A comparative study of the porous TiNi shape-memory alloys fabricated by three different processes

Porous TiNi shape-memory alloys (SMAs) have been successfully fabricated by three different processes, including capsule-free hot isostatic pressing (CF-HIP), conventional sintering (CS), and self-propagating high-temperature synthesis (SHS). A systematically comparative investigation was made on their phase transformation behaviors, mechanical properties, superelasticity, and damping performance. The results show that the CF-HIP process is the best among these methods. By controlling the processing parameters of CF-HIP, the porous TiNi SMA shows the expected pore characteristics, such as a round pore shape and a homogeneous pore distribution. The porous TiNi SMA produced by CF-HIP also exhibits good properties, such as superior superelasticity (up to 4 pct recoverable strain), a flat stress yield plateau, and a high compressive strength, similar to those of the dense TiNi SMAs. In addition, the porous TiNi SMA produced by CF-HIP has a much smaller strain hysteresis, superior damping performance to a porous TiNi SMAs produced with CS, and SHS.