Development and Propagation of cracks in Vacuum Annealed NiTi Thin Films

Nickel Titanium thin films are used in various industries for their shape memory and superelastic capabilities. The shape memory effect depends on a thermally, or stress activated phase transformation within the crystalline grains. The present work examines the mechanical properties of amorphous magnetron sputtered Nickel Titanium films and the evolution of those properties as a function a vacuum annealing. This is examined primarily through in-situ tensile testing and SEM examination of the formation of cracks within the films as they are progressively deformed. The tests yielded results revealing that mild annealing treatments densify the formerly columnar amorphous films and induce few crystals and titanium oxides that can act as absorbers and crack deflectors in the film films during deformation.