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In this article, the phase compositions, microstructures, and magnetic properties of PrNd-free Ce-Fe-B-based sintered magnets with the nominal composition of (Ce0.78Y0.17La0.05)16.28Febal.B7.44M1.94 (at.%: M = Co, Al, Cu, and Nb) have been investigated. It shows that a lamellar crystalline structure is formed in the Ce-Fe-B-based strip casting (SC) alloy. The Y-substituted Ce-Fe-B-based SC alloy is mainly composed of R2Fe14B and RFe2 phases. It suggests that Y substitution is helpful for depressing the $\alpha $ -Fe phase generated in the SC alloy. The island-like intermediate phases exist in the RFe2 region, which are probably caused by the incomplete peritectic reaction during alloy solidification. The Curie temperature $T_{\mathrm {c}}$ of the Y-substituted Ce-Fe-B-based alloy is about 463 K, which is higher than that of the Ce2Fe14B compound ( $T_{\mathrm {c}} =424$ K). For the experimental Ce-Fe-B-based sintered magnet without PrNd addition, the remanence $B_{\mathrm {r}}$ of 8.31 kG, the coercivity $H_{\mathrm {cj}}$ of 0.92 kOe, and the maximum energy product (BH)max of 5.30 MGOe have been obtained. A good combination of coercivity $H_{\mathrm {cj}}$ (= 5.57 kOe) and maximum energy product (BH)max (= 20.17 MGOe) has been achieved in the Ce-Fe-B-based blended magnet with PrNd/ $\sum $ RE = 25% prepared using a binary main phase (BMP) method. The heterogeneous elemental distributions and microstructure characteristics of the BMP magnet are also analyzed.

In this paper, dependence of magnetic properties on microstructure and composition of Ce-Fe-B sintered magnets with Cu-doped Ce-rich alloy addition was investigated. It shows that the maximum energy product (BH)max and coercivity Hcj of Ce-Fe-B sintered magnet are improved from 6.76 to 9.13 MGOe by 35.1%, and from 1.44 to 1.67 kOe by 16.0%, respectively, via adding 5 wt% liquid phase alloy of Ce35.58Fe57.47Cu6B0.95 (at%). Compared with the magnet without Ce-rich alloy addition, the volume fraction of the grain-boundary phase with low melting point increases in the magnet with Ce-rich alloy addition, which is beneficial to improving the microstructure and promoting the coercivity enhancement of the magnet. In the Ce-Fe-B magnet with Ce-rich alloy addition, Cu and Ce enrich in the grain boundaries of the magnet after annealing, therefore the as-annealed magnet has a higher coercivity than the as-sintered magnet. A distinct Fe-rich layer with the average thickness of 60 nm is found in the grain boundaries in the magnet without Ce-rich alloy addition, but it seems that Fe-rich phase disappears in the magnet with Ce-rich alloy addition. The present work suggests that the further improvement of coercivity in the Ce-Fe-B sintered magnets is expectable by designing the composition and structure of added liquid phase alloys.

Ce-based magnets have attracted extensive attention in both academia and industry due to their excellent property–price ratio and distinctive phase structures. Characteristically, Ce-based sintered magnets have widely tunable magnetic properties with changing Ce contents. Therefore, they can be used to meet many different application requirements from packaging market to driving motors, etc. The intrinsic magnetic properties, phase composition, and microstructures of the Ce-based sintered magnets with different Ce contents have been summarized. The service performances such as temperature stability, corrosion resistance, mechanical properties and thermal expansion of commercial Ce-based sintered magnets are introduced. The research and development trends of the Ce-based magnets in the future are pointed out.

