The elasticity of both the austenite and martensite states of a NiMnGa Heusler alloy was investigated by using a continuous wave method. A magnetic field was used to detwin the martensite. The symmetrized elastic constants of both austenite and martensite were determined by exiting different modes of wave propagation. In austenite, the shear elastic constant (C11-C12)/2 equals 7Gpz, which means the alloy is very soft as is typically the case in near second order shape memory alloys. Similarily, in martensite, (C11-C12)/2 equals 9GPa. Moreover, in the martensitic state the two rhombohedral elastic constants, C44 and C66, equaling 51GPa and 49GPz, respectively are almost the same.
The alloy Fe3Pd undergoes a reversible structural phase transformation between FCC and FCT crystal structures at approximately 20 degrees C. The FCT structure has lattice parameters relative to the parent phase with lattice parameter a0, where a/a0 > 1 and c/a0 < 1. In addition the three martensite variants of the FCT structure are also ferromagnetic. Magnetic measurements have shown that the easy magnetic axes correspond to the FCT axes with the lattice parameter a. A new instrument called a Magneto-Mechanical Testing Machine (MMTM) is used to study the magneto-mechanical response of this alloy. This instrument allows a specimen to be loaded mechanically uniaxially, while the magnetic field can be rotated in a plane containing the loading axis. In addition, the temperature of the specimen can be controlled while the microstructure on its surface is observed using an optical microscope equipped to view surface tilt using differential interference contrast (DIC). The results of experiments that control the rearrangement of the martensite variants through applied compressive loading and magnetic field, will be discussed.
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