Neodymium-iron-boron magnet and preparation method thereof

Abstract

The invention discloses a neodymium iron boron magnet and a preparation method thereof. The neodymium iron boron magnet disclosed by the invention has the following composition: RE Ce Fe < 100-a-b-c-d-e > M < c > B < d > Ti < e > (I), wherein RE is selected from one or more of La, Pr, Nd, Y, Ho, Dy, Gd, Tb and Er, and M is Co, Al, Cu, Zr and Ga; wherein 4 < = b < = 18, 0.3 < = c < = 5, 0.8 < = d < = 0.98, 0.07 < = e < = 0.2, and 27.5 < = a + b < = 32.5; wherein a to e respectively represent the weight parts of the elements. The neodymium-iron-boron magnet is high in cerium content, good in magnetic performance and low in hardness.

Description

Technical Field

[0001] The invention relates to a neodymium iron boron magnet and a preparation method thereof. Background Art

[0002] Rare earth permanent magnet neodymium iron boron (Nd-Fe-B) has a high magnetic energy product and is widely used in machinery, transportation, medical and other fields. The types of rare earth elements in Nd-Fe-B magnets are mainly Pr, Nd and Dy, and the content of rare earth elements in Nd-Fe-B magnets is about 30wt%, which leads to the use of a large amount of Pr, Nd and Dy. Due to the symbiotic characteristics of rare earth elements, the production of Nd-Fe-B magnets has caused unbalanced utilization of rare earth resources. The reserves of rare earth element cerium in the earth's crust are much higher than the content of Pr, Nd and Dy, and the price is much lower than Pr, Nd and Dy. Partially replacing rare earth elements such as Pr, Nd and Dy with Ce can not only effectively reduce costs, but also promote the comprehensive and balanced utilization of rare earth resources. However, the increase in the content of Ce in the magnet will reduce the magnetic properties of the magnet, affecting the promotion of Ce-containing neodymium iron boron magnets.

[0003] CN119230231A discloses a high-strength and high-thermal RTB rare earth permanent magnet, R: 28.5-34.0wt%, R is one or more of Nd, Pr, Dy, Tb, B: 0.85-1.1wt%, Ti: 0.1-0.4wt%, Nb: 0.05-0.5wt%, M: 0.01-8.0wt%, M is at least one of Al, Cu, Ga, Ni, Zn, Sn, Mn, Zr. The rare earth permanent magnet does not contain Ce and has a high cost.

[0004] CN119560253A discloses a NdFeB sintered magnet, comprising: R, R has a mass content of 28-33wt%, R includes Nd and Ce, and optionally includes or excludes at least one of Pr, Dy, Tb, Ho, and Gd; M, M has a mass content of 1.5-2.5wt%, and M is selected from at least one of Co, Cu, Ga, Al, Mn, Nb, W, Hf, and Cr; B, B has a mass content of 0.95-1.05wt%; Ti, Ti has a mass content of 0.1-0.25wt%; Fe is the remainder; Ce has a content of 0.3-5wt%. The magnet has a low cerium content and a high hardness. Summary of the invention

[0005] In view of this, one object of the present invention is to provide a NdFeB magnet having a high cerium content, good magnetic properties and low hardness. Another object of the present invention is to provide a method for preparing a NdFeB magnet, which can improve the magnetic properties of the NdFeB magnet with a high cerium content and reduce the hardness.

[0006] The present invention achieves the above-mentioned purpose through the following technical solutions.

[0007] In one aspect, the present invention provides a neodymium iron boron magnet, characterized in that the neodymium iron boron magnet has a composition as shown below: RE a Ce b Fe 100-a-b-c-d-e M c B d Ti e (I); wherein RE is selected from one or more of La, Pr, Nd, Y, Ho, Dy, Gd, Tb, Er, and M is Co, Al, Cu, Zr, and Ga; Among them, 4≤b≤18, 0.3≤c≤5, 0.8≤d≤0.98, 0.07≤e≤0.2, 27.5≤a+b≤32.5; Wherein, a~e represent the weight percentage of each element respectively.

[0008] According to the NdFeB magnet of the present invention, preferably, the grain boundary phase of the NdFeB magnet contains REFe2 phase.

[0009] According to the NdFeB magnet of the present invention, preferably, the content of RE in the REFe2 phase is 17-33at%, and the content of Fe is 57-74at%.

