Influence of chemical composition and pre-heating temperature on the structure and martensitic transformation in porous TiNi-based shape memory alloys, produced by self-propagating high-temperature synthesis

A study of the influence of the chemical composition and the pre-heating temperature of the Ti–Ni powder mixture on kinetics of martensitic transformation and structure in the porous TiNi alloys produced by SHS was carried out. It was found that a variation in the nickel concentration in the powder mixture influenced the volume fraction of the TiNi phase undergoing martensitic transformation. An increase in the nickel concentration from 45 at.% to 52 at.% led to an increase in the volume fraction of the TiNi phase from 60% to 90% in the alloy and a decrease in the alloy volume undergoing martensitic transformation from 60% to 10%. It was shown that in the porous TiNi alloys with the Ni concentration varied from 48 at.% to 50 at.% the martensitic transformations were found in two temperature intervals. The first interval was from 347 K to 304 K and it was due to the B2 → B19′ transformation occurring in the volume of the TiNi phase with a nickel concentration close to 50.0 at.%. The second temperature interval was from 252 K to 198 K and it was caused by the same transformation occurring in the volumes of the TiNi phase with a nickel concentration close to 51%. The value of the pre-heating temperature did not influence the characteristics of the martensitic transformations, except in the Ti – 48 at.% Ni alloy where an increase in the pre-heating temperature resulted in an increase in the volume fraction of the TiNi phase undergoing martensitic transformation from 30% to 60%.