Fe-Al alloy, Fe-Al alloy member, and method for producing the Fe-Al alloy.

Abstract

To provide an Fe-Al alloy having improved vibration-damping properties, an Fe-Al alloy member, an Fe-Al alloy powder and a method for producing an Fe-Al alloy.SOLUTION: An Fe-Al alloy comprises, in mass%, Al: 4.0-12.0% with the balance being Fe and inevitable impurities. The area ratio of fine crystal grains with an average grain size of more than 700 μm and 2000 μm or less and a grain size of less than 100 μm is less than 20%.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to an Fe-Al alloy used as a vibration-damping alloy, an Fe-Al alloy member, an Fe-Al alloy powder, and a method for producing an Fe-Al alloy. [Background technology]

[0002] To improve the quietness of automobiles and other vehicles, there is a demand for metallic materials with excellent vibration-damping properties. Examples of vibration-damping alloys include Fe-Al alloys, Fe-Cr-Al alloys, and Fe-Co-V alloys, which are known as ferromagnetic vibration-damping alloys. All of these alloys exhibit high magnetostriction, which causes domain walls within the material to move due to the magnitude of strain associated with vibration, thereby absorbing the elastic energy of vibration. Other vibration-damping alloys include Mn-Cu alloys, which utilize twinning during thermoelastic martensitic transformation and lose their vibration-damping effect above the transformation temperature. Ferromagnetic types maintain their vibration-damping effect up to relatively high temperatures, and Fe-Al alloys, among others, are known for their low raw material costs and excellent vibration-damping properties.

[0003] This Fe-Al alloy is often used as a plate after plastic working such as rolling. For example, Patent Document 1 (JP 2014-80676 A) discloses a manufacturing process for cold-rolled material with a thickness of 1.4 mm or less, and Patent Document 2 (JP 2014-114468 A) discloses a cold working process in which plastic working by hot working and cold rolling are performed. In these plastically processed materials, the grain boundaries hinder the movement of magnetic domain walls, so the larger the grains, the greater the magnetostriction, which has the effect of increasing internal friction. Patent Document 3 (JP 2001-59139 A) specifies the average grain size to be within the range of 300 to 700 μm. If the grain size is too large, cold workability will decrease and there is a concern that the strength required for structural materials will decrease, so an upper limit has been set.

[0004] Patent Document 4 also discloses an Fe-Al alloy vibration-damping member obtained by locally melting and solidifying Fe-Al alloy powder using a laser or other method on these rolled materials to form a structure of any shape. This manufacturing method is characterized by including a shaping step to obtain a shaped body and an annealing step to set the crystal grain size to the range of 700 to 2000 μm. This method makes it possible to obtain vibration-damping members of any shape that cannot be produced by plastic processing such as rolling. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent Publication No. 2014-80676 [Patent Document 2] Patent Publication No. 2014-114468 [Patent Document 3] JP 2001-59139 [Patent Document 4] WO2020 / 241530 issue Summary of the Invention [Problem to be solved by the invention]

[0006] However, when a large number of vibration-damping members are manufactured using the additive manufacturing method described above, some of the members may have poor vibration-damping properties. Patent Documents 1 to 4 do not mention this issue, leaving room for further investigation. An object of the present invention is to provide an Fe-Al alloy, an Fe-Al alloy member, an Fe-Al alloy powder, and a method for producing an Fe-Al alloy, which have improved vibration-damping properties. [Means for solving the problem]

[0007] The present invention is an Fe-Al alloy consisting of, by mass%, 4.0 to 12.0% Al, the remainder being Fe and unavoidable impurities, in which the average crystal grain size is greater than 700 μm and less than 2000 μm, and the area ratio of fine crystal grains having a crystal grain size of less than 100 μm is less than 20%.

[0008] Preferably, the alloy further contains Ga, and the total of Al and Ga is more than 4.0% and 12.0% or less by mass.

[0009] The present invention also provides an Fe-Al alloy member, characterized in that the member contains 4.0 to 12.0% Al, the remainder being Fe and unavoidable impurities, has an average crystal grain size of more than 700 μm and 2000 μm or less, an area ratio of fine crystal grains having a crystal grain size of less than 100 μm is less than 20%, and has an internal friction of 0.0020 or more at 22°C measured by a central vibration method.

