Effect of microstructure on field-induced strain in Fe-Pd ferromagnetic shape memory alloys

Two types of Fe-30.5at.%Pd polycrystals, one is composed of columnar grains oriented near [0011 direction, the other equiaxed grains having random orientation, were prepared to examine the effect of texture, grain boundary character and grain size on the ferromagnetic shape memory effect. The field-induced strain of Fe-Pd alloys depended strongly on the microstructure. The magnetostriction of the columnar crystals was much higher than that of the equiaxed ones. In the columnar crystals, the strain compatibility of the transformation strain across the grain boundaries was easy to be maintained because of its [001] fiber texture, resulting in the increase in the strain. Moreover, the field-induced strain of the columnar crystals was dependent on the direction of external magnetic field, which is closely related to the martensite variants selected in the crystals. Grain size dependence of the magnetostriction in Fe-Pd alloy was also discussed.