Martín-García, J.M. (José Manuel)
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- Effect of particle size on grain growth of Nd-Fe-B powders produced by gas atomization(Elsevier, 2023-02) Sarriegui-Estupiñan, G.C. (Gabriela Carolina); Ipatov, M.S. (Mihail S.); Zhukov, A. (Arcady); Martín-García, J.M. (José Manuel); González-Estévez, J.M. (Julián María); Burgos-García, N. (Nerea)Gas atomized Nd-Fe-B powders of several compositions were separated in different size fractions by sieving. These fractions were annealed between 1100 degrees C and 1150 degrees C for 24 and 96 h. The oxygen content of the powders was measured before and after annealing for the different size fractions. The oxygen concentration of the powders depends strongly on the particle size and increases significantly during annealing, particularly in the case of small particle sizes. The effect of particle size on the microstructural changes was analyzed in detail, particularly on grain growth, using high resolution scanning electron microscopy and transmission electron microscopy. Electron back scattering diffraction was used to measure grain size. When the particle size rises, the degree of sintering decreases and the higher solid/vapor surface area reduces the mobility of grain boundaries. Oxidation also reduces grain growth rate and its effect is more evident for particles sizes below 45-63 mu m and high Nd concentrations. Nb addition leads to the formation of intra- and intergranular precipitates. The size of these Nb-Fe-containing precipitates increases with the particle size for equivalent annealing conditions. At 1150 degrees C, Nb loses its effect as an inhibitor of grain growth in the particle size fractions larger than 45-63 mu m.
- Experimental study of the influence of operational and geometric variables on the powders produced by close-coupled gas atomisation.(ELSEVIER, 2021-02) Urionabarrenetxea, E. (Ernesto); Martín-García, J.M. (José Manuel); Avello-Iturriagagoitia, A. (Alejo); Rivas-Nieto, A. (Alejandro)The effect of several operational and geometric variables on the particle size distribution of powders produced by close-coupled gas atomisation is analysed from a total of 66 experiments. Powders of three pure metals (copper, tin and iron) and two alloys (bronze Cu-15 wt% Sn and stainless steel SS 316 L) have been produced. Nitrogen, argon and helium were used as atomising gases. It is shown that the gas-to-metal ratio of volume flow rates (GMRV) is more relevant than the ratio of mass flow rates (GMR) in order to analyse the effect of atomisation variables on the particle size. Kishidaka's equation, originally proposed for water atomisation, is modified to predict the median particle size in gas atomisation. The accuracy of the new equation is compared with that of Lubanska, and Rao and Mehrotra. Kishidaka's modified empirical correlation is the most accurate in predicting the median particle size of the powders produced in this work. The morphology of the produced powders is studied by scanning electron microscopy (SEM) and it is observed that the melt superheat can play an important role in the aggregation of fine particles (< 10 mu m), which increases the fraction of large particles (> 100 mu m).
- Multiphase model to predict particle size distributions in close-coupled gas atomization(Elsevier, 2022) Urionabarrenetxea, E. (Ernesto); Martín-García, J.M. (José Manuel); Avello-Iturriagagoitia, A. (Alejo); Amatriain, A. (Aitor)A novel two-stage multiphase model is developed for close-coupled gas atomization by combining formulations available in the literature. Primary atomization is simulated using an Eulerian atomization model, and the outputsa reused as input so fa Lagrangian particle tracking approach to predict the particle size distribution resulting from second aryatomization. Theresults given by the primary atomization mode lare validated with published Direct Numerical Simulations (DNS) values and by comparisonwith experimental images of the spray, while the particle size distributions obtained are accurately fitted toa log-normal distribution, and with powder meandiameters showing good agreemen twith experimental data. The variation of powder characteristic diameters 𝑑10,𝑑50,and𝑑 90 as a function of thegas-to-meltmass flow rate ratio follows correct trends, and the value sofpowder mean diameters 𝑑50 are correctly predicted by the model.