Effect of the linear velocity during the melt spinning process on shape memory transformation of Ni-Ti ribbons
- PDF / 225,205 Bytes
- 6 Pages / 432 x 648 pts Page_size
- 85 Downloads / 152 Views
Effect of the linear velocity during the melt spinning process on shape memory transformation of Ni-Ti ribbons E. Nuñez-Mendoza 1-2, E. López Cuellar 1-2, Walman Benicio de Castro3, B. López Walle 1-2 1
CIIDIT, Universidad Autónoma de Nuevo León, parque PIIT km. 10 autopista al Aeropuerto Internacional de Monterrey, Apodaca, N.L., México Cd. 2 División de Estudios de Posgrado, FIME, Universidad Autónoma de Nuevo León, Ciudad Universitaria, C.P. 66451, San Nicolás de los Garza, N.L., México. 3 Universidade Federal de Campina Grande, Aprigio Veloso 882-Bodocongó C.P. 10069, Campina Grande, Paraíba, Brasil. 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. Keywords: Shape Memory Alloys, Melt Spinning Process, Martensitic Transformation, R-phase transformation 1. Introduction NiTi shape memory alloys (SMAs) are interesting materials, due to their shape memory effect (SME) and the superelasticity property. Based on these properties, NiTi shape memory alloys have a large range of applications as smart materials in a variety of fields, such as aerospace, biomechanical, biomedical and microelectronic. Among the known shape memory alloys, this alloy is the most commonly used because of its excellent mechanical properties, corrosion resistance and biocompatibility [2, 3]. Near equiatomic NiTi alloys are well known to undergo a thermo-elastic martensitic transformation, from the B2 austenite parent phase to
Data Loading...