[0010] It is also preferable that the thickness of the film is 5 mm or more.

[0011] The present invention also provides an Fe-Al alloy powder characterized by containing, by mass%, Al: 4.0% or more and less than 12.0%, Ga: more than 0%, and the balance being Fe and unavoidable impurities, and the total of Al and Ga being more than 4.0% and 12.0% or less.

[0012] The average particle size is preferably 10 μm or more and 200 μm or less.

[0013] Also, atomized powder is preferred.

[0014] The present invention also provides a powder containing, by mass%, 4.0 to 12.0% Al, the balance being Fe and unavoidable impurities, in a form having a surface energy density of 2.6 to 4.8 J / mm 2 and an annealing step in which the shaped body is held at a temperature above 1050°C and not higher than 1250°C for one hour or more.

[0015] Preferably, the powder further contains Ga, and the total of Al and Ga is greater than 4.0% and less than or equal to 12.0% by mass. [Effects of the Invention]

[0016] According to the present invention, it is possible to provide an Fe-Al-based alloy, an Fe-Al-based alloy member, an Fe-Al-based alloy powder, and a method for producing an Fe-Al-based alloy with improved vibration damping characteristics.

Brief Description of the Drawings

[0017] [Figure 1] It is a cross-sectional photograph before annealing of an example of the present invention, showing a low magnification image in (a) and a high magnification image in (b). [Figure 2] It is a cross-sectional photograph after annealing of an example of the present invention. [Figure 3] It is a cross-sectional photograph before annealing of a comparative example, showing a low magnification image in (a) and a high magnification image in (b). [Figure 4] It is a cross-sectional photograph after annealing of a comparative example. [Figure 5] It is a cross-sectional photograph before annealing of another comparative example. [Figure 6] It is a cross-sectional photograph after annealing of another comparative example.

Modes for Carrying Out the Invention

[0018] Hereinafter, embodiments of the present invention will be specifically described. The Fe-Al-based alloy of the present invention contains, in mass%, Al: 4.0 to 12.0%, and the balance Fe and inevitable impurities, and has an average crystal grain size exceeding 700 μm and within 2000 μm, and one of the characteristics is that the area ratio of fine crystal grains having a crystal grain size of less than 100 μm is less than 20%.

[0019] <Fe-Al-based alloy> (Al) Al dissolves in Fe and contributes to vibration damping by increasing magnetostriction. As Al increases, magnetostriction increases and reaches a maximum around 10%. On the other hand, the magnetic permeability decreases as Al increases, making it difficult for magnetic walls to move. Therefore, Al is set to 4.0 to 12.0%. The preferable lower limit is 6.0% and the upper limit is 10.0%.

[0020] (Ga) In addition to Al, Ga, an element of the same group as Al, may be added. Like Al, Ga dissolves in Fe and contributes to vibration damping by increasing magnetostriction. Ga (atomic radius: 0.141 nm) has a smaller atomic radius than Al (atomic radius: 0.143 nm) and is closer to Fe (atomic radius: 0.126 nm). This is thought to reduce lattice strain and facilitate grain boundary movement during annealing. Like Al, the more Ga added, the greater the magnetostriction. However, increasing the amount of Ga increases the formation of compounds (e.g., Ga3Fe) rather than dissolving, resulting in embrittlement. For this reason, the total amount of Ga added with Al is set to more than 4.0% but not more than 12.0%. The preferred lower limit of the total amount with Al is 6.0%, and the preferred upper limit is 12.0%. Furthermore, to achieve the desired effect of Ga addition, Ga should be added in an amount greater than 0%, more preferably 0.1% or more.

[0021] The damping member of this embodiment is also characterized by having an average crystal grain size in the range of more than 700 μm and no more than 2000 μm. The damping member of this embodiment is characterized by having an area ratio of less than 20% (including 0) of fine crystal grains (also called residual fine crystal grains) with a crystal grain size of less than 100 μm, which are generated in the rapid melting, rapid cooling, and solidification process in additive manufacturing. If the damping member contains 20% or more fine crystal grains, the domain wall movement is hindered, resulting in a deterioration of damping characteristics.

