RECOVERABLE STRAINS IN SHAPE-MEMORY POLYCRYSTALS

Many alloys display the shape-memory effect in single crystal form, ho wever the degree to which they retain this effect in polycrystalline f orm varies widely. We propose a theoretical explanation for this diffe rence, showing that the recoverable strain of a polycrystal depends on the texture of the polycrystal, the transformation strain of the unde rlying martensitic transformation and especially critically on the cha nge of symmetry during the underlying transformation. Roughly, we find that the greater the change in symmetry during transformation, the gr eater the recoverable strain. Our results agree with experimental obse rvations, and provide guidance for the improvement of the shape-memory effect in polycrystals.