Influence of annealing on martensitic transformations in porous TiNi-based alloys produced by self-propagating high-temperature synthesis

Porous TiNi alloys produced by self-propagating high-temperature synthesis (SHS) are characterized by complex phase composition and the nonuniform distribution of the Ni concentration. Thus, the small volume fraction of the alloy is able to undergo a martensitic transformation that results in a poor demonstration of shape memory effects and pseudoelasticity. To improve the functional properties of porous TiNi alloys it is necessary to modify the crystalline structure of the alloy and to increase the volume fraction of the alloys undergoing phase transitions. The main focus of the present work is the influence of annealing on the crystalline structure and kinetics of martensitic transformation in porous TiNi alloys of different compositions. The mixtures of Ti–45 at.% Ni, Ti–48 at.% Ni, Ti–50 at.% Ni and Ti–52 at.% Ni were used for the preparation of TiNi alloys by SHS. All samples were subjected to annealing at temperatures of 300, 400 and 500 °C for 30 min, 60 min, 120 min and 240 min. It was found that annealing practically did not influence the crystalline structure and kinetics of martensitic transformation in Ti–45 at.% Ni alloy. At the same time an increase in a duration of annealing resulted in increase in the volume fraction of the Ti3Ni4 particles and influenced strongly the kinetics of phase transitions in the TiNi alloys with the Ni concentration from 48 at.% to 52 at.%.

Graphical abstractFigure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Annealing does not influence the volumes of the TiNi phase with a cNi close to 50%. ► Annealing strongly affected TiNi phase volumes with cNi equal to 51 at.% or more. ► Variation in the sequence of phase transition occurred within 60 min of annealing. ► Annealing increases the volume fraction of the TiNi phase in the porous TiNi alloys.