Grain Boundary Diffusion Research Articles

Understanding the coercivity enhancement mechanism of grain boundary diffused Nd-Fe-B magnets by comparing with commercial equivalent coercivity magnets

The grain boundary diffusion (GBD) technology effectively utilizes heavy rare earth (HRE) elements to improve the coercivity of sintered Nd-Fe-B magnet. Significantly, clarifying its coercivity improvement mechanism is essential for further optimizing the process and performance. Through comparative analysis with commercial conventional magnets (CSH) processing equivalent coercivity, this study investigated the specific mechanism by which the GBD method enhances the coercivity of HRE elements in an efficient manner. To achieve the same coercivity (∼21.4 kOe), GBD magnets contained only 0.25 wt% Tb, whereas CSH magnets had 1.17 wt% Dy and 1.18 wt% Tb. The microstructure analysis revealed that the Tb element in the GBD magnet was concentrated in the outer layer of the grain, constituting 17.37 wt% of the total rare earth content. While, in CSH magnets, the HRE element in the main phase grains accounted for only 9.58 wt% of the total rare earth elements, including Dy (3.83 wt%) and Tb (5.75 wt%). The characteristic core-shell structural grains in GBD magnet also endowed it with an uneven magnetic domain structure and a more concentrated “abrupt” magnetization reversal. Based on the characterization results the nucleation positions of the two types of magnets were analyzed by fitting Hci/Ms and Ha/Ms. The results can serve as a guide for enhancing coercivity in grain boundary diffusion sintered Nd-Fe-B magnets, aiding in process and property optimization, and advancing the understanding of nucleation type mechanisms.

The onset of anelastic behavior in fine-grained synthetic dunite

Micromechanical models suggest that the onset of anelastic relaxation in polycrystalline olivine, critical to interpretation of the seismic wave attenuation and dispersion in the upper mantle, should be a mild dissipation peak caused by elastically accommodated grain-boundary sliding. Such behavior has been tentatively invoked to explain both a short-period shear modulus deficit and a dissipation plateau poorly resolved at 900–700 °C in previous forced-oscillation experiments on fine-grained dunite tested within mild-steel jackets. However, these observations may have been complicated by the austenite to ferrite plus cementite phase transition in the jacket material, compliance associated with interfacial Ni70Fe30 foils, and modeling of the mechanical properties of polycrystalline alumina as control specimen. To investigate the influence of these complications within the experimental setup and provide forced-oscillation data of better quality especially at moderate temperatures, we have conducted further forced-oscillation tests for which we removed the interfacial foils, employed single-crystal sapphire as reference sample, and used alternative jacket materials (stainless steel or copper) which experience no phase transition during the staged cooling. The newly acquired forced-oscillation data, although broadly consistent with the previous results, differ significantly especially in temperature sensitivity, and allow refinement of an appropriate Burgers creep-function model. A mild dissipation peak superimposed on monotonic dissipation background during the onset of anelastic relaxation in dry, melt-free and fine-grained dunite has now been consistently observed at temperatures of ∼950–1050 °C and seismic periods of 1–1000 s. Such a dissipation peak with relaxation strength 0.02 ± 0.01 is attributed to elastically accommodated grain-boundary sliding. The high activation energy (> 600 kJ/mol) of viscoelastic behavior involving both dissipation and related dispersion suggests that grain-boundary diffusion may be limited by interfacial reaction within grain boundaries. The reduced relaxation strength makes it difficult to attribute the oceanic lithosphere-asthenosphere boundary to water-mediated elastically accommodated grain-boundary sliding.

Novel (Ti, W)C–SiC–WSi2 ceramics fabricated via in situ reaction spark plasma sintering at 1600 °C

Novel (Ti, W)C–SiC–WSi2 ceramics were fabricated by in situ reaction spark plasma sintering (SPS) at 1600 °C using (Ti, W)C and Si powders. The effect of Si content on densification behavior, microstructures, and mechanical properties was investigated. The in situ reaction and the formation of carbon vacancies reduced the sintering temperature. The densification mechanism of (Ti, W)C-based ceramics transforms from reaction to grain-boundary sliding and diffusion. The WSi2 and primary SiC generated by in situ reactions are distributed along the grain boundaries and have a specific crystallographic orientation relationship. Intragranular secondary SiC formed because of rapid densification, grain-boundary diffusion, and (Ti, W1−y)C1−x particle migration. This multiscale particle-reinforced microstructure can improve the mechanical properties of (Ti, W)C ceramics, giving the TW10S (4.80 wt% SiC–5.01 wt% WSi2) good sintering performance, a fine-grained microstructure, high hardness (23.3 ± 1.6 GPa), and flexural strength (425 ± 24 MPa). The SiC and WSi2 produced through in situ reactions have exceptional intrinsic oxidation resistance, allowing the ceramics to achieve outstanding oxidation resistance.

