La Roca, Paulo Matías
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La Roca
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Paulo Matías
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InaMat2. Instituto de Investigación en Materiales Avanzados y Matemáticas
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Publication Open Access A short review on the effect of Cr on the fcc-hcp phase transition in Fe-Mn-based alloys(Springer, 2020) Guerrero, L.M.; La Roca, Paulo Matías; Malamud, M.F.; Baruj, A.; Sade, M.; Ciencias; ZientziakThe effect of Cr on the fcc–hcp martensitic transformation in the Fe–Mn–Cr system has been discussed considering different aspects: (a) the relative phase stabilities, (b) the magnetic order of the fcc phase, (c) the structural parameters and volume change between fcc and hcp, (d) the driving force of the martensitic transformation and relevant thermodynamics quantities, (e) the thermal cycling behavior, and (f) the pseudoelastic effect. Particularly, in this work it has been found that when Cr content increases, the effect of cycling on the energy barrier decreases. This may be explained by a small volume change, which could lead to a slighter introduction of plastic deformation during thermal cycling through the martensitic transition.Publication Open Access Designing a wider superelastic window(American Association for the Advancement of Science, 2020) La Roca, Paulo Matías; Sade, M.; Ciencias; ZientziakAdding chromium to an iron alloy enables shape recovery over a wide temperature rangePublication Open Access Strategies to increase austenite FCC relative phase stability in high-Mn steels(Elsevier, 2021) Guerrero, L.M.; La Roca, Paulo Matías; Malamud, M.F.; Butera, A.; Baruj, A.; Sade, M.; Institute for Advanced Materials and Mathematics - INAMAT2Several strategies to increase the FCC austenite stability compared to BCC and HCP martensites have been tested and are discussed. The relative stability of the different phases was analyzed by studying the effects of: a) grain size, b) antiferromagnetic ordering of the austenite, c) thermal cycling through the FCC-HCP transition, d) plastic deformation of the austenite and e) combined effects. As a first step, the effect of decreasing the grain size was analyzed in Fe-Mn alloys for Mn contents smaller than 18 wt.%, where BCC and HCP martensites compete in stability. Formation of the BCC phase is inhibited for 15 wt.% and 17 wt.% of Mn for grain sizes smaller than 2 μm. This enabled, for the first time at these compositions, the measurement of the Neel temperature of the austenite using specific heat and magnetic measurements. A comparison of the obtained transition temperatures with accepted models is discussed. The effect of modifying the grain size on the FCC-HCP transition temperatures was also analyzed for 15 wt.% and 17 wt.% Mn contents showing a complete HCP inhibition for grain sizes smaller than 200 nm. A nucleation model for the HCP martensite is considered which includes an additional resistance to the transformation term depending on the austenitic grain size. Additional combined effects on the FCC stabilization are discussed like the interaction between the antiferromagnetic ordering and the introduction of defects by thermal cycling through the martensitic transformation. The analysis can be easily applied to systems with a larger number of components. Results obtained in the Fe-Mn-Cr system are also presented.Publication Open Access Alternative thermal cycling treatment to produce abnormal grain growth in feMnAlNi alloys: study of composition variations and effects on the relative phase stabilities(Springer, 2021) La Roca, Paulo Matías; Guerrero, L.M.; Baruj, A.; Vallejos, J. M.; Sade, M.; Institute for Advanced Materials and Mathematics - INAMAT2An alternative method to obtain abnormal grain growth in Fe–Mn–Al–Ni system is presented. A crucible is used to control the cooling speed of the samples from 1200 °C enabling the nucleation of the equilibrium fcc phase. This fcc structure leads to an abnormal grain growth after heating to 1200 °C, temperature at which the bcc phase is stable. In this way, crystals with a mean diameter of 18 mm are obtained after 4 thermal cycles which take approximately 2 h. Additionally, precise composition measurements using neutron activation allowed the detection of a decrease in Mn content after each thermal cycle. Using electrical resistivity measurements, the effect of the variation of Mn content on the relative phase stability between the bcc austenite and the fcc martensite has been observed and is discussed here.