CE-marked sintered NDFEB magnet and manufacturing process therefor

Description

BACKGROUND OF THE INVENTIONField of the Invention

[0001] The present invention relates to a Ce-containing and sintered NdFeB magnet and a corresponding manufacturing method thereof.Description of the Prior Art

[0002] Elements with high abundance, such as La and Ce, are often doped into NdFeB magnets for price reasons. However, since La and Ce have lower magnetic performance parameters, this leads to a significant decrease in magnetic performance after addition. To optimize such magnets, the industry has adopted a multi-principal phase process, surface grain boundary diffusion and other ways to optimize magnets.

[0003] CN102800454A relates to a low-cost dual-phase Ce permanent magnet alloy and a preparing method thereof, which can obtain higher magnetic properties by forming Nd-Fe-B and (Ce, Re)-Fe-B phases. However, the magnetocrystalline anisotropy field constant (HA) of the (Ce, Re)-Fe-B principal phase in this method is reduced too much, which limits the improvement of magnetic properties.

[0004] WO 2020 / 233316 A1 relates to a method of diffusing rare earth elements into the basic magnet which contains a CeFe 2 phase. Thereby, the magnetic performance of the CeFe 2 phase can be enhanced by transforming the same into an REFe 2 phase. However, REFe 2 easily appears in the grain boundary phase with high proportion addition of Ce. Further, the single REFe 2 phase has weak magnetic isolation effect, which reduces the coercivity of magnet.

[0005] Y. Zhang et al., Acta Mater. 2017, 128, 22-30 relates to the effects of REFe 2 on microstructure and magnetic properties of Nd-Ce-Fe-B sintered magnets. The publication states that by sintering of the green compacts above the melting point of the REFe 2 phase, densification of the magnet and the formation of continuous and smooth grain boundary phases is promoted.SUMMARY OF THE INVENTION

[0006] The invention is defined by the appended claims. The description that follows is subjected to this limitation. Any disclosure lying outside the scope of said claims is only intended for illustrative as well as comparative purposes.

[0007] In particular, the present invention relates to a Ce-containing and sintered NdFeB magnet as defined in claim 1 and a corresponding manufacturing method thereof as defined in claim 5.

[0008] Further aspects of the present disclosure could be learned from the dependent claims or the following description.BRIEF DESCRIPTION OF THE DRAWING

[0009] Features will become apparent to those of ordinary skill in the art by describing in detail exemplary embodiments with reference to the attached drawings in which: Figure 1 is a schematic diagram of magnet with a multi-layered grain boundary structure. Figure 2 is an image obtained by high-angle annular dark-field imaging in scanning transmission electron microscopy (HAADF-STEM) and energy-dispersive X-ray spectroscopy (EDS) of a grain boundary location of the magnet of Implementing Example 1. DETAILED DESCRIPTION

[0010] Reference will now be made in detail to embodiments, examples of which are illustrated in the accompanying drawings. Effects and features of the exemplary embodiments, and implementation methods thereof will be described with reference to the accompanying drawings. In the drawings, like reference numerals denote like elements, and redundant descriptions are omitted. The present disclosure, however, is limited by the scope of the appended claims.General Concept

[0011] The present invention provides a Ce-containing and sintered NdFeB magnet comprising grains composed of a RE 2 Fe 14 B-type main phase and a multi-layered grain boundary structure between the grains. The multi-layered grain boundary structure includes or consists of - from outside to inside of the multi-layered grain boundary structure and in direct order - layers composed of (or consisting of) the following phases: a RE-rich phase, a Fe-rich phase, and a REFe 2 phase. RE is a rare earth metal including Ce and at least one of Nd and Pr. A weight content of Ce at the magnet alloy composition (i.e. the sum of all elements forming the alloy of the sintered NdFeB magnet) is in the range of 3.00wt.% to 15.00wt. %.

