Basaran, Burak (2009-12). Magnetic field-induced phase transformation & power harvesting capabilities in magnetic shape memory alloys. Doctoral Dissertation. Thesis uri icon


  • Magnetic Shape Memory Alloys (MSMAs) combine shape-change/deformationrecovery
    abilities of heat driven conventional shape memory alloys (SMA) and magnetic
    field driven magnetostrictives through martensitic transformation. They are promising
    for actuator applications, and can be employed as sensors/power-harvesters due to their
    capability to convert mechanical stimuli into magnetic response or vice versa.
    The purpose of the present work was to investigate magneto-thermo-mechanical
    (MTM) response of various MSMAs, under simultaneously applied magnetic field, heat
    and stress. To accomplish this, two novel testing systems which allowed absolute control
    on magnetic field and stress/strain in a wide and stable range of temperature were
    designed and manufactured.
    MTM characterization of MSMAs enabled us to determine the effects of main
    parameters on reversible magnetic field-induced phase transformation (FIPT), such as
    magnetocrystalline anisotropy energy, Zeeman energy, stress hysteresis, thermal
    hysteresis, critical stress to start stress induced phase transformation and crystal
    orientation. Conventional SMA characteristics of single crystalline Ni2MnGa and
    NiMnCoIn and polycrystalline NiMnCoAl and NiMnCoSn MSMAs were investigated
    using the macroscopic MTM testing system to reveal how these conventional properties
    were linked to magnetic-field-induced actuation. An actuation stress of 5 MPa and a
    work output of 157 kJm?3 were obtained by the field-induced martensite variant reorientation (VR) in NiMnGa alloys. FIPT was investigated both in Ni2MnGa MSMA
    and in NiMnCoIn metamagnetic SMA. It proved as an alternative governing mechanism
    of field-induced shape change to VR in Ni2MnGa single crystals: one-way and reversible
    (0.5% cyclic magnetic field induced strain (MFIS) under 22 MPa) stress-assisted FIPTs
    were realized under low field magnitudes (< 0.7 Tesla) resulting in at least an order of
    magnitude higher actuation stress levels than those in shape memory alloys literature.
    The possibility of harvesting waste mechanical work as electrical power by
    means of VR in NiMnGa MSMAs was explored: without enhanced pickup coil
    parameters or optimized power conditioning circuitry, 280 mV was harvested at 10 Hz
    frequency within a strain range of 4.9%.
    For the first time in magnetic shape memory alloys literature, a fully recoverable
    MFIS of 3% under 125 MPa was attained on single crystalline metamagnetic SMA
    NiMnCoIn by means of our microscopic MTM testing system to understand the
    evolution of FIPT under simultaneously applied magnetic field and stress.
    Conventional SMA characteristics of polycrystalline bulk NiMnCoAl and
    sintered compacted-powder NiMnCoSn metamagnetic SMAs were also investigated,
    with and without applied field.

publication date

  • December 2009