent Publication No. 2003-28532 Japanese Patent Publication No. 2006-89839

[0008] PHYSICAL REVIEW B 67, 104416 (2003) Journal of Alloys and Compounds 950 (2023) 169883 Journal of Alloys and Compounds 765 (2018) 538-543

[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.

[0011] As a result of diligent research to achieve the above objective, the inventors of the present invention have 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 ｗ An alloy represented by the compositional formula, where x, y, z, and w satisfy the following conditions: 0.08 ≤ x ≤ 0.13, 12.3 ≤ y ≤ 13.2, 0.005 ≤ z ≤ 0.25, and 0 ≤ w ≤ H. 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 and RE of the crystal structure ２ Fe １４ The main phase includes a subphase containing phase X, and the Si concentration in the main phase is Si １－１３ , the RE ２ Fe １４ The Si concentration in the X phase is Si２－１４－１ When that happens, Si １－１３ / Si ２－１４－１ An alloy having a value of ≤ 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 z is 0.005 or greater. [3] 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 described in [2] above. [4] The alloy described in any one of [1] to [3] above, wherein the α-Fe phase content is 6 volume% or less. [5] The RE ２ Fe 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.

[0013] According to the present invention, it is possible to provide a B-added alloy that has a high magnetocaloric effect.

[0014] 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 is a graph showing the z for Comparative Example 1 and Examples 1 to 4. Ｂ This is a graph showing the change in Tc with respect to . Figure 3 shows the RE(Fe,Si) when composition 3 is subjected to homogenization treatment at different temperatures for 45 hours. １３ A and RE ２ Fe １４Figure 4 is a graph showing the change in Si concentration in the X phase. Figure 5 is a graph showing the dm / dT-T characteristics of Example 5 and Comparative Example 3. Figure 6 is a graph showing the dm / dT-T characteristics of Example 6 and Comparative Example 4. Figure 7 is a graph showing the split progression when Comparative Example 1 and Examples 1 and 2 are held in a constant temperature bath set to the transition temperature of each sample. Figure 8 is a graph showing the split progression when Comparative Examples 6-7 and Examples 8-9 are held in a constant temperature bath set to the transition temperature of each sample. Figure 9 is a graph showing the split progression when Comparative Example 8 and Examples 10-12 are held in a constant temperature bath set to the transition temperature of each sample. 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.

[0015] The alloy of the present invention is RE(M １－ｘ A ｘ ) ｙ X ｚ H ｗ An alloy represented by the compositional formula, where x, y, z, and w satisfy the following conditions: 0.08 ≤ x ≤ 0.13, 12.3 ≤ y ≤ 13.2, 0.005 ≤ z ≤ 0.25, and 0 ≤ w ≤ H. ｓａｔ (H ｓａｔ The alloy of the present invention satisfies the saturation hydrogen content at room temperature. １３ Main phase and RE of the crystal structure ２ Fe １４ It includes a subphase containing the X phase. Furthermore, the Si concentration in the main phase is Si １－１３ RE ２ Fe 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 RE contains elements other than La, homogenization becomes more difficult as the amount of substitution increases. The maximum amount of Ce that can be contained is 40 atomic percent or less of the total RE, Pr 60 atomic percent or less, and Nd 40 atomic percent or less. 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, a portion of the RE in the subphase can also 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. In addition, a portion 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. In addition, a portion of the Si in the subphase can also be substituted 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 further contain at least one element from C and N. C and N are inevitably included 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 in the above composition from the symmetric chemical ratio of the main phase of 13.0 to produce the alloy, the hydrogen storage behavior can be controlled. However, if y in the above composition 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 greater. Furthermore, y is preferably 13.1 or less.

[0023] The z of the above composition 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 material is held at the magnetic phase transition temperature for a long 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 progression of split cannot be effectively suppressed. Also, if z is less than 0.005 or greater than 0.25, lowering the Tc of the alloy may reduce 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 ＮWhen expressed as z Ｂ is preferably 0.005 or more, more preferably 0.01 or more. Also, it is preferably 0.25 or less, more preferably 0.05 or less, and even more preferably 0.01 or less. When within such a range, when the alloy occludes hydrogen in the range of 0 < w < H ｓａｔ it is possible to obtain a high-performance material in which the split progress is more effectively suppressed, and while reducing Tc, the performance degradation is suppressed.

