Systematic analysis of the crystal structure, chemical ordering, and microstructure of Ni-Mn-Ga ferromagnetic shape memory alloys

Ni-n-Ga based ferromagnetic shape-memory alloys (FSMAs) have shown great promise as an active material that yields a large output strain over a range of actuation frequencies. The maximum strain has been reported to be 6% in the tetragonal martensitic phase and up to 10% in the orthorhombic phase. There has been a large body of work exploring the engineering properties of these alloys but less extensive work in the understanding of the underlying structure and its connection to the material properties. This is particularly true for the off-stoichiometry compositions that are of most practical interest. The crystal structure of Ni-Mn-Ga ferromagnetic shape-memory alloys is extremely sensitive to composition. Several martensitic structures including tetragonal (5-layer), orthorhombic (7-layer) and non-modulated tetragonal have been identified. A systematic exploration of the composition-structure relationship has been performed using x-ray diffraction on samples taken from several single crystals with different compositions. A room temperature phase diagram has been constructed delineating the fields where the tetragonal and orthorhombic martensites are found.

Department dc:contributor.department

Massachusetts Institute of Technology. Dept. of Materials Science and Engineering.

Grantor dc:publisher

Massachusetts Institute of Technology

Year dc:date.issued

2005

Author dc:creator

• Richard, Marc Louis

Advisor dc:contributor.advisor

• Samuel M. Allen and Robert C. O'Handley.

• Materials Science and Engineering.

Statement dc:rights

• M.I.T. theses are protected by copyright. They may be viewed from this source for any purpose, but reproduction or distribution in any format is prohibited without written permission. See provided URL for inquiries about permission.

Licence dc:rights.uri

• http://dspace.mit.edu/handle/1721.1/7582

Language dc:language.iso

eng

Handle dc:identifier.uri

http://hdl.handle.net/1721.1/33168

OAI identifier oai:identifier

oai:dspace.mit.edu:1721.1/33168