Analysis on coercivity enhancement mechanism of grain-boundary-diffused and Dual-alloyed Nd-Fe-B Magnets

With the rapid development of application fields, such as the green energy industry, has resulted in increased demand for magnetic characteristics, especially the coercivity (Hcj). In this paper, two types of (Nd, Dy)-Fe-B magnets with comparable Hcj values were prepared using by grain boundary diffusion (GBD) method and dual alloy (DA) method. The composition, microstructure, domain structure, and magnetization reversal process of GBD and DA magnets were subjected to comparison. Additionally, an analysis of the specific coercivity mechanism was also conducted by fitting the Brown's equation. The results of composition and microstructure analysis revealed the formation of core-shell structural grains were formed in both GBD and DA methods. Specifically, the GBD method exhibited a higher concentration of Dy in the shell, constituting 26.8 % of the total rare earth (RE) content. In contrast the DA magnets had Dy accounting for 15.8 % of the total RE content in the shell. This discrepancy was identified as the primary factor contributing to the superior efficiency in enhancing the coercivity (Hcj) observed in the GBD method. The fitting results showed that GBD magnets were more inclined to nucleate in the core region in grain, whereas DA magnets nucleate at the edge of the grain shell layer. Both the observation of magnetic domains and magnetization reversal processes analysis revealed that the demagnetization process in GBD magnets is more uniform, which leads to better squareness. Our finding can provide theoretical and experimental basis for the preparation of high-performance Nd-Fe-B magnets.

Study on magnetic properties and demagnetization process of the c-plane in the grain boundary diffusion magnet

Grain boundary diffusion (GBD) can effectively increase the coercivity of sintered Nd-Fe-B magnets. Tb is deposited in the specific areas of the c-plane rather than the entire c-plane to reduce the amount of heavy rare earth elements. In this work, we investigate the magnetic properties and demagnetization process of the c-plane using experimentation and micromagnetic simulation. The c-plane is divided into the center area without Tb deposition and the edge area with Tb deposition. According to the results of the experiment and micromagnetic simulation, it has been found that diffusion on the edge area can decrease the amount of Tb by 58% and increase the contribution of Tb to coercivity (ΔHcj/wt.% Tb) to 20.55 kOe/wt.%. Compared to the other areas on the c-plane, diffusing on the edge area offers the vast majority of Hcj for the GBD and has the highest ΔHcj/wt.% Tb. Diffusing a small amount of Tb onto the center area can supplement the remaining Hcj. Micromagnetic simulation and Magneto-optical Kerr microscopy are used to study the differences in magnetic properties among different areas on the c-plane by simulating the demagnetization process. Because the edge area is more likely to be demagnetized than the center area, the diffusion of Tb in the edge area can significantly strengthen Hcj.

Modeling the oxidation process of TiAl and Ti<sub>3</sub> Al intermetallic compounds due to grain-boundary diffusion of oxygen

A diffusion-kinetic model was proposed to analyze the oxidation process in a nanostructured material with explicit identification of grain boundaries. It was assumed that oxygen migrates faster along the boundaries than it does in the grain volume. The model takes into account the stages of decomposition and formation of intermetallic compounds, as well as the formation of oxides, both within the boundaries and in the grain volume. The problem was solved numerically, and the oxidation dynamics were compared for various materials with different grain properties.

Correlation between Ce content and Tb–Cu grain boundary diffusion efficiency in Ce-containing Nd–Fe–B magnets

Ce-containing Nd–Fe–B magnets have been widely used because of their low cost, but the effects of Ce content in the magnets on the grain boundary diffusion (GBD) behavior are still unclear.

