Study of the transformation sequence on a high temperature martensitic transformation Ni-Mn-Ga-Co shape memory alloy

Ni-Mn-Ga alloys show the highest magnetic-field-induced strain among ferromagnetic shape memory alloys. A great effort is being done in this alloy system to increase the application temperature range. In this sense, the addition of small amounts of Cobalt to NiMnGa alloys has been proved to increase the MT temperatures through the increase of the electron per atom relation (e/a). In this work, the analysis of the crystal structure of the present phases and the phase transformations has been performed on a Ni-Mn-Ga-Co alloy by neutron diffraction measurements from 10 K to 673 K. The study has been completed by means of calorimetric and magnetic measurements. On cooling the alloy undergoes a martensitic transformation from a face centered cubic structure to a nonmodulated tetragonal martensite. The appearance of intermartensite transformations can be disregarded in the whole temperature range below the martensitic transformation. However, a jump in the unit-cell volume of the tetragonal martensite has been observed at 325 K. Since this temperature is close to the Curie temperature of the alloy both, the structural and magnetic contributions are taken into account to explain the results

Influence of defects on the irreversible phase transition in the Fe-Pd doped with Co and Mn

The appearance of BCT martensite in Fe-Pd-based ferromagnetic shape memory alloys, which develops at lower temperatures than the thermoelastic martensitic transition, deteriorates the shape memory properties. In a previous work performed in Fe70Pd30, it was shown that a reduction in defects density reduces the non thermoelastic FCT-BCT transformation temperature. In the present work, the influence of quenched-in-defects upon the intensity and temperature of the thermoelastic martensitic (FCC-FCT) and the non thermoelastic (FCT-BCT) transitions in Fe-Pd doped with Co and Mn is studied. Differential scanning calorimetric and mechanical spectroscopy studies demonstrate that a reduction in the dislocation density the stability range of the FCC-FCT reversible transformation in Fe67Pd30Co3 and Fe66.8Pd30.7Mn2.5 ferromagnetic shape memory alloys.Fil: Bonifacich, Federico Guillermo. Universidad Nacional de Rosario. Facultad de Ciencias Exactas Ingeniería y Agrimensura. Escuela de Ingeniería Eléctrica. Laboratorio de Extensión e Investigación en Materiales; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Lambri, Osvaldo Agustin F.. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de Rosario. Facultad de Ciencias Exactas Ingeniería y Agrimensura. Escuela de Ingeniería Eléctrica. Laboratorio de Extensión e Investigación en Materiales; ArgentinaFil: Gargicevich, Damian. Universidad Nacional de Rosario. Facultad de Ciencias Exactas Ingeniería y Agrimensura. Escuela de Ingeniería Eléctrica. Laboratorio de Extensión e Investigación en Materiales; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Zelada, Griselda Irene. Universidad Nacional de Rosario. Facultad de Ciencias Exactas Ingeniería y Agrimensura. Escuela de Ingeniería Eléctrica. Laboratorio de Extensión e Investigación en Materiales; ArgentinaFil: Pérez Landazábal, J. I.. Universidad Publica de Navarra; EspañaFil: Recarte, V.. Universidad Publica de Navarra; EspañaFil: Sánchez Alarcos, V.. Universidad Publica de Navarra; Españ

Testing the Applicability of 119Sn Mössbauer Spectroscopy for the Internal Stress Study in Ternary and Co-Doped Ni-Mn-Sn Metamagnetic Alloys

The influence of both the Co addition and the internal stress on the atomic level magnetism is comparatively studied in Ni50Mn37Sn13 and Ni45Mn38Sn13Co4 alloys by magnetic measurements and 119Sn Mössbauer spectroscopy. The results show that the saturation magnetization and the hyperfine field follow the same temperature trend. The internal stress state is investigated by subjecting the samples to milling and annealing treatments, and tracking the singlet component revealed by 119Sn Mössbauer spectroscopy. Contrary to what was expected, in the Co-doped Ni-Mn-Sn sample the singlet component can be resolved between the milled and annealed states in both martensite and austenite phases. Therefore, the results demonstrate the feasibility of tracking the singlet component upon the structural recovery in Co-doped Ni-Mn-Sn alloys in a much wider range than in ternary alloys. In addition, it is concluded that the transferred dipolar field at Sn from the neighbor magnetic atoms depends very strongly on the stress field and on the microstructural order surrounding Sn atoms. The observed sensitivity of Sn Mössbauer probe atoms to slight microstructural distortions make 119 Sn a powerful technique for the characterization of the stress present in Sn containing metamagnetic shape memory alloys.This research was funded by Projects RTI2018-094683-B-C5 (4,5) (MCIU/AEI/FEDER, UE) and Basque Government Grant IT-1005–16

Influence of Structural Defects on the Properties of Metamagnetic Shape Memory Alloys

The production of μ-particles of Metamagnetic Shape Memory Alloys by crushing and subsequent ball milling process has been analyzed. The high energy involved in the milling process induces large internal stresses and high density of defects with a strong influence on the martensitic transformation; the interphase creation and its movement during the martensitic transformation produces frictional contributions to the entropy change (exothermic process) both during forward and reverse transformation. The frictional contribution increases with the milling time as a consequence of the interaction between defects and interphases. The influence of the frictional terms on the magnetocaloric effect has been evidenced. Besides, the presence of antiphase boundaries linked to superdislocations helps to understand the spin-glass behavior at low temperatures in martensite. Finally, the particles in the deformed state were introduced in a photosensitive polymer. The mechanical damping associated to the Martensitic Transformation (MT) of the particles is clearly distinguished in the produced composite, which could be interesting for the development of magnetically-tunable mechanical dampers.This research was funded by Projects RTI2018-094683-B-C5 (4,5) (MCIU/AEI/FEDER,UE); ASACTEI Pcia.Santa Fe IO-2017-00138, PID-UNR ING 575 and ING 612 (2018–202

