Influence of Magnetic Field Direction on Rearrangement of Martensite Variants in an Fe-Pd Alloy

Abstract

Influence of magnetic field direction on rearrangement of martensite variants in an Fe-31.2Pd(at%) single crystal has been investigated using thermal expansion measurement in a cooling process under the magnetic field applied along [001]P, [011]P and [111]P (‘‘P’’ represents ‘‘parent’’ phase). We also observe these rearrangements of variants in the cooling processes under the magnetic field applied along [001]P, [011]P and [111]P by optical microscope. From the thermal expansion measurement and the optical microscope observation, the following results are obtained: the variants are rearranged almost perfectly into the variants whose a axes are parallel to the magnetic field applied along [001]P, imperfectly into the variants whose c axis is perpendicular to the magnetic field applied along [011]P and hardly along [111]P. We explain these results considering the following criterion: rearrangement of variants proceeds when a kind of shear stress generated by applying a magnetic field acting on the twinning plane is larger than the stress required for the rearrangement of variants.