Ferrous Polycrystalline Shape-Memory Alloy Showing Huge Superelasticity

Abstract

Shape-memory alloys, such as Ni-Ti and Cu-Zn-Al, show a large reversible strain of more than several percent due to superelasticity. In particular, the Ni-Ti-based alloy, which exhibits some ductility and excellent superelastic strain, is the only superelastic material available for practical applications at present. We herein describe a ferrous polycrystalline, high-strength, shape-memory alloy exhibiting a superelastic strain of more than 13%, with a tensile strength above 1 gigapascal, which is almost twice the maximum superelastic strain obtained in the Ni-Ti alloys. Furthermore, this ferrous alloy has a very large damping capacity and exhibits a large reversible change in magnetization during loading and unloading. This ferrous shape-memory alloy has great potential as a high-damping and sensor material.

Stable magnetostructural coupling with tunable magnetoresponsive effects in hexagonal ferromagnets

“…Recently, the magnetic-field-induced shape memory effect based on the magnetostructural coupling has also been found in another type of materials 28 , the hexagonal ternary compounds with the Ni 2 In structure [29][30][31] . With the FMMTs in these materials, large magnetocaloric effects are also associated [32][33][34][35][36] .…”

“…T he ferromagnetic martensitic transition (FMMT) [1][2][3] , a coinciding crystallographic and magnetic transition mainly found in Fe-based and Heusler ferromagnetic alloys, is receiving increasing attention from both the magnetism and the material science community due to the massive variations of associated magnetoresponsive effects, such as magnetic-field-induced shape memory/strain effect [4][5][6][7] , magnetoresistance 8,9 , Hall effect 10 and magnetocaloric effect 11,12 . These effects are of interest for many potential technological applications like magnetic actuators 13,14 , sensors 15 , energy-harvesting devices 16 and solid-state magnetic refrigeration 17 .…”

Microstructure and Mechanical Properties in B-Doped Fe-31.9Ni-9.6Co-4.7Ti Alloys

“…In case of the Fe-Ni-Co-Al-based and Fe-MnAl-Ni alloys, strengthening of the parent phase resulting from fine and coherent precipitates of the c 0 phase with the L1 2 structure and the b phase with the B2 structure by aging heat treatment are important to realize thermoelastic transformation and SE properties, respectively. Especially, in Fe-Ni-Co-Al-Ta-B alloy, the polycrystalline sheet specimens strengthened by the c 0 -(Ni, Fe, Co) 3 (Al, Ta) phase and strongly textured by thermomechanical treatment exhibit large maximum SE strain of about 13.5 %, which is approximately twice that of Ni-Ti alloy [9]. Furthermore, noted SE strains of more than 4 % were also confirmed in not only Fe-Ni-Co-Al-Ta single-crystal alloys [10][11][12][13][14] but also in Fe-Ni-Co-Al-Nb-based polycrystalline [16] and Fe-Ni-Co-Al-Ti-based [17][18][19] single-crystal alloys, where Ta is substituted by Nb and Ti, well known as c 0 stabilizer elements in Ni-based alloys [29].…”

“…Furthermore, noted SE strains of more than 4 % were also confirmed in not only Fe-Ni-Co-Al-Ta single-crystal alloys [10][11][12][13][14] but also in Fe-Ni-Co-Al-Nb-based polycrystalline [16] and Fe-Ni-Co-Al-Ti-based [17][18][19] single-crystal alloys, where Ta is substituted by Nb and Ti, well known as c 0 stabilizer elements in Ni-based alloys [29]. The addition of B in Fe-Ni-Co-Al-based singlecrystal alloys is unnecessary because being a nucleation site of grain boundary precipitation, it does not contain grain boundaries, whereas in the case of polycrystalline alloys [9,16,18,20], the addition of a small amount of boron plays an important role in the drastic suppression of the undesirable b-NiAl B2 phase appearing on grain boundaries. However, improvement of ductility and SE strain is not satisfied only by the addition of boron.…”

“…Recently, a number of research groups have reported three different kinds of ferrous SMAs, Fe-Ni-Co-Al-based alloys (from fcc to bct) [9][10][11][12][13][14][15][16][17][18][19][20], Fe-Mn-Ga alloy (from L2 1 to D0 22 ) [21,22], and Fe-Mn-Al-Ni alloy (from bcc to nano-twinned fcc) [23][24][25][26][27][28], showing thermoelastic transformation. In case of the Fe-Ni-Co-Al-based and Fe-MnAl-Ni alloys, strengthening of the parent phase resulting from fine and coherent precipitates of the c 0 phase with the L1 2 structure and the b phase with the B2 structure by aging heat treatment are important to realize thermoelastic transformation and SE properties, respectively.…”