[0010] According to the NdFeB magnet of the present invention, preferably, RE comprises Gd, Pr and Nd; the content of Gd is 0.25 to 0.4 parts by weight, the content of Pr is 5.5 to 6.5 parts by weight, and the content of Nd is 16 to 19 parts by weight.

[0011] According to the NdFeB magnet of the present invention, preferably, 6≤b≤15, 0.5≤c≤4, 0.85≤d≤0.95, and 0.09≤e≤0.15.

[0012] According to the NdFeB magnet of the present invention, preferably, the hardness of the NdFeB magnet is ≤660 HV.

[0013] On the other hand, the present invention provides a method for preparing the above-mentioned NdFeB magnet, comprising the following steps: (1) Orienting and pressing the alloy fine powder, and then isostatically pressing to obtain a green body; (2) Sintering the green body at 1000-1100°C to obtain a sintered body; subjecting the sintered body to primary tempering at 800-980°C, and then to secondary tempering at 580-700°C to obtain a NdFeB magnet.

[0014] According to the preparation method of the present invention, preferably, the alloy fine powder is formed by mixing a first alloy fine powder and a second alloy fine powder; The first alloy fine powder has a composition as shown in formula (II), and the second alloy fine powder has a composition as shown in formula (III): RE a Ce b Fe 100-a-b-c-α-e M c B α Ti e (II) RE a Ce b Fe 100-a-b-c-β-e M c B β Ti e (III) Among them, 0.8≤α≤0.9, 0.9≤β≤0.98, α≠β.

[0015] According to the preparation method of the present invention, preferably, the average particle size of the alloy fine powder is 2.5-4 μm, the orientation pressing is carried out under the condition that the magnetic field intensity is greater than 1.8 T, and the isostatic pressing pressure is 170-250 MPa.

[0016] According to the preparation method of the present invention, preferably, the following steps are further included: melting the raw materials to obtain alloy liquid; spinning the alloy liquid into sheets to obtain alloy sheets with a thickness of 0.2 to 0.4 mm; The alloy flakes are hydrogen crushed to obtain alloy coarse powder; the alloy coarse powder is jet milled to obtain alloy fine powder.

[0017] The invention makes the NdFeB magnet with high cerium content have high coercivity and low hardness by regulating the element composition and microstructure of the magnet. The magnet of the invention has low rare earth content and low cost. The preparation method of the invention can effectively improve the microstructure of the magnet, increase the coercivity of the magnet and reduce the hardness. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 This is a scanning electron microscope image of the NdFeB magnet of Example 1.

[0019] Figure 2 This is a scanning electron microscope image of the NdFeB magnet of Example 2.

[0020] Figure 3 This is a scanning electron microscope image of the neodymium boron magnet of Example 3.

[0021] Figure 4 This is a scanning electron microscope image of the NdFeB magnet of Example 4.

[0022] Figure 5This is a scanning electron microscope image of the NdFeB magnet of Example 5.

[0023] Figure 6 This is a scanning electron microscope image of the NdFeB magnet of Example 6.

[0024] Figure 7 This is a scanning electron microscope image of the NdFeB magnet of Example 7.

[0025] Figure 8 This is a scanning electron microscope image of the NdFeB magnet of Example 8.

[0026] Fig. 9 This is a scanning electron microscope image of the NdFeB magnet of Example 9. DETAILED DESCRIPTION

[0027] The present invention is further described below in conjunction with specific embodiments, but the protection scope of the present invention is not limited thereto.

[0028] NdFeB magnets The NdFeB magnet of the present invention has the following composition: RE a Ce b Fe 100-a-b-c-d-e M c B d Ti e (I).

[0029] RE is Gd, Pr and Nd. a is the weight percentage of RE. 4≤a≤27; preferably, 23.3≤a≤24.5. In certain embodiments, 23.8≤a≤24.3.

[0030] The content of Gd is 0.25 to 0.4 parts by weight, preferably 0.3 to 0.35 parts by weight, and more preferably 0.33 to 0.34 parts by weight. The content of heavy rare earth elements in the magnet of the present invention is relatively low.

[0031] The content of Pr is 5.5 to 6.5 parts by weight, preferably 5.74 to 6 parts by weight, and more preferably 5.87 to 5.99 parts by weight.

