Properties of Ni-Ti-(Fe,Co,Al) Shape Memory Alloys Prepared by Self-Propagating High-Temperature Synthesis

Abstract

Shape memory, superelasticity and pseudoplasticity are the exceptional properties of Ni-Ti alloys, which are listed among SMAs (Shape Memory Alloys). The carrier of these properties is the intermetallic NiTi phase. In addition to this phase, the Ti2Ni phase is always present, which is hard and brittle, and therefore it is undesirable in the Ni-Ti alloys. The aim of this work was to determine the influence of selected alloying elements (iron, cobalt and aluminium) in two different amounts (1 wt. % and 3 wt. %) on the microstructure, phase composition and amount of the Ti2Ni phase, hardness and transformation temperature of Ni-Ti-X alloy. The samples examined were prepared by self-propagating high-temperature synthesis at sintering temperature of 1100 °C. By altering the selected elements, the Ti2Ni phase was not reduced, on the contrary aluminium increased its amount. The Ni-Ti alloys alloyed with these three alloying elements proved to be harder. The phase transformations were observed only in the sample with 1 wt. % of aluminium at heating and cooling curves from differential scanning calorimetry.