Burgos-García, N. (Nerea)
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- Coercivity and Magnetic Anisotropy of (Fe0.76Si0.09B0.10P0.05)97.5Nb2.0Cu0.5 Amorphous and Nanocrystalline Alloy Produced by Gas Atomization Process(2020) Ipatov, M.S. (Mihail S.); Gonzalez, J. (Julián); Martín, J.M. (José Manuel); Domínguez, L. (Lourdes); Burgos-García, N. (Nerea); Álvarez, K.L. (Kenny)We present the evolution of magnetic anisotropy obtained from the magnetization curve of (Fe0.76Si0.09B0.10P0.05)97.5Nb2.0Cu0.5 amorphous and nanocrystalline alloy produced by a gas atomization process. The material obtained by this process is a powder exhibiting amorphous character in the as-atomized state. Heat treatment at 480 ◦C provokes structural relaxation, while annealing the powder at 530 ◦C for 30 and 60 min develops a fine nanocrystalline structure. Magnetic anisotropy distribution is explained by considering dipolar effects and the modified random anisotropy model.
- Novel predictive methodology of amorphisation of gas-atomised Fe-Si-B alloy powders(Elsevier, 2021) Masood, A. (Ansar); Martín, J. M. (José M.); González, J. M. (Julián María); McCloskey, P. (Paul); Ahmadian-Baghbaderani, H. (Hasan); Burgos-García, N. (Nerea); Álvarez, K.L. (Kenny)The present work is focused on developing amorphisation capability criteria to predict regions with high amorphous forming ability (AFA) in the Fe-Si-B phase diagram. First, the AFA of Fe-Si-B alloy powders was evaluated by conventional empirical glass forming parameters, which eventually did not guide to the best AFA alloy. Then, AFA analysis was extended to the ternary phase diagram, calculated using CALPHAD, along with superimposed mathematical model based on topological instability factor (λ), estimated critical cooling rate (RC) and critical particle size (dC), to confine the phase diagram regions with larger AFA. The alloy with the highest AFA shows optimum atomic size mismatch when λ = 0.204. Furthermore, the optimal region in the phase di- agram to design alloys with high AFA is where Fe2B is the first solid phase under equilibrium solidification. Within these two limits, the alloys with lower liquidus temperatures show the highest AFA for the gas-atomised powders
- Internal friction associated with ? martensite in shape memory steels produced by casting route and through additive manufacturing: Influence of thermal cycling on the martensitic transformation.(Elsevier, 2022-10) Del-Rio-Orduña, D. (David); Veiga, A. (Angela); Ruiz-Larrea, I. (Isabel); No, M.L. (María L.); Sota, A. (Ángel); San Juan, J.M. (José Maria); Gómez-Cortés, J.F. (José Fernando); Ausejo-Muñoz, S. (Sergio); Pérez-Casero, I. (Iñigo); Pérez-Cerrato, M. (Mikel); Burgos-García, N. (Nerea)Among the different families of shape memory alloys (SMA), the Fe-Mn-Si-Cr-Ni alloys have attracted a renewed interest because of its low cost, high corrosion resistance and high recovery strength during the shape memory effect, and the new technologies of additive manufacturing offer unforeseen possibilities for this family of SMA. In the present work, the reversible gamma - epsilon martensitic transformation (MT), responsible for the shape memory effect, is studied in two Fe-Mn-Si-Cr-Ni alloys with high (20.2 wt%) and low (15.8 wt%) Mn content, produced by the conventional route of casting and rolling, in comparison with the MT in another similar alloy, with intermediate Mn content (19.4 wt%), which was produced by gas atomization and additive manufacturing through laser metal deposition. The forward and reverse gamma - epsilon MT is studied by mechanical spectroscopy through the internal friction spectra and the dynamic modulus variation, together with a parallel microstructural characterization including in-situ observation of the gamma - epsilon MT during cooling and heating at the scanning electron microscope. The evolution of the transformed fraction of epsilon martensite, evaluated through the integral area of the internal friction peak, was followed along thermal cycling in all three alloys. Both, the internal friction and the electron microscopy studies show that the epsilon martensite amount increases very fast during the first few cycles, and then decreases with a tendency towards its stabilization for many tens of cycles. The results show that the gamma - epsilon MT is more stable on cycling in the additive manufactured sample than in the conventionally processed samples, opening new avenues for designing shape memory steels to be specifically processed through additive manufacturing.