[0012] Thus, the sintered NdFeB magnet is a rare earth iron alloy of RE 2 Fe 14 B-type. The main phase of the alloy has a composition of two rare earth atoms (RE) to 14 iron atoms with one boron atom. Cobalt is partially substituted for iron to improve high temperature performance. Besides at least Nd and / or Pr, the magnet alloy includes Ce as rare earth mandatory elements in an amount of 3.00wt.% to 15.00wt.% based on a total weight of the magnet alloy composition. The magnet alloy may also include other rare earth metals, for example Dy and Tb. Furthermore, the magnet alloy may include other metallic or non-metallic alloy components that can be added to optimize the magnet properties for the particular application. Metallic alloy components include Al, Cu, Ga and Ti, and non-metallic alloy components may include small amounts of, for example, H, C, F, N and O.

[0013] The sintered NdFeB magnet has a RE-T-B-M magnet alloy composition where RE is a rare earth metal including Ce and at least one of Nd and Pr; T is one or both of Fe and Co; B stands for boron; M is one or more element selected from the group consisting of Al, Cu, Ga, and Ti; and wherein the weight contents of the RE-T-B-M magnet alloy composition are set as follows: RE: 28.50wt.% to 35.00wt.%, preferably 29.50wt.% to 34.00wt.%, in particular 30.10wt.% to 33.50wt. %; Ce: 3.00wt.% to 15.00wt.%; preferably 5.00wt.% to 10.00wt.%; Nd and Pr: 14.00wt.% to 29.00wt.%, preferably 15.00wt.% to 28.00wt.%, in particular 15.30wt. % to 27.10wt. %; B: 0.70wt.% to 1.20wt.%, preferably 0.80wt.% to 1.10wt.%, in particular 0.85wt.% to 1.05wt. %; Co: 0.10 wt. % to 3.00wt. %, preferably 0.50 wt.% to 2.00wt. %; M: 0.10wt.% to 3.00wt.%, preferably 0.30wt.% to 1.50wt.%, in particular 0.55wt.% to 1.20wt.%; and the residual is Fe and unavoidable impurities (caused, for example, by condition of manufacturing).

[0014] According to a preferred embodiment, the weight contents of Al, Cu, Ga, and Ti as metallic alloy components of the RE-T-B-M magnet alloy composition are independently from each other set as follows: Al: 0.01wt.% to 1.00wt.%, preferably 0.05wt.% to 0.60wt.%; Cu: 0.01wt.% to 1.00wt.%, preferably 0.10wt.% to 0.50wt.%; Ga: 0.01wt.% to 1.00wt.%, preferably 0.10wt.% to 0.50wt.%; and Ti: 0.01wt.% to 1.00wt.%, preferably 0.10wt.% to 0.40wt.%.

[0015] In particular, the Ce-containing and sintered NdFeB magnet may have the following RE-T-B-M magnet alloy composition: RE: 30.10wt.% to 33.50wt.% and 3.00wt.% to 15wt.% thereof Ce; B: 0.85wt.% to 1.05wt.%; Al: 0.05wt. % to 0.60wt. %; Cu: 0.10wt.% to 0.50wt.%; Co: 0.50 wt. % to 2.00wt. %; Ga: 0.10wt. % to 0.50wt.%; and Ti: 0.10wt. % to 0.40wt.%, wherein the residual is Fe and unavoidable impurities.

[0016] In accordance with the before mentioned embodiments or independently thereof, the compositions of the layers of the multi-layered grain boundary structure are set as follows.

[0017] In the RE-rich phase, RE takes an atomic proportion of 50.0at.% to 63.0at.%, preferably 50.2at.% to 62.3at.%, Fe plus Co takes an atomic proportion of 30.0at.% to 40.0at.%, preferably 32.2at.% to 39.7at.%, and M takes an atomic proportion of 2.0at.% to 12.0at.%, preferably 2.2at.% to 10.1at.%, wherein the components plus unavoidable impurities add up to 100at. %.

[0018] In the Fe-rich phase, RE takes an atomic proportion of 10.0at.% to 30.0at.%, preferably 12.4at.% to 26.0at.%, Fe plus Co takes an atomic proportion of 65.0at.% to 85.0at.%, preferably 68.1at.% to 81.4at.%, and M takes an atomic proportion of 1.0at.% to 7.0at.%, preferably 1.3at.% to 6.2at.% , wherein the components plus unavoidable impurities add up to 100at.%.

