"Influence of the Texture On the Shape Memory Effect of Fe-28%Ni Alloy"

An influence of the crystallographic texture on the shape memory effect (SME) is demonstrated as applied to sheet samples from Fe-28%Ni-5%Mo alloy. The setting deformation of samples was realized by means of tension as well as by winding on arbor along different directions in liquid nitrogen. In the latter case one side of sample experiences tension, whereas its opposite side – compression. Under these conditions the deformation martensite arises and by following heating up to 200-400^oC the reverse martensitic transformation alpha→gamma takes place. It was shown, that both by tension and winding on arbor in the transversal direction (TD), perpendicular to the direction of previous cold rolling (RD), SME of samples is significantly lower, than in the case of tension or winding along RD. A reason of this phenomenon consists in easy reorientation of γ- and α-phases crystallites in rolled samples under TD-tension, since at that the initial texture proves to be unstable, lightly changes by operation of a single slip system, so that after reverse martensitic transformation the sample’s texture does not return to its former condition and the value of SME falls. The maximal value of SME is observed for the sample, cold-rolled and heated up to 560^oC with a rate of 20 degrees/min, after its tension along RD by 4,7%, when the degree of shape recovery is equal to 100%. According to the X-ray method of generalized pole figures, allowing to see inhomogeneities of strain hardening depending on grain orientations, the deformation martensite arises first of all in grains, characterized by the greatest strain hardening. The Nishiyama’s orientation relationship between martensitic phases of studied alloy in the textured polycrystal is fulfilled only on average.