Nd-rich Alloy Research Articles

Thermal corrosion behavior of cemented carbide under the molten Nd-rich alloy

To clarify the reason for the failure of YG15 cemented carbide mold during the Nd-Fe-B hot-deformation process, the thermal corrosion behavior between YG15 and liquid Nd-rich alloy (Nd76.5Fe23.5) was investigated at 900 ℃ with different times (12–96 h). XRD results showed that Nd3Co phase was formed in Nd-rich alloy, while WC particles in cemented carbide decomposed to elemental W phase. HAADF and HRTEM revealed that new phases of W18O49, NdCoC2 and Nd3Fe29C3.55 appeared in corroded YG15 for 96 h. Furthermore, the hardness of corroded YG15 was significantly reduced due to the decrease of WC content and loss of Co element.

Thermal Corrosion Behavior of Cemented Carbide Under the Molten Nd-Rich Alloy

Thermal Corrosion Behavior of Cemented Carbide Under the Molten Nd-Rich Alloy

An overstoichiometric Nd-Fe-B hard magnetic material

A commercial Nd-rich Nd-Fe-B-based hard magnetic material was studied. The obtained results were compared before and after recording of the thermomagnetic curve up to 800?C. The curve itself showed clearly besides Curie points of the Nd2Fe14B phase and ?-Fe also another critical temperature. M?ssbauer spectroscopic (MS) phase analysis and X-Ray diffraction analysis (XRD) showed in addition to the commonly known phases Nd2Fe14B and NdFe4B4 also some paramagnetic and ferromagnetic iron atoms (MS) and Fe17Nd2 intermetallics (XRD). During the exerted thermal treatment, the content of the Nd2Fe14B and NdFe4B4 phases remained almost unchanged, while iron atoms from remnant minor phases built a separate ?-Fe phase. The XRD pattern also showed the presence of some minor Nd phase. The results of SQUID magnetic measurements suggest a nanocrystalline decoupled structure of the Nd-rich alloy in the optimized magnetic state. Measurement of the magnetization loop showed, in spite of small changes in the phase composition, that magnetic properties of the quality material deteriorated during the thermal treatment.

Primary Creep of Die-Cast Magnesium–Rare Earth Based Alloys

The creep response of die-cast Mg-2.5RE-0.6Zn (wt pct) alloys with different rare earth (RE) mixtures has been investigated at 177 °C. The Nd-rich alloy displayed significantly lower primary creep than its La-rich counterpart. Microstructural analyses revealed the formation of additional Nd-containing precipitates on dislocations in the Nd-rich alloy during creep. The degree of supersaturation of RE solutes in the α-Mg matrix after die casting is suggested to be the key factor in influencing primary creep.

Study of Nd-Fe-B alloys with nonstoichiometric Nd content in optimal magnetic state

Characterization of two rapid-quenched Nd-Fe-B alloys with nonstoichiometric Nd content in the optimized magnetic state was carried out using the X-ray diffractometry (XRD), 57Fe M?ssbauer spectroscopic phase analysis (MS), electron microscopy (TEM), high resolution TEM (HREM) and Superconducting Quantum Interference Device (SQUID) magnetometer. The experimental results demonstrate the fundamental difference in the structure and magnetic properties of the two investigated alloys in the optimized magnetic state. The Nd-Fe-B alloy with the reduced Nd content (Nd4.5Fe77B18.5) was found to have the nanocomposite structure of Fe3B/Nd2Fe14B and partly ?-Fe/Nd2Fe14B, with mean grain size below 30 nm. On the other side, the overstoichiometric Nd14Fe79B7 alloy has almost a monophase structure with the dominant content of the hard magnetic phase Nd2Fe14B (up to 95 wt. %) and a mean crystallite size about 60 nm, as determined by XRD and TEM analysis. The results of magnetic measurements on SQUID magnetometer also suggest the nanocomposite structure of the Nd-low alloy and nanocrystalline decoupled structure of the Nd-rich alloy after the optimal heat treatment.

Reproduction of Nd-Fe-B Sintered Magnet Scraps Using a Binary Alloy Blending Technique

Nd-Fe-B sintered magnet scraps were reproduced as the corresponding sintered magnets from the ground powders (mean particle ≤3μm) by using a binary alloy blending technique. Although the magnets re-sintered from the as-ground powders only provided poor magnetic properties, especially the observed coercivity values (∼20 kAm -1 ), the magnetic properties were considerably improved compared with the as-ground powders by adding an Nd-rich alloy (80 and 20 mass% for Nd and Fe, respectively) with the mass ratio of 90 (scrap powders) to 10 (Nd-rich alloy). Typical magnetic parameters of the recovered magnets were B r = ∼1.21 T, H cJ = ∼1.6 MAm -1 and (BH) max = ∼251 kJm -3 . It was found that the Nd-Fe-B sintered magnet scraps were reproduced as the practically usable magnets by the above process.

Phase formation in undercooled NdFeB alloy droplets

Small droplets of Nd x Fe 100−1.5 x B 0.5 x alloys ( x=11.8–15) were undercooled and solidified using the drop tube technique for the purpose of studying metastable phase formation in this technically important alloy system. It was found that primary γ-Fe phase has been suppressed in most of the droplets due to significant undercooling levels achieved prior to solidification. Consequently, the primary crystallization either of metastable Nd 2Fe 17B y ( y≈1) phase or of Nd 2Fe 14B phase has been favored. The former occurs predominantly to low Nd alloys ( x=11.8–13), while the latter prevails in Nd-rich alloys ( x=14–15). By means of thermomagnetic analysis and powder X-ray diffraction analysis, it was determined that the metastable Nd 2Fe 17B y phase has a Curie temperature of about 100°C and a hexagonal structure with lattice parameters as a=0.496 and c=0.416 nm.

