Different mechanical response of TiNi film induced by the shape of indenter during nanoindentation

Nanoindentation was conducted for magnetron sputtered TiNi thin film, which exhibits different mechanical responses induced by varied indenter shapes. Superelasticity and incomplete phase transition (A → R) were clearly depicted by spherical indentation. Under the peak load of 500 μN, the depth recovery ratios are 100% and 68% determined by spherical and Berkovich indentations, respectively. The different response is due to the varied stress distribution beneath two types of indenters. Large plastic deformation hinders the reverse phase transition (R → A) in Berkovich indentation, resulting lower recovery. Moreover, significant difference in indentation size effect for TiNi film was revealed comparing to traditional metals. And phase transition contributed considerably to the abnormal hardness evolution.