Solid-liquid phase separation diffused Nd-Fe-B sintered magnets by using DyH3 nanopowder realize high-efficiency coercivity improvement and overcome thickness limit

In this study, new grain boundary diffusion (GBD) technology is applied to Nd-Fe-B sintered magnets with different thicknesses utilizing DyH3 nanopowder. The weight ratio is 0.25 wt.%. For comparison, the GBD processes include solid-liquid phase separation diffusion (SepD) and solid-liquid phase simultaneous diffusion (SimD). The magnetic properties and microstructure of GBD magnets with different thicknesses are thoroughly investigated. The comprehensive magnetic properties of SepD magnets are higher than SimD magnets. When the magnets are 8 mm thick, the SepD magnet obtains a coercivity of 18.10 kOe, which is higher than the SimD magnets (17.00 kOe). It was determined that SepD can manufacture thick magnets with excellent coercivity. In SepD magnets, the Dy element diffusion distance is deeper than in SimD magnets. For SepD magnets, there are core-shell structures formed in the surface region, while there are anti-core-shell structures that are unfavorable to magnetic properties in the surface region of the SimD magnets. The enhanced coercivity and temperature stability of the SepD magnets is primarily due to the more continuous core-shell structures produced by the deeper diffusion depth of the Dy element. This study will provide more theoretical guidance for the application of SepD in magnets with different thicknesses.

Oxygen grain-boundary diffusion in (La,Sr)FeO3−δ perovskite-oxides probed by molecular-dynamics simulations

Faster grain-boundary diffusion of oxygen has been observed experimentally in polycrystalline samples of Fe-based perovskite oxides at low temperatures, but this behaviour is at present not well understood.

Understanding the sintering behavior of AlCrFeNiTi high entropy alloy via phase field modeling illustration

In this study, a computational approach is employed to understand the densification behavior of a multi-component alloy system during the sintering process by generating a phase field modeling image. First, a single-phase body-centered cubic (BCC) AlCrFeNiTi high entropy alloy (HEA) is prepared via a mechanical alloying (MA) route, and the powder-processed HEA is shown to exhibit dual BCC phases after spark plasma sintering (SPS). Then, phase field modeling (PFM) is used to generate a generalized image and to understand densification behavior during the sintering process. The results indicate that bulk and grain-boundary diffusion take place during the early stage and grain growth of the powder particles starts when the particles interact with their adjacent grains. Subsequently, in the final sintering stage point contacts and necking were observed. This understanding has been presented based on the phase field simulation to explore the different stages of the sintering during the processing.

The reinforcement strategy of electrophoretic deposition coating assisted by PVP for grain boundary diffusion of Nd-Fe-B magnet

In this study, we aimed to enhance the quality of electrophoretic deposition (EPD) coatings for Nd-Fe-B grain boundary diffusion (GBD) by addressing issues related to the adhesion and densification of coating. We introduced a novel approach by incorporating polyvinyl pyrrolidone (PVP) into an alcohol suspension containing TbH3 nano-powders. The addition of PVP resulted in the formation of a dense coating with superior adhesion and a smooth surface. To evaluate the effectiveness of the EPD coating with PVP, we compared the EPD rate of the TbH3 nano-powders alcohol suspension with and without PVP. The EPD rate of the suspension with PVP exhibited a significant 30-fold increase compared to the suspension without PVP, indicating a substantial improvement in the electrophoretic efficiency. Based on our experimental findings, we recommend depositing the EPD coating at a voltage of 120 V and adjusting the deposition time accordingly to achieve a desired coating weight percentage of 1.0 wt% with a thickness of approximately 30 μm. Following the GBD process, the coercivity of the magnet with PVP increased from 1131 kA/m to 1896 kA/m, which improved the high-temperature stability of the magnet. Overall, our research offers a promising approach to overcome the limitations associated with EPD coatings for GBD applications, providing a potential solution for enhancing the performance and industrial viability of these coatings.

Impact of crystalline orientation on Cu–Cu solid-state bonding behavior by molecular dynamics simulations

