Liquid Phase Sintering Process Research Articles

Enhancement of the magnetic property of Nd-Fe-B sintered magnets through novel powder rounding modification

Two types of sintered Nd-Fe-B magnets were fabricated by the process of powder metallurgy technology through two different powder preparation processes i.e., conventional powder preparation process and novel powder rounding modification. The microstructure, composition and properties of the two type powders have been studied including the particle size distributions and flowabilities. Furthermore, magnetic properties, microstructure and alignment degree of the magnets prepared by the corresponding powder also have been investigated. The novel powder rounding modification rounds the sharp edges and corners of the particles compared to the conventional powder preparation process, thereby reducing friction between the particles and improving flowability of the powder. As a result, the alignment degree of the sintered magnet is enhanced, which contribute to the improvement of the remanence and the energy product density. The powder that experienced rounding process changed the distribution of RE (rare earth)-rich particles, causing tiny RE-rich particles to adhere around the main phase particles, facilitating the compact of bulk during liquid-phase sintering process and achieving uniform distribution of RE-rich phases around the Nd2Fe14B main phase, resulting in increasing the magnet density and coercivity. As a consequence, we have produced the magnet with Br = 1.43 T, Hcj = 1049 kA/m and (BH)max = 393.2 kJ/m3, which is fully superior to conventional magnet with Br = 1.41 T, Hcj = 969 kA/m and (BH)max = 383.7 kJ/m3 by adopting powder rounding process. This indicates that the novel powder rounding modification is an efficient approach for synchronous improvement of magnetic performance of sintered Nd-Fe-B without any heavy rare earth elements.

Analysis of initial stage of liquid-phase sintering by combined multi-phase-field/discrete-element method

A combined multi-phase-field/discrete-element method in two dimensions is applied to the liquid phase sintering process of blended elemental powders. The boundary migration, diffusion of elements, and phase transformation between two dissimilar particles are calculated using a multi-phase-field method for sintering based on Gibbs energy functions. The sintering shrinkage is computed with the discrete-element method taking account of the neck size and sintering force, which are obtained from a multi-phase-field simulation. In this study, a pair or small cluster consisting of two elemental powders in a binary eutectic alloy is used as a model system. First, the formation of a liquid phase around the contact area between two dissimilar particles above the eutectic temperature of the system, and the motions of the particles due to grain boundary sliding along the liquid films are confirmed. Second, an Sn–Bi system is selected as the real eutectic system, and the sintering behavior of powder compacts with various mixing ratios of Sn and Bi particles is demonstrated. Finally, transient liquid-phase sintering of Sn–Bi system is simulated, that is, the generation and extinction of the liquid phase due to interdiffusion between Sn and Bi particles are calculated.

Selective laser sintering of amorphous nanoparticles: Molecular dynamics simulations

The paper investigates the process of liquid-phase sintering of amorphous iron-based nanoparticles by the method of molecular dynamics simulations. The classical molecular dynamics package LAMMPS was used for modeling. Visual analysis of the atomic configurations of nanoparticles during their rapid cooling revealed the self-purification effect of the particles. Partial pair correlation functions and coordination number distribution functions were used to analyze the atomic structure of nanoparticles after sintering. As a result of the analysis of the main structural parameters, which were obtained using the specified functions, differences in the atomic composition and structure of the volume and surface of nanoparticles were established.

Dielectric properties of the Ca0.25Cu0.75-xAlxTiO3 ceramics: experimental and computational investigations

In this study, we employed a solid-state reaction method to synthesize Ca0.25Cu0.75-xAlxTiO3 ceramics, investigating the impact of Al doping at concentrations of x = 0 and 0.0125. Notably, all ceramics exhibited a primary phase of Ca0.25Cu0.75TiO3. The addition of Al3+ induced a significant increase in grain size. Density functional theory analyses revealed a preferential occupation of Cu sites by Al, leading to liquid-phase sintering processes attributed to excess Cu. Moreover, it was also found from DFT that the Al dopant cannot induce an oxygen vacancy in the lattice. Charge density analysis revealed that Cu+ and Ti3+ observed via XPS originate from the presence of an oxygen vacancy. The Ca0.25Cu0.7375Al0.0125TiO3 ceramic exhibited a very high dielectric permittivity of 9.23 × 104 and a low dielectric loss tangent of 0.057 at 1 kHz and room temperature. Importantly, the dielectric permittivity exhibited impressive stability over a temperature range of −60 °C to 110 °C, perfectly meeting the practical requirements for utilization in X5R ceramic capacitors. Our investigation indicates that the improved dielectric properties may be attributed to enhanced grain boundary responses, influenced by oxygen enrichment and the presence of metastable insulating layers at grain boundaries. Combining experimental findings with theoretical evidence, our study elucidates that the excellent dielectric properties of the Ca0.25Cu0.7375Al0.0125TiO3 ceramic originate from an extrinsic effect arising from grain boundary enhancement. This work not only contributes to advancing the understanding of the underlying mechanisms governing dielectric behavior in doped ceramics, but also emphasizes the potential of Ca0.25Cu0.7375Al0.0125TiO3 as a promising material for applications demanding superior dielectric performance.