[0019] In the REFe 2 phase, RE takes an atomic proportion of 25.0at.% to 35.0at.%, preferably 28.1at.% to 33.8at.%, Fe plus Co takes an atomic proportion of 60.0at.% to 72.0at.%, preferably 61.4at.% to 69.8at.%, and M takes an atomic proportion of 0.5at.% to 6.0at.%, preferably 0.6at.% to 4.8at.% , wherein the components plus unavoidable impurities add up to 100at.%.

[0020] In the multi-layered grain boundary structure, the RE-rich phase layer has a thickness of 1nm to 21nm, the Fe-rich phase layer has a thickness of 1nm to 15nm, and the REFe 2 phase layer has a thickness of 8nm to 550nm.

[0021] Thus, the magnet includes a multi-layered grain boundary phase structure. A first layer of the multi-layered structure is a RE-rich phase, which is deposited on the main phase grains of the magnet composition. Atomic ratio of rare earth elements is over 50% and atomic ratio of Fe element is less than 50% in the RE-rich phase. This kind of grain phase has poor magnetic conductivity and better magnetic isolation effect during demagnetization. In addition, surface defects of main phase grains are reduced due to the presence of the RE-rich phase with high concentration of rare earth elements. The reverse magnetic domains are difficult to be nucleated.

[0022] The second layer of the multi-layered structure is a Fe-rich phase with high concentration of Fe element. But the magnetic conductivity of reverse magnetic domains already gets weaker after passing the first layer of the multi-layered structure.

[0023] The third layer of the multi-layered structure is a REFe 2 phase which has weaker magnetic isolation effect compared with the first layer. But the third layer has larger thickness which can also restrain the extension of reverse magnetic domains. The multi-layered grain boundary phase structure improves the magnetic isolation effect and enhanced the coercivity.Preparation Method

[0024] A manufacturing method of the Ce-containing and sintered NdFeB magnet comprising grains composed of a RE 2 Fe 14 B-type main phase and a multi-layered grain boundary structure between the grains as defined above includes the following steps: a) Preparing alloy flakes of the magnet alloy composition by a strip casting process, subjecting the alloys flakes to hydrogen decrepitation und pulverizing the product by jet milling to obtain an alloy powder; b) Pressing the magnetic powder into a green compact under a magnetic field for orientation followed by cold isostatic pressing; c) sintering the green compact at 950°C to 1100°C for 2 to 15h, preferably at 1000°C to 1050°C for 4 to 12h, for example, 1010°C for a duration time of 6 hours; d) After sintering, subjecting the obtained sintered NdFeB magnets to a three step annealing treatment, wherein in a first step of the annealing treatment a temperature is in the range of 600°C to 750°C, preferably 630°C to 730°C, for example 650°C, for 1h to 5h, preferably 2h to 4h, for example 3h, in a second step of the annealing treatment a temperature is in the range of 800°C to 950°C, preferably 820°C to 930°C, for example 850°C, for 1h to 5h, preferably 2h to 4h, for example 3h, and in a third step of the annealing treatment a temperature is in the range of 420°C to 560°C, preferably 450°C to 540°C, for example 480°C, for 1h to 5h, preferably 2h to 4h, for example 3h.

[0025] A cooling rate in each of the three steps may be at least 10°C / min.

[0026] The alloy flakes are separately prepared by the strip casting process using vacuum induction furnace. The alloys of the strip casting are subjected to hydrogen decrepitation and a jet milling process to be pulverized into magnetic powders.

[0027] The magnetic powders are then pressed into green compacts under a magnetic field for orientation. The green compacts are subjected to cold isostatic pressing for increasing density and homogeneity.

[0028] The temperature interval of the sintering step may be, for example, at 1000°C to 1050°C with a duration time of 4 to 12 hours. In particular, the sintering temperature can be set to 1010°C for a duration time of 6 hours.

