Effect of hydrogen on the two-way shape memory effect in TiNi single crystals

Abstract

[1¯12]-oriented single crystals of Ti-51.3Ni (at. %) alloy, aged at 823 K for 1.5 h under a tensile stress of 150 MPa, have been investigated regarding the two-way shape memory effect (TWSME) in a hydrogen-free state and after hydrogenation. It has been established that a TWSME, with a value of -1.1 %, is observed in hydrogen-free [1¯12]-oriented single crystals with one variant of dispersed Ti3Ni4 particles. The physical reason for the TWSME occurrence is associated with the advent of orienting internal compressive stresses from one variant of Ti3Ni4 particles, which results from ageing under a tensile stress of 150 MPa. It has been shown that hydrogen suppresses the TWSME. Therefore, it has been confirmed that suppression of the TWSME occurs in [1¯12]-oriented single crystals of Ti-51.3Ni (at. %) alloy with one variant of dispersed Ti3Ni4 particles, which are associated with shielding the stress fields from one variant of Ti3Ni4 particles, and with the multiple generation of the R- and B19'-martensite variants in crystals with the presence of hydrogen.