- Development of anisotropic Nd-Fe-B powder from isotropic gas atomized powder.(2024) Sarriegui-Estupiñan, G.C. (Gabriela Carolina); Ipatov, M.S. (Mihail S.); González, J. (Julián); Sheridan, R. (Richard); Pickering, L. (Lydia); Martín, J.M. (José Manuel); Degri, M. (Malik); Walton, A. (Allan); Burgos-García, N. (Nerea)This work presents an innovative approach to obtain anisotropic Nd-Fe-B powder from isotropic gas atomized powder. The new process was developed using a ternary Nd-Fe-B alloy, without the requirement for additional heavy rare earth or other critical raw materials. It comprises the following steps: (a) gas atomization to produce a polycrystalline isotropic powder; (b) annealing at high temperature to induce grain growth; (c) hydrogen decrepitation to obtain a monocrystalline powder; and (d) hydrogenation-disproportionation-desorptionrecombination to obtain the final ultrafine anisotropic particles. The final particle shape is polygonal, which should improve the injection molding characteristics of current powder. The final powder exhibits both high remanence (0.97 T) and coercivity (1354 kA/m) for laboratory batch sizes, which is a result of its anisotropic ultrafine microstructure. Thus, gas atomization is considered a feasible alternative to casting methods as a first step to produce powders for anisotropic bonded magnet.
- 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.
- Designing for shape memory in additive manufacturing of Cu-Al-Ni shape memory alloy processed by laser powder bed fusion(MDPI, 2022-09) Ruiz-Larrea, I. (Isabel); Urionabarrenetxea, E. (Ernesto); Fraile, I. (Itziar); Cerdeño, M.L. (María Luisa); San Juan, J.M. (José Maria); Gómez-Cortés, J.F. (José Fernando); Pérez-Cerrato, M. (Mikel); González, I. (Ivan); Burgos-García, N. (Nerea)Shape memory alloys (SMAs) are functional materials that are being applied in practically all industries, from aerospace to biomedical sectors, and at present the scientific and technologic communities are looking to gain the advantages offered by the new processing technologies of additive manufacturing (AM). However, the use of AM to produce functional materials, like SMAs, constitutes a real challenge due to the particularly well controlled microstructure required to exhibit the functional property of shape memory. In the present work, the design of the complete AM processing route, from powder atomization to laser powder bed fusion for AM and hot isostatic pressing (HIP), is approached for Cu-Al-Ni SMAs. The microstructure of the different processing states is characterized in relationship with the processing parameters. The thermal martensitic transformation, responsible for the functional properties, is analyzed in a comparative way for each one of the different processed samples. The present results demonstrate that a final post-processing thermal treatment to control the microstructure is crucial to obtain the expected functional properties. Finally, it is demonstrated that using the designed processing route of laser powder bed fusion followed by a post-processing HIP and a final specific thermal treatment, a satisfactory shape memory behavior can be obtained in Cu-Al-Ni SMAs, paving the road for further applications.
- Additive manufacturing of Fe-Mn-Si-based shape memory alloys: state of the art, challenges and opportunities(MDPI, 2023-12) Del Rio, L. (Lucía); San Sebastián, M. (María); Gómez, R. (Raúl); No, M.L. (María L.); Urionabarrenetxea, E. (Ernesto); García-Sesma, L. (Leire); Ortega, P. (Pablo); Burgos-García, N. (Nerea); Mancisidor, A. (Ane)Additive manufacturing (AM) constitutes the new paradigm in materials processing and its use on metals and alloys opens new unforeseen possibilities, but is facing several challenges regarding the design of the microstructure, which is particularly awkward in the case of functional materials, like shape memory alloys (SMA), as they require a robust microstructure to withstand the constraints appearing during their shape change. In the present work, the attention is focused on the AM of the important Fe-Mn-Si-based SMA family, which is attracting a great technological interest in many industrial sectors. Initially, an overview on the design concepts of this SMA family is offered, with special emphasis to the problems arising during AM. Then, such concepts are considered in order to experimentally develop the AM production of the Fe-20Mn-6Si-9Cr-5Ni (wt%) SMA through laser powder bed fusion (LPBF). The complete methodology is approached, from the gas atomization of powders to the LPBF production and the final thermal treatments to functionalize the SMA. The microstructure is characterized by scanning and transmission electron microscopy after each step of the processing route. The reversibility of the epsilon martensitic transformation and its evolution on cycling are studied by internal friction and electron microscopy. An outstanding 14% of fully reversible thermal transformation of epsilon martensite is obtained. The present results show that, in spite of the still remaining challenges, AM by LPBF offers a good approach to produce this family of Fe-Mn-Si-based SMA, opening new opportunities for its applications.
- Effect of particle size on grain growth of Nd-Fe-B powders produced by gas atomization(Elsevier, 2022) Sarriegui-Estupiñan, G.C. (Gabriela Carolina); Ipatov, M.S. (Mihail S.); Zhukov, A. (Arcady); Gonzalez, J.M. (Julián María); Martín, J.M. (José Manuel); 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 ◦C and 1150 ◦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 μm 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 ◦C, Nb loses its effect as an inhibitor of grain growth in the particle size fractions larger than 45–63 μm.