High-density electronics are hindered by the constraints of Sn-based solder joints, necessitating the exploration of Cu–Cu solid-state bonding. However, current bonding methods are expensive and time-consuming; therefore, understanding the Cu–Cu bonding mechanism is crucial for optimization. This study utilizes molecular dynamics (MD) simulation to elucidate the Cu–Cu solid-state bonding behavior, focusing on interfacial densification and diffusion phenomena. Furthermore, it highlights the influence of crystal orientation on the interfacial bonding behavior. To analyze the impact of crystal orientation, monocrystalline Cu slabs with a simplified periodic surface structure were employed to replicate surface roughness and subsequently bonded at a specific temperature. The results indicate the critical influence of crystalline orientations on the bonding process: identical orientations result in slower densification at the interface, whereas misoriented orientations significantly accelerate it. This effect, attributed to the grain boundary (GB) structures formed owing to misorientation, suggests a central role for GB diffusion in bonding progression. Diffusion coefficients calculated using the mean square displacement (MSD) confirmed these findings and exhibited significantly larger values for misoriented joints. Additionally, the simulations reveal an activation energy for GB diffusion that is lower than conventional values, highlighting the impact of the crystallographic orientation and voids at the bonding interface. Our research elucidates the role of crystalline orientation in diffusion phenomena at bonding interfaces, offering valuable implications for optimizing bonding-based manufacturing processes.

Coercivity enhancement with reduced Tb usage for NdFeB sintered magnets by grain boundary diffusion with multicomponent Tb-Ce-Al-Cu-Zn alloy powders

In this work, coercivity enhancement and thermal stability improvement for NdFeB sintered magnets by grain boundary diffusion (GBD) with Tb75Cu25-xZnx (x = 0–25) alloy powders are investigated. The coercivity (iHc) is enhanced from 10.6 kOe to 19.5–22.5 kOe by GBD with Tb75Cu25-xZnx (x = 0–25). Proper Zn addition into diffusion source can further improve the coercivity and its thermal stability for NdFeB sintered magnets. Besides, the costs of the diffusion sources have been significantly reduced by multicomponent Tb75-y-zAlyCez (Cu, Zn)25 alloy powders, and nearly without sacrificing the magnetic properties. Coercivity is significantly increased to 20.3–22.1 kOe by GBD with Tb75-yAlyCu20Zn5 (y = 0–30) alloy powders, and large coercivity increment (ΔiHc) of 11.0–11.5 kOe is found for y = 0–30. To further reduce the Tb usage, Tb45-zCezAl30Cu20Zn5 (z = 0–25) alloy powders are adopted as diffusion sources. Although the ΔiHc is gradually decreased as Ce content increases, the large coercivity of 18.4–21.6 kOe can be attained for z = 0–25. The formation of (Nd, Tb)2Fe14B shells can inhibit the nucleation of reverse domain. While Ce, Al, Cu and Zn prefer to distribute at grain boundary and triple junction, which can strengthen the decoupling effect between adjacent grains. Both effects contribute to the large coercivity enhancement. The optimized magnetic properties of iHc = 20.5 kOe, ΔiHc = 9.9 kOe and (BH)max = 49.1 MGOe can be achieved for the magnet GBD with Tb30Ce15Al30Cu20Zn5 alloy powders.

Coercivity saturation in Nd-Fe-B sintered magnets treated by grain boundary diffusion process of Tb-Ni-Al alloy

Microstructures of Nd-Fe-B sintered magnets treated by a grain boundary diffusion (GBD) process with different Tb coating amounts are investigated by scanning electron microscopy (SEM) and scanning transmission electron microscopy (STEM). Tb-substituted shell structures are formed in the outer portion of all Nd2Fe14B grains in the magnets. However, thick Tb-rich shells are formed on a micrometer scale on Nd2Fe14B grains in the region up to about 0.5 mm from the coating surface of the magnet, and thin Tb-rich shells several tens of nanometers in size are also formed in the inner region. As the Tb coating amount increases, the Tb concentration and thickness of the thick Tb-rich shells increase. At the same time, the Nd replaced by Tb forms Nd-rich grain boundary (GB) phases, and a large amount of those Nd-rich GB phases are discharged to the coating surface. The coercivity enhancement in GBD is mostly due to the formation of the thin Tb-rich shells, whereas the formation of thick Tb-rich shells wastes a large amount of Tb, causing coercivity saturation. Therefore, it is important to suppress the formation of thick Tb-rich shells and form thin Tb-rich shells with a high Tb concentration uniformly throughout the magnets.