[0022] By controlling the average crystal grain size to exceed 700 μm, the domain wall movement is less likely to be hindered, and vibration damping properties can be exhibited.

[0023] On the other hand, if the average crystal grain size becomes too large, the ductility of the vibration-damping member tends to decrease, so the upper limit is set to 2000 μm. The lower limit of the average crystal grain size is preferably 800 μm, and more preferably 900 μm. The upper limit of the average crystal grain size is preferably 1800 μm, more preferably 1600 μm, even more preferably 1400 μm, and particularly preferably 1200 μm. The average grain size in this specification can be determined by a cutting method from the distance between the intersection of a line segment parallel to the lamination direction and the grain boundary when observing a cross section of a sample.

[0024] If there are too many defects such as voids introduced during molding, sufficient vibration-damping properties cannot be obtained even if the average crystal grain size is as described above, so it is preferable that the cross-sectional defect rate is less than 0.1%. This cross-sectional defect rate can be measured, for example, by mirror-polishing a cross section parallel to the thickness direction of the member, observing it with an optical microscope, and analyzing the obtained image to determine the area rate.

[0025] Furthermore, an embodiment of an Fe-Al alloy member using an Fe-Al alloy has the characteristics of the above-mentioned Fe-Al alloy, specifically, one of the characteristics is that it contains, by mass%, 4.0 to 12.0% Al, the remainder being Fe and unavoidable impurities, the area ratio of fine crystal grains having an average crystal grain size of more than 700 μm but not exceeding 2000 μm and a crystal grain size of less than 100 μm is less than 20%, and the internal friction at 22°C measured by the central vibration method is 0.0020 or more. Furthermore, for example, it is preferable that the plate-shaped Fe-Al alloy member has a portion having a thickness of 5 mm or more.

[0026] (Fe-Al alloy powder) The Fe-Al alloy powder of this embodiment contains, by mass%, 4.0 to 12.0% Al, with the balance being Fe and unavoidable impurities. Another embodiment of the Fe-Al alloy powder is characterized in that it contains, by mass%, 4.0% or more but less than 12.0% Al, more than 0% Ga, with the balance being Fe and unavoidable impurities, and the sum of Al and Ga is more than 4.0% but not more than 12.0%.

[0027] The average particle size of the Fe-Al alloy powder (hereinafter referred to as alloy powder 20) is preferably 10 μm or more and 200 μm or less from the viewpoints of handling property and filling property. Also, the suitable average particle size varies depending on the additive manufacturing method used. For the Selective Laser Melting (SLM) method, it is more preferably 10 μm or more and 50 μm or less, and for the Electron Beam Melting (EBM) method, it is more preferably 45 μm or more and 105 μm or less. Further, for the Laser Metal Deposition (LMD) method, it is preferably 50 μm or more and 150 μm or less. If the average particle size is 10 μm or more, it becomes difficult for the alloy powder 20 to fly up in the subsequent additive manufacturing process, and it is easy to suppress the decrease in the shape accuracy of the alloy laminated body. On the other hand, by setting the average particle size to 200 μm or less, it is easy to suppress an increase in the surface roughness of the laminated body in the subsequent additive manufacturing process or insufficient melting of the alloy powder 20. Note that the average particle size referred to in this specification refers to the value of the median diameter (D50) measured by the laser diffraction method.

[0028] <Manufacturing method of Fe-Al alloy> Next, the manufacturing method of the Fe-Al alloy of the present embodiment will be described. First, an alloy powder having the composition of a desired vibration damping member is prepared. The alloy powder to be used can be obtained, for example, by an atomization method. There is no particular limitation on the atomization method, and conventional methods can be used. For example, gas atomization methods (such as vacuum gas atomization method, electrode induction melting type gas atomization method, etc.), centrifugal atomization methods (such as disk atomization method, plasma rotating electrode atomization method, etc.), plasma atomization methods, etc. can be preferably used.

