Effect of Nitrogen Addition on TiNi Shape Memory Alloys

Abstract

In present paper we will show how nitrogen effects microstructures, transformation temperatures, and mechanical properties of equiatomic Ti-50-Ni-50 and Ti-rich Ti-51-Ni-49 binary shape memory alloys. 0.5 at.% of nitrogen was added to prepare Ti-50-Ni-49.5-N-0.5, and Ti-51-Ni-48.5-N-0.5 (at.%) alloys by arc-melting. Microstructures were investigated by scanning electron microscope (SEM), phase constitutions were investigated by X-ray diffraction (XRD), transformation temperatures were investigated by differential scanning calorimeter (DSC) and mechanical properties were tested by tensile tests. Solutions treated Ti-Ni-N shape memory alloys contain TiNi matrix without nitrogen, Ti2Ni type phase containing a small amount of nitrogen and a new Ti2N type phase containing a small amount of nickel. Compared with Ti-50-Ni-50 and Ti-51-Ni-49 binary alloys, the martensitic transformation starts temperatures (Ms) of Ti-50-Ni-49.5-N-0.5 and Ti-51-Ni-48.5-N-0.5 ternary alloys decreased from 63.4 degrees C to 41.6 degrees C and from 85.3 degrees C to 79.4 degrees C, respectively. By adding N, fracture strain decreased and incomplete superelasticity was observed.