Construct Amorphous Polymer Interface to Enhance the Thermoelectric Performance of Commercial Bi0.5Sb1.5Te3 Materials.

Interfaces, such as grain boundaries and phase boundaries in thermoelectric (TE) materials, play a crucial role in the carrier/phonon transport. Accurate control of the features of interfaces, including composition, crystalline nature, and thickness may give rise to a promising pathway to break the trade-off between phonon and carrier transport properties, which is essential to design high-performance TE materials. In this work, the amorphous polymer interface (API) layer is introduced to the p-type commercial Bi0.5Sb1.5Te3 (BST) TE material by the liquid-phase sintering process. Due to the larger mismatch in the acoustic impedance or phonon spectra between the amorphous polymer layer and the BST phase, the additional interfacial thermal resistance is introduced, which results in a large decrease in lattice thermal conductivity. It is found that the interfacial thermal resistance at the API is much higher than that of normal grain boundary and hetero interface reported in the literature. Conversely, taking advantage of the strong electron and phonon scattering, a large net get of ZT was achieved. A maximum ZT of ∼1.22 at 350 K was obtained in the BST/polyimide-0.5% sample, which is considerably greater than that of the commercial BST matrix (∼0.99 at 350 K). Furthermore, the optimized BST/polymer sample also exhibited almost 20% enhancement in hardness compared with the pure BST sample. This work has opened a new window for designing high-performance TE composites, which may extend to other material systems.

Investigation of curing behavior and mechanical properties of SiC ceramics prepared by vat photopolymerization combined with pressureless liquid-phase sintering using Al2O3-coated SiC powder

Preparation of SiC ceramics via vat photopolymerization can enhance the use of SiC ceramics in defense, aerospace, and other fields. However, the high ultraviolet absorbance and refractive index of SiC powder present challenges in achieving the desired curing depth for SiC slurry in vat photopolymerization. Additionally, the low sintering activity of SiC powder hinders the densification of 3D-printed SiC ceramics. Consequently, the fabrication of SiC ceramics using vat photopolymerization 3D printing technology encounters significant challenges. This study proposes a method of improving the curing properties of SiC slurry with Al2O3-coated SiC powder. The gap between SiC particles was optimized by incorporating small particle β-SiC with enhanced sintering activity. The effects of Al2O3 coating modification and β-SiC percentage in SiC powder system on the UV absorbance of SiC powder, rheology and curing properties of SiC slurries, and sintering properties of SiC ceramics were thoroughly investigated. Furthermore, the density, flexural strength, and elastic modulus of the sintered parts prepared by vat photopolymerization combined with the pressureless liquid-phase sintering process achieve 2.82 ± 0.07 g/cm3, 225.3 ± 13.6 MPa, and 94.9 ± 5.5 GPa, respectively. These properties are comparable to those of other currently available 3D-printed SiC ceramics but are easier to manipulate and achieve, showcasing its competitiveness.

Simulation on liquid phase sintering of CeO2-CoO ceramic by diffusional Monte Carlo Potts model

Difficulty in control of in-situ crystal growth of CeO2-CoO ceramics limits its catalyst application of solid oxide fuel cells. It is necessary to explore a method to simulate the microstructure growth process of this ceramics under high temperature. In this work, the diffusional Monte Carlo Potts model for the simulation on liquid phase sintering of CeO2-CoO ceramics is established. With geometric and concentration-dependent probability calculated, the phenomena of solidification and melting in liquid phase sintering process are simulated. Moreover, effects of diffusion and grain consolidation are also taken into consideration. The simulation on both isothermal sintering and cooling process is run. The properties of grain growth, grain size distribution and sintering neck evolution are studied. It is found that the grain growth exponent, temporal revolution of grain number and sintering neck obtained from simulation basically agree with relevant theories. In addition, grain size distribution basically remains constant and follows lognormal distribution during the sintering process. This work provides a method to study the in-situ crystal growth process of liquid phase sintered ceramics.

