Influence of Ti additions on the martensitic phase transformation and mechanical properties of Cu–Al–Ni shape memory alloys

TLDR: In this article, the effect of Ti additions on the microstructure and mechanical properties of Cu-Al-Ni shape memory alloys (SMA) was studied by means of a differential scanning calorimeter, field emission scanning electron microscopy and X-ray diffraction (XRD).

Abstract: The effect of Ti additions on the microstructure and mechanical properties of Cu–Al–Ni shape memory alloys (SMA) was studied by means of a differential scanning calorimeter, field emission scanning electron microscopy, transmission electron microscopy, X-ray diffraction (XRD), a tensile test, a hardness test, and a shape memory effect test. The experimental results show that the Ti additions have an effective influence on the phase transformation behavior through generating a new phase into the microstructure, which is known as X-phase and/or controlling the grain size. The results of the XRD confirmed that the X-phase is a combination of two compounds, AlNi2Ti and Ti3·3Al. Nevertheless, it was found that with 0.7 mass% of Ti, the best phase transformation temperatures and mechanical properties were obtained. These improvements were due to the highest existence of the X-phase into the alloy along with a noticeable decrement of grain size. The Ti additions to the Cu–Al–Ni SMA were found to increase the ductility from 1.65 to 3.2 %, corresponding with increasing the strain recovery by the shape memory effect from 50 to 100 %; in other words, a complete recovery occurred after Ti additions.