Shape Memory Characteristics and Superelasticity of Ti-Ni-Cu Alloy Ribbons with Nano Ti₂Ni Particles

Abstract

Microstructures and deformation behaviour of Ti-45Ni-5Cu and Ti-46Ni-5Cu alloy ribbons prepared by melt spinning were investigated by transmission electron microscopy, thermal cycling tests under constant load and tensile tests. Spherical Ti2Ni particles coherent with the B2 parent phase were observed in the alloy ribbons when the melt spinning temperature was higher than 1773 K. Average size of Ti2Ni particles in the ribbons obtained at 1873 K was 8 nm, which was smaller than that (10 nm) in the ribbons obtained at 1773 K. Volume fraction of Ti2Ni phase in the ribbons obtained at 1873 K was 40%, which was larger than that (20%) in the ribbons obtained at 1773 K. The stress required at temperatures of Af + 10 K for the stress-induced martensitic transformation increased from 93 MPa to 229 MPa and apparent elastic modulus of the B2 parent phase increased from 56 GPa to 250 GPa with increasing the melt spinning temperature from 1673 K to 1873 K in Ti-45Ni-5Cu alloy ribbons. The critical stress for slip deformation of the ribbons increased by coherent Ti2Ni particles, and thus residual elongation did not occur even at 160 MPa, while considerable plastic deformation occurred at 60 MPa in the ribbons without Ti2Ni particles. Almost perfect superelastic recovery was found in the ribbons with coherent Ti2Ni particles, while only partial superelastic recovery was observed in the ribbons without coherent Ti2Ni particles.

Martensitic transformation of Ti50Ni30Cu20 alloy prepared by powder metallurgy

“…After 10 h mechanical milling, the orthorhombic phase is the majority one and by increasing the milling time, the content of monoclinic and non-transforming Ti 2 (NiCu) phases increases. This last phase was generally reported in Ti rich NiTi based alloys prepared by classical routes but also in thin films or melt spun ribbons, being always induced after a thermal treatment [10,11]. For under discussion samples, the Ti 2 Ni phase is most probably formed by a eutectic reaction at 942C during the sintering process (at 950C).…”

Dual Phase TiOxNy/TiN Charge Trapping Layer for Low-Voltage and High-Speed Flash Memory Application

“…[1][2][3][4] Therefore, various high-k materials have been proposed for the advanced nanoscaled Flash memory application. [1][2][3][4][5][6] For example, it has been reported that the P/E speeds of Flash memory with a Hf-or Al-based charge trapping layer were enhanced for the enlarged c or enlarged v 2 3 Among the high-k trapping materials, it is noted that the dual phase TiO x N y /TiN could be a promising candidate for the Flash memory application due to the midgap work function (4.6 eV) 7 of TiN which makes a deeper quantum well ( c compared to the electron affinity of Si or Ge. On the other hand, TiO x has deep v (3.4 eV) to SiO 2 .…”