This is a shape memory alloy, which has appoximately equivalent weights of titanium and Nickel. It is used in many engineering applications, for fasteners, actuators and couplings.

Nitinol couplings have been used in Submarine plumbings and fittings. These are expanded by ~4% in Liquid Nitrogen and placed around tubes. After warming to room temperature, these contract to their original shape, producing a tight seal.