After 50 years of its discovery, potential applications of TiNi shape memory alloys (SMA) are still emerging. Some of these applications require SMAs to operate as an actuator performing work against a biasing force at elevated temperatures, such as an aircraft or automobile engine. However, conventional binary TiNi SMAs have low transformation temperatures limiting their uses well below 100°C. Alloying with Pd has successfully increased the transformation temperatures of TiNi up to 500°C. Yet, as with any material exposed to high temperatures, high temperature SMAs (HTSMA) also suffer from dislocation processes and other thermally driven mechanisms such as recovery, recrystallization and creep in addition to transformation induced plasticity. All these problems contribute to the deterioration of the shape memory behavior, significantly worsening the dimensional stability.

One method to alleviate the dimensional instability problem is thermo-mechanical processing in order to refine the microstructure and develop desired crystallographic texture. Here, we employ the equal channel angular extrusion (ECAE) process followed by annealing heat treatments to improve the shape memory behavior, especially dimensional stability under thermo-mechanical cycling, of a Ti_50.5Ni_24.5Pd₂₅ HTSMA. Under the light of thermo-mechanical testing and electron microscopy results, it is shown that the processed material displays enhanced shape memory behavior, such as smaller residual strain upon thermal cycling under load and narrower thermal hysteresis, as compared to the unprocessed material due to increased strength and the resistance to dislocation slip.