Crystallographic Characterization on Polycrystalline Ni-Mn-Ga Alloys with Strong Preferred Orientation

Abstract

Heusler type Ni-Mn-Ga ferromagnetic shape memory alloys can demonstrate excellent magnetic shape memory effect in single crystals. However, such effect in polycrystalline alloys is greatly weakened due to the random distribution of crystallographic orientation. Microstructure optimization and texture control are of great significance and challenge to improve the functional behaviors of polycrystalline alloys. In this paper, we summarize our recent progress on the microstructure control in polycrystalline Ni-Mn-Ga alloys in the form of bulk alloys, melt-spun ribbons and thin films, based on the detailed crystallographic characterizations through neutron diffraction, X-ray diffraction and electron backscatter diffraction. The presented results are expected to offer some guidelines for the microstructure modification and functional performance control of ferromagnetic shape memory alloys.

Microstructural Model of Magnetic and Deformation Behavior of Single Crystals and Polycrystals of Ferromagnetic Shape Memory Alloy

“…Using direct multiplication, we can easily show that tensors (17) are the inverse of tensors ( 11) and ( 15) and tensors (18) are the inverse of tensors ( 13) and ( 16).…”

“…However, such materials can be not only isotropic but also textured. The structures of polycrystals, which originate from single twin crystals of Ni-Mn-Ga alloys and correspond to different textures, are described in many works (see, for example, [15][16][17][18][19]. We will use this information while modeling the behavior of polycrystalline material based on the behavior of single crystals.…”

Crystallography and Microstructure of 7M Martensite in Ni-Mn-Ga Thin Films Epitaxially Grown on (1 1 2¯ 0)-Oriented Al2O3 Substrate

“…Among these functionalities, the giant magnetic field-induced strain has gained much attention, since both the single crystalline and polycrystalline bulk materials have demonstrated giant magnetic field-induced strain as much as 6–12% and 1% [ 1 , 2 , 3 , 4 , 5 ], respectively. Such giant magnetic field-induced strains also promote the research interest in epitaxial Ni-Mn-Ga thin films, as the films possess a cost-effective advantage in the application of magnetic micro-electro-mechanical systems [ 13 , 14 , 15 , 16 , 17 , 18 , 19 , 20 , 21 , 22 , 23 ]. So far, the magnetically induced reorientation of martensite variant has been reported in the <1 0 0> A -oriented Ni-Mn-Ga thin films epitaxially grown on the MgO(1 0 0) substrate and NaCl (1 0 0) substrate.…”

Microstructure and magnetic properties of as-cast Ni2MnGa rods and tubes solidified by suction casting

“…Magnetic-field-induced strains in polycrystalline Ni-Mn-Ga alloys are vanishingly small compared to the ones obtained for single crystals, because the random distribution of crystallographic orientations greatly weakens the field controlled functional behavior [14,15]. However, from the application point of view, research has been directed towards polycrystalline materials because of their much simpler and lower-cost fabrication process.…”

“…However, from the application point of view, research has been directed towards polycrystalline materials because of their much simpler and lower-cost fabrication process. Larger MFIS can be generated in magnetically trained, highly textured, coarse-grained or highly porous samples, in the form of thin films, ribbons, textured polycrystalline bulks or foams [15][16][17][18][19]. In this sense, ultra-rapid solidification routes, such as single-and double-roller melt-spinning techniques, have been successfully adopted as effective single-step processes to produce nearly homogeneous Ni 2 MnGa ribbons, in which the crystallographic texture and the internal stress state in the material give rise to the magnetic shape memory effect [20][21][22][23].…”