[0029] One embodiment of the manufacturing method of the Fe-Al alloy is characterized by comprising a shaping step of melting and solidifying a powder containing Al: 4.0 to 12.0% by mass and the balance being Fe and inevitable impurities with a heat source having a surface energy density of 2.6 to 4.8 J / mm2 to obtain a shaped body, and an annealing step of holding the shaped body at a temperature exceeding 1050 °C and 1250 °C or lower for 1 hour or more. (modeling process) In the shaping process of this embodiment, the alloy powder is melted and solidified using a heat source to obtain a shaped body. The heat source may have a surface energy density of 2.6 to 4.8 J / mm2. This surface energy density is calculated as P / (v·p), where P is the power of the scanning heat source, v is the scanning speed, and p is the scanning interval. By melting and solidifying the metal powder within the above-mentioned surface energy density range, it is possible to prevent the occurrence of bubbles and unmelted voids as mentioned above and to stably obtain coarse crystal grains after annealing.

[0030] The above-mentioned surface energy density of 2.6 to 4.8 J / mm2 can be achieved, for example, by setting the scanning speed of the heat source to 50 mm / sec to 3000 mm / sec. The lower limit of the scanning speed is more preferably 100 mm / sec, and even more preferably 700 mm / sec. The upper limit is more preferably 2000 mm / sec, and even more preferably 1700 mm / sec. The scanning interval is preferably between 0.01 mm and 0.4 mm, more preferably between 0.02 mm and 0.2 mm, and can be adjusted according to the scanning speed to achieve the above-mentioned surface energy density. When observing the shaped body after this shaping process, the structure obtained by the rapid solidification process contains fine crystal grains, with an average crystal grain size of, for example, 5 μm to 300 μm.

[0031] Setting the scanning speed of the heat source at 50 mm / s or higher facilitates the formation of a stable melt pool and prevents the incorporation of air bubbles into the molded body. Setting the scanning speed of the heat source at 3000 mm / s or lower prevents the raw material powder from remaining unmelted and prevents the formation of voids in the molded body. Suppressing the formation of these bubbles and voids is also important for the coarsening of crystal grains.

[0032] In this embodiment, the commonly known powder additive manufacturing method may be used as the means for melting and solidifying the powder. Examples of powder additive manufacturing methods include the powder bed method and the direct metal deposition method. The heat source may also be appropriately selected from laser, electron beam, arc, plasma, etc. In this embodiment, the powder bed method using a laser as the heat source is selected.

[0033] In order to anneal the molded body after the molding process to produce coarse crystal grains exceeding 700 μm, it is necessary to leave a moderate amount of internal strain in the molded body. Internal strain is introduced by thermal stress due to rapid heating and cooling and transformation stress associated with phase transformation, and the magnitude of this strain serves as the driving force for recrystallization during the annealing process. The inventors' investigation of the additive manufacturing process and annealing process confirmed that recrystallization occurs over a wide range of additive manufacturing conditions by increasing the temperature in the annealing process, as described below, or by adding Ga.

[0034] The shaped body of this embodiment has a metal structure consisting of a collection of rapidly solidified structures after the additive manufacturing process. The microstructure has a columnar structure aligned in the stacking direction.

[0035] (Annealing process) In the annealing step of this embodiment, the obtained shaped body is annealed. This is because, since the shaped body as is only capable of producing crystal grains of approximately 100 μm at most, it is necessary to coarsen the crystal grains by annealing and recrystallizing them. In order to recrystallize the additive manufacturing body containing fine crystal grains obtained in the additive manufacturing step described above, the lower limit of the annealing temperature is preferably above 1050°C, and more preferably above 1100°C. Furthermore, at temperatures above 1250°C, grain growth slows and heat treatment deformation increases, so the upper limit can be set at 1250°C. The addition of Ga is also preferred because it promotes grain coarsening during the annealing process. An annealing time of 1 hour or more is preferred because it stabilizes properties. Longer annealing times are possible, but considering the possibility of surface changes during heat treatment, it is best to set it to 12 hours or less. The annealing atmosphere is selected from air, vacuum, hydrogen flow, and inert gas atmospheres such as nitrogen, argon, and helium. A hydrogen flow or inert gas atmosphere is preferred to prevent surface oxidation during heat treatment. After annealing, cooling can be performed at a rate of approximately 100°C / min by, for example, forced cooling using hydrogen gas or inert gas, opening the furnace to the atmosphere, or rapid cooling by immersion in a liquid.