[0025] The alloy of the present invention is an alloy in which w of the above composition is 0 or more and H ｓａｔ or less. Since the effect of the present invention can be obtained regardless of the presence or absence of hydrogen content, it may contain hydrogen of w = H ｓａｔ (saturated hydrogen amount at room temperature) or less. H ｓａｔ varies depending on the composition and the like, but generally it is said that when w = about 1.4 to 1.7, and if it is about 1.8, it can be said that the saturated hydrogen amount is sufficient. Note that H ｓａｔ is the saturated hydrogen amount at room temperature in the alloy of each composition. In the present invention, when hydrogen is occluded for at least 5 hours or more in a hydrogen atmosphere of 0.10 to 0.25 MPa at a temperature of 30 ° C, when the Tc does not increase any further, the hydrogen amount is defined as H ｓａｔ . Before the hydrogen occlusion treatment, an activation treatment is generally often performed. For example, a heat treatment is performed at 300 to 500 ° C for 1 to 2 hours in a vacuum or a hydrogen atmosphere.

[0026] When the alloy of the present invention stores hydrogen, w < H ｓａｔ That is, P Ｈ (= w / H ｓａｔ ) is less than 1, splitting occurs. The smaller P Ｈ is, the faster the progress of splitting is. P Ｈ of the alloy of the present invention is preferably 0.95 or less, more preferably 0.90 or less, and even more preferably 0.85 or less. The lower limit value of the range of P Ｈ of the alloy of the present invention is not particularly limited, but P 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 a LECO oxygen / nitrogen / hydrogen analyzer ONH836.

[0027] The alloy of the present invention preferably has a Tc that is 2 K or more lower than 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 more lower than Tc when w = H while keeping the composition other than the value of w the same, more preferably 10 K or more lower, still more preferably 20 K or more lower. ｓａｔ ｓａｔ ｓａｔ ｓａｔ

[0028] The alloy of the present invention has the lattice constant c Ｂ when z Ｂ = 0 with the composition other than the value of z the same, and has the lattice constant c ０ when z Ｂ > 0 with the composition other than the value of z the same. In this case, it is preferable that c Ｂ ≦ c Ｂ . Thereby, a magnetic refrigeration material with suppressed split and high characteristics can be obtained. From such a viewpoint, when the lattice constant at the minimum value is c Ｂ ０ ｍｉｎ ｍｉｎ ｍｉｎ ｍｉｎ ｍｉｎ ≦ c Ｂ ≦ c ０ ０

[0029] Normally, it is generally assumed that light elements such as B, C, and N penetrate the lattice in a solid solution form, expanding the crystal lattice and increasing the lattice constant monotonically. However, when a small amount of B is added and the amount is increased, the lattice constant initially decreases, reaches a minimum value at a certain point, then reverses and begins to increase. Simultaneously, Tc also decreases once, reaches a minimum value, and then increases. The reason for this is not entirely clear, but it is presumed that in the case of small amounts of B added, the lattice constant decreases because B substitutes, for example, at Fe sites in a substitutional solid solution form, whereas when a certain amount or more of B is added, substitutional solid solution becomes difficult, and B begins to solid dissolve in the lattice in an interstitial solid solution form, causing the lattice constant to increase.

[0030] Under the above assumptions, the stability of the main phase hydride in paramagnetic and ferromagnetic states was evaluated for three cases: no B solid solution, B substitution type solid solution, and B interstitial type solid solution. In the case of substitution type solid solution, the difference in stability between paramagnetic and ferromagnetic states became smaller in the total hydrogen content region, showing a tendency for splitting to be further suppressed. In the case of interstitial type solid solution, H ｓａｔ In the low hydrogen concentration region shown below, the difference in stability between paramagnetism and ferromagnetism was small, and a tendency for splitting to be suppressed was observed. Therefore, it is thought that splitting is suppressed in the region where the lattice tends to shrink when B is added, and even in the region where the lattice tends to expand. However, while increasing the amount of B added can suppress the progression of splitting, increasing it too much increases the amount of heterogeneous phase formation and degrades the properties, so the lattice constant when B is added is z Ｂ It is preferable that the value is approximately equal to or less than the lattice constant when the value is 0.

