High elastic strain in shape memory alloys exhibiting significant lattice softening -- critical phenomenon under stress

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Elastic limits of conventional metals and alloys are smaller than 1%, although the ideal values obtained by theoretical calculations is 10% and higher. We found that Fe3Pt and Fe-Pd alloys exhibits elastic strain of more than 6% when stress is applied in the [001] direction. These alloys exhibit weak first order martensitic transformations and softening in elastic constant C' occurs on approaching the transformation temperature. We confirmed that the high elastic strain is due to continuous change in lattice parameter by neutron diffraction experiments under compressive stresses. Moreover, we found that the transformation strain, which is characteristic feature of first order martensitic transformations, disappears as the compressive stress in the [001] direction increases.