Effect of Spun Velocities and Composition on the R‒phase and Thermomechanical Behavior in Ti‒Ni Ribbons Electrically Heated

Abstract

This work deals with structural, electrical and mechanical characterization of Ti-50.13Ni and Ti-49.62Ni (at.%) shape memory alloys (SMAs) fabricated at different circumferential wheel velocities. The effect of wheel velocity, chemical composition and heat treatments are investigated. The characterization of crystallographic phases of the Ti-Ni ribbons was carried out using X-ray diffraction. Electrical resistance variations as function of temperature (∆R/R %) were analyzed using a non-commercial technique, which consists in a thermal-adjustable bath apparatus revealing the temperatures of B2→R→B19´ two stage transformation, whereby the presence of R-phase can be definitively confirmed. The Stress-Assisted Two-Way Memory Effect was measured by an own designed apparatus with an Linear Variable Differential Transformer captor and a current controlled heating, and results indicate that the as-spun condition, promotes the Stress-Assisted Two-Way Memory Effect. On the other hand, increments in Ni content tend to decrease transformation temperatures and high wheel velocities help to the R-phase formation.