Magnetic properties of Ce-containing Pr/Nd-Fe-B sintered magnets by diffusing Nd-Dy-Al alloy

In this study, 5% wt Ce-containing sintered Pr/Nd-Ce-Fe-B magnets were processed by grain boundary diffusion (GBD) with NdxDy90-xAl10 alloy (x = 0, 10, and 20 correspond to N0, N10, and N20, respectively). After the GBD process, the coercivity of magnets increased from 1,124.7 to 1,656.4, 1,673.9, and 1,584.8 kA/m, for N0, N10, and N20, respectively. Microstructure analysis revealed continuous RE-rich intergranular phases around matrix grains, which by weakening the magnetic coupling effect between ferromagnetic matrix grains, thus, leads to coercivity improvement. N10 had the same coercivity enhancement as N0, while the Dy utilization for N10 is lower than that for N0. The SEM results showed that the inclusion of Nd leads to the formation of a network of low-melting grain boundary phases, providing channels for subsequent Dy diffusion. A CeFe2 phase was found in the 5% wt Ce-containing magnet, which hindered diffusion due to its high melting point; in order to inhibit the negative impact of CeFe2 and reveal the diffusion mechanism in the Ce-containing magnet, DyH3, as a diffusion source, was applied to 5% wt-Ce-containing magnets simultaneously; after the GBD process, Nd10Dy90Al10 alloy, as a diffusion source, has better coercivity enhancement than DyH3, due to the deeper diffusion of the Dy element in the Nd10Dy90Al10 diffusion.

Modeling the effect of grain boundary diffusivity and trapping on hydrogen transport using a phase-field compatible formulation

Hydrogen grain boundary (GB) trapping is widely accepted as the main cause for hydrogen induced intergranular failure. Several studies were conducted to unveil the role of GBs on hydrogen transport; however, a clear understanding is yet to be attained. This is due to the limitations of the state-of-the-art experimental procedures for such highly kinetic processes. In this study, we aim at providing a deeper understanding of hydrogen-GB interactions using full-field representative volume element (RVE). The phase-field method is chosen for generating RVEs, since it is an appropriate numerical tool to represent GBs. A novel fully-kinetic formulation for hydrogen diffusion and GB trapping is presented, which is compatible with the phase-field based RVEs. GB diffusivity (Dgb) and trap-binding energy (Egb) were used as parameters to understand the interactions between diffusion and GB trapping. Uptake and permeation simulations were performed with constant and gradient occupancy boundary conditions respectively. In both cases, increasing Egb, increased the hydrogen GB occupancy. The permeation simulations showed that the hydrogen flux along the GBs increased with increasing both, Dgb and, surprisingly, Egb. Since trapping increases the hydrogen occupancy along GBs, it also increases the occupancy gradients, resulting in a higher flux. This led to the conclusion that, in the case of an external occupancy gradient, GB trapping and diffusion cooperate, rather than compete, to increase the hydrogen flux. On the other hand, the decisive factor for the retention of hydrogen at the GBs in permeation simulations was Dgb rather than Egb.

Inhibiting the abnormal grain growth for grain boundary diffused Nd-Fe-B magnets through Tb3O4 grain boundary construction

The grain boundary diffusion (GBD) process has been widely applied to effectively improve the coercivity of sintered Nd-Fe-B magnets. However, the abnormal grain growth and shallow diffusion depth were not conducive to coercivity enhancement. In this work, 0.2wt.% of Tb3O4 powder addition during the sintering process was applied to inhibit the abnormal grain growth and increase the continuous GB phase, and thus a superior coercivity of 26.22kOe was achieved after Tb GBD by comparing with that of 24.15kOe for the GBD magnet without Tb3O4 powder addition. Correlated with the electron probe microanalyzer (EPMA) and transmission electron microscopy (TEM) characterizations, a deeper diffusion depth, a thicker Tb-rich shell, and finer Nd2Fe14B phase grains make synergetic contributions to this coercivity enhancement. Furthermore, the Nd6Fe13Ga phase is formed surrounding the Tb3O4 intergranular phase, which is conductive to reduce magnetic coupling. The relationships among the coercivity, grain size, and core-shell structure are further confirmed by micromagnetic simulation. This work provides a dependable approach to further coercivity enhancement by grain boundary regulation.

