The effect of porosity on phase transformation behavior of porous Ti–50.8 at.% Ni shape memory alloys prepared by capsule-free hot isostatic pressing

The porous Ti–50.8 at.% Ni shape memory alloys (SMAs) were successfully fabricated by capsule-free hot isostatic pressing (CF-HIP) method. The phase transformation behaviors of the fabricated porous NiTi SMAs with various porosity ratios were investigated. It was seen that the porous alloys show a uniform pore distribution with the spherical pore size ranging mainly from 50 to 200 μm. And their phase transformation behaviors are similar to that of conventional cast dense Ni-rich TiNi alloys. It has also been seen that phase transformation during cooling process occurs by two steps, that is, R-phase transformation and B19′ martensitic transformation, respectively. In addition, it was also found that the pores have a significant influence on B19′ martensitic transformation, while little influence on R-phase transformation. The characteristic transformation temperatures and latent heats of B19′ martensitic transformation in porous Ti–50.8 at.% Ni SMAs were found to decrease with increasing porosity ratio.