Laser annealing of amorphous NiTi shape memory alloy thin films to locally induce shape memory properties

We present the results of a crystallization study on NiTi shape memory thin films in which amorphous films are annealed by ascanning laser. This technique has the advantage that shape memory properties can be spatially distributed as required by the application.A kinetics study shows that nucleation of the crystalline phase occurs homogenously in the films. Consequently, the laserannealing process produces polycrystalline films with a random crystallographic texture. The crystallized films have a uniformmicrostructure across the annealed areas. The material in the crystalline regions transforms reversibly to martensite on cooling fromelevated temperature and stress measurements show that a significant recovery stress is achieved in the films upon transformation.