Obtain high coercivity of Nd–Ce–Fe–B magnet via grain boundary diffusion with Dy80Al10Cu10 alloy

Dy80Al10Cu10 and DyH3 were employed as diffusion sources to perform grain boundary diffusion (GBD) on 7 wt% Ce containing Nd-Fe-B magnets. The coated samples underwent a heat treatment at 1193.2 K for 6 h, followed by an annealing process at 913.2 K for 5 h. As a result, the coercivity increased from the original 1268.0 kA/m to 1681.1 kA/m and 1618.2 kA/m in Dy80Al10Cu10 and DyH3 diffused magnets, respectively. Notably, Dy80Al10Cu10 exhibited a more pronounced diffusion effect than DyH3. After GBD, continuous intergranular phases were observed around the matrix grains, which weakening the magnetic coupling effect between the ferromagnetic matrix grains, which in turn improved coercivity. Microstructure analysis revealed the presence of CeFe2 phase, which impeded the effectiveness of GBD due to its high melting point. However, when Dy80Al10Cu10 was employed as the diffusion source, the detrimental impact of CeFe2 was better inhibited compared to DyH3. The inclusion of Cu and Al elements in the Dy80Al10Cu10 alloy optimized the wettability and facilitated the formation of an antiferromagnetic RE6Fe13Cu phase at the triple junctions (TJs), which leads to the depletion of Fe and enrichment of RE in adjacent GBs. Furthermore, Cu aided in dissolving high melting point CeFe2 and promoting the formation of GBs with improved wettability, thereby contributing to an increase of coercivity.

Thermal stability improvement and microstructure optimization of high cobalt content Nd-Fe-B magnets via terbium grain boundary diffusion

The substitution of Fe by Co in the 2:14:1 phase is an effective method to increase the Curie temperature and enhance the thermal stability of the Nd-Fe-B magnets. However, the accumulation of Co element at the grain boundaries (GBs) changes the GBs from nonmagnetic to ferromagnetic and causes the thin-layer GBs to become rare. In this paper, the method of diffusing Tb element was chosen to improve the microstructure and temperature stability of high-Co magnets. Three original sintered Nd28.5Dy3-CoxFebalM0.6B1 (x = 0, 6 wt%, 12 wt%; M = Cu, Al, Zr) magnets with different Co contents were diffused with Tb by grain boundary diffusion (GBD). After GBD, high-Co magnets exhibit more continuously distributed thin-layer GBs, and their thermal stability is significantly improved. In high-Co magnets (x = 6 wt%), the absolute value of the temperature coefficient of coercivity decreases from 0.603%/K to 0.508%/K in the temperature range of 293–413 K, that of remanence decreases from 0.099%/K to 0.091%/K, and the coercivity increases from 18.44 to 25.04 kOe. Transmission electron microscopy (TEM) characterization reveals that there are both the 1:2 phase and the amorphous phase in the high-Co magnet before and after GBD. EDS elemental analysis shows that Tb element is more likely to preferentially replace the rare earth elements in the 2:14:1 main phase than in the 1:2 phase and the amorphous phase. The concentration of Tb at the edge of the main phase is much higher than that in the 1:2 phase and amorphous phase, which is beneficial to the improvement of the microstructure. The preferential replacement of Tb elements at the edge of the 2:14:1 phase and thin-layer GBs with a more continuous distribution are synergistically responsible for improving the thermal stability of high-Co magnets. The study indicates that GBD is an effective method to improve the microstructure and thermal stability of high-Co magnets.

Coercivity Enhancement of Sintered Nd-Pr-Fe-B Magnets by Cost-Effective Grain Boundary Diffusion of Dy/Tb Films

High-performance sintered Nd-Pr-Fe-B magnets were successfully prepared by depositing Dy/Tb films on the surface using magnetron sputtering, which resulted in superior grain boundary diffusion (GBD) under heat treatments. The course of the diffusion was assessed using an electron probe microanalyzer (EPMA) and inductively coupled plasma (ICP). The magnetic properties and thermal stability of the magnets before and after diffusion were investigated. The results show that, mainly due to the increased and optimized Nd-Pr-rich phases and the formation of the (Nd,Pr,Dy/Tb)2Fe14B shell structure surrounding the (Nd,Pr)2Fe14B grains, the coercivity of the Dy- and Tb-diffused magnets was enhanced from 16.7 kOe to 24.8 kOe and 28.4 kOe, respectively, while the corresponding maximum energy product (BHmax) was 48.1 MGOe and 48.5 MGOe, respectively. The consumption of Dy/Tb in this work (0.35 wt% Dy in the Dy-diffused magnet and 0.42 wt% Tb in the Tb-diffused magnet) is much lower than that of previously reported magnets with comparable coercivity. Furthermore, Dy- or Tb-diffused magnets exhibit better thermal stability than that of the original magnet, owing to the better resistance to thermal disturbances of the magnets with optimized microstructure. This work can provide useful guidance for preparing Nd-Fe-B magnets with low cost and high performance.