Peculiarities of mechanical behaviour of porous TiNi alloy, prepared by self-propagating high-temperature synthesis

An experimental investigation of the three-point bending behaviour of porous TiNi alloy prepared by self-propagating high-temperature synthesis was carried out. Martensitic transformations in a porous TiNi alloy were observed in a very wide temperature range from 380 K to 206 K. It was assumed that this phenomenon was due to the nonuniform distribution of Ni in the TiNi phase. It was found that the mechanical behaviour of porous TiNi alloy was determined by the volume ratio of the austenite and martensite phases. Thus the stress–strain diagrams may be austenite-like or martensite-like depending on the prevalence of the austenite or martensite fraction. It was suggested that heat treatment may lead to the redistribution of Ni and, as a result, to variation in properties of a porous TiNi alloy. It was found that annealing a porous TiNi alloy at 573 K for 30 min resulted in variation in the temperatures and sequence of martensitic transformations and influences the mechanical properties of the alloy.

Research highlights▶ It was found that martensitic transformation occurred at a very wide temperature range (from 380 K to 206 K). These are due to the nonuniform distribution of Ni in the TiNi phase. ▶ The stress–strain diagrams were measured at a wide temperature range from 410 K to 100 K. It was shown that as a porous TiNi alloy was in a two-phase state (austenite and martensite) at temperatures below 340 K its mechanical behaviour was determined by the volume ratio of the austenite and martensite phases. ▶ It was found that annealing a porous TiNi alloy influenced a variation in the temperatures and sequence of martensitic transformation and the mechanical properties of the alloy.