In this article, the phase constitution, microstructures and melting points of Ce35.58Fe63.47-xAlxB0.95 alloys (at.%; x = 0, 3, 5, 10) have been investigated. It indicated that the Ce-rich alloy with x = 0 was mainly composed of CeFe2, Ce2Fe17 and γ-Ce phases. The AlCe3 phase was found in the alloy with x = 3. The microstructures and phase distribution characteristics of the alloys have obviously changed with increasing Al content (x = 5,10). The volume fractions of CeFe2 and Ce2Fe17 decreased. Some dispersed Ce-Al eutectic structures with low melting point were found in the alloy with x = 10. It is showed that the melting points of Ce-rich alloys have a decreasing tendency with increasing Al content, the melting points reduced from 942 °C at x = 0–856 °C at x = 10. Furthermore, the influences of the Ce35.58Fe53.47Al10B0.95 alloy addition on the microstructures and magnetic properties of sintered Ce-Fe-B magnets, were also discussed. The remanence Br slightly decreased, while the intrinsic coercivity Hcj, maximum energy product (BH)m and squareness Hk/Hcj (the ratio of knee coercivity to intrinsic coercivity) of the magnets had significant improvements, and these indexes increased by 8%, 22%, 24%, respectively.

The (R,Ce)–Fe–B magnets have been successfully industrialized in recent years. The mechanical property of sintered permanent magnets is one important aspect of their comprehensive performances, which directly influences the service reliability and the production cost. In this paper, the bending strength, fracture toughness, Vickers hardness, and brittleness index of commercial (R1– x Ce x )30.5–31.5Febal.B1M1 magnets with different cerium contents have been investigated. The micro-fractures of the magnets were observed by a scanning electron microscopy equipped with energy dispersive X-ray analysis system. It shows that the bending strength and the fracture toughness of (R,Ce)–Fe–B magnets have a downward tendency with increasing Ce content x, while the Vickers hardness of the magnets varies irregularly with Ce contents in this paper. The optimum mechanical properties have been obtained in the (R1– x Ce x )30.5–31.5Febal.B1M1 magnet with $x = 0.15$ ; the bending strength, fracture toughness and brittleness index of the magnet with $x =0.15$ are obviously superior to those of the ordinary sintered Nd–Fe–B magnets. Some flocculent oxide phases have been discovered in the (R,Ce)–Fe–B magnet with $x = 0.15$ . The flocculent phases may absorb the crack propagating energy, and reduce the stress concentration at a crack tip, which is beneficial to strengthening and toughening of (R,Ce)–Fe–B magnets. However, the mechanical properties are obviously worse for the magnet with $x = 0.45$ (Ce/ $\sum $ RE = 45%). That is probably because the microstructures of the magnet with $x = 0.45$ become deteriorated, in which abnormally large grains have been observed.

Waste Nd–Fe–B sintered magnets (grade 33H) were recycled to manufacture anisotropic sintered magnets by adding Ce-rich alloys. The influences of additive amounts of Ce-rich alloys on the microstructure and magnetic properties of the recycled sintered magnets were investigated. It showed that the recycled sintered Nd–Fe–B magnet without Ce-rich alloy addition has rather lower density; the density of the magnet is slightly raised with increased sintering temperature, but the recycled magnet is prone to oxidation, even cracking. For recycled sintered magnets with Ce-rich alloy addition, the densities of the magnets are upgraded with increasing amounts of Ce-rich alloy, and the magnetic properties are obviously improved. This suggests that Ce-rich alloy plays the important role of sintering-aid in the densification of the recycled magnet. However, the coercivity ( $H_{{\text {cj}}}$ ) of the recycled magnets is decreased, when the additive amounts of Ce-rich alloy are over 8 wt.%. This is probably because excessive Ce-rich alloy addition can cause RE-rich phase aggregation at the triple grain boundary junctions, and deteriorate the microstructure of the recycled magnets. The recycled magnet with 5 wt.% Ce-rich alloy, sintered at 1080 °C, exhibits the following optimal magnetic properties: $B_{r}$ of 11.67 kGs; $H_{{\text {cj}}}$ of 18.94 kOe; and maximum energy product $[(BH)_{\max }]$ of 33.1 MGOe. The magnetic properties of the recycled magnets are comparative to those of the waste magnets. Recycled magnets have a higher coercivity and perfect squareness of demagnetization curve ( $H_{k}/H_{{\text {cj}}} =0.972$ ).