Using particle-loaded inks to selectively change the material properties in binder-jetted WC–Co parts

Functionally graded hardmetals offer a superior combination of fracture toughness and wear resistance and alleviate the compromise that conventional hardmetals must face between these two material properties. In tooling applications, they exhibit superior cutting performance compared to the conventionally employed hardmetals. Traditionally, graded tools are enabled by a surface treatment with nitrogen or carbon. This enables a tungsten carbide–cobalt (WC–Co) tool with a surface layer containing less cobalt (Co) than the core of the part. With this Co gradation, the wear properties can be improved due to the harder surface. If different loads act at different points in a tool and the geometric complexity of a tool increases, the requirements for a targeted positioning of the Co gradients become higher. A simple surface treatment does not allow a flexible distribution of the desired gradients. Binder jetting provides a solution to produce location-independent graded structures. In this work, the process was evaluated for the generation of Co gradients in WC–Co structures. Inks loaded with graphite particle contents of 2.5, 5, 7.5, and 10 m% were used to create differences in the carbon content in the green part. This induced a Co migration during the liquid phase sintering process. The sintering parameters were varied in time and temperature and studied regarding their effect on the microstructure and the porosity, the formation of the Co gradient, and the hardness. At low sintering times and temperatures, all carbon differences led to a Co gradient in the sintering part with a deviation of up to 10 m%. With an increase in sintering time and temperature, the Co distribution began to even out, and a deviation was observed only in the parts created with the inks containing 7.5 and 10 m% of particles. Hardness values of up to 1300 HV10 were obtained, which is comparable to conventionally produced WC–Co parts. The excess of carbon resulted in porosity in the parts leading to a reduced density. However, with inks containing 10 m% particles, densities of 94.26% were achieved at the longest sintering times and the highest temperature.

Research on hot isostatic pressing sintering behavior of 90W–Ni–Fe–Cu alloy

In order to understand the underlying material evolution during liquid phase sintering (LPS) process in hot isostatic pressing process (HIP), microstructure and mechanical properties of 90 W–Ni–Fe–Cu alloys fabricated at 1400 °C/150 MPa are examined systematically. For 90W-4.2Ni-1.8Fe–4Cu alloy, the typical LPS microstructure, which are spherical W grains uniformly surrounded by continuously distributed γ- (Ni, Fe, Cu) matrix phase with the lowest W–W contiguity of 0.31, is achieved successfully after HIP at 1400 °C/150 MPa. The excellent tensile strength reaches as high as 873 MPa with elongation of 17.3% due to the soft γ- (Ni, Fe, Cu) matrix phase. Moreover, the relationship between the microstructure parameters VM(1−CW−W) and elongation ε are established and analyze the association with dislocation motion in depth through electron backscattered diffraction (EBSD) characterization. To our best knowledge, the LPS behavior of tungsten alloy is in-situ revealed by high-temperature confocal scanning laser microscopy (HT-CSLM) for the first time. The current research provides a novel strategy for designing and fabricating powder metallurgy materials by LPS with pressure.

Effect of Niobium on Sintering Process of Gamma Phase Uranium Alloys Fuel Pellets

Abstract As a candidate material for metallic fuel, U-Mo metal fuel pellets are the most promising. U-Mo and U-Mo-Nb alloy pellets with a certain porosity were successfully prepared by the process of hydrogenation/dehydrogenation—compression molding—argon liquid-phase sintering. In order to study the effect of Nb addition on γ phase uranium alloy fuel pellets, microstructure and thermophysical properties of the samples were investigated using scanning electron microscope (SEM), in situ synchrotron X-ray diffraction (XRD), and differential scanning calorimeter (DSC) measurements. Results showed that with the increase of Nb content in the pellets from the nonadd to micro-adding, Nb can facilitate the diffusion of Mo into the U matrix, resulting in the formation of a metastable γ-U phase. Meanwhile, during the same liquid phase sintering process of U-Mo fuel pellets, with the increase of Nb content, the number of secondary phases in U-Mo fuel pellets gradually decreased, while the size and number of voids of the secondary phases decreased. The specific heat capacity and thermal diffusivity of porous γ phase uranium alloys fuel pellets with different density were measured and thermal conductivity from 100 °C to 600 °C were calculated according to the experiment results. It is suggested that the thermal conductivity will increase with the density of pellets increasing.

