Relationship between martensitic plate size and austenitic grain size in martensitic transformations

A systematic experimental analysis based on an assessment of the mean martensite plate size (hplate) in sub-grain domains was implemented to characterize the martensite morphology in polycrystalline Cu-based shape memory alloys. In the grain size range below 100μm, a linear relationship between the average width of the martensite plates and the mean grain size was obtained for a thermal-induced martensitic transformation. This evaluation allows us to perform an analysis of how microstructural length scales affect the martensitic transformation.Fil: la Roca, Paulo Matías. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario. Instituto de Física de Rosario. Universidad Nacional de Rosario. Instituto de Física de Rosario; ArgentinaFil: Isola, Lucio Manuel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario. Instituto de Física de Rosario. Universidad Nacional de Rosario. Instituto de Física de Rosario; ArgentinaFil: Vermaut, Ph.. Institut de Recherche de Chimie Paris; Francia. Centre National de la Recherche Scientifique; Francia. Université Pierre et Marie Curie; FranciaFil: Malarria, Jorge Alberto. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario. Instituto de Física de Rosario. Universidad Nacional de Rosario. Instituto de Física de Rosario; Argentin

Strategies to increase austenite FCC relative phase stability in high-Mn steels

Several 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.The authors acknowledge the financial support from ANPCyT (PICT-2017-2198), CONICET (PIP 2015-112-201501-00521), CONICET (PIP 2017e2019 GI 0634), ANPCyT (PICT-2017-4518), and Universidad Nacional de Cuyo (06/C516 and 06/C588)

Grain size effect on the thermal-induced martensitic transformation in polycrystalline Cu-based shape memory alloys

In Cu-based SMA alloys, the grain size (d) effect on the martensitic transformation temperature was investigated for a wide range of d. Specimens were prepared by different heat treatments in order to create a range of grain sizes, from about 500 nm (ribbons and tapes obtained by rapid solidification techniques) up to 6 mm diameter single-crystals (grown by the Bridgman method). Information obtained from the literature was also included in the set of analyzed experimental data. The reduction of grain size shifts the forward transformation temperature downwards. These grain-size effects are observed in specimens with d below ∼ 100 μm, and become more pronounced for d below ∼ 20 μm. An empirical expression was obtained that describes the grain-size effect over the whole temperature range. The obtained curve differs considerably from the Hall-Petch behaviour reported in the literature by some other investigators.Fil: la Roca, Paulo Matías. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Rosario. Instituto de Física de Rosario (i); Argentina. Universidad Nacional de Rosario. Facultad de Ciencias Exactas, Ingeniería y Agrimensura; ArgentinaFil: Isola, Lucio Manuel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Rosario. Instituto de Física de Rosario (i); Argentina. Universidad Nacional de Rosario. Facultad de Ciencias Exactas, Ingeniería y Agrimensura; ArgentinaFil: Sobrero, Cesar Enrique. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Rosario. Instituto de Física de Rosario (i); Argentina. Universidad Nacional de Rosario. Facultad de Ciencias Exactas, Ingeniería y Agrimensura; ArgentinaFil: Vermaut, P.. Ecole Nationale Superieure de Chimie de Paris; FranciaFil: Malarria, Jorge Alberto. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Rosario. Instituto de Física de Rosario (i); Argentina. Universidad Nacional de Rosario. Facultad de Ciencias Exactas, Ingeniería y Agrimensura; Argentin

Effect of high-energy ball-milling on the magnetostructural properties of a Ni45Co5Mn35Sn15 alloy

[EN] The effect of high-energy ball-milling on the magnetostructural properties of a Ni45Co5Mn35Sn15 alloy in austenitic phase at room temperature has been analyzed by neutron and high-resolution X-ray diffraction. The ball milling promotes a mechanically-induced martensitic transformation as well as the appearance of amorphous-like non-transforming regions, following a double stage; for short milling times (below 30 min), a strong size reduction and martensite induction occur. On the opposite, for longer times, the increase of strains predominates and consequently a larger amount of non-transforming regions appears. The effect of the microstructural defects brought by milling (as dislocations) on both the enthalpy change at the martensitic transformation and the high field magnetization of the austenite has been quantitatively estimated and correlated to the internal strains. Contrary to what occurs in ternary Ni-Mn-Sn alloys, the mechanically induced defects do not change the ferromagnetic coupling between Mn atoms, but just cause a net reduction on the magnetic moments.This work has been carried out with the financial support of the Spanish “Ministerio de Economía y Competitividad” (Projects number MAT2015-65165-C2-R) “Agencia Estatal de Investigación (AEI), Ministerio de Ciencia, Innovación y Universidades” (Projects number RTI2018-094683-B-C54 (MCIU/AEI/FEDER, UE)), Navarra Government (Project number PC017-018 AMELEC) and Basque Government Grant No. IT-1005-16. We acknowledge ILL and ALBA for the beam time allocations: (http://doi.org/10.5291/ILL-DATA. INTER-411), CRG-2352, and ALBA BL04_MPSD beamline at ALBA Synchrotron with the collaboration of ALBA staff. PLR has received funding from “la Caixa” and "Caja Navarra" Foundations, under agreement LCF/PR/PR13/51080004