[0032] The content of Nd is 16 to 19 parts by weight, preferably 17.23 to 18.5 parts by weight, and more preferably 17.6 to 17.97 parts by weight.

[0033] b represents the weight percentage of Ce. 4≤b≤18; preferably, 6.5≤b≤10; more preferably, 7.5≤b≤8.

[0034] 27.5≤a+b≤32.5; preferably, 29≤a+b≤32; more preferably, 30≤a+b≤31.5.

[0035] M is Co, Al, Cu, Zr and Ga. c represents the weight fraction of M. 0.3≤c≤5; preferably, 1≤c≤2; more preferably, 1.5≤c≤1.8.

[0036] The content of Co may be 0.1 to 1.5 parts by weight, preferably 0.3 to 1 parts by weight, and more preferably 0.6 to 0.8 parts by weight.

[0037] The content of Al may be 0.1 to 1.5 parts by weight, preferably 0.3 to 1 part by weight, and more preferably 0.5 to 0.7 part by weight.

[0038] The content of Cu may be 0.05 to 0.5 parts by weight, preferably 0.1 to 0.3 parts by weight, and more preferably 0.2 to 0.25 parts by weight.

[0039] The content of Zr may be 0.05 to 0.5 parts by weight, preferably 0.1 to 0.3 parts by weight, and more preferably 0.2 to 0.25 parts by weight.

[0040] The content of Ga may be 0.03 to 0.5 parts by weight, preferably 0.05 to 0.3 parts by weight, and more preferably 0.1 to 0.2 parts by weight.

[0041] d is the weight fraction of B. 0.8≤d≤0.98; preferably, 0.85≤d≤0.95; more preferably, 0.88≤d≤0.91.

[0042] e is the weight percentage of Ti. 0.07≤e≤0.25; preferably, 0.09≤e≤0.15; more preferably, 0.09≤e≤0.1.

[0043] 100-abcde is the weight fraction of Fe. 65≤100-abcde≤67.5; preferably, 66≤100-abcde≤67. In some embodiments, 100-abcde=66.09. In other embodiments, 100-abcde=66.12.

[0044] The grain boundary phase of the NdFeB magnet of the present invention contains REFe2 phase. In certain embodiments, the grain boundary phase also contains RE-rich phase.

[0045] In the REFe2 phase, the content of RE can be 17 to 33 at %, preferably 25 to 32 at %.

[0046] In the REFe2 phase, the Fe content can be 57 to 74 at %, preferably 57 to 63 at %.

[0047] The coercive force of the NdFeB magnet of the present invention may be ≥10 kOe, ≥16 kOe, or ≥16.5 kOe. In some embodiments, the coercive force is ≥17 kOe.

[0048] The hardness of the NdFeB magnet of the present invention is ≤660 HV; preferably, the hardness is ≤600 HV; more preferably, the hardness is ≤615 HV. The hardness of the NdFeB magnet can be ≥580 HV; or ≥570 HV.

[0049] Preparation method of NdFeB magnet The method for preparing the NdFeB magnet of the present invention comprises the following steps: (1) preparing a green body; (2) sintering and tempering. In some embodiments, it also comprises the steps of smelting and preparing alloy sheets and powder making. Each step is described in detail below.

[0050] Steps for preparing the green body The invention orients and presses the alloy fine powder, and then performs isostatic pressing to obtain a green body. The composition of the alloy fine powder is determined according to the composition of the NdFeB magnet.

[0051] The average particle size of the alloy fine powder may be 2.5 to 4 μm.

[0052] Orientation pressing can be carried out under the condition of magnetic field strength greater than 1.8T.

[0053] The isostatic pressure may be 170 to 250 MPa, preferably 190 to 220 MPa.

[0054] In certain embodiments, the alloy fine powder is formed by mixing a first alloy fine powder and a second alloy fine powder.

[0055] The first alloy fine powder has a composition as shown in formula (II): RE a Ce b Fe 100-a-b-c-α-e M c B α Ti e (II) The second alloy fine powder has a composition as shown in formula (III): RE a Ce b Fe 100-a-b-c-β-e M c B β Ti e (III) In formula (II) and formula (III), the meanings and values ​​of a, b, c and e are as described above and will not be repeated here. In formula (II) and formula (III), α≠β.