Recycling of silicon from waste PV diamond wire sawing silicon powders: A strategy of Na2CO3-assisted pressure-less sintering and acid leaching

Recycling diamond wire sawing silicon powders (DWSSP) from photovoltaic (PV) silicon wafers production has become an urgent problem. The challenge of recovery is the surface oxidation and contamination of the ultra-fine powder with impurities during the sawing and collection process. In this study, a clean recovery strategy of Na2CO3-assisted sintering and acid leaching was proposed. Due to the Al contamination from the perlite filter aid, the introduced Na2CO3 sintering aid can react with the SiO2 shell of DWSSP to form a slag phase with accumulated impurity Al during the pressure-less sintering process. Meanwhile, the evaporation of CO2 contributed to the formation of ring-like pores surrounded by a slag phase, which can be easily removed by acid leaching. When 15 % Na2CO3 was added, the content of impurity Al in DWSSP could be reduced to 0.07 ppm with a removal rate of 99.9 % after acid leaching. The mechanism suggested that the addition of Na2CO3 can trigger the liquid phase sintering (LPS) process of the powders, and the cohesive force and liquid pressures difference generated during the process facilitated the transportation of impurity Al from the SiO2 shell of DWSSP to the formed liquid slag phase. The efficient silicon recovery and impurity removal of this strategy demonstrated its potential for solid waste resource utilization in the PV industry.

Investigations on Thermal Conductivity of Two-Phase WC-Co-Ni Cemented Carbides through a Novel Model and Key Experiments

Excellent thermal conductivity is beneficial for the fast heat release during service of cemented carbides. Thus, thermal conductivity is a significant property of cemented carbides, considerably affecting their service life. Still, there is a lack of systematic investigation into the thermal conductivity of two-phase WC-Co-Ni cemented carbides. To remedy this situation, we integrated experiments and models to study its thermal conductivity varying the phase composition, temperature and WC grain size. To conduct the experiments, WC-Co-Ni samples with two-phase structure were designed via the CALPHAD (Calculation of Phase Diagrams) approach and then prepared via the liquid-phase sintering process. Key thermal conductivity measurements of these prepared samples were then taken via LFA (Laser Flash Analysis). As for modeling, the thermal conductivities of (Co, Ni) binder phase and WC hard phase were firstly evaluated through our previously developed models for single-phase solid solutions. Integrating the present key measurements and models, the values of ITR (Interface Thermal Resistance) between WC hard phase and (Co, Ni) binder phase were evaluated and thus the model to calculate thermal conductivity of two-phase WC-Co-Ni was established. Meanwhile, this model was verified to be reliable through comparing the model-evaluated thermal conductivities with the experimental data. Furthermore, using this developed model, the thermal conductivity of two-phase WC-Co-Ni varying with phase-fraction, temperature and grain size of WC was predicted, which can contribute to its design for obtaining desired thermal conductivities.

Grain boundary engineering in Nd-based ThMn12 magnets and their nitrides: A comprehensive study of challenges and limitations

Grain boundaries in rare earth permanent magnets are of major importance to optimize coercivity and densification during sintering. In this work, grain boundary engineering of Nd-based ThMn12 magnets and their nitrides was systematically investigated. First, the parent compound with excess Nd (5, 20 and 40 at%) was studied. It is shown that a paramagnetic dhcp-Nd grain boundary is formed with excess of Nd above 20 at%. This intergranular phase promotes the liquid-phase sintering process at ∼ 700 °C and a bulk nanostructured Nd1.2(Fe,Mo)12 sample with a relative density of 95 % using SPS was obtained. By further doping with Cu, the grain boundary phase properties were tuned by lowering its melting point below 500 °C. Next, the focus is on the nitrides which have a coercivity of ∼ 0.6 T. During the nitrogenation process, the dhcp-Nd grain boundary phase reacts with nitrogen to form a paramagnetic NdN phase, which does not influence coercivity. However, NdN inhibits liquid-phase sintering of the ThMn12 magnets, due to its high melting point (> 1500 °C), limiting the relative density to 65 % after SPS. Thus, a proper grain boundary for nitrides is yet to be found but this work elucidates in detail the specific challenges of grain boundary engineering in Nd-based ThMn12 magnets, non-nitrided and nitrided.

