In this study, a series of nanoindentations was made on NiTi shape memory alloy thin films at millinewton loads with a Berkovich indenter. Mapping of the indentation topography using atomic force microscopy reveals direct evidence that the thermally induced martensitic transformation of these films allows for partial indent recovery on the nanoscale. Indeed, recovery is nearly complete at indentation depths of less than 100 nm. A hemispherical cavity model is presented to predict an upper limit to shape memory recovery of sharp indentations.

The objective of this research is to establish a shape-memory effect in sputter-deposited films of nickel titanium. The alloy, generically called nitinol, was prepared from sputtering targets in two different compositions. Films were deposited up to 10 μm in thickness on glass substrates using a dc magnetron sputtering source. The as-deposited films were amorphous in structure and did not exhibit a shape memory. The amorphous films were crystallized with a suitable annealing process, and the transformation properties were measured using differential scanning calorimetry. The crystallized films showed transition temperatures that were much lower than those of the parent material. X-ray diffraction patterns indicated that the films were not a single phase but showed evidence of a second phase. However, the annealed films demonstrated a strong shape-memory effect. Stress/strain measurements and physical manipulation were used to evaluate the shape recovery. These tests demonstrated sustained tensile stresses of up to 480 MPa in the high-temperature phase, and a characteristic plastic deformation in the low-temperature phase.

Thin-film nickel-titanium shape memory alloy has been vacuum sputter deposited, characterized by crystallographic. electrical, and mechanical tests, and incorporated as a n actuator in miniature devices. The composition and heat treatment of the film are critical as contamination by oxygen and other utilized. with good adhesion. Shape memory behavior comparable to that of bulk TiNi has been observed in free-standing film. The work output per unit volume of TiNi is much greater than can be achieved with electrostatic or piezoactuators. Actuators in the few-micrometer size domain are feasible and have desirable characteristics for electrical and optical activation. Anticipated applications include miniature valves, bistable optical memory elements, and microactuators for silicon microelectromechanical devices

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Nickel-titanium shape memory alloy films, between 2 and 10 μm thick, were sputter deposited onto (100) silicon substrates. Films deposited onto a substrate at ambient temperature were amorphous; however, several post-deposition annealing procedures produced crystalline films exhibiting the B2-to-B19′ phase transition that gives rise to the shape memory effect. Films that were deposited onto a heated substrate, 350–460 °C, crystallized during deposition, eliminating the need for a separate annealing step. Powder x-ray diffraction indicated that these films were highly oriented, with the NiTi (110)B2 face parallel to the silicon substrate (100) face.