The role of gamma-phase on the thermo-mechanical properties of NiMnGaFe alloys polycrystalline samples

The addition of Fe as a replacement of Ni or Mn in the NiMnGa system was considered in the last years as a possible way to improve the functional properties, particularly concerning the magnetic response and the ductility of the material. The addition of Fe in certain composition corresponds to a formation of a secondary phase denominated gamma-phase, particularly rich in Fe content. Two series of polycrystalline NiMnGaFe alloys were prepared and thermal treated to obtain different distribution of gamma-phase in the material. The microstructural conditions were investigated by calorimetric and microscopic analysis. The influence of gamma-phase in the mechanical performance was characterized by dynamic and mechanical measurements in flexion and compression configuration at different temperatures. The gamma-phase generally reduces the brittleness of the material and modifies the pseudoelastic and martensite reorientation properties of the alloys. The best condition has been reached when the gamma-phase is localized at grain boundaries. (C) 2018 Elsevier B.V. All rights reserved.