Kinetics of Cu6Sn5 and Cu3Sn intermetallic compounds growth and isothermal solidification during Cu-Sn transient liquid phase sintering process

The kinetics of Cu-Sn intermetallic compounds (IMCs) growth relates to the materials preparation, process regulation and reliability prediction in the new energy field and electronic packaging industry. As a typical instance that Cu-Sn IMCs are involved with, this work investigated the kinetics of Cu-Sn IMCs growth and isothermal solidification of Cu-Sn transient liquid phase sintering (TLPS) process for high temperature resistant packaging of the third-generation semiconductors power devices. A three-dimensional kinetics model of Cu/Sn solid/liquid interfacial reaction and the corresponding kinetics equations of Cu6Sn5 and Cu3Sn growth was established. Based on Cu-Sn IMCs growth kinetics, a parameter ξSn called the residual rate of Sn was defined to characterize the isothermal solidification kinetics of Cu-Sn TLPS process. By measuring the volume fraction of Cu and Sn, the quality fraction of residual Cu and Sn and produced Cu-Sn IMCs were determined, and thus the kinetics of Cu-Sn IMCs growth and the isothermal solidification of Cu-Sn TLPS process were experimentally studied to validate the theoretical model. The results showed that the theoretical results predicted by the model were well-matched with experimental results. Besides rising temperature, the kinetics of Cu-Sn IMCs growth and the isothermal solidification can be remarkably accelerated by decreasing Cu particle size. Reducing Sn content does not affect the kinetics of Cu-Sn IMCs growth but helps to shorten the isothermal solidification time of Cu-Sn TLPS process.

Influence of aluminum addition on the laser powder bed fusion of copper-aluminum mixtures

• Created a system in which the liquid phase sintering process is established. • Aluminum was added to pure Cu to form Cu-rich mixtures with different Al contents. • The in-situ alloying of Cu-Al was achieved with an energy density (ED) two times lower than the ED used with pure Cu, leading to smoother and denser parts. • Achieved simultaneous joining and 3D printing mixtures of highly reflective metals. The high optical reflectivity of copper (Cu) in the near infrared (NIR) domain and its elevated heat dissipation make Cu a challenging metal for laser powder bed fusion (LPBF), even with high energy densities (EDs). In this study, we demonstrated that adding aluminum (Al) powder by as little as 0.75, 1.5, and 3 wt.% substantially enhances Cu processability, leading to denser (up to 98 %) and smoother (Ra = 3.3 μm) Cu-Al parts as compared to 95% and 18 μm, respectively, for the parts printed using pure Cu. In addition, this method reduces the ED required by a factor of two for the additive manufacturing of the Cu-based parts while maintaining a significant heat dissipation. These improvements are achieved due to the coexistence of solid Cu particles with liquid Al at the vicinity of the molten pool, accomodating the predensification of the powder mixture. The development of the semi-liquid 3D printing approach opens up a new path to easily print materials difficult to be printed for broadening their applications.

Micro-fracture behavior of a single-aggregated cBN grain and its relation to material removal in high-speed grinding of Ti–6Al–4V alloys

Aggregated cubic boron nitride (cBN) abrasive grains were developed using high-temperature liquid phase sintering processes and then the single-grain scratching trial was conducted to study the grain wear behavior and material removal characteristics. Characterizations of grain wear evolutions and related surface scratches grinded by aggregated and monocrystalline cBN grains are performed, respectively. The evaluations of wear-resistance and self-sharpening abilities of both abrasive grains are carried out based on the proposed indicators of volumetric pile-up ratio, volumetric groove removal rate, and grain grinding ratio. Compared to the monocrystalline cBN grain, the as-developed aggregated cBN grain exhibits the more stable grinding process, excellent self-sharpening ability as well as a higher material removal volume provided by the dynamic balance between microfracture and partial macrofracture of multi-layer micro cBN particles.

