Magnetic field-induced phase transformation and variant reorientation in Ni2MnGa and NiMnCoIn magnetic shape memory alloys

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dc.contributor.advisor Karaman , Ibrahim en_US
dc.contributor.committeeMember Hartwig , Karl Ted en_US
dc.creator Karaca , Haluk Ersin en_US 2010 -01 -14T23 :58 :45Z 2014 -02 -19T19 :37 :40Z 2010 -01 -14T23 :58 :45Z 2014 -02 -19T19 :37 :40Z 2007 -08 en_US 2009 -05 -15 en_US
dc.identifier.uri http : / /hdl .handle .net /1969 .1 /ETD -TAMU -1562
dc.description.abstract The purpose of this work is to reveal the governing mechanisms responsible for the magnetic field -induced i ) martensite reorientation in Ni2MnGa single crystals , ii ) stress -assisted phase transformation in Ni2MnGa single crystals and iii ) phase transformation in NiMnCoIn alloys . The ultimate goal of utilizing these mechanisms is to increase the actuation stress levels in magnetic shape memory alloys (MSMAs ) . Extensive experimental work on magneto -thermo -mechanical (MTM ) characterization of these materials enabled us to i ) better understand the ways to increase the actuation stress and strain and decrease the required magnetic field for actuation in MSMAs , ii ) determine the effects of main MTM parameters on reversible magnetic field induced phase transformation , such as magnetocrystalline anisotropy energy (MAE ) , Zeeman energy (ZE ) , stress hysteresis , thermal hysteresis , critical stress for the stress induced phase transformation and crystal orientation , iii ) find out the feasibility of employing polycrystal MSMAs , and iv ) formulate a thermodynamical framework to capture the energetics of magnetic field -induced phase transformations in MSMAs . Magnetic shape memory properties of Ni2MnGa single crystals were characterized by monitoring magnetic field -induced strain (MFIS ) as a function of compressive stress and stress -induced strain as a function of magnetic field . It is revealed that the selection of the operating temperature with respect to martensite start and Curie temperatures is critical in optimizing actuator performance . The actuation stress of 5 MPa and work output of 157 kJm ?3 are obtained by the field -induced variant reorientation in NiMnGa alloys . Reversible and one -way stress -assisted field -induced phase transformations are observed in Ni2MnGa single crystals under low field magnitudes ( <0 .7T ) and resulted in at least an order of magnitude higher actuation stress levels . It is very promising to provide higher work output levels and operating temperatures than variant reorientation mechanisms in NiMnGa alloys . Reversible field -induced phase transformation and shape memory characteristics of NiMnCoIn single crystals are also studied . Reversible field -induced phase transformation is observed only under high magnetic fields ( >4T ) . Necessary magnetic and mechanical conditions , and materials design and selection guidelines are proposed to search for field -induced phase transformation in other ferromagnetic materials that undergo thermoelastic martensitic phase transformation . en_US
dc.format.medium electronic en_US
dc.format.mimetype application /pdf en_US
dc.language.iso en _US en_US
dc.subject magnetic shape memory alloys en_US
dc.title Magnetic field -induced phase transformation and variant reorientation in Ni2MnGa and NiMnCoIn magnetic shape memory alloys en_US
dc.type Book en
dc.type.genre Electronic Dissertation en_US
dc.type.material text en_US
dc.format.digitalOrigin born digital en_US


Magnetic field-induced phase transformation and variant reorientation in Ni2MnGa and NiMnCoIn magnetic shape memory alloys. Available electronically from http : / /hdl .handle .net /1969 .1 /ETD -TAMU -1562 .

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