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

Resumo

On the example of Ti_49.2Ni_50.8 (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 Ti_49.2Ni_50.8 [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 εTWSME = 2.4%, and aging under tensile loading leads to compressive TWSME (ε_TWSME = –1.2%).