[0029] After sintering, the magnets are subjected to a three steps of annealing treatment. For example, a first step temperature is between 630°C to 730°C which is near the eutectic point of RE-rich phase. Thereby, the RE-rich phase has a better wettability and is easy to coat around the main phase grains to form a first grain boundary layer.

[0030] In a second step of the annealing treatment, the temperature is raised to be between, for example, 820°C to 930°C, which is near the eutectic point of the REFe 2 phase. Rare earth elements can separate out from the REFe 2 phase and diffuse into the RE-rich of the first grain boundary layer, the RE-rich phase then has a higher rare earth element concentration. Thereby, a part of the REFe 2 phase is transformed into a Fe-rich phase because of the reduction of rare earth element concentration. The Fe-rich phase forms the second grain boundary layer.

[0031] The residual part of the REFe 2 phase that joins the Fe-rich phase and is farthest from the main phase grains and maintained in its original state. The residual part of the REFe 2 phase forms the third grain boundary layer. The annealing temperature during the third step of the annealing treatment is, for example, in the range of 450°C to 540°C for optimizing the grain boundary distribution.

[0032] More preferably, in the Implementing Examples, the first step annealing temperature was set as 650°C and the cooling rate was at least 10°C / min. The second step annealing temperature was set as 850°C and the cooling rate was at least 10°C / min. The third step annealing temperature was set as 480°C and the cooling rate was at least 10°C / min.Testing method of the grain boundary phase thickness and composition in the multi-layered structure

[0033] The longest continuous grain boundary around the main phase grain was divided into five equal sections by four dividing lines (line 5 in fig.1, left), then the thickness of the separately corresponding grain boundary phases was measured, that means the thickness of the layers consisting of the RE-rich grain boundary phase 2, the Fe-rich grain boundary phase 3, and the ReFe 2 grain boundary phase 4 (cf. Fig 1, right) are determined. Five main phase grains were measured by the method for each sample in total.

[0034] Then twenty groups of data were obtained for every sample and averages, minima, and maxima value were summarized.

[0035] Further, energy dispersive spectroscopy (EDS) was used to detect the element content in the width center of the dividing lines for different grain boundary phases. Five main phase grains were measured by the same method for the same sample. Twenty groups of data were obtained for every sample and averages of the element contents were summarized.

[0036] To have a better understanding of the present invention, the examples set forth below provide illustrations of the present invention. The examples are only used to illustrate the present invention and do not limit the scope of the present invention.Examples

[0037] Alloy flakes were separately prepared by strip casting process using vacuum induction furnace according to composition of Implementing Examples 1 to 4 and Comparative Examples 1 and 2. The alloys were subjected to hydrogen decrepitation under a hydrogen pressure of 0.2MPa for a duration time of 2 hours. And then the alloys were heated to 550°C for dehydrogenation for a duration time of 6 hours.

[0038] The alloy flakes after hydrogen treatment were then pulverized to magnetic powders with average particle size of 4.0µm by jet milling. Then the magnetic powders were pressed into green compacts under a 2.0T magnetic field for orientation. The green compacts were subjected to cold isostatic pressing under a pressure of 200MPa. The green compacts were sintered at 1010°C for a duration time of 6 hours in a vacuum furnace.

[0039] After cooling to room temperature, the sintered magnets were reheated to 650°C for a duration time of 3 hours and then cooled to room temperature with a cooling rate at least 10°C / min. Then the magnets were reheated to 850°C for a duration time of 3 hours, after which the magnets were cooled to room temperature with a cooling rate at least 10°C / min. At last the magnets were reheated to 480°C for a duration time of 3 hours and then cooled to room temperature with a cooling rate at least 10°C / min.

[0040] The annealed magnets were machined into cylinders for magnetic testing. Transmission electron microscope (TEM) and energy dispersive spectroscopy (EDS) were used for analysing the microstructure.

