Microstructures and shape memory characteristics of Ti–25Ni–25Cu(at.%) alloy ribbons

Abstract

Ti-25Ni-25Cu(at.%) alloy ribbons have been fabricated by melt spinning with a linear velocity of 51.0 m s −1 , and then their microstructures and shape memory characteristics were investigated by means of optical microscopy, transmission electron microscopy, x-ray diffraction, thermal cycling tests under constant load and tensile tests. As-spun ribbon made at the melt spinning temperature of 1803 K was amorphous; below this it was a mixture of amorphous and crystal structure. The crystallization temperature was measured to be about 727 K, irrespective of the melt spinning temperature. The activation energy for crystallization obtained from the Kissinger plot was 136.63 ± 3.41 kJ mol −1 . Annealing the as-spun ribbons with the melt spinning temperature of 1803 K at 738 K for 0.6 ks, they were crystallized with the average grain size of 130 nm. The B2-B19 transformation occurred in the ribbons and the B19 martensites with a single-pair variant were found in most of the grains. The transformation elongation and thermal hysteresis were found to be 2.6% and 5 K under the applied stress of 231 MPa, respectively. The ribbons showed a perfect superelasticity and their stress hysteresis was as small as 30 MPa. The small hysteresis was attributed to very small grain size and single-pair martensite variants formed in the small grain.

Properties of rapidly annealed Ti50Ni25Cu25 melt-spun ribbon

“…Thus, various efforts were made to produce TiNiCu melt-spun ribbon with initially amorphous microstructures. TiNiCu melt-spun ribbon with 25 at.% Cu has received particular interest recently [1][2][3][4][5][6][7]. Most of the previous research has been focused on the microstructure change as a result of crystallization.…”

Effect of annealing conditions on microstructures and shape memory characteristics of Ti50–Ni30–Cu20 alloy ribbons

“…Shape memory and superelastic characteristics were investigated by means of thermal cycling test under constant loads and tensile test. Details for the test methods were presented in the previous paper [11].…”

Structural and Mössbauer spectroscopic investigation of Fe substituted Ti–Ni shape memory alloys

“…The substitution of Cu for Ni in Ti-Ni reduces the composition sensitivity of martensitic transformation temperature M s as well as transformation hysteresis [15]. Fabrication of Ti-Ni-Cu ribbon by melt-spinning technique has been proved suitable for producing alloys with Cu content up to 25 at.% [16]. Ti 50 Ni 25 Cu 25 ribbon has been widely studied because of its one-stage B2-B19 transformation (high temperature cubic phase (B2-type structure) to the orthorhombic martensite (B19-type structure) the small transformation hysteresis, and most attractively, the large transformation strain [17].…”