Modification of preferred martensitic variant distribution by high magnetic field annealing in an Ni–Mn–Ga alloy

Abstract

The preferred martensitic variant distribution in Ni 53 Mn 25 Ga 22 ferromagnetic shape memory alloy (FSMA) samples annealed without and with a high magnetic field of 12 T applied during the annealing process was investigated by electron backscatter diffraction. It is revealed that the high magnetic field applied during annealing enhances the regular arrangement of martensitic variants from the morphological point of view and effectively modifies the preferred orientation distribution of martensitic variants without changing the misorientation between them from the crystallographic point of view. Only one texture component, f110gh332i, exists in the sample annealed without a magnetic field, whereas two additional texture components, f463gh312i and f110gh110i, are developed in the sample annealed in a high magnetic field. The new finding that the preferred martensitic variant distribution can be efficiently modified by introducing a high magnetic field during the annealing process will shed light on the development of high-performance polycrystalline FSMAs via novel processing techniques. Figure 5(a) ODF sections with '2 constant (0 , 5 , 10 etc.) in the Ni 53 Mn 25 Ga 22 samples annealed without a magnetic field.

Effect of directional solidification on texture and magnetic-field-induced strain in Ni–Mn–Ga foams with coarse grains

“…In Figure 3a for the bulk sample, grain boundaries are not identified, and it appears that the grain size is on the order of millimeters, based on the interconnected martensitic twins in this cross section. This microstructure is very similar to reported microstructures of bulk MSMA studied with electron backscatter diffraction [19,20]. Figure 3b and c show a different microstructure for Ni-Mn-Ga foams without and with DS at the same magnification.…”

Application of Electron Backscatter Diffraction to Shape Memory Alloys

“…Manual indexation was used also by Li and coworkers, for correct evaluation of orientation differences of commensurate 5M martensite submicrometer lamellae in Ni-Mn-Ga [42]. Some problems related to lack of workability, composition control and texture development still remain, fostering research on new alloys and processes [47][48][53][54]58].…”