Special Features of the Two-Way Shape Memory Effect in Stress-Assisted Aged Ti49.2Ni50.8 Single Crystals Oriented Along the [111] Direction

Abstract

On the example of Ti49.2Ni50.8 (at.%) single crystals oriented along the [111]B2 directions, influence of aging at 673 and 823 K for 1 h under tensile and compressive load of 150 MPa was studied on the magnitude and sign of the two-way shape memory effect (TWSME). It is experimentally shown that the TWSME sign (tension/compression) and magnitude are determined by the size of disperse Ti3Ni4 particles, the character of interaction of the disperse particles with martensitic crystals, and the direction of external load application during aging. For one variant of nanodimensional Ti3Ni4 particles (d < 30 nm, stress-assisted aging at 673 K for 1 h), the TWSME makes 1.3–1.7%, and the TWSME sign is independent of the direction (tension/compression) of stress application during aging: the sample size increases upon cooling and is restored upon heating. In the Ti49.2Ni50.8 [111]B2 single crystals (with particle size d = 390 nm) during stressassisted aging at 823 K for 1 h, the TWSME magnitude and sign are determined by the direction of external loading application during aging: aging under compressive loading leads to tensile TWSME with reversible strain eTWSME = 2.4%, and aging under tensile loading leads to compressive TWSME (eTWSME = –1.2%).