Designing a wider superelastic window

Conventional metal alloys can only recover their original shape if subjected to very small elastic deformations. Superelastic alloys (also named pseudoelastic alloys) can recover their shape after deformations as great as 20% (1) just by unloading the force on the material. They are part of the larger group of shape-memory alloys but do not require a temperature change for recovery, and they have found applications in areas including robotics, structural engineering of buildings, and aerospace engineering (2, 3). A superelastic alloy usually exhibits this property only over a well-determined and often small temperature range normally called a “superelastic window.” On page 855 of this issue, Xia et al. (4) describe superelastic “invar” alloys with functional properties that are independent of temperature over the largest superelastic window reported, from 10 to 473 K.Fil: la Roca, Paulo Matías. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; Argentina. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; Argentina. Comisión Nacional de Energía Atómica. Gerencia del Área de Energía Nuclear. Instituto Balseiro; ArgentinaFil: Sade Lichtmann, Marcos Leonel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; Argentina. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; Argentina. Comisión Nacional de Energía Atómica. Gerencia del Área de Energía Nuclear. Instituto Balseiro; Argentin

Shape memory effect and pseudoelasticity in Fe-Mn-based alloys

Several Fe-based alloys are being considered as potential candidates for applications which require shape-memory behavior or superelastic properties. The possibility of using fabrication methods which are well known in the steel industry is very attractive and encourages a large amount of research in the field. In the present article, Fe–Mn-based alloys are mainly addressed. On the one hand, attention is paid to the shape-memory effect where the alloys contain (a) a maximum amount of Mn up to around 30 wt%, (b) several possible substitutional elements like Si, Cr, Ni, Co, and Nb and (c) some possible interstitial elements like C. On the other hand, superelastic alloys are analyzed, mainly the Fe–Mn–Al–Ni system discovered a few years ago. The most noticeable properties resulting from the martensitic transformations which are responsible for the mentioned properties, i.e., the fcc–hcp in the first case and the bcc–fcc in the latter are discussed. Selected potential applications are also analyzed.Fil: la Roca, Paulo Matías. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; Argentina. Comisión Nacional de Energía Atómica. Gerencia del Área de Energía Nuclear. Instituto Balseiro; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; ArgentinaFil: Baruj, Alberto Leonardo. Comisión Nacional de Energía Atómica; Argentina. Comisión Nacional de Energía Atómica. Gerencia del Área de Energía Nuclear. Instituto Balseiro; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; ArgentinaFil: Sade Lichtmann, Marcos Leonel. Comisión Nacional de Energía Atómica; Argentina. Comisión Nacional de Energía Atómica. Gerencia del Área de Energía Nuclear. Instituto Balseiro; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; Argentin

Role of Mn and Cr on structural parameters and strain energy during FCC-HCP martensitic transformation in Fe-Mn-Cr shape memory alloys

Fe-Mn-based alloys show the shape memory effect which is mainly related to the FCC-HCP martensitic transformation. Cr is one of the additional elements which improve the properties of these alloys. In the present work structural data are obtained for the FCC austenite, and both martensitic structures, HCP and BCC, for an extended composition range where the FCC-HCP transition takes place. Lattice parameters are determined by X-Ray diffraction measurements performed at room temperature. The volume change between the austenite and each martensitic structure plays a significant role on relevant properties for martensitic transformations, like the strain energy associated to the transition. The effect of Mn and Cr on lattice parameters and volume change between FCC and HCP is determined and modeling of the data is presented. This result allows estimating the strain energy associated to the phase change. By using this information, the strain energy contribution to the balance of energy for the HCP nucleation is discussed. The addition of Cr decreases the volume change between FCC and HCP for contents larger than 12 wt% Cr which leads to a decrease of the strain energy. Both effects favor an increased shape memory effect associated to the FCC-HCP martensitic transition.Fil: Malamud, Florencia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; Argentina. Comision Nacional de Energía Atómica. Gerencia de Área Investigaciones y Aplicaciones no Nucleares. Gerencia de Física (Centro Atómico Bariloche). División Física de Metales; Argentina. Comisión Nacional de Energía Atómica. Gerencia del Área de Energía Nuclear. Instituto Balseiro; ArgentinaFil: Guerrero, L. M.. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Comision Nacional de Energía Atómica. Gerencia de Área Investigaciones y Aplicaciones no Nucleares. Gerencia de Física (Centro Atómico Bariloche). División Física de Metales; Argentina. Comisión Nacional de Energía Atómica. Gerencia del Área de Energía Nuclear. Instituto Balseiro; ArgentinaFil: la Roca, Paulo Matías. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; Argentina. Comision Nacional de Energía Atómica. Gerencia de Área Investigaciones y Aplicaciones no Nucleares. Gerencia de Física (Centro Atómico Bariloche). División Física de Metales; Argentina. Comisión Nacional de Energía Atómica. Gerencia del Área de Energía Nuclear. Instituto Balseiro; ArgentinaFil: Sade Lichtmann, Marcos Leonel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; Argentina. Comision Nacional de Energía Atómica. Gerencia de Área Investigaciones y Aplicaciones no Nucleares. Gerencia de Física (Centro Atómico Bariloche). División Física de Metales; Argentina. Comisión Nacional de Energía Atómica. Gerencia del Área de Energía Nuclear. Instituto Balseiro; ArgentinaFil: Baruj, Alberto Leonardo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; Argentina. Comision Nacional de Energía Atómica. Gerencia de Área Investigaciones y Aplicaciones no Nucleares. Gerencia de Física (Centro Atómico Bariloche). División Física de Metales; Argentina. Comisión Nacional de Energía Atómica. Gerencia del Área de Energía Nuclear. Instituto Balseiro; Argentin