Improving the connectivity of MgB2 bulk superconductors by a novel liquid phase sintering process

This work investigates a new processing method developed to improve the connectivity of ex-situ MgB2 bulks at low sintering temperatures. Mg additions (1–10 wt.%) were mixed to pre-synthesised MgB2 to make composite powders that were sintered at 900 ∘C by the field assisted sintering technique. Addition of 10 wt.% Mg resulted in a substantial increase in density from 68% to 79% and a dramatic reduction in MgB4 from 11 to ∼0 wt.%. Pressure and dilatometry data recorded in-situ during the sintering process revealed that Mg additions led to different sintering mechanisms depending on the Mg fraction. For large Mg fractions (6 and 10 wt.%) a Mg liquid phase was formed and led to significant density improvements, and all pre-existing MgB4 was transformed into MgB2. A small amount of residual Mg remained in the bulks after the sintering process. Connectivity was improved with Mg additions, increasing four fold in the 10 wt.% Mg-MgB2 sample compared to unmodified MgB2. J c values at low field were also significantly improved by Mg additions, in particular the 6 and 10 wt.% Mg-MgB2 specimens showed J c (20 K, 0 T) values 4–5 times higher than for unmodified MgB2.

Low-temperature densification of high-entropy (Ti,Zr,Nb,Ta,Mo)C\u2014Co composites with high hardness and high toughness

In order to prepare high toughness (Ti,Zr,Nb,Ta,Mo)C ceramics at low temperatures while maintaining high hardness, a liquid-phase sintering process combined with Co-based liquid-phase extrusion strategy was adopted in this study. The densification temperature can be lowered to 1350 °C, which is much lower than the solid-state sintering temperature (∼2000 °C) generally employed for high-entropy carbide ceramics. When sintered at 1550 °C and 30 MPa applied pressure, part of the Co-based liquid-phase was squeezed out of the graphite mold, such that only ∼3.21 vol% of Co remained in the high-entropy ceramic. Compared to the Co-free solid-state sintered (Ti,Zr,Nb,Ta,Mo)C ceramics, prepared at 2000 °C and 35 MPa, the hardness was slightly decreased from 25.06±0.32 to 24.11±0.75 GPa, but the toughness was increased from 2.25±0.22 to 4.07±0.13 MPa·m1/2. This work provides a new strategy for low-temperature densification of high-entropy carbides with both high hardness and high toughness.

Effect of Borax On Sintering Kinetics, Microstructure and Mechanical Properties of Porous Glass-Ceramics From Coal Fly Ash by Direct Overfiring

The direct sintering process of coal fly ash for the preparation of glass-ceramics is the liquid-phase sintering process, from non-densification to densification. When the temperature exceeds the densification temperature point, the porosity of glass-ceramics on the contrary increases and the pore diameter increases. This provides a basis to prepare porous glass-ceramics by direct overfiring. Adding borax to coal fly ash can reduce the temperature of liquid phase formation, reduce the preparing temperature of porous glass-ceramics, achieve the purpose of energy saving. The effects of borax on the structure, properties and sintering kinetics of porous glass-ceramics prepared from coal fly ash by overfiring were investigated. It is found that the introduction of B-O bond can change the network structure of non-crystalline vitreous in coal fly ash, reduce the melting temperature, promote the formation of liquid phase, and thus increase the porosity of porous glass-ceramics. This paper provides a certain experimental basis for the preparation of porous glass-ceramics by direct overfiring of coal fly ash at low temperature without adding pore-forming agent, and provides a new possibility for the high-value resource utilization of coal fly ash.

希土類-鉄化合物を用いた高性能ボンド磁石の開発における最新動向

Permanent magnets, and particularly rare earth magnets such as Nd-Fe-B, have attracted much attention because of their magnetic properties. There are two well-established techniques for obtaining sintered magnets and bonded Nd-Fe-B magnets. Powder metallurgy is used to obtain high-performance anisotropic sintered magnets. To produce bonded magnets, either melt-spinning or the hydrogenation, disproportionation, desorption, and recombination process is used to produce magnet powders, which are then mixed with binders. Since the development of Nd-Fe-B magnets, several kinds of intermetallic compounds have been reported, such as Sm2Fe17Nx and Sm(Fe,M)12 (M: Ti, V, etc.). However, it is difficult to apply a liquid-phase sintering process similar to the one used for Nd-Fe-B sintered magnets in order to produce high-performance Sm-Fe–based sintered magnets because of the low decomposition temperature of the compound and the lack of a liquid grain boundary phase like that in the Nd-Fe-B system. Therefore, bonded magnets are useful in the production of bulk magnets using these Sm-Fe based compounds. This article reviews recent progress in our work on the development of high-performance bonded magnets using Nd2Fe14B and Sm2Fe17Nx compounds.