Correlation between crystallographic and microstructural features and low hysteresis behavior in Ni50.0Mn35.25In14.75 melt-spun ribbons

In this work, crystallographic, microstructural and magnetocaloric investigations were performed on textured Ni50Mn35.25In14.75 melt-spun ribbons with low thermal (6 K) and magnetic-field induced hysteresis (-0.731 kg(-1) at 2 T) and moderate maximum magnetic entropy change Delta S-M(max)(11 J kg(-1) K-1 at 5 T) at room temperature (302 K). The austenite in the ribbons crystallizes into a L2(1) structure, whereas martensite has a monoclinic incommensurate 6 M modulated structure as determined with the super space theory. By means of electron backscatter diffraction technique, the morphological and crystallographic features of microstructure were systematically characterized. Ribbons possess a fine microstructure with an average grain size (initial austenite phase) of around 10 mu m, whereas the 6 M martensite has a self-accommodated microstructure with 4 kinds of twin-related martensite variants. During inverse martensitic transformation, the austenite prefers to nucleate at the grain boundaries of initial austenite. By means of cofactor conditions and crystallographic orientation analyses, the good geometrical compatibility between austenite and martensite was confirmed. Based on the crystal structure and microstructure information obtained, the reason of the low thermal hysteresis was discussed. (C) 2018 Elsevier B.V. All rights reserved.