Textures and compressive properties of ferromagnetic shape-memory alloy Ni₄₈Mn₂₅Ga₂₂Co₅ prepared by isothermal forging process

Abstract

A ferromagnetic shape-memory alloy Ni 48 Mn 25 Ga 22 Co 5 was prepared by the induction melting and isothermal forging process. Dynamic recrystallization occurs during the isothermal forging. The deformation texture was studied by the neutron diffraction technique. The main texture components consist of (110) [112] and (001)[100], which suggested that in-plane plastic flow anisotropy should be expected in the as-forged condition. The uniaxial compression fracture strain in the forged alloy reaches over 9.5%. The final room-temperature fracture of the polycrystalline Ni 48 Mn 25 Ga 22 Co 5 is controlled mainly by intergranular mode.

Magnetocaloric effects in magnetic microwires for magnetic refrigeration applications

“…X-ray diffraction shows a single crystalline structure of tetragonal martensitic structure with a lattice parameters a ¼ 3.75 Å and c ¼ 6.78 Å for microwire with 44 mm in diameter (Figure 19.7). However, the structure is elongated along the c axis (compared to bulk materials - Cong et al, 2007;Wang et al, 2006). It is assumed that the high levels of stress originating from the difference between the thermal expansion coefficients of the metallic core and the glass coating may be responsible for these deviations in lattice parameters.…”

In-Situ High-Energy X-Ray Diffuse-Scattering Study of the Phase Transition of Ni2MnGa Single Crystal under High Magnetic Field

“…[1][2][3] The origin of the extremely large magnetic-field-induced strain is explained by the rearrangement of martensite variants due to an external magnetic field, whose driving force is related to the large magnetocrystalline anisotropy energy of the martensite phase. A lot of progress has been made in this kind of alloy through intensive studies toward many scientific aspects, including the composition dependence of phase transformation behaviors, [4] magnetic properties, [5] magnetocaloric effects, [6] martensite stabilization, [7] crystal structure and twinning crystallography, [8][9][10][11][12] and the effect of uniaxial pressure and magnetic fields on the premartensitic (PM) and martensitic transition of NiMnGa alloys. [12][13][14][15][16] An exploration on the phase transition process and the rearrangement of martensite variants in response to multiple external parameters (stress, temperature, and magnetic fields) is very important to enable the quick response and remote control of NiMnGa alloys used as actuator and sensor.…”

In-Situ High-Energy X-Ray Diffuse-Scattering Study of the Phase Transition in a Ni2MnGa Ferromagnetic Shape-Memory Crystal

“…[1,2] In the past decade, much more progress has been made in the FSMAs through intensive studies toward many scientific aspects, including the composition dependence of phase transformation behaviors, [3] magnetic properties, [4] magnetocaloric effects, [5] martensite stabilization, [6] and crystal structure and twinning crystallography. [7][8][9][10][11] The large magnetic field-driven strain in the Ni 2 MnGa is attributed to the motion of twin boundaries [1,2] or reselections of martensitic variants under applied magnetic fields. It is well known that the SME is strongly dependent on the crystallographic orientation of austenite along the applied magnetic field and the arrangements of martensitic variants.…”