[0036] According to the manufacturing method of this embodiment, the introduction of strain by plastic processing is not required in the manufacturing process, and the fine crystal grains that have been a problem in additive manufacturing methods can be reduced, making it possible to manufacture Fe—Al-based alloy members of any shape. This effect is particularly suitable for manufacturing plate-shaped Fe—Al-based alloy members having a thickness of 5 mm or more, for which the application of plastic processing has been difficult.

[0037] Although the embodiments of the present invention have been described in detail above, the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the spirit of the present invention as set forth in the claims.

[0038] The Fe-Al alloy and its manufacturing method of the present invention can provide an Fe-Al alloy member with improved vibration-damping properties by reducing the number of fine crystal grains, which makes it possible to apply the alloy to vibration-damping members of any desired shape, for example, a thickness of more than 5 mm, for parts such as vehicle parts for automobiles that require higher quietness and vibration countermeasures. [Example]

[0039] Gas-atomized powder (hereafter referred to as Raw Material A) containing 8.4% Al, the remainder being Fe and unavoidable impurities, and gas-atomized powder (hereafter referred to as Raw Material B) containing 7.0% Al and 2.0% Ga (total of Al and Ga: 9.0%), the remainder being Fe and unavoidable impurities, were prepared and classified to an average particle size D50 of 30–35 μm. Gas atomization was performed by high-frequency melting in a vacuum, dropping the molten alloy from a 5 mm diameter nozzle below the crucible, and atomizing it with high-pressure argon. Using these as raw material powders, a 3D additive manufacturing machine (EOS, EOS-M290) was used to fabricate 2.5 mm wide, 60 mm long, and 11 mm high-rise models using a powder bed method with an S45C base plate and high-speed melting and rapid solidification via laser irradiation. The layer thickness per layer was 40 μm, and the irradiation direction was rotated 67° for each layer. The laser beam diameter was approximately 0.1 mm and the laser output was 300 W. The molding conditions are shown in Table 1. Annealing was performed by heating and holding the material in a hydrogen gas flow at the annealing temperature shown in Table 1 for 0.25 hours (15 minutes), 0.5 hours (30 minutes), or 1 hour (60 minutes), followed by cooling at approximately 100°C / min.

[0040] Next, the structure was observed and various properties were measured. The microstructure was observed on a cross section perpendicular to the thickness direction (stacking direction) for both before and after annealing. Specifically, the cross section perpendicular to the thickness direction was mirror-polished and then examined with a scanning electron microscope (magnification: 200x, measurement range: 10mm). 2 Ten horizontal and ten vertical lines were drawn at equal intervals on the obtained image, and the number of intersections where fine crystal grains (residual fine grains) existed was taken as the area ratio of fine crystal grains (fine crystal part ratio). Ten images were extracted per cross section, and the average value of the area ratio of fine crystal grains measured was calculated.

[0041] The crystal grain size was calculated by observing the sample under an optical microscope (magnification: 100x), drawing a 3 mm line perpendicular to the thickness direction, and counting the number of intersections with the grain boundaries in the area excluding the fine crystals mentioned above. Ten lines were drawn at random so as not to intersect with the same crystal grain, and the average value was taken as the average crystal grain size. The results are also shown in Table 1. Hardness was measured using a micro Vickers hardness tester (Future Tech) at a load of 0.5 kgf for 10 seconds, and the average value was calculated at five points on the sample surface.

[0042] The vibration damping characteristics were evaluated by cutting the above-mentioned shaped bodies into strip-shaped test specimens measuring 1.5 mm in width, 60 mm in length, and 10 mm in stacking height, and then annealing them.The internal friction was then measured at room temperature (22°C) using a free resonance central excitation method.