[0056] 0.9≤β≤0.98; preferably, 0.9≤β≤0.96; more preferably, 0.92≤β≤0.94.

[0057] 0.8≤α≤0.9; preferably, 0.81≤α≤0.85; more preferably, 0.82≤α≤0.83.

[0058] The mass ratio of the first alloy fine powder to the second alloy fine powder may be 1:(0.5-2); preferably 1:(0.8-1.5); and more preferably 1:(1-1.2).

[0059] Sintering and tempering steps The invention sintered the green body at 1000-1100°C to obtain a sintered body; performed primary tempering at 800-980°C and then performed secondary tempering at 580-700°C to obtain a NdFeB magnet.

[0060] The sintering temperature is 1000-1100°C; preferably 1020-1070°C.

[0061] The sintering time may be 1 to 8 hours, preferably 4 to 6 hours, and more preferably 4 to 5 hours.

[0062] Preferably, the primary tempering temperature is 850-950°C; more preferably 880-910°C.

[0063] The primary tempering time may be 1 to 8 h, preferably 2 to 6 h, and more preferably 2.5 to 3 h.

[0064] Preferably, the secondary tempering temperature is 600-680°C; more preferably 640-650°C.

[0065] The secondary tempering time may be 1 to 8 hours, preferably 3 to 7 hours, and more preferably 4 to 5 hours.

[0066] This helps to form a proper microstructure, improve the magnetic properties of the magnet and reduce hardness.

[0067] Steps for melting and preparing alloy sheets The invention melts raw materials to obtain alloy liquid; and slices the alloy liquid to obtain alloy sheets.

[0068] The thickness of the alloy sheet is 0.2 to 0.4 mm.

[0069] The melting temperature may be 1000-1800°C; preferably, the melting temperature is 1200-1500°C.

[0070] Melting can be carried out under vacuum conditions. Vacuum can refer to a pressure less than or equal to 0.05MPa; it can also refer to a pressure less than or equal to 0.01MPa.

[0071] Flour making steps The invention hydrogen-crushes alloy flakes to obtain alloy coarse powder; and air-grinds the alloy coarse powder to obtain alloy fine powder.

[0072] Hydrogen crushing includes the steps of hydrogen absorption and dehydrogenation.

[0073] The hydrogen absorption may be carried out at 0.08 to 0.11 MPa; preferably, the hydrogen absorption is carried out at 0.09 to 0.1 MPa; more preferably, the hydrogen absorption is carried out at 0.095 to 0.1 MPa.

[0074] The hydrogen absorption time may be 1 to 5 hours; preferably, the hydrogen absorption time is 2 to 4 hours; more preferably, the hydrogen absorption time is 2 to 3 hours.

[0075] The dehydrogenation temperature may be 500-650°C; preferably, the dehydrogenation temperature is 550-600°C; more preferably, the dehydrogenation temperature is 580-590°C.

[0076] The dehydrogenation time may be 5 to 10 hours; preferably, the dehydrogenation time is 6 to 9 hours; more preferably, the dehydrogenation time is 7 to 8 hours.

[0077] The average particle size of the alloy coarse powder may be 0.1 to 3 mm, preferably 0.5 to 2 mm, and more preferably 0.5 to 1.5 mm.

[0078] The hydrogen content of the alloy coarse powder may be 800 to 1200 ppm.

[0079] The average particle size of the alloy fine powder may be 2.5 to 4 μm.

[0080] Here is the test method: Magnetic properties: The cylindrical specimens were prepared by wire cutting, coreless grinding and end grinding. The demagnetization curve of the specimens was tested at 20°C using the NIM-62000 permanent magnet material magnetic properties measurement system to obtain magnetic properties such as remanence, coercive force, magnetic energy product, and squareness.

[0081] Hardness: The sample size is 15mm×15mm×4mm. A Vickers hardness tester is used on the 15mm×15mm surface. The loading pressure is 0.5kg and the holding time is 15s. 10 points are measured for each sample and the average value is taken.

[0082] Backscattered SEM images: The images were taken using a Quanta 250 FEG scanning electron microscope.

[0083] Examples 1 to 9 According to the composition of the NdFeB magnet, raw materials are provided, and the raw materials are melted in a medium frequency induction melting furnace under vacuum (pressure < 0.05MPa) and at a temperature of 1200-1500°C to obtain alloy liquid. The alloy liquid is spun into sheets to obtain alloy sheets with a thickness of 0.2-0.4mm.