Nucleation and growth of Nd 2Fe 14B crystals from rapidly quenched amorphous alloys: a kinetic study

The kinetic analysis of the Nd 2Fe 14B primary crystallisation activated by heat treatment from the amorphous state is presented for two alloy compositions: Nd 13Fe 79B 8 and Nd 16Fe 76B 8. In the Fe-rich alloy, the transformation results in a mixture of primary crystals and a remaining discorded phase in metastable equilibrium; secondary crystallisation being promoted by heat treatment at higher temperatures. In the Nd-rich alloy, the secondary crystallisation starts as soon as a certain degree of primary crystallisation is attained. Magnetic behaviour vs. heat treatment is discussed in terms of microstructure developed by controlled crystallisation.

Thermal properties of injection moulded dielectromagnets : T.Kulesza et al. (Technical University of Warsaw, Poland.)

The strong, permanent magnets of rare-earth compounds SmCo5, Sm2Co17 and Nd2Fe14B have much greater potential with respect to magnetic energy than ordinary ferrite magnets. Discovered less than ten years ago, the NdFeB hard magnetic material now has a wide market. The high coercivity of this material is determined by the Nd-rich alloys of the Nd-Fe system (see F.A.O. Cabrai, R.S. Turtelli, S. Gama and F.L.A. Machado, IEEE Trans Magn. MAG 25 (1989) 3338). We have prepared high-purity (RRR = 50–70) polycrystalline samples of Pr and studied the temperature dependences of the magnetic susceptibility, χ, in the range 300–1000 K. The temperature dependence of χ exhibits weak anomalies at 550–580 K, probably connected with changes in the electronic structure. We have also prepared Pr-Fe solid solutions with iron concentrations 0.1, 0.5, 1.0, 2.0 wt% and investigated the temperature dependence of χ in the range 300–1000 K. The addition of Fe leads to a sharp intensification of the above-mentioned anomalies up to the magnetic phase transition. χ(T) curves for Pr, Fe-samples with Fe content >0.10 wt% exhibit ferromagnetic behaviour with a Curie temperature Tc = (545±5) K. The nonmagnetic ground state is formed as a result of the sample cooling from T>700 K, but the dependence of χ on the applied field indicates short-range magnetic ordering at room temperature. We explain the experimental data on the basis of the Fe atom redistribution on the nonequivalent sites of the Pr lattice.

Evolution of the magnetic phase of Pr-rich Pr-Fe alloys in the temperature range 300–1000 K

The strong, permanent magnets of rare-earth compounds SmCo 5, Sm 2Co 17 and Nd 2Fe 14B have much greater potential with respect to magnetic energy than ordinary ferrite magnets. Discovered less than ten years ago, the NdFeB hard magnetic material now has a wide market. The high coercivity of this material is determined by the Nd-rich alloys of the Nd-Fe system (see F.A.O. Cabrai, R.S. Turtelli, S. Gama and F.L.A. Machado, IEEE Trans Magn. MAG 25 (1989) 3338). We have prepared high-purity (RRR = 50–70) polycrystalline samples of Pr and studied the temperature dependences of the magnetic susceptibility, χ, in the range 300–1000 K. The temperature dependence of χ exhibits weak anomalies at 550–580 K, probably connected with changes in the electronic structure. We have also prepared Pr-Fe solid solutions with iron concentrations 0.1, 0.5, 1.0, 2.0 wt% and investigated the temperature dependence of χ in the range 300–1000 K. The addition of Fe leads to a sharp intensification of the above-mentioned anomalies up to the magnetic phase transition. χ(T) curves for Pr, Fe-samples with Fe content >0.10 wt% exhibit ferromagnetic behaviour with a Curie temperature T c = (545±5) K. The nonmagnetic ground state is formed as a result of the sample cooling from T>700 K, but the dependence of χ on the applied field indicates short-range magnetic ordering at room temperature. We explain the experimental data on the basis of the Fe atom redistribution on the nonequivalent sites of the Pr lattice.

Phase relationships in the neodymium-magnesium alloy system

The Nd-Mg system was studied using differential thermal analysis (DTA), X-ray examination, metallography, and microprobe analysis. The following intermetallic compounds were found to exist and their crystal structures confirmed or determined: NdMg (cubic, cP2 CsCl type, melting point 800 °C), NdMg2 (cubic, cF24 MgCu2 type, peritectic formation ∼755 °C), NdMg3 (cubic, cF16 BiF3 type, melting point 780 °C), and Nd5Mg41 (tetragonal, tI92 Ce5Mg41 type, decomposes peritectically at 560 °C). The NdMg2 phase undergoes a eutectoidal decomposition at 660 °C. Three eutectic equilibria were observed to occur at 42.5 at. pct Mg and 775 °C, 64.5 at. pct Mg and 750 °C, and 92.5 at. pct Mg and 545 °C, respectively. In the Nd-rich alloys, previously determined data[15] concerning the Mg solubility in α-Nd (8.2 at. pct Mg, ≈550 °C) were accepted. The Mg solubility in β-Nd was evaluated as 34 at. pct Mg at 775 °C. The β-Nd phase was observed to decompose eutectoidally at 17 at. pct Mg and 545 °C. Moreover, in the Mgrich alloys, a metastable NdMg12 phase (tetragonal, tI26 ThMn12 type) was observed in samples quenched from the liquid. The general properties of the Nd-Mg phases are compared with those of the R-Mg compounds and briefly discussed.