Evaluation of reversible shape memory effect in porous SHS TiNi-based compounds fabricated at various ignition temperature

Abstract

The present study focuses on the relationship between the structural features and reversible shape memory effect (SME) including the related martensitic transformation (MT) in porous TiNi-based compounds fabricated by self-propagating high-temperature synthesis (SHS) at various ignition temperatures. Exploring the as-synthesized samples (S-1 and S-2) ignited at T1 = 400 and T2 = 600 °C, respectively, using a set of research instruments has revealed a key feature that modulates the resultant porous structure and SME parameters. Evidently, the one-step B2 ↔ B19′ MT in both samples is considered to be diffuse within a broad temperature gap, where the hysteresis loop width excels 70 degrees. The fine-porous S-1 indicated the well-developed macrostructure having a rough surface pattern of pore walls, whereas the high-porous S-2 did a dissimilar macrostructure having an even pore surface topology. From a phase-chemical point of view, the metal matrix of S-2 was found to be more homogeneous as compared to that of S-1, that in turn has led to the distinctive SME performance in terms of ε-T upon thermocycling. The extremely heterogeneous S-1 featured by more uniform pore shape and distribution has demonstrated the feasible strain behavior despite the fewer TiNi volume fraction and depressed MT was observed. Conversely, the SME performance for S-2 was shown to be impaired because of the discrepancy in the deformation behavior of small and large pore walls, even though the redundant TiNi volume fraction facilitated the MT.