Commercial N50 sintered Nd–Fe–B magnets were grain boundary diffusion (GBD) processed with TbHx powders. The diffusion temperature and time dependent microstructure and magnetic properties of the GBD processed magnets were investigated. High remanence and coercivity were obtained when the magnet was GBD processed at 875 °C for 14 h; the coercivity of the magnet increased from 12.57 kOe to 22.65 kOe. The relationships between microstructure and coercivity, remanence, and thermal stability of the GBD processed magnets were analyzed and discussed.

In this article, evaluations of the microstructure and HRE distribution of grain boundary diffused (GBD) Nd-Fe-B sintered magnets with diffusion time (t) and diffusion depth (d) were investigated. The coercivity (Hcj) first increases and then decreases with increasing t; while the remanence (Br) and the maximun energy product ((BH)m) of GBD magnets have an opposite changing trend. A large amount of Tb diffused into the inner of grains, and formed extensive Tb-rich areas in the surface layer at the beginning of GBD process. This suggests that Tb diffuses not only along grain boundaries, but also via grains in the surface layer because of high concentration gradient of Tb. As the concentration gradient of Tb is reduced, Tb diffuses mainly along grain boundaries. The grain boundary acts as the GBD path, but not as a Tb enriched area. There are two coexisting processes, namely, one process is diffusing from the surface to the inside of the magnet, the other is diffusing from the grain boundaries to the shell, then to the inner of grains. The two diffusion processes cause the changes of microstructure and Tb distribution, thus, the magnetic properties of the GBD samples vary correspondingly.

The relationship between the microstructure and magnetic properties of Nd–Fe–B sintered magnet compressed by shock wave with 6.26 GPa ≤ p ≤ 7.16 GPa was investigated. It reveals that Nd–Fe–B magnets show a demagnetization behavior after compressed by shock wave. The intergranular fracture is the main occurring phenomenon in the shock wave-compressed magnets. The coercivity of the shock wave-compressed Nd–Fe–B magnets could be recovered after repeating the annealing process. It suggests that only the morphology change just like the intergranular fracture occurs, and there is no structural change in the grain boundary phase in the shock wave-compressed magnet. Matrix phase grain interconnection, microcracks and pores, and alterant orientation relationship between matrix phase and grain boundaries phase are considered as induced factors of demagnetization.

Nd-Fe-B/NdF 3 composite magnets have been prepared by two different mixing methods: 1) mixing in agate mortar without lubricant and 2) milling in a planetary ball mill with heptane. The comparison of two mixing methods and their influences on the electrical and magnetic properties of the Nd-Fe-B/NdF 3 composite magnets have been investigated. The results show that the microstructures of the composite magnets fabricated by mixing in agate mortar without lubricant were not uniform. But method 1 contributed a better magnetic property compared with method 2. The electrical resistivities of the Nd-Fe-B/NdF 3 composite magnets fabricated by method 1 in the direction parallel to the pressing direction increased with increasing NdF 3 amounts. The remanence and maximum energy products of the Nd-Fe-B/NdF 3 composite magnets prepared by method 1 reduced to some extent with increasing NdF 3 amount. Method 2 contributed to obtaining a more homogenous microstructure. Method 2 has little influence on the electrical resistivity when the amounts of NdF 3 were kept constant. But, it is detrimental to the magnetic properties of the composite magnets.