[0084] The alloy flakes were placed in a hydrogen crushing furnace, the hydrogen crushing furnace was evacuated, and then hydrogen was introduced to 0.098MPa, so that the alloy flakes absorbed hydrogen for 3 hours to obtain hydrogen-absorbed alloy flakes. The hydrogen-absorbed alloy flakes were dehydrogenated at 580°C for 8 hours to obtain alloy coarse powder with an average particle size (SMD) of 0.1 to 3 mm. The alloy coarse powder was jet-milled to obtain alloy fine powder with an average particle size (SMD) of 2.5 to 4 μm.

[0085] The alloy fine powder is oriented and pressed in a magnetic field forming press with an orientation magnetic field greater than 1.8 T, and then isostatically pressed at a pressure of 200 MPa to obtain a green body.

[0086] The green body was sintered at 1060°C for 5 hours to obtain a sintered body, and the sintered body was tempered at 910°C for 3 hours and then tempered at 640°C for 5 hours to obtain a NdFeB magnet.

[0087] The hydrogen content in the alloy coarse powder is shown in Table 1. The element composition, magnetic properties and hardness of the NdFeB magnets of various embodiments are shown in Table 2.

[0088] Three points were randomly selected from the REFe2 phase in the scanning electron microscope image of Example 3, and they were recorded as S1, S2 and S3. Four points were randomly selected from the REFe2 phase in the scanning electron microscope image of Example 9, and they were recorded as M1, M2, M3 and M4. The contents of RE and Fe in the above points are shown in Table 3.

[0089]

[0090]

[0091] It can be seen from Examples 1-6 that when the B content decreases to a certain value, the coercivity gradually increases, but as the B content further increases, the coercivity gradually decreases. Figure 1-6 It can be seen that the content of the REF2 phase in the grain boundary phase of the magnet of Examples 1-6 gradually increases, the coercive force shows a trend of first increasing and then decreasing, and the hardness shows a trend of gradually decreasing. It can be seen that the content of the REF2 phase has an important influence on the magnetic properties and hardness of the magnet. This may be due to the increase in the content of the REF2 phase, the isolation effect between the grains is enhanced, which effectively weakens the exchange coupling between adjacent grains, but too much REF2 phase will become a nucleation point during the demagnetization process of the magnet, causing the coercive force to decrease.

[0092] Comparing Example 3 with Example 9, it can be seen that the Ti content and the contents of RE and Fe in the REFe2 phase have an important influence on the magnetic properties and hardness of the magnet. This may be due to the increase in the Fe content in the REFe2 phase, which enhances the exchange coupling between the main phase grains and leads to a decrease in coercivity.

[0093] Example 10 According to the composition of the first alloy sheet, raw materials are provided, and the raw materials for forming the first alloy sheet are melted in a medium frequency induction melting furnace under vacuum (pressure < 0.05 MPa) and at a temperature of 1200-1500° C. to obtain a first alloy liquid. The first alloy liquid is spun into sheets to obtain a first alloy sheet with a thickness of 0.2-0.4 mm.

[0094] According to the composition of the second alloy sheet, raw materials are provided, and the raw materials for forming the second alloy sheet are melted in a medium frequency induction melting furnace under vacuum (pressure < 0.05 MPa) and at a temperature of 1200-1500° C. to obtain a second alloy liquid. The second alloy liquid is spun into sheets to obtain a second alloy sheet with a thickness of 0.2-0.4 mm.

[0095] The first alloy sheet and the second alloy sheet are hydrogen crushed to obtain the first alloy coarse powder with an average particle size (SMD) of 0.1 to 3 mm and the second alloy coarse powder with an average particle size (SMD) of 0.1 to 3 mm. The steps of hydrogen crushing are as follows: The alloy flakes were placed in a hydrogen crushing furnace, the hydrogen crushing furnace was evacuated, and then hydrogen was introduced to 0.098 MPa to allow the alloy flakes to absorb hydrogen for 3 hours to obtain hydrogen-absorbed alloy flakes. The hydrogen-absorbed alloy flakes were dehydrogenated at 580°C for 8 hours.