[0041] Composition and magnetic performance information of the samples is summarized in Table 1, thickness of various grain boundary phases in the multi-layered structure are summarized in Table 2, element contents of RE-rich phase are summarized in Table 3, element contents of Fe-rich phase are summarized in Table 4, element contents of REFe 2 phase are summarized in Table 5. Table 1 - Composition and magnetic performance of the magnetselement composition (wt.%)magnetic propertiesAlBCoCuFeGaNd / PrTiCeΣReBr(T)Hcj (kA / m)Implementing Example 10.050.920.900.15bal.0.2024.300.156.0030.301.38995.80Implementing Example 20.601.050.500.10bal.0.1027.100.403.0030.101.391313.40Implementing Example 30.100.852.000.50bal.0.5026.500.107.0033.501.291277.58Implementing Example 40.050.920.90.15bal.0.2015.300.1515.0030.301.31827.84Comparative Example 10.050.920.900.15bal.0.2028.300.152.0030.301.411086.54Comparative Example 20.050.920.900.15bal.0.2012.300.1518.0030.301.27644.76 Table 2 - Thickness of grain boundary phase in the multi-layered structure thickness of RE-rich phasethickness of Fe-rich phasethickness of REFe 2 phaseMax. (nm)Min. (nm)Ave. (nm)Max. (nm)Min. (nm)Ave (nm)Max. (nm)Min. (nm)Ave. (nm)Implementing Example 1814723471947Implementing Example 2713613436841Implementing Example 3212815275501258Implementing Example 419179265351153Comparative Example 1no multi-layered structureComparative Example 2no multi-layered structure Table 3 - Element composition of RE-rich phase in the multi-layered structure element composition of RE-rich phase (at.%)RE (at.%)Fe+Co (at. %)Al (at.%)Cu (at.%)Ga (at.%)Ti (at. %)M(Al+Cu+Ga+Ti) (at.%)Implementing Example 154.942.90.40.80.50.52.2Implementing Example 250.239.73.81.71.53.110.1Implementing Example 362.332.21.80.81.41.55.5Implementing Example 456.341.40.30.70.60.72.3Comparative Example 1no multi-layered structureComparative Example 2no multi-layered structure Table 4 - Element composition of Fe-rich phase in the multi-layered structure element composition of Fe-rich phase (at.%)RE (at.%)Fe+Co (at. %)Al (at.%)Cu (at.%)Ga (at.%)Ti (at. %)M(Al+Cu+Ga+Ti) (at.%)Implementing Example 119.279.50.30.30.30.41.3Implementing Example 212.481.43.30.80.91.26.2Implementing Example 326.068.11.22.11.41.25.9Implementing Example 422.375.40.60.70.50.52.3Comparative Example 1no multi-layered structureComparative Example 2no multi-layered structure Table 5 - Element composition of REFe 2 phase in the multi-layered structure element composition of REFe 2 phase (at.%)RE (at.%)Fe+Co (at. %)Al (at.%)Cu (at.%)Ga (at.%)Ti (at. %)M(Al+Cu+Ga+Ti) (at.%)Implementing Example 130.169.30.20.20.10.10.6Implementing Example 228.169.81.10.20.40.42.1Implementing Example 333.861.40.81.71.40.94.8Implementing Example 428.568.10.60.81.01.03.4Comparative Example 1no multi-layered structureComparative Example 2no multi-layered structure

[0042] The Ce additive weight ratio of Implementing Example 1 was 6.0%, and the sample had a Br of 1.38 T, and a Hcj of 995.80 kA / m.

[0043] The Ce additive weight ratio of Implementing Example 4 was as high as 15.0wt%. Hcj was still 827.84 kA / m.

[0044] In the magnet of Implementing Examples 1 to 4 there exists a multi-layered structure in the grain boundary phase. From outside to inside of the multi-layered structure, layers with the following phases are found in direct order: the RE-rich phase, the Fe-rich phase, and the REFe 2 phase. This multi-layered grain boundary phase structure could restrain the reduction of Hcj even in case of high ratio addition of Ce element.

