Fe-Si-B-Nb-Cu alloy powders, with and without P additions, were produced by gas atomization. The particles smaller than 20 mm are fully amorphous, exhibiting good soft magnetic properties. The crystallization process was studied by differential scanning calorimetry, demonstrating that its kinetics changes dramatically with small variations in the composition. The (Fe0.76Si0.09B0.10P0.05)(97.5)Nb2.0Cu0.5 (at. %) alloy was annealed in the supercooled liquid region (480 degrees C) and at the first crystallization peak (530 degrees C). The structural characterization by means of differential scanning calorimetry, X-ray diffraction, and transmission electron microscopy provided information that explained the excellent soft magnetic properties. Annealing at 480 degrees C produced an amorphous relaxed structure with improved soft magnetic properties. At 530 degrees C, a two-phase material formed by nanocrystals with an average grain size of 16-17 nm embedded in an amorphous matrix was developed. Partial nanocrystallization increased the saturation magnetization from 139 to 144 emu/g and reduced the coercivity from 2.24 to 0.69 Oe. These results can be understood in terms of the algebraic contribution of both phases to the magnetization and the application of the random anisotropy model to nanocrystalline soft magnetic materials. (C) 2019 Elsevier B.V. All rights reserved.

We report on the magnetic properties of NdFeB powders produced by gas atomization, which is a powder manufacturing technology scarcely used in the past to produce such alloys. Using this technique, we have produced several ternary NdFeB alloys with Nd contents between 26.9 wt.% and 28.5 wt.%. The as-atomized powders were split into different size fractions by sieving. Subsequently, we measured the magnetic properties as a function of temperature, between 10 and 400 K, and particle size. The magnetic behavior depends strongly on the microstructure of the material, which in turn is determined by the particle size. It is reported a slope anomaly in the curve of magnetization as a function of temperature at around 150 K due to a spin-reorientation transition. Since gas-atomized powders are isotropic, this magnetic transition produces an increment of the magnetization below this temperature.

In this paper, we report the effect of thermal treatment at different temperatures (523, 623, and 723 K) on the magnetic properties of an amorphous powder with composition Fe72.5Si12.5B15 obtained by gas atomization. Differential scanning calorimetry curves indicate that a significant structural rearrangement takes place during annealing before crystallization. As expected, the intrinsic coercivity decreases with the annealing temperature, being the most significant drop from 3.26 to 0.44 Oe for the powder with a particle size < 20 mu m, non-annealed, and annealed at 723 K, respectively. An analysis of the effect of annealing on the anisotropy field distribution obtained directly from the magnetization curve is presented for both the non-annealed and the annealed sample with the lowest value of coercive field. The probability density function of the anisotropy field exhibits a lower applied field value at the maximum and is better fit by a Gaussian distribution after the heat treatment, which is a sign of better amorphicity after structural relaxation.

We report a research describing a new route for the production of Fe-Si-B powders, which is the so-called gas atomisation technology, being one of the challenges to study the conditions under which the glass structure is achieved. There have been produced powders of five different compositions in the Fe-Si-B ternary system. The particles with a diameter below 10 mm of the alloy Fe70Si18B12 (at%) were completely amorphous, exhibiting an excellent soft magnetic behaviour (coercivity of around 7 Oe), which is, without any doubt, of significant scientific merit and supports the use of this new route to produce soft amorphous magnetic materials. (C) 2017 Elsevier B.V. All rights reserved.

Present empirical correlations to predict the median particle size of water atomised powders have a validity restricted to a particular atomiser and alloy family. This work proposes a mathematical function that takes into account the influence of the heat transfer coefficient and, therefore, of the solidification time on the median particle size. This equation is applied in combination with previously proposed empirical correlations to extend their validity to a broader range of alloys. Experiments were conducted with alloys of different melting point (Fe base, Cu base and Sn). Quantitative measurements of the median particle size, tap density and several shape factors, and qualitative observations of the particle shape confirmed the importance of the heat transfer rate. It is shown that the inclusion of the solidification time effect results in a better agreement between calculated and experimental data when both low and high melting temperature alloys are taken together.

The present paper focuses on the initial stage of the liquid phase sintering (LPS) of a commercially available P/M Al-Si alloy, with nominal composition A1-14Si-2.5Cu-0.5Mg (in wt%). The microstructural examination of the as-received powder showed that it is constituted by pure Al particles and master alloy particles with composition Al-28Si-5Cu-1 Mg (in wt%). Its compressibility is lower than for the conventional elemental P/M aluminium premixes, but it is still better than for prealloyed Al powders and other P/M powders. Thermogravimetry experiments showed that the elimination of the organic lubricant takes place between 275 and 490 degrees C during heating to the sintering temperature. The phase transformations leading to the formation of the liquid phase were studied by differential scanning calorimetry (DSC). The dimensional changes associated with the generation of the liquid were measured by dilatometry. Samples quenched into water from different temperatures (between 450 and 575 degrees C) and times (between 0 and 30 min) were studied to reveal the microstructural evolution of the alloy. The first liquid is formed inside the master alloy particles at around 505 degrees C. This liquid spreads across the compact, enhancing the chemical homogenization of the material. The alloying elements diffuse from the liquid inside the originally pure Al particles, reducing their melting temperature. This alloying process is almost concluded at around 535 degrees C. When the temperature is increased the liquid starts to be formed also in the originally pure Al particles. The melting of the FCC Al-rich phase finishes around 575-590 degrees C. The full melting of the alloy occurs at about 635-645 degrees C. After analyzing the different possible causes, it is concluded that the main swelling mechanism is the volume change associated with the melting of a fraction of the material when the temperature is increased. The phases detected by X-ray diffraction (XRD) in the as-received powder and in the sintered compact are FCC Al-rich solid solution, Si, theta-phase (CuAl(2)), and Q-phase (Cu(2)Mg(8)Si(6)Al(5)). (C) 2010 Elsevier B.V. All rights reserved.