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

6th Meeting of the Spanish Neutron Scattering Association

Recarte, V.^1 ; Pérez-Landazábal, J.I.^1 ; Sánchez-Alarcos, V.^1 ; Rodríguez-Velamazán, J.A.^2,3

Departamento de Física, Universidad Pública de Navarra, Campus de Arrosadía S/n, Pamplona

31006, Spain^1

Instituto de Ciencia de Materiales de Aragón, CSIC, Universidad de Zaragoza, Zaragoza, Spain^2

Institut Laue-Langevin, CRG's D1B - D15, Grenoble

F-38042, France^3

关键词: Face centered cubic structure;    Ferromagnetic shape memory alloy;    High temperature;    Magnetic contribution;    Magnetic field-induced strain;    Neutron diffraction measurements;    Temperature range;    Transformation sequences;   

Others  :  https://iopscience.iop.org/article/10.1088/1742-6596/549/1/012017/pdf
DOI  :  10.1088/1742-6596/549/1/012017

来源: IOP

【 摘 要 】

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.