[0043] [Table 1]

[0044] [Table 2]

[0045] From the results in Table 1, in Examples 1 to 5 of Raw Material A and Examples 6 to 14 of Raw Material B, in which the annealing (heat treatment) temperature was set to 1100°C, the microcrystalline portion ratio (area ratio of fine crystal grains) after annealing was less than 10%. The average crystal grain size exceeded 700 μm, and the defect rate was also less than 0.1%. All of Examples 1 to 14 achieved good internal friction values ​​of 0.0020 or more. In particular, Examples 6 to 14, in which the microcrystalline portion ratio was 0, showed even better values ​​of 0.0030 or more. All of Examples 1 to 14 showed stable Vickers hardness characteristics of 170 HV to 210 HV, confirming that they had strength that would not pose a problem in practical use.

[0046] 1 and 2 show the microstructures of Example 6 before and after annealing as a representative example of the microstructures before and after annealing. Before annealing, fine columnar crystal grains growing in the stacking direction were observed, with a width of approximately 10 μm. On the other hand, after annealing, these fine columnar crystal grains disappeared, and coarse recrystallized grains with an average crystal grain size of approximately 1360 μm were formed. Similarly, for the other Examples, it was confirmed that recrystallization occurred during annealing, most of the fine crystal grains disappeared, and the area ratio (area ratio) of the fine crystal grains was less than 20%.

[0047] On the other hand, in Comparative Examples 1 to 4, the annealing (heat treatment) temperature was 1050°C or less, and the fine crystal grains were not sufficiently removed during annealing, resulting in an area ratio of 20% or more. As an example, for Comparative Example 4, Fig. 3 shows the microstructure before annealing, and Fig. 4 shows the microstructure after annealing. As shown in Fig. 3, before annealing, fine columnar crystal grains that had grown in the stacking direction were observed, with a width of about 10 µm. The internal friction was less than 0.0020 in all cases.

[0048] In Comparative Example 5, the surface energy density was 5 J / mm 2 In the case of the above, there were many defects before annealing, with the defect rate exceeding 0.1%. It was confirmed that recrystallization occurred after annealing, but the crystal grain size was small. For Comparative Example 5, Fig. 5 shows the microstructure before annealing, and Fig. 6 shows the microstructure after annealing. As shown in Fig. 5, before annealing, fine columnar crystal grains that grew in the stacking direction were observed, with a width of about 10 µm. Furthermore, as shown in Fig. 6, recrystallization was observed after annealing, but the disappearance of the fine crystal grains was insufficient. From the above, it is believed that the internal friction value of the damping alloy of Comparative Example 5 was less than 0.0020, which was lower than the values ​​of Examples 1 to 14.

Claims

1. In mass%, Al: 4.0% to 12.0%; Ga: 0.1% or more and 2.0% or less, The balance consists of Fe and unavoidable impurities, The average crystal grain size is more than 700 μm and less than 2000 μm, The area ratio of fine crystal grains having a crystal grain size of less than 100 μm is less than 20%. The Fe-Al alloy is characterized by:

2. In mass%, Al: 4.0% or more and 12.0% or less; Ga: 0.1% or more and 2.0% or less, The balance consists of Fe and unavoidable impurities, The average crystal grain size is more than 700 μm and less than 2000 μm, The area ratio of fine crystal grains having a crystal grain size of less than 100 μm is less than 20%, The internal friction measured by the central excitation method at 22°C is 0.0020 or more. The Fe-Al alloy member is characterized by:

3. The Fe-Al alloy member according to claim 2, having a portion having a thickness of 5 mm or more.

4. In mass%, Al: 4.0% to 12.0%; Ga: 0.1% or more and 2.0% or less, a shaping step in which the powder, the balance of which is Fe and unavoidable impurities, is melted and solidified using a heat source with a surface energy density of 2.6 to 4.8 J / mm to obtain a shaped body; and an annealing step in which the shaped body is held at a temperature higher than 1050°C and not higher than 1250°C for one hour or longer, so that the area ratio of fine crystal grains having an average crystal grain size of more than 700 μm and not more than 2000 μm and a crystal grain size of less than 100 μm becomes less than 20%.

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