The double hard magnetic phase magnets with nominal compositions of Nd30–xDyxFe69B1(x=2, and 4) (wt.%) were prepared. The magnetic properties of the magnets were measured with a NIM-2000H hysteresigraph. The crystalline structures of the magnets were identified by X-ray diffraction (XRD). The Rietveld refinement was carried out using the FULLPROF software. The scanning electron microscopy (SEM) and transmission electron microscopy (TEM) analyses were carried out in order to investigate the microstructure of the magnets. It showed that the magnets consisted mainly of Nd2Fe14B phase, and some Nd-rich phase. Two types of matrix-phase grains in dark grey and light grey were found in the magnets with x=2 and 4. The Dy content was obviously different in the two types of grains, which proved that the double hard magnetic phases (Dy-rich and Dy-lean phases) coexisted in the magnet. It revealed that the Nd-rich phases in junction regions had fcc structure, with the unit cell parameter of about 0.52–0.56 nm. The weak superlattice spots were found in the SAD patterns of the junction Nd-rich phases with large scale. The double hard magnetic phase structure seemed to improve the magnetic properties of NdFeB magnets with high coercivity, while decrease the consumption of Dy element, compared with the single alloy magnet.

In this paper, the structure and magnetic properties of the (Ce, Nd)–Fe–B magnets without Dy and Tb substitution have been investigated. The purpose of the investigation is to develop the applicable Ce–Fe–B magnets with Ce content over 50 wt.%. Sintered (Ce, Nd)–Fe–B magnets with the nominal composition of (Nd1− x Ce x )30(Fe, TM)balB1 ( $x=0$ –0.75) in wt.% were fabricated by advanced powder metallurgy processes. The effects of Ce substitution on the microstructure and magnetic properties of the (Ce, Nd)–Fe–B magnets were discussed. It was found that the (Ce, Nd)-rich boundary phase with lower melting point is helpful to obtain improved boundary microstructures and refined grain magnets. Good magnetic properties of Br = 13.5 kG, $H_{\mathrm {cj}}= 9.5$ kOe, and $(BH)_{\mathrm {max}} = 42.8$ MGOe were obtained in the Dy-free (Ce, Nd)–Fe–B magnets with 30 wt.% Ce substitution. A higher coercivity (>10 kOe) has been achieved in the Ce–Fe–B type magnets by the modifications of alloy compositions and the optimization of preparation conditions, in which the proportion of Nd and/or Pr is lower than 35 wt.% of the total rare-earth content.

Nd-Fe-B composite magnets with different amounts of CaF2 have been prepared by sintering at different temperatures. The microstructure and densities of the Nd-Fe-B composite magnets were investigated by scanning electron microscope and Archimedes method. The electrical and magnetic properties were measured with a four probe electrical resistivity meter and a NIM-2000HF hysteresisgraph meter. The results show that CaF2 was distributed in the grain boundary. The electrical resistances of the composite magnets increased with the increase of the amounts of CaF2, while the magnetic properties of the magnets deteriorated markedly. The electrical resistances of the Nd-Fe-B composite magnets with 3, 6 and 9 wt.% as-bought CaF2 sintered at 1050°C were 270, 320 and 400 μΩ cm, which increased approximately 17%, 39% and 74% over that of the magnet without CaF2 ( 230 μΩ cm). The maximum energy products, (BH)max, of the composite magnets with 3, 6 and 9 wt.% as-bought CaF2 sintered at 1050°C were 41.03, 35.77 and 28.66 MGOe, respectively. The densities of the composite magnets decreased with the increase of the amounts of CaF2. High energy ball milling can refine CaF2 to nanoscale and thus improve its distribution in the composite magnets. The (BH)max of the Nd-Fe-B magnets with 3 wt% CaF2 first increased and then decreased with the increase of milling time. But the electrical resistivities of the sintered Nd-Fe-B magnets with the CaF2 without milling and after high energy ball milling have little change.

Microstructure of the sintered Sm(Co,Fe,Cu,Zr)z magnet was investigated by TEM. Twinning relationships in the rhombohedral Sm2Co17 phase were analyzed. Formation of the twinning is related to the ordered substitution of Sm atoms by Co atomic pairs along different directions in the crystal structure. The atomic structures of twinning were discussed on the base of TEM observation.

