Texture and Microstructure of Ti-Ni Melt-Spun Shape Memory Alloy Ribbons

Abstract

The shape memory behavior, texture and microstructure were studied for Ti-Ni ribbons fabricated by a melt-spinning method where the Ni contents were designed to be 49.0 at%, 50.0 at% and 51.0 at%. The texture of the parent B2 phase was determined by X-ray diffraction pole figures. A strong h100i fiber texture was found in both pole figures and orientation distribution functions (ODF). TEM observation revealed that all the ribbons are fully crystallized and that disk-type precipitates of about 10 nm in length locate on {100} of B2 phase uniformly. The thermal cyclic tests under various constant stresses showed shape recoverable strains exceeding 5% and critical stresses for plastic deformation being higher than 400 MPa for Ti-49.0 at%Ni and Ti-50.0 at%Ni as-spun ribbons. These excellent shape memory characteristics of the melt-spun ribbons are due to the formation of these disk-type precipitates. In addition, Ti 2 Ni precipitates of 25 nm in diameter appeared along grain boundaries of Ti-51.0 at%Ni as-spun ribbon. Since the Ni content of the matrix is condensed due to the formation of Ti 2 Ni precipitates, no shape memory effect was observed in Ti-51.0 at%Ni as-spun ribbon under the experimental conditions.

Annealing effects on the crystallization and shape memory effect of Ti50Ni25Cu25 melt-spun ribbons

“…The high h100i texture of the crystallized grains perpendicular to the ribbon surface is due to the heat flow associated with ribbon processing which is normal to the spin wheel during the rapid solidification process. This result is similar to that of the orientation distribution function (ODF) obtained in the Ti 50 Ni 25 Cu 25 melt-spun ribbon [28,29]. Through prolonging the annealing time, however, the intensity of the (110) B2 peak which is widely obtained in most TieNieCu bulk alloys [5] drastically increases and becomes the dominant peak.…”

Shape memory characteristics of as-spun and annealed Ti51Ni49 crystalline ribbons

“…On the contrary, as-spun Ti-Ni binary SMA ribbons manufactured by similar melt-spinning technique are usually crystalline and can be expected to behave better SME. Some literatures have investigated the textures, shape memory properties and the microstructures of as-spun Ti 51 Ni 49 , Ti 50 Ni 50 and Ti 49 Ni 51 ribbons [19][20][21]. However, the annealing effect on the TiNi binary melt-spun ribbons has not been studied in detail yet.…”

Comparison of shape memory characteristics of a Ti-50.9 At. Pct Ni alloy aged at 473 and 673 K

“…Commercial Ni-rich Ti-Ni alloys are usually aged above 600 K for relatively short times for optimum pseudoelasticity. Thus, much work has been done to investigate the effect of aging above 600 K on the shape memory properties of thin films fabricated by radio frequency magnetron sputtering [13,14] and of rapidly solidified ribbons [15] as well as bulk alloys. [1,2,16,17] However, the effect of aging at low temperatures (Ͻ600 K) on mechanical properties such as maximum recovery strain and critical stress for slip of Ni-rich Ti-Ni alloys has not yet been systematically investigated by varying the aging condition over a wide range.…”