[0096] The first alloy coarse powder and the second alloy coarse powder are respectively subjected to air flow milling to obtain a first alloy fine powder with an average particle size (SMD) of 2.5 to 4 μm and a second alloy fine powder with an average particle size (SMD) of 2.5 to 4 μm.

[0097] The first alloy fine powder and the second alloy fine powder are mixed in a mass ratio of 1:1 to obtain a mixed alloy fine powder. The mixed alloy fine powder is oriented and pressed in a magnetic field forming press with an orientation magnetic field greater than 1.8 T, and then isostatically pressed at a pressure of 200 MPa to obtain a green body.

[0098] The green body was sintered at 1060°C for 5 hours to obtain a sintered body, and the sintered body was tempered at 910°C for 3 hours and then tempered at 650°C for 5 hours to obtain a NdFeB magnet.

[0099] The element composition, phase content of the first alloy sheet, the second alloy sheet and the NdFeB magnet, and the properties of the NdFeB magnet are shown in Table 4.

[0100]

[0101] It can be seen from Example 4 and Example 10 that the coercive force of the magnet prepared by the dual alloy process is higher than that by the single alloy process, and the hardness is lower than that by the single alloy process.

[0102] The present invention is not limited to the above-mentioned embodiments. Without departing from the essential content of the present invention, any deformation, improvement and substitution that can be conceived by those skilled in the art shall fall within the scope of the present invention.

Claims

1. A neodymium iron boron magnet, characterized in that: The NdFeB magnet has the following composition: RE a What b Fe 100-a-b-c-d-e M c B d IT e (I); wherein RE is selected from one or more of La, Pr, Nd, Y, Ho, Dy, Gd, Tb, Er, and M is Co, Al, Cu, Zr, and Ga; Among them, 4≤b≤18, 0.3≤c≤5, 0.8≤d≤0.98, 0.07≤e≤0.2, 27.5≤a+b≤32.5; Wherein, a~e represent the weight percentage of each element respectively.

2. The NdFeB magnet according to claim 1, characterized in that: The grain boundary phase of the NdFeB magnet contains REFe2 phase.

3. The NdFeB magnet according to claim 2, characterized in that: The content of RE in the REFe2 phase is 17-33at%, and the content of Fe is 57-74at%.

4. The NdFeB magnet according to claim 1, characterized in that: RE includes Gd, Pr and Nd; the content of Gd is 0.25 to 0.4 parts by weight, the content of Pr is 5.5 to 6.5 parts by weight, and the content of Nd is 16 to 19 parts by weight.

5. The NdFeB magnet according to claim 1, characterized in that: 6≤b≤15, 0.5≤c≤4, 0.85≤d≤0.95, 0.09≤e≤0.

15.

6. The NdFeB magnet according to any one of claims 1 to 5, characterized in that: The hardness of the NdFeB magnet is ≤660 HV.

7. The method for preparing a NdFeB magnet according to any one of claims 1 to 6, characterized in that: The steps include: (1) Orienting and pressing the alloy fine powder, and then isostatically pressing to obtain a green body; (2) Sintering the green body at 1000-1100°C to obtain a sintered body; subjecting the sintered body to primary tempering at 800-980°C, and then to secondary tempering at 580-700°C to obtain a NdFeB magnet.

8. The preparation method according to claim 7, characterized in that: The alloy fine powder is formed by mixing a first alloy fine powder and a second alloy fine powder; The first alloy fine powder has a composition as shown in formula (II), and the second alloy fine powder has a composition as shown in formula (III) composition: RE a What b Fe 100-a-b-c-α-e M c B α IT e (II) RE a What b Fe 100-a-b-c-β-e M c B β IT e (III) Among them, 0.8≤α≤0.9, 0.9≤β≤0.98, α≠β.

9. The preparation method according to claim 7, characterized in that: The average particle size of the alloy fine powder is 2.5-4 μm, the orientation pressing is carried out under the condition that the magnetic field intensity is greater than 1.8 T, and the isostatic pressing pressure is 170-250 MPa.

10. The preparation method according to claim 7, characterized in that: The following steps are also included: The raw materials are melted to obtain alloy liquid; the alloy liquid is spun to obtain alloy sheets with a thickness of 0.2 to 0.4 mm; The alloy flakes are hydrogen crushed to obtain alloy coarse powder; the alloy coarse powder is jet milled to obtain alloy fine powder.

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