Triple-Shape Memory Effect and Self-Healing Using NiTi Shape Memory Alloys

We present two novel applications of NiTi shape memory alloys (SMAs) here, namely triple-shape memory effect (SME) and self-healing.

Uniformly programming a piece of shape memory material (SMM) so that the shape recovery follows a predetermined sequence, from a temporary shape to the original shape through one or more intermediate shapes, so called triple-SME or multiple-SME, has been achieved in shape memory polymers (SMPs), but seemingly has never been explored in SMAs unless a gradient transformation temperature field, either permanent or temporary, is introduced. Here, we demonstrate two approaches to achieve the triple-SME in NiTi SMAs, so that a pre-programmed piece of SMA can either bend downward and then upward or twist forward and then backward upon gradually being heated inside a water tank.

In the other application, we integrate NiTi SMA with a shape memory hybrid (SMH), which has the thermally induced self-healing function, to realize repeated instant shape and strength recovery.