[0031] The alloy of the present invention is NaZn １３ The main phase has a type crystal structure, and RE ２ Fe １４ It includes a subphase containing the X phase. For example, by adding B as the element X, RE is added as the subphase. ２ Fe １４ The X phase can be formed in the alloy. The alloy of the present invention is RE ２ Fe １４ It is preferable that the X phase is present in a volume of 0.01% or more. This allows for more effective suppression of splitting. Furthermore, the alloy of the present invention is RE２ Fe １４ It is preferable that the X phase be present in a volume percentage of 6% or less. This suppresses 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, for example, by binarizing an SEM image acquired using JSM-IT300LV (manufactured by JEOL Corporation) using the difference in contrast due to composition, calculating the area of ​​each phase, and considering the area fraction as the volume fraction. ２ Fe １４ The reason why the X phase can suppress the progression of the split is not entirely clear, but it is thought to be as follows: When the sample is hydrogenated, not only the main phase but also RE ２ Fe １４ Although the X phase can also form hydrides, 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 observed. １３ In addition, a third RE with different hydride stabilities ２ Fe 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, RE ２ Fe １４ It is known that the B-phase can have some of its B-sites replaced with C. In the present invention, C caused by impurities or intentionally added is RE ２ Fe １４ It is thought that the B site of phase B is being replaced. Therefore, it is inevitably included as an impurity, but even if C is intentionally added as X, RE ２ Fe １４ It is presumed that the formation of (B, C) is promoted, enhancing the split-suppressing effect.

[0033] As shown 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 RE formed by the addition of X. ２ Fe 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 RE ２ Fe 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. １－１３ / Si ２－１４－１ >1.2 If Tc is reduced by adding B, the magnetic properties may deteriorate. The subphase is RE ２ Fe １４ When the X phase is present, changing the homogenization temperature (temperature, time, etc.) results in RE(Fe,Si) １３ A and RE ２ Fe １４ The amount of Si in the X phase changes, which is because the constituent phases change due to the homogenization conditions, and RE ２ Fe 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, adding B and RE ２ Fe １４ Even in environments where the 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. Although not particularly limited, the Si concentration in each phase can be measured by point analysis using EDS with, for example, 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 alloy is held above its Tc for a sufficiently long period of time. In measurements that detect the magnetic phase transition of magnetic refrigeration materials, such as DSC-T characteristics by DSC measurement or dm / dT-T characteristics by VSM measurement, the temperature difference between each separated magnetic phase transition temperature can be used for evaluation. 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. Also, there is usually a difference between the temperature of the measuring device such as DSC measurement and the temperature of the constant temperature bath, so it is necessary to hold the sample at a temperature that takes 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] The magnetic phase transition temperature (Tc) of the alloy of the present invention, and the alloy of the present invention at 300°C and 0.10 MPaH. ２It is preferable that the magnetic phase transition temperature difference between the temperature at which the hydrogen absorption treatment is performed up to the saturation hydrogen amount, the temperature at which the split is allowed to progress (held at the magnetic phase transition temperature for 300 hours), and the magnetic phase transition temperature at which the split is allowed to progress 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 on the vertical axis 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. At this time, 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 the lifespan of a split through accelerated testing.

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

[0042] Next, the method for producing the magnetic refrigeration alloy of the present invention will be described. The method for producing the alloy of the present invention comprises a melting step of melting 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 higher. 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 structure. Using the liquid quenching method allows for even faster cooling, making it easier to obtain an even finer and better structure.

[0044] In the homogenization process, the alloy obtained in the melting process is subjected to heat treatment to create a homogeneous RE(Fe,Si) １３A heat treatment is performed to form a 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 of 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 example, a hydrogen atmosphere of 0.1-0.35 MPa can be used for the hydrogenation treatment. The hydrogenation temperature 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, and considering mass productivity and the attainment of hydrogen saturation concentration, a time of 3 hours to 30 hours is more preferable.

[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 melted in a high-frequency induction furnace in an Ar gas atmosphere at 1500°C, and then cooled at a rate of 300–1000°C / sec using the strip casting method to produce alloy strips with an average thickness of approximately 300 μm. The resulting alloys were then heat-treated in an Ar atmosphere for 45 hours, varying the homogenization temperature between 1000–1250°C. Table 1 shows the composition of the prepared samples and the optimal homogenization temperature. Furthermore, the Si concentration in the main phase of the samples homogenized at the optimal homogenization temperature was determined. １－１３ Toshi, RE ２ Fe １４ The Si concentration in the X phase is Si ２－１４－１ When Si is considered as such 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, DSC3500Siris) measurements after the hydrogenation treatment described later, and the time when 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]