Coarse and fine TiB whiskers were formed during the reaction synthesized TiB reinforced Ti matrix composites. The microstructure of the as-synthesized TiB whiskers has been investigated by TEM and HREM. Dislocations and stacking faults were observed in the coarse TiB whiskers, and only high-density stacking faults presented in the fine TiB whiskers. The formation of dislocations is related to the stacking faults, the formation mechanism and atomic structure of dislocations in the in situ synthesized TiB whiskers was suggested.

A blended elemental (BE) route was used to mix, uniformly distributed FeMo and B or TiB2 particles into titanium powder by ball milling. The work presented here has demonstrated the influences of milling time, different powder mixture, process control agent (PCA), and size of milling ball and rotated speed on BE powder for reaction sintering of the TiB/Ti–4.0Fe–7.3Mo composite. The as milled powders were investigated by XRD analysis and SEM observation. The in situ reaction synthesized TiB reinforced Ti matrix composite has been successful prepared by ball milling and hot press sintering.

In situ TiB whisker reinforced Ti-4.0Fe-7.3Mo matrix composites have been fabricated by spark plasma sintering (SPS). The microstructure of the in situ TiB whiskers and interfacial structures in th...

The in situ TiB particle reinforced titanium metal matrix composites were prepared using MA followed by park plasma sintering (SPS) with a heating rate of 50 °C/min. The in situ TiB were synthesized by chemical reaction between TiB2 and Ti during the SPS process. The microstructure of the composites sintered at 800, 1000 and 1200 °C were investigated. TiB whiskers are needle-shape and uniformly dispersed in the titanium matrix. The interface between the in situ TiB needles and the titanium matrix is singular and faceted. The composite sintered at 1000 °C has a maximum value of relative density of 99.6%, and good mechanical properties with a flexural strength of 1007 MPa, Young's modulus of 146 GPa and fracture toughness of 8.64 MPa·m1/2, respectively. The fractographs of all composites exhibit a predominantly brittle cleavage fracture mechanism. The elastic modulus of synthesized TiB was estimated.

A six-layer functionally gradient material (FGM) of Ti–TiB–TiB2 was rapidly fabricated by spark plasma sintering (SPS) in vacuum. Both B and TiB2 were used and reacted with Ti to synthesize TiB. Adjusting the content ratio of B to TiB2 in individual layers could control the amount of synthesized TiB by two steps during sintering. The composition and microstructure of the layers in FGM were investigated by XRD, SEM and TEM. The synthesized TiB has needle-like, agglomerated and elongated morphologies. The content of agglomerated TiB increased and that of needle shape TiB decreased with increasing the target TiB volume fraction ranging from 20 to 60%. The elongated TiB was observed in the other two layers with higher target TiB volume fraction, which structure is similar to the agglomerated TiB. The FGM with Ti on one side to Ti–TiB–TiB2 on the other were fabricated at relative low sintering temperature and short dwelling time by spark plasma sintering.

The in situ TiB/Ti–4.0Fe–7.3Mo composites were fabricated by plasma spark sintering (SPS) technique using mechanical alloying of Ti, Fe65Mo and B powder. The effects of sintering temperature on densification of the composites and microstructure of the in situ synthesized TiB were investigated using scanning electron microscope (SEM) and transmission electron microscope (TEM). A dense composite was obtained after sintering at 1000 °C for 5 min. Under proper ball milling and SPS conditions in situ TiB reinforced Ti–4.0Fe–7.3Mo composites have been prepared. The in situ TiB showed a typical needle shape grow along [0 1 0] direction. The transverse cross-section of TiB grain is a hexagonal shape with the planes of (1 0 0), (1 0 1) and ( 1 0 1 ¯ ) . The stacking faults in the (1 0 0) plane were observed in the TiB needles.