[0045] In the magnet of Comparative Example 1, a REFe 2 phase and multi-layered structure was not found by the microstructure analysis for low addition ratio of Ce element (2.00wt.%). Even though the remanence (Br) was high at 1.41 T, the intrinsic coercivity (Hcj) dropped down to only 1086.54 kA / m. From the comparison of Comparative Example 1 with Implementing Example 2 including 3.00wt.% Ce (intrinsic coercivity Hcj of 1313.40 kA / m and remanence Br at 1.39 T) it can thus be deduced that a content of at least 3.00wt.% of Ce is necessary for forming the multi-layered structure and thereby enhancing the intrinsic coercivity Hcj.

[0046] In the magnet of Comparative Example 2, a large amount of REFe 2 phase was found for high addition ratio of Ce element (18wt.%). The REFe 2 phase was widely distributed between the main grains, and the multi-layered grain boundary structure was hard to form. As a consequence, the intrinsic coercivity Hcj dropped down to only 644.76 kA / m at even low remanence Br of 1.27 T.

[0047] The Ce content thus has an influence on forming the desired multi-layered grain boundary structure. In absence of the multi-layered grain boundary structure, the magnets of the Comparative Examples have lower intrinsic coercivity.List of Reference Signs

[0048] 1grains formed of main phase 2RE-rich layer of grain boundary phase multi-layered structure 2awidth center of RE-rich layer 3Fe-rich layer of grain boundary phase multi-layered structure 3awidth center of Fe-rich layer 4REFe 2 layer of grain boundary phase multi-layered structure 5thickness test location of multi-layered structure

Claims

1. A Ce-containing and sintered NdFeB magnet comprising grains (1) composed of a RE2Fe14B-type main phase and a multi-layered grain boundary structure between the grains (1), wherein the multi-layered grain boundary structure includes from outside to inside of the multi-layered structure and in direct order layers (2, 3, 4) composed of the following phases: a RE-rich phase, a Fe-rich phase, and a REFe2 phase, wherein the magnet alloy composition is a RE-T-B-M magnet alloy composition where • RE is a rare earth metal including Ce and at least one of Nd and Pr; • T is one or both of Fe and Co; • B stands for boron; • M is one or more element selected from the group consisting of Al, Cu, Ga, and Ti; wherein the weight contents of the RE-T-B-M magnet alloy composition are set as follows: • RE: 28.50wt.% to 35.00wt.%; • Ce: 3.00wt.% to 15.00wt.%; • Nd and Pr: 14.00wt.% to 29.00wt.%; • B: 0.70wt.% to 1.20wt.%; • Co: 0.10 wt. % to 3.00wt.%; • M: 0.10wt. % to 3.00wt.%; and • the residual is Fe and unavoidable impurities; characterised in that (i) in the RE-rich phase, RE takes an atomic proportion of 50.0at.% to 63.0at.%, Fe plus Co takes an atomic proportion of 30.0at.% to 40.0at.%, and M takes an atomic proportion of 2.0at.% to 12.0at.%, wherein the components plus unavoidable impurities add up to 100at.%; (ii) in the Fe-rich phase, RE takes an atomic proportion of 10.0at.% to 30.0at.%, Fe plus Co takes an atomic proportion of 65.0at.% to 85.0at.%, and M takes an atomic proportion of 1.0at.% to 7.0at.%, wherein the components plus unavoidable impurities add up to 1 00at.%; (iii) in the REFe2 phase, RE takes an atomic proportion of 25.0at.% to 35.0at.%, Fe plus Co takes an atomic proportion of 60.0at.% to 72.0at.%, and M takes an atomic proportion of 0.5at.% to 6.0at.%, wherein the components plus unavoidable impurities add up to 100at.%; and wherein the RE-rich phase layer (2) has a thickness of 1nm to 21nm, the Fe-rich phase layer (3) has a thickness of 1nm to 15nm, and the REFe2 phase layer (4) has a thickness of 8nm to 550nm.

