Magnetic Material with Large Magnetic-Field-Induced Deformation (27050)

INVENTION: Polycrystalline Ni-Mn-Ga foam magnetic shape-memory alloys exhibiting significant reversible magnetic field-induced strain.

ADVANTAGES: A polycrystalline Ni-Mn-Ga foam magnetic shape-memory alloy exhibiting magnetically induced strain about 50 times larger than reported for nonporous, fine-grained Ni-Mn-Ga materials.

SUMMARY: Magnetic shape-memory alloys are active materials enabling rapid, large-strain actuation upon application of a magnetic field. Large magnetoplastic strains are reported for single crystals of off-stoichiometric Ni2MnGa Heusler alloys, when optimally oriented to the magnetic field. However, growth of Ni-Mn-Ga single crystals is slow and leads to severe segregation, affecting local composition, crystal structure and magnetoplastic strain. No magnetoplastic strain has been reported for bulk, fine grained Ni-Mn-Ga alloys. The decrease in magnetoplasticity for polycrystalline Ni-Mn-Ga versus single crystals can be attributed to internal crystalline constraints suppressing dislocation motions. This invention overcomes these constraints by creating foam structures with pores that significantly reduce internal crystal constraints to dislocation, in the presence of a magnetic field.

Open-cell Ni-Mn-Ga foams are produced in a casting process that yield a material with 76% porosity (Foam B, Figure 1). Magnetomechanical measurements on Foam B in a 0.97 T rotating magnetic field produced a magnetoplastic strain reaching 0.115% over 105 magneto-mechanical cycles (Figure 2), which continue to display strains of 0.080 - 0.115% over 107 cycles. These fully reversible magnetically induced strain values are about 50 times larger than reported for nonporous, fine-grained Ni-Mn-Ga materials. The foam structures are comparable in strain and response time to leading nonmagnetoplastic magnetorestrictive materials such as Terfenol D, which requires a bias stress for full strain potential, and contains the more expensive Tb and Dy metals.

The new Ni-Mn-Ga magnetic foams have wide application potential such as sensors, actuators, transducers, heat-transfer agent for magnetic refrigeration, magnetic displacement of fluids and new composite materials.

REFERENCE: Physical Review Letters (2007), 99(24), 247201/1-4

Inventor(s): David Dunand, Yuttanant Boonyongmaneerat, Peter Mullner and Markus Chmielus

Type of Offer: Licensing



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