The spark plasma sintered in situ TiB reinforced titanium metal matrix composite was investigated by EBSD and TEM. The sintered composite consists of 30.8% α-Ti phase, 55.7% β-Ti phase and 12.9% in situ TiB reinforcements. Most of the TiB whiskers distributed along phase boundaries between α-Ti and β-Ti, others located within α-Ti and β-Ti grains. Some β-Ti grains with parallel TiB whiskers were observed in the orientation imaging micrograph (OIM). The TiB grows along [010] direction and forms whisker with a hexagonal cross-section. The [010] direction of paralleled TiB whiskers is parallel to [111] direction of cubic β-Ti. High density stacking faults are formed in (100) T i B planes to minimizing the lattice mismatch between TiB and the Ti matrix.

The in situ synthesized TiB reinforced titanium matrix composites have been prepared by spark plasma sintering at 800–1200 °C under 20 MPa for 5 min. The effects of sintering temperature and reinforcement volume fraction on flexural strength, Young’s modulus and fracture toughness of the composites are investigated. The titanium matrix consists of α-Ti and β-Ti phases, and the volume fraction of β-Ti increases with increasing sintering temperatures. The in situ synthesized TiB reinforcements are distributed randomly and uniformly in matrix. The transverse section of TiB has a hexagonal shape aligned along [0 1 0] direction, and the crystallographic planes of the TiB needles are always of the type ( 1 0 0 ) , ( 1 0 1 ) and ( 1 0 1 ¯ ) . The 10 vol% TiB reinforced composite sintered at 1000 °C exhibits excellent mechanical properties. The flexural strength, Young’s modulus and fracture toughness of this composite are 1560 MPa, 137 GPa and 8.64 MPa · m1/2, respectively.

The substitution of cerium, a more abundant rare-earth element, for sintered Nd-Fe-B magnets has drawn intense interest. In the present work, nominal composition of Ce15Nd15FebalB1 (wt. %), with cerium constitutes increased to 50% of the total rare-earth content, was used. And Ce-free Nd30FebalB1 (wt. %) was prepared by the same preparation process as comparison. The microstructure of the sintered magnets has been investigated by means of X-ray diffraction and transmission electron microscope. The results show that there are three kinds of RE-rich phases in the same magnet, i.e., fcc-(Ce,Nd)Ox (a=0.547nm), hcp-(Ce,Nd)2O3 (a=0.386nm, c=0.604nm) and bcc-(Ce,Nd)2O3 (a=1.113nm). Ors of (140)(Ce,Nd)2Fe14B// (1-21)bcc-(Ce,Nd)2O3(∼3°), [001](Ce,Nd)2Fe14B// [-214]bcc-(Ce,Nd)2O3; (01-1)(Ce,Nd)2Fe14B// (101)fcc- (Ce,Nd)Ox(∼2°), [101](Ce,Nd)2Fe14B// [12-1]fcc-(Ce,Nd)Ox were found through selected area electron diffraction (SAED) analysis. According to the analysis, it can be concluded that cerium has partly substituted for neodymium by occupying the corresponding atom sites in the Ce15Nd15FebalB1 magnet, without changing the crystal configuration.

The Sm2Co17 magnet is the most promising candidate for high temperature applications. The microstructure evolutions and losses in the magnetic properties of the magnet in high temperature aging status have been investigated. The Sm(CobalFe0.22Cu0.068Zr0.025)7.75 magnets were prepared using the conventional powder sintering method. The magnet samples were isothermally aged at 500°C, 600 °C, and 700 °C for 72 h, respectively. The magnetic properties and the demagnetization curve were kept invariable for the magnet samples aged at 500 °C. The coercivity Hcj of the magnet samples decreased with increasing aging temperature. The Hcj decreased from 29.2 kOe for the original status samples to 10.8 kOe for the samples aged at 700 °C. The cell structure in the magnet is not destroyed after aging at 700 °C for 72 h. The deterioration of the magnetic properties and the demagnetization-curve squareness was caused by an increasing lattice mismatch between the 2:17R cell phase and the cell-boundary 1:5H phase, and by an increasing cell diameter for the magnet sample aged at a high temperature.