2. The Ce-containing and sintered NdFeB magnet of claim 1, wherein the weight contents of the RE-T-B-M magnet alloy composition are set as follows: • RE: 29.50wt.% to 34.00wt.%, in particular 30.10wt.% to 33.50wt.%; • Ce: 5.00wt.% to 10.00wt.%; • Nd and Pr: 15.00wt.% to 28.00wt.%, in particular 15.30wt.% to 27.10wt.%; • B: 0.80wt.% to 1.10wt.%, in particular 0.85 wt.% to 1.05wt.%; • Co: 0.50 wt. % to 2.00wt. %; • M: 0.30wt.% to 1.50wt.%, in particular 0.55wt.% to 1.20wt.%; and • the residual is Fe and unavoidable impurities.

3. The Ce-containing and sintered NdFeB magnet of claim 2, wherein the weight contents of Al, Cu, Ga, and Ti as metallic alloy components of the RE-T-B-M magnet alloy composition are independently from each other set as follows: Al: 0.01 wt.% to 1.00wt.%, preferably 0.05 wt.% to 0.60wt.%; Cu: 0.01 wt.% to 1.00wt.%, preferably 0.10 wt.% to 0.50wt.%; Ga: 0.01 wt.% to 1.00wt.%, preferably 0.10 wt.% to 0.50wt.%; and Ti: 0.01 wt.% to 1.00wt.%, preferably 0.10 wt.% to 0.40wt.%.

4. The Ce-containing and sintered NdFeB magnet of any one of the preceding claims, wherein (ii) in the Fe-rich phase, RE takes an atomic proportion of 12.4at.% to 26.0at.%, Fe plus Co takes an atomic proportion of 68.1at.% to 81.4at.%, and M takes an atomic proportion of 1.3at.% to 6.2at.% , wherein the components plus unavoidable impurities add up to 100at.%; and / or (iii) in the REFe2 phase, RE takes an atomic proportion of 28.1at.% to 33.8at.%, Fe plus Co takes an atomic proportion of 61.4at.% to 69.8at.%, and M takes an atomic proportion of 0.6at.% to 4.8at.% , wherein the components plus unavoidable impurities add up to 100at.%.

5. A manufacturing method of a Ce-containing and sintered NdFeB magnet comprising grains composed of a RE2Fe14B-type main phase and a multi-layered grain boundary structure between the grains as defined in any one of the preceding claims, the method including the following steps: a) Preparing alloy flakes of the magnet alloy composition by a strip casting process, subjecting the alloys flakes to hydrogen decrepitation und pulverizing the product by jet milling to obtain an alloy powder, wherein the magnet alloy composition is a RE-T-B-M magnet alloy composition where • RE is a rare earth metal including Ce and at least one of Nd and Pr; • T is one or both of Fe and Co; • B stands for boron; • M is one or more element selected from the group consisting of Al, Cu, Ga, and Ti; And wherein the weight contents of the RE-T-B-M magnet alloy composition are set as follows: • RE: 28.50wt.% to 35.00wt.%; • Ce: 3.00wt.% to 15.00wt.%; • Nd and Pr: 14.00wt.% to 29.00wt.%; • B: 0.70wt.% to 1.20wt.%; • Co: 0.10 wt. % to 3.00wt.%; • M: 0.10wt. % to 3.00wt.%; and • the residual is Fe and unavoidable impurities; b) Pressing the magnetic powder into a green compact under a magnetic field for orientation followed by cold isostatic pressing; c) sintering the green compact at 950°C to 1100°C for 2 to 15h, preferably at 1000°C to 1050°C for 4 to 12h, for example, 1010°C for a duration time of 6 hours; d) After sintering, subjecting the obtained sintered NdFeB magnets to an annealing treatment, characterised in that the annealing treatment consists of three steps, wherein - in a first step of the annealing treatment a temperature is in the range of 600°C to 750°C, preferably 630°C to 730°C, for example 650°C, for 1h to 5h, preferably 2h to 4h, for example 3h, - in a second step of the annealing treatment a temperature is in the range of 800°C to 950°C, preferably 820°C to 930°C, for example 850°C, for 1h to 5h, preferably 2h to 4h, for example 3h, and - in a third step of the annealing treatment a temperature is in the range of 420°C to 560°C, preferably 450°C to 540°C, for example 480°C, for 1h to 5h, preferably 2h to 4h, for example 3h.