[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; therefore, 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 constant temperature, removed after a certain period of time, and their m-T characteristics were measured using a VersaLab VSM unit (manufactured by Quantum Design Co., Ltd.). 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, 2, Examples 1-4] Compositions 1-6 were subjected to homogenization treatment at the optimal homogenization temperature for 45 hours, followed by heating at 300°C for 15 hours at 0.10 MPaH. ２ The alloys that underwent hydrogen storage are Comparative Example 1, Examples 1-4, 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 Toshi, RE ２ Fe １４ The Si concentration in the X phase is Si ２－１４－１ When Si is considered as such １－１３ / Si ２－１４－１ The values ​​are shown in 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, Ｂ At 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 temperature to the range where it is ≤ 1.2, it is possible to adjust Tc while maintaining the characteristics of a high-performance 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 RE of Comparative Examples 1 and 2, and Examples 1 to 4. ２ Fe １４ This shows the volume fraction of X. Increasing the amount of B added increases α-Fe and RE. ２ Fe １４The amount of X formed increases, which reduces the proportion of the main phase. 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, RE ２ Fe １４ It is preferable that X is 6% by volume or less, and more preferably 5% by volume or less.

[0056]

[0057] [Examples 5-7, Comparative Examples 3-5] RE(Fe,Si) when composition 3 was subjected to homogenization treatment at different temperatures for 45 hours. １３ Si concentration of the phase (Si １－１３ ) and RE ２ Fe １４ Si concentration in phase X (Si ２－１４－１ The change in ) 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, RE ２ Fe 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. Si １－１３ / 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] Compared to Example 5 and Comparative Example 3, 0.10 MPaH at 300°C for 15 hours. ２ The alloys subjected to hydrogen storage were designated as Example 6 and Comparative Example 4, respectively. Ｈ The values ​​are shown in Table 5. Figure 5 shows the dm / dT-T characteristics of Example 6 and Comparative Example 4. From the above, 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 properties even when controlling the amount of hydrogen absorbed and stored.

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

[0061]

[0062] [Examples 1 and 2, Comparative Example 1] Figure 7 shows the progress 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 progress of splitting is suppressed.

[0063] [Comparative Examples 6-7, Examples 8-9] Compositions 1 and 3 were homogenized under optimal homogenization conditions, followed by heating at 275°C for 148 hours at 0.10 MPaH. ２ Hydrogenated alloys were obtained by hydrogen absorption. Comparative Example 6 is obtained by performing the above treatment on composition 1, and Example 8 is obtained by performing the above treatment on composition 3. Compositions 1 and 3 were homogenized under optimal homogenization conditions, and then heated at 250°C for 166 hours at 0.10 MPaH. ２ Hydrogenated alloys were obtained by hydrogen absorption. Comparative Example 7 is obtained by performing the above treatment on composition 1, and Example 9 is obtained by performing the above treatment on composition 3. The P of the alloys of Examples 8 and 9 and Comparative Examples 6 and 7 Ｈ The values ​​are shown in Table 6.

[0064]

[0065] Figure 8 shows the progress of splitting when Comparative Examples 6 and 7 and Examples 8 and 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. ＨIn the sample with a high amount of B added, it took longer for the temperature difference between peaks to widen, indicating that the progression of splitting was suppressed. From this, it can be concluded that, regardless of the hydrogen concentration, if the alloy contains B at a predetermined concentration, the progression of splitting will be suppressed.

[0066] [Examples 10-12, Comparative Example 8] Compositions 7-10 were homogenized under optimal homogenization conditions, followed by heating at 275°C for 148 hours at 0.10 MPaH. ２ Hydrogenated alloys were obtained by hydrogen absorption. 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. The P of the alloys in Examples 10 to 12 and Comparative Example 8 Ｈ The values ​​are shown in Table 7.

[0067]

[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. 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 respectively satisfy 0.08 ≤ x ≤ 0.13, 12.3 ≤ y ≤ 13.2, 0.005 ≤ z ≤ 0.25, 0 ≤ w ≤ H ｓａｔ (H ｓａｔ is the saturated hydrogen amount at room temperature), RE is one or more elements selected from rare earth elements and Zr and La is essential, M is one or more elements selected from Fe, Co, Mn, Ni, Nb, W, Ta, Cr, Cu, Ag, and Ti and Fe is essential, A is one or more elements selected from Si, Al, Ga, P, Ge, Sn, and In and Si is essential, X is one or more elements selected from B, C, and N and B is essential, and a NaZn １３ type crystal structure main phase and a RE ２ Fe １４ X phase-containing 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 , Si １－１３ / Si ２－１４－１ ≤ 1.2 alloy.

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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