Shape memory behavior of sputter-deposited Ni46.2Ti51.1Co2.7 (at.%) thin films

MALVASIO, B.F.; ISOLA, L.M.; GIORDANA, M.F.; MALARRIA, J.A.

JOURNAL OF ALLOYS AND COMPOUNDS

ELSEVIER SCIENCE SA

Lugar: Amsterdam; Año: 2022 vol. 918 p. 165671 - 165680

0925-8388

In order to analyze the relationship between the shape memory behaviorof Ti-rich NiTiCo thin films and the different microstructures obtained afterdifferent annealing treatments, a batch of Ni46:2Ti51:1Co2:7 (at.%) thin filmswere produced by magnetron cosputtering and annealed at 773 K, 873 K and 973 Kfor 60 min. The microstructure of the thin films was studied by X-ray diffractionand transmission electron microscopy. Electrical resistivity measurements were performedto determine martensitic transformation temperatures. Additionally, a home-madedevice was specially designed for studying the mechanical behavior associatedwith the martensitic transformations of the thin films at different constantexternal stresses. The sample annealed at 773 K presented Guinier-Preston (GP)zones within the NiTiCo grains, while the samples annealed at 873 K and 973 Kshowed Ti2Ni precipitates inside the grains with semi-coherent interface withthe matrix. The appearance of GP zones can explain why the sample annealed at773 K reaches higher values of recoverable strain, with negligible irreversiblestrain, than the other samples. The maximum recoverable strain of 5.7% for thisspecimen represents a noticeable improvement in comparison with thin films ofthe binary alloy with similar Ti concentration. The maximum recoverable strainswere analyzed in terms of the Sachs bound, which represents an upper limit forits value.