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Effect of the linear velocity during the melt spinning process on shape memory transformation of Ni-Ti ribbons

Published online by Cambridge University Press:  20 February 2012

E. Nuñez-Mendoza
Affiliation:
CIIDIT, Universidad Autónoma de Nuevo León, parque PIIT km. 10 autopista al Aeropuerto Internacional de Monterrey, Apodaca, N.L., México Cd. División de Estudios de Posgrado, FIME, Universidad Autónoma de Nuevo León, Ciudad Universitaria, C.P. 66451, San Nicolás de los Garza, N.L., México.
E. López Cuellar
Affiliation:
CIIDIT, Universidad Autónoma de Nuevo León, parque PIIT km. 10 autopista al Aeropuerto Internacional de Monterrey, Apodaca, N.L., México Cd. División de Estudios de Posgrado, FIME, Universidad Autónoma de Nuevo León, Ciudad Universitaria, C.P. 66451, San Nicolás de los Garza, N.L., México.
Walman Benicio de Castro
Affiliation:
Universidade Federal de Campina Grande, Aprigio Veloso 882-Bodocongó C.P. 10069, Campina Grande, Paraíba, Brasil.
B. López Walle
Affiliation:
CIIDIT, Universidad Autónoma de Nuevo León, parque PIIT km. 10 autopista al Aeropuerto Internacional de Monterrey, Apodaca, N.L., México Cd. División de Estudios de Posgrado, FIME, Universidad Autónoma de Nuevo León, Ciudad Universitaria, C.P. 66451, San Nicolás de los Garza, N.L., México.
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Abstract

The usual process to produce NiTi shape memory alloys is vacuum induction melting (VIM). Currently a new alternative process to produce NiTi shape memory alloys by rapid solidification structures called Melt Spinning has been studied. In this work, results of ribbons with a chemical composition Ti-55.2 Ni (wt %) alloy prepared by this method are presented. The ribbons are prepared at two different linear velocities: 30 m/s and 50 m/s. After that, samples are heat treated at 350 °C during 1 hour. The alloys are characterized by Scanning Electron Microscopy (SEM), Differential Scanning Calorimetry (DSC) and X-Ray Diffraction. According to the cycled DSC test, transformation peaks are associated with the B2→R→B19´ transformation during cooling and B19´→R→B2 during heating, showing transformation in multi-peaks. The martensite B19´ start (Ms) is varying from 35 to 39°C and the martensite finish (Mf) from 15 to 21°C, 42-47°C for austenite B2 start (As) and 65-69°C for austenite finish (Af) approximately. All analyzed ribbons show very similar values of transformation hysteresis temperatures at 50% of transformation of around 28°C. In order to change solidification rate, linear velocity is varied during the melt spinning process. Results indicate that linear velocity affects directly the temperature of transformation. When the linear velocity is increasing, crystallographic Ti-rich precipitates are developed, but dendritic growth disappears, changing the microstructure and decreasing these transformation temperatures. Then changes in linear velocity can dramatically affect shape memory properties, and in this case a velocity of 50 m/s produces a more homogenous alloy.

Type
Articles
Copyright
Copyright © Materials Research Society 2012

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