Zener Relaxation in Al-Li Binary Alloys

Internal fiction (I.F.) and modulus measurements have been carried out as a function of temperature in order to study the Li mobility in an Al - 8.1 at% Li - 0.03 at% Zr alloy. The results show that the sequence of δ' and δ precipitation can be followed through the evolution of the internal friction spectra. Two peaks appear in the internal friction spectrum. The low temperature peak Pz (450 K), has associated a dynamic modulus defect, an activation energy of 1.2 eV and the width of a Debye peak. The analysis of the behaviour of this relaxation allows us to identify the Pz peak with the Zener relaxation process. The relaxation parameters lead us to determine the activation energy and the diffusion coefficient of Li in Aluminium

Dependence of the martensitic transformation and magnetic transition on the atomic order in Ni-Mn-In metamagnetic shape memory alloys

The analysis of atomic order and its influence on the magnetic and structural properties of Ni-Mn-In metamagnetic shape memory alloys has been performed. The effect of the different thermal treatments on the magnetic and structural transformation temperatures, as well as on the thermodynamics of the martensitic transformation, has been made by calorimetric measurements. The evolution of the degree of long-range atomic order with temperature has been determined by neutron diffraction experiments, thus confirming the effect of thermal treatments on the atomic order. Calorimetric and structural results allow thermal treatments to be directly related to atomic order, and to allow the effect of the atomic order on the martensitic and magnetic transformations in Ni-Mn-In alloys to be quantified. The thermodynamics of the martensitic transformation depends on the atomic order as indicated out by its influence on the transformation entropy. In addition, a correlation between the transformation entropy and changes in the magnetic-field-induced transformation temperatures has been found through the evolution of the atomic order. © 2012 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.This work has been carried out with the financial support of FEDER and the Spanish “Ministerio de Ciencia y Tecnología” (Project number MAT2009-07928 and MAT2007-61621).Peer Reviewe

Influencia del orden atómico de largo alcance en la transformación martensítica de aleaciones con memoria de forma magnéticas basadas en Ni-Mn

Resumen del póster presentado a la VI Reunión de la Sociedad Española de Técnicas Neutrónicas celebrada en Segovia (España) del 24 al 27 de junio de 2012.-- et al.El efecto del ordenamiento atómico de largo alcance en la transformación martensítica y las propiedades magnéticas de las aleaciones Ni-Mn-X (X=Ga, In, Sn, Sb) se ha analizado a partir del estudio combinado de la evolución del grado de orden atómico a segundos vecinos (tipo L2) y de las temperaturas de transformación bajo trataminetos térmicos de templado y de envejecimineto post-templado. Se ha encontrado que, en todos los casos, la temperatura de Curie y la imanción de saturación aumentan al aumentar el grado de orden atómico, como consecuencia del incremento del acoplamiento de intercambio ferromagnético. Por el contrario, la temperatura de transformación martensítica aumenta en las aleaciones Ni-Mn-Ga mientras que disminuye en las aleaciones metamagnéticas Ni-Mn-In, Ni-Mn-Sn y Ni-Mn-Sb. Por otro lado, se ha observado que, independientemente de la composición, las variaciones de orden atómico asociadas a los tratamientos térmicos únicamente afectan a la temperatura de transformación martenstíca en aquellas aleaciones en las que al menos una de las fases estructurales presenta orden magnético a la temperatura de transformación. Los diferentes comportamientos observados se pueden atribuir al efecto que las variaciones en el acoplamiento de intercambio ferromagnético asociadas al ordenamiento atómico producen en la diferencia de energia libre entre austenita y martensita. en Pparticular, el ordenamiento atómico parece estabilizar siempre la fase estructural con mayor mometo magnético, tal y como ocurre bajo la acción de un campo magnético externo, lo que pondría de manifiesto el determinante rol del magnetismo en la transformación martensítica.Peer reviewe

Effect of high-temperature quenching on the magnetostructural transformations and the long-range atomic order of Ni-Mn-Sn and Ni-Mn-Sb metamagnetic shape memory alloys

et al.The influence of high-temperature thermal treatments on the martensitic transformation and the magnetic properties of Ni-Mn-Sn and Ni-Mn-Sb metamagnetic shape memory alloys have been investigated by calorimetric and magnetic measurements. Contrary to Ni-Mn-Ga and Ni-Mn-In systems, the martensitic transformation and Curie temperatures of Ni-Mn-Sn and Ni-Mn-Sb alloys are found to be unaffected by the increasing quenching temperature. Neutron diffraction measurements confirm the null effect of quenching on the next-nearest-neighbors atomic order due to the negligible L21 atomic disorder achieved with high-temperature annealings. The analysis of long-range order also suggests that no L21-B2 ordering transition takes place in the studied alloys, thus indicating an unusually high stability of the L21 structure. The obtained results show that the magnetostructural properties of Ni-Mn-Sn and Ni-Mn-Sb alloys cannot be properly tuned by means of standard thermal treatments. © 2013 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.This work has been carried out with the financial support of the Spanish “Ministerio de Ciencia y Tecnología” (Projects Nos. MAT2009-07928 and MAT2012-37923-C02-01).Peer Reviewe