Phase transformation behaviors in porous Ni-rich NiTi shape memory alloy fabricated by combustion synthesis

The phase transformation behaviors that change with the aging temperature in the SHS-synthesized porous Ni-rich NiTi SMA after solution treated at 1050 °C for 2 h were investigated by differential scanning calorimeter (DSC). The experimental results show that the type of phase transformation changes from one-step (after solution treatment) to two-step (after subsequent aging treatment). With increasing aging temperatures, the transformation temperatures (Rs and As) decrease, and the positions of the first peaks on the DSC charts during cooling and the last peaks on the DSC charts during heating shift to lower temperatures. The positions of the last peaks on DSC charts on cooling of the porous Ni-rich NiTi SMA aged at different temperatures between 400 and 550 °C for 1 h correspond to the position of the single DSC peak obtained for the solution treated materials. The interpretation for the features in the phase transformation behaviors of the porous Ni-rich